Collect occurrences of for mismatched braces diagnostic

Change-Id: I20ba0b62308370ee961141fa1aefc4b9c9f0cb3a

Author: XiangQingW

src/libsyntax/parse/lexer/tokentrees.rs

@@ -126,7 +126,7 @@ impl<'a> TokenTreesReader<'a> {
                         let (open_brace, open_brace_span) = self.open_braces.pop().unwrap();
                         let close_brace_span = self.token.span;
 
-                        if close_brace_span.lo() == open_brace_span.hi() {
+                        if tts.is_empty() {
                             let empty_block_span = open_brace_span.to(close_brace_span);
                             self.last_delim_empty_block_spans.insert(delim, empty_block_span);
                         }

src/test/ui/parser/mismatched-delim-brace-empty-block.rs

@@ -1,3 +1,5 @@
-fn main() {}
+fn main() {
+
+}
     let _ = ();
 } //~ ERROR unexpected close delimiter

src/test/ui/parser/mismatched-delim-brace-empty-block.stderr

@@ -1,11 +1,14 @@
 error: unexpected close delimiter: `}`
-  --> $DIR/mismatched-delim-brace-empty-block.rs:3:1
+  --> $DIR/mismatched-delim-brace-empty-block.rs:5:1
    |
-LL | fn main() {}
-   |           -- this block is empty, you might have not meant to close it
-LL |     let _ = ();
-LL | }
-   | ^ unexpected close delimiter
+LL |   fn main() {
+   |  ___________-
+LL | |
+LL | | }
+   | |_- this block is empty, you might have not meant to close it
+LL |       let _ = ();
+LL |   }
+   |   ^ unexpected close delimiter
 
 error: aborting due to previous error