[Clang] fix confusing diagnostics for lambdas with init-captures inside braced initializers #166180
+22
−10
Conversation
This file contains hidden or bidirectional Unicode text that may be interpreted or compiled differently than what appears below. To review, open the file in an editor that reveals hidden Unicode characters.
Learn more about bidirectional Unicode characters
…de braced initializers
llvmbot
added
clang
Member
|
@llvm/pr-subscribers-clang Author: Oleksandr T. (a-tarasyuk) ChangesFixes #163498 This PR addresses the issue of confusing diagnostics for lambdas with init-captures appearing inside braced initializers. Cases such as: S s{[a(42), &] {}};were misparsed as C99 array designators, producing unrelated diagnostics, such as llvm-project/clang/lib/Parse/ParseInit.cpp Line 470 in bb9bd5f llvm-project/clang/include/clang/Parse/Parser.h Lines 4652 to 4655 in bb9bd5f llvm-project/clang/lib/Parse/ParseExprCXX.cpp Lines 871 to 879 in 24c22b7 The tentative parser now returns Clang now correctly recognizes such constructs as malformed lambda introducers and emits the expected diagnostic — for example, “capture-default must be first” — consistent with direct initialization cases such as: S s([a(42), &] {});Full diff: https://github.com/llvm/llvm-project/pull/166180.diff 3 Files Affected:
diff --git a/clang/docs/ReleaseNotes.rst b/clang/docs/ReleaseNotes.rst
index 92fc9381a5868..63faf46895989 100644
--- a/clang/docs/ReleaseNotes.rst
+++ b/clang/docs/ReleaseNotes.rst
@@ -496,6 +496,7 @@ Bug Fixes to C++ Support
nontrivial member when another member has an initializer. (#GH81774)
- Fixed a template depth issue when parsing lambdas inside a type constraint. (#GH162092)
- Diagnose unresolved overload sets in non-dependent compound requirements. (#GH51246) (#GH97753)
+- Fix incorrect diagnostics for lambdas with init-captures inside braced initializers. (#GH163498)
Bug Fixes to AST Handling
^^^^^^^^^^^^^^^^^^^^^^^^^
diff --git a/clang/lib/Parse/ParseExprCXX.cpp b/clang/lib/Parse/ParseExprCXX.cpp
index 74f87a8cb63c3..03ae727168df0 100644
--- a/clang/lib/Parse/ParseExprCXX.cpp
+++ b/clang/lib/Parse/ParseExprCXX.cpp
@@ -772,9 +772,10 @@ bool Parser::ParseLambdaIntroducer(LambdaIntroducer &Intro,
// Produce a diagnostic if we're not tentatively parsing; otherwise track
// that our parse has failed.
- auto Invalid = [&](llvm::function_ref<void()> Action) {
+ auto Result = [&](llvm::function_ref<void()> Action,
+ LambdaIntroducerTentativeParse State) {
if (Tentative) {
- *Tentative = LambdaIntroducerTentativeParse::Invalid;
+ *Tentative = State;
return false;
}
Action();
@@ -824,9 +825,11 @@ bool Parser::ParseLambdaIntroducer(LambdaIntroducer &Intro,
break;
}
- return Invalid([&] {
- Diag(Tok.getLocation(), diag::err_expected_comma_or_rsquare);
- });
+ return Result(
+ [&] {
+ Diag(Tok.getLocation(), diag::err_expected_comma_or_rsquare);
+ },
+ LambdaIntroducerTentativeParse::Invalid);
}
ConsumeToken();
}
@@ -861,9 +864,11 @@ bool Parser::ParseLambdaIntroducer(LambdaIntroducer &Intro,
ConsumeToken();
Kind = LCK_StarThis;
} else {
- return Invalid([&] {
- Diag(Tok.getLocation(), diag::err_expected_star_this_capture);
- });
+ return Result(
+ [&] {
+ Diag(Tok.getLocation(), diag::err_expected_star_this_capture);
+ },
+ LambdaIntroducerTentativeParse::Invalid);
}
} else if (Tok.is(tok::kw_this)) {
Kind = LCK_This;
@@ -875,8 +880,9 @@ bool Parser::ParseLambdaIntroducer(LambdaIntroducer &Intro,
// or the start of a capture (in the "&" case) with the rest of the
// capture missing. Both are an error but a misplaced capture-default
// is more likely if we don't already have a capture default.
- return Invalid(
- [&] { Diag(Tok.getLocation(), diag::err_capture_default_first); });
+ return Result(
+ [&] { Diag(Tok.getLocation(), diag::err_capture_default_first); },
+ LambdaIntroducerTentativeParse::Incomplete);
} else {
TryConsumeToken(tok::ellipsis, EllipsisLocs[0]);
@@ -899,14 +905,16 @@ bool Parser::ParseLambdaIntroducer(LambdaIntroducer &Intro,
Id = Tok.getIdentifierInfo();
Loc = ConsumeToken();
} else if (Tok.is(tok::kw_this)) {
- return Invalid([&] {
- // FIXME: Suggest a fixit here.
