Do not emit "incorrect close delimiter" twice in the same place

src/libsyntax/parse/lexer/mod.rs

@@ -67,6 +67,7 @@ pub struct StringReader<'a> {
     span_src_raw: Span,
     open_braces: Vec<(token::DelimToken, Span)>,
     crate override_span: Option<Span>,
+    last_unclosed_found_span: Option<Span>,
 }
 
 impl<'a> StringReader<'a> {
@@ -195,6 +196,7 @@ impl<'a> StringReader<'a> {
             span_src_raw: syntax_pos::DUMMY_SP,
             open_braces: Vec::new(),
             override_span,
+            last_unclosed_found_span: None,
         }
     }
 

src/libsyntax/parse/lexer/tokentrees.rs

@@ -77,17 +77,23 @@ impl<'a> StringReader<'a> {
                     // Incorrect delimiter.
                     token::CloseDelim(other) => {
                         let token_str = token_to_string(&self.token);
-                        let msg = format!("incorrect close delimiter: `{}`", token_str);
-                        let mut err = self.sess.span_diagnostic.struct_span_err(self.span, &msg);
-                        err.span_label(self.span, "incorrect close delimiter");
-                        // This is a conservative error: only report the last unclosed delimiter.
-                        // The previous unclosed delimiters could actually be closed! The parser
-                        // just hasn't gotten to them yet.
-                        if let Some(&(_, sp)) = self.open_braces.last() {
-                            err.span_label(sp, "unclosed delimiter");
-                        };
-                        err.emit();
-
+                        if self.last_unclosed_found_span != Some(self.span) {
+                            // do not complain about the same unclosed delimiter multiple times
+                            self.last_unclosed_found_span = Some(self.span);
+                            let msg = format!("incorrect close delimiter: `{}`", token_str);
+                            let mut err = self.sess.span_diagnostic.struct_span_err(
+                                self.span,
+                                &msg,
+                            );
+                            err.span_label(self.span, "incorrect close delimiter");
+                            // This is a conservative error: only report the last unclosed
+                            // delimiter. The previous unclosed delimiters could actually be
+                            // closed! The parser just hasn't gotten to them yet.
+                            if let Some(&(_, sp)) = self.open_braces.last() {
+                                err.span_label(sp, "unclosed delimiter");
+                            };
+                            err.emit();
+                        }
                         self.open_braces.pop().unwrap();
 
                         // If the incorrect delimiter matches an earlier opening

src/test/ui/resolve/token-error-correct.rs

@@ -15,4 +15,3 @@ fn main() {
     //~^ ERROR: expected expression, found `;`
 }
 //~^ ERROR: incorrect close delimiter: `}`
-//~| ERROR: incorrect close delimiter: `}`

src/test/ui/resolve/token-error-correct.stderr

@@ -7,20 +7,11 @@ LL |     //~^ ERROR: expected expression, found `;`
 LL | }
    | ^ incorrect close delimiter
 
-error: incorrect close delimiter: `}`
-  --> $DIR/token-error-correct.rs:16:1
-   |
-LL |     foo(bar(;
-   |        - unclosed delimiter
-LL |     //~^ ERROR: expected expression, found `;`
-LL | }
-   | ^ incorrect close delimiter
-
 error: expected expression, found `;`
   --> $DIR/token-error-correct.rs:14:13
    |
 LL |     foo(bar(;
    |             ^ expected expression
 
-error: aborting due to 3 previous errors
+error: aborting due to 2 previous errors