diff --git a/src/libsyntax/diagnostic_list.rs b/src/libsyntax/diagnostic_list.rs
index c3cf4747835..d841281e485 100644
--- a/src/libsyntax/diagnostic_list.rs
+++ b/src/libsyntax/diagnostic_list.rs
@@ -317,6 +317,31 @@ fn main() {
 ```
 "##,
 
+E0658: r##"
+An unstable feature was used.
+
+Erroneous code example:
+
+```compile_fail,E658
+let x = ::std::u128::MAX; // error: use of unstable library feature 'i128'
+```
+
+If you're using a stable or a beta version of rustc, you won't be able to use
+any unstable features. In order to do so, please switch to a nightly version of
+rustc (by using rustup).
+
+If you're using a nightly version of rustc, just add the corresponding feature
+to be able to use it:
+
+```
+#![feature(i128)]
+
+fn main() {
+    let x = ::std::u128::MAX; // ok!
+}
+```
+"##,
+
 }
 
 register_diagnostics! {
diff --git a/src/libsyntax/diagnostics/macros.rs b/src/libsyntax/diagnostics/macros.rs
index c01836b6194..61f3e7046f1 100644
--- a/src/libsyntax/diagnostics/macros.rs
+++ b/src/libsyntax/diagnostics/macros.rs
@@ -105,6 +105,14 @@ macro_rules! struct_span_err {
     })
 }
 
+#[macro_export]
+macro_rules! stringify_error_code {
+    ($code:ident) => ({
+        __diagnostic_used!($code);
+        $crate::errors::DiagnosticId::Error(stringify!($code).to_owned())
+    })
+}
+
 #[macro_export]
 macro_rules! type_error_struct {
     ($session:expr, $span:expr, $typ:expr, $code:ident, $($message:tt)*) => ({
diff --git a/src/libsyntax/feature_gate.rs b/src/libsyntax/feature_gate.rs
index c3bf5dbff5c..196fadcc997 100644
--- a/src/libsyntax/feature_gate.rs
+++ b/src/libsyntax/feature_gate.rs
@@ -1179,7 +1179,9 @@ fn leveled_feature_err<'a>(sess: &'a ParseSess, feature: &str, span: Span, issue
     };
 
     let mut err = match level {
-        GateStrength::Hard => diag.struct_span_err(span, &explanation),
+        GateStrength::Hard => {
+            diag.struct_span_err_with_code(span, &explanation, stringify_error_code!(E0658))
+        }
         GateStrength::Soft => diag.struct_span_warn(span, &explanation),
     };
 
diff --git a/src/test/compile-fail/E0658.rs b/src/test/compile-fail/E0658.rs
new file mode 100644
index 00000000000..d30068eb1fe
--- /dev/null
+++ b/src/test/compile-fail/E0658.rs
@@ -0,0 +1,13 @@
+// Copyright 2018 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+fn main() {
+    let _ = ::std::u128::MAX; //~ ERROR E0658
+}
diff --git a/src/test/ui/feature-gate-abi-msp430-interrupt.stderr b/src/test/ui/feature-gate-abi-msp430-interrupt.stderr
index b05be6e4391..e1621d34d46 100644
--- a/src/test/ui/feature-gate-abi-msp430-interrupt.stderr
+++ b/src/test/ui/feature-gate-abi-msp430-interrupt.stderr
@@ -1,4 +1,4 @@
-error: msp430-interrupt ABI is experimental and subject to change (see issue #38487)
+error[E0658]: msp430-interrupt ABI is experimental and subject to change (see issue #38487)
   --> $DIR/feature-gate-abi-msp430-interrupt.rs:14:1
    |
 14 | extern "msp430-interrupt" fn foo() {}
diff --git a/src/test/ui/feature-gate-abi.stderr b/src/test/ui/feature-gate-abi.stderr
index 7d2ad0be391..ce31474caed 100644
--- a/src/test/ui/feature-gate-abi.stderr
+++ b/src/test/ui/feature-gate-abi.stderr
@@ -1,4 +1,4 @@
-error: intrinsics are subject to change
+error[E0658]: intrinsics are subject to change
   --> $DIR/feature-gate-abi.rs:19:1
    |
 19 | extern "rust-intrinsic" fn f1() {} //~ ERROR intrinsics are subject to change
@@ -6,7 +6,7 @@ error: intrinsics are subject to change
    |
    = help: add #![feature(intrinsics)] to the crate attributes to enable
 
-error: platform intrinsics are experimental and possibly buggy (see issue #27731)
+error[E0658]: platform intrinsics are experimental and possibly buggy (see issue #27731)
   --> $DIR/feature-gate-abi.rs:20:1
    |
 20 | extern "platform-intrinsic" fn f2() {} //~ ERROR platform intrinsics are experimental
@@ -14,7 +14,7 @@ error: platform intrinsics are experimental and possibly buggy (see issue #27731
    |
    = help: add #![feature(platform_intrinsics)] to the crate attributes to enable
 
-error: vectorcall is experimental and subject to change
+error[E0658]: vectorcall is experimental and subject to change
   --> $DIR/feature-gate-abi.rs:21:1
    |
 21 | extern "vectorcall" fn f3() {} //~ ERROR vectorcall is experimental and subject to change
@@ -22,7 +22,7 @@ error: vectorcall is experimental and subject to change
    |
    = help: add #![feature(abi_vectorcall)] to the crate attributes to enable
 
-error: rust-call ABI is subject to change (see issue #29625)
+error[E0658]: rust-call ABI is subject to change (see issue #29625)
   --> $DIR/feature-gate-abi.rs:22:1
    |
 22 | extern "rust-call" fn f4() {} //~ ERROR rust-call ABI is subject to change
@@ -30,7 +30,7 @@ error: rust-call ABI is subject to change (see issue #29625)
    |
    = help: add #![feature(unboxed_closures)] to the crate attributes to enable
 
-error: msp430-interrupt ABI is experimental and subject to change (see issue #38487)
+error[E0658]: msp430-interrupt ABI is experimental and subject to change (see issue #38487)
   --> $DIR/feature-gate-abi.rs:23:1
    |
 23 | extern "msp430-interrupt" fn f5() {} //~ ERROR msp430-interrupt ABI is experimental
@@ -38,7 +38,7 @@ error: msp430-interrupt ABI is experimental and subject to change (see issue #38
    |
    = help: add #![feature(abi_msp430_interrupt)] to the crate attributes to enable
 
-error: PTX ABIs are experimental and subject to change
+error[E0658]: PTX ABIs are experimental and subject to change
   --> $DIR/feature-gate-abi.rs:24:1
    |
 24 | extern "ptx-kernel" fn f6() {} //~ ERROR PTX ABIs are experimental and subject to change
@@ -46,7 +46,7 @@ error: PTX ABIs are experimental and subject to change
    |
    = help: add #![feature(abi_ptx)] to the crate attributes to enable
 
-error: x86-interrupt ABI is experimental and subject to change (see issue #40180)
+error[E0658]: x86-interrupt ABI is experimental and subject to change (see issue #40180)
   --> $DIR/feature-gate-abi.rs:25:1
    |
 25 | extern "x86-interrupt" fn f7() {} //~ ERROR x86-interrupt ABI is experimental
@@ -54,7 +54,7 @@ error: x86-interrupt ABI is experimental and subject to change (see issue #40180
    |
    = help: add #![feature(abi_x86_interrupt)] to the crate attributes to enable
 
-error: thiscall is experimental and subject to change
+error[E0658]: thiscall is experimental and subject to change
   --> $DIR/feature-gate-abi.rs:26:1
    |
 26 | extern "thiscall" fn f8() {} //~ ERROR thiscall is experimental and subject to change
@@ -62,7 +62,7 @@ error: thiscall is experimental and subject to change
    |
    = help: add #![feature(abi_thiscall)] to the crate attributes to enable
 
-error: intrinsics are subject to change
+error[E0658]: intrinsics are subject to change
   --> $DIR/feature-gate-abi.rs:30:5
    |
 30 |     extern "rust-intrinsic" fn m1(); //~ ERROR intrinsics are subject to change
@@ -70,7 +70,7 @@ error: intrinsics are subject to change
    |
    = help: add #![feature(intrinsics)] to the crate attributes to enable
 
-error: platform intrinsics are experimental and possibly buggy (see issue #27731)
+error[E0658]: platform intrinsics are experimental and possibly buggy (see issue #27731)
   --> $DIR/feature-gate-abi.rs:31:5
    |
 31 |     extern "platform-intrinsic" fn m2(); //~ ERROR platform intrinsics are experimental
@@ -78,7 +78,7 @@ error: platform intrinsics are experimental and possibly buggy (see issue #27731
    |
    = help: add #![feature(platform_intrinsics)] to the crate attributes to enable
 
-error: vectorcall is experimental and subject to change
+error[E0658]: vectorcall is experimental and subject to change
   --> $DIR/feature-gate-abi.rs:32:5
    |
 32 |     extern "vectorcall" fn m3(); //~ ERROR vectorcall is experimental and subject to change
@@ -86,7 +86,7 @@ error: vectorcall is experimental and subject to change
    |
    = help: add #![feature(abi_vectorcall)] to the crate attributes to enable
 
-error: rust-call ABI is subject to change (see issue #29625)
+error[E0658]: rust-call ABI is subject to change (see issue #29625)
   --> $DIR/feature-gate-abi.rs:33:5
    |
 33 |     extern "rust-call" fn m4(); //~ ERROR rust-call ABI is subject to change
@@ -94,7 +94,7 @@ error: rust-call ABI is subject to change (see issue #29625)
    |
    = help: add #![feature(unboxed_closures)] to the crate attributes to enable
 
-error: msp430-interrupt ABI is experimental and subject to change (see issue #38487)
+error[E0658]: msp430-interrupt ABI is experimental and subject to change (see issue #38487)
   --> $DIR/feature-gate-abi.rs:34:5
    |
 34 |     extern "msp430-interrupt" fn m5(); //~ ERROR msp430-interrupt ABI is experimental
@@ -102,7 +102,7 @@ error: msp430-interrupt ABI is experimental and subject to change (see issue #38
    |
    = help: add #![feature(abi_msp430_interrupt)] to the crate attributes to enable
 
-error: PTX ABIs are experimental and subject to change
+error[E0658]: PTX ABIs are experimental and subject to change
   --> $DIR/feature-gate-abi.rs:35:5
    |
 35 |     extern "ptx-kernel" fn m6(); //~ ERROR PTX ABIs are experimental and subject to change
@@ -110,7 +110,7 @@ error: PTX ABIs are experimental and subject to change
    |
    = help: add #![feature(abi_ptx)] to the crate attributes to enable
 
-error: x86-interrupt ABI is experimental and subject to change (see issue #40180)
+error[E0658]: x86-interrupt ABI is experimental and subject to change (see issue #40180)
   --> $DIR/feature-gate-abi.rs:36:5
    |
 36 |     extern "x86-interrupt" fn m7(); //~ ERROR x86-interrupt ABI is experimental
@@ -118,7 +118,7 @@ error: x86-interrupt ABI is experimental and subject to change (see issue #40180
    |
    = help: add #![feature(abi_x86_interrupt)] to the crate attributes to enable
 
-error: thiscall is experimental and subject to change
+error[E0658]: thiscall is experimental and subject to change
   --> $DIR/feature-gate-abi.rs:37:5
    |
 37 |     extern "thiscall" fn m8(); //~ ERROR thiscall is experimental and subject to change
@@ -126,7 +126,7 @@ error: thiscall is experimental and subject to change
    |
    = help: add #![feature(abi_thiscall)] to the crate attributes to enable
 
-error: intrinsics are subject to change
+error[E0658]: intrinsics are subject to change
   --> $DIR/feature-gate-abi.rs:39:5
    |
 39 |     extern "rust-intrinsic" fn dm1() {} //~ ERROR intrinsics are subject to change
@@ -134,7 +134,7 @@ error: intrinsics are subject to change
    |
    = help: add #![feature(intrinsics)] to the crate attributes to enable
 
-error: platform intrinsics are experimental and possibly buggy (see issue #27731)
+error[E0658]: platform intrinsics are experimental and possibly buggy (see issue #27731)
   --> $DIR/feature-gate-abi.rs:40:5
    |
 40 |     extern "platform-intrinsic" fn dm2() {} //~ ERROR platform intrinsics are experimental
@@ -142,7 +142,7 @@ error: platform intrinsics are experimental and possibly buggy (see issue #27731
    |
    = help: add #![feature(platform_intrinsics)] to the crate attributes to enable
 
-error: vectorcall is experimental and subject to change
+error[E0658]: vectorcall is experimental and subject to change
   --> $DIR/feature-gate-abi.rs:41:5
    |
 41 |     extern "vectorcall" fn dm3() {} //~ ERROR vectorcall is experimental and subject to change
@@ -150,7 +150,7 @@ error: vectorcall is experimental and subject to change
    |
    = help: add #![feature(abi_vectorcall)] to the crate attributes to enable
 
-error: rust-call ABI is subject to change (see issue #29625)
+error[E0658]: rust-call ABI is subject to change (see issue #29625)
   --> $DIR/feature-gate-abi.rs:42:5
    |
 42 |     extern "rust-call" fn dm4() {} //~ ERROR rust-call ABI is subject to change
@@ -158,7 +158,7 @@ error: rust-call ABI is subject to change (see issue #29625)
    |
    = help: add #![feature(unboxed_closures)] to the crate attributes to enable
 
-error: msp430-interrupt ABI is experimental and subject to change (see issue #38487)
+error[E0658]: msp430-interrupt ABI is experimental and subject to change (see issue #38487)
   --> $DIR/feature-gate-abi.rs:43:5
    |
 43 |     extern "msp430-interrupt" fn dm5() {} //~ ERROR msp430-interrupt ABI is experimental
@@ -166,7 +166,7 @@ error: msp430-interrupt ABI is experimental and subject to change (see issue #38
    |
    = help: add #![feature(abi_msp430_interrupt)] to the crate attributes to enable
 
-error: PTX ABIs are experimental and subject to change
+error[E0658]: PTX ABIs are experimental and subject to change
   --> $DIR/feature-gate-abi.rs:44:5
    |
 44 |     extern "ptx-kernel" fn dm6() {} //~ ERROR PTX ABIs are experimental and subject to change
@@ -174,7 +174,7 @@ error: PTX ABIs are experimental and subject to change
    |
    = help: add #![feature(abi_ptx)] to the crate attributes to enable
 
-error: x86-interrupt ABI is experimental and subject to change (see issue #40180)
+error[E0658]: x86-interrupt ABI is experimental and subject to change (see issue #40180)
   --> $DIR/feature-gate-abi.rs:45:5
    |
 45 |     extern "x86-interrupt" fn dm7() {} //~ ERROR x86-interrupt ABI is experimental
@@ -182,7 +182,7 @@ error: x86-interrupt ABI is experimental and subject to change (see issue #40180
    |
    = help: add #![feature(abi_x86_interrupt)] to the crate attributes to enable
 
-error: thiscall is experimental and subject to change
+error[E0658]: thiscall is experimental and subject to change
   --> $DIR/feature-gate-abi.rs:46:5
    |
 46 |     extern "thiscall" fn dm8() {} //~ ERROR thiscall is experimental and subject to change
@@ -190,7 +190,7 @@ error: thiscall is experimental and subject to change
    |
    = help: add #![feature(abi_thiscall)] to the crate attributes to enable
 
-error: intrinsics are subject to change
+error[E0658]: intrinsics are subject to change
   --> $DIR/feature-gate-abi.rs:53:5
    |
 53 |     extern "rust-intrinsic" fn m1() {} //~ ERROR intrinsics are subject to change
@@ -198,7 +198,7 @@ error: intrinsics are subject to change
    |
    = help: add #![feature(intrinsics)] to the crate attributes to enable
 
-error: platform intrinsics are experimental and possibly buggy (see issue #27731)
+error[E0658]: platform intrinsics are experimental and possibly buggy (see issue #27731)
   --> $DIR/feature-gate-abi.rs:54:5
    |
 54 |     extern "platform-intrinsic" fn m2() {} //~ ERROR platform intrinsics are experimental
@@ -206,7 +206,7 @@ error: platform intrinsics are experimental and possibly buggy (see issue #27731
    |
    = help: add #![feature(platform_intrinsics)] to the crate attributes to enable
 
-error: vectorcall is experimental and subject to change
+error[E0658]: vectorcall is experimental and subject to change
   --> $DIR/feature-gate-abi.rs:55:5
    |
 55 |     extern "vectorcall" fn m3() {} //~ ERROR vectorcall is experimental and subject to change
@@ -214,7 +214,7 @@ error: vectorcall is experimental and subject to change
    |
    = help: add #![feature(abi_vectorcall)] to the crate attributes to enable
 
-error: rust-call ABI is subject to change (see issue #29625)
+error[E0658]: rust-call ABI is subject to change (see issue #29625)
   --> $DIR/feature-gate-abi.rs:56:5
    |
 56 |     extern "rust-call" fn m4() {} //~ ERROR rust-call ABI is subject to change
@@ -222,7 +222,7 @@ error: rust-call ABI is subject to change (see issue #29625)
    |
    = help: add #![feature(unboxed_closures)] to the crate attributes to enable
 
-error: msp430-interrupt ABI is experimental and subject to change (see issue #38487)
+error[E0658]: msp430-interrupt ABI is experimental and subject to change (see issue #38487)
   --> $DIR/feature-gate-abi.rs:57:5
    |
 57 |     extern "msp430-interrupt" fn m5() {} //~ ERROR msp430-interrupt ABI is experimental
@@ -230,7 +230,7 @@ error: msp430-interrupt ABI is experimental and subject to change (see issue #38
    |
    = help: add #![feature(abi_msp430_interrupt)] to the crate attributes to enable
 
-error: PTX ABIs are experimental and subject to change
+error[E0658]: PTX ABIs are experimental and subject to change
   --> $DIR/feature-gate-abi.rs:58:5
    |
 58 |     extern "ptx-kernel" fn m6() {} //~ ERROR PTX ABIs are experimental and subject to change
@@ -238,7 +238,7 @@ error: PTX ABIs are experimental and subject to change
    |
    = help: add #![feature(abi_ptx)] to the crate attributes to enable
 
-error: x86-interrupt ABI is experimental and subject to change (see issue #40180)
+error[E0658]: x86-interrupt ABI is experimental and subject to change (see issue #40180)
   --> $DIR/feature-gate-abi.rs:59:5
    |
 59 |     extern "x86-interrupt" fn m7() {} //~ ERROR x86-interrupt ABI is experimental
@@ -246,7 +246,7 @@ error: x86-interrupt ABI is experimental and subject to change (see issue #40180
    |
    = help: add #![feature(abi_x86_interrupt)] to the crate attributes to enable
 
-error: thiscall is experimental and subject to change
+error[E0658]: thiscall is experimental and subject to change
   --> $DIR/feature-gate-abi.rs:60:5
    |
 60 |     extern "thiscall" fn m8() {} //~ ERROR thiscall is experimental and subject to change
@@ -254,7 +254,7 @@ error: thiscall is experimental and subject to change
    |
    = help: add #![feature(abi_thiscall)] to the crate attributes to enable
 
-error: intrinsics are subject to change
+error[E0658]: intrinsics are subject to change
   --> $DIR/feature-gate-abi.rs:65:5
    |
 65 |     extern "rust-intrinsic" fn im1() {} //~ ERROR intrinsics are subject to change
@@ -262,7 +262,7 @@ error: intrinsics are subject to change
    |
    = help: add #![feature(intrinsics)] to the crate attributes to enable
 
-error: platform intrinsics are experimental and possibly buggy (see issue #27731)
+error[E0658]: platform intrinsics are experimental and possibly buggy (see issue #27731)
   --> $DIR/feature-gate-abi.rs:66:5
    |
 66 |     extern "platform-intrinsic" fn im2() {} //~ ERROR platform intrinsics are experimental
@@ -270,7 +270,7 @@ error: platform intrinsics are experimental and possibly buggy (see issue #27731
    |
    = help: add #![feature(platform_intrinsics)] to the crate attributes to enable
 
-error: vectorcall is experimental and subject to change
+error[E0658]: vectorcall is experimental and subject to change
   --> $DIR/feature-gate-abi.rs:67:5
    |
 67 |     extern "vectorcall" fn im3() {} //~ ERROR vectorcall is experimental and subject to change
@@ -278,7 +278,7 @@ error: vectorcall is experimental and subject to change
    |
    = help: add #![feature(abi_vectorcall)] to the crate attributes to enable
 
-error: rust-call ABI is subject to change (see issue #29625)
+error[E0658]: rust-call ABI is subject to change (see issue #29625)
   --> $DIR/feature-gate-abi.rs:68:5
    |
 68 |     extern "rust-call" fn im4() {} //~ ERROR rust-call ABI is subject to change
@@ -286,7 +286,7 @@ error: rust-call ABI is subject to change (see issue #29625)
    |
    = help: add #![feature(unboxed_closures)] to the crate attributes to enable
 
-error: msp430-interrupt ABI is experimental and subject to change (see issue #38487)
