[clang] [Clang][Sema] Diagnose friend function specialization definitions (PR #72863)
Krystian Stasiowski via cfe-commits
cfe-commits at lists.llvm.org
Mon Nov 20 04:59:35 PST 2023
https://github.com/sdkrystian created https://github.com/llvm/llvm-project/pull/72863
Per [[class.friend]p6](http://eel.is/c++draft/class.friend#6) a friend function shall not be defined if its name isn't unqualified. A _template-id_ is not a name, meaning that a friend function specialization does not meet this criteria and cannot be defined.
GCC, MSVC, and EDG all consider friend function specialization definitions to be invalid de facto explicit specializations and diagnose them as such.
Instantiating a dependent friend function specialization definition [currently trips an assert](https://godbolt.org/z/sonhbKWKT) in `FunctionDecl::setFunctionTemplateSpecialization`. This happens because we do not set the `TemplateSpecializationKind` of the `FunctionDecl` created by template argument deduction to `TSK_ExplicitSpecialization` for friend functions [here](https://github.com/llvm/llvm-project/blob/main/clang/lib/Sema/SemaTemplate.cpp#L9600). I changed the assert condition because I believe this is the correct behavior.
>From 3e191f245325742338eba223a3f98b6bb5ad414b Mon Sep 17 00:00:00 2001
From: Krystian Stasiowski <sdkrystian at gmail.com>
Date: Mon, 20 Nov 2023 07:11:41 -0500
Subject: [PATCH] [Clang][Sema] Diagnose friend function specialization
definitions
---
clang/include/clang/Basic/DiagnosticSemaKinds.td | 2 ++
clang/lib/AST/Decl.cpp | 1 +
clang/lib/Sema/SemaDeclCXX.cpp | 14 ++++++++++++++
clang/test/CXX/class.access/class.friend/p6.cpp | 13 +++++++++++++
clang/test/CXX/temp/temp.decls/temp.friend/p1.cpp | 8 +++++---
.../CXX/temp/temp.spec/temp.expl.spec/p20-2.cpp | 3 ++-
6 files changed, 37 insertions(+), 4 deletions(-)
diff --git a/clang/include/clang/Basic/DiagnosticSemaKinds.td b/clang/include/clang/Basic/DiagnosticSemaKinds.td
index 3f6ca64baf23ae6..35acbb40a4b4f38 100644
--- a/clang/include/clang/Basic/DiagnosticSemaKinds.td
+++ b/clang/include/clang/Basic/DiagnosticSemaKinds.td
@@ -1669,6 +1669,8 @@ def err_qualified_friend_def : Error<
"friend function definition cannot be qualified with '%0'">;
def err_friend_def_in_local_class : Error<
"friend function cannot be defined in a local class">;
+def err_friend_specialization_def : Error<
+ "friend function specialization cannot be defined">;
def err_friend_not_first_in_declaration : Error<
"'friend' must appear first in a non-function declaration">;
def err_using_decl_friend : Error<
diff --git a/clang/lib/AST/Decl.cpp b/clang/lib/AST/Decl.cpp
index c5c2edf1bfe3aba..527ea6042daa034 100644
--- a/clang/lib/AST/Decl.cpp
+++ b/clang/lib/AST/Decl.cpp
@@ -4150,6 +4150,7 @@ FunctionDecl::setFunctionTemplateSpecialization(ASTContext &C,
assert(TSK != TSK_Undeclared &&
"Must specify the type of function template specialization");
assert((TemplateOrSpecialization.isNull() ||
+ getFriendObjectKind() != FOK_None ||
TSK == TSK_ExplicitSpecialization) &&
"Member specialization must be an explicit specialization");
FunctionTemplateSpecializationInfo *Info =
diff --git a/clang/lib/Sema/SemaDeclCXX.cpp b/clang/lib/Sema/SemaDeclCXX.cpp
index 3688192e6cbe5c5..2bfb02da08bde54 100644
--- a/clang/lib/Sema/SemaDeclCXX.cpp
+++ b/clang/lib/Sema/SemaDeclCXX.cpp
@@ -17960,6 +17960,20 @@ NamedDecl *Sema::ActOnFriendFunctionDecl(Scope *S, Declarator &D,
DCScope = getScopeForDeclContext(S, DC);
+ // C++ [class.friend]p6:
+ // A function may be defined in a friend declaration of a class if and
+ // only if the class is a non-local class, and the function name is
+ // unqualified.
