Rollup merge of #64763 - GuillaumeGomez:long-err-explanation-E0734, r=estebank

Add E0734 and its long explanation

Part of https://github.com/rust-lang/rust/issues/61137

src/librustc/error_codes.rs

@@ -2217,6 +2217,23 @@ Examples of erroneous code:
 static X: u32 = 42;
 ```
 "##,
+
+E0734: r##"
+A stability attribute has been used outside of the standard library.
+
+Erroneous code examples:
+
+```compile_fail,E0734
+#[rustc_deprecated(since = "b", reason = "text")] // invalid
+#[stable(feature = "a", since = "b")] // invalid
+#[unstable(feature = "b", issue = "0")] // invalid
+fn foo(){}
+```
+
+These attributes are meant to only be used by the standard library and are
+rejected in your own crates.
+"##,
+
 ;
 //  E0006, // merged with E0005
 //  E0101, // replaced with E0282

src/librustc/middle/stability.rs

@@ -199,8 +199,12 @@ impl<'a, 'tcx> Annotator<'a, 'tcx> {
                 let name = attr.name_or_empty();
                 if [sym::unstable, sym::stable, sym::rustc_deprecated].contains(&name) {
                     attr::mark_used(attr);
-                    self.tcx.sess.span_err(attr.span, "stability attributes may not be used \
-                                                        outside of the standard library");
+                    struct_span_err!(
+                        self.tcx.sess,
+                        attr.span,
+                        E0734,
+                        "stability attributes may not be used outside of the standard library",
+                    ).emit();
                 }
             }
 

src/test/ui/feature-gate/issue-43106-gating-of-rustc_deprecated.stderr

@@ -1,40 +1,40 @@
-error: stability attributes may not be used outside of the standard library
+error[E0734]: stability attributes may not be used outside of the standard library
   --> $DIR/issue-43106-gating-of-rustc_deprecated.rs:7:1
    |
 LL | #![rustc_deprecated()]
    | ^^^^^^^^^^^^^^^^^^^^^^
 
-error: stability attributes may not be used outside of the standard library
+error[E0734]: stability attributes may not be used outside of the standard library
   --> $DIR/issue-43106-gating-of-rustc_deprecated.rs:10:1
    |
 LL | #[rustc_deprecated()]
    | ^^^^^^^^^^^^^^^^^^^^^
 
-error: stability attributes may not be used outside of the standard library
+error[E0734]: stability attributes may not be used outside of the standard library
   --> $DIR/issue-43106-gating-of-rustc_deprecated.rs:13:17
    |
 LL |     mod inner { #![rustc_deprecated()] }
    |                 ^^^^^^^^^^^^^^^^^^^^^^
 
-error: stability attributes may not be used outside of the standard library
+error[E0734]: stability attributes may not be used outside of the standard library
   --> $DIR/issue-43106-gating-of-rustc_deprecated.rs:16:5
    |
 LL |     #[rustc_deprecated()] fn f() { }
    |     ^^^^^^^^^^^^^^^^^^^^^
 
-error: stability attributes may not be used outside of the standard library
+error[E0734]: stability attributes may not be used outside of the standard library
   --> $DIR/issue-43106-gating-of-rustc_deprecated.rs:19:5
    |
 LL |     #[rustc_deprecated()] struct S;
    |     ^^^^^^^^^^^^^^^^^^^^^
 
-error: stability attributes may not be used outside of the standard library
+error[E0734]: stability attributes may not be used outside of the standard library
   --> $DIR/issue-43106-gating-of-rustc_deprecated.rs:22:5
    |
 LL |     #[rustc_deprecated()] type T = S;
    |     ^^^^^^^^^^^^^^^^^^^^^
 
-error: stability attributes may not be used outside of the standard library
+error[E0734]: stability attributes may not be used outside of the standard library
   --> $DIR/issue-43106-gating-of-rustc_deprecated.rs:25:5
    |
 LL |     #[rustc_deprecated()] impl S { }
@@ -42,3 +42,4 @@ LL |     #[rustc_deprecated()] impl S { }
 
 error: aborting due to 7 previous errors
 
+For more information about this error, try `rustc --explain E0734`.

