Downgrade "definition of dllimport static field" error to warning for class templates (PR19902)

[hans]

Summary

This allows us to compile the following kind of code, which occurs in MSVC headers:

template <typename> struct S {
  __declspec(dllimport) static int x;
};
template <typename T> int S<T>::x;

Please take a look.

[hans]

Uploading new version of the patch.

[rnk]

lgtm

Alp's suggested 'IsInvalid' renaming seems reasonable.

[hans]

Closed by commit rL210141 (authored by @hans).

include/clang/Basic/DiagnosticSemaKinds.td

 def err_attribute_dllimport_function_definition : Error<
   "dllimport cannot be applied to non-inline function definition">;
 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 not allowed">,
+  InGroup<DiagGroup<"dllimport-static-field-def">>;
 def err_attribute_dll_member_of_dll_class : Error<
   "attribute %q0 cannot be applied to member of %q1 class">;
 def err_attribute_weakref_not_static : Error<
   "weakref declaration must have internal linkage">;
 def err_attribute_weakref_not_global_context : Error<
   "weakref declaration of %0 must be in a global context">;
 def err_attribute_weakref_without_alias : Error<
   "weakref declaration of %0 must also have an alias attribute">;

lib/Sema/SemaDecl.cpp

if (!VD)
     return;
 
   checkAttributesAfterMerging(*this, *VD);
 
   // Imported static data members cannot be defined out-of-line.
   if (const DLLImportAttr *IA = VD->getAttr<DLLImportAttr>()) {
     if (VD->isStaticDataMember() && VD->isOutOfLine() &&
         VD->isThisDeclarationADefinition()) {
+      // Definitions of dllimport class template static data members occurs
+      // in MSVC header files. Downgrade to a warning.
+      bool JustWarn = cast<CXXRecordDecl>(VD->getFirstDecl()->getDeclContext())
+                          ->getDescribedClassTemplate();
+
       Diag(VD->getLocation(),
-           diag::err_attribute_dllimport_static_field_definition);
+           JustWarn ? diag::warn_attribute_dllimport_static_field_definition
+                    : diag::err_attribute_dllimport_static_field_definition);
       Diag(IA->getLocation(), diag::note_attribute);
+      if (!JustWarn)
         VD->setInvalidDecl();
     }
   }
 
   if (UsedAttr *Attr = VD->getAttr<UsedAttr>()) {
     if (!Attr->isInherited() && !VD->isThisDeclarationADefinition()) {
       Diag(Attr->getLocation(), diag::warn_attribute_ignored) << Attr;
       VD->dropAttr<UsedAttr>();
     }

test/SemaCXX/dllimport.cpp

 template<typename T>        void ImportClassTmplMembers<T>::normalInlineDecl() {}
 template<typename T>        void ImportClassTmplMembers<T>::virtualDef() {} // expected-warning{{'ImportClassTmplMembers::virtualDef' redeclared without 'dllimport' attribute: previous 'dllimport' ignored}}
 template<typename T> inline void ImportClassTmplMembers<T>::virtualInlineDef() {}
 template<typename T>        void ImportClassTmplMembers<T>::virtualInlineDecl() {}
 template<typename T>        void ImportClassTmplMembers<T>::staticDef() {} // expected-warning{{'ImportClassTmplMembers::staticDef' redeclared without 'dllimport' attribute: previous 'dllimport' ignored}}
 template<typename T> inline void ImportClassTmplMembers<T>::staticInlineDef() {}
 template<typename T>        void ImportClassTmplMembers<T>::staticInlineDecl() {}
 
-template<typename T>        int  ImportClassTmplMembers<T>::StaticFieldDef; // expected-error{{definition of dllimport static field not allowed}}
-template<typename T> const  int  ImportClassTmplMembers<T>::StaticConstFieldDef = 1; // expected-error{{definition of dllimport static field not allowed}}
-template<typename T> constexpr int ImportClassTmplMembers<T>::ConstexprFieldDef; // expected-error{{definition of dllimport static field not allowed}}
+template<typename T>        int  ImportClassTmplMembers<T>::StaticFieldDef; // expected-warning{{definition of dllimport static field not allowed}}
+template<typename T> const  int  ImportClassTmplMembers<T>::StaticConstFieldDef = 1; // expected-warning{{definition of dllimport static field not allowed}}
+template<typename T> constexpr int ImportClassTmplMembers<T>::ConstexprFieldDef; // expected-warning{{definition of dllimport static field not allowed}}
 