+error[E0658]: msp430-interrupt ABI is experimental and subject to change (see issue #38487)
   --> $DIR/feature-gate-abi.rs:69:5
    |
 69 |     extern "msp430-interrupt" fn im5() {} //~ ERROR msp430-interrupt ABI is experimental
@@ -294,7 +294,7 @@ error: msp430-interrupt ABI is experimental and subject to change (see issue #38
    |
    = help: add #![feature(abi_msp430_interrupt)] to the crate attributes to enable
 
-error: PTX ABIs are experimental and subject to change
+error[E0658]: PTX ABIs are experimental and subject to change
   --> $DIR/feature-gate-abi.rs:70:5
    |
 70 |     extern "ptx-kernel" fn im6() {} //~ ERROR PTX ABIs are experimental and subject to change
@@ -302,7 +302,7 @@ error: PTX ABIs are experimental and subject to change
    |
    = help: add #![feature(abi_ptx)] to the crate attributes to enable
 
-error: x86-interrupt ABI is experimental and subject to change (see issue #40180)
+error[E0658]: x86-interrupt ABI is experimental and subject to change (see issue #40180)
   --> $DIR/feature-gate-abi.rs:71:5
    |
 71 |     extern "x86-interrupt" fn im7() {} //~ ERROR x86-interrupt ABI is experimental
@@ -310,7 +310,7 @@ error: x86-interrupt ABI is experimental and subject to change (see issue #40180
    |
    = help: add #![feature(abi_x86_interrupt)] to the crate attributes to enable
 
-error: thiscall is experimental and subject to change
+error[E0658]: thiscall is experimental and subject to change
   --> $DIR/feature-gate-abi.rs:72:5
    |
 72 |     extern "thiscall" fn im8() {} //~ ERROR thiscall is experimental and subject to change
@@ -318,7 +318,7 @@ error: thiscall is experimental and subject to change
    |
    = help: add #![feature(abi_thiscall)] to the crate attributes to enable
 
-error: intrinsics are subject to change
+error[E0658]: intrinsics are subject to change
   --> $DIR/feature-gate-abi.rs:76:11
    |
 76 | type A1 = extern "rust-intrinsic" fn(); //~ ERROR intrinsics are subject to change
@@ -326,7 +326,7 @@ error: intrinsics are subject to change
    |
    = help: add #![feature(intrinsics)] to the crate attributes to enable
 
-error: platform intrinsics are experimental and possibly buggy (see issue #27731)
+error[E0658]: platform intrinsics are experimental and possibly buggy (see issue #27731)
   --> $DIR/feature-gate-abi.rs:77:11
    |
 77 | type A2 = extern "platform-intrinsic" fn(); //~ ERROR platform intrinsics are experimental
@@ -334,7 +334,7 @@ error: platform intrinsics are experimental and possibly buggy (see issue #27731
    |
    = help: add #![feature(platform_intrinsics)] to the crate attributes to enable
 
-error: vectorcall is experimental and subject to change
+error[E0658]: vectorcall is experimental and subject to change
   --> $DIR/feature-gate-abi.rs:78:11
    |
 78 | type A3 = extern "vectorcall" fn(); //~ ERROR vectorcall is experimental and subject to change
@@ -342,7 +342,7 @@ error: vectorcall is experimental and subject to change
    |
    = help: add #![feature(abi_vectorcall)] to the crate attributes to enable
 
-error: rust-call ABI is subject to change (see issue #29625)
+error[E0658]: rust-call ABI is subject to change (see issue #29625)
   --> $DIR/feature-gate-abi.rs:79:11
    |
 79 | type A4 = extern "rust-call" fn(); //~ ERROR rust-call ABI is subject to change
@@ -350,7 +350,7 @@ error: rust-call ABI is subject to change (see issue #29625)
    |
    = help: add #![feature(unboxed_closures)] to the crate attributes to enable
 
-error: msp430-interrupt ABI is experimental and subject to change (see issue #38487)
+error[E0658]: msp430-interrupt ABI is experimental and subject to change (see issue #38487)
   --> $DIR/feature-gate-abi.rs:80:11
    |
 80 | type A5 = extern "msp430-interrupt" fn(); //~ ERROR msp430-interrupt ABI is experimental
@@ -358,7 +358,7 @@ error: msp430-interrupt ABI is experimental and subject to change (see issue #38
    |
    = help: add #![feature(abi_msp430_interrupt)] to the crate attributes to enable
 
-error: PTX ABIs are experimental and subject to change
+error[E0658]: PTX ABIs are experimental and subject to change
   --> $DIR/feature-gate-abi.rs:81:11
    |
 81 | type A6 = extern "ptx-kernel" fn (); //~ ERROR PTX ABIs are experimental and subject to change
@@ -366,7 +366,7 @@ error: PTX ABIs are experimental and subject to change
    |
    = help: add #![feature(abi_ptx)] to the crate attributes to enable
 
-error: x86-interrupt ABI is experimental and subject to change (see issue #40180)
+error[E0658]: x86-interrupt ABI is experimental and subject to change (see issue #40180)
   --> $DIR/feature-gate-abi.rs:82:11
    |
 82 | type A7 = extern "x86-interrupt" fn(); //~ ERROR x86-interrupt ABI is experimental
@@ -374,7 +374,7 @@ error: x86-interrupt ABI is experimental and subject to change (see issue #40180
    |
    = help: add #![feature(abi_x86_interrupt)] to the crate attributes to enable
 
-error: thiscall is experimental and subject to change
+error[E0658]: thiscall is experimental and subject to change
   --> $DIR/feature-gate-abi.rs:83:11
    |
 83 | type A8 = extern "thiscall" fn(); //~ ERROR thiscall is experimental and subject to change
@@ -382,7 +382,7 @@ error: thiscall is experimental and subject to change
    |
    = help: add #![feature(abi_thiscall)] to the crate attributes to enable
 
-error: intrinsics are subject to change
+error[E0658]: intrinsics are subject to change
   --> $DIR/feature-gate-abi.rs:86:1
    |
 86 | extern "rust-intrinsic" {} //~ ERROR intrinsics are subject to change
@@ -390,7 +390,7 @@ error: intrinsics are subject to change
    |
    = help: add #![feature(intrinsics)] to the crate attributes to enable
 
-error: platform intrinsics are experimental and possibly buggy (see issue #27731)
+error[E0658]: platform intrinsics are experimental and possibly buggy (see issue #27731)
   --> $DIR/feature-gate-abi.rs:87:1
    |
 87 | extern "platform-intrinsic" {} //~ ERROR platform intrinsics are experimental
@@ -398,7 +398,7 @@ error: platform intrinsics are experimental and possibly buggy (see issue #27731
    |
    = help: add #![feature(platform_intrinsics)] to the crate attributes to enable
 
-error: vectorcall is experimental and subject to change
+error[E0658]: vectorcall is experimental and subject to change
   --> $DIR/feature-gate-abi.rs:88:1
    |
 88 | extern "vectorcall" {} //~ ERROR vectorcall is experimental and subject to change
@@ -406,7 +406,7 @@ error: vectorcall is experimental and subject to change
    |
    = help: add #![feature(abi_vectorcall)] to the crate attributes to enable
 
-error: rust-call ABI is subject to change (see issue #29625)
+error[E0658]: rust-call ABI is subject to change (see issue #29625)
   --> $DIR/feature-gate-abi.rs:89:1
    |
 89 | extern "rust-call" {} //~ ERROR rust-call ABI is subject to change
@@ -414,7 +414,7 @@ error: rust-call ABI is subject to change (see issue #29625)
    |
    = help: add #![feature(unboxed_closures)] to the crate attributes to enable
 
-error: msp430-interrupt ABI is experimental and subject to change (see issue #38487)
+error[E0658]: msp430-interrupt ABI is experimental and subject to change (see issue #38487)
   --> $DIR/feature-gate-abi.rs:90:1
    |
 90 | extern "msp430-interrupt" {} //~ ERROR msp430-interrupt ABI is experimental
@@ -422,7 +422,7 @@ error: msp430-interrupt ABI is experimental and subject to change (see issue #38
    |
    = help: add #![feature(abi_msp430_interrupt)] to the crate attributes to enable
 
-error: PTX ABIs are experimental and subject to change
+error[E0658]: PTX ABIs are experimental and subject to change
   --> $DIR/feature-gate-abi.rs:91:1
    |
 91 | extern "ptx-kernel" {} //~ ERROR PTX ABIs are experimental and subject to change
@@ -430,7 +430,7 @@ error: PTX ABIs are experimental and subject to change
    |
    = help: add #![feature(abi_ptx)] to the crate attributes to enable
 
-error: x86-interrupt ABI is experimental and subject to change (see issue #40180)
+error[E0658]: x86-interrupt ABI is experimental and subject to change (see issue #40180)
   --> $DIR/feature-gate-abi.rs:92:1
    |
 92 | extern "x86-interrupt" {} //~ ERROR x86-interrupt ABI is experimental
@@ -438,7 +438,7 @@ error: x86-interrupt ABI is experimental and subject to change (see issue #40180
    |
    = help: add #![feature(abi_x86_interrupt)] to the crate attributes to enable
 
-error: thiscall is experimental and subject to change
+error[E0658]: thiscall is experimental and subject to change
   --> $DIR/feature-gate-abi.rs:93:1
    |
 93 | extern "thiscall" {} //~ ERROR thiscall is experimental and subject to change
diff --git a/src/test/ui/feature-gate-abi_unadjusted.stderr b/src/test/ui/feature-gate-abi_unadjusted.stderr
index 3cc43847156..b3f7cd218d3 100644
--- a/src/test/ui/feature-gate-abi_unadjusted.stderr
+++ b/src/test/ui/feature-gate-abi_unadjusted.stderr
@@ -1,4 +1,4 @@
-error: unadjusted ABI is an implementation detail and perma-unstable
+error[E0658]: unadjusted ABI is an implementation detail and perma-unstable
   --> $DIR/feature-gate-abi_unadjusted.rs:11:1
    |
 11 | / extern "unadjusted" fn foo() {
diff --git a/src/test/ui/feature-gate-advanced-slice-features.stderr b/src/test/ui/feature-gate-advanced-slice-features.stderr
index 815593d07a5..63ede50e1ea 100644
--- a/src/test/ui/feature-gate-advanced-slice-features.stderr
+++ b/src/test/ui/feature-gate-advanced-slice-features.stderr
@@ -1,4 +1,4 @@
-error: multiple-element slice matches anywhere but at the end of a slice (e.g. `[0, ..xs, 0]`) are experimental (see issue #23121)
+error[E0658]: multiple-element slice matches anywhere but at the end of a slice (e.g. `[0, ..xs, 0]`) are experimental (see issue #23121)
   --> $DIR/feature-gate-advanced-slice-features.rs:18:9
    |
 18 |         [ xs.., 4, 5 ] => {}    //~ ERROR multiple-element slice matches
@@ -6,7 +6,7 @@ error: multiple-element slice matches anywhere but at the end of a slice (e.g. `
    |
    = help: add #![feature(advanced_slice_patterns)] to the crate attributes to enable
 
-error: multiple-element slice matches anywhere but at the end of a slice (e.g. `[0, ..xs, 0]`) are experimental (see issue #23121)
+error[E0658]: multiple-element slice matches anywhere but at the end of a slice (e.g. `[0, ..xs, 0]`) are experimental (see issue #23121)
   --> $DIR/feature-gate-advanced-slice-features.rs:19:9
    |
 19 |         [ 1, xs.., 5 ] => {}    //~ ERROR multiple-element slice matches
diff --git a/src/test/ui/feature-gate-allocator_internals.stderr b/src/test/ui/feature-gate-allocator_internals.stderr
index f1f4705b3bb..76d96f929be 100644
--- a/src/test/ui/feature-gate-allocator_internals.stderr
+++ b/src/test/ui/feature-gate-allocator_internals.stderr
@@ -1,4 +1,4 @@
-error: the `#[default_lib_allocator]` attribute is an experimental feature
+error[E0658]: the `#[default_lib_allocator]` attribute is an experimental feature
   --> $DIR/feature-gate-allocator_internals.rs:11:1
    |
 11 | #![default_lib_allocator] //~ ERROR: attribute is an experimental feature
diff --git a/src/test/ui/feature-gate-allow-internal-unsafe-nested-macro.stderr b/src/test/ui/feature-gate-allow-internal-unsafe-nested-macro.stderr
index 40bdde37ee8..31de8d76285 100644
--- a/src/test/ui/feature-gate-allow-internal-unsafe-nested-macro.stderr
+++ b/src/test/ui/feature-gate-allow-internal-unsafe-nested-macro.stderr
@@ -1,4 +1,4 @@
-error: allow_internal_unsafe side-steps the unsafe_code lint
+error[E0658]: allow_internal_unsafe side-steps the unsafe_code lint
   --> $DIR/feature-gate-allow-internal-unsafe-nested-macro.rs:18:9
    |
 18 |         #[allow_internal_unsafe] //~ ERROR allow_internal_unsafe side-steps
diff --git a/src/test/ui/feature-gate-allow-internal-unstable-nested-macro.stderr b/src/test/ui/feature-gate-allow-internal-unstable-nested-macro.stderr
index 60d72fbc3b3..3e2573eda21 100644
--- a/src/test/ui/feature-gate-allow-internal-unstable-nested-macro.stderr
+++ b/src/test/ui/feature-gate-allow-internal-unstable-nested-macro.stderr
@@ -1,4 +1,4 @@
-error: allow_internal_unstable side-steps feature gating and stability checks
+error[E0658]: allow_internal_unstable side-steps feature gating and stability checks
   --> $DIR/feature-gate-allow-internal-unstable-nested-macro.rs:18:9
    |
 18 |         #[allow_internal_unstable] //~ ERROR allow_internal_unstable side-steps
diff --git a/src/test/ui/feature-gate-allow-internal-unstable-struct.stderr b/src/test/ui/feature-gate-allow-internal-unstable-struct.stderr
index 2fb86ce8f4e..e19f3288e81 100644
--- a/src/test/ui/feature-gate-allow-internal-unstable-struct.stderr
+++ b/src/test/ui/feature-gate-allow-internal-unstable-struct.stderr
@@ -1,4 +1,4 @@
-error: allow_internal_unstable side-steps feature gating and stability checks
+error[E0658]: allow_internal_unstable side-steps feature gating and stability checks
   --> $DIR/feature-gate-allow-internal-unstable-struct.rs:14:1
    |
 14 | #[allow_internal_unstable] //~ ERROR allow_internal_unstable side-steps
diff --git a/src/test/ui/feature-gate-allow-internal-unstable.stderr b/src/test/ui/feature-gate-allow-internal-unstable.stderr
index a5740a1a789..f110afb35a0 100644
--- a/src/test/ui/feature-gate-allow-internal-unstable.stderr
+++ b/src/test/ui/feature-gate-allow-internal-unstable.stderr
@@ -1,4 +1,4 @@
-error: allow_internal_unstable side-steps feature gating and stability checks
+error[E0658]: allow_internal_unstable side-steps feature gating and stability checks
   --> $DIR/feature-gate-allow-internal-unstable.rs:13:1
    |
 13 | #[allow_internal_unstable] //~ ERROR allow_internal_unstable side-steps
diff --git a/src/test/ui/feature-gate-allow_fail.stderr b/src/test/ui/feature-gate-allow_fail.stderr
index 65cd137459a..e04f44886dd 100644
--- a/src/test/ui/feature-gate-allow_fail.stderr
+++ b/src/test/ui/feature-gate-allow_fail.stderr
@@ -1,4 +1,4 @@
-error: allow_fail attribute is currently unstable (see issue #42219)
+error[E0658]: allow_fail attribute is currently unstable (see issue #42219)
   --> $DIR/feature-gate-allow_fail.rs:13:1
    |
 13 | #[allow_fail] //~ ERROR allow_fail attribute is currently unstable
diff --git a/src/test/ui/feature-gate-arbitrary-self-types.stderr b/src/test/ui/feature-gate-arbitrary-self-types.stderr
index 2ef517cc9e1..ca47d40dc8f 100644
--- a/src/test/ui/feature-gate-arbitrary-self-types.stderr
+++ b/src/test/ui/feature-gate-arbitrary-self-types.stderr
@@ -1,4 +1,4 @@
-error: arbitrary `self` types are unstable (see issue #44874)
+error[E0658]: arbitrary `self` types are unstable (see issue #44874)
   --> $DIR/feature-gate-arbitrary-self-types.rs:14:18
    |
 14 |     fn foo(self: Rc<Box<Self>>); //~ ERROR arbitrary `self` types are unstable
@@ -7,7 +7,7 @@ error: arbitrary `self` types are unstable (see issue #44874)
    = help: add #![feature(arbitrary_self_types)] to the crate attributes to enable
    = help: consider changing to `self`, `&self`, `&mut self`, or `self: Box<Self>`
 
-error: arbitrary `self` types are unstable (see issue #44874)
+error[E0658]: arbitrary `self` types are unstable (see issue #44874)
   --> $DIR/feature-gate-arbitrary-self-types.rs:20:18
    |
 20 |     fn foo(self: Rc<Box<Self>>) {} //~ ERROR arbitrary `self` types are unstable
@@ -16,7 +16,7 @@ error: arbitrary `self` types are unstable (see issue #44874)
    = help: add #![feature(arbitrary_self_types)] to the crate attributes to enable
    = help: consider changing to `self`, `&self`, `&mut self`, or `self: Box<Self>`
 
-error: arbitrary `self` types are unstable (see issue #44874)
+error[E0658]: arbitrary `self` types are unstable (see issue #44874)
   --> $DIR/feature-gate-arbitrary-self-types.rs:24:18
    |
 24 |     fn bar(self: Box<Rc<Self>>) {} //~ ERROR arbitrary `self` types are unstable
diff --git a/src/test/ui/feature-gate-arbitrary_self_types-raw-pointer.stderr b/src/test/ui/feature-gate-arbitrary_self_types-raw-pointer.stderr
index d629ac4c60f..33e8806678d 100644
--- a/src/test/ui/feature-gate-arbitrary_self_types-raw-pointer.stderr
+++ b/src/test/ui/feature-gate-arbitrary_self_types-raw-pointer.stderr
@@ -1,4 +1,4 @@
-error: raw pointer `self` is unstable (see issue #44874)
+error[E0658]: raw pointer `self` is unstable (see issue #44874)
   --> $DIR/feature-gate-arbitrary_self_types-raw-pointer.rs:19:18
    |
 19 |     fn bar(self: *const Self);
@@ -7,7 +7,7 @@ error: raw pointer `self` is unstable (see issue #44874)
    = help: add #![feature(arbitrary_self_types)] to the crate attributes to enable
    = help: consider changing to `self`, `&self`, `&mut self`, or `self: Box<Self>`
 
-error: raw pointer `self` is unstable (see issue #44874)
+error[E0658]: raw pointer `self` is unstable (see issue #44874)
   --> $DIR/feature-gate-arbitrary_self_types-raw-pointer.rs:14:18
    |
 14 |     fn foo(self: *const Self) {}
@@ -16,7 +16,7 @@ error: raw pointer `self` is unstable (see issue #44874)
    = help: add #![feature(arbitrary_self_types)] to the crate attributes to enable
    = help: consider changing to `self`, `&self`, `&mut self`, or `self: Box<Self>`
 
-error: raw pointer `self` is unstable (see issue #44874)
+error[E0658]: raw pointer `self` is unstable (see issue #44874)
   --> $DIR/feature-gate-arbitrary_self_types-raw-pointer.rs:24:18
    |
 24 |     fn bar(self: *const Self) {}
diff --git a/src/test/ui/feature-gate-asm.stderr b/src/test/ui/feature-gate-asm.stderr
index ff68a4fb23e..481e6dc7055 100644
--- a/src/test/ui/feature-gate-asm.stderr
+++ b/src/test/ui/feature-gate-asm.stderr
@@ -1,4 +1,4 @@
-error: inline assembly is not stable enough for use and is subject to change (see issue #29722)
+error[E0658]: inline assembly is not stable enough for use and is subject to change (see issue #29722)
   --> $DIR/feature-gate-asm.rs:13:9
    |
 13 |         asm!(""); //~ ERROR inline assembly is not stable enough
diff --git a/src/test/ui/feature-gate-asm2.stderr b/src/test/ui/feature-gate-asm2.stderr
index 1e02cede61d..aba0f72d35c 100644
--- a/src/test/ui/feature-gate-asm2.stderr
+++ b/src/test/ui/feature-gate-asm2.stderr
@@ -1,4 +1,4 @@
-error: inline assembly is not stable enough for use and is subject to change (see issue #29722)
+error[E0658]: inline assembly is not stable enough for use and is subject to change (see issue #29722)
   --> $DIR/feature-gate-asm2.rs:15:24
    |
 15 |         println!("{}", asm!("")); //~ ERROR inline assembly is not stable
diff --git a/src/test/ui/feature-gate-assoc-type-defaults.stderr b/src/test/ui/feature-gate-assoc-type-defaults.stderr
index 5e288469168..1d44797cddc 100644
--- a/src/test/ui/feature-gate-assoc-type-defaults.stderr
+++ b/src/test/ui/feature-gate-assoc-type-defaults.stderr
@@ -1,4 +1,4 @@
-error: associated type defaults are unstable (see issue #29661)
+error[E0658]: associated type defaults are unstable (see issue #29661)
   --> $DIR/feature-gate-assoc-type-defaults.rs:14:5
    |
 14 |     type Bar = u8; //~ ERROR associated type defaults are unstable
diff --git a/src/test/ui/feature-gate-box-expr.stderr b/src/test/ui/feature-gate-box-expr.stderr
index cef5adbd15a..f9cccde3761 100644
--- a/src/test/ui/feature-gate-box-expr.stderr
+++ b/src/test/ui/feature-gate-box-expr.stderr
