CWG issue 727: Fix numerous bugs in support for class-scope explicit

specializations for variable templates.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@359947 91177308-0d34-0410-b5e6-96231b3b80d8

3 files changed, 108 insertions, 97 deletions

diff --git a/lib/Sema/SemaExpr.cpp b/lib/Sema/SemaExpr.cpp
index 9564c8f0cb..2d9dbdd342 100644
--- a/lib/Sema/SemaExpr.cpp
+++ b/lib/Sema/SemaExpr.cpp
@@ -15721,7 +15721,12 @@ static void DoMarkVarDeclReferenced(Sema &SemaRef, SourceLocation Loc,
          "Invalid Expr argument to DoMarkVarDeclReferenced");
   Var->setReferenced();
 
-  TemplateSpecializationKind TSK = Var->getTemplateSpecializationKind();
+  if (Var->isInvalidDecl())
+    return;
+
+  auto *MSI = Var->getMemberSpecializationInfo();
+  TemplateSpecializationKind TSK = MSI ? MSI->getTemplateSpecializationKind()
+                                       : Var->getTemplateSpecializationKind();
 
   bool OdrUseContext = isOdrUseContext(SemaRef);
   bool UsableInConstantExpr =
@@ -15754,11 +15759,15 @@ static void DoMarkVarDeclReferenced(Sema &SemaRef, SourceLocation Loc,
         (TSK == TSK_ExplicitInstantiationDeclaration && UsableInConstantExpr);
 
     if (TryInstantiating) {
-      SourceLocation PointOfInstantiation = Var->getPointOfInstantiation();
+      SourceLocation PointOfInstantiation =
+          MSI ? MSI->getPointOfInstantiation() : Var->getPointOfInstantiation();
       bool FirstInstantiation = PointOfInstantiation.isInvalid();
       if (FirstInstantiation) {
         PointOfInstantiation = Loc;
-        Var->setTemplateSpecializationKind(TSK, PointOfInstantiation);
+        if (MSI)
+          MSI->setPointOfInstantiation(PointOfInstantiation);
+        else
+          Var->setTemplateSpecializationKind(TSK, PointOfInstantiation);
       }
 
       bool InstantiationDependent = false;
diff --git a/lib/Sema/SemaTemplate.cpp b/lib/Sema/SemaTemplate.cpp
index 939941a4c2..58ad439747 100644
--- a/lib/Sema/SemaTemplate.cpp
+++ b/lib/Sema/SemaTemplate.cpp
@@ -3927,13 +3927,6 @@ DeclResult Sema::ActOnVarTemplateSpecialization(
     Specialization->setAccess(VarTemplate->getAccess());
   }
 
-  // Link instantiations of static data members back to the template from
-  // which they were instantiated.
-  if (Specialization->isStaticDataMember())
-    Specialization->setInstantiationOfStaticDataMember(
-        VarTemplate->getTemplatedDecl(),
-        Specialization->getSpecializationKind());
-
   return Specialization;
 }
 
@@ -9198,7 +9191,7 @@ DeclResult Sema::ActOnExplicitInstantiation(Scope *S,
 
     if (!PrevTemplate) {
       if (!Prev || !Prev->isStaticDataMember()) {
-        // We expect to see a data data member here.
+        // We expect to see a static data member here.
         Diag(D.getIdentifierLoc(), diag::err_explicit_instantiation_not_known)
             << Name;
         for (LookupResult::iterator P = Previous.begin(), PEnd = Previous.end();
diff --git a/lib/Sema/SemaTemplateInstantiateDecl.cpp b/lib/Sema/SemaTemplateInstantiateDecl.cpp
index 90ae8989c1..653eb69326 100644
--- a/lib/Sema/SemaTemplateInstantiateDecl.cpp
+++ b/lib/Sema/SemaTemplateInstantiateDecl.cpp
@@ -3132,13 +3132,10 @@ TemplateDeclInstantiator::VisitClassTemplateSpecializationDecl(
          "for a member class template");
 
