When encountering unclosed delimiters during parsing, check for diff markers

Fix #116252.

Author: estebank

Diff for: compiler/rustc_parse/src/lexer/mod.rs

@@ -64,10 +64,10 @@ pub(crate) fn parse_token_trees<'a>(
         override_span,
         nbsp_is_whitespace: false,
     };
-    let (token_trees, unmatched_delims) =
+    let (stream, res, unmatched_delims) =
         tokentrees::TokenTreesReader::parse_all_token_trees(string_reader);
-    match token_trees {
-        Ok(stream) if unmatched_delims.is_empty() => Ok(stream),
+    match res {
+        Ok(()) if unmatched_delims.is_empty() => Ok(stream),
         _ => {
             // Return error if there are unmatched delimiters or unclosed delimiters.
             // We emit delimiter mismatch errors first, then emit the unclosing delimiter mismatch
@@ -79,7 +79,7 @@ pub(crate) fn parse_token_trees<'a>(
                     err.buffer(&mut buffer);
                 }
             }
-            if let Err(err) = token_trees {
+            if let Err(err) = res {
                 // Add unclosing delimiter error
                 err.buffer(&mut buffer);
             }

Diff for: compiler/rustc_parse/src/lexer/tokentrees.rs

@@ -18,36 +18,39 @@ pub(super) struct TokenTreesReader<'a> {
 impl<'a> TokenTreesReader<'a> {
     pub(super) fn parse_all_token_trees(
         string_reader: StringReader<'a>,
-    ) -> (PResult<'a, TokenStream>, Vec<UnmatchedDelim>) {
+    ) -> (TokenStream, PResult<'a, ()>, Vec<UnmatchedDelim>) {
         let mut tt_reader = TokenTreesReader {
             string_reader,
             token: Token::dummy(),
             diag_info: TokenTreeDiagInfo::default(),
         };
-        let res = tt_reader.parse_token_trees(/* is_delimited */ false);
-        (res, tt_reader.diag_info.unmatched_delims)
+        let (stream, res) = tt_reader.parse_token_trees(/* is_delimited */ false);
+        (stream, res, tt_reader.diag_info.unmatched_delims)
     }
 
     // Parse a stream of tokens into a list of `TokenTree`s.
-    fn parse_token_trees(&mut self, is_delimited: bool) -> PResult<'a, TokenStream> {
+    fn parse_token_trees(&mut self, is_delimited: bool) -> (TokenStream, PResult<'a, ()>) {
         self.token = self.string_reader.next_token().0;
         let mut buf = Vec::new();
         loop {
             match self.token.kind {
-                token::OpenDelim(delim) => buf.push(self.parse_token_tree_open_delim(delim)?),
+                token::OpenDelim(delim) => {
+                    buf.push(match self.parse_token_tree_open_delim(delim) {
+                        Ok(val) => val,
+                        Err(err) => return (TokenStream::new(buf), Err(err)),
+                    })
+                }
                 token::CloseDelim(delim) => {
-                    return if is_delimited {
-                        Ok(TokenStream::new(buf))
-                    } else {
-                        Err(self.close_delim_err(delim))
-                    };
+                    return (
+                        TokenStream::new(buf),
+                        if is_delimited { Ok(()) } else { Err(self.close_delim_err(delim)) },
+                    );
                 }
                 token::Eof => {
-                    return if is_delimited {
-                        Err(self.eof_err())
-                    } else {
-                        Ok(TokenStream::new(buf))
-                    };
+                    return (
+                        TokenStream::new(buf),
+                        if is_delimited { Err(self.eof_err()) } else { Ok(()) },
+                    );
                 }
                 _ => {
                     // Get the next normal token. This might require getting multiple adjacent
@@ -106,7 +109,20 @@ impl<'a> TokenTreesReader<'a> {
         // Parse the token trees within the delimiters.
         // We stop at any delimiter so we can try to recover if the user
         // uses an incorrect delimiter.
-        let tts = self.parse_token_trees(/* is_delimited */ true)?;
+        let (tts, res) = self.parse_token_trees(/* is_delimited */ true);
+        if let Err(mut err) = res {
+            // If there are unclosed delims, see if there are diff markers and if so, point them
+            // out instead of complaining about the unclosed delims.
+            let mut parser = crate::stream_to_parser(self.string_reader.sess, tts, None);
+            while parser.token != token::Eof {
+                if let Err(mut diff_err) = parser.err_diff_marker() {
+                    diff_err.emit();
+                    err.delay_as_bug();
+                }
+                parser.bump();
+            }
+            return Err(err);
+        }
 
