[clang-format] Fix a bug in parsing C-style cast of lambdas (llvm#136099)

Fix llvm#135959

Author: owenca

clang/lib/Format/UnwrappedLineParser.cpp

@@ -2368,13 +2368,25 @@ bool UnwrappedLineParser::tryToParseLambdaIntroducer() {
   const FormatToken *Previous = FormatTok->Previous;
   const FormatToken *LeftSquare = FormatTok;
   nextToken();
-  if ((Previous && ((Previous->Tok.getIdentifierInfo() &&
-                     !Previous->isOneOf(tok::kw_return, tok::kw_co_await,
-                                        tok::kw_co_yield, tok::kw_co_return)) ||
-                    Previous->closesScope())) ||
-      LeftSquare->isCppStructuredBinding(IsCpp)) {
-    return false;
+  if (Previous) {
+    if (Previous->Tok.getIdentifierInfo() &&
+        !Previous->isOneOf(tok::kw_return, tok::kw_co_await, tok::kw_co_yield,
+                           tok::kw_co_return)) {
+      return false;
+    }
+    if (Previous->closesScope()) {
+      // Not a potential C-style cast.
+      if (Previous->isNot(tok::r_paren))
+        return false;
+      const auto *BeforeRParen = Previous->getPreviousNonComment();
+      // Lambdas can be cast to function types only, e.g. `std::function<int()>`
+      // and `int (*)()`.
+      if (!BeforeRParen || !BeforeRParen->isOneOf(tok::greater, tok::r_paren))
+        return false;
+    }
   }
+  if (LeftSquare->isCppStructuredBinding(IsCpp))
+    return false;
   if (FormatTok->is(tok::l_square) || tok::isLiteral(FormatTok->Tok.getKind()))
     return false;
   if (FormatTok->is(tok::r_square)) {

clang/unittests/Format/TokenAnnotatorTest.cpp

@@ -2165,6 +2165,16 @@ TEST_F(TokenAnnotatorTest, UnderstandsLambdas) {
   // FIXME:
   // EXPECT_TOKEN(Tokens[13], tok::l_paren, TT_LambdaDefinitionLParen);
   EXPECT_TOKEN(Tokens[17], tok::l_brace, TT_LambdaLBrace);
+
+  Tokens = annotate("auto foo{(std::function<int()>)[] { return 0; }};");
+  ASSERT_EQ(Tokens.size(), 23u) << Tokens;
+  EXPECT_TOKEN(Tokens[13], tok::l_square, TT_LambdaLSquare);
+  EXPECT_TOKEN(Tokens[15], tok::l_brace, TT_LambdaLBrace);
+
+  Tokens = annotate("auto foo{(int (*)())[] { return 0; }};");
+  ASSERT_EQ(Tokens.size(), 21u) << Tokens;
+  EXPECT_TOKEN(Tokens[11], tok::l_square, TT_LambdaLSquare);
+  EXPECT_TOKEN(Tokens[13], tok::l_brace, TT_LambdaLBrace);
 }
 
 TEST_F(TokenAnnotatorTest, UnderstandsFunctionAnnotations) {