Warn about dllexported explicit class template instantiation declarations (PR22035)

[hans]

Summary

Clang would previously become confused and crash here.

It does not make a lot of sense to export these, so warning seems appropriate.

MSVC will export some member functions for this kind of specializations, whereas MinGW ignores the dllexport-edness. The latter behaviour seems better.

[rnk]

David really wanted this to be an error, but personally I think it should be a warning. Have you encountered this warning in Chrome?

[majnemer]

LGTM.

[hans]

David really wanted this to be an error, but personally I think it should be a warning. Have you encountered this warning in Chrome?

No, we don't hit this in Chromium.

cfe/trunk/include/clang/Basic/DiagnosticSemaKinds.td

def err_attribute_dll_deleted : Error<
   "attribute %q0 cannot be applied to a deleted function">;
 def err_attribute_dllimport_data_definition : Error<
   "definition of dllimport data">;
 def err_attribute_dllimport_static_field_definition : Error<
   "definition of dllimport static field not allowed">;
 def warn_attribute_dllimport_static_field_definition : Warning<
   "definition of dllimport static field">,
   InGroup<DiagGroup<"dllimport-static-field-def">>;
+def warn_attribute_dllexport_explicit_instantiation_decl : Warning<
+  "explicit instantiation declaration should not be 'dllexport'">,
+  InGroup<DiagGroup<"dllexport-explicit-instantation-decl">>;
 def warn_invalid_initializer_from_system_header : Warning<
   "invalid constructor form class in system header, should not be explicit">,
   InGroup<DiagGroup<"invalid-initializer-from-system-header">>;
 def note_used_in_initialization_here : Note<"used in initialization here">;
 def err_attribute_dll_member_of_dll_class : Error<
   "attribute %q0 cannot be applied to member of %q1 class">;
 def warn_attribute_dll_instantiated_base_class : Warning<
   "propagating dll attribute to %select{already instantiated|explicitly specialized}0 "

cfe/trunk/lib/Sema/SemaDeclCXX.cpp

static void checkDLLAttribute(Sema &S, CXXRecordDecl *Class) {
   if (Class->getDescribedClassTemplate())
     // Don't inherit dll attribute until the template is instantiated.
     return;
 
   // The class is either imported or exported.
   const bool ClassExported = ClassAttr->getKind() == attr::DLLExport;
   const bool ClassImported = !ClassExported;
 
+  TemplateSpecializationKind TSK = Class->getTemplateSpecializationKind();
+
+  // Don't dllexport explicit class template instantiation declarations.
+  if (ClassExported && TSK == TSK_ExplicitInstantiationDeclaration) {
+    Class->dropAttr<DLLExportAttr>();
+    return;
+  }
+
   // Force declaration of implicit members so they can inherit the attribute.
   S.ForceDeclarationOfImplicitMembers(Class);
 
   // FIXME: MSVC's docs say all bases must be exportable, but this doesn't
   // seem to be true in practice?
 
-  TemplateSpecializationKind TSK =
-    Class->getTemplateSpecializationKind();
-
   for (Decl *Member : Class->decls()) {
     VarDecl *VD = dyn_cast<VarDecl>(Member);
     CXXMethodDecl *MD = dyn_cast<CXXMethodDecl>(Member);
 
     // Only methods and static fields inherit the attributes.
     if (!VD && !MD)
       continue;
 

cfe/trunk/lib/Sema/SemaTemplate.cpp

Diag(ClassTemplate->getTemplatedDecl()->getLocation(),
          diag::note_previous_use);
     Kind = ClassTemplate->getTemplatedDecl()->getTagKind();
   }
 
   // C++0x [temp.explicit]p2:
   //   There are two forms of explicit instantiation: an explicit instantiation
   //   definition and an explicit instantiation declaration. An explicit
   //   instantiation declaration begins with the extern keyword. [...]
-  TemplateSpecializationKind TSK
-    = ExternLoc.isInvalid()? TSK_ExplicitInstantiationDefinition
+  TemplateSpecializationKind TSK = ExternLoc.isInvalid()
+                                       ? TSK_ExplicitInstantiationDefinition
                                        : TSK_ExplicitInstantiationDeclaration;
 
+  if (TSK == TSK_ExplicitInstantiationDeclaration) {
+    // Check for dllexport class template instantiation declarations.
+    for (AttributeList *A = Attr; A; A = A->getNext()) {
+      if (A->getKind() == AttributeList::AT_DLLExport) {
+        Diag(ExternLoc,
+             diag::warn_attribute_dllexport_explicit_instantiation_decl);
+        Diag(A->getLoc(), diag::note_attribute);
+        break;
+      }
+    }
+
+    if (auto *A = ClassTemplate->getTemplatedDecl()->getAttr<DLLExportAttr>()) {
+      Diag(ExternLoc,
+           diag::warn_attribute_dllexport_explicit_instantiation_decl);
+      Diag(A->getLocation(), diag::note_attribute);
+    }
+  }
+
   // Translate the parser's template argument list in our AST format.
   TemplateArgumentListInfo TemplateArgs(LAngleLoc, RAngleLoc);
   translateTemplateArguments(TemplateArgsIn, TemplateArgs);
 
