[Clang] Fix a wrong diagnostic about a local variable inside a lambda in unevaluated context need capture

[Backl1ght]

Fixes #163837

We should return true here

llvm-project/clang/lib/Sema/SemaExpr.cpp

Lines 19398 to 19400 in 035f811

	if (IsInScopeDeclarationContext &&
	FunctionScopesIndex == MaxFunctionScopesIndex && VarDC == DC)
	return true;

, but we won't currently due to mismatch of VarDC and DC while DC is instantiated version of VarDC.

The reason of mismatch is that FindInstantiatedDecl to result returns uninstantiated version incorrectly here

llvm-project/clang/lib/Sema/SemaTemplateInstantiateDecl.cpp

Lines 7064 to 7065 in 059d90d

	if (!ParentDependsOnArgs)
	return D;

We should return instantiated version if we can find one.

[github-actions]

✅ With the latest revision this PR passed the C/C++ code formatter.

[llvmbot]

@llvm/pr-subscribers-clang

Author: Zhikai Zeng (Backl1ght)

Changes

Fixes #163837

We should return true here

llvm-project/clang/lib/Sema/SemaExpr.cpp

Lines 19398 to 19400 in 035f811

	if (IsInScopeDeclarationContext &&
	FunctionScopesIndex == MaxFunctionScopesIndex && VarDC == DC)
	return true;

, but we won't currently due to mismatch of VarDC and DC while DC is instantiated version of VarDC.

The reason of mismatch is that FindInstantiatedDecl to result returns uninstantiated version incorrectly here

llvm-project/clang/lib/Sema/SemaTemplateInstantiateDecl.cpp

Lines 7064 to 7065 in 059d90d

	if (!ParentDependsOnArgs)
	return D;

We should return instantiated version if we can find one.

---

Full diff: https://github.com/llvm/llvm-project/pull/165098.diff

3 Files Affected:

• (modified) clang/docs/ReleaseNotes.rst (+2)
• (modified) clang/lib/Sema/SemaTemplateInstantiateDecl.cpp (+8-1)
• (modified) clang/test/SemaCXX/lambda-unevaluated.cpp (+19)

diff --git a/clang/docs/ReleaseNotes.rst b/clang/docs/ReleaseNotes.rst index e6e33e7a9a280..dd7206ba2b253 100644 --- a/clang/docs/ReleaseNotes.rst +++ b/clang/docs/ReleaseNotes.rst @@ -429,6 +429,8 @@ Bug Fixes in This Version - Fixed a failed assertion with empty filename arguments in ``__has_embed``. (#GH159898) - Fixed a failed assertion with empty filename in ``#embed`` directive. (#GH162951) - Fixed a crash triggered by unterminated ``__has_embed``. (#GH162953) +- Fixed a wrong diagnostic about a local variable inside a lambda in unevaluated + contexts need capture. (#GH163837) Bug Fixes to Compiler Builtins ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ diff --git a/clang/lib/Sema/SemaTemplateInstantiateDecl.cpp b/clang/lib/Sema/SemaTemplateInstantiateDecl.cpp index 28925cca8f956..439a5317f06f1 100644 --- a/clang/lib/Sema/SemaTemplateInstantiateDecl.cpp +++ b/clang/lib/Sema/SemaTemplateInstantiateDecl.cpp @@ -7061,8 +7061,15 @@ NamedDecl *Sema::FindInstantiatedDecl(SourceLocation Loc, NamedDecl *D, // anonymous unions in class templates). } - if (!ParentDependsOnArgs) + if (!ParentDependsOnArgs) { + if (auto Found = + CurrentInstantiationScope + ? CurrentInstantiationScope->getInstantiationOfIfExists(D) + : nullptr) { + return cast<NamedDecl>(Found->dyn_cast<Decl *>()); + } return D; + } ParentDC = FindInstantiatedContext(Loc, ParentDC, TemplateArgs); if (!ParentDC) diff --git a/clang/test/SemaCXX/lambda-unevaluated.cpp b/clang/test/SemaCXX/lambda-unevaluated.cpp index 9289fc9ec1243..4b0e1abdb38f0 100644 --- a/clang/test/SemaCXX/lambda-unevaluated.cpp +++ b/clang/test/SemaCXX/lambda-unevaluated.cpp @@ -282,3 +282,22 @@ static_assert(__is_same_as(int, helper<int>)); } // namespace GH138018 + +namespace GH163837 { + +template<int N> +void f(); + +template<class> +struct X { + using type = decltype([](auto) { + f<[]{ + int result = 0; + return result; + }()>(); + }(0)); +}; + +X<void> l; + +} // namespace GH163837 

[zyn0217]

FYI @mizvekov is working on a large patch that resolves a lot of lambda context related bugs and aims to remove these workarounds in the end.

[Fznamznon]

Nits in case this patch goes in before the mentioned patch

[Fznamznon]

I find ternary operator inside of an if uncommon, can we simply do

Suggested change

	if (auto Found =
	CurrentInstantiationScope
	? CurrentInstantiationScope->getInstantiationOfIfExists(D)
	: nullptr) {
	if (CurrentInstantiationScope) {
	llvm::PointerUnion<... > * Found = CurrentInstantiationScope->getInstantiationOfIfExists(D)
	...

and spell out the type?

[Fznamznon]

Using of dyn_cast is strange here IMO, since the outer cast doesn't expect null. If that is always a Decl there, we probably need to use get instead.