+ //
+ // Per [basic.pre]p4, a template-id is not a name. Therefore, if we have
+ // a template-id, the function name is not unqualified because these is no
+ // name. While the wording requires some reading in-between the lines, GCC,
+ // MSVC, and EDG all consider a friend function specialization definitions
+ // to be de facto explicit specialization and diagnose them as such.
+ if (D.isFunctionDefinition() && isTemplateId) {
+ Diag(NameInfo.getBeginLoc(), diag::err_friend_specialization_def);
+ }
+
// - There's a non-dependent scope specifier, in which case we
// compute it and do a previous lookup there for a function
// or function template.
diff --git a/clang/test/CXX/class.access/class.friend/p6.cpp b/clang/test/CXX/class.access/class.friend/p6.cpp
index 2fe20fe77fc8f21..47104e29dc6b3c7 100644
--- a/clang/test/CXX/class.access/class.friend/p6.cpp
+++ b/clang/test/CXX/class.access/class.friend/p6.cpp
@@ -22,3 +22,16 @@ void local() {
friend void f() { } // expected-error{{friend function cannot be defined in a local class}}
};
}
+
+template<typename T> void f3(T);
+
+namespace N {
+ template<typename T> void f4(T);
+}
+
+template<typename T> struct A {
+ friend void f3(T) {}
+ friend void f3<T>(T) {} // expected-error{{friend function specialization cannot be defined}}
+ friend void N::f4(T) {} // expected-error{{friend function definition cannot be qualified with 'N::'}}
+ friend void N::f4<T>(T) {} // expected-error{{friend function definition cannot be qualified with 'N::'}}
+};
diff --git a/clang/test/CXX/temp/temp.decls/temp.friend/p1.cpp b/clang/test/CXX/temp/temp.decls/temp.friend/p1.cpp
index ab1b9f7a73eec89..974b080f2783934 100644
--- a/clang/test/CXX/temp/temp.decls/temp.friend/p1.cpp
+++ b/clang/test/CXX/temp/temp.decls/temp.friend/p1.cpp
@@ -17,7 +17,7 @@ template <typename T> struct Num {
for (U count = n.count_; count; --count)
x += a;
return x;
- }
+ }
};
friend Num operator+(const Num &a, const Num &b) {
@@ -145,7 +145,7 @@ namespace test5 {
namespace Dependent {
template<typename T, typename Traits> class X;
- template<typename T, typename Traits>
+ template<typename T, typename Traits>
X<T, Traits> operator+(const X<T, Traits>&, const T*);
template<typename T, typename Traits> class X {
@@ -249,7 +249,7 @@ namespace test11 {
};
template struct Foo::IteratorImpl<int>;
- template struct Foo::IteratorImpl<long>;
+ template struct Foo::IteratorImpl<long>;
}
// PR6827
@@ -373,6 +373,7 @@ template <class T> void foo() {} // expected-note{{candidate ignored: not a memb
}
using ns::foo;
template <class T> struct A {
+ // expected-error at +1{{friend function specialization cannot be defined}}
friend void foo<T>() {} // expected-error{{no candidate function template was found for dependent friend function template specialization}}
};
}
@@ -384,6 +385,7 @@ using ns1::foo; // expected-note {{found by name lookup}}
using ns2::foo; // expected-note {{found by name lookup}}
template <class T> class A {
+ // expected-error at +1{{friend function specialization cannot be defined}}
friend void foo<T>() {} // expected-error {{ambiguous}} expected-error{{no candidate function template was found for dependent friend function template specialization}}
};
}
diff --git a/clang/test/CXX/temp/temp.spec/temp.expl.spec/p20-2.cpp b/clang/test/CXX/temp/temp.spec/temp.expl.spec/p20-2.cpp
index 7bc5f13cd7375bd..8fdc7d454828a88 100644
--- a/clang/test/CXX/temp/temp.spec/temp.expl.spec/p20-2.cpp
+++ b/clang/test/CXX/temp/temp.spec/temp.expl.spec/p20-2.cpp
@@ -4,7 +4,8 @@ void f(T);
template<typename T>
struct A {
- // expected-error at +1{{cannot declare an explicit specialization in a friend}}
+ // expected-error at +2{{cannot declare an explicit specialization in a friend}}
+ // expected-error at +1{{friend function specialization cannot be defined}}
template <> friend void f<>(int) {}
};
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