[clang] [clang-format] Fix a bug in parsing C-style cast lambda (PR #136099)

[Owen Pan via cfe-commits]

https://github.com/owenca updated https://github.com/llvm/llvm-project/pull/136099

>From 53033b278f89a508d079614eadd58b103211d5dd Mon Sep 17 00:00:00 2001
From: Owen Pan <owenpiano at gmail.com>
Date: Thu, 17 Apr 2025 00:35:19 -0700
Subject: [PATCH 1/2] [clang-format] Fix a bug in parsing C-style cast lambda

Fix #135959
---
 clang/lib/Format/UnwrappedLineParser.cpp      | 3 ++-
 clang/unittests/Format/TokenAnnotatorTest.cpp | 5 +++++
 2 files changed, 7 insertions(+), 1 deletion(-)

diff --git a/clang/lib/Format/UnwrappedLineParser.cpp b/clang/lib/Format/UnwrappedLineParser.cpp
index b9430d4389feb..4442e965e0f51 100644
--- a/clang/lib/Format/UnwrappedLineParser.cpp
+++ b/clang/lib/Format/UnwrappedLineParser.cpp
@@ -2371,7 +2371,8 @@ bool UnwrappedLineParser::tryToParseLambdaIntroducer() {
   if ((Previous && ((Previous->Tok.getIdentifierInfo() &&
                      !Previous->isOneOf(tok::kw_return, tok::kw_co_await,
                                         tok::kw_co_yield, tok::kw_co_return)) ||
-                    Previous->closesScope())) ||
+                    (Previous->closesScope() &&
+                     !Previous->endsSequence(tok::r_paren, tok::greater)))) ||
       LeftSquare->isCppStructuredBinding(IsCpp)) {
     return false;
   }
diff --git a/clang/unittests/Format/TokenAnnotatorTest.cpp b/clang/unittests/Format/TokenAnnotatorTest.cpp
index 2c7319ccefec2..7a07fbd0250be 100644
--- a/clang/unittests/Format/TokenAnnotatorTest.cpp
+++ b/clang/unittests/Format/TokenAnnotatorTest.cpp
@@ -2159,6 +2159,11 @@ 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);
 }
 
 TEST_F(TokenAnnotatorTest, UnderstandsFunctionAnnotations) {

>From 3dd4a35e22fd58f89bb83016a66ceb112043a529 Mon Sep 17 00:00:00 2001
From: Owen Pan <owenpiano at gmail.com>
Date: Fri, 18 Apr 2025 20:04:13 -0700
Subject: [PATCH 2/2] Also handle casting to function pointer types

---
 clang/lib/Format/UnwrappedLineParser.cpp      | 25 +++++++++++++------
 clang/unittests/Format/TokenAnnotatorTest.cpp |  5 ++++
 2 files changed, 23 insertions(+), 7 deletions(-)

diff --git a/clang/lib/Format/UnwrappedLineParser.cpp b/clang/lib/Format/UnwrappedLineParser.cpp
index 4442e965e0f51..df58e5ef4d6a3 100644
--- a/clang/lib/Format/UnwrappedLineParser.cpp
+++ b/clang/lib/Format/UnwrappedLineParser.cpp
@@ -2368,14 +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() &&
-                     !Previous->endsSequence(tok::r_paren, tok::greater)))) ||
-      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)) {
diff --git a/clang/unittests/Format/TokenAnnotatorTest.cpp b/clang/unittests/Format/TokenAnnotatorTest.cpp
index 7a07fbd0250be..596594b0cf49c 100644
--- a/clang/unittests/Format/TokenAnnotatorTest.cpp
+++ b/clang/unittests/Format/TokenAnnotatorTest.cpp
@@ -2164,6 +2164,11 @@ TEST_F(TokenAnnotatorTest, UnderstandsLambdas) {
   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) {