@@ -1,4 +1,4 @@
-error: box expression syntax is experimental; you can call `Box::new` instead. (see issue #27779)
+error[E0658]: box expression syntax is experimental; you can call `Box::new` instead. (see issue #27779)
   --> $DIR/feature-gate-box-expr.rs:22:13
    |
 22 |     let x = box 'c'; //~ ERROR box expression syntax is experimental
diff --git a/src/test/ui/feature-gate-box_patterns.stderr b/src/test/ui/feature-gate-box_patterns.stderr
index 0a30de58a1f..ca009331b69 100644
--- a/src/test/ui/feature-gate-box_patterns.stderr
+++ b/src/test/ui/feature-gate-box_patterns.stderr
@@ -1,4 +1,4 @@
-error: box pattern syntax is experimental (see issue #29641)
+error[E0658]: box pattern syntax is experimental (see issue #29641)
   --> $DIR/feature-gate-box_patterns.rs:12:9
    |
 12 |     let box x = Box::new('c'); //~ ERROR box pattern syntax is experimental
diff --git a/src/test/ui/feature-gate-box_syntax.stderr b/src/test/ui/feature-gate-box_syntax.stderr
index 9b21dd03051..eefaa724650 100644
--- a/src/test/ui/feature-gate-box_syntax.stderr
+++ b/src/test/ui/feature-gate-box_syntax.stderr
@@ -1,4 +1,4 @@
-error: box expression syntax is experimental; you can call `Box::new` instead. (see issue #27779)
+error[E0658]: box expression syntax is experimental; you can call `Box::new` instead. (see issue #27779)
   --> $DIR/feature-gate-box_syntax.rs:14:13
    |
 14 |     let x = box 3;
diff --git a/src/test/ui/feature-gate-catch_expr.stderr b/src/test/ui/feature-gate-catch_expr.stderr
index f486373d225..4b3bfbbe27a 100644
--- a/src/test/ui/feature-gate-catch_expr.stderr
+++ b/src/test/ui/feature-gate-catch_expr.stderr
@@ -1,4 +1,4 @@
-error: `catch` expression is experimental (see issue #31436)
+error[E0658]: `catch` expression is experimental (see issue #31436)
   --> $DIR/feature-gate-catch_expr.rs:12:24
    |
 12 |       let catch_result = do catch { //~ ERROR `catch` expression is experimental
diff --git a/src/test/ui/feature-gate-cfg-target-feature.stderr b/src/test/ui/feature-gate-cfg-target-feature.stderr
index 60dc6fbb57e..f808e78acce 100644
--- a/src/test/ui/feature-gate-cfg-target-feature.stderr
+++ b/src/test/ui/feature-gate-cfg-target-feature.stderr
@@ -1,4 +1,4 @@
-error: `cfg(target_feature)` is experimental and subject to change (see issue #29717)
+error[E0658]: `cfg(target_feature)` is experimental and subject to change (see issue #29717)
   --> $DIR/feature-gate-cfg-target-feature.rs:12:12
    |
 12 | #[cfg_attr(target_feature = "x", x)] //~ ERROR `cfg(target_feature)` is experimental
@@ -6,7 +6,7 @@ error: `cfg(target_feature)` is experimental and subject to change (see issue #2
    |
    = help: add #![feature(cfg_target_feature)] to the crate attributes to enable
 
-error: `cfg(target_feature)` is experimental and subject to change (see issue #29717)
+error[E0658]: `cfg(target_feature)` is experimental and subject to change (see issue #29717)
   --> $DIR/feature-gate-cfg-target-feature.rs:11:7
    |
 11 | #[cfg(target_feature = "x")] //~ ERROR `cfg(target_feature)` is experimental
@@ -14,7 +14,7 @@ error: `cfg(target_feature)` is experimental and subject to change (see issue #2
    |
    = help: add #![feature(cfg_target_feature)] to the crate attributes to enable
 
-error: `cfg(target_feature)` is experimental and subject to change (see issue #29717)
+error[E0658]: `cfg(target_feature)` is experimental and subject to change (see issue #29717)
   --> $DIR/feature-gate-cfg-target-feature.rs:15:19
    |
 15 | #[cfg(not(any(all(target_feature = "x"))))] //~ ERROR `cfg(target_feature)` is experimental
@@ -22,7 +22,7 @@ error: `cfg(target_feature)` is experimental and subject to change (see issue #2
    |
    = help: add #![feature(cfg_target_feature)] to the crate attributes to enable
 
-error: `cfg(target_feature)` is experimental and subject to change (see issue #29717)
+error[E0658]: `cfg(target_feature)` is experimental and subject to change (see issue #29717)
   --> $DIR/feature-gate-cfg-target-feature.rs:19:10
    |
 19 |     cfg!(target_feature = "x");
diff --git a/src/test/ui/feature-gate-cfg-target-has-atomic.stderr b/src/test/ui/feature-gate-cfg-target-has-atomic.stderr
index 5daf5de7123..ace23b38d2d 100644
--- a/src/test/ui/feature-gate-cfg-target-has-atomic.stderr
+++ b/src/test/ui/feature-gate-cfg-target-has-atomic.stderr
@@ -1,4 +1,4 @@
-error: `cfg(target_has_atomic)` is experimental and subject to change (see issue #32976)
+error[E0658]: `cfg(target_has_atomic)` is experimental and subject to change (see issue #32976)
   --> $DIR/feature-gate-cfg-target-has-atomic.rs:23:7
    |
 23 | #[cfg(target_has_atomic = "8")]
@@ -6,7 +6,7 @@ error: `cfg(target_has_atomic)` is experimental and subject to change (see issue
    |
    = help: add #![feature(cfg_target_has_atomic)] to the crate attributes to enable
 
-error: `cfg(target_has_atomic)` is experimental and subject to change (see issue #32976)
+error[E0658]: `cfg(target_has_atomic)` is experimental and subject to change (see issue #32976)
   --> $DIR/feature-gate-cfg-target-has-atomic.rs:29:7
    |
 29 | #[cfg(target_has_atomic = "8")]
@@ -14,7 +14,7 @@ error: `cfg(target_has_atomic)` is experimental and subject to change (see issue
    |
    = help: add #![feature(cfg_target_has_atomic)] to the crate attributes to enable
 
-error: `cfg(target_has_atomic)` is experimental and subject to change (see issue #32976)
+error[E0658]: `cfg(target_has_atomic)` is experimental and subject to change (see issue #32976)
   --> $DIR/feature-gate-cfg-target-has-atomic.rs:34:7
    |
 34 | #[cfg(target_has_atomic = "16")]
@@ -22,7 +22,7 @@ error: `cfg(target_has_atomic)` is experimental and subject to change (see issue
    |
    = help: add #![feature(cfg_target_has_atomic)] to the crate attributes to enable
 
-error: `cfg(target_has_atomic)` is experimental and subject to change (see issue #32976)
+error[E0658]: `cfg(target_has_atomic)` is experimental and subject to change (see issue #32976)
   --> $DIR/feature-gate-cfg-target-has-atomic.rs:39:7
    |
 39 | #[cfg(target_has_atomic = "16")]
@@ -30,7 +30,7 @@ error: `cfg(target_has_atomic)` is experimental and subject to change (see issue
    |
    = help: add #![feature(cfg_target_has_atomic)] to the crate attributes to enable
 
-error: `cfg(target_has_atomic)` is experimental and subject to change (see issue #32976)
+error[E0658]: `cfg(target_has_atomic)` is experimental and subject to change (see issue #32976)
   --> $DIR/feature-gate-cfg-target-has-atomic.rs:44:7
    |
 44 | #[cfg(target_has_atomic = "32")]
@@ -38,7 +38,7 @@ error: `cfg(target_has_atomic)` is experimental and subject to change (see issue
    |
    = help: add #![feature(cfg_target_has_atomic)] to the crate attributes to enable
 
-error: `cfg(target_has_atomic)` is experimental and subject to change (see issue #32976)
+error[E0658]: `cfg(target_has_atomic)` is experimental and subject to change (see issue #32976)
   --> $DIR/feature-gate-cfg-target-has-atomic.rs:49:7
    |
 49 | #[cfg(target_has_atomic = "32")]
@@ -46,7 +46,7 @@ error: `cfg(target_has_atomic)` is experimental and subject to change (see issue
    |
    = help: add #![feature(cfg_target_has_atomic)] to the crate attributes to enable
 
-error: `cfg(target_has_atomic)` is experimental and subject to change (see issue #32976)
+error[E0658]: `cfg(target_has_atomic)` is experimental and subject to change (see issue #32976)
   --> $DIR/feature-gate-cfg-target-has-atomic.rs:54:7
    |
 54 | #[cfg(target_has_atomic = "64")]
@@ -54,7 +54,7 @@ error: `cfg(target_has_atomic)` is experimental and subject to change (see issue
    |
    = help: add #![feature(cfg_target_has_atomic)] to the crate attributes to enable
 
-error: `cfg(target_has_atomic)` is experimental and subject to change (see issue #32976)
+error[E0658]: `cfg(target_has_atomic)` is experimental and subject to change (see issue #32976)
   --> $DIR/feature-gate-cfg-target-has-atomic.rs:59:7
    |
 59 | #[cfg(target_has_atomic = "64")]
@@ -62,7 +62,7 @@ error: `cfg(target_has_atomic)` is experimental and subject to change (see issue
    |
    = help: add #![feature(cfg_target_has_atomic)] to the crate attributes to enable
 
-error: `cfg(target_has_atomic)` is experimental and subject to change (see issue #32976)
+error[E0658]: `cfg(target_has_atomic)` is experimental and subject to change (see issue #32976)
   --> $DIR/feature-gate-cfg-target-has-atomic.rs:64:7
    |
 64 | #[cfg(target_has_atomic = "ptr")]
@@ -70,7 +70,7 @@ error: `cfg(target_has_atomic)` is experimental and subject to change (see issue
    |
    = help: add #![feature(cfg_target_has_atomic)] to the crate attributes to enable
 
-error: `cfg(target_has_atomic)` is experimental and subject to change (see issue #32976)
+error[E0658]: `cfg(target_has_atomic)` is experimental and subject to change (see issue #32976)
   --> $DIR/feature-gate-cfg-target-has-atomic.rs:69:7
    |
 69 | #[cfg(target_has_atomic = "ptr")]
@@ -78,7 +78,7 @@ error: `cfg(target_has_atomic)` is experimental and subject to change (see issue
    |
    = help: add #![feature(cfg_target_has_atomic)] to the crate attributes to enable
 
-error: `cfg(target_has_atomic)` is experimental and subject to change (see issue #32976)
+error[E0658]: `cfg(target_has_atomic)` is experimental and subject to change (see issue #32976)
   --> $DIR/feature-gate-cfg-target-has-atomic.rs:76:10
    |
 76 |     cfg!(target_has_atomic = "8");
@@ -86,7 +86,7 @@ error: `cfg(target_has_atomic)` is experimental and subject to change (see issue
    |
    = help: add #![feature(cfg_target_has_atomic)] to the crate attributes to enable
 
-error: `cfg(target_has_atomic)` is experimental and subject to change (see issue #32976)
+error[E0658]: `cfg(target_has_atomic)` is experimental and subject to change (see issue #32976)
   --> $DIR/feature-gate-cfg-target-has-atomic.rs:78:10
    |
 78 |     cfg!(target_has_atomic = "16");
@@ -94,7 +94,7 @@ error: `cfg(target_has_atomic)` is experimental and subject to change (see issue
    |
    = help: add #![feature(cfg_target_has_atomic)] to the crate attributes to enable
 
-error: `cfg(target_has_atomic)` is experimental and subject to change (see issue #32976)
+error[E0658]: `cfg(target_has_atomic)` is experimental and subject to change (see issue #32976)
   --> $DIR/feature-gate-cfg-target-has-atomic.rs:80:10
    |
 80 |     cfg!(target_has_atomic = "32");
@@ -102,7 +102,7 @@ error: `cfg(target_has_atomic)` is experimental and subject to change (see issue
    |
    = help: add #![feature(cfg_target_has_atomic)] to the crate attributes to enable
 
-error: `cfg(target_has_atomic)` is experimental and subject to change (see issue #32976)
+error[E0658]: `cfg(target_has_atomic)` is experimental and subject to change (see issue #32976)
   --> $DIR/feature-gate-cfg-target-has-atomic.rs:82:10
    |
 82 |     cfg!(target_has_atomic = "64");
@@ -110,7 +110,7 @@ error: `cfg(target_has_atomic)` is experimental and subject to change (see issue
    |
    = help: add #![feature(cfg_target_has_atomic)] to the crate attributes to enable
 
-error: `cfg(target_has_atomic)` is experimental and subject to change (see issue #32976)
+error[E0658]: `cfg(target_has_atomic)` is experimental and subject to change (see issue #32976)
   --> $DIR/feature-gate-cfg-target-has-atomic.rs:84:10
    |
 84 |     cfg!(target_has_atomic = "ptr");
diff --git a/src/test/ui/feature-gate-cfg-target-thread-local.stderr b/src/test/ui/feature-gate-cfg-target-thread-local.stderr
index 9e2eea6e0a4..a0a03bdcd46 100644
--- a/src/test/ui/feature-gate-cfg-target-thread-local.stderr
+++ b/src/test/ui/feature-gate-cfg-target-thread-local.stderr
@@ -1,4 +1,4 @@
-error: `cfg(target_thread_local)` is experimental and subject to change (see issue #29594)
+error[E0658]: `cfg(target_thread_local)` is experimental and subject to change (see issue #29594)
   --> $DIR/feature-gate-cfg-target-thread-local.rs:19:16
    |
 19 |     #[cfg_attr(target_thread_local, thread_local)]
diff --git a/src/test/ui/feature-gate-cfg-target-vendor.stderr b/src/test/ui/feature-gate-cfg-target-vendor.stderr
index c5709600dba..3e4a74636f9 100644
--- a/src/test/ui/feature-gate-cfg-target-vendor.stderr
+++ b/src/test/ui/feature-gate-cfg-target-vendor.stderr
@@ -1,4 +1,4 @@
-error: `cfg(target_vendor)` is experimental and subject to change (see issue #29718)
+error[E0658]: `cfg(target_vendor)` is experimental and subject to change (see issue #29718)
   --> $DIR/feature-gate-cfg-target-vendor.rs:12:12
    |
 12 | #[cfg_attr(target_vendor = "x", x)] //~ ERROR `cfg(target_vendor)` is experimental
@@ -6,7 +6,7 @@ error: `cfg(target_vendor)` is experimental and subject to change (see issue #29
    |
    = help: add #![feature(cfg_target_vendor)] to the crate attributes to enable
 
-error: `cfg(target_vendor)` is experimental and subject to change (see issue #29718)
+error[E0658]: `cfg(target_vendor)` is experimental and subject to change (see issue #29718)
   --> $DIR/feature-gate-cfg-target-vendor.rs:11:7
    |
 11 | #[cfg(target_vendor = "x")] //~ ERROR `cfg(target_vendor)` is experimental
@@ -14,7 +14,7 @@ error: `cfg(target_vendor)` is experimental and subject to change (see issue #29
    |
    = help: add #![feature(cfg_target_vendor)] to the crate attributes to enable
 
-error: `cfg(target_vendor)` is experimental and subject to change (see issue #29718)
+error[E0658]: `cfg(target_vendor)` is experimental and subject to change (see issue #29718)
   --> $DIR/feature-gate-cfg-target-vendor.rs:15:19
    |
 15 | #[cfg(not(any(all(target_vendor = "x"))))] //~ ERROR `cfg(target_vendor)` is experimental
@@ -22,7 +22,7 @@ error: `cfg(target_vendor)` is experimental and subject to change (see issue #29
    |
    = help: add #![feature(cfg_target_vendor)] to the crate attributes to enable
 
-error: `cfg(target_vendor)` is experimental and subject to change (see issue #29718)
+error[E0658]: `cfg(target_vendor)` is experimental and subject to change (see issue #29718)
   --> $DIR/feature-gate-cfg-target-vendor.rs:19:10
    |
 19 |     cfg!(target_vendor = "x");
diff --git a/src/test/ui/feature-gate-compiler-builtins.stderr b/src/test/ui/feature-gate-compiler-builtins.stderr
index ebf42b2bdd8..edb3c5d62ae 100644
--- a/src/test/ui/feature-gate-compiler-builtins.stderr
+++ b/src/test/ui/feature-gate-compiler-builtins.stderr
@@ -1,4 +1,4 @@
-error: the `#[compiler_builtins]` attribute is used to identify the `compiler_builtins` crate which contains compiler-rt intrinsics and will never be stable
+error[E0658]: the `#[compiler_builtins]` attribute is used to identify the `compiler_builtins` crate which contains compiler-rt intrinsics and will never be stable
   --> $DIR/feature-gate-compiler-builtins.rs:11:1
    |
 11 | #![compiler_builtins] //~ ERROR the `#[compiler_builtins]` attribute is
diff --git a/src/test/ui/feature-gate-concat_idents.stderr b/src/test/ui/feature-gate-concat_idents.stderr
index c980668c298..d0a07e3d3c9 100644
--- a/src/test/ui/feature-gate-concat_idents.stderr
+++ b/src/test/ui/feature-gate-concat_idents.stderr
@@ -1,4 +1,4 @@
-error: `concat_idents` is not stable enough for use and is subject to change (see issue #29599)
+error[E0658]: `concat_idents` is not stable enough for use and is subject to change (see issue #29599)
   --> $DIR/feature-gate-concat_idents.rs:15:13
    |
 15 |     let a = concat_idents!(X, Y_1); //~ ERROR `concat_idents` is not stable
@@ -6,7 +6,7 @@ error: `concat_idents` is not stable enough for use and is subject to change (se
    |
    = help: add #![feature(concat_idents)] to the crate attributes to enable
 
-error: `concat_idents` is not stable enough for use and is subject to change (see issue #29599)
+error[E0658]: `concat_idents` is not stable enough for use and is subject to change (see issue #29599)
   --> $DIR/feature-gate-concat_idents.rs:16:13
    |
 16 |     let b = concat_idents!(X, Y_2); //~ ERROR `concat_idents` is not stable
diff --git a/src/test/ui/feature-gate-concat_idents2.stderr b/src/test/ui/feature-gate-concat_idents2.stderr
index 9cfd954eec8..0ef6921c64d 100644
--- a/src/test/ui/feature-gate-concat_idents2.stderr
+++ b/src/test/ui/feature-gate-concat_idents2.stderr
@@ -1,4 +1,4 @@
-error: `concat_idents` is not stable enough for use and is subject to change (see issue #29599)
+error[E0658]: `concat_idents` is not stable enough for use and is subject to change (see issue #29599)
   --> $DIR/feature-gate-concat_idents2.rs:14:5
    |
 14 |     concat_idents!(a, b); //~ ERROR `concat_idents` is not stable enough
diff --git a/src/test/ui/feature-gate-concat_idents3.stderr b/src/test/ui/feature-gate-concat_idents3.stderr
index 8399ca3c501..a9a1e493a45 100644
--- a/src/test/ui/feature-gate-concat_idents3.stderr
+++ b/src/test/ui/feature-gate-concat_idents3.stderr
@@ -1,4 +1,4 @@
-error: `concat_idents` is not stable enough for use and is subject to change (see issue #29599)
+error[E0658]: `concat_idents` is not stable enough for use and is subject to change (see issue #29599)
   --> $DIR/feature-gate-concat_idents3.rs:17:20
    |
 17 |     assert_eq!(10, concat_idents!(X, Y_1)); //~ ERROR `concat_idents` is not stable
@@ -6,7 +6,7 @@ error: `concat_idents` is not stable enough for use and is subject to change (se
    |
    = help: add #![feature(concat_idents)] to the crate attributes to enable
 
-error: `concat_idents` is not stable enough for use and is subject to change (see issue #29599)
+error[E0658]: `concat_idents` is not stable enough for use and is subject to change (see issue #29599)
   --> $DIR/feature-gate-concat_idents3.rs:18:20
    |
 18 |     assert_eq!(20, concat_idents!(X, Y_2)); //~ ERROR `concat_idents` is not stable
diff --git a/src/test/ui/feature-gate-conservative_impl_trait.stderr b/src/test/ui/feature-gate-conservative_impl_trait.stderr
index 72a4f52926a..f3d39477387 100644
--- a/src/test/ui/feature-gate-conservative_impl_trait.stderr
+++ b/src/test/ui/feature-gate-conservative_impl_trait.stderr
@@ -1,4 +1,4 @@
-error: `impl Trait` in return position is experimental (see issue #34511)
+error[E0658]: `impl Trait` in return position is experimental (see issue #34511)
   --> $DIR/feature-gate-conservative_impl_trait.rs:11:13
    |
 11 | fn foo() -> impl Fn() { || {} }
diff --git a/src/test/ui/feature-gate-const_fn.stderr b/src/test/ui/feature-gate-const_fn.stderr
index c62229ac71b..ecd1ff5a6c4 100644
--- a/src/test/ui/feature-gate-const_fn.stderr
+++ b/src/test/ui/feature-gate-const_fn.stderr
@@ -16,7 +16,7 @@ error[E0379]: trait fns cannot be declared const
 27 |     const fn foo() -> u32 { 0 } //~ ERROR const fn is unstable
    |     ^^^^^ trait fns cannot be const
 
-error: const fn is unstable (see issue #24111)
+error[E0658]: const fn is unstable (see issue #24111)
   --> $DIR/feature-gate-const_fn.rs:13:1
    |
 13 | const fn foo() -> usize { 0 } //~ ERROR const fn is unstable
@@ -24,7 +24,7 @@ error: const fn is unstable (see issue #24111)
    |
    = help: add #![feature(const_fn)] to the crate attributes to enable
 
-error: const fn is unstable (see issue #24111)
+error[E0658]: const fn is unstable (see issue #24111)
   --> $DIR/feature-gate-const_fn.rs:16:5
    |
