Auto merge of #88835 - FabianWolff:issue-88770, r=petrochenkov

Fix error recovery in format macro parsing

Fixes #88770. Basically, the assumption in the following comment is incorrect:
https://github.com/rust-lang/rust/blob/b69fe57261086e70aea9d5b58819a1794bf7c121/compiler/rustc_builtin_macros/src/format.rs#L167-L172

This is only true in the first iteration of the loop, when [`p.clear_expected_tokens()`](https://github.com/rust-lang/rust/blob/b69fe57261086e70aea9d5b58819a1794bf7c121/compiler/rustc_builtin_macros/src/format.rs#L164) is called. In subsequent iterations, `p.expected_tokens` won't be empty, so `p.expect()` won't actually call `unexpected_try_recover()`:
https://github.com/rust-lang/rust/blob/b69fe57261086e70aea9d5b58819a1794bf7c121/compiler/rustc_parse/src/parser/mod.rs#L487-L498

Instead, it will call `expect_one_of()`, which _can_ recover and return `Ok()`. This PR handles this case to fix the ICE in #88770.

compiler/rustc_builtin_macros/src/format.rs

@@ -164,23 +164,22 @@ fn parse_args<'a>(
                 p.clear_expected_tokens();
             }
 
-            // `Parser::expect` tries to recover using the
-            // `Parser::unexpected_try_recover` function. This function is able
-            // to recover if the expected token is a closing delimiter.
-            //
-            // As `,` is not a closing delimiter, it will always return an `Err`
-            // variant.
-            let mut err = p.expect(&token::Comma).unwrap_err();
-
-            match token::TokenKind::Comma.similar_tokens() {
-                Some(tks) if tks.contains(&p.token.kind) => {
-                    // If a similar token is found, then it may be a typo. We
-                    // consider it as a comma, and continue parsing.
-                    err.emit();
-                    p.bump();
+            match p.expect(&token::Comma) {
+                Err(mut err) => {
+                    match token::TokenKind::Comma.similar_tokens() {
+                        Some(tks) if tks.contains(&p.token.kind) => {
+                            // If a similar token is found, then it may be a typo. We
+                            // consider it as a comma, and continue parsing.
+                            err.emit();
+                            p.bump();
+                        }
+                        // Otherwise stop the parsing and return the error.
+                        _ => return Err(err),
+                    }
+                }
+                Ok(recovered) => {
+                    assert!(recovered);
                 }
-                // Otherwise stop the parsing and return the error.
-                _ => return Err(err),
             }
         }
         first = false;

compiler/rustc_parse/src/parser/diagnostics.rs

@@ -277,7 +277,7 @@ impl<'a> Parser<'a> {
                 self.struct_span_err(sp, &msg)
                     .span_suggestion_short(sp, "change this to `;`", ";".to_string(), appl)
                     .emit();
-                return Ok(false);
+                return Ok(true);
             } else if self.look_ahead(0, |t| {
                 t == &token::CloseDelim(token::Brace)
                     || (
@@ -295,7 +295,7 @@ impl<'a> Parser<'a> {
                     .span_label(self.token.span, "unexpected token")
                     .span_suggestion_short(sp, "add `;` here", ";".to_string(), appl)
                     .emit();
-                return Ok(false);
+                return Ok(true);
             }
         }
 

src/test/ui/parser/issue-88770.rs

@@ -0,0 +1,11 @@
+// Regression test for the ICE described in #88770.
+
+// error-pattern:this file contains an unclosed delimiter
+// error-pattern:expected one of
+// error-pattern:missing `in` in `for` loop
+// error-pattern:expected `;`, found `e`
+
+fn m(){print!("",(c for&g
+u
+e
+e

src/test/ui/parser/issue-88770.stderr

@@ -0,0 +1,66 @@
+error: this file contains an unclosed delimiter
+  --> $DIR/issue-88770.rs:11:3
+   |
+LL | fn m(){print!("",(c for&g
+   |       -      -   - unclosed delimiter
+   |       |      |
+   |       |      unclosed delimiter
+   |       unclosed delimiter
+...
+LL | e
+   |   ^
+
+error: this file contains an unclosed delimiter
+  --> $DIR/issue-88770.rs:11:3
+   |
+LL | fn m(){print!("",(c for&g
+   |       -      -   - unclosed delimiter
+   |       |      |
+   |       |      unclosed delimiter
+   |       unclosed delimiter
+...
+LL | e
+   |   ^
+
+error: this file contains an unclosed delimiter
+  --> $DIR/issue-88770.rs:11:3
+   |
+LL | fn m(){print!("",(c for&g
+   |       -      -   - unclosed delimiter
+   |       |      |
+   |       |      unclosed delimiter
+   |       unclosed delimiter
+...
+LL | e
+   |   ^
+
+error: missing `in` in `for` loop
+  --> $DIR/issue-88770.rs:8:26
+   |
+LL |   fn m(){print!("",(c for&g
+   |  __________________________^
+LL | | u
+   | |_ help: try adding `in` here
+
+error: expected one of `!`, `)`, `,`, `.`, `::`, `?`, `{`, or an operator, found keyword `for`
+  --> $DIR/issue-88770.rs:8:21
+   |
+LL | fn m(){print!("",(c for&g
+   |                     ^^^ expected one of 8 possible tokens
+
+error: expected `;`, found `e`
+  --> $DIR/issue-88770.rs:10:2
+   |
+LL | e
+   |  ^ help: add `;` here
+LL | e
+   | - unexpected token
+
+error: expected one of `!`, `,`, `.`, `::`, `?`, `{`, or an operator, found `)`
+  --> $DIR/issue-88770.rs:11:3
+   |
+LL | e
+   |   ^ expected one of 7 possible tokens
+
+error: aborting due to 7 previous errors
+