- Diag(Tok.getLocation(), diag::err_this_captured_by_reference);
- });
+ return Result(
+ [&] {
+ // FIXME: Suggest a fixit here.
+ Diag(Tok.getLocation(), diag::err_this_captured_by_reference);
+ },
+ LambdaIntroducerTentativeParse::Invalid);
} else {
- return Invalid([&] {
- Diag(Tok.getLocation(), diag::err_expected_capture);
- });
+ return Result(
+ [&] { Diag(Tok.getLocation(), diag::err_expected_capture); },
+ LambdaIntroducerTentativeParse::Invalid);
}
TryConsumeToken(tok::ellipsis, EllipsisLocs[2]);
diff --git a/clang/test/Parser/lambda-misplaced-capture-default.cpp b/clang/test/Parser/lambda-misplaced-capture-default.cpp
index d65b875102da7..4f5bd6d7fa5e9 100644
--- a/clang/test/Parser/lambda-misplaced-capture-default.cpp
+++ b/clang/test/Parser/lambda-misplaced-capture-default.cpp
@@ -36,3 +36,12 @@ template <typename... Args> void Test(Args... args) {
[... xs = &args, &] {}; // expected-error {{capture default must be first}}
}
} // namespace misplaced_capture_default_pack
+
+namespace GH163498 {
+struct S {
+ template <class T> S(T) {}
+};
+void t() {
+ S s{[a(42), &] {}}; // expected-error {{capture default must be first}}
+}
+}
|
cor3ntin
approved these changes
Nov 5, 2025
… into fix/163498
vinay-deshmukh
pushed a commit
to vinay-deshmukh/llvm-project
that referenced
this pull request
Nov 8, 2025
…de braced initializers (llvm#166180) Fixes llvm#163498 --- This PR addresses the issue of confusing diagnostics for lambdas with init-captures appearing inside braced initializers. Cases such as: ```cpp S s{[a(42), &] {}}; ``` were misparsed as C99 array designators, producing unrelated diagnostics, such as `use of undeclared identifier 'a'`, and `expected ']'` --- https://github.com/llvm/llvm-project/blob/bb9bd5f263226840194b28457ddf9861986db51f/clang/lib/Parse/ParseInit.cpp#L470 https://github.com/llvm/llvm-project/blob/bb9bd5f263226840194b28457ddf9861986db51f/clang/lib/Parse/ParseInit.cpp#L74 https://github.com/llvm/llvm-project/blob/bb9bd5f263226840194b28457ddf9861986db51f/clang/include/clang/Parse/Parser.h#L4652-L4655 https://github.com/llvm/llvm-project/blob/24c22b7de620669aed9da28de323309c44a58244/clang/lib/Parse/ParseExprCXX.cpp#L871-L879 The tentative parser now returns `Incomplete` for partially valid lambda introducers, preserving the `lambda` interpretation and allowing the proper diagnostic to be issued later. --- Clang now correctly recognizes such constructs as malformed lambda introducers and emits the expected diagnostic — for example, “capture-default must be first” — consistent with direct initialization cases such as: ```cpp S s([a(42), &] {}); ```
Sign up for free
to join this conversation on GitHub.
Already have an account?
Sign in to comment
4 participants
Add this suggestion to a batch that can be applied as a single commit.
This suggestion is invalid because no changes were made to the code.
Suggestions cannot be applied while the pull request is closed.
Suggestions cannot be applied while viewing a subset of changes.
Only one suggestion per line can be applied in a batch.
Add this suggestion to a batch that can be applied as a single commit.
Applying suggestions on deleted lines is not supported.
You must change the existing code in this line in order to create a valid suggestion.
Outdated suggestions cannot be applied.
This suggestion has been applied or marked resolved.
Suggestions cannot be applied from pending reviews.
Suggestions cannot be applied on multi-line comments.
Suggestions cannot be applied while the pull request is queued to merge.
Suggestion cannot be applied right now. Please check back later.
Fixes #163498
This PR addresses the issue of confusing diagnostics for lambdas with init-captures appearing inside braced initializers.
Cases such as:
S s{[a(42), &] {}};were misparsed as C99 array designators, producing unrelated diagnostics, such as
use of undeclared identifier 'a', andexpected ']'llvm-project/clang/lib/Parse/ParseInit.cpp
Line 470 in bb9bd5f
llvm-project/clang/lib/Parse/ParseInit.cpp
Line 74 in bb9bd5f
llvm-project/clang/include/clang/Parse/Parser.h
Lines 4652 to 4655 in bb9bd5f
llvm-project/clang/lib/Parse/ParseExprCXX.cpp
Lines 871 to 879 in 24c22b7
The tentative parser now returns
Incompletefor partially valid lambda introducers, preserving thelambdainterpretation and allowing the proper diagnostic to be issued later.Clang now correctly recognizes such constructs as malformed lambda introducers and emits the expected diagnostic — for example, “capture-default must be first” — consistent with direct initialization cases such as: