syntax: also warn about edition "umbrella" features being implied by --edition.

src/libsyntax/feature_gate.rs

@@ -1923,6 +1923,14 @@ pub fn get_features(span_handler: &Handler, krate_attrs: &[ast::Attribute],
     let mut features = Features::new();
     let mut edition_enabled_features = FxHashMap();
 
+    for &edition in ALL_EDITIONS {
+        if edition <= crate_edition {
+            // The `crate_edition` implies its respective umbrella feature-gate
+            // (i.e. `#![feature(rust_20XX_preview)]` isn't needed on edition 20XX).
+            edition_enabled_features.insert(Symbol::intern(edition.feature_name()), edition);
+        }
+    }
+
     for &(name, .., f_edition, set) in ACTIVE_FEATURES {
         if let Some(f_edition) = f_edition {
             if f_edition <= crate_edition {
@@ -1993,25 +2001,26 @@ pub fn get_features(span_handler: &Handler, krate_attrs: &[ast::Attribute],
                 continue
             };
 
+            if let Some(edition) = edition_enabled_features.get(&name) {
+                struct_span_warn!(
+                    span_handler,
+                    mi.span,
+                    E0705,
+                    "the feature `{}` is included in the Rust {} edition",
+                    name,
+                    edition,
+                ).emit();
+                continue;
+            }
+
             if ALL_EDITIONS.iter().any(|e| name == e.feature_name()) {
                 // Handled in the separate loop above.
                 continue;
             }
 
             if let Some((.., set)) = ACTIVE_FEATURES.iter().find(|f| name == f.0) {
-                if let Some(edition) = edition_enabled_features.get(&name) {
-                    struct_span_warn!(
-                        span_handler,
-                        mi.span,
-                        E0705,
-                        "the feature `{}` is included in the Rust {} edition",
-                        name,
-                        edition,
-                    ).emit();
-                } else {
-                    set(&mut features, mi.span);
-                    features.declared_lang_features.push((name, mi.span, None));
-                }
+                set(&mut features, mi.span);
+                features.declared_lang_features.push((name, mi.span, None));
                 continue
             }
 

src/test/rustdoc/async-fn.rs

@@ -13,7 +13,7 @@
 
 // FIXME: once `--edition` is stable in rustdoc, remove that `compile-flags` directive
 
-#![feature(rust_2018_preview, async_await, futures_api)]
+#![feature(async_await, futures_api)]
 
 // @has async_fn/struct.S.html
 // @has - '//code' 'pub async fn f()'

src/test/ui/editions/edition-feature-ok.rs

@@ -8,7 +8,6 @@
 // option. This file may not be copied, modified, or distributed
 // except according to those terms.
 
-// compile-flags:--edition 2018
 // compile-pass
 
 #![feature(rust_2018_preview)]

src/test/ui/editions/edition-feature-redundant.rs

@@ -0,0 +1,17 @@
+// 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.
+
+// edition:2018
+// compile-pass
+
+#![feature(rust_2018_preview)]
+//~^ WARN the feature `rust_2018_preview` is included in the Rust 2018 edition
+
+fn main() {}

src/test/ui/editions/edition-feature-redundant.stderr

@@ -0,0 +1,6 @@
+warning[E0705]: the feature `rust_2018_preview` is included in the Rust 2018 edition
+  --> $DIR/edition-feature-redundant.rs:14:12
+   |
+LL | #![feature(rust_2018_preview)]
+   |            ^^^^^^^^^^^^^^^^^
+

src/test/ui/rust-2018/extern-crate-idiomatic-in-2018.fixed

@@ -15,7 +15,6 @@
 // The "normal case". Ideally we would remove the `extern crate` here,
 // but we don't.
 
-#![feature(rust_2018_preview)]
 #![deny(rust_2018_idioms)]
 #![allow(dead_code)]
 

src/test/ui/rust-2018/extern-crate-idiomatic-in-2018.rs

@@ -15,7 +15,6 @@
 // The "normal case". Ideally we would remove the `extern crate` here,
 // but we don't.
 
-#![feature(rust_2018_preview)]
 #![deny(rust_2018_idioms)]
 #![allow(dead_code)]
 

src/test/ui/rust-2018/extern-crate-idiomatic-in-2018.stderr

@@ -1,18 +1,18 @@
 error: unused extern crate
-  --> $DIR/extern-crate-idiomatic-in-2018.rs:22:1
+  --> $DIR/extern-crate-idiomatic-in-2018.rs:21:1
    |
 LL | extern crate edition_lint_paths;
    | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: remove it
    |
 note: lint level defined here
-  --> $DIR/extern-crate-idiomatic-in-2018.rs:19:9
+  --> $DIR/extern-crate-idiomatic-in-2018.rs:18:9
    |
 LL | #![deny(rust_2018_idioms)]
    |         ^^^^^^^^^^^^^^^^
    = note: #[deny(unused_extern_crates)] implied by #[deny(rust_2018_idioms)]
 
 error: `extern crate` is not idiomatic in the new edition
-  --> $DIR/extern-crate-idiomatic-in-2018.rs:25:1
+  --> $DIR/extern-crate-idiomatic-in-2018.rs:24:1
    |
 LL | extern crate edition_lint_paths as bar;
    | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: convert it to a `use`