fix an ICE in macro's diagnostic message

Author: Guanqun Lu

src/librustc_parse/parser/item.rs

@@ -1742,14 +1742,25 @@ impl<'a> Parser<'a> {
     }
 
     fn report_invalid_macro_expansion_item(&self) {
+        let has_close_delim = self.sess.source_map()
+            .span_to_snippet(self.prev_span)
+            .map(|s| s.ends_with(")") || s.ends_with("]"))
+            .unwrap_or(false);
+        let right_brace_span = if has_close_delim {
+            // it's safe to peel off one character only when it has the close delim
+            self.prev_span.with_lo(self.prev_span.hi() - BytePos(1))
+        } else {
+            self.sess.source_map().next_point(self.prev_span)
+        };
+
         self.struct_span_err(
             self.prev_span,
             "macros that expand to items must be delimited with braces or followed by a semicolon",
         ).multipart_suggestion(
             "change the delimiters to curly braces",
             vec![
-                (self.prev_span.with_hi(self.prev_span.lo() + BytePos(1)), String::from(" {")),
-                (self.prev_span.with_lo(self.prev_span.hi() - BytePos(1)), '}'.to_string()),
+                (self.prev_span.with_hi(self.prev_span.lo() + BytePos(1)), "{".to_string()),
+                (right_brace_span, '}'.to_string()),
             ],
             Applicability::MaybeIncorrect,
         ).span_suggestion(

src/test/ui/parser/macros-no-semicolon-items.stderr

@@ -6,8 +6,8 @@ LL | macro_rules! foo()
    |
 help: change the delimiters to curly braces
    |
-LL | macro_rules! foo {}
-   |                  ^^
+LL | macro_rules! foo{}
+   |                 ^^
 help: add a semicolon
    |
 LL | macro_rules! foo();
@@ -26,7 +26,7 @@ LL | | )
    |
 help: change the delimiters to curly braces
    |
-LL | bar! {
+LL | bar!{
 LL |     blah
 LL |     blah
 LL |     blah

src/test/ui/parser/mbe_missing_right_paren.rs

@@ -0,0 +1,3 @@
+// ignore-tidy-trailing-newlines
+// error-pattern: aborting due to 3 previous errors
+macro_rules! abc(ؼ

src/test/ui/parser/mbe_missing_right_paren.stderr

@@ -0,0 +1,31 @@
+error: this file contains an un-closed delimiter
+  --> $DIR/mbe_missing_right_paren.rs:3:19
+   |
+LL | macro_rules! abc(ؼ
+   |                 - ^
+   |                 |
+   |                 un-closed delimiter
+
+error: macros that expand to items must be delimited with braces or followed by a semicolon
+  --> $DIR/mbe_missing_right_paren.rs:3:17
+   |
+LL | macro_rules! abc(ؼ
+   |                 ^^
+   |
+help: change the delimiters to curly braces
+   |
+LL | macro_rules! abc{ؼ}
+   |                 ^ ^
+help: add a semicolon
+   |
+LL | macro_rules! abc(ؼ;
+   |                   ^
+
+error: unexpected end of macro invocation
+  --> $DIR/mbe_missing_right_paren.rs:3:1
+   |
+LL | macro_rules! abc(ؼ
+   | ^^^^^^^^^^^^^^^^^^ missing tokens in macro arguments
+
+error: aborting due to 3 previous errors
+