 16 |     const fn foo() -> u32; //~ ERROR const fn is unstable
@@ -32,7 +32,7 @@ error: const fn is unstable (see issue #24111)
    |
    = help: add #![feature(const_fn)] to the crate attributes to enable
 
-error: const fn is unstable (see issue #24111)
+error[E0658]: const fn is unstable (see issue #24111)
   --> $DIR/feature-gate-const_fn.rs:18:5
    |
 18 |     const fn bar() -> u32 { 0 } //~ ERROR const fn is unstable
@@ -40,7 +40,7 @@ error: const fn is unstable (see issue #24111)
    |
    = help: add #![feature(const_fn)] to the crate attributes to enable
 
-error: const fn is unstable (see issue #24111)
+error[E0658]: const fn is unstable (see issue #24111)
   --> $DIR/feature-gate-const_fn.rs:23:5
    |
 23 |     const fn baz() -> u32 { 0 } //~ ERROR const fn is unstable
@@ -48,7 +48,7 @@ error: const fn is unstable (see issue #24111)
    |
    = help: add #![feature(const_fn)] to the crate attributes to enable
 
-error: const fn is unstable (see issue #24111)
+error[E0658]: const fn is unstable (see issue #24111)
   --> $DIR/feature-gate-const_fn.rs:27:5
    |
 27 |     const fn foo() -> u32 { 0 } //~ ERROR const fn is unstable
diff --git a/src/test/ui/feature-gate-crate_in_paths.stderr b/src/test/ui/feature-gate-crate_in_paths.stderr
index b13c82ecfc9..322a38a996f 100644
--- a/src/test/ui/feature-gate-crate_in_paths.stderr
+++ b/src/test/ui/feature-gate-crate_in_paths.stderr
@@ -1,4 +1,4 @@
-error: `crate` in paths is experimental (see issue #45477)
+error[E0658]: `crate` in paths is experimental (see issue #45477)
   --> $DIR/feature-gate-crate_in_paths.rs:14:15
    |
 14 |     let _ = ::crate::S; //~ ERROR `crate` in paths is experimental
diff --git a/src/test/ui/feature-gate-crate_visibility_modifier.stderr b/src/test/ui/feature-gate-crate_visibility_modifier.stderr
index 0862744b87b..fadc76bc0c0 100644
--- a/src/test/ui/feature-gate-crate_visibility_modifier.stderr
+++ b/src/test/ui/feature-gate-crate_visibility_modifier.stderr
@@ -1,4 +1,4 @@
-error: `crate` visibility modifier is experimental (see issue #45388)
+error[E0658]: `crate` visibility modifier is experimental (see issue #45388)
   --> $DIR/feature-gate-crate_visibility_modifier.rs:11:1
    |
 11 | crate struct Bender { //~ ERROR `crate` visibility modifier is experimental
diff --git a/src/test/ui/feature-gate-custom_attribute.stderr b/src/test/ui/feature-gate-custom_attribute.stderr
index 866ebfe8f2f..f4d726c8c41 100644
--- a/src/test/ui/feature-gate-custom_attribute.stderr
+++ b/src/test/ui/feature-gate-custom_attribute.stderr
@@ -1,4 +1,4 @@
-error: The attribute `fake_attr` is currently unknown to the compiler and may have meaning added to it in the future (see issue #29642)
+error[E0658]: The attribute `fake_attr` is currently unknown to the compiler and may have meaning added to it in the future (see issue #29642)
   --> $DIR/feature-gate-custom_attribute.rs:17:1
    |
 17 | #[fake_attr] //~ ERROR attribute `fake_attr` is currently unknown
@@ -6,7 +6,7 @@ error: The attribute `fake_attr` is currently unknown to the compiler and may ha
    |
    = help: add #![feature(custom_attribute)] to the crate attributes to enable
 
-error: The attribute `fake_attr` is currently unknown to the compiler and may have meaning added to it in the future (see issue #29642)
+error[E0658]: The attribute `fake_attr` is currently unknown to the compiler and may have meaning added to it in the future (see issue #29642)
   --> $DIR/feature-gate-custom_attribute.rs:18:1
    |
 18 | #[fake_attr(100)] //~ ERROR attribute `fake_attr` is currently unknown
@@ -14,7 +14,7 @@ error: The attribute `fake_attr` is currently unknown to the compiler and may ha
    |
    = help: add #![feature(custom_attribute)] to the crate attributes to enable
 
-error: The attribute `fake_attr` is currently unknown to the compiler and may have meaning added to it in the future (see issue #29642)
+error[E0658]: The attribute `fake_attr` is currently unknown to the compiler and may have meaning added to it in the future (see issue #29642)
   --> $DIR/feature-gate-custom_attribute.rs:19:1
    |
 19 | #[fake_attr(1, 2, 3)] //~ ERROR attribute `fake_attr` is currently unknown
@@ -22,7 +22,7 @@ error: The attribute `fake_attr` is currently unknown to the compiler and may ha
    |
    = help: add #![feature(custom_attribute)] to the crate attributes to enable
 
-error: The attribute `fake_attr` is currently unknown to the compiler and may have meaning added to it in the future (see issue #29642)
+error[E0658]: The attribute `fake_attr` is currently unknown to the compiler and may have meaning added to it in the future (see issue #29642)
   --> $DIR/feature-gate-custom_attribute.rs:20:1
    |
 20 | #[fake_attr("hello")] //~ ERROR attribute `fake_attr` is currently unknown
@@ -30,7 +30,7 @@ error: The attribute `fake_attr` is currently unknown to the compiler and may ha
    |
    = help: add #![feature(custom_attribute)] to the crate attributes to enable
 
-error: The attribute `fake_attr` is currently unknown to the compiler and may have meaning added to it in the future (see issue #29642)
+error[E0658]: The attribute `fake_attr` is currently unknown to the compiler and may have meaning added to it in the future (see issue #29642)
   --> $DIR/feature-gate-custom_attribute.rs:21:1
    |
 21 | #[fake_attr(name = "hello")] //~ ERROR attribute `fake_attr` is currently unknown
@@ -38,7 +38,7 @@ error: The attribute `fake_attr` is currently unknown to the compiler and may ha
    |
    = help: add #![feature(custom_attribute)] to the crate attributes to enable
 
-error: The attribute `fake_attr` is currently unknown to the compiler and may have meaning added to it in the future (see issue #29642)
+error[E0658]: The attribute `fake_attr` is currently unknown to the compiler and may have meaning added to it in the future (see issue #29642)
   --> $DIR/feature-gate-custom_attribute.rs:22:1
    |
 22 | #[fake_attr(1, "hi", key = 12, true, false)] //~ ERROR attribute `fake_attr` is currently unknown
@@ -46,7 +46,7 @@ error: The attribute `fake_attr` is currently unknown to the compiler and may ha
    |
    = help: add #![feature(custom_attribute)] to the crate attributes to enable
 
-error: The attribute `fake_attr` is currently unknown to the compiler and may have meaning added to it in the future (see issue #29642)
+error[E0658]: The attribute `fake_attr` is currently unknown to the compiler and may have meaning added to it in the future (see issue #29642)
   --> $DIR/feature-gate-custom_attribute.rs:23:1
    |
 23 | #[fake_attr(key = "hello", val = 10)] //~ ERROR attribute `fake_attr` is currently unknown
@@ -54,7 +54,7 @@ error: The attribute `fake_attr` is currently unknown to the compiler and may ha
    |
    = help: add #![feature(custom_attribute)] to the crate attributes to enable
 
-error: The attribute `fake_attr` is currently unknown to the compiler and may have meaning added to it in the future (see issue #29642)
+error[E0658]: The attribute `fake_attr` is currently unknown to the compiler and may have meaning added to it in the future (see issue #29642)
   --> $DIR/feature-gate-custom_attribute.rs:24:1
    |
 24 | #[fake_attr(key("hello"), val(10))] //~ ERROR attribute `fake_attr` is currently unknown
@@ -62,7 +62,7 @@ error: The attribute `fake_attr` is currently unknown to the compiler and may ha
    |
    = help: add #![feature(custom_attribute)] to the crate attributes to enable
 
-error: The attribute `fake_attr` is currently unknown to the compiler and may have meaning added to it in the future (see issue #29642)
+error[E0658]: The attribute `fake_attr` is currently unknown to the compiler and may have meaning added to it in the future (see issue #29642)
   --> $DIR/feature-gate-custom_attribute.rs:25:1
    |
 25 | #[fake_attr(enabled = true, disabled = false)] //~ ERROR attribute `fake_attr` is currently unknown
@@ -70,7 +70,7 @@ error: The attribute `fake_attr` is currently unknown to the compiler and may ha
    |
    = help: add #![feature(custom_attribute)] to the crate attributes to enable
 
-error: The attribute `fake_attr` is currently unknown to the compiler and may have meaning added to it in the future (see issue #29642)
+error[E0658]: The attribute `fake_attr` is currently unknown to the compiler and may have meaning added to it in the future (see issue #29642)
   --> $DIR/feature-gate-custom_attribute.rs:26:1
    |
 26 | #[fake_attr(true)] //~ ERROR attribute `fake_attr` is currently unknown
@@ -78,7 +78,7 @@ error: The attribute `fake_attr` is currently unknown to the compiler and may ha
    |
    = help: add #![feature(custom_attribute)] to the crate attributes to enable
 
-error: The attribute `fake_attr` is currently unknown to the compiler and may have meaning added to it in the future (see issue #29642)
+error[E0658]: The attribute `fake_attr` is currently unknown to the compiler and may have meaning added to it in the future (see issue #29642)
   --> $DIR/feature-gate-custom_attribute.rs:27:1
    |
 27 | #[fake_attr(pi = 3.14159)] //~ ERROR attribute `fake_attr` is currently unknown
@@ -86,7 +86,7 @@ error: The attribute `fake_attr` is currently unknown to the compiler and may ha
    |
    = help: add #![feature(custom_attribute)] to the crate attributes to enable
 
-error: The attribute `fake_attr` is currently unknown to the compiler and may have meaning added to it in the future (see issue #29642)
+error[E0658]: The attribute `fake_attr` is currently unknown to the compiler and may have meaning added to it in the future (see issue #29642)
   --> $DIR/feature-gate-custom_attribute.rs:28:1
    |
 28 | #[fake_attr(b"hi")] //~ ERROR attribute `fake_attr` is currently unknown
@@ -94,7 +94,7 @@ error: The attribute `fake_attr` is currently unknown to the compiler and may ha
    |
    = help: add #![feature(custom_attribute)] to the crate attributes to enable
 
-error: The attribute `fake_doc` is currently unknown to the compiler and may have meaning added to it in the future (see issue #29642)
+error[E0658]: The attribute `fake_doc` is currently unknown to the compiler and may have meaning added to it in the future (see issue #29642)
   --> $DIR/feature-gate-custom_attribute.rs:29:1
    |
 29 | #[fake_doc(r"doc")] //~ ERROR attribute `fake_doc` is currently unknown
diff --git a/src/test/ui/feature-gate-custom_attribute2.stderr b/src/test/ui/feature-gate-custom_attribute2.stderr
index 3e4ea58a7a3..08878e17204 100644
--- a/src/test/ui/feature-gate-custom_attribute2.stderr
+++ b/src/test/ui/feature-gate-custom_attribute2.stderr
@@ -1,4 +1,4 @@
-error: The attribute `lt_struct` is currently unknown to the compiler and may have meaning added to it in the future (see issue #29642)
+error[E0658]: The attribute `lt_struct` is currently unknown to the compiler and may have meaning added to it in the future (see issue #29642)
   --> $DIR/feature-gate-custom_attribute2.rs:23:13
    |
 23 | struct StLt<#[lt_struct] 'a>(&'a u32);
@@ -6,7 +6,7 @@ error: The attribute `lt_struct` is currently unknown to the compiler and may ha
    |
    = help: add #![feature(custom_attribute)] to the crate attributes to enable
 
-error: The attribute `ty_struct` is currently unknown to the compiler and may have meaning added to it in the future (see issue #29642)
+error[E0658]: The attribute `ty_struct` is currently unknown to the compiler and may have meaning added to it in the future (see issue #29642)
   --> $DIR/feature-gate-custom_attribute2.rs:25:13
    |
 25 | struct StTy<#[ty_struct] I>(I);
@@ -14,7 +14,7 @@ error: The attribute `ty_struct` is currently unknown to the compiler and may ha
    |
    = help: add #![feature(custom_attribute)] to the crate attributes to enable
 
-error: The attribute `lt_enum` is currently unknown to the compiler and may have meaning added to it in the future (see issue #29642)
+error[E0658]: The attribute `lt_enum` is currently unknown to the compiler and may have meaning added to it in the future (see issue #29642)
   --> $DIR/feature-gate-custom_attribute2.rs:28:11
    |
 28 | enum EnLt<#[lt_enum] 'b> { A(&'b u32), B }
@@ -22,7 +22,7 @@ error: The attribute `lt_enum` is currently unknown to the compiler and may have
    |
    = help: add #![feature(custom_attribute)] to the crate attributes to enable
 
-error: The attribute `ty_enum` is currently unknown to the compiler and may have meaning added to it in the future (see issue #29642)
+error[E0658]: The attribute `ty_enum` is currently unknown to the compiler and may have meaning added to it in the future (see issue #29642)
   --> $DIR/feature-gate-custom_attribute2.rs:30:11
    |
 30 | enum EnTy<#[ty_enum] J> { A(J), B }
@@ -30,7 +30,7 @@ error: The attribute `ty_enum` is currently unknown to the compiler and may have
    |
    = help: add #![feature(custom_attribute)] to the crate attributes to enable
 
-error: The attribute `lt_trait` is currently unknown to the compiler and may have meaning added to it in the future (see issue #29642)
+error[E0658]: The attribute `lt_trait` is currently unknown to the compiler and may have meaning added to it in the future (see issue #29642)
   --> $DIR/feature-gate-custom_attribute2.rs:33:12
    |
 33 | trait TrLt<#[lt_trait] 'c> { fn foo(&self, _: &'c [u32]) -> &'c u32; }
@@ -38,7 +38,7 @@ error: The attribute `lt_trait` is currently unknown to the compiler and may hav
    |
    = help: add #![feature(custom_attribute)] to the crate attributes to enable
 
-error: The attribute `ty_trait` is currently unknown to the compiler and may have meaning added to it in the future (see issue #29642)
+error[E0658]: The attribute `ty_trait` is currently unknown to the compiler and may have meaning added to it in the future (see issue #29642)
   --> $DIR/feature-gate-custom_attribute2.rs:35:12
    |
 35 | trait TrTy<#[ty_trait] K> { fn foo(&self, _: K); }
@@ -46,7 +46,7 @@ error: The attribute `ty_trait` is currently unknown to the compiler and may hav
    |
    = help: add #![feature(custom_attribute)] to the crate attributes to enable
 
-error: The attribute `lt_type` is currently unknown to the compiler and may have meaning added to it in the future (see issue #29642)
+error[E0658]: The attribute `lt_type` is currently unknown to the compiler and may have meaning added to it in the future (see issue #29642)
   --> $DIR/feature-gate-custom_attribute2.rs:38:11
    |
 38 | type TyLt<#[lt_type] 'd> = &'d u32;
@@ -54,7 +54,7 @@ error: The attribute `lt_type` is currently unknown to the compiler and may have
    |
    = help: add #![feature(custom_attribute)] to the crate attributes to enable
 
-error: The attribute `ty_type` is currently unknown to the compiler and may have meaning added to it in the future (see issue #29642)
+error[E0658]: The attribute `ty_type` is currently unknown to the compiler and may have meaning added to it in the future (see issue #29642)
   --> $DIR/feature-gate-custom_attribute2.rs:40:11
    |
 40 | type TyTy<#[ty_type] L> = (L, );
@@ -62,7 +62,7 @@ error: The attribute `ty_type` is currently unknown to the compiler and may have
    |
    = help: add #![feature(custom_attribute)] to the crate attributes to enable
 
-error: The attribute `lt_inherent` is currently unknown to the compiler and may have meaning added to it in the future (see issue #29642)
+error[E0658]: The attribute `lt_inherent` is currently unknown to the compiler and may have meaning added to it in the future (see issue #29642)
   --> $DIR/feature-gate-custom_attribute2.rs:43:6
    |
 43 | impl<#[lt_inherent] 'e> StLt<'e> { }
@@ -70,7 +70,7 @@ error: The attribute `lt_inherent` is currently unknown to the compiler and may
    |
    = help: add #![feature(custom_attribute)] to the crate attributes to enable
 
-error: The attribute `ty_inherent` is currently unknown to the compiler and may have meaning added to it in the future (see issue #29642)
+error[E0658]: The attribute `ty_inherent` is currently unknown to the compiler and may have meaning added to it in the future (see issue #29642)
   --> $DIR/feature-gate-custom_attribute2.rs:45:6
    |
 45 | impl<#[ty_inherent] M> StTy<M> { }
@@ -78,7 +78,7 @@ error: The attribute `ty_inherent` is currently unknown to the compiler and may
    |
    = help: add #![feature(custom_attribute)] to the crate attributes to enable
 
-error: The attribute `lt_impl_for` is currently unknown to the compiler and may have meaning added to it in the future (see issue #29642)
+error[E0658]: The attribute `lt_impl_for` is currently unknown to the compiler and may have meaning added to it in the future (see issue #29642)
   --> $DIR/feature-gate-custom_attribute2.rs:48:6
    |
 48 | impl<#[lt_impl_for] 'f> TrLt<'f> for StLt<'f> {
@@ -86,7 +86,7 @@ error: The attribute `lt_impl_for` is currently unknown to the compiler and may
    |
    = help: add #![feature(custom_attribute)] to the crate attributes to enable
 
-error: The attribute `ty_impl_for` is currently unknown to the compiler and may have meaning added to it in the future (see issue #29642)
+error[E0658]: The attribute `ty_impl_for` is currently unknown to the compiler and may have meaning added to it in the future (see issue #29642)
   --> $DIR/feature-gate-custom_attribute2.rs:52:6
    |
 52 | impl<#[ty_impl_for] N> TrTy<N> for StTy<N> {
@@ -94,7 +94,7 @@ error: The attribute `ty_impl_for` is currently unknown to the compiler and may
    |
    = help: add #![feature(custom_attribute)] to the crate attributes to enable
 
-error: The attribute `lt_fn` is currently unknown to the compiler and may have meaning added to it in the future (see issue #29642)
+error[E0658]: The attribute `lt_fn` is currently unknown to the compiler and may have meaning added to it in the future (see issue #29642)
   --> $DIR/feature-gate-custom_attribute2.rs:57:9
    |
 57 | fn f_lt<#[lt_fn] 'g>(_: &'g [u32]) -> &'g u32 { loop { } }
@@ -102,7 +102,7 @@ error: The attribute `lt_fn` is currently unknown to the compiler and may have m
    |
    = help: add #![feature(custom_attribute)] to the crate attributes to enable
 
-error: The attribute `ty_fn` is currently unknown to the compiler and may have meaning added to it in the future (see issue #29642)
+error[E0658]: The attribute `ty_fn` is currently unknown to the compiler and may have meaning added to it in the future (see issue #29642)
   --> $DIR/feature-gate-custom_attribute2.rs:59:9
    |
 59 | fn f_ty<#[ty_fn] O>(_: O) { }
@@ -110,7 +110,7 @@ error: The attribute `ty_fn` is currently unknown to the compiler and may have m
    |
    = help: add #![feature(custom_attribute)] to the crate attributes to enable
 
-error: The attribute `lt_meth` is currently unknown to the compiler and may have meaning added to it in the future (see issue #29642)
+error[E0658]: The attribute `lt_meth` is currently unknown to the compiler and may have meaning added to it in the future (see issue #29642)
   --> $DIR/feature-gate-custom_attribute2.rs:63:13
    |
 63 |     fn m_lt<#[lt_meth] 'h>(_: &'h [u32]) -> &'h u32 { loop { } }
@@ -118,7 +118,7 @@ error: The attribute `lt_meth` is currently unknown to the compiler and may have
    |
    = help: add #![feature(custom_attribute)] to the crate attributes to enable
 