   // Lookup the already-instantiated declaration in the instantiation
-  // of the class template. FIXME: Diagnose or assert if this fails?
-  DeclContext::lookup_result Found
-    = Owner->lookup(ClassTemplate->getDeclName());
-  if (Found.empty())
-    return nullptr;
-  ClassTemplateDecl *InstClassTemplate
-    = dyn_cast<ClassTemplateDecl>(Found.front());
+  // of the class template.
+  ClassTemplateDecl *InstClassTemplate =
+      cast_or_null<ClassTemplateDecl>(SemaRef.FindInstantiatedDecl(
+          D->getLocation(), ClassTemplate, TemplateArgs));
   if (!InstClassTemplate)
     return nullptr;
 
@@ -3247,6 +3244,7 @@ TemplateDeclInstantiator::VisitClassTemplateSpecializationDecl(
   // Instantiate the members of the class-scope explicit specialization eagerly.
   // We don't have support for lazy instantiation of an explicit specialization
   // yet, and MSVC eagerly instantiates in this case.
+  // FIXME: This is wrong in standard C++.
   if (D->isThisDeclarationADefinition() &&
       SemaRef.InstantiateClass(D->getLocation(), InstD, D, TemplateArgs,
                                TSK_ImplicitInstantiation,
@@ -3264,6 +3262,12 @@ Decl *TemplateDeclInstantiator::VisitVarTemplateSpecializationDecl(
   assert(VarTemplate &&
          "A template specialization without specialized template?");
 
+  VarTemplateDecl *InstVarTemplate =
+      cast_or_null<VarTemplateDecl>(SemaRef.FindInstantiatedDecl(
+          D->getLocation(), VarTemplate, TemplateArgs));
+  if (!InstVarTemplate)
+    return nullptr;
+
   // Substitute the current template arguments.
   const TemplateArgumentListInfo &TemplateArgsInfo = D->getTemplateArgsInfo();
   VarTemplateArgsInfo.setLAngleLoc(TemplateArgsInfo.getLAngleLoc());
@@ -3275,28 +3279,33 @@ Decl *TemplateDeclInstantiator::VisitVarTemplateSpecializationDecl(
 
   // Check that the template argument list is well-formed for this template.
   SmallVector<TemplateArgument, 4> Converted;
-  if (SemaRef.CheckTemplateArgumentList(
-          VarTemplate, VarTemplate->getBeginLoc(),
-          const_cast<TemplateArgumentListInfo &>(VarTemplateArgsInfo), false,
-          Converted))
+  if (SemaRef.CheckTemplateArgumentList(InstVarTemplate, D->getLocation(),
+                                        VarTemplateArgsInfo, false, Converted))
     return nullptr;
 
-  // Find the variable template specialization declaration that
-  // corresponds to these arguments.
+  // Check whether we've already seen a declaration of this specialization.
   void *InsertPos = nullptr;
-  if (VarTemplateSpecializationDecl *VarSpec = VarTemplate->findSpecialization(
-          Converted, InsertPos))
-    // If we already have a variable template specialization, return it.
-    return VarSpec;
+  VarTemplateSpecializationDecl *PrevDecl =
+      InstVarTemplate->findSpecialization(Converted, InsertPos);
+
+  // Check whether we've already seen a conflicting instantiation of this
+  // declaration (for instance, if there was a prior implicit instantiation).
+  bool Ignored;
+  if (PrevDecl && SemaRef.CheckSpecializationInstantiationRedecl(
+                      D->getLocation(), D->getSpecializationKind(), PrevDecl,
+                      PrevDecl->getSpecializationKind(),
+                      PrevDecl->getPointOfInstantiation(), Ignored))
+    return nullptr;
 
