[clang] ad24d2e - [clang] Don't assert on paren-less lambdas with dependent return type (#176296)

[via cfe-commits]

Author: Nico Weber
Date: 2026-01-17T10:43:51-05:00
New Revision: ad24d2e9a5a9ea33dce43bf4223cd1ccad8fdcc9

URL: https://github.com/llvm/llvm-project/commit/ad24d2e9a5a9ea33dce43bf4223cd1ccad8fdcc9
DIFF: https://github.com/llvm/llvm-project/commit/ad24d2e9a5a9ea33dce43bf4223cd1ccad8fdcc9.diff

LOG: [clang] Don't assert on paren-less lambdas with dependent return type (#176296)

The initial implementation of C++23 style lambdas without parameter
lists, 0620e6f4b76a9, removed `DeclLoc`, which was used to intitialize
`DeclEndLoc`.

This code was then moved around a bit in behavior-preserving ways in
https://reviews.llvm.org/D124351 and 2eb1e75f42d7e09e.

If a lambda has no parentheses, no exception-specification,
attribute-specifier, *and* a decltype() return type (which leads to
`ParseTrailingReturnType` returning a range where
`Range.getEnd().isValid()` is false), then we no longer set a valid
`DeclEndLoc`. Fix this by restoring `DeclLoc` and using it as it was
used before 0620e6f4b76a9.

Fixes #176256.

Added: 
    

Modified: 
    clang/lib/Parse/ParseExprCXX.cpp
    clang/test/Parser/cxx2b-lambdas.cpp

Removed: 
    


################################################################################
diff  --git a/clang/lib/Parse/ParseExprCXX.cpp b/clang/lib/Parse/ParseExprCXX.cpp
index 7a5d28caf8521..842b52375eb14 100644
--- a/clang/lib/Parse/ParseExprCXX.cpp
+++ b/clang/lib/Parse/ParseExprCXX.cpp
@@ -1224,6 +1224,8 @@ ExprResult Parser::ParseLambdaExpressionAfterIntroducer(
                                    Scope::FunctionPrototypeScope);
 
   Actions.PushLambdaScope();
+  SourceLocation DeclLoc = Tok.getLocation();
+
   Actions.ActOnLambdaExpressionAfterIntroducer(Intro, getCurScope());
 
   ParsedAttributes Attributes(AttrFactory);
@@ -1308,7 +1310,7 @@ ExprResult Parser::ParseLambdaExpressionAfterIntroducer(
   TypeResult TrailingReturnType;
   SourceLocation TrailingReturnTypeLoc;
   SourceLocation LParenLoc, RParenLoc;
-  SourceLocation DeclEndLoc;
+  SourceLocation DeclEndLoc = DeclLoc;
   bool HasParentheses = false;
   bool HasSpecifiers = false;
   SourceLocation MutableLoc;

diff  --git a/clang/test/Parser/cxx2b-lambdas.cpp b/clang/test/Parser/cxx2b-lambdas.cpp
index 758ec9a42f56d..cda7f556691e6 100644
--- a/clang/test/Parser/cxx2b-lambdas.cpp
+++ b/clang/test/Parser/cxx2b-lambdas.cpp
@@ -27,6 +27,10 @@ auto L6 = [s = 1] mutable {};
 auto L7 = [s = 1] constexpr mutable noexcept {}; // cxx11-error {{return type 'void' is not a literal type}}
 #endif
 auto L8 = [] -> bool { return true; };
+#if __cplusplus >= 201103L
+template <typename> struct PR176256 {};
+PR176256<void> token = [] -> decltype(token) { return {}; }();
+#endif
 auto L9 = []<typename T> { return true; };
 #if __cplusplus >= 201103L
 auto L10 = []<typename T> noexcept { return true; };