Suggest using raw identifiers in 2018 edition when using keywords

src/libsyntax/parse/parser.rs

@@ -798,6 +798,18 @@ impl<'a> Parser<'a> {
         let mut err = self.struct_span_err(self.span,
                                            &format!("expected identifier, found {}",
                                                     self.this_token_descr()));
+        if let token::Ident(ident, false) = &self.token {
+            if ident.is_reserved() && !ident.is_path_segment_keyword() &&
+                ident.name != keywords::Underscore.name()
+            {
+                err.span_suggestion_with_applicability(
+                    self.span,
+                    "you can escape reserved keywords to use them as identifiers",
+                    format!("r#{}", ident),
+                    Applicability::MaybeIncorrect,
+                );
+            }
+        }
         if let Some(token_descr) = self.token_descr() {
             err.span_label(self.span, format!("expected identifier, found {}", token_descr));
         } else {

src/test/ui/editions/edition-keywords-2015-2018-expansion.stderr

@@ -5,6 +5,10 @@ LL |     produces_async! {} //~ ERROR expected identifier, found reserved keywor
    |     ^^^^^^^^^^^^^^^^^^ expected identifier, found reserved keyword
    |
    = note: this error originates in a macro outside of the current crate (in Nightly builds, run with -Z external-macro-backtrace for more info)
+help: you can escape reserved keywords to use them as identifiers
+   |
+LL | (  ) => ( pub fn r#async (  ) {  } )
+   |                  ^^^^^^^
 
 error: aborting due to previous error
 

src/test/ui/editions/edition-keywords-2018-2015-parsing.stderr

@@ -3,12 +3,20 @@ error: expected identifier, found reserved keyword `async`
    |
 LL |     let mut async = 1; //~ ERROR expected identifier, found reserved keyword `async`
    |             ^^^^^ expected identifier, found reserved keyword
+help: you can escape reserved keywords to use them as identifiers
+   |
+LL |     let mut r#async = 1; //~ ERROR expected identifier, found reserved keyword `async`
+   |             ^^^^^^^
 
 error: expected identifier, found reserved keyword `async`
   --> $DIR/edition-keywords-2018-2015-parsing.rs:18:13
    |
 LL |     module::async(); //~ ERROR expected identifier, found reserved keyword `async`
    |             ^^^^^ expected identifier, found reserved keyword
+help: you can escape reserved keywords to use them as identifiers
+   |
+LL |     module::r#async(); //~ ERROR expected identifier, found reserved keyword `async`
+   |             ^^^^^^^
 
 error: no rules expected the token `r#async`
   --> $DIR/edition-keywords-2018-2015-parsing.rs:12:31

src/test/ui/editions/edition-keywords-2018-2018-expansion.stderr

@@ -5,6 +5,10 @@ LL |     produces_async! {} //~ ERROR expected identifier, found reserved keywor
    |     ^^^^^^^^^^^^^^^^^^ expected identifier, found reserved keyword
    |
    = note: this error originates in a macro outside of the current crate (in Nightly builds, run with -Z external-macro-backtrace for more info)
+help: you can escape reserved keywords to use them as identifiers
+   |
+LL | (  ) => ( pub fn r#async (  ) {  } )
+   |                  ^^^^^^^
 
 error: aborting due to previous error
 

src/test/ui/editions/edition-keywords-2018-2018-parsing.stderr

@@ -3,12 +3,20 @@ error: expected identifier, found reserved keyword `async`
    |
 LL |     let mut async = 1; //~ ERROR expected identifier, found reserved keyword `async`
    |             ^^^^^ expected identifier, found reserved keyword
+help: you can escape reserved keywords to use them as identifiers
+   |
+LL |     let mut r#async = 1; //~ ERROR expected identifier, found reserved keyword `async`
+   |             ^^^^^^^
 
