[clang-format] Fix a crash on formatting missing r_paren/r_brace

[owenca]

Fix #138097

[llvmbot]

@llvm/pr-subscribers-clang-format

Author: Owen Pan (owenca)

Changes

Fix #138097

---

Full diff: https://github.com/llvm/llvm-project/pull/138230.diff

2 Files Affected:

• (modified) clang/lib/Format/UnwrappedLineParser.cpp (+2-2)
• (modified) clang/unittests/Format/FormatTest.cpp (+2)

diff --git a/clang/lib/Format/UnwrappedLineParser.cpp b/clang/lib/Format/UnwrappedLineParser.cpp
index 837146f0c6483..863df987ab230 100644
--- a/clang/lib/Format/UnwrappedLineParser.cpp
+++ b/clang/lib/Format/UnwrappedLineParser.cpp
@@ -1834,8 +1834,8 @@ void UnwrappedLineParser::parseStructuralElement(
       nextToken();
       if (FormatTok->is(tok::l_paren)) {
         parseParens();
-        assert(FormatTok->Previous);
-        if (FormatTok->Previous->endsSequence(tok::r_paren, tok::kw_auto,
+        if (FormatTok->Previous &&
+            FormatTok->Previous->endsSequence(tok::r_paren, tok::kw_auto,
                                               tok::l_paren)) {
           Line->SeenDecltypeAuto = true;
         }
diff --git a/clang/unittests/Format/FormatTest.cpp b/clang/unittests/Format/FormatTest.cpp
index c4fcc5506d152..5605777c20ae2 100644
--- a/clang/unittests/Format/FormatTest.cpp
+++ b/clang/unittests/Format/FormatTest.cpp
@@ -14259,6 +14259,8 @@ TEST_F(FormatTest, IncorrectCodeUnbalancedBraces) {
   verifyNoCrash("struct Foo {\n"
                 "  operator foo(bar\n"
                 "};");
+  verifyNoCrash("decltype( {\n"
+                "  {");
 }
 
 TEST_F(FormatTest, IncorrectUnbalancedBracesInMacrosWithUnicode) {