 
 // Redeclarations cannot add dllimport.
 template<typename T>
 struct CTMR /*ClassTmplMemberRedecl*/ {
                  void normalDef();         // expected-note{{previous declaration is here}}
                  void normalInlineDef();   // expected-note{{previous declaration is here}}
           inline void normalInlineDecl();  // expected-note{{previous declaration is here}}

 template<typename T> __declspec(dllimport) inline void CTMR<T>::virtualInlineDef() {}  // expected-error{{redeclaration of 'CTMR::virtualInlineDef' cannot add 'dllimport' attribute}}
 template<typename T> __declspec(dllimport)        void CTMR<T>::virtualInlineDecl() {} // expected-error{{redeclaration of 'CTMR::virtualInlineDecl' cannot add 'dllimport' attribute}}
 template<typename T> __declspec(dllimport)        void CTMR<T>::staticDef() {}         // expected-error{{redeclaration of 'CTMR::staticDef' cannot add 'dllimport' attribute}}
                                                                                        // expected-error@-1{{dllimport cannot be applied to non-inline function definition}}
 template<typename T> __declspec(dllimport) inline void CTMR<T>::staticInlineDef() {}   // expected-error{{redeclaration of 'CTMR::staticInlineDef' cannot add 'dllimport' attribute}}
 template<typename T> __declspec(dllimport)        void CTMR<T>::staticInlineDecl() {}  // expected-error{{redeclaration of 'CTMR::staticInlineDecl' cannot add 'dllimport' attribute}}
 
 template<typename T> __declspec(dllimport)        int  CTMR<T>::StaticField = 1;       // expected-error{{redeclaration of 'CTMR::StaticField' cannot add 'dllimport' attribute}}
-                                                                                       // expected-error@-1{{definition of dllimport static field not allowed}}
+                                                                                       // expected-warning@-1{{definition of dllimport static field not allowed}}
                                                                                        // expected-note@-2{{attribute is here}}
 template<typename T> __declspec(dllimport) const  int  CTMR<T>::StaticConstField = 1;  // expected-error{{redeclaration of 'CTMR::StaticConstField' cannot add 'dllimport' attribute}}
-                                                                                       // expected-error@-1{{definition of dllimport static field not allowed}}
+                                                                                       // expected-warning@-1{{definition of dllimport static field not allowed}}
                                                                                        // expected-note@-2{{attribute is here}}
 template<typename T> __declspec(dllimport) constexpr int CTMR<T>::ConstexprField;      // expected-error{{redeclaration of 'CTMR::ConstexprField' cannot add 'dllimport' attribute}}
-                                                                                       // expected-error@-1{{definition of dllimport static field not allowed}}
+                                                                                       // expected-warning@-1{{definition of dllimport static field not allowed}}
                                                                                        // expected-note@-2{{attribute is here}}
 
 
 
 //===----------------------------------------------------------------------===//
 // Class template member templates
 //===----------------------------------------------------------------------===//
 

 template<typename T> template<typename U>        void ImportClsTmplMemTmpl<T>::normalDef() {} // expected-warning{{'ImportClsTmplMemTmpl::normalDef' redeclared without 'dllimport' attribute: previous 'dllimport' ignored}}
 template<typename T> template<typename U> inline void ImportClsTmplMemTmpl<T>::normalInlineDef() {}
 template<typename T> template<typename U>        void ImportClsTmplMemTmpl<T>::normalInlineDecl() {}
 template<typename T> template<typename U>        void ImportClsTmplMemTmpl<T>::staticDef() {} // expected-warning{{'ImportClsTmplMemTmpl::staticDef' redeclared without 'dllimport' attribute: previous 'dllimport' ignored}}
 template<typename T> template<typename U> inline void ImportClsTmplMemTmpl<T>::staticInlineDef() {}
 template<typename T> template<typename U>        void ImportClsTmplMemTmpl<T>::staticInlineDecl() {}
 