 error: expected identifier, found reserved keyword `async`
   --> $DIR/edition-keywords-2018-2018-parsing.rs:18:13
    |
 LL |     module::async(); //~ ERROR expected identifier, found reserved keyword `async`
    |             ^^^^^ expected identifier, found reserved keyword
+help: you can escape reserved keywords to use them as identifiers
+   |
+LL |     module::r#async(); //~ ERROR expected identifier, found reserved keyword `async`
+   |             ^^^^^^^
 
 error: no rules expected the token `r#async`
   --> $DIR/edition-keywords-2018-2018-parsing.rs:12:31

src/test/ui/issues/issue-28433.stderr

@@ -3,6 +3,10 @@ error: expected identifier, found keyword `pub`
    |
 LL |     pub duck,
    |     ^^^ expected identifier, found keyword
+help: you can escape reserved keywords to use them as identifiers
+   |
+LL |     r#pub duck,
+   |     ^^^^^
 
 error: expected one of `(`, `,`, `=`, `{`, or `}`, found `duck`
   --> $DIR/issue-28433.rs:4:9

src/test/ui/issues/issue-44406.stderr

@@ -3,6 +3,10 @@ error: expected identifier, found keyword `true`
    |
 LL |     foo!(true); //~ ERROR expected type, found keyword
    |          ^^^^ expected identifier, found keyword
+help: you can escape reserved keywords to use them as identifiers
+   |
+LL |     foo!(r#true); //~ ERROR expected type, found keyword
+   |          ^^^^^^
 
 error: expected type, found keyword `true`
   --> $DIR/issue-44406.rs:8:10

src/test/ui/issues/issue-57198.stderr

@@ -3,6 +3,10 @@ error: expected identifier, found keyword `for`
    |
 LL |     m::for();
    |        ^^^ expected identifier, found keyword
+help: you can escape reserved keywords to use them as identifiers
+   |
+LL |     m::r#for();
+   |        ^^^^^
 
 error: aborting due to previous error
 

src/test/ui/lifetime_starts_expressions.stderr

@@ -3,6 +3,10 @@ error: expected identifier, found keyword `loop`
    |
 LL |     loop { break 'label: loop { break 'label 42; }; }
    |                          ^^^^ expected identifier, found keyword
+help: you can escape reserved keywords to use them as identifiers
+   |
+LL |     loop { break 'label: r#loop { break 'label 42; }; }
+   |                          ^^^^^^
 
 error: expected type, found keyword `loop`
   --> $DIR/lifetime_starts_expressions.rs:6:26

src/test/ui/parser/associated-types-project-from-hrtb-explicit.stderr

@@ -3,6 +3,10 @@ error: expected identifier, found keyword `for`
    |
 LL | fn foo2<I>(x: <I as for<'x> Foo<&'x isize>>::A)
    |                     ^^^ expected identifier, found keyword
+help: you can escape reserved keywords to use them as identifiers
+   |
+LL | fn foo2<I>(x: <I as r#for<'x> Foo<&'x isize>>::A)
+   |                     ^^^^^
 
 error: expected one of `::` or `>`, found `Foo`
   --> $DIR/associated-types-project-from-hrtb-explicit.rs:12:29

src/test/ui/parser/bad-value-ident-false.stderr

@@ -3,6 +3,10 @@ error: expected identifier, found keyword `false`
    |
 LL | fn false() { } //~ ERROR expected identifier, found keyword `false`
    |    ^^^^^ expected identifier, found keyword
+help: you can escape reserved keywords to use them as identifiers
+   |
+LL | fn r#false() { } //~ ERROR expected identifier, found keyword `false`
+   |    ^^^^^^^
 
 error: aborting due to previous error
 

src/test/ui/parser/bad-value-ident-true.stderr

@@ -3,6 +3,10 @@ error: expected identifier, found keyword `true`
    |
 LL | fn true() { } //~ ERROR expected identifier, found keyword `true`
    |    ^^^^ expected identifier, found keyword
+help: you can escape reserved keywords to use them as identifiers
+   |
+LL | fn r#true() { } //~ ERROR expected identifier, found keyword `true`
+   |    ^^^^^^
 