-error: The attribute `ty_meth` is currently unknown to the compiler and may have meaning added to it in the future (see issue #29642)
+error[E0658]: The attribute `ty_meth` is currently unknown to the compiler and may have meaning added to it in the future (see issue #29642)
   --> $DIR/feature-gate-custom_attribute2.rs:65:13
    |
 65 |     fn m_ty<#[ty_meth] P>(_: P) { }
@@ -126,7 +126,7 @@ error: The attribute `ty_meth` is currently unknown to the compiler and may have
    |
    = help: add #![feature(custom_attribute)] to the crate attributes to enable
 
-error: The attribute `lt_hof` is currently unknown to the compiler and may have meaning added to it in the future (see issue #29642)
+error[E0658]: The attribute `lt_hof` is currently unknown to the compiler and may have meaning added to it in the future (see issue #29642)
   --> $DIR/feature-gate-custom_attribute2.rs:70:19
    |
 70 |     where Q: for <#[lt_hof] 'i> Fn(&'i [u32]) -> &'i u32
diff --git a/src/test/ui/feature-gate-custom_derive.stderr b/src/test/ui/feature-gate-custom_derive.stderr
index e806c808631..86066285a55 100644
--- a/src/test/ui/feature-gate-custom_derive.stderr
+++ b/src/test/ui/feature-gate-custom_derive.stderr
@@ -1,4 +1,4 @@
-error: attributes of the form `#[derive_*]` are reserved for the compiler (see issue #29644)
+error[E0658]: attributes of the form `#[derive_*]` are reserved for the compiler (see issue #29644)
   --> $DIR/feature-gate-custom_derive.rs:11:1
    |
 11 | #[derive_Clone]
diff --git a/src/test/ui/feature-gate-decl_macro.stderr b/src/test/ui/feature-gate-decl_macro.stderr
index 49ce4eb10b6..c7144f09bd6 100644
--- a/src/test/ui/feature-gate-decl_macro.stderr
+++ b/src/test/ui/feature-gate-decl_macro.stderr
@@ -1,4 +1,4 @@
-error: `macro` is experimental (see issue #39412)
+error[E0658]: `macro` is experimental (see issue #39412)
   --> $DIR/feature-gate-decl_macro.rs:13:1
    |
 13 | macro m() {} //~ ERROR `macro` is experimental (see issue #39412)
diff --git a/src/test/ui/feature-gate-doc_cfg.stderr b/src/test/ui/feature-gate-doc_cfg.stderr
index c2d8a934ab8..e009e0bc3c4 100644
--- a/src/test/ui/feature-gate-doc_cfg.stderr
+++ b/src/test/ui/feature-gate-doc_cfg.stderr
@@ -1,4 +1,4 @@
-error: #[doc(cfg(...))] is experimental (see issue #43781)
+error[E0658]: #[doc(cfg(...))] is experimental (see issue #43781)
   --> $DIR/feature-gate-doc_cfg.rs:11:1
    |
 11 | #[doc(cfg(unix))] //~ ERROR: #[doc(cfg(...))] is experimental
diff --git a/src/test/ui/feature-gate-doc_masked.stderr b/src/test/ui/feature-gate-doc_masked.stderr
index 11020765304..ee2d384e998 100644
--- a/src/test/ui/feature-gate-doc_masked.stderr
+++ b/src/test/ui/feature-gate-doc_masked.stderr
@@ -1,4 +1,4 @@
-error: #[doc(masked)] is experimental (see issue #44027)
+error[E0658]: #[doc(masked)] is experimental (see issue #44027)
   --> $DIR/feature-gate-doc_masked.rs:11:1
    |
 11 | #[doc(masked)] //~ ERROR: #[doc(masked)] is experimental
diff --git a/src/test/ui/feature-gate-doc_spotlight.stderr b/src/test/ui/feature-gate-doc_spotlight.stderr
index b743a1e94bc..36d854892be 100644
--- a/src/test/ui/feature-gate-doc_spotlight.stderr
+++ b/src/test/ui/feature-gate-doc_spotlight.stderr
@@ -1,4 +1,4 @@
-error: #[doc(spotlight)] is experimental (see issue #45040)
+error[E0658]: #[doc(spotlight)] is experimental (see issue #45040)
   --> $DIR/feature-gate-doc_spotlight.rs:11:1
    |
 11 | #[doc(spotlight)] //~ ERROR: #[doc(spotlight)] is experimental
diff --git a/src/test/ui/feature-gate-dotdoteq_in_patterns.stderr b/src/test/ui/feature-gate-dotdoteq_in_patterns.stderr
index 5319dcef2d5..2d26c6ae8eb 100644
--- a/src/test/ui/feature-gate-dotdoteq_in_patterns.stderr
+++ b/src/test/ui/feature-gate-dotdoteq_in_patterns.stderr
@@ -1,4 +1,4 @@
-error: `..=` syntax in patterns is experimental (see issue #28237)
+error[E0658]: `..=` syntax in patterns is experimental (see issue #28237)
   --> $DIR/feature-gate-dotdoteq_in_patterns.rs:13:9
    |
 13 |         0 ..= 3 => {} //~ ERROR `..=` syntax in patterns is experimental
diff --git a/src/test/ui/feature-gate-dropck-ugeh.stderr b/src/test/ui/feature-gate-dropck-ugeh.stderr
index b030ebcd881..cdeca7026b0 100644
--- a/src/test/ui/feature-gate-dropck-ugeh.stderr
+++ b/src/test/ui/feature-gate-dropck-ugeh.stderr
@@ -1,4 +1,4 @@
-error: unsafe_destructor_blind_to_params has been replaced by may_dangle and will be removed in the future (see issue #28498)
+error[E0658]: unsafe_destructor_blind_to_params has been replaced by may_dangle and will be removed in the future (see issue #28498)
   --> $DIR/feature-gate-dropck-ugeh.rs:29:5
    |
 29 |     #[unsafe_destructor_blind_to_params] // This is the UGEH attribute
diff --git a/src/test/ui/feature-gate-dyn-trait.stderr b/src/test/ui/feature-gate-dyn-trait.stderr
index 28ecfdf1131..d6ba4b8ad66 100644
--- a/src/test/ui/feature-gate-dyn-trait.stderr
+++ b/src/test/ui/feature-gate-dyn-trait.stderr
@@ -1,4 +1,4 @@
-error: `dyn Trait` syntax is unstable (see issue #44662)
+error[E0658]: `dyn Trait` syntax is unstable (see issue #44662)
   --> $DIR/feature-gate-dyn-trait.rs:12:14
    |
 12 | type A = Box<dyn Trait>; //~ ERROR `dyn Trait` syntax is unstable
diff --git a/src/test/ui/feature-gate-exclusive-range-pattern.stderr b/src/test/ui/feature-gate-exclusive-range-pattern.stderr
index c6785d6f29d..3185281ce4b 100644
--- a/src/test/ui/feature-gate-exclusive-range-pattern.stderr
+++ b/src/test/ui/feature-gate-exclusive-range-pattern.stderr
@@ -1,4 +1,4 @@
-error: exclusive range pattern syntax is experimental (see issue #37854)
+error[E0658]: exclusive range pattern syntax is experimental (see issue #37854)
   --> $DIR/feature-gate-exclusive-range-pattern.rs:13:9
    |
 13 |         0 .. 3 => {} //~ ERROR exclusive range pattern syntax is experimental
diff --git a/src/test/ui/feature-gate-extern_in_paths.stderr b/src/test/ui/feature-gate-extern_in_paths.stderr
index ac68e79e1ca..022e53b6be0 100644
--- a/src/test/ui/feature-gate-extern_in_paths.stderr
+++ b/src/test/ui/feature-gate-extern_in_paths.stderr
@@ -1,4 +1,4 @@
-error: `extern` in paths is experimental (see issue #44660)
+error[E0658]: `extern` in paths is experimental (see issue #44660)
   --> $DIR/feature-gate-extern_in_paths.rs:14:13
    |
 14 |     let _ = extern::std::vec::Vec::new(); //~ ERROR `extern` in paths is experimental
diff --git a/src/test/ui/feature-gate-extern_types.stderr b/src/test/ui/feature-gate-extern_types.stderr
index 3815862e899..71caa37963f 100644
--- a/src/test/ui/feature-gate-extern_types.stderr
+++ b/src/test/ui/feature-gate-extern_types.stderr
@@ -1,4 +1,4 @@
-error: extern types are experimental (see issue #43467)
+error[E0658]: extern types are experimental (see issue #43467)
   --> $DIR/feature-gate-extern_types.rs:12:5
    |
 12 |     type T; //~ ERROR extern types are experimental
diff --git a/src/test/ui/feature-gate-external_doc.stderr b/src/test/ui/feature-gate-external_doc.stderr
index 5479ab8bc91..db6c99bceed 100644
--- a/src/test/ui/feature-gate-external_doc.stderr
+++ b/src/test/ui/feature-gate-external_doc.stderr
@@ -1,4 +1,4 @@
-error: #[doc(include = "...")] is experimental (see issue #44732)
+error[E0658]: #[doc(include = "...")] is experimental (see issue #44732)
   --> $DIR/feature-gate-external_doc.rs:11:1
    |
 11 | #[doc(include="asdf.md")] //~ ERROR: #[doc(include = "...")] is experimental
diff --git a/src/test/ui/feature-gate-fundamental.stderr b/src/test/ui/feature-gate-fundamental.stderr
index 0fc75ee30b9..28d8a80e602 100644
--- a/src/test/ui/feature-gate-fundamental.stderr
+++ b/src/test/ui/feature-gate-fundamental.stderr
@@ -1,4 +1,4 @@
-error: the `#[fundamental]` attribute is an experimental feature (see issue #29635)
+error[E0658]: the `#[fundamental]` attribute is an experimental feature (see issue #29635)
   --> $DIR/feature-gate-fundamental.rs:11:1
    |
 11 | #[fundamental] //~ ERROR the `#[fundamental]` attribute is an experimental feature
diff --git a/src/test/ui/feature-gate-generators.stderr b/src/test/ui/feature-gate-generators.stderr
index 82acb401338..f559227f717 100644
--- a/src/test/ui/feature-gate-generators.stderr
+++ b/src/test/ui/feature-gate-generators.stderr
@@ -1,4 +1,4 @@
-error: yield syntax is experimental
+error[E0658]: yield syntax is experimental
   --> $DIR/feature-gate-generators.rs:12:5
    |
 12 |     yield true; //~ ERROR yield syntax is experimental
diff --git a/src/test/ui/feature-gate-generic_associated_types.stderr b/src/test/ui/feature-gate-generic_associated_types.stderr
index 7b2507e1fb1..c047914fb3b 100644
--- a/src/test/ui/feature-gate-generic_associated_types.stderr
+++ b/src/test/ui/feature-gate-generic_associated_types.stderr
@@ -1,4 +1,4 @@
-error: generic associated types are unstable (see issue #44265)
+error[E0658]: generic associated types are unstable (see issue #44265)
   --> $DIR/feature-gate-generic_associated_types.rs:14:5
    |
 14 |     type Pointer<T>: Deref<Target = T>;
@@ -6,7 +6,7 @@ error: generic associated types are unstable (see issue #44265)
    |
    = help: add #![feature(generic_associated_types)] to the crate attributes to enable
 
-error: generic associated types are unstable (see issue #44265)
+error[E0658]: generic associated types are unstable (see issue #44265)
   --> $DIR/feature-gate-generic_associated_types.rs:16:5
    |
 16 |     type Pointer2<T>: Deref<Target = T> where T: Clone, U: Clone;
@@ -14,7 +14,7 @@ error: generic associated types are unstable (see issue #44265)
    |
    = help: add #![feature(generic_associated_types)] to the crate attributes to enable
 
-error: generic associated types are unstable (see issue #44265)
+error[E0658]: generic associated types are unstable (see issue #44265)
   --> $DIR/feature-gate-generic_associated_types.rs:22:5
    |
 22 |     type Pointer<usize> = Box<usize>;
@@ -22,7 +22,7 @@ error: generic associated types are unstable (see issue #44265)
    |
    = help: add #![feature(generic_associated_types)] to the crate attributes to enable
 
-error: generic associated types are unstable (see issue #44265)
+error[E0658]: generic associated types are unstable (see issue #44265)
   --> $DIR/feature-gate-generic_associated_types.rs:24:5
    |
 24 |     type Pointer2<u32> = Box<u32>;
diff --git a/src/test/ui/feature-gate-generic_param_attrs.stderr b/src/test/ui/feature-gate-generic_param_attrs.stderr
index da2e6403029..a18d104cc2b 100644
--- a/src/test/ui/feature-gate-generic_param_attrs.stderr
+++ b/src/test/ui/feature-gate-generic_param_attrs.stderr
@@ -1,4 +1,4 @@
-error: attributes on lifetime bindings are experimental (see issue #34761)
+error[E0658]: attributes on lifetime bindings are experimental (see issue #34761)
   --> $DIR/feature-gate-generic_param_attrs.rs:22:13
    |
 22 | struct StLt<#[rustc_lt_struct] 'a>(&'a u32);
@@ -6,7 +6,7 @@ error: attributes on lifetime bindings are experimental (see issue #34761)
    |
    = help: add #![feature(generic_param_attrs)] to the crate attributes to enable
 
-error: attributes on type parameter bindings are experimental (see issue #34761)
+error[E0658]: attributes on type parameter bindings are experimental (see issue #34761)
   --> $DIR/feature-gate-generic_param_attrs.rs:24:13
    |
 24 | struct StTy<#[rustc_ty_struct] I>(I);
@@ -14,7 +14,7 @@ error: attributes on type parameter bindings are experimental (see issue #34761)
    |
    = help: add #![feature(generic_param_attrs)] to the crate attributes to enable
 
-error: attributes on lifetime bindings are experimental (see issue #34761)
+error[E0658]: attributes on lifetime bindings are experimental (see issue #34761)
   --> $DIR/feature-gate-generic_param_attrs.rs:27:11
    |
 27 | enum EnLt<#[rustc_lt_enum] 'b> { A(&'b u32), B }
@@ -22,7 +22,7 @@ error: attributes on lifetime bindings are experimental (see issue #34761)
    |
    = help: add #![feature(generic_param_attrs)] to the crate attributes to enable
 
-error: attributes on type parameter bindings are experimental (see issue #34761)
+error[E0658]: attributes on type parameter bindings are experimental (see issue #34761)
   --> $DIR/feature-gate-generic_param_attrs.rs:29:11
    |
 29 | enum EnTy<#[rustc_ty_enum] J> { A(J), B }
@@ -30,7 +30,7 @@ error: attributes on type parameter bindings are experimental (see issue #34761)
    |
    = help: add #![feature(generic_param_attrs)] to the crate attributes to enable
 
-error: attributes on lifetime bindings are experimental (see issue #34761)
+error[E0658]: attributes on lifetime bindings are experimental (see issue #34761)
   --> $DIR/feature-gate-generic_param_attrs.rs:32:12
    |
 32 | trait TrLt<#[rustc_lt_trait] 'c> { fn foo(&self, _: &'c [u32]) -> &'c u32; }
@@ -38,7 +38,7 @@ error: attributes on lifetime bindings are experimental (see issue #34761)
    |
    = help: add #![feature(generic_param_attrs)] to the crate attributes to enable
 
-error: attributes on type parameter bindings are experimental (see issue #34761)
+error[E0658]: attributes on type parameter bindings are experimental (see issue #34761)
   --> $DIR/feature-gate-generic_param_attrs.rs:34:12
    |
 34 | trait TrTy<#[rustc_ty_trait] K> { fn foo(&self, _: K); }
@@ -46,7 +46,7 @@ error: attributes on type parameter bindings are experimental (see issue #34761)
    |
    = help: add #![feature(generic_param_attrs)] to the crate attributes to enable
 
-error: attributes on lifetime bindings are experimental (see issue #34761)
+error[E0658]: attributes on lifetime bindings are experimental (see issue #34761)
   --> $DIR/feature-gate-generic_param_attrs.rs:37:11
    |
 37 | type TyLt<#[rustc_lt_type] 'd> = &'d u32;
@@ -54,7 +54,7 @@ error: attributes on lifetime bindings are experimental (see issue #34761)
    |
    = help: add #![feature(generic_param_attrs)] to the crate attributes to enable
 
-error: attributes on type parameter bindings are experimental (see issue #34761)
+error[E0658]: attributes on type parameter bindings are experimental (see issue #34761)
   --> $DIR/feature-gate-generic_param_attrs.rs:39:11
    |
 39 | type TyTy<#[rustc_ty_type] L> = (L, );
@@ -62,7 +62,7 @@ error: attributes on type parameter bindings are experimental (see issue #34761)
    |
    = help: add #![feature(generic_param_attrs)] to the crate attributes to enable
 
-error: attributes on lifetime bindings are experimental (see issue #34761)
+error[E0658]: attributes on lifetime bindings are experimental (see issue #34761)
   --> $DIR/feature-gate-generic_param_attrs.rs:42:6
    |
 42 | impl<#[rustc_lt_inherent] 'e> StLt<'e> { }
@@ -70,7 +70,7 @@ error: attributes on lifetime bindings are experimental (see issue #34761)
    |
    = help: add #![feature(generic_param_attrs)] to the crate attributes to enable
 
-error: attributes on type parameter bindings are experimental (see issue #34761)
+error[E0658]: attributes on type parameter bindings are experimental (see issue #34761)
   --> $DIR/feature-gate-generic_param_attrs.rs:44:6
    |
 44 | impl<#[rustc_ty_inherent] M> StTy<M> { }
@@ -78,7 +78,7 @@ error: attributes on type parameter bindings are experimental (see issue #34761)
    |
    = help: add #![feature(generic_param_attrs)] to the crate attributes to enable
 
-error: attributes on lifetime bindings are experimental (see issue #34761)
+error[E0658]: attributes on lifetime bindings are experimental (see issue #34761)
   --> $DIR/feature-gate-generic_param_attrs.rs:47:6
    |
 47 | impl<#[rustc_lt_impl_for] 'f> TrLt<'f> for StLt<'f> {
@@ -86,7 +86,7 @@ error: attributes on lifetime bindings are experimental (see issue #34761)
    |
    = help: add #![feature(generic_param_attrs)] to the crate attributes to enable
 
-error: attributes on type parameter bindings are experimental (see issue #34761)
+error[E0658]: attributes on type parameter bindings are experimental (see issue #34761)
   --> $DIR/feature-gate-generic_param_attrs.rs:51:6
    |
 51 | impl<#[rustc_ty_impl_for] N> TrTy<N> for StTy<N> {
@@ -94,7 +94,7 @@ error: attributes on type parameter bindings are experimental (see issue #34761)
    |
    = help: add #![feature(generic_param_attrs)] to the crate attributes to enable
 
-error: attributes on lifetime bindings are experimental (see issue #34761)
+error[E0658]: attributes on lifetime bindings are experimental (see issue #34761)
   --> $DIR/feature-gate-generic_param_attrs.rs:56:9
    |
 56 | fn f_lt<#[rustc_lt_fn] 'g>(_: &'g [u32]) -> &'g u32 { loop { } }
@@ -102,7 +102,7 @@ error: attributes on lifetime bindings are experimental (see issue #34761)
    |
    = help: add #![feature(generic_param_attrs)] to the crate attributes to enable
 
-error: attributes on type parameter bindings are experimental (see issue #34761)
+error[E0658]: attributes on type parameter bindings are experimental (see issue #34761)
   --> $DIR/feature-gate-generic_param_attrs.rs:58:9
    |
 58 | fn f_ty<#[rustc_ty_fn] O>(_: O) { }
@@ -110,7 +110,7 @@ error: attributes on type parameter bindings are experimental (see issue #34761)
    |
    = help: add #![feature(generic_param_attrs)] to the crate attributes to enable
 
-error: attributes on lifetime bindings are experimental (see issue #34761)
+error[E0658]: attributes on lifetime bindings are experimental (see issue #34761)
   --> $DIR/feature-gate-generic_param_attrs.rs:62:13
    |
 62 |     fn m_lt<#[rustc_lt_meth] 'h>(_: &'h [u32]) -> &'h u32 { loop { } }
@@ -118,7 +118,7 @@ error: attributes on lifetime bindings are experimental (see issue #34761)
    |
    = help: add #![feature(generic_param_attrs)] to the crate attributes to enable
 
-error: attributes on type parameter bindings are experimental (see issue #34761)
+error[E0658]: attributes on type parameter bindings are experimental (see issue #34761)
   --> $DIR/feature-gate-generic_param_attrs.rs:64:13
    |
 64 |     fn m_ty<#[rustc_ty_meth] P>(_: P) { }
@@ -126,7 +126,7 @@ error: attributes on type parameter bindings are experimental (see issue #34761)
    |
    = help: add #![feature(generic_param_attrs)] to the crate attributes to enable
 
-error: attributes on lifetime bindings are experimental (see issue #34761)
+error[E0658]: attributes on lifetime bindings are experimental (see issue #34761)
   --> $DIR/feature-gate-generic_param_attrs.rs:69:19
    |
 69 |     where Q: for <#[rustc_lt_hof] 'i> Fn(&'i [u32]) -> &'i u32
diff --git a/src/test/ui/feature-gate-global_allocator.stderr b/src/test/ui/feature-gate-global_allocator.stderr
index 7e6c4288ff3..8d82f6ee9e3 100644
--- a/src/test/ui/feature-gate-global_allocator.stderr
+++ b/src/test/ui/feature-gate-global_allocator.stderr
@@ -1,4 +1,4 @@
-error: the `#[global_allocator]` attribute is an experimental feature
+error[E0658]: the `#[global_allocator]` attribute is an experimental feature
   --> $DIR/feature-gate-global_allocator.rs:11:1
    |
 11 | #[global_allocator] //~ ERROR: attribute is an experimental feature
diff --git a/src/test/ui/feature-gate-global_asm.stderr b/src/test/ui/feature-gate-global_asm.stderr
index de0ba1a7b32..ca946579f5d 100644
--- a/src/test/ui/feature-gate-global_asm.stderr
+++ b/src/test/ui/feature-gate-global_asm.stderr
@@ -1,4 +1,4 @@