 #if __has_feature(cxx_variable_templates)
-template<typename T> template<typename U>        int  ImportClsTmplMemTmpl<T>::StaticFieldDef; // expected-error{{definition of dllimport static field not allowed}}
-template<typename T> template<typename U> const  int  ImportClsTmplMemTmpl<T>::StaticConstFieldDef = 1; // expected-error{{definition of dllimport static field not allowed}}
-template<typename T> template<typename U> constexpr int ImportClsTmplMemTmpl<T>::ConstexprFieldDef; // expected-error{{definition of dllimport static field not allowed}}
+template<typename T> template<typename U>        int  ImportClsTmplMemTmpl<T>::StaticFieldDef; // expected-warning{{definition of dllimport static field not allowed}}
+template<typename T> template<typename U> const  int  ImportClsTmplMemTmpl<T>::StaticConstFieldDef = 1; // expected-warning{{definition of dllimport static field not allowed}}
+template<typename T> template<typename U> constexpr int ImportClsTmplMemTmpl<T>::ConstexprFieldDef; // expected-warning{{definition of dllimport static field not allowed}}
 #endif // __has_feature(cxx_variable_templates)
 
 
 // Redeclarations cannot add dllimport.
 template<typename T>
 struct CTMTR /*ClassTmplMemberTmplRedecl*/ {
   template<typename U>               void normalDef();         // expected-note{{previous declaration is here}}
   template<typename U>               void normalInlineDef();   // expected-note{{previous declaration is here}}

 template<typename T> template<typename U> __declspec(dllimport)        void CTMTR<T>::normalInlineDecl() {}  // expected-error{{redeclaration of 'CTMTR::normalInlineDecl' cannot add 'dllimport' attribute}}
 template<typename T> template<typename U> __declspec(dllimport)        void CTMTR<T>::staticDef() {}         // expected-error{{redeclaration of 'CTMTR::staticDef' cannot add 'dllimport' attribute}}
                                                                                                              // expected-error@-1{{dllimport cannot be applied to non-inline function definition}}
 template<typename T> template<typename U> __declspec(dllimport) inline void CTMTR<T>::staticInlineDef() {}   // expected-error{{redeclaration of 'CTMTR::staticInlineDef' cannot add 'dllimport' attribute}}
 template<typename T> template<typename U> __declspec(dllimport)        void CTMTR<T>::staticInlineDecl() {}  // expected-error{{redeclaration of 'CTMTR::staticInlineDecl' cannot add 'dllimport' attribute}}
 
 #if __has_feature(cxx_variable_templates)
 template<typename T> template<typename U> __declspec(dllimport)        int  CTMTR<T>::StaticField = 1;       // expected-error{{redeclaration of 'CTMTR::StaticField' cannot add 'dllimport' attribute}}
-                                                                                                             // expected-error@-1{{definition of dllimport static field not allowed}}
+                                                                                                             // expected-warning@-1{{definition of dllimport static field not allowed}}
                                                                                                              // expected-note@-2{{attribute is here}}
 template<typename T> template<typename U> __declspec(dllimport) const  int  CTMTR<T>::StaticConstField = 1;  // expected-error{{redeclaration of 'CTMTR::StaticConstField' cannot add 'dllimport' attribute}}
-                                                                                                             // expected-error@-1{{definition of dllimport static field not allowed}}
+                                                                                                             // expected-warning@-1{{definition of dllimport static field not allowed}}
                                                                                                              // expected-note@-2{{attribute is here}}
 template<typename T> template<typename U> __declspec(dllimport) constexpr int CTMTR<T>::ConstexprField;      // expected-error{{redeclaration of 'CTMTR::ConstexprField' cannot add 'dllimport' attribute}}
-                                                                                                             // expected-error@-1{{definition of dllimport static field not allowed}}
+                                                                                                             // expected-warning@-1{{definition of dllimport static field not allowed}}
                                                                                                              // expected-note@-2{{attribute is here}}
 #endif // __has_feature(cxx_variable_templates)
 
 
 
 //===----------------------------------------------------------------------===//
 // Classes
 //===----------------------------------------------------------------------===//