Accurately portray raw identifiers in error messages

When refering to or suggesting raw identifiers, refer to them with `r#`.

Fix #65634.

src/librustc/ty/print/pretty.rs

@@ -1282,6 +1282,9 @@ impl<F: fmt::Write> Printer<'tcx> for FmtPrinter<'_, 'tcx, F> {
             if !self.empty_path {
                 write!(self, "::")?;
             }
+            if ast::Ident::from_str(&name).is_raw_guess() {
+                write!(self, "r#")?;
+            }
             write!(self, "{}", name)?;
 
             // FIXME(eddyb) this will print e.g. `{{closure}}#3`, but it

src/libsyntax_pos/symbol.rs

@@ -840,12 +840,18 @@ impl Hash for Ident {
 
 impl fmt::Debug for Ident {
     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        if self.is_raw_guess() {
+            write!(f, "r#")?;
+        }
         write!(f, "{}{:?}", self.name, self.span.ctxt())
     }
 }
 
 impl fmt::Display for Ident {
     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        if self.is_raw_guess() {
+            write!(f, "r#")?;
+        }
         fmt::Display::fmt(&self.name, f)
     }
 }

src/test/ui/parser/raw/raw-literal-keywords.rs

@@ -11,11 +11,11 @@ fn test_union() {
 }
 
 fn test_if_2() {
-    let _ = r#if; //~ ERROR cannot find value `if` in this scope
+    let _ = r#if; //~ ERROR cannot find value `r#if` in this scope
 }
 
 fn test_struct_2() {
-    let _ = r#struct; //~ ERROR cannot find value `struct` in this scope
+    let _ = r#struct; //~ ERROR cannot find value `r#struct` in this scope
 }
 
 fn test_union_2() {

src/test/ui/parser/raw/raw-literal-keywords.stderr

@@ -16,13 +16,13 @@ error: expected one of `!`, `.`, `::`, `;`, `?`, `{`, `}`, or an operator, found
 LL |     r#union Test;
    |             ^^^^ expected one of 8 possible tokens
 
-error[E0425]: cannot find value `if` in this scope
+error[E0425]: cannot find value `r#if` in this scope
   --> $DIR/raw-literal-keywords.rs:14:13
    |
 LL |     let _ = r#if;
    |             ^^^^ not found in this scope
 
-error[E0425]: cannot find value `struct` in this scope
+error[E0425]: cannot find value `r#struct` in this scope
   --> $DIR/raw-literal-keywords.rs:18:13
    |
 LL |     let _ = r#struct;

src/test/ui/raw-ident-suggestion.rs

@@ -0,0 +1,22 @@
+#![allow(non_camel_case_types)]
+
+trait r#async {
+    fn r#struct(&self) {
+        println!("async");
+    }
+}
+
+trait r#await {
+    fn r#struct(&self) {
+        println!("await");
+    }
+}
+
+struct r#fn {}
+
+impl r#async for r#fn {}
+impl r#await for r#fn {}
+
+fn main() {
+    r#fn {}.r#struct(); //~ ERROR multiple applicable items in scope
+}

src/test/ui/raw-ident-suggestion.stderr

@@ -0,0 +1,22 @@
+error[E0034]: multiple applicable items in scope
+  --> $DIR/raw-ident-suggestion.rs:21:13
+   |
+LL |     r#fn {}.r#struct();
+   |             ^^^^^^^^ multiple `r#struct` found
+   |
+note: candidate #1 is defined in an impl of the trait `async` for the type `r#fn`
+  --> $DIR/raw-ident-suggestion.rs:4:5
+   |
+LL |     fn r#struct(&self) {
+   |     ^^^^^^^^^^^^^^^^^^
+   = help: to disambiguate the method call, write `async::r#struct(r#fn {})` instead
+note: candidate #2 is defined in an impl of the trait `await` for the type `r#fn`
+  --> $DIR/raw-ident-suggestion.rs:10:5
+   |
+LL |     fn r#struct(&self) {
+   |     ^^^^^^^^^^^^^^^^^^
+   = help: to disambiguate the method call, write `await::r#struct(r#fn {})` instead
+
+error: aborting due to previous error
+
+For more information about this error, try `rustc --explain E0034`.

src/test/ui/suggestions/raw-name-use-suggestion.rs

@@ -5,5 +5,5 @@ mod foo {
 
 fn main() {
     foo::let(); //~ ERROR expected identifier, found keyword `let`
-    r#break(); //~ ERROR cannot find function `break` in this scope
+    r#break(); //~ ERROR cannot find function `r#break` in this scope
 }

src/test/ui/suggestions/raw-name-use-suggestion.stderr

@@ -20,7 +20,7 @@ help: you can escape reserved keywords to use them as identifiers
 LL |     foo::r#let();
    |          ^^^^^
 
-error[E0425]: cannot find function `break` in this scope
+error[E0425]: cannot find function `r#break` in this scope
   --> $DIR/raw-name-use-suggestion.rs:8:5
    |
 LL |     r#break();