-error: `global_asm!` is not stable enough for use and is subject to change (see issue #35119)
+error[E0658]: `global_asm!` is not stable enough for use and is subject to change (see issue #35119)
   --> $DIR/feature-gate-global_asm.rs:11:1
    |
 11 | global_asm!(""); //~ ERROR `global_asm!` is not stable
diff --git a/src/test/ui/feature-gate-i128_type.stderr b/src/test/ui/feature-gate-i128_type.stderr
index df623cac49a..06fdeadbbf6 100644
--- a/src/test/ui/feature-gate-i128_type.stderr
+++ b/src/test/ui/feature-gate-i128_type.stderr
@@ -1,4 +1,4 @@
-error: 128-bit integers are not stable (see issue #35118)
+error[E0658]: 128-bit integers are not stable (see issue #35118)
   --> $DIR/feature-gate-i128_type.rs:12:5
    |
 12 |     0i128; //~ ERROR 128-bit integers are not stable
@@ -6,7 +6,7 @@ error: 128-bit integers are not stable (see issue #35118)
    |
    = help: add #![feature(i128_type)] to the crate attributes to enable
 
-error: 128-bit integers are not stable (see issue #35118)
+error[E0658]: 128-bit integers are not stable (see issue #35118)
   --> $DIR/feature-gate-i128_type.rs:16:5
    |
 16 |     0u128; //~ ERROR 128-bit integers are not stable
diff --git a/src/test/ui/feature-gate-i128_type2.stderr b/src/test/ui/feature-gate-i128_type2.stderr
index 26653a5739b..ee81a269214 100644
--- a/src/test/ui/feature-gate-i128_type2.stderr
+++ b/src/test/ui/feature-gate-i128_type2.stderr
@@ -1,4 +1,4 @@
-error: 128-bit type is unstable (see issue #35118)
+error[E0658]: 128-bit type is unstable (see issue #35118)
   --> $DIR/feature-gate-i128_type2.rs:13:15
    |
 13 | fn test1() -> i128 { //~ ERROR 128-bit type is unstable
@@ -6,7 +6,7 @@ error: 128-bit type is unstable (see issue #35118)
    |
    = help: add #![feature(i128_type)] to the crate attributes to enable
 
-error: 128-bit type is unstable (see issue #35118)
+error[E0658]: 128-bit type is unstable (see issue #35118)
   --> $DIR/feature-gate-i128_type2.rs:17:17
    |
 17 | fn test1_2() -> u128 { //~ ERROR 128-bit type is unstable
@@ -14,7 +14,7 @@ error: 128-bit type is unstable (see issue #35118)
    |
    = help: add #![feature(i128_type)] to the crate attributes to enable
 
-error: 128-bit type is unstable (see issue #35118)
+error[E0658]: 128-bit type is unstable (see issue #35118)
   --> $DIR/feature-gate-i128_type2.rs:22:12
    |
 22 |     let x: i128 = 0; //~ ERROR 128-bit type is unstable
@@ -22,7 +22,7 @@ error: 128-bit type is unstable (see issue #35118)
    |
    = help: add #![feature(i128_type)] to the crate attributes to enable
 
-error: 128-bit type is unstable (see issue #35118)
+error[E0658]: 128-bit type is unstable (see issue #35118)
   --> $DIR/feature-gate-i128_type2.rs:26:12
    |
 26 |     let x: u128 = 0; //~ ERROR 128-bit type is unstable
@@ -32,7 +32,7 @@ error: 128-bit type is unstable (see issue #35118)
 
 error[E0601]: main function not found
 
-error: repr with 128-bit type is unstable (see issue #35118)
+error[E0658]: repr with 128-bit type is unstable (see issue #35118)
   --> $DIR/feature-gate-i128_type2.rs:30:1
    |
 30 | / enum A { //~ ERROR 128-bit type is unstable
diff --git a/src/test/ui/feature-gate-intrinsics.stderr b/src/test/ui/feature-gate-intrinsics.stderr
index 5382122e30e..918c749504a 100644
--- a/src/test/ui/feature-gate-intrinsics.stderr
+++ b/src/test/ui/feature-gate-intrinsics.stderr
@@ -1,4 +1,4 @@
-error: intrinsics are subject to change
+error[E0658]: intrinsics are subject to change
   --> $DIR/feature-gate-intrinsics.rs:11:1
    |
 11 | / extern "rust-intrinsic" {   //~ ERROR intrinsics are subject to change
@@ -8,7 +8,7 @@ error: intrinsics are subject to change
    |
    = help: add #![feature(intrinsics)] to the crate attributes to enable
 
-error: intrinsics are subject to change
+error[E0658]: intrinsics are subject to change
   --> $DIR/feature-gate-intrinsics.rs:15:1
    |
 15 | / extern "rust-intrinsic" fn baz() {  //~ ERROR intrinsics are subject to change
diff --git a/src/test/ui/feature-gate-lang-items.stderr b/src/test/ui/feature-gate-lang-items.stderr
index dab8ce23192..28e3dab8fa7 100644
--- a/src/test/ui/feature-gate-lang-items.stderr
+++ b/src/test/ui/feature-gate-lang-items.stderr
@@ -1,4 +1,4 @@
-error: language items are subject to change
+error[E0658]: language items are subject to change
   --> $DIR/feature-gate-lang-items.rs:11:1
    |
 11 | #[lang="foo"]   //~ ERROR language items are subject to change
diff --git a/src/test/ui/feature-gate-link_args.stderr b/src/test/ui/feature-gate-link_args.stderr
index d6d059007d1..78070d52f1f 100644
--- a/src/test/ui/feature-gate-link_args.stderr
+++ b/src/test/ui/feature-gate-link_args.stderr
@@ -1,4 +1,4 @@
-error: the `link_args` attribute is experimental and not portable across platforms, it is recommended to use `#[link(name = "foo")] instead (see issue #29596)
+error[E0658]: the `link_args` attribute is experimental and not portable across platforms, it is recommended to use `#[link(name = "foo")] instead (see issue #29596)
   --> $DIR/feature-gate-link_args.rs:22:1
    |
 22 | #[link_args = "-l expected_use_case"]
@@ -6,7 +6,7 @@ error: the `link_args` attribute is experimental and not portable across platfor
    |
    = help: add #![feature(link_args)] to the crate attributes to enable
 
-error: the `link_args` attribute is experimental and not portable across platforms, it is recommended to use `#[link(name = "foo")] instead (see issue #29596)
+error[E0658]: the `link_args` attribute is experimental and not portable across platforms, it is recommended to use `#[link(name = "foo")] instead (see issue #29596)
   --> $DIR/feature-gate-link_args.rs:26:1
    |
 26 | #[link_args = "-l unexected_use_on_non_extern_item"]
@@ -14,7 +14,7 @@ error: the `link_args` attribute is experimental and not portable across platfor
    |
    = help: add #![feature(link_args)] to the crate attributes to enable
 
-error: the `link_args` attribute is experimental and not portable across platforms, it is recommended to use `#[link(name = "foo")] instead (see issue #29596)
+error[E0658]: the `link_args` attribute is experimental and not portable across platforms, it is recommended to use `#[link(name = "foo")] instead (see issue #29596)
   --> $DIR/feature-gate-link_args.rs:19:1
    |
 19 | #![link_args = "-l unexpected_use_as_inner_attr_on_mod"]
diff --git a/src/test/ui/feature-gate-link_cfg.stderr b/src/test/ui/feature-gate-link_cfg.stderr
index bbc52bd9d20..8aada72fb0c 100644
--- a/src/test/ui/feature-gate-link_cfg.stderr
+++ b/src/test/ui/feature-gate-link_cfg.stderr
@@ -1,4 +1,4 @@
-error: is feature gated (see issue #37406)
+error[E0658]: is feature gated (see issue #37406)
   --> $DIR/feature-gate-link_cfg.rs:11:1
    |
 11 | #[link(name = "foo", cfg(foo))]
diff --git a/src/test/ui/feature-gate-link_llvm_intrinsics.stderr b/src/test/ui/feature-gate-link_llvm_intrinsics.stderr
index b2e2caaa51a..136658f23fd 100644
--- a/src/test/ui/feature-gate-link_llvm_intrinsics.stderr
+++ b/src/test/ui/feature-gate-link_llvm_intrinsics.stderr
@@ -1,4 +1,4 @@
-error: linking to LLVM intrinsics is experimental (see issue #29602)
+error[E0658]: linking to LLVM intrinsics is experimental (see issue #29602)
   --> $DIR/feature-gate-link_llvm_intrinsics.rs:13:5
    |
 13 |     fn sqrt(x: f32) -> f32;
diff --git a/src/test/ui/feature-gate-linkage.stderr b/src/test/ui/feature-gate-linkage.stderr
index 62d857ddf2c..54764b1920c 100644
--- a/src/test/ui/feature-gate-linkage.stderr
+++ b/src/test/ui/feature-gate-linkage.stderr
@@ -1,4 +1,4 @@
-error: the `linkage` attribute is experimental and not portable across platforms (see issue #29603)
+error[E0658]: the `linkage` attribute is experimental and not portable across platforms (see issue #29603)
   --> $DIR/feature-gate-linkage.rs:12:5
    |
 12 |     #[linkage = "extern_weak"] static foo: isize;
diff --git a/src/test/ui/feature-gate-linker-flavor.stderr b/src/test/ui/feature-gate-linker-flavor.stderr
index 383e75e3d17..e58693d35c2 100644
--- a/src/test/ui/feature-gate-linker-flavor.stderr
+++ b/src/test/ui/feature-gate-linker-flavor.stderr
@@ -1,4 +1,4 @@
-error: the `#[used]` attribute is an experimental feature (see issue #40289)
+error[E0658]: the `#[used]` attribute is an experimental feature (see issue #40289)
   --> $DIR/feature-gate-linker-flavor.rs:16:1
    |
 16 | #[used]
diff --git a/src/test/ui/feature-gate-log_syntax.stderr b/src/test/ui/feature-gate-log_syntax.stderr
index f1c0d305f6c..363b1753f4a 100644
--- a/src/test/ui/feature-gate-log_syntax.stderr
+++ b/src/test/ui/feature-gate-log_syntax.stderr
@@ -1,4 +1,4 @@
-error: `log_syntax!` is not stable enough for use and is subject to change (see issue #29598)
+error[E0658]: `log_syntax!` is not stable enough for use and is subject to change (see issue #29598)
   --> $DIR/feature-gate-log_syntax.rs:12:5
    |
 12 |     log_syntax!() //~ ERROR `log_syntax!` is not stable enough
diff --git a/src/test/ui/feature-gate-log_syntax2.stderr b/src/test/ui/feature-gate-log_syntax2.stderr
index b1bb5557eed..f47a5076e79 100644
--- a/src/test/ui/feature-gate-log_syntax2.stderr
+++ b/src/test/ui/feature-gate-log_syntax2.stderr
@@ -1,4 +1,4 @@
-error: `log_syntax!` is not stable enough for use and is subject to change (see issue #29598)
+error[E0658]: `log_syntax!` is not stable enough for use and is subject to change (see issue #29598)
   --> $DIR/feature-gate-log_syntax2.rs:14:20
    |
 14 |     println!("{}", log_syntax!()); //~ ERROR `log_syntax!` is not stable
diff --git a/src/test/ui/feature-gate-macro-lifetime-matcher.stderr b/src/test/ui/feature-gate-macro-lifetime-matcher.stderr
index e78f7684cf2..553a7d3d131 100644
--- a/src/test/ui/feature-gate-macro-lifetime-matcher.stderr
+++ b/src/test/ui/feature-gate-macro-lifetime-matcher.stderr
@@ -1,4 +1,4 @@
-error: :lifetime fragment specifier is experimental and subject to change (see issue #46895)
+error[E0658]: :lifetime fragment specifier is experimental and subject to change (see issue #46895)
   --> $DIR/feature-gate-macro-lifetime-matcher.rs:14:19
    |
 14 | macro_rules! m { ($lt:lifetime) => {} }
diff --git a/src/test/ui/feature-gate-macro-vis-matcher.stderr b/src/test/ui/feature-gate-macro-vis-matcher.stderr
index 09db5009165..ee1844c0922 100644
--- a/src/test/ui/feature-gate-macro-vis-matcher.stderr
+++ b/src/test/ui/feature-gate-macro-vis-matcher.stderr
@@ -1,4 +1,4 @@
-error: :vis fragment specifier is experimental and subject to change (see issue #41022)
+error[E0658]: :vis fragment specifier is experimental and subject to change (see issue #41022)
   --> $DIR/feature-gate-macro-vis-matcher.rs:14:19
    |
 14 | macro_rules! m { ($v:vis) => {} }
diff --git a/src/test/ui/feature-gate-main.stderr b/src/test/ui/feature-gate-main.stderr
index 90cf12822c8..56e9c8b37e3 100644
--- a/src/test/ui/feature-gate-main.stderr
+++ b/src/test/ui/feature-gate-main.stderr
@@ -1,4 +1,4 @@
-error: declaration of a nonstandard #[main] function may change over time, for now a top-level `fn main()` is required (see issue #29634)
+error[E0658]: declaration of a nonstandard #[main] function may change over time, for now a top-level `fn main()` is required (see issue #29634)
   --> $DIR/feature-gate-main.rs:12:1
    |
 12 | fn foo() {} //~ ERROR: declaration of a nonstandard #[main] function may change over time
diff --git a/src/test/ui/feature-gate-match_beginning_vert.stderr b/src/test/ui/feature-gate-match_beginning_vert.stderr
index 88053adfafa..1d45dedb497 100644
--- a/src/test/ui/feature-gate-match_beginning_vert.stderr
+++ b/src/test/ui/feature-gate-match_beginning_vert.stderr
@@ -1,4 +1,4 @@
-error: Use of a '|' at the beginning of a match arm is experimental (see issue #44101)
+error[E0658]: Use of a '|' at the beginning of a match arm is experimental (see issue #44101)
   --> $DIR/feature-gate-match_beginning_vert.rs:24:9
    |
 24 |         | A => println!("A"),
@@ -6,7 +6,7 @@ error: Use of a '|' at the beginning of a match arm is experimental (see issue #
    |
    = help: add #![feature(match_beginning_vert)] to the crate attributes to enable
 
-error: Use of a '|' at the beginning of a match arm is experimental (see issue #44101)
+error[E0658]: Use of a '|' at the beginning of a match arm is experimental (see issue #44101)
   --> $DIR/feature-gate-match_beginning_vert.rs:26:9
    |
 26 |         | B | C => println!("BC!"),
@@ -14,7 +14,7 @@ error: Use of a '|' at the beginning of a match arm is experimental (see issue #
    |
    = help: add #![feature(match_beginning_vert)] to the crate attributes to enable
 
-error: Use of a '|' at the beginning of a match arm is experimental (see issue #44101)
+error[E0658]: Use of a '|' at the beginning of a match arm is experimental (see issue #44101)
   --> $DIR/feature-gate-match_beginning_vert.rs:28:9
    |
 28 |         | _ => {},
diff --git a/src/test/ui/feature-gate-match_default_bindings.stderr b/src/test/ui/feature-gate-match_default_bindings.stderr
index d86e8248f08..1bedfb7f8be 100644
--- a/src/test/ui/feature-gate-match_default_bindings.stderr
+++ b/src/test/ui/feature-gate-match_default_bindings.stderr
@@ -1,4 +1,4 @@
-error: non-reference pattern used to match a reference (see issue #42640)
+error[E0658]: non-reference pattern used to match a reference (see issue #42640)
   --> $DIR/feature-gate-match_default_bindings.rs:13:9
    |
 13 |         Some(n) => {},
diff --git a/src/test/ui/feature-gate-may-dangle.stderr b/src/test/ui/feature-gate-may-dangle.stderr
index e51723d058e..a3a3f7bd174 100644
--- a/src/test/ui/feature-gate-may-dangle.stderr
+++ b/src/test/ui/feature-gate-may-dangle.stderr
@@ -1,4 +1,4 @@
-error: may_dangle has unstable semantics and may be removed in the future (see issue #34761)
+error[E0658]: may_dangle has unstable semantics and may be removed in the future (see issue #34761)
   --> $DIR/feature-gate-may-dangle.rs:18:6
    |
 18 | impl<#[may_dangle] A> Drop for Pt<A> {
diff --git a/src/test/ui/feature-gate-naked_functions.stderr b/src/test/ui/feature-gate-naked_functions.stderr
index 9655982574c..5f72234e5df 100644
--- a/src/test/ui/feature-gate-naked_functions.stderr
+++ b/src/test/ui/feature-gate-naked_functions.stderr
@@ -1,4 +1,4 @@
-error: the `#[naked]` attribute is an experimental feature (see issue #32408)
+error[E0658]: the `#[naked]` attribute is an experimental feature (see issue #32408)
   --> $DIR/feature-gate-naked_functions.rs:11:1
    |
 11 | #[naked]
@@ -6,7 +6,7 @@ error: the `#[naked]` attribute is an experimental feature (see issue #32408)
    |
    = help: add #![feature(naked_functions)] to the crate attributes to enable
 
-error: the `#[naked]` attribute is an experimental feature (see issue #32408)
+error[E0658]: the `#[naked]` attribute is an experimental feature (see issue #32408)
   --> $DIR/feature-gate-naked_functions.rs:15:1
    |
 15 | #[naked]
diff --git a/src/test/ui/feature-gate-needs-allocator.stderr b/src/test/ui/feature-gate-needs-allocator.stderr
index 5124c10cb47..11b8c31e6df 100644
--- a/src/test/ui/feature-gate-needs-allocator.stderr
+++ b/src/test/ui/feature-gate-needs-allocator.stderr
@@ -1,4 +1,4 @@
-error: the `#[needs_allocator]` attribute is an experimental feature
+error[E0658]: the `#[needs_allocator]` attribute is an experimental feature
   --> $DIR/feature-gate-needs-allocator.rs:11:1
    |
 11 | #![needs_allocator] //~ ERROR the `#[needs_allocator]` attribute is
diff --git a/src/test/ui/feature-gate-never_type.stderr b/src/test/ui/feature-gate-never_type.stderr
index c242e613ead..2fd04f51e7e 100644
--- a/src/test/ui/feature-gate-never_type.stderr
+++ b/src/test/ui/feature-gate-never_type.stderr
@@ -1,4 +1,4 @@
-error: The `!` type is experimental (see issue #35121)
+error[E0658]: The `!` type is experimental (see issue #35121)
   --> $DIR/feature-gate-never_type.rs:17:17
    |
 17 | type Ma = (u32, !, i32); //~ ERROR type is experimental
@@ -6,7 +6,7 @@ error: The `!` type is experimental (see issue #35121)
    |
    = help: add #![feature(never_type)] to the crate attributes to enable
 
-error: The `!` type is experimental (see issue #35121)
+error[E0658]: The `!` type is experimental (see issue #35121)
   --> $DIR/feature-gate-never_type.rs:18:20
    |
 18 | type Meeshka = Vec<!>; //~ ERROR type is experimental
@@ -14,7 +14,7 @@ error: The `!` type is experimental (see issue #35121)
    |
    = help: add #![feature(never_type)] to the crate attributes to enable
 
-error: The `!` type is experimental (see issue #35121)
+error[E0658]: The `!` type is experimental (see issue #35121)
   --> $DIR/feature-gate-never_type.rs:19:16
    |
 19 | type Mow = &fn(!) -> !; //~ ERROR type is experimental
@@ -22,7 +22,7 @@ error: The `!` type is experimental (see issue #35121)
    |
    = help: add #![feature(never_type)] to the crate attributes to enable
 
-error: The `!` type is experimental (see issue #35121)
+error[E0658]: The `!` type is experimental (see issue #35121)
   --> $DIR/feature-gate-never_type.rs:20:19
    |
 20 | type Skwoz = &mut !; //~ ERROR type is experimental
@@ -30,7 +30,7 @@ error: The `!` type is experimental (see issue #35121)
    |
    = help: add #![feature(never_type)] to the crate attributes to enable
 
-error: The `!` type is experimental (see issue #35121)
+error[E0658]: The `!` type is experimental (see issue #35121)
   --> $DIR/feature-gate-never_type.rs:23:16
    |
 23 |     type Wub = !; //~ ERROR type is experimental
diff --git a/src/test/ui/feature-gate-no-debug.stderr b/src/test/ui/feature-gate-no-debug.stderr
index 83a8189c095..c7af8cf6aab 100644
--- a/src/test/ui/feature-gate-no-debug.stderr
+++ b/src/test/ui/feature-gate-no-debug.stderr
@@ -1,4 +1,4 @@
-error: the `#[no_debug]` attribute was an experimental feature that has been deprecated due to lack of demand (see issue #29721)
+error[E0658]: the `#[no_debug]` attribute was an experimental feature that has been deprecated due to lack of demand (see issue #29721)
   --> $DIR/feature-gate-no-debug.rs:13:1
    |
 13 | #[no_debug] //~ ERROR the `#[no_debug]` attribute was
diff --git a/src/test/ui/feature-gate-no_core.stderr b/src/test/ui/feature-gate-no_core.stderr
index 02e0b176249..7fc89852002 100644
--- a/src/test/ui/feature-gate-no_core.stderr
+++ b/src/test/ui/feature-gate-no_core.stderr
@@ -1,4 +1,4 @@
-error: no_core is experimental (see issue #29639)
+error[E0658]: no_core is experimental (see issue #29639)
   --> $DIR/feature-gate-no_core.rs:11:1
    |
 11 | #![no_core] //~ ERROR no_core is experimental
diff --git a/src/test/ui/feature-gate-non_ascii_idents.stderr b/src/test/ui/feature-gate-non_ascii_idents.stderr
index 90d0b8daee7..deb707752b0 100644
--- a/src/test/ui/feature-gate-non_ascii_idents.stderr
+++ b/src/test/ui/feature-gate-non_ascii_idents.stderr
@@ -1,4 +1,4 @@
-error: non-ascii idents are not fully supported. (see issue #28979)
+error[E0658]: non-ascii idents are not fully supported. (see issue #28979)
   --> $DIR/feature-gate-non_ascii_idents.rs:11:1
    |
 11 | extern crate core as bäz; //~ ERROR non-ascii idents
@@ -6,7 +6,7 @@ error: non-ascii idents are not fully supported. (see issue #28979)
    |
    = help: add #![feature(non_ascii_idents)] to the crate attributes to enable
 