         // Expand to cover the entire delimited token tree
         let delim_span = DelimSpan::from_pair(pre_span, self.token.span);

Diff for: compiler/rustc_parse/src/parser/diagnostics.rs

@@ -2808,8 +2808,15 @@ impl<'a> Parser<'a> {
     }
 
     pub fn recover_diff_marker(&mut self) {
+        if let Err(mut err) = self.err_diff_marker() {
+            err.emit();
+            FatalError.raise();
+        }
+    }
+
+    pub fn err_diff_marker(&mut self) -> PResult<'a, ()> {
         let Some(start) = self.diff_marker(&TokenKind::BinOp(token::Shl), &TokenKind::Lt) else {
-            return;
+            return Ok(());
         };
         let mut spans = Vec::with_capacity(3);
         spans.push(start);
@@ -2856,8 +2863,7 @@ impl<'a> Parser<'a> {
             "for an explanation on these markers from the `git` documentation, visit \
              <https://git-scm.com/book/en/v2/Git-Tools-Advanced-Merging#_checking_out_conflicts>",
         );
-        err.emit();
-        FatalError.raise()
+        Err(err)
     }
 
     /// Parse and throw away a parenthesized comma separated

Diff for: tests/ui/parser/diff-markers/unclosed-delims-in-macro.rs

@@ -0,0 +1,9 @@
+macro_rules! foo {
+<<<<<<< HEAD
+    //~^ ERROR encountered diff marker
+    () {
+=======
+    () { //
+>>>>>>> 7a4f13c blah blah blah
+    }
+}

Diff for: tests/ui/parser/diff-markers/unclosed-delims-in-macro.stderr

@@ -0,0 +1,18 @@
+error: encountered diff marker
+  --> $DIR/unclosed-delims-in-macro.rs:2:1
+   |
+LL | <<<<<<< HEAD
+   | ^^^^^^^ after this is the code before the merge
+...
+LL | =======
+   | -------
+LL |     () { //
+LL | >>>>>>> 7a4f13c blah blah blah
+   | ^^^^^^^ above this are the incoming code changes
+   |
+   = help: if you're having merge conflicts after pulling new code, the top section is the code you already had and the bottom section is the remote code
+   = help: if you're in the middle of a rebase, the top section is the code being rebased onto and the bottom section is the code coming from the current commit being rebased
+   = note: for an explanation on these markers from the `git` documentation, visit <https://git-scm.com/book/en/v2/Git-Tools-Advanced-Merging#_checking_out_conflicts>
+
+error: aborting due to previous error
+

Diff for: tests/ui/parser/diff-markers/unclosed-delims.rs

@@ -0,0 +1,14 @@
+mod tests {
+    #[test]
+<<<<<<< HEAD
+//~^ ERROR encountered diff marker
+//~| NOTE after this is the code before the merge
+//~| NOTE for an explanation on these markers
+    fn test1() {
+=======
+//~^ NOTE
+    fn test2() {
+>>>>>>> 7a4f13c blah blah blah
+//~^ NOTE above this are the incoming code changes
+    }
+}

Diff for: tests/ui/parser/diff-markers/unclosed-delims.stderr

@@ -0,0 +1,18 @@
+error: encountered diff marker
+  --> $DIR/unclosed-delims.rs:3:1
+   |
+LL | <<<<<<< HEAD
+   | ^^^^^^^ after this is the code before the merge
+...
+LL | =======
+   | -------
+...
+LL | >>>>>>> 7a4f13c blah blah blah
+   | ^^^^^^^ above this are the incoming code changes
+   |
+   = help: if you're having merge conflicts after pulling new code, the top section is the code you already had and the bottom section is the remote code
+   = help: if you're in the middle of a rebase, the top section is the code being rebased onto and the bottom section is the code coming from the current commit being rebased
+   = note: for an explanation on these markers from the `git` documentation, visit <https://git-scm.com/book/en/v2/Git-Tools-Advanced-Merging#_checking_out_conflicts>
+
+error: aborting due to previous error
+