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Before C++20, MSVC was supporting not mentioning the template argument of the
base class when initializing a class inheriting a templated base class.
So the following code compiled correctly:
template <class T>
class Base {
};
template <class T>
class Derived : public Base<T> {
public:
Derived() : Base() {}
};
void test() {
Derived<int> d;
}
See https://godbolt.org/z/Pxxe7nccx for a conformance view.
This patch adds support for such construct when in MSVC compatibility mode.
Repository:
rG LLVM Github Monorepo
https://reviews.llvm.org/D124666
Files:
clang/include/clang/Basic/DiagnosticSemaKinds.td
clang/lib/Sema/SemaDeclCXX.cpp
clang/test/SemaTemplate/ms-unqualified-base-class.cpp
Index: clang/test/SemaTemplate/ms-unqualified-base-class.cpp
===================================================================
--- /dev/null
+++ clang/test/SemaTemplate/ms-unqualified-base-class.cpp
@@ -0,0 +1,80 @@
+// RUN: %clang_cc1 -std=c++17 -fms-compatibility -fsyntax-only -verify=before,expected %s
+// RUN: %clang_cc1 -std=c++17 -fms-compatibility -fdelayed-template-parsing -fsyntax-only -verify=before,expected %s
+// RUN: %clang_cc1 -std=c++20 -fms-compatibility -fsyntax-only -verify=after,expected %s
+// RUN: %clang_cc1 -std=c++20 -fms-compatibility -fdelayed-template-parsing -fsyntax-only -verify=after,expected %s
+
+template <class T>
+class Base {
+};
+
+template <class T>
+class Derived : public Base<T> {
+public:
+ // after-error@+1 {{member initializer 'Base' does not name a non-static data member or base class}}
+ Derived() : Base() {} // before-warning {{unqualified base initializer of class templates is a Microsoft extension}}
+};
+
+template<class T> struct AggregateBase {
+ T i;
+};
+
+template<class T>
+struct AggregateDerived : public AggregateBase<T> {
+ int i;
+
+ // after-error@+1 {{member initializer 'AggregateBase' does not name a non-static data member or base class}}
+ AggregateDerived(T j) : AggregateBase{ 4 }, i{ j } {} // before-warning {{unqualified base initializer of class templates is a Microsoft extension}}
+ int f() {
+ return i + AggregateBase::i; // expected-warning {{use of undeclared identifier 'AggregateBase'; unqualified lookup into dependent bases of class template 'AggregateDerived' is a Microsoft extension}}
+ }
+};
+
+template<class T, typename U> struct MultiTypesBase {
+};
+
+template<class T, class U>
+struct MultiTypesDerived : public MultiTypesBase<T, U> {
+ // after-error@+1 {{member initializer 'MultiTypesBase' does not name a non-static data member or base class}}
+ MultiTypesDerived() : MultiTypesBase{} {} // before-warning {{unqualified base initializer of class templates is a Microsoft extension}}
+};
+
+template<int I> struct IntegerBase {
+};
+
+template<int I>
+struct IntegerDerived : public IntegerBase<I> {
+ // after-error@+1 {{member initializer 'IntegerBase' does not name a non-static data member or base class}}
+ IntegerDerived() : IntegerBase{} {} // before-warning {{unqualified base initializer of class templates is a Microsoft extension}}
+};
+
+template<class T> struct ConformingBase {
+ T i;
+};
+
+template<class T>
+struct ConformingDerived : public ConformingBase<T> {
+ int i;
+
+ ConformingDerived(T j) : ConformingBase<T>{ 4 }, i{ j } {}
+ int f() {
+ return i + ConformingBase<T>::i;
+ }
+};
+
+int main() {
+ int I;
+ Derived<int> t;
+
+ AggregateDerived<int> AD{ 2 };
+ AD.AggregateBase::i = 3;
+ I = AD.f();
+
+ MultiTypesDerived<int, double> MTD;
+
+ IntegerDerived<4> ID;
+
+ ConformingDerived<int> CD{ 2 };
+ I = CD.f();
+
+ return I;
+}
Index: clang/lib/Sema/SemaDeclCXX.cpp
===================================================================
--- clang/lib/Sema/SemaDeclCXX.cpp
+++ clang/lib/Sema/SemaDeclCXX.cpp
@@ -4345,6 +4345,15 @@
}
}
+ if (getLangOpts().MSVCCompat && !getLangOpts().CPlusPlus20) {
+ auto UnqualifiedBase = R.getAsSingle<ClassTemplateDecl>();
+ if (UnqualifiedBase) {
+ Diag(IdLoc, diag::ext_unqualified_base_class)
+ << SourceRange(IdLoc, Init->getSourceRange().getEnd());
+ BaseType = UnqualifiedBase->getInjectedClassNameSpecialization();
+ }
+ }
+
if (!TyD && BaseType.isNull()) {
Diag(IdLoc, diag::err_mem_init_not_member_or_class)
<< MemberOrBase << SourceRange(IdLoc,Init->getSourceRange().getEnd());
Index: clang/include/clang/Basic/DiagnosticSemaKinds.td
===================================================================
--- clang/include/clang/Basic/DiagnosticSemaKinds.td
+++ clang/include/clang/Basic/DiagnosticSemaKinds.td
@@ -5508,6 +5508,9 @@
def ext_found_later_in_class : ExtWarn<
"use of member %0 before its declaration is a Microsoft extension">,
InGroup<MicrosoftTemplate>;
+def ext_unqualified_base_class : ExtWarn<
+ "unqualified base initializer of class templates is a Microsoft extension">,
+ InGroup<MicrosoftTemplate>;
def note_dependent_member_use : Note<
"must qualify identifier to find this declaration in dependent base class">;
def err_not_found_by_two_phase_lookup : Error<"call to function %0 that is neither "
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