-error: non-ascii idents are not fully supported. (see issue #28979)
+error[E0658]: non-ascii idents are not fully supported. (see issue #28979)
   --> $DIR/feature-gate-non_ascii_idents.rs:13:5
    |
 13 | use föö::bar; //~ ERROR non-ascii idents
@@ -14,7 +14,7 @@ error: non-ascii idents are not fully supported. (see issue #28979)
    |
    = help: add #![feature(non_ascii_idents)] to the crate attributes to enable
 
-error: non-ascii idents are not fully supported. (see issue #28979)
+error[E0658]: non-ascii idents are not fully supported. (see issue #28979)
   --> $DIR/feature-gate-non_ascii_idents.rs:15:1
    |
 15 | mod föö { //~ ERROR non-ascii idents
@@ -22,7 +22,7 @@ error: non-ascii idents are not fully supported. (see issue #28979)
    |
    = help: add #![feature(non_ascii_idents)] to the crate attributes to enable
 
-error: non-ascii idents are not fully supported. (see issue #28979)
+error[E0658]: non-ascii idents are not fully supported. (see issue #28979)
   --> $DIR/feature-gate-non_ascii_idents.rs:19:1
    |
 19 | / fn bär( //~ ERROR non-ascii idents
@@ -36,7 +36,7 @@ error: non-ascii idents are not fully supported. (see issue #28979)
    |
    = help: add #![feature(non_ascii_idents)] to the crate attributes to enable
 
-error: non-ascii idents are not fully supported. (see issue #28979)
+error[E0658]: non-ascii idents are not fully supported. (see issue #28979)
   --> $DIR/feature-gate-non_ascii_idents.rs:20:5
    |
 20 |     bäz: isize //~ ERROR non-ascii idents
@@ -44,7 +44,7 @@ error: non-ascii idents are not fully supported. (see issue #28979)
    |
    = help: add #![feature(non_ascii_idents)] to the crate attributes to enable
 
-error: non-ascii idents are not fully supported. (see issue #28979)
+error[E0658]: non-ascii idents are not fully supported. (see issue #28979)
   --> $DIR/feature-gate-non_ascii_idents.rs:22:9
    |
 22 |     let _ö: isize; //~ ERROR non-ascii idents
@@ -52,7 +52,7 @@ error: non-ascii idents are not fully supported. (see issue #28979)
    |
    = help: add #![feature(non_ascii_idents)] to the crate attributes to enable
 
-error: non-ascii idents are not fully supported. (see issue #28979)
+error[E0658]: non-ascii idents are not fully supported. (see issue #28979)
   --> $DIR/feature-gate-non_ascii_idents.rs:25:10
    |
 25 |         (_ä, _) => {} //~ ERROR non-ascii idents
@@ -60,7 +60,7 @@ error: non-ascii idents are not fully supported. (see issue #28979)
    |
    = help: add #![feature(non_ascii_idents)] to the crate attributes to enable
 
-error: non-ascii idents are not fully supported. (see issue #28979)
+error[E0658]: non-ascii idents are not fully supported. (see issue #28979)
   --> $DIR/feature-gate-non_ascii_idents.rs:29:1
    |
 29 | struct Föö { //~ ERROR non-ascii idents
@@ -68,7 +68,7 @@ error: non-ascii idents are not fully supported. (see issue #28979)
    |
    = help: add #![feature(non_ascii_idents)] to the crate attributes to enable
 
-error: non-ascii idents are not fully supported. (see issue #28979)
+error[E0658]: non-ascii idents are not fully supported. (see issue #28979)
   --> $DIR/feature-gate-non_ascii_idents.rs:30:5
    |
 30 |     föö: isize //~ ERROR non-ascii idents
@@ -76,7 +76,7 @@ error: non-ascii idents are not fully supported. (see issue #28979)
    |
    = help: add #![feature(non_ascii_idents)] to the crate attributes to enable
 
-error: non-ascii idents are not fully supported. (see issue #28979)
+error[E0658]: non-ascii idents are not fully supported. (see issue #28979)
   --> $DIR/feature-gate-non_ascii_idents.rs:33:1
    |
 33 | enum Bär { //~ ERROR non-ascii idents
@@ -84,7 +84,7 @@ error: non-ascii idents are not fully supported. (see issue #28979)
    |
    = help: add #![feature(non_ascii_idents)] to the crate attributes to enable
 
-error: non-ascii idents are not fully supported. (see issue #28979)
+error[E0658]: non-ascii idents are not fully supported. (see issue #28979)
   --> $DIR/feature-gate-non_ascii_idents.rs:34:5
    |
 34 |     Bäz { //~ ERROR non-ascii idents
@@ -92,7 +92,7 @@ error: non-ascii idents are not fully supported. (see issue #28979)
    |
    = help: add #![feature(non_ascii_idents)] to the crate attributes to enable
 
-error: non-ascii idents are not fully supported. (see issue #28979)
+error[E0658]: non-ascii idents are not fully supported. (see issue #28979)
   --> $DIR/feature-gate-non_ascii_idents.rs:35:9
    |
 35 |         qüx: isize //~ ERROR non-ascii idents
@@ -100,7 +100,7 @@ error: non-ascii idents are not fully supported. (see issue #28979)
    |
    = help: add #![feature(non_ascii_idents)] to the crate attributes to enable
 
-error: non-ascii idents are not fully supported. (see issue #28979)
+error[E0658]: non-ascii idents are not fully supported. (see issue #28979)
   --> $DIR/feature-gate-non_ascii_idents.rs:40:5
    |
 40 |     fn qüx();  //~ ERROR non-ascii idents
diff --git a/src/test/ui/feature-gate-non_exhaustive.stderr b/src/test/ui/feature-gate-non_exhaustive.stderr
index 775e65b90fa..320f40e31b8 100644
--- a/src/test/ui/feature-gate-non_exhaustive.stderr
+++ b/src/test/ui/feature-gate-non_exhaustive.stderr
@@ -1,4 +1,4 @@
-error: non exhaustive is an experimental feature (see issue #44109)
+error[E0658]: non exhaustive is an experimental feature (see issue #44109)
   --> $DIR/feature-gate-non_exhaustive.rs:13:1
    |
 13 | #[non_exhaustive] //~ERROR non exhaustive is an experimental feature (see issue #44109)
diff --git a/src/test/ui/feature-gate-omit-gdb-pretty-printer-section.stderr b/src/test/ui/feature-gate-omit-gdb-pretty-printer-section.stderr
index e50e1b4c0b5..4ceb697d0df 100644
--- a/src/test/ui/feature-gate-omit-gdb-pretty-printer-section.stderr
+++ b/src/test/ui/feature-gate-omit-gdb-pretty-printer-section.stderr
@@ -1,4 +1,4 @@
-error: the `#[omit_gdb_pretty_printer_section]` attribute is just used for the Rust test suite
+error[E0658]: the `#[omit_gdb_pretty_printer_section]` attribute is just used for the Rust test suite
   --> $DIR/feature-gate-omit-gdb-pretty-printer-section.rs:11:1
    |
 11 | #[omit_gdb_pretty_printer_section] //~ ERROR the `#[omit_gdb_pretty_printer_section]` attribute is
diff --git a/src/test/ui/feature-gate-on-unimplemented.stderr b/src/test/ui/feature-gate-on-unimplemented.stderr
index 06944a14736..b1658c3be16 100644
--- a/src/test/ui/feature-gate-on-unimplemented.stderr
+++ b/src/test/ui/feature-gate-on-unimplemented.stderr
@@ -1,4 +1,4 @@
-error: the `#[rustc_on_unimplemented]` attribute is an experimental feature (see issue #29628)
+error[E0658]: the `#[rustc_on_unimplemented]` attribute is an experimental feature (see issue #29628)
   --> $DIR/feature-gate-on-unimplemented.rs:14:1
    |
 14 | #[rustc_on_unimplemented = "test error `{Self}` with `{Bar}`"]
diff --git a/src/test/ui/feature-gate-optin-builtin-traits.stderr b/src/test/ui/feature-gate-optin-builtin-traits.stderr
index d66da1224f8..beb734a8ef8 100644
--- a/src/test/ui/feature-gate-optin-builtin-traits.stderr
+++ b/src/test/ui/feature-gate-optin-builtin-traits.stderr
@@ -1,4 +1,4 @@
-error: auto traits are experimental and possibly buggy (see issue #13231)
+error[E0658]: auto traits are experimental and possibly buggy (see issue #13231)
   --> $DIR/feature-gate-optin-builtin-traits.rs:20:1
    |
 20 | auto trait AutoDummyTrait {}
@@ -6,7 +6,7 @@ error: auto traits are experimental and possibly buggy (see issue #13231)
    |
    = help: add #![feature(optin_builtin_traits)] to the crate attributes to enable
 
-error: negative trait bounds are not yet fully implemented; use marker types for now (see issue #13231)
+error[E0658]: negative trait bounds are not yet fully implemented; use marker types for now (see issue #13231)
   --> $DIR/feature-gate-optin-builtin-traits.rs:23:1
    |
 23 | impl !DummyTrait for DummyStruct {}
diff --git a/src/test/ui/feature-gate-placement-expr.stderr b/src/test/ui/feature-gate-placement-expr.stderr
index fdb7b506711..c588cabe239 100644
--- a/src/test/ui/feature-gate-placement-expr.stderr
+++ b/src/test/ui/feature-gate-placement-expr.stderr
@@ -1,4 +1,4 @@
-error: placement-in expression syntax is experimental and subject to change. (see issue #27779)
+error[E0658]: placement-in expression syntax is experimental and subject to change. (see issue #27779)
   --> $DIR/feature-gate-placement-expr.rs:24:13
    |
 24 |     let x = HEAP <- 'c'; //~ ERROR placement-in expression syntax is experimental
diff --git a/src/test/ui/feature-gate-plugin.stderr b/src/test/ui/feature-gate-plugin.stderr
index b94d3299abc..b54b2d89994 100644
--- a/src/test/ui/feature-gate-plugin.stderr
+++ b/src/test/ui/feature-gate-plugin.stderr
@@ -1,4 +1,4 @@
-error: compiler plugins are experimental and possibly buggy (see issue #29597)
+error[E0658]: compiler plugins are experimental and possibly buggy (see issue #29597)
   --> $DIR/feature-gate-plugin.rs:13:1
    |
 13 | #![plugin(foo)]
diff --git a/src/test/ui/feature-gate-plugin_registrar.stderr b/src/test/ui/feature-gate-plugin_registrar.stderr
index 3710239142a..fb5bd9d1afe 100644
--- a/src/test/ui/feature-gate-plugin_registrar.stderr
+++ b/src/test/ui/feature-gate-plugin_registrar.stderr
@@ -1,4 +1,4 @@
-error: compiler plugins are experimental and possibly buggy (see issue #29597)
+error[E0658]: compiler plugins are experimental and possibly buggy (see issue #29597)
   --> $DIR/feature-gate-plugin_registrar.rs:16:1
    |
 16 | pub fn registrar() {}
diff --git a/src/test/ui/feature-gate-prelude_import.stderr b/src/test/ui/feature-gate-prelude_import.stderr
index df44dfff40b..5487ae21f3b 100644
--- a/src/test/ui/feature-gate-prelude_import.stderr
+++ b/src/test/ui/feature-gate-prelude_import.stderr
@@ -1,4 +1,4 @@
-error: `#[prelude_import]` is for use by rustc only
+error[E0658]: `#[prelude_import]` is for use by rustc only
   --> $DIR/feature-gate-prelude_import.rs:11:1
    |
 11 | #[prelude_import] //~ ERROR `#[prelude_import]` is for use by rustc only
diff --git a/src/test/ui/feature-gate-profiler-runtime.stderr b/src/test/ui/feature-gate-profiler-runtime.stderr
index c3165438cdb..f2893cbb97d 100644
--- a/src/test/ui/feature-gate-profiler-runtime.stderr
+++ b/src/test/ui/feature-gate-profiler-runtime.stderr
@@ -1,4 +1,4 @@
-error: the `#[profiler_runtime]` attribute is used to identify the `profiler_builtins` crate which contains the profiler runtime and will never be stable
+error[E0658]: the `#[profiler_runtime]` attribute is used to identify the `profiler_builtins` crate which contains the profiler runtime and will never be stable
   --> $DIR/feature-gate-profiler-runtime.rs:11:1
    |
 11 | #![profiler_runtime] //~ ERROR the `#[profiler_runtime]` attribute is
diff --git a/src/test/ui/feature-gate-repr-simd.stderr b/src/test/ui/feature-gate-repr-simd.stderr
index a2ff06dd59f..e430a04a3e8 100644
--- a/src/test/ui/feature-gate-repr-simd.stderr
+++ b/src/test/ui/feature-gate-repr-simd.stderr
@@ -1,4 +1,4 @@
-error: SIMD types are experimental and possibly buggy (see issue #27731)
+error[E0658]: SIMD types are experimental and possibly buggy (see issue #27731)
   --> $DIR/feature-gate-repr-simd.rs:11:1
    |
 11 | #[repr(simd)] //~ error: SIMD types are experimental
diff --git a/src/test/ui/feature-gate-repr128.stderr b/src/test/ui/feature-gate-repr128.stderr
index c59964887b5..982ebb01016 100644
--- a/src/test/ui/feature-gate-repr128.stderr
+++ b/src/test/ui/feature-gate-repr128.stderr
@@ -1,4 +1,4 @@
-error: repr with 128-bit type is unstable (see issue #35118)
+error[E0658]: repr with 128-bit type is unstable (see issue #35118)
   --> $DIR/feature-gate-repr128.rs:12:1
    |
 12 | / enum A { //~ ERROR repr with 128-bit type is unstable
diff --git a/src/test/ui/feature-gate-repr_align.stderr b/src/test/ui/feature-gate-repr_align.stderr
index 16fdc135a5f..dd88067d58f 100644
--- a/src/test/ui/feature-gate-repr_align.stderr
+++ b/src/test/ui/feature-gate-repr_align.stderr
@@ -1,4 +1,4 @@
-error: the struct `#[repr(align(u16))]` attribute is experimental (see issue #33626)
+error[E0658]: the struct `#[repr(align(u16))]` attribute is experimental (see issue #33626)
   --> $DIR/feature-gate-repr_align.rs:12:1
    |
 12 | #[repr(align(64))] //~ error: the struct `#[repr(align(u16))]` attribute is experimental
diff --git a/src/test/ui/feature-gate-rustc-attrs.stderr b/src/test/ui/feature-gate-rustc-attrs.stderr
index c818b57ef12..f47588c3a7d 100644
--- a/src/test/ui/feature-gate-rustc-attrs.stderr
+++ b/src/test/ui/feature-gate-rustc-attrs.stderr
@@ -1,4 +1,4 @@
-error: the `#[rustc_variance]` attribute is just used for rustc unit tests and will never be stable (see issue #29642)
+error[E0658]: the `#[rustc_variance]` attribute is just used for rustc unit tests and will never be stable (see issue #29642)
   --> $DIR/feature-gate-rustc-attrs.rs:15:1
    |
 15 | #[rustc_variance] //~ ERROR the `#[rustc_variance]` attribute is just used for rustc unit tests and will never be stable
@@ -6,7 +6,7 @@ error: the `#[rustc_variance]` attribute is just used for rustc unit tests and w
    |
    = help: add #![feature(rustc_attrs)] to the crate attributes to enable
 
-error: the `#[rustc_error]` attribute is just used for rustc unit tests and will never be stable (see issue #29642)
+error[E0658]: the `#[rustc_error]` attribute is just used for rustc unit tests and will never be stable (see issue #29642)
   --> $DIR/feature-gate-rustc-attrs.rs:16:1
    |
 16 | #[rustc_error] //~ ERROR the `#[rustc_error]` attribute is just used for rustc unit tests and will never be stable
@@ -14,7 +14,7 @@ error: the `#[rustc_error]` attribute is just used for rustc unit tests and will
    |
    = help: add #![feature(rustc_attrs)] to the crate attributes to enable
 
-error: unless otherwise specified, attributes with the prefix `rustc_` are reserved for internal compiler diagnostics (see issue #29642)
+error[E0658]: unless otherwise specified, attributes with the prefix `rustc_` are reserved for internal compiler diagnostics (see issue #29642)
   --> $DIR/feature-gate-rustc-attrs.rs:17:1
    |
 17 | #[rustc_foo]
diff --git a/src/test/ui/feature-gate-rustc_const_unstable.stderr b/src/test/ui/feature-gate-rustc_const_unstable.stderr
index c32abb8b857..922898b7d36 100644
--- a/src/test/ui/feature-gate-rustc_const_unstable.stderr
+++ b/src/test/ui/feature-gate-rustc_const_unstable.stderr
@@ -1,4 +1,4 @@
-error: the `#[rustc_const_unstable]` attribute is an internal feature
+error[E0658]: the `#[rustc_const_unstable]` attribute is an internal feature
   --> $DIR/feature-gate-rustc_const_unstable.rs:18:1
    |
 18 | #[rustc_const_unstable(feature="fzzzzzt")] //~ERROR internal feature
diff --git a/src/test/ui/feature-gate-sanitizer-runtime.stderr b/src/test/ui/feature-gate-sanitizer-runtime.stderr
index b9a43f8098d..6d77161864f 100644
--- a/src/test/ui/feature-gate-sanitizer-runtime.stderr
+++ b/src/test/ui/feature-gate-sanitizer-runtime.stderr
@@ -1,4 +1,4 @@
-error: the `#[sanitizer_runtime]` attribute is used to identify crates that contain the runtime of a sanitizer and will never be stable
+error[E0658]: the `#[sanitizer_runtime]` attribute is used to identify crates that contain the runtime of a sanitizer and will never be stable
   --> $DIR/feature-gate-sanitizer-runtime.rs:11:1
    |
 11 | #![sanitizer_runtime] //~ ERROR the `#[sanitizer_runtime]` attribute is
diff --git a/src/test/ui/feature-gate-simd.stderr b/src/test/ui/feature-gate-simd.stderr
index b3225d580bf..447706ab858 100644
--- a/src/test/ui/feature-gate-simd.stderr
+++ b/src/test/ui/feature-gate-simd.stderr
@@ -1,4 +1,4 @@
-error: SIMD types are experimental and possibly buggy (see issue #27731)
+error[E0658]: SIMD types are experimental and possibly buggy (see issue #27731)
   --> $DIR/feature-gate-simd.rs:14:1
    |
 14 | #[repr(simd)] //~ ERROR SIMD types are experimental
diff --git a/src/test/ui/feature-gate-slice-patterns.stderr b/src/test/ui/feature-gate-slice-patterns.stderr
index e5ba318b336..7a2e67c8982 100644
--- a/src/test/ui/feature-gate-slice-patterns.stderr
+++ b/src/test/ui/feature-gate-slice-patterns.stderr
@@ -1,4 +1,4 @@
-error: slice pattern syntax is experimental (see issue #23121)
+error[E0658]: slice pattern syntax is experimental (see issue #23121)
   --> $DIR/feature-gate-slice-patterns.rs:16:9
    |
 16 |         [1, 2, xs..] => {} //~ ERROR slice pattern syntax is experimental
diff --git a/src/test/ui/feature-gate-start.stderr b/src/test/ui/feature-gate-start.stderr
index b36fae2aacf..61cbe42d0fb 100644
--- a/src/test/ui/feature-gate-start.stderr
+++ b/src/test/ui/feature-gate-start.stderr
@@ -1,4 +1,4 @@
-error: a #[start] function is an experimental feature whose signature may change over time (see issue #29633)
+error[E0658]: a #[start] function is an experimental feature whose signature may change over time (see issue #29633)
   --> $DIR/feature-gate-start.rs:12:1
    |
 12 | fn foo() {} //~ ERROR: a #[start] function is an experimental feature
diff --git a/src/test/ui/feature-gate-static-nobundle.stderr b/src/test/ui/feature-gate-static-nobundle.stderr
index 052516fad76..9ec4f6480b1 100644
--- a/src/test/ui/feature-gate-static-nobundle.stderr
+++ b/src/test/ui/feature-gate-static-nobundle.stderr
@@ -1,4 +1,4 @@
-error: kind="static-nobundle" is feature gated (see issue #37403)
+error[E0658]: kind="static-nobundle" is feature gated (see issue #37403)
   --> $DIR/feature-gate-static-nobundle.rs:11:1
    |
 11 | #[link(name="foo", kind="static-nobundle")]
diff --git a/src/test/ui/feature-gate-stmt_expr_attributes.stderr b/src/test/ui/feature-gate-stmt_expr_attributes.stderr
index 80910594d1c..4d2e2f671c5 100644
--- a/src/test/ui/feature-gate-stmt_expr_attributes.stderr
+++ b/src/test/ui/feature-gate-stmt_expr_attributes.stderr
@@ -1,4 +1,4 @@
-error: attributes on non-item statements and expressions are experimental. (see issue #15701)
+error[E0658]: attributes on non-item statements and expressions are experimental. (see issue #15701)
   --> $DIR/feature-gate-stmt_expr_attributes.rs:11:16
    |
 11 | const X: i32 = #[allow(dead_code)] 8;
diff --git a/src/test/ui/feature-gate-target_feature.stderr b/src/test/ui/feature-gate-target_feature.stderr
index 8c89eabf753..b6ad1b65691 100644
--- a/src/test/ui/feature-gate-target_feature.stderr
+++ b/src/test/ui/feature-gate-target_feature.stderr
@@ -1,4 +1,4 @@
-error: the `#[target_feature]` attribute is an experimental feature
+error[E0658]: the `#[target_feature]` attribute is an experimental feature
   --> $DIR/feature-gate-target_feature.rs:11:1
    |
 11 | #[target_feature = "+sse2"]
diff --git a/src/test/ui/feature-gate-thread_local.stderr b/src/test/ui/feature-gate-thread_local.stderr
index 2608018528c..0f932abe4ee 100644
--- a/src/test/ui/feature-gate-thread_local.stderr
+++ b/src/test/ui/feature-gate-thread_local.stderr
@@ -1,4 +1,4 @@
-error: `#[thread_local]` is an experimental feature, and does not currently handle destructors. There is no corresponding `#[task_local]` mapping to the task model (see issue #29594)
+error[E0658]: `#[thread_local]` is an experimental feature, and does not currently handle destructors. There is no corresponding `#[task_local]` mapping to the task model (see issue #29594)
