[Format] Don't crash on mismatched brackets

Author: sam-mccall

clang/lib/Format/TokenAnnotator.cpp

@@ -2837,7 +2837,7 @@ static bool isFunctionDeclarationName(bool IsCpp, const FormatToken &Current,
     if (!Current.is(TT_StartOfName) || Current.NestingLevel != 0)
       return false;
     for (; Next; Next = Next->Next) {
-      if (Next->is(TT_TemplateOpener)) {
+      if (Next->is(TT_TemplateOpener) && Next->MatchingParen) {
         Next = Next->MatchingParen;
       } else if (Next->is(tok::coloncolon)) {
         Next = Next->Next;

clang/unittests/Format/FormatTestCSharp.cpp

@@ -1600,5 +1600,9 @@ TEST_F(FormatTestCSharp, ShortFunctions) {
                Style);
 }
 
+TEST_F(FormatTestCSharp, BrokenBrackets) {
+  EXPECT_NE("", format("int where b <")); // reduced from crasher
+}
+
 } // namespace format
 } // end namespace clang