src/test/ui/feature-gate/issue-43106-gating-of-stable.stderr

@@ -1,40 +1,40 @@
-error: stability attributes may not be used outside of the standard library
+error[E0734]: stability attributes may not be used outside of the standard library
   --> $DIR/issue-43106-gating-of-stable.rs:7:1
    |
 LL | #![stable()]
    | ^^^^^^^^^^^^
 
-error: stability attributes may not be used outside of the standard library
+error[E0734]: stability attributes may not be used outside of the standard library
   --> $DIR/issue-43106-gating-of-stable.rs:10:1
    |
 LL | #[stable()]
    | ^^^^^^^^^^^
 
-error: stability attributes may not be used outside of the standard library
+error[E0734]: stability attributes may not be used outside of the standard library
   --> $DIR/issue-43106-gating-of-stable.rs:13:17
    |
 LL |     mod inner { #![stable()] }
    |                 ^^^^^^^^^^^^
 
-error: stability attributes may not be used outside of the standard library
+error[E0734]: stability attributes may not be used outside of the standard library
   --> $DIR/issue-43106-gating-of-stable.rs:16:5
    |
 LL |     #[stable()] fn f() { }
    |     ^^^^^^^^^^^
 
-error: stability attributes may not be used outside of the standard library
+error[E0734]: stability attributes may not be used outside of the standard library
   --> $DIR/issue-43106-gating-of-stable.rs:19:5
    |
 LL |     #[stable()] struct S;
    |     ^^^^^^^^^^^
 
-error: stability attributes may not be used outside of the standard library
+error[E0734]: stability attributes may not be used outside of the standard library
   --> $DIR/issue-43106-gating-of-stable.rs:22:5
    |
 LL |     #[stable()] type T = S;
    |     ^^^^^^^^^^^
 
-error: stability attributes may not be used outside of the standard library
+error[E0734]: stability attributes may not be used outside of the standard library
   --> $DIR/issue-43106-gating-of-stable.rs:25:5
    |
 LL |     #[stable()] impl S { }
@@ -42,3 +42,4 @@ LL |     #[stable()] impl S { }
 
 error: aborting due to 7 previous errors
 
+For more information about this error, try `rustc --explain E0734`.

src/test/ui/feature-gate/issue-43106-gating-of-unstable.stderr

@@ -1,40 +1,40 @@
-error: stability attributes may not be used outside of the standard library
+error[E0734]: stability attributes may not be used outside of the standard library
   --> $DIR/issue-43106-gating-of-unstable.rs:7:1
    |
 LL | #![unstable()]
    | ^^^^^^^^^^^^^^
 
-error: stability attributes may not be used outside of the standard library
+error[E0734]: stability attributes may not be used outside of the standard library
   --> $DIR/issue-43106-gating-of-unstable.rs:10:1
    |
 LL | #[unstable()]
    | ^^^^^^^^^^^^^
 
-error: stability attributes may not be used outside of the standard library
+error[E0734]: stability attributes may not be used outside of the standard library
   --> $DIR/issue-43106-gating-of-unstable.rs:13:17
    |
 LL |     mod inner { #![unstable()] }
    |                 ^^^^^^^^^^^^^^
 
-error: stability attributes may not be used outside of the standard library
+error[E0734]: stability attributes may not be used outside of the standard library
   --> $DIR/issue-43106-gating-of-unstable.rs:16:5
    |
 LL |     #[unstable()] fn f() { }
    |     ^^^^^^^^^^^^^
 
-error: stability attributes may not be used outside of the standard library
+error[E0734]: stability attributes may not be used outside of the standard library
   --> $DIR/issue-43106-gating-of-unstable.rs:19:5
    |
 LL |     #[unstable()] struct S;
    |     ^^^^^^^^^^^^^
 
-error: stability attributes may not be used outside of the standard library
+error[E0734]: stability attributes may not be used outside of the standard library
   --> $DIR/issue-43106-gating-of-unstable.rs:22:5
    |
 LL |     #[unstable()] type T = S;
    |     ^^^^^^^^^^^^^
 
-error: stability attributes may not be used outside of the standard library
+error[E0734]: stability attributes may not be used outside of the standard library
   --> $DIR/issue-43106-gating-of-unstable.rs:25:5
    |
 LL |     #[unstable()] impl S { }
@@ -42,3 +42,4 @@ LL |     #[unstable()] impl S { }
 
 error: aborting due to 7 previous errors
 
+For more information about this error, try `rustc --explain E0734`.