-  return VisitVarTemplateSpecializationDecl(VarTemplate, D, InsertPos,
-                                            VarTemplateArgsInfo, Converted);
+  return VisitVarTemplateSpecializationDecl(
+      InstVarTemplate, D, InsertPos, VarTemplateArgsInfo, Converted, PrevDecl);
 }
 
 Decl *TemplateDeclInstantiator::VisitVarTemplateSpecializationDecl(
     VarTemplateDecl *VarTemplate, VarDecl *D, void *InsertPos,
     const TemplateArgumentListInfo &TemplateArgsInfo,
-    ArrayRef<TemplateArgument> Converted) {
+    ArrayRef<TemplateArgument> Converted,
+    VarTemplateSpecializationDecl *PrevDecl) {
 
   // Do substitution on the type of the declaration
   TypeSourceInfo *DI =
@@ -3323,8 +3332,8 @@ Decl *TemplateDeclInstantiator::VisitVarTemplateSpecializationDecl(
   if (SubstQualifier(D, Var))
     return nullptr;
 
-  SemaRef.BuildVariableInstantiation(Var, D, TemplateArgs, LateAttrs,
-                                     Owner, StartingScope);
+  SemaRef.BuildVariableInstantiation(Var, D, TemplateArgs, LateAttrs, Owner,
+                                     StartingScope, false, PrevDecl);
 
   return Var;
 }
@@ -4339,7 +4348,19 @@ void Sema::BuildVariableInstantiation(
     const MultiLevelTemplateArgumentList &TemplateArgs,
     LateInstantiatedAttrVec *LateAttrs, DeclContext *Owner,
     LocalInstantiationScope *StartingScope,
-    bool InstantiatingVarTemplate) {
+    bool InstantiatingVarTemplate,
+    VarTemplateSpecializationDecl *PrevDeclForVarTemplateSpecialization) {
+  // Instantiating a partial specialization to produce a partial
+  // specialization.
+  bool InstantiatingVarTemplatePartialSpec =
+      isa<VarTemplatePartialSpecializationDecl>(OldVar) &&
+      isa<VarTemplatePartialSpecializationDecl>(NewVar);
+  // Instantiating from a variable template (or partial specialization) to
+  // produce a variable template specialization.
+  bool InstantiatingSpecFromTemplate =
+      isa<VarTemplateSpecializationDecl>(NewVar) &&
+      (OldVar->getDescribedVarTemplate() ||
+       isa<VarTemplatePartialSpecializationDecl>(OldVar));
 
   // If we are instantiating a local extern declaration, the
   // instantiation belongs lexically to the containing function.
@@ -4385,8 +4406,11 @@ void Sema::BuildVariableInstantiation(
             NewVar->getLocation(), OldVar->getPreviousDecl(), TemplateArgs))
       Previous.addDecl(NewPrev);
   } else if (!isa<VarTemplateSpecializationDecl>(NewVar) &&
-             OldVar->hasLinkage())
+             OldVar->hasLinkage()) {
     LookupQualifiedName(Previous, NewVar->getDeclContext(), false);
+  } else if (PrevDeclForVarTemplateSpecialization) {
+    Previous.addDecl(PrevDeclForVarTemplateSpecialization);
+  }
   CheckVariableDeclaration(NewVar, Previous);
 
   if (!InstantiatingVarTemplate) {
@@ -4402,23 +4426,44 @@ void Sema::BuildVariableInstantiation(
 
   // Link instantiations of static data members back to the template from
   // which they were instantiated.
-  if (NewVar->isStaticDataMember() && !InstantiatingVarTemplate)
+  //
+  // Don't do this when instantiating a template (we link the template itself
+  // back in that case) nor when instantiating a static data member template
+  // (that's not a member specialization).
+  if (NewVar->isStaticDataMember() && !InstantiatingVarTemplate &&
+      !InstantiatingSpecFromTemplate)
     NewVar->setInstantiationOfStaticDataMember(OldVar,
                                                TSK_ImplicitInstantiation);
 
