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[Clang][Sema] fix noexecpt mismatch of friend declaration #102267

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[Clang][Sema] fix noexecpt mismatch of friend declaration #102267

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2 changes: 2 additions & 0 deletions clang/docs/ReleaseNotes.rst
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Original file line number Diff line number Diff line change
Expand Up @@ -192,6 +192,8 @@ Bug Fixes to C++ Support
- Clang now preserves the unexpanded flag in a lambda transform used for pack expansion. (#GH56852), (#GH85667),
(#GH99877).
- Fixed a bug when diagnosing ambiguous explicit specializations of constrained member functions.
- Fix mismatch of noexecpt in friend function declaration by copying template instantiated parameters to
current local scope.(#GH101330).

Bug Fixes to AST Handling
^^^^^^^^^^^^^^^^^^^^^^^^^
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15 changes: 15 additions & 0 deletions clang/lib/Sema/SemaTemplateInstantiateDecl.cpp
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Expand Up @@ -4698,7 +4698,22 @@ void Sema::InstantiateExceptionSpec(SourceLocation PointOfInstantiation,
// Enter the scope of this instantiation. We don't use
// PushDeclContext because we don't have a scope.
Sema::ContextRAII savedContext(*this, Decl);

FunctionDecl *Source = Proto->getExtProtoInfo().ExceptionSpec.SourceTemplate;
FunctionTemplateDecl *SourceTemplate = Source->getDescribedFunctionTemplate();
llvm::SmallDenseMap<clang::Decl *, clang::Decl *> InstTemplateParams;
if (CurrentInstantiationScope && SourceTemplate)
if (TemplateParameterList *TPL = SourceTemplate->getTemplateParameters())
for (NamedDecl *TemplateParam : *TPL)
if (auto *Found =
CurrentInstantiationScope->findInstantiationOf(TemplateParam))
if (auto *InstTemplateParam = Found->dyn_cast<clang::Decl *>())
InstTemplateParams[TemplateParam] = InstTemplateParam;

Comment on lines +4707 to +4712
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I don't think this is handling the pack case..
Do we have a generic way to copy instantiated template params? @zyn0217 @mizvekov @Sirraide
We do similar things in a bunch of places (including when checking constraints)

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Not that I’m aware of. I think we can wait for @sdkrystian‘s refactoring patch of MLTAL which might make such things easier.

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... including when checking constraints ...

This might not be the case for template parameters, as we (almost always, in my recollection) would have transformed the associated template parameters before calling the constraint matching function, so...

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Yeah, we should wait until I reland #106585 and then we can fix this. What we can then do is normalize the exception specification the same way we normalize constraints prior to comparing them.

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... the same way we normalize constraints prior to comparing them.

Which means we don't need an individual instantiation scope for the noexcept specification thereafter, so the question here could be resolved naturally I presume?

LocalInstantiationScope Scope(*this);
for (auto [TemplateParam, InstTemplateParam] : InstTemplateParams) {
Scope.InstantiatedLocal(TemplateParam, InstTemplateParam);
}

MultiLevelTemplateArgumentList TemplateArgs =
getTemplateInstantiationArgs(Decl, Decl->getLexicalDeclContext(),
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16 changes: 16 additions & 0 deletions clang/test/SemaCXX/pr101330.cpp
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@@ -0,0 +1,16 @@
// RUN: %clang_cc1 -fsyntax-only -verify -std=c++11 %s
// expected-no-diagnostics

template <typename T>
struct C {
template <int N, typename U>
friend void func(const C<U> &m) noexcept(N == 0);
};

template <int N, typename U>
void func(const C<U> &m) noexcept(N == 0) {}

int main() {
C<int> t;
return 0;
}
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