src/test/ui/feature-gates/feature-gate-staged_api.stderr

@@ -1,10 +1,10 @@
-error: stability attributes may not be used outside of the standard library
+error[E0734]: stability attributes may not be used outside of the standard library
   --> $DIR/feature-gate-staged_api.rs:1:1
    |
 LL | #![stable(feature = "a", since = "b")]
    | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 
-error: stability attributes may not be used outside of the standard library
+error[E0734]: stability attributes may not be used outside of the standard library
   --> $DIR/feature-gate-staged_api.rs:8:1
    |
 LL | #[stable(feature = "a", since = "b")]
@@ -12,3 +12,4 @@ LL | #[stable(feature = "a", since = "b")]
 
 error: aborting due to 2 previous errors
 
+For more information about this error, try `rustc --explain E0734`.

src/test/ui/stability-attribute/stability-attribute-non-staged-force-unstable.stderr

@@ -1,16 +1,16 @@
-error: stability attributes may not be used outside of the standard library
+error[E0734]: stability attributes may not be used outside of the standard library
   --> $DIR/stability-attribute-non-staged-force-unstable.rs:3:1
    |
 LL | #[unstable()]
    | ^^^^^^^^^^^^^
 
-error: stability attributes may not be used outside of the standard library
+error[E0734]: stability attributes may not be used outside of the standard library
   --> $DIR/stability-attribute-non-staged-force-unstable.rs:4:1
    |
 LL | #[stable()]
    | ^^^^^^^^^^^
 
-error: stability attributes may not be used outside of the standard library
+error[E0734]: stability attributes may not be used outside of the standard library
   --> $DIR/stability-attribute-non-staged-force-unstable.rs:5:1
    |
 LL | #[rustc_deprecated()]
@@ -18,3 +18,4 @@ LL | #[rustc_deprecated()]
 
 error: aborting due to 3 previous errors
 
+For more information about this error, try `rustc --explain E0734`.

src/test/ui/stability-attribute/stability-attribute-non-staged.stderr

@@ -1,16 +1,16 @@
-error: stability attributes may not be used outside of the standard library
+error[E0734]: stability attributes may not be used outside of the standard library
   --> $DIR/stability-attribute-non-staged.rs:1:1
    |
 LL | #[unstable()]
    | ^^^^^^^^^^^^^
 
-error: stability attributes may not be used outside of the standard library
+error[E0734]: stability attributes may not be used outside of the standard library
   --> $DIR/stability-attribute-non-staged.rs:2:1
    |
 LL | #[stable()]
    | ^^^^^^^^^^^
 
-error: stability attributes may not be used outside of the standard library
+error[E0734]: stability attributes may not be used outside of the standard library
   --> $DIR/stability-attribute-non-staged.rs:3:1
    |
 LL | #[rustc_deprecated()]
@@ -18,3 +18,4 @@ LL | #[rustc_deprecated()]
 
 error: aborting due to 3 previous errors
 
+For more information about this error, try `rustc --explain E0734`.

src/tools/tidy/src/features.rs

@@ -384,7 +384,7 @@ fn map_lib_features(base_src_path: &Path,
         let file = entry.path();
         let filename = file.file_name().unwrap().to_string_lossy();
         if !filename.ends_with(".rs") || filename == "features.rs" ||
-           filename == "diagnostic_list.rs" {
+           filename == "diagnostic_list.rs" || filename == "error_codes.rs" {
             return;
         }