+  // If the pattern is an (in-class) explicit specialization, then the result
+  // is also an explicit specialization.
+  if (VarTemplateSpecializationDecl *OldVTSD =
+          dyn_cast<VarTemplateSpecializationDecl>(OldVar)) {
+    if (OldVTSD->getSpecializationKind() == TSK_ExplicitSpecialization &&
+        !isa<VarTemplatePartialSpecializationDecl>(OldVTSD))
+      cast<VarTemplateSpecializationDecl>(NewVar)->setSpecializationKind(
+          TSK_ExplicitSpecialization);
+  }
+
   // Forward the mangling number from the template to the instantiated decl.
   Context.setManglingNumber(NewVar, Context.getManglingNumber(OldVar));
   Context.setStaticLocalNumber(NewVar, Context.getStaticLocalNumber(OldVar));
 
-  // Delay instantiation of the initializer for variable templates or inline
-  // static data members until a definition of the variable is needed. We need
-  // it right away if the type contains 'auto'.
-  if ((!isa<VarTemplateSpecializationDecl>(NewVar) &&
-       !InstantiatingVarTemplate &&
-       !(OldVar->isInline() && OldVar->isThisDeclarationADefinition() &&
-         !NewVar->isThisDeclarationADefinition())) ||
-      NewVar->getType()->isUndeducedType())
+  // Figure out whether to eagerly instantiate the initializer.
+  if (InstantiatingVarTemplate || InstantiatingVarTemplatePartialSpec) {
+    // We're producing a template. Don't instantiate the initializer yet.
+  } else if (NewVar->getType()->isUndeducedType()) {
+    // We need the type to complete the declaration of the variable.
     InstantiateVariableInitializer(NewVar, OldVar, TemplateArgs);
+  } else if (InstantiatingSpecFromTemplate ||
+             (OldVar->isInline() && OldVar->isThisDeclarationADefinition() &&
+              !NewVar->isThisDeclarationADefinition())) {
+    // Delay instantiation of the initializer for variable template
+    // specializations or inline static data members until a definition of the
+    // variable is needed.
+  } else {
+    InstantiateVariableInitializer(NewVar, OldVar, TemplateArgs);
+  }
 
   // Diagnose unused local variables with dependent types, where the diagnostic
   // will have been deferred.
@@ -4518,15 +4563,23 @@ void Sema::InstantiateVariableDefinition(SourceLocation PointOfInstantiation,
   if (Var->isInvalidDecl())
     return;
 
-  VarTemplateSpecializationDecl *VarSpec =
-      dyn_cast<VarTemplateSpecializationDecl>(Var);
-  VarDecl *PatternDecl = nullptr, *Def = nullptr;
+  // Never instantiate an explicitly-specialized entity.
+  TemplateSpecializationKind TSK =
+      Var->getTemplateSpecializationKindForInstantiation();
+  if (TSK == TSK_ExplicitSpecialization)
+    return;
+
+  // Find the pattern and the arguments to substitute into it.
+  VarDecl *PatternDecl = Var->getTemplateInstantiationPattern();
+  assert(PatternDecl && "no pattern for templated variable");
   MultiLevelTemplateArgumentList TemplateArgs =
       getTemplateInstantiationArgs(Var);
 
+  VarTemplateSpecializationDecl *VarSpec =
+      dyn_cast<VarTemplateSpecializationDecl>(Var);
   if (VarSpec) {
     // If this is a variable template specialization, make sure that it is
-    // non-dependent, then find its instantiation pattern.
+    // non-dependent.
     bool InstantiationDependent = false;
     assert(!TemplateSpecializationType::anyDependentTemplateArguments(
                VarSpec->getTemplateArgsInfo(), InstantiationDependent) &&
@@ -4534,37 +4587,6 @@ void Sema::InstantiateVariableDefinition(SourceLocation PointOfInstantiation,
            "not type-dependent");
     (void)InstantiationDependent;
 
