[clang] [clang-format] Fix an assertion failure on invalid C++ lambda (PR #185349)

[via cfe-commits]

https://github.com/owenca created https://github.com/llvm/llvm-project/pull/185349

Fixes #185268

>From 81e6247e4b23453e4379aeaa786ad3fe7f09f056 Mon Sep 17 00:00:00 2001
From: Owen Pan <owenpiano at gmail.com>
Date: Sun, 8 Mar 2026 22:48:17 -0700
Subject: [PATCH] [clang-format] Fix an assertion failure on invalid C++ lambda

Fixes #185268
---
 clang/lib/Format/TokenAnnotator.cpp   | 2 +-
 clang/unittests/Format/FormatTest.cpp | 4 ++++
 2 files changed, 5 insertions(+), 1 deletion(-)

diff --git a/clang/lib/Format/TokenAnnotator.cpp b/clang/lib/Format/TokenAnnotator.cpp
index 1b588435d6302..965c9195aa7f4 100644
--- a/clang/lib/Format/TokenAnnotator.cpp
+++ b/clang/lib/Format/TokenAnnotator.cpp
@@ -4147,7 +4147,7 @@ void TokenAnnotator::calculateFormattingInformation(AnnotatedLine &Line) const {
         if (Tok->is(TT_CtorInitializerColon))
           break;
         if (Tok->is(tok::arrow)) {
-          Tok->setType(TT_TrailingReturnArrow);
+          Tok->overwriteFixedType(TT_TrailingReturnArrow);
           break;
         }
         if (Tok->isNot(TT_TrailingAnnotation))
diff --git a/clang/unittests/Format/FormatTest.cpp b/clang/unittests/Format/FormatTest.cpp
index 33af71de398be..f2503a0a27bb5 100644
--- a/clang/unittests/Format/FormatTest.cpp
+++ b/clang/unittests/Format/FormatTest.cpp
@@ -29245,6 +29245,10 @@ TEST_F(FormatTest, UnbalancedAngleBrackets) {
                 getLLVMStyleWithColumns(50));
 }
 
+TEST_F(FormatTest, LambdaArrowAsTrailingReturnArrow) {
+  verifyNoCrash("void foo()([] consteval -> int {}())");
+}
+
 } // namespace
 } // namespace test
 } // namespace format