https://github.com/sdkrystian created
https://github.com/llvm/llvm-project/pull/86817
Currently, clang erroneously rejects the following:
```cpp
template<typename T>
struct A
{
template<typename U>
auto f();
};
template<>
template<typename U>
auto A<int>::f(); // error: conflicting types for 'f'
```
This happens because the explicit specialization of `f` has its return type
replaced with a dependent `AutoType` in `ActOnFunctionDeclarator`, but no such
replacement occurs for the implicitly instantiated function template
`A<int>::f`. Since the return types don't match, the explicit specialization is
diagnosed as an invalid redeclaration.
This patch moves the replacement of the return type to
`CheckFunctionDeclaration` so it also happens during instantiation.
`setObjectOfFriendDecl` will have been called by then, so the `isFriend &&
CurContext->isDependentContext()` condition is made redundant & removed (as it
already happens in `DeclContext::isDependentContext`). `Sema::IsOverload` only
checks the _declared_ return type (which isn't changed by the adjustment), so
adjusting the return type afterwards should be safe.
>From 647052c0545d73fbf5cb4fa4930bf5c38b575985 Mon Sep 17 00:00:00 2001
From: Krystian Stasiowski <sdkryst...@gmail.com>
Date: Wed, 27 Mar 2024 11:23:19 -0400
Subject: [PATCH] [Clang][Sema] Fix explicit specializations of member function
templates with a deduced return type
---
.../clang-tidy/infrastructure/diagnostic.cpp | 2 -
clang/lib/Sema/SemaDecl.cpp | 50 ++++++++++++-------
.../SemaCXX/deduced-return-type-cxx14.cpp | 18 +++++++
3 files changed, 51 insertions(+), 19 deletions(-)
diff --git a/clang-tools-extra/test/clang-tidy/infrastructure/diagnostic.cpp
b/clang-tools-extra/test/clang-tidy/infrastructure/diagnostic.cpp
index d0efc5ca763753..e333c83b895ee7 100644
--- a/clang-tools-extra/test/clang-tidy/infrastructure/diagnostic.cpp
+++ b/clang-tools-extra/test/clang-tidy/infrastructure/diagnostic.cpp
@@ -68,6 +68,4 @@ auto S<>::foo(auto)
{
return 1;
}
-// CHECK8: error: conflicting types for 'foo' [clang-diagnostic-error]
-// CHECK8: note: previous declaration is here
#endif
diff --git a/clang/lib/Sema/SemaDecl.cpp b/clang/lib/Sema/SemaDecl.cpp
index 9a286e0b26a4c6..d7388f6cc6aa2a 100644
--- a/clang/lib/Sema/SemaDecl.cpp
+++ b/clang/lib/Sema/SemaDecl.cpp
@@ -10119,23 +10119,6 @@ Sema::ActOnFunctionDeclarator(Scope *S, Declarator &D,
DeclContext *DC,
Diag(D.getDeclSpec().getVirtualSpecLoc(), diag::err_auto_fn_virtual);
}
- if (getLangOpts().CPlusPlus14 &&
- (NewFD->isDependentContext() ||
- (isFriend && CurContext->isDependentContext())) &&
- NewFD->getReturnType()->isUndeducedType()) {
- // If the function template is referenced directly (for instance, as a
- // member of the current instantiation), pretend it has a dependent type.
- // This is not really justified by the standard, but is the only sane
- // thing to do.
- // FIXME: For a friend function, we have not marked the function as being
- // a friend yet, so 'isDependentContext' on the FD doesn't work.
- const FunctionProtoType *FPT =
- NewFD->getType()->castAs<FunctionProtoType>();
- QualType Result = SubstAutoTypeDependent(FPT->getReturnType());
- NewFD->setType(Context.getFunctionType(Result, FPT->getParamTypes(),
- FPT->getExtProtoInfo()));
- }
-
// C++ [dcl.fct.spec]p3:
// The inline specifier shall not appear on a block scope function
// declaration.
@@ -12107,6 +12090,39 @@ bool Sema::CheckFunctionDeclaration(Scope *S,
FunctionDecl *NewFD,
CheckConstPureAttributesUsage(*this, NewFD);
+ // C++23 [dcl.spec.auto.general]p12:
+ // Return type deduction for a templated function with a placeholder in its
+ // declared type occurs when the definition is instantiated even if the
+ // function body contains a return statement with a non-type-dependent
+ // operand.
+ //
+ // C++23 [temp.dep.expr]p3:
+ // An id-expression is type-dependent if it is a template-id that is not a
+ // concept-id and is dependent; or if its terminal name is:
+ // - [...]
+ // - associated by name lookup with one or more declarations of member
+ // functions of a class that is the current instantiation declared with a
+ // return type that contains a placeholder type,
+ // - [...]
+ //
+ // If this is a templated function with a placeholder in its return type,
+ // make the placeholder type dependent since it won't be deduced until the
+ // definition is instantiated. We do this here because it needs to happen
+ // for implicitly instantiated member functions/member function templates.
+ if (getLangOpts().CPlusPlus14 &&
+ (NewFD->isDependentContext() &&
+ NewFD->getReturnType()->isUndeducedType())) {
+ // If the function template is referenced directly (for instance, as a
+ // member of the current instantiation), pretend it has a dependent type.
+ // This is not really justified by the standard, but is the only sane
+ // thing to do.
+ const FunctionProtoType *FPT =
+ NewFD->getType()->castAs<FunctionProtoType>();
+ QualType NewReturnType = SubstAutoTypeDependent(FPT->getReturnType());
+ NewFD->setType(Context.getFunctionType(NewReturnType, FPT->getParamTypes(),
+ FPT->getExtProtoInfo()));
+ }
+
// C++11 [dcl.constexpr]p8:
// A constexpr specifier for a non-static member function that is not
// a constructor declares that member function to be const.
diff --git a/clang/test/SemaCXX/deduced-return-type-cxx14.cpp
b/clang/test/SemaCXX/deduced-return-type-cxx14.cpp
index 431d77ca785b8e..c33e07088ba32f 100644
--- a/clang/test/SemaCXX/deduced-return-type-cxx14.cpp
+++ b/clang/test/SemaCXX/deduced-return-type-cxx14.cpp
@@ -237,6 +237,24 @@ namespace Templates {
int (S::*(*p)())(double) = f;
int (S::*(*q)())(double) = f<S, double>;
}
+
+ template<typename T>
+ struct MemberSpecialization {
+ auto f();
+ template<typename U> auto f(U);
+ template<typename U> auto *f(U);
+ };
+
+ template<>
+ auto MemberSpecialization<int>::f();
+
+ template<>
+ template<typename U>
+ auto MemberSpecialization<int>::f(U);
+
+ template<>
+ template<typename U>
+ auto *MemberSpecialization<int>::f(U);
}
auto fwd_decl_using();
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