 error: aborting due to previous error
 

src/test/ui/parser/issue-15980.stderr

@@ -6,6 +6,10 @@ LL |         Err(ref e) if e.kind == io::EndOfFile {
 LL |             //~^ NOTE while parsing this struct
 LL |             return
    |             ^^^^^^ expected identifier, found keyword
+help: you can escape reserved keywords to use them as identifiers
+   |
+LL |             r#return
+   |
 
 error: expected one of `.`, `=>`, `?`, or an operator, found `_`
   --> $DIR/issue-15980.rs:15:9

src/test/ui/parser/keyword.stderr

@@ -3,6 +3,10 @@ error: expected identifier, found keyword `break`
    |
 LL | pub mod break {
    |         ^^^^^ expected identifier, found keyword
+help: you can escape reserved keywords to use them as identifiers
+   |
+LL | pub mod r#break {
+   |         ^^^^^^^
 
 error: aborting due to previous error
 

src/test/ui/parser/macro-keyword.stderr

@@ -3,6 +3,10 @@ error: expected identifier, found reserved keyword `macro`
    |
 LL | fn macro() {  //~ ERROR expected identifier, found reserved keyword `macro`
    |    ^^^^^ expected identifier, found reserved keyword
+help: you can escape reserved keywords to use them as identifiers
+   |
+LL | fn r#macro() {  //~ ERROR expected identifier, found reserved keyword `macro`
+   |    ^^^^^^^
 
 error: aborting due to previous error
 

src/test/ui/parser/removed-syntax-field-let.stderr

@@ -3,6 +3,10 @@ error: expected identifier, found keyword `let`
    |
 LL |     let foo: (),
    |     ^^^ expected identifier, found keyword
+help: you can escape reserved keywords to use them as identifiers
+   |
+LL |     r#let foo: (),
+   |     ^^^^^
 
 error: expected `:`, found `foo`
   --> $DIR/removed-syntax-field-let.rs:4:9

src/test/ui/parser/use-as-where-use-ends-with-mod-sep.stderr

@@ -3,6 +3,10 @@ error: expected identifier, found keyword `as`
    |
 LL | use std::any:: as foo; //~ ERROR expected identifier, found keyword `as`
    |                ^^ expected identifier, found keyword
+help: you can escape reserved keywords to use them as identifiers
+   |
+LL | use std::any:: r#as foo; //~ ERROR expected identifier, found keyword `as`
+   |                ^^^^
 
 error: expected one of `::`, `;`, or `as`, found `foo`
   --> $DIR/use-as-where-use-ends-with-mod-sep.rs:3:19

src/test/ui/rust-2018/dyn-trait-compatibility.stderr

@@ -3,6 +3,10 @@ error: expected identifier, found keyword `dyn`
    |
 LL | type A1 = dyn::dyn; //~ERROR expected identifier, found keyword `dyn`
    |                ^^^ expected identifier, found keyword
+help: you can escape reserved keywords to use them as identifiers
+   |
+LL | type A1 = dyn::r#dyn; //~ERROR expected identifier, found keyword `dyn`
+   |                ^^^^^
 
 error: expected identifier, found `<`
   --> $DIR/dyn-trait-compatibility.rs:5:14

src/test/ui/try-block/try-block-in-edition2015.stderr

@@ -6,6 +6,10 @@ LL |     let try_result: Option<_> = try {
 LL |     //~^ ERROR expected struct, variant or union type, found macro `try`
 LL |         let x = 5; //~ ERROR expected identifier, found keyword
    |         ^^^ expected identifier, found keyword
+help: you can escape reserved keywords to use them as identifiers
+   |
+LL |         r#let x = 5; //~ ERROR expected identifier, found keyword
+   |         ^^^^^
 
 error[E0574]: expected struct, variant or union type, found macro `try`
   --> $DIR/try-block-in-edition2015.rs:4:33