   // Check that the template argument list is well-formed for this
   // template.
   SmallVector<TemplateArgument, 4> Converted;
   if (CheckTemplateArgumentList(ClassTemplate, TemplateNameLoc,

cfe/trunk/test/CodeGenCXX/dllexport.cpp

template <typename T> struct ExplicitInstConstexprMembers {
   ExplicitInstConstexprMembers(const ExplicitInstConstexprMembers&) = default;
   // M32-DAG: define weak_odr dllexport x86_thiscallcc %struct.ExplicitInstConstexprMembers* @"\01??0?$ExplicitInstConstexprMembers@X@@QAE@ABU0@@Z"
 
   constexpr int f() const { return 42; }
   // M32-DAG: define weak_odr dllexport x86_thiscallcc i32 @"\01?f@?$ExplicitInstConstexprMembers@X@@QBEHXZ"
 };
 template struct __declspec(dllexport) ExplicitInstConstexprMembers<void>;
 
+template <typename T> struct ExplicitInstantiationDeclTemplate { void f() {} };
+extern template struct __declspec(dllexport) ExplicitInstantiationDeclTemplate<int>;
+USEMEMFUNC(ExplicitInstantiationDeclTemplate<int>, f);
+// M32-DAG: {{declare|define available_externally}} x86_thiscallcc void @"\01?f@?$ExplicitInstantiationDeclTemplate@H@@QAEXXZ"
+
+template <typename T> struct __declspec(dllexport) ExplicitInstantiationDeclExportedTemplate { void f() {} };
+extern template struct ExplicitInstantiationDeclExportedTemplate<int>;
+USEMEMFUNC(ExplicitInstantiationDeclExportedTemplate<int>, f);
+// M32-DAG: {{declare|define available_externally}} x86_thiscallcc void @"\01?f@?$ExplicitInstantiationDeclExportedTemplate@H@@QAEXXZ"
+
+
 //===----------------------------------------------------------------------===//
 // Classes with template base classes
 //===----------------------------------------------------------------------===//
 
 template <typename T> struct ClassTemplate { void func() {} };
 template <typename T> struct __declspec(dllexport) ExportedClassTemplate { void func() {} };
 template <typename T> struct __declspec(dllimport) ImportedClassTemplate { void func(); };
 template <typename T> void ImportedClassTemplate<T>::func() {}

cfe/trunk/test/SemaCXX/dllexport.cpp

 struct IncompleteType;
 template <typename T> struct __declspec(dllexport) ImplicitlyInstantiatedExportedTemplate {
   int f() { return sizeof(T); } // no-error
 };
 ImplicitlyInstantiatedExportedTemplate<IncompleteType> implicitlyInstantiatedExportedTemplate;
 
 // Don't instantiate class members of templates with explicit instantiation declarations, even if they are exported.
 struct IncompleteType2;
-template <typename T> struct __declspec(dllexport) ExportedTemplateWithExplicitInstantiationDecl {
+template <typename T> struct __declspec(dllexport) ExportedTemplateWithExplicitInstantiationDecl { // expected-note{{attribute is here}}
   int f() { return sizeof(T); } // no-error
 };
-extern template struct ExportedTemplateWithExplicitInstantiationDecl<IncompleteType2>;
+extern template struct ExportedTemplateWithExplicitInstantiationDecl<IncompleteType2>; // expected-warning{{explicit instantiation declaration should not be 'dllexport'}}
 
 // Instantiate class members for explicitly instantiated exported templates.
 struct IncompleteType3; // expected-note{{forward declaration of 'IncompleteType3'}}
 template <typename T> struct __declspec(dllexport) ExplicitlyInstantiatedExportedTemplate {
   int f() { return sizeof(T); } // expected-error{{invalid application of 'sizeof' to an incomplete type 'IncompleteType3'}}
 };
 template struct ExplicitlyInstantiatedExportedTemplate<IncompleteType3>; // expected-note{{in instantiation of member function 'ExplicitlyInstantiatedExportedTemplate<IncompleteType3>::f' requested here}}
 

 
 // Don't instantiate members of explicitly exported class templates that are base classes of exported classes.
 struct IncompleteType5;
 template <typename T> struct __declspec(dllexport) ExportedBaseClassTemplateOfExportedClass {
   int f() { return sizeof(T); }; // no-error
 };
 struct __declspec(dllexport) ExportedBaseClass2 : public ExportedBaseClassTemplateOfExportedClass<IncompleteType5> {};
 
+// Warn about explicit instantiation declarations of dllexport classes.
+template <typename T> struct ExplicitInstantiationDeclTemplate {};
+extern template struct __declspec(dllexport) ExplicitInstantiationDeclTemplate<int>; // expected-warning{{explicit instantiation declaration should not be 'dllexport'}} expected-note{{attribute is here}}
 
+template <typename T> struct __declspec(dllexport) ExplicitInstantiationDeclExportedTemplate {}; // expected-note{{attribute is here}}
+extern template struct ExplicitInstantiationDeclExportedTemplate<int>; // expected-warning{{explicit instantiation declaration should not be 'dllexport'}}
 
 //===----------------------------------------------------------------------===//
 // Classes with template base classes
 //===----------------------------------------------------------------------===//
 
 template <typename T> class ClassTemplate {};
 template <typename T> class __declspec(dllexport) ExportedClassTemplate {};
 template <typename T> class __declspec(dllimport) ImportedClassTemplate {};