-    // Find the variable initialization that we'll be substituting. If the
-    // pattern was instantiated from a member template, look back further to
-    // find the real pattern.
-    assert(VarSpec->getSpecializedTemplate() &&
-           "Specialization without specialized template?");
-    llvm::PointerUnion<VarTemplateDecl *,
-                       VarTemplatePartialSpecializationDecl *> PatternPtr =
-        VarSpec->getSpecializedTemplateOrPartial();
-    if (PatternPtr.is<VarTemplatePartialSpecializationDecl *>()) {
-      VarTemplatePartialSpecializationDecl *Tmpl =
-          PatternPtr.get<VarTemplatePartialSpecializationDecl *>();
-      while (VarTemplatePartialSpecializationDecl *From =
-                 Tmpl->getInstantiatedFromMember()) {
-        if (Tmpl->isMemberSpecialization())
-          break;
-
-        Tmpl = From;
-      }
-      PatternDecl = Tmpl;
-    } else {
-      VarTemplateDecl *Tmpl = PatternPtr.get<VarTemplateDecl *>();
-      while (VarTemplateDecl *From =
-                 Tmpl->getInstantiatedFromMemberTemplate()) {
-        if (Tmpl->isMemberSpecialization())
-          break;
-
-        Tmpl = From;
-      }
-      PatternDecl = Tmpl->getTemplatedDecl();
-    }
-
     // If this is a static data member template, there might be an
     // uninstantiated initializer on the declaration. If so, instantiate
     // it now.
@@ -4608,20 +4630,12 @@ void Sema::InstantiateVariableDefinition(SourceLocation PointOfInstantiation,
       Local.Exit();
       GlobalInstantiations.perform();
     }
-
-    // Find actual definition
-    Def = PatternDecl->getDefinition(getASTContext());
   } else {
-    // If this is a static data member, find its out-of-line definition.
-    assert(Var->isStaticDataMember() && "not a static data member?");
-    PatternDecl = Var->getInstantiatedFromStaticDataMember();
-
-    assert(PatternDecl && "data member was not instantiated from a template?");
-    assert(PatternDecl->isStaticDataMember() && "not a static data member?");
-    Def = PatternDecl->getDefinition();
+    assert(Var->isStaticDataMember() && PatternDecl->isStaticDataMember() &&
+           "not a static data member?");
   }
 
-  TemplateSpecializationKind TSK = Var->getTemplateSpecializationKind();
+  VarDecl *Def = PatternDecl->getDefinition(getASTContext());
 
   // If we don't have a definition of the variable template, we won't perform
   // any instantiation. Rather, we rely on the user to instantiate this
@@ -4643,7 +4657,6 @@ void Sema::InstantiateVariableDefinition(SourceLocation PointOfInstantiation,
       }
       return;
     }
-
   }
 
   // FIXME: We need to track the instantiation stack in order to know which
@@ -4655,11 +4668,6 @@ void Sema::InstantiateVariableDefinition(SourceLocation PointOfInstantiation,
                                      /*Complain*/DefinitionRequired))
     return;
 
-
-  // Never instantiate an explicit specialization.
-  if (TSK == TSK_ExplicitSpecialization)
-    return;
-
   // C++11 [temp.explicit]p10:
   //   Except for inline functions, const variables of literal types, variables
   //   of reference types, [...] explicit instantiation declarations
@@ -5495,7 +5503,8 @@ void Sema::PerformPendingInstantiations(bool LocalOnly) {
 
     // Check if the most recent declaration has changed the specialization kind
     // and removed the need for implicit instantiation.
-    switch (Var->getMostRecentDecl()->getTemplateSpecializationKind()) {
+    switch (Var->getMostRecentDecl()
+                ->getTemplateSpecializationKindForInstantiation()) {
     case TSK_Undeclared:
       llvm_unreachable("Cannot instantitiate an undeclared specialization.");
     case TSK_ExplicitInstantiationDeclaration: