Rollup merge of #120460 - nnethercote:fix-120397, r=compiler-errors

Be more careful about interpreting a label/lifetime as a mistyped char literal.

Currently the parser interprets any label/lifetime in certain positions as a mistyped char literal, on the assumption that the trailing single quote was accidentally omitted. In such cases it gives an error with a suggestion to add the trailing single quote, and then puts the appropriate char literal into the AST. This behaviour was introduced in #101293.

This is reasonable for a case like this:
```
let c = 'a;
```
because `'a'` is a valid char literal. It's less reasonable for a case like this:
```
let c = 'abc;
```
because `'abc'` is not a valid char literal.

Prior to #120329 this could result in some sub-optimal suggestions in error messages, but nothing else. But #120329 changed `LitKind::from_token_lit` to assume that the char/byte/string literals it receives are valid, and to assert if not. This is reasonable because the lexer does not produce invalid char/byte/string literals in general. But in this "interpret label/lifetime as unclosed char literal" case the parser can produce an invalid char literal with contents such as `abc`, which triggers an assertion failure.

This PR changes the parser so it's more cautious about interpreting labels/lifetimes as unclosed char literals.

Fixes #120397.

r? `@compiler-errors`

2 files changed, 94 insertions, 20 deletions

diff --git a/tests/ui/parser/label-is-actually-char.rs b/tests/ui/parser/label-is-actually-char.rs
index 183da603da4..74df898d191 100644
--- a/tests/ui/parser/label-is-actually-char.rs
+++ b/tests/ui/parser/label-is-actually-char.rs
@@ -1,16 +1,43 @@
+// Note: it's ok to interpret 'a as 'a', but but not ok to interpret 'abc as
+// 'abc' because 'abc' is not a valid char literal.
+
 fn main() {
     let c = 'a;
     //~^ ERROR expected `while`, `for`, `loop` or `{` after a label
     //~| HELP add `'` to close the char literal
-    match c {
+
+    let c = 'abc;
+    //~^ ERROR expected `while`, `for`, `loop` or `{` after a label
+    //~| ERROR expected expression, found `;`
+}
+
+fn f() {
+    match 'a' {
         'a'..='b => {}
         //~^ ERROR unexpected token: `'b`
         //~| HELP add `'` to close the char literal
-        _ => {}
+        'c'..='def => {}
+        //~^ ERROR unexpected token: `'def`
     }
-    let x = ['a, 'b];
-    //~^ ERROR expected `while`, `for`, `loop` or `{` after a label
-    //~| ERROR expected `while`, `for`, `loop` or `{` after a label
-    //~| HELP add `'` to close the char literal
-    //~| HELP add `'` to close the char literal
+}
+
+fn g() {
+   match 'g' {
+       'g => {}
+       //~^ ERROR expected pattern, found `=>`
+       //~| HELP add `'` to close the char literal
+       'hij => {}
+       //~^ ERROR expected pattern, found `'hij`
+       _ => {}
+   }
+}
+
+fn h() {
+   let x = ['a, 'b, 'cde];
+   //~^ ERROR expected `while`, `for`, `loop` or `{` after a label
+   //~| HELP add `'` to close the char literal
+   //~| ERROR expected `while`, `for`, `loop` or `{` after a label
+   //~| HELP add `'` to close the char literal
+   //~| ERROR expected `while`, `for`, `loop` or `{` after a label
+   //~| ERROR expected expression, found `]`
 }
diff --git a/tests/ui/parser/label-is-actually-char.stderr b/tests/ui/parser/label-is-actually-char.stderr
index 28c8d2ada3a..10a7e1803b5 100644
--- a/tests/ui/parser/label-is-actually-char.stderr
+++ b/tests/ui/parser/label-is-actually-char.stderr
@@ -1,5 +1,5 @@
 error: expected `while`, `for`, `loop` or `{` after a label
-  --> $DIR/label-is-actually-char.rs:2:15
+  --> $DIR/label-is-actually-char.rs:5:15
    |
 LL |     let c = 'a;
    |               ^ expected `while`, `for`, `loop` or `{` after a label
@@ -9,8 +9,20 @@ help: add `'` to close the char literal
 LL |     let c = 'a';
    |               +
 
+error: expected `while`, `for`, `loop` or `{` after a label
+  --> $DIR/label-is-actually-char.rs:9:17
+   |
+LL |     let c = 'abc;
+   |                 ^ expected `while`, `for`, `loop` or `{` after a label
+
+error: expected expression, found `;`
+  --> $DIR/label-is-actually-char.rs:9:17
+   |
+LL |     let c = 'abc;
+   |                 ^ expected expression
+
 error: unexpected token: `'b`
-  --> $DIR/label-is-actually-char.rs:6:15
+  --> $DIR/label-is-actually-char.rs:16:15
    |
 LL |         'a'..='b => {}
    |               ^^
@@ -20,27 +32,62 @@ help: add `'` to close the char literal
 LL |         'a'..='b' => {}
    |                 +
 
+error: unexpected token: `'def`
+  --> $DIR/label-is-actually-char.rs:19:15
+   |
+LL |         'c'..='def => {}
+   |               ^^^^
+
+error: expected pattern, found `=>`
+  --> $DIR/label-is-actually-char.rs:26:11
+   |
+LL |        'g => {}
+   |           ^^ expected pattern
+   |
+help: add `'` to close the char literal
+   |
+LL |        'g' => {}
+   |          +
+
+error: expected pattern, found `'hij`
+  --> $DIR/label-is-actually-char.rs:29:8
+   |
+LL |        'hij => {}
+   |        ^^^^ expected pattern
+
 error: expected `while`, `for`, `loop` or `{` after a label
-  --> $DIR/label-is-actually-char.rs:11:16
+  --> $DIR/label-is-actually-char.rs:36:15
    |
-LL |     let x = ['a, 'b];
-   |                ^ expected `while`, `for`, `loop` or `{` after a label
+LL |    let x = ['a, 'b, 'cde];
+   |               ^ expected `while`, `for`, `loop` or `{` after a label
    |
 help: add `'` to close the char literal
    |
-LL |     let x = ['a', 'b];
-   |                +
+LL |    let x = ['a', 'b, 'cde];
+   |               +
 
 error: expected `while`, `for`, `loop` or `{` after a label
-  --> $DIR/label-is-actually-char.rs:11:20
+  --> $DIR/label-is-actually-char.rs:36:19
    |
-LL |     let x = ['a, 'b];
-   |                    ^ expected `while`, `for`, `loop` or `{` after a label
+LL |    let x = ['a, 'b, 'cde];
+   |                   ^ expected `while`, `for`, `loop` or `{` after a label
    |
 help: add `'` to close the char literal
    |
-LL |     let x = ['a, 'b'];
-   |                    +
+LL |    let x = ['a, 'b', 'cde];
+   |                   +
+
+error: expected `while`, `for`, `loop` or `{` after a label
+  --> $DIR/label-is-actually-char.rs:36:25
+   |
+LL |    let x = ['a, 'b, 'cde];
+   |                         ^ expected `while`, `for`, `loop` or `{` after a label
+
+error: expected expression, found `]`
+  --> $DIR/label-is-actually-char.rs:36:25
+   |
+LL |    let x = ['a, 'b, 'cde];
+   |                         ^ expected expression
 
-error: aborting due to 4 previous errors
+error: aborting due to 11 previous errors