add loop keyword to error diag

Author: y21

compiler/rustc_parse/locales/en-US.ftl

@@ -153,6 +153,7 @@ parse_missing_expression_in_for_loop = missing expression to iterate on in `for`
 
 parse_loop_else = `{$loop_kind}...else` loops are not supported
     .note = consider moving this `else` clause to a separate `if` statement and use a `bool` variable to control if it should run
+    .loop_keyword = `else` is attached to this loop
 
 parse_missing_comma_after_match_arm = expected `,` following `match` arm
     .suggestion = missing a comma here to end this `match` arm

compiler/rustc_parse/src/errors.rs

@@ -458,6 +458,8 @@ pub(crate) struct LoopElseNotSupported {
     #[primary_span]
     pub span: Span,
     pub loop_kind: &'static str,
+    #[label(parse_loop_keyword)]
+    pub loop_kw: Span,
 }
 
 #[derive(Diagnostic)]

compiler/rustc_parse/src/parser/expr.rs

@@ -2492,20 +2492,21 @@ impl<'a> Parser<'a> {
 
         let kind = ExprKind::ForLoop(pat, expr, loop_block, opt_label);
 
-        self.recover_loop_else("for")?;
+        self.recover_loop_else("for", lo)?;
 
         Ok(self.mk_expr_with_attrs(lo.to(self.prev_token.span), kind, attrs))
     }
 
     /// Recovers from an `else` clause after a loop (`for...else`, `while...else`)
-    fn recover_loop_else(&mut self, loop_kind: &'static str) -> PResult<'a, ()> {
+    fn recover_loop_else(&mut self, loop_kind: &'static str, loop_kw: Span) -> PResult<'a, ()> {
         if self.token.is_keyword(kw::Else) && self.may_recover() {
             let else_span = self.token.span;
             self.bump();
             let else_clause = self.parse_else_expr()?;
             self.sess.emit_err(errors::LoopElseNotSupported {
                 span: else_span.to(else_clause.span),
                 loop_kind,
+                loop_kw,
             });
         }
         Ok(())
@@ -2536,7 +2537,7 @@ impl<'a> Parser<'a> {
             err
         })?;
 
-        self.recover_loop_else("while")?;
+        self.recover_loop_else("while", lo)?;
 
         Ok(self.mk_expr_with_attrs(
             lo.to(self.prev_token.span),

tests/ui/for/for-else-err.rs

@@ -1,6 +1,6 @@
 fn main() {
     for _ in 0..1 {
-
+        //~^ NOTE `else` is attached to this loop
     } else {
         //~^ ERROR `for...else` loops are not supported
         //~| NOTE consider moving this `else` clause to a separate `if` statement and use a `bool` variable to control if it should run

tests/ui/for/for-else-err.stderr

@@ -1,6 +1,9 @@
 error: `for...else` loops are not supported
   --> $DIR/for-else-err.rs:4:7
    |
+LL |       for _ in 0..1 {
+   |       --- `else` is attached to this loop
+LL |
 LL |       } else {
    |  _______^
 LL | |

tests/ui/for/for-else-let-else-err.rs

@@ -1,6 +1,6 @@
 fn main() {
     let _ = for _ in 0..1 {
-
+        //~^ NOTE `else` is attached to this loop
     } else {
         //~^ ERROR `for...else` loops are not supported
         //~| NOTE consider moving this `else` clause to a separate `if` statement and use a `bool` variable to control if it should run

tests/ui/for/for-else-let-else-err.stderr

@@ -1,6 +1,9 @@
 error: `for...else` loops are not supported
   --> $DIR/for-else-let-else-err.rs:4:7
    |
+LL |       let _ = for _ in 0..1 {
+   |               --- `else` is attached to this loop
+LL |
 LL |       } else {
    |  _______^
 LL | |

tests/ui/while/while-else-err.rs

@@ -1,6 +1,6 @@
 fn main() {
     while false {
-
+        //~^ NOTE `else` is attached to this loop
     } else {
         //~^ ERROR `while...else` loops are not supported
         //~| NOTE consider moving this `else` clause to a separate `if` statement and use a `bool` variable to control if it should run

tests/ui/while/while-else-err.stderr

@@ -1,6 +1,9 @@
 error: `while...else` loops are not supported
   --> $DIR/while-else-err.rs:4:7
    |
+LL |       while false {
+   |       ----- `else` is attached to this loop
+LL |
 LL |       } else {
    |  _______^
 LL | |

tests/ui/while/while-else-let-else-err.rs

@@ -1,6 +1,6 @@
 fn main() {
     let _ = while false {
-
+        //~^ NOTE `else` is attached to this loop
     } else {
         //~^ ERROR `while...else` loops are not supported
         //~| NOTE consider moving this `else` clause to a separate `if` statement and use a `bool` variable to control if it should run

tests/ui/while/while-else-let-else-err.stderr

@@ -1,6 +1,9 @@
 error: `while...else` loops are not supported
   --> $DIR/while-else-let-else-err.rs:4:7
    |
+LL |       let _ = while false {
+   |               ----- `else` is attached to this loop
+LL |
 LL |       } else {
    |  _______^
 LL | |