release/20.x: [clang-format] Fix a crash on formatting missing r_pare…

[owenca]

…n/r_brace (#138230)

Backport 79210fe

[llvmbot]

@llvm/pr-subscribers-clang-format

Author: Owen Pan (owenca)

Changes

…n/r_brace (#138230)

Backport 79210fe

---

Full diff: https://github.com/llvm/llvm-project/pull/139345.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 c3ffabce15ec8..673b3e6c4b8c2 100644
--- a/clang/lib/Format/UnwrappedLineParser.cpp
+++ b/clang/lib/Format/UnwrappedLineParser.cpp
@@ -1837,8 +1837,8 @@ 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 49e1fde1d9ccf..90a79230e9f4c 100644
--- a/clang/unittests/Format/FormatTest.cpp
+++ b/clang/unittests/Format/FormatTest.cpp
@@ -13962,6 +13962,8 @@ TEST_F(FormatTest, IncorrectCodeUnbalancedBraces) {
   verifyNoCrash("struct Foo {\n"
                 "  operator foo(bar\n"
                 "};");
+  verifyNoCrash("decltype( {\n"
+                "  {");
 }
 
 TEST_F(FormatTest, IncorrectUnbalancedBracesInMacrosWithUnicode) {

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