Warn about dllexported explicit class template instantiation declarations (PR22035)

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.

Differential Revision: http://reviews.llvm.org/D6984

llvm-svn: 226208

2 files changed, 29 insertions, 6 deletions

diff --git a/clang/lib/Sema/SemaDeclCXX.cpp b/clang/lib/Sema/SemaDeclCXX.cpp
index 54de4b97939..79529d5547e 100644
--- a/clang/lib/Sema/SemaDeclCXX.cpp
+++ b/clang/lib/Sema/SemaDeclCXX.cpp
@@ -4709,15 +4709,20 @@ static void checkDLLAttribute(Sema &S, CXXRecordDecl *Class) {
   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);
diff --git a/clang/lib/Sema/SemaTemplate.cpp b/clang/lib/Sema/SemaTemplate.cpp
index 67c36a5fb5e..254e78fa017 100644
--- a/clang/lib/Sema/SemaTemplate.cpp
+++ b/clang/lib/Sema/SemaTemplate.cpp
@@ -7165,9 +7165,27 @@ Sema::ActOnExplicitInstantiation(Scope *S,
   //   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
-                           : TSK_ExplicitInstantiationDeclaration;
+  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);