Explicitly suggest 'type_ascription' feature

Author: VirrageS

src/libsyntax/parse/diagnostics.rs

@@ -858,8 +858,8 @@ impl<'a> Parser<'a> {
                     Applicability::MaybeIncorrect,
                 );
             } else {
-                err.note("type ascription is a nightly-only feature that lets \
-                          you annotate an expression with a type: `<expr>: <type>`")
+                err.note("#![feature(type_ascription)] lets you annotate an \
+                          expression with a type: `<expr>: <type>`")
                     .span_note(
                         lhs_span,
                         "this expression expects an ascribed type after the colon",

src/test/ui/issues/issue-22644.stderr

@@ -89,7 +89,7 @@ error: expected type, found `4`
 LL |     println!("{}", a: &mut 4);
    |                            ^ expecting a type here because of type ascription
    |
-   = note: type ascription is a nightly-only feature that lets you annotate an expression with a type: `<expr>: <type>`
+   = note: #![feature(type_ascription)] lets you annotate an expression with a type: `<expr>: <type>`
 note: this expression expects an ascribed type after the colon
   --> $DIR/issue-22644.rs:34:20
    |

src/test/ui/issues/issue-34255-1.stderr

@@ -4,7 +4,7 @@ error: expected type, found `42`
 LL |     Test::Drill(field: 42);
    |                        ^^ expecting a type here because of type ascription
    |
-   = note: type ascription is a nightly-only feature that lets you annotate an expression with a type: `<expr>: <type>`
+   = note: #![feature(type_ascription)] lets you annotate an expression with a type: `<expr>: <type>`
 note: this expression expects an ascribed type after the colon
   --> $DIR/issue-34255-1.rs:8:17
    |

src/test/ui/lifetime_starts_expressions.stderr

@@ -14,7 +14,7 @@ error: expected type, found keyword `loop`
 LL |     loop { break 'label: loop { break 'label 42; }; }
    |                          ^^^^ expecting a type here because of type ascription
    |
-   = note: type ascription is a nightly-only feature that lets you annotate an expression with a type: `<expr>: <type>`
+   = note: #![feature(type_ascription)] lets you annotate an expression with a type: `<expr>: <type>`
 note: this expression expects an ascribed type after the colon
   --> $DIR/lifetime_starts_expressions.rs:6:12
    |

src/test/ui/parser/recover-from-bad-variant.stderr

@@ -4,7 +4,7 @@ error: expected type, found `3`
 LL |     let x = Enum::Foo(a: 3, b: 4);
    |                          ^ expecting a type here because of type ascription
    |
-   = note: type ascription is a nightly-only feature that lets you annotate an expression with a type: `<expr>: <type>`
+   = note: #![feature(type_ascription)] lets you annotate an expression with a type: `<expr>: <type>`
 note: this expression expects an ascribed type after the colon
   --> $DIR/recover-from-bad-variant.rs:7:23
    |

src/test/ui/type/type-ascription-instead-of-statement-end.stderr

@@ -12,7 +12,7 @@ error: expected type, found `0`
 LL |     println!("test"): 0;
    |                       ^ expecting a type here because of type ascription
    |
-   = note: type ascription is a nightly-only feature that lets you annotate an expression with a type: `<expr>: <type>`
+   = note: #![feature(type_ascription)] lets you annotate an expression with a type: `<expr>: <type>`
 note: this expression expects an ascribed type after the colon
   --> $DIR/type-ascription-instead-of-statement-end.rs:9:5
    |