   --> $DIR/feature-gate-thread_local.rs:18:1
    |
 18 | #[thread_local] //~ ERROR `#[thread_local]` is an experimental feature
diff --git a/src/test/ui/feature-gate-trace_macros.stderr b/src/test/ui/feature-gate-trace_macros.stderr
index aca74099b7d..eae3baa7e4d 100644
--- a/src/test/ui/feature-gate-trace_macros.stderr
+++ b/src/test/ui/feature-gate-trace_macros.stderr
@@ -1,4 +1,4 @@
-error: `trace_macros` is not stable enough for use and is subject to change (see issue #29598)
+error[E0658]: `trace_macros` is not stable enough for use and is subject to change (see issue #29598)
   --> $DIR/feature-gate-trace_macros.rs:12:5
    |
 12 |     trace_macros!(true); //~ ERROR: `trace_macros` is not stable
diff --git a/src/test/ui/feature-gate-type_ascription.stderr b/src/test/ui/feature-gate-type_ascription.stderr
index d2a3ee2cf8f..fa6ef84a7f5 100644
--- a/src/test/ui/feature-gate-type_ascription.stderr
+++ b/src/test/ui/feature-gate-type_ascription.stderr
@@ -1,4 +1,4 @@
-error: type ascription is experimental (see issue #23416)
+error[E0658]: type ascription is experimental (see issue #23416)
   --> $DIR/feature-gate-type_ascription.rs:14:13
    |
 14 |     let a = 10: u8; //~ ERROR type ascription is experimental
diff --git a/src/test/ui/feature-gate-unboxed-closures-manual-impls.stderr b/src/test/ui/feature-gate-unboxed-closures-manual-impls.stderr
index 280fc12f1a6..ae14054b6e3 100644
--- a/src/test/ui/feature-gate-unboxed-closures-manual-impls.stderr
+++ b/src/test/ui/feature-gate-unboxed-closures-manual-impls.stderr
@@ -1,4 +1,4 @@
-error: rust-call ABI is subject to change (see issue #29625)
+error[E0658]: rust-call ABI is subject to change (see issue #29625)
   --> $DIR/feature-gate-unboxed-closures-manual-impls.rs:20:5
    |
 20 |     extern "rust-call" fn call(self, args: ()) -> () {}
@@ -6,7 +6,7 @@ error: rust-call ABI is subject to change (see issue #29625)
    |
    = help: add #![feature(unboxed_closures)] to the crate attributes to enable
 
-error: rust-call ABI is subject to change (see issue #29625)
+error[E0658]: rust-call ABI is subject to change (see issue #29625)
   --> $DIR/feature-gate-unboxed-closures-manual-impls.rs:25:5
    |
 25 |     extern "rust-call" fn call_once(self, args: ()) -> () {}
@@ -14,7 +14,7 @@ error: rust-call ABI is subject to change (see issue #29625)
    |
    = help: add #![feature(unboxed_closures)] to the crate attributes to enable
 
-error: rust-call ABI is subject to change (see issue #29625)
+error[E0658]: rust-call ABI is subject to change (see issue #29625)
   --> $DIR/feature-gate-unboxed-closures-manual-impls.rs:30:5
    |
 30 |     extern "rust-call" fn call_mut(&self, args: ()) -> () {}
@@ -22,7 +22,7 @@ error: rust-call ABI is subject to change (see issue #29625)
    |
    = help: add #![feature(unboxed_closures)] to the crate attributes to enable
 
-error: rust-call ABI is subject to change (see issue #29625)
+error[E0658]: rust-call ABI is subject to change (see issue #29625)
   --> $DIR/feature-gate-unboxed-closures-manual-impls.rs:35:5
    |
 35 |     extern "rust-call" fn call_once(&self, args: ()) -> () {}
diff --git a/src/test/ui/feature-gate-unboxed-closures-method-calls.stderr b/src/test/ui/feature-gate-unboxed-closures-method-calls.stderr
index 1167bf0a696..a27b00aaac0 100644
--- a/src/test/ui/feature-gate-unboxed-closures-method-calls.stderr
+++ b/src/test/ui/feature-gate-unboxed-closures-method-calls.stderr
@@ -1,4 +1,4 @@
-error: use of unstable library feature 'fn_traits' (see issue #29625)
+error[E0658]: use of unstable library feature 'fn_traits' (see issue #29625)
   --> $DIR/feature-gate-unboxed-closures-method-calls.rs:14:7
    |
 14 |     f.call(()); //~ ERROR use of unstable library feature 'fn_traits'
@@ -6,7 +6,7 @@ error: use of unstable library feature 'fn_traits' (see issue #29625)
    |
    = help: add #![feature(fn_traits)] to the crate attributes to enable
 
-error: use of unstable library feature 'fn_traits' (see issue #29625)
+error[E0658]: use of unstable library feature 'fn_traits' (see issue #29625)
   --> $DIR/feature-gate-unboxed-closures-method-calls.rs:15:7
    |
 15 |     f.call_mut(()); //~ ERROR use of unstable library feature 'fn_traits'
@@ -14,7 +14,7 @@ error: use of unstable library feature 'fn_traits' (see issue #29625)
    |
    = help: add #![feature(fn_traits)] to the crate attributes to enable
 
-error: use of unstable library feature 'fn_traits' (see issue #29625)
+error[E0658]: use of unstable library feature 'fn_traits' (see issue #29625)
   --> $DIR/feature-gate-unboxed-closures-method-calls.rs:16:7
    |
 16 |     f.call_once(()); //~ ERROR use of unstable library feature 'fn_traits'
diff --git a/src/test/ui/feature-gate-unboxed-closures-ufcs-calls.stderr b/src/test/ui/feature-gate-unboxed-closures-ufcs-calls.stderr
index 7eb491cebfe..3d0dd15b07f 100644
--- a/src/test/ui/feature-gate-unboxed-closures-ufcs-calls.stderr
+++ b/src/test/ui/feature-gate-unboxed-closures-ufcs-calls.stderr
@@ -1,4 +1,4 @@
-error: use of unstable library feature 'fn_traits' (see issue #29625)
+error[E0658]: use of unstable library feature 'fn_traits' (see issue #29625)
   --> $DIR/feature-gate-unboxed-closures-ufcs-calls.rs:14:5
    |
 14 |     Fn::call(&f, ()); //~ ERROR use of unstable library feature 'fn_traits'
@@ -6,7 +6,7 @@ error: use of unstable library feature 'fn_traits' (see issue #29625)
    |
    = help: add #![feature(fn_traits)] to the crate attributes to enable
 
-error: use of unstable library feature 'fn_traits' (see issue #29625)
+error[E0658]: use of unstable library feature 'fn_traits' (see issue #29625)
   --> $DIR/feature-gate-unboxed-closures-ufcs-calls.rs:15:5
    |
 15 |     FnMut::call_mut(&mut f, ()); //~ ERROR use of unstable library feature 'fn_traits'
@@ -14,7 +14,7 @@ error: use of unstable library feature 'fn_traits' (see issue #29625)
    |
    = help: add #![feature(fn_traits)] to the crate attributes to enable
 
-error: use of unstable library feature 'fn_traits' (see issue #29625)
+error[E0658]: use of unstable library feature 'fn_traits' (see issue #29625)
   --> $DIR/feature-gate-unboxed-closures-ufcs-calls.rs:16:5
    |
 16 |     FnOnce::call_once(f, ()); //~ ERROR use of unstable library feature 'fn_traits'
diff --git a/src/test/ui/feature-gate-unboxed-closures.stderr b/src/test/ui/feature-gate-unboxed-closures.stderr
index b79165147e5..ca8a5924946 100644
--- a/src/test/ui/feature-gate-unboxed-closures.stderr
+++ b/src/test/ui/feature-gate-unboxed-closures.stderr
@@ -1,4 +1,4 @@
-error: rust-call ABI is subject to change (see issue #29625)
+error[E0658]: rust-call ABI is subject to change (see issue #29625)
   --> $DIR/feature-gate-unboxed-closures.rs:16:5
    |
 16 | /     extern "rust-call" fn call_once(self, (a, b): (u32, u32)) -> u32 {
diff --git a/src/test/ui/feature-gate-underscore-lifetimes.stderr b/src/test/ui/feature-gate-underscore-lifetimes.stderr
index 875b958aa88..07c5e1ad640 100644
--- a/src/test/ui/feature-gate-underscore-lifetimes.stderr
+++ b/src/test/ui/feature-gate-underscore-lifetimes.stderr
@@ -1,4 +1,4 @@
-error: underscore lifetimes are unstable (see issue #44524)
+error[E0658]: underscore lifetimes are unstable (see issue #44524)
   --> $DIR/feature-gate-underscore-lifetimes.rs:13:23
    |
 13 | fn foo(x: &u8) -> Foo<'_> { //~ ERROR underscore lifetimes are unstable
diff --git a/src/test/ui/feature-gate-universal.stderr b/src/test/ui/feature-gate-universal.stderr
index 7f889f96224..978ce5982ba 100644
--- a/src/test/ui/feature-gate-universal.stderr
+++ b/src/test/ui/feature-gate-universal.stderr
@@ -1,4 +1,4 @@
-error: `impl Trait` in argument position is experimental (see issue #34511)
+error[E0658]: `impl Trait` in argument position is experimental (see issue #34511)
   --> $DIR/feature-gate-universal.rs:13:11
    |
 13 | fn foo(x: impl std::fmt::Debug) { print!("{:?}", x); }
diff --git a/src/test/ui/feature-gate-unsized_tuple_coercion.stderr b/src/test/ui/feature-gate-unsized_tuple_coercion.stderr
index f166b10613a..4714df9e96c 100644
--- a/src/test/ui/feature-gate-unsized_tuple_coercion.stderr
+++ b/src/test/ui/feature-gate-unsized_tuple_coercion.stderr
@@ -1,4 +1,4 @@
-error: Unsized tuple coercion is not stable enough for use and is subject to change (see issue #42877)
+error[E0658]: Unsized tuple coercion is not stable enough for use and is subject to change (see issue #42877)
   --> $DIR/feature-gate-unsized_tuple_coercion.rs:12:24
    |
 12 |     let _ : &(Send,) = &((),);
diff --git a/src/test/ui/feature-gate-untagged_unions.stderr b/src/test/ui/feature-gate-untagged_unions.stderr
index 26b698912bc..14b66cb5c81 100644
--- a/src/test/ui/feature-gate-untagged_unions.stderr
+++ b/src/test/ui/feature-gate-untagged_unions.stderr
@@ -1,4 +1,4 @@
-error: unions with non-`Copy` fields are unstable (see issue #32836)
+error[E0658]: unions with non-`Copy` fields are unstable (see issue #32836)
   --> $DIR/feature-gate-untagged_unions.rs:19:1
    |
 19 | / union U3 { //~ ERROR unions with non-`Copy` fields are unstable
@@ -8,7 +8,7 @@ error: unions with non-`Copy` fields are unstable (see issue #32836)
    |
    = help: add #![feature(untagged_unions)] to the crate attributes to enable
 
-error: unions with non-`Copy` fields are unstable (see issue #32836)
+error[E0658]: unions with non-`Copy` fields are unstable (see issue #32836)
   --> $DIR/feature-gate-untagged_unions.rs:23:1
    |
 23 | / union U4<T> { //~ ERROR unions with non-`Copy` fields are unstable
@@ -18,7 +18,7 @@ error: unions with non-`Copy` fields are unstable (see issue #32836)
    |
    = help: add #![feature(untagged_unions)] to the crate attributes to enable
 
-error: unions with `Drop` implementations are unstable (see issue #32836)
+error[E0658]: unions with `Drop` implementations are unstable (see issue #32836)
   --> $DIR/feature-gate-untagged_unions.rs:27:1
    |
 27 | / union U5 { //~ ERROR unions with `Drop` implementations are unstable
diff --git a/src/test/ui/feature-gate-unwind-attributes.stderr b/src/test/ui/feature-gate-unwind-attributes.stderr
index 02d8bf914eb..d9b555e2634 100644
--- a/src/test/ui/feature-gate-unwind-attributes.stderr
+++ b/src/test/ui/feature-gate-unwind-attributes.stderr
@@ -1,4 +1,4 @@
-error: #[unwind] is experimental
+error[E0658]: #[unwind] is experimental
   --> $DIR/feature-gate-unwind-attributes.rs:21:5
    |
 21 |     #[unwind] //~ ERROR #[unwind] is experimental
diff --git a/src/test/ui/feature-gate-use_nested_groups.stderr b/src/test/ui/feature-gate-use_nested_groups.stderr
index 79f1d1a168f..6ae691c384b 100644
--- a/src/test/ui/feature-gate-use_nested_groups.stderr
+++ b/src/test/ui/feature-gate-use_nested_groups.stderr
@@ -1,4 +1,4 @@
-error: nested groups in `use` are experimental (see issue #44494)
+error[E0658]: nested groups in `use` are experimental (see issue #44494)
   --> $DIR/feature-gate-use_nested_groups.rs:27:12
    |
 27 | use a::{B, d::{*, g::H}};  //~ ERROR glob imports in `use` groups are experimental
@@ -6,7 +6,7 @@ error: nested groups in `use` are experimental (see issue #44494)
    |
    = help: add #![feature(use_nested_groups)] to the crate attributes to enable
 
-error: glob imports in `use` groups are experimental (see issue #44494)
+error[E0658]: glob imports in `use` groups are experimental (see issue #44494)
   --> $DIR/feature-gate-use_nested_groups.rs:27:16
    |
 27 | use a::{B, d::{*, g::H}};  //~ ERROR glob imports in `use` groups are experimental
@@ -14,7 +14,7 @@ error: glob imports in `use` groups are experimental (see issue #44494)
    |
    = help: add #![feature(use_nested_groups)] to the crate attributes to enable
 
-error: paths in `use` groups are experimental (see issue #44494)
+error[E0658]: paths in `use` groups are experimental (see issue #44494)
   --> $DIR/feature-gate-use_nested_groups.rs:27:19
    |
 27 | use a::{B, d::{*, g::H}};  //~ ERROR glob imports in `use` groups are experimental
diff --git a/src/test/ui/feature-gate-used.stderr b/src/test/ui/feature-gate-used.stderr
index 228cf12a08b..6d5ab1fd2c5 100644
--- a/src/test/ui/feature-gate-used.stderr
+++ b/src/test/ui/feature-gate-used.stderr
@@ -1,4 +1,4 @@
-error: the `#[used]` attribute is an experimental feature (see issue #40289)
+error[E0658]: the `#[used]` attribute is an experimental feature (see issue #40289)
   --> $DIR/feature-gate-used.rs:11:1
    |
 11 | #[used]
diff --git a/src/test/ui/feature-gate-wasm_import_memory.stderr b/src/test/ui/feature-gate-wasm_import_memory.stderr
index c0486d0d5f5..10190ef93f0 100644
--- a/src/test/ui/feature-gate-wasm_import_memory.stderr
+++ b/src/test/ui/feature-gate-wasm_import_memory.stderr
@@ -1,4 +1,4 @@
-error: wasm_import_memory attribute is currently unstable
+error[E0658]: wasm_import_memory attribute is currently unstable
   --> $DIR/feature-gate-wasm_import_memory.rs:11:1
    |
 11 | #![wasm_import_memory] //~ ERROR: currently unstable
diff --git a/src/test/ui/non_modrs_mods/non_modrs_mods.stderr b/src/test/ui/non_modrs_mods/non_modrs_mods.stderr
index 95a2539ed64..f60d2e93e36 100644
--- a/src/test/ui/non_modrs_mods/non_modrs_mods.stderr
+++ b/src/test/ui/non_modrs_mods/non_modrs_mods.stderr
@@ -1,4 +1,4 @@
-error: mod statements in non-mod.rs files are unstable (see issue #44660)
+error[E0658]: mod statements in non-mod.rs files are unstable (see issue #44660)
   --> $DIR/modrs_mod/inner_foors_mod.rs:11:9
    |
 11 | pub mod innest;
@@ -7,7 +7,7 @@ error: mod statements in non-mod.rs files are unstable (see issue #44660)
    = help: add #![feature(non_modrs_mods)] to the crate attributes to enable
    = help: on stable builds, rename this file to inner_foors_mod/mod.rs
 
-error: mod statements in non-mod.rs files are unstable (see issue #44660)
+error[E0658]: mod statements in non-mod.rs files are unstable (see issue #44660)
   --> $DIR/foors_mod.rs:13:9
    |
 13 | pub mod inner_modrs_mod;
@@ -16,7 +16,7 @@ error: mod statements in non-mod.rs files are unstable (see issue #44660)
    = help: add #![feature(non_modrs_mods)] to the crate attributes to enable
    = help: on stable builds, rename this file to foors_mod/mod.rs
 
-error: mod statements in non-mod.rs files are unstable (see issue #44660)
+error[E0658]: mod statements in non-mod.rs files are unstable (see issue #44660)
   --> $DIR/foors_mod.rs:14:9
    |
 14 | pub mod inner_foors_mod;
@@ -25,7 +25,7 @@ error: mod statements in non-mod.rs files are unstable (see issue #44660)
    = help: add #![feature(non_modrs_mods)] to the crate attributes to enable
    = help: on stable builds, rename this file to foors_mod/mod.rs
 
-error: mod statements in non-mod.rs files are unstable (see issue #44660)
+error[E0658]: mod statements in non-mod.rs files are unstable (see issue #44660)
   --> $DIR/foors_mod/inner_foors_mod.rs:11:9
    |
 11 | pub mod innest;
diff --git a/src/test/ui/pat-slice-old-style.stderr b/src/test/ui/pat-slice-old-style.stderr
index 5e7cd10235d..29c41c49cc4 100644
--- a/src/test/ui/pat-slice-old-style.stderr
+++ b/src/test/ui/pat-slice-old-style.stderr
@@ -1,4 +1,4 @@
-error: non-reference pattern used to match a reference (see issue #42640)
+error[E0658]: non-reference pattern used to match a reference (see issue #42640)
   --> $DIR/pat-slice-old-style.rs:19:9
    |
 19 |         [a, b..] => {},
diff --git a/src/test/ui/rfc-2005-default-binding-mode/suggestion.stderr b/src/test/ui/rfc-2005-default-binding-mode/suggestion.stderr
index ebf9e498ffd..8aa17adbcb3 100644
--- a/src/test/ui/rfc-2005-default-binding-mode/suggestion.stderr
+++ b/src/test/ui/rfc-2005-default-binding-mode/suggestion.stderr
@@ -1,4 +1,4 @@
-error: non-reference pattern used to match a reference (see issue #42640)
+error[E0658]: non-reference pattern used to match a reference (see issue #42640)
   --> $DIR/suggestion.rs:12:12
    |
 12 |     if let Some(y) = &Some(22) { //~ ERROR non-reference pattern
diff --git a/src/test/ui/span/gated-features-attr-spans.stderr b/src/test/ui/span/gated-features-attr-spans.stderr
index d067470942e..74a2c1d742b 100644
--- a/src/test/ui/span/gated-features-attr-spans.stderr
+++ b/src/test/ui/span/gated-features-attr-spans.stderr
@@ -1,4 +1,4 @@
-error: the struct `#[repr(align(u16))]` attribute is experimental (see issue #33626)
+error[E0658]: the struct `#[repr(align(u16))]` attribute is experimental (see issue #33626)
   --> $DIR/gated-features-attr-spans.rs:13:1
    |
 13 | #[repr(align(16))] //~ ERROR is experimental
@@ -6,7 +6,7 @@ error: the struct `#[repr(align(u16))]` attribute is experimental (see issue #33
    |
    = help: add #![feature(repr_align)] to the crate attributes to enable
 
-error: SIMD types are experimental and possibly buggy (see issue #27731)
+error[E0658]: SIMD types are experimental and possibly buggy (see issue #27731)
   --> $DIR/gated-features-attr-spans.rs:20:1
    |
 20 | #[repr(simd)] //~ ERROR are experimental
diff --git a/src/test/ui/span/issue-36530.stderr b/src/test/ui/span/issue-36530.stderr
index 50908b2ca39..7f392104393 100644
--- a/src/test/ui/span/issue-36530.stderr
+++ b/src/test/ui/span/issue-36530.stderr
@@ -1,4 +1,4 @@
-error: The attribute `foo` is currently unknown to the compiler and may have meaning added to it in the future (see issue #29642)
+error[E0658]: The attribute `foo` is currently unknown to the compiler and may have meaning added to it in the future (see issue #29642)
   --> $DIR/issue-36530.rs:11:1
    |
 11 | #[foo] //~ ERROR is currently unknown to the compiler
@@ -6,7 +6,7 @@ error: The attribute `foo` is currently unknown to the compiler and may have mea
    |
    = help: add #![feature(custom_attribute)] to the crate attributes to enable
 
-error: The attribute `foo` is currently unknown to the compiler and may have meaning added to it in the future (see issue #29642)
+error[E0658]: The attribute `foo` is currently unknown to the compiler and may have meaning added to it in the future (see issue #29642)
   --> $DIR/issue-36530.rs:13:5
    |
 13 |     #![foo] //~ ERROR is currently unknown to the compiler
diff --git a/src/test/ui/specialization-feature-gate-default.stderr b/src/test/ui/specialization-feature-gate-default.stderr
index e17d1308385..96e0fe13dc9 100644
--- a/src/test/ui/specialization-feature-gate-default.stderr
+++ b/src/test/ui/specialization-feature-gate-default.stderr
@@ -1,4 +1,4 @@
-error: specialization is unstable (see issue #31844)
+error[E0658]: specialization is unstable (see issue #31844)
   --> $DIR/specialization-feature-gate-default.rs:20:5
    |
 20 |     default fn foo(&self) {} //~ ERROR specialization is unstable
diff --git a/src/test/ui/suggestions/dont-suggest-dereference-on-arg.stderr b/src/test/ui/suggestions/dont-suggest-dereference-on-arg.stderr
index 799d9080b9d..5413dcddcd7 100644
--- a/src/test/ui/suggestions/dont-suggest-dereference-on-arg.stderr
+++ b/src/test/ui/suggestions/dont-suggest-dereference-on-arg.stderr
@@ -1,4 +1,4 @@
-error: non-reference pattern used to match a reference (see issue #42640)
+error[E0658]: non-reference pattern used to match a reference (see issue #42640)
   --> $DIR/dont-suggest-dereference-on-arg.rs:16:18
    |
 16 |         .filter(|&(ref a, _)| foo(a))