Introduce a new kind of TemplateName that captures a substituted

template template parameter pack that cannot be fully expanded because
its enclosing pack expansion could not be expanded. This form of
TemplateName plays the same role as SubstTemplateTypeParmPackType and
SubstNonTypeTemplateParmPackExpr do for template type parameter packs
and non-type template parameter packs, respectively.

We should now handle these multi-level pack expansion substitutions
anywhere. The largest remaining gap in our variadic-templates support
is that we cannot cope with non-type template parameter packs whose
type is a pack expansion.

llvm-svn: 123521

1 files changed, 59 insertions, 6 deletions

diff --git a/clang/lib/Sema/SemaTemplateInstantiate.cpp b/clang/lib/Sema/SemaTemplateInstantiate.cpp
index 8943daa3698..98fa390febc 100644
--- a/clang/lib/Sema/SemaTemplateInstantiate.cpp
+++ b/clang/lib/Sema/SemaTemplateInstantiate.cpp
@@ -697,6 +697,10 @@ namespace {
                                    ElaboratedTypeKeyword Keyword,
                                    NestedNameSpecifier *NNS, QualType T);
 
+    TemplateName TransformTemplateName(TemplateName Name,
+                                       QualType ObjectType = QualType(),
+                                       NamedDecl *FirstQualifierInScope = 0);
+
     ExprResult TransformPredefinedExpr(PredefinedExpr *E);
     ExprResult TransformDeclRefExpr(DeclRefExpr *E);
     ExprResult TransformCXXDefaultArgExpr(CXXDefaultArgExpr *E);
@@ -762,12 +766,7 @@ Decl *TemplateInstantiator::TransformDecl(SourceLocation Loc, Decl *D) {
         assert(Arg.getKind() == TemplateArgument::Pack && 
                "Missing argument pack");
         
-        if (getSema().ArgumentPackSubstitutionIndex == -1) {
-          // FIXME: Variadic templates fun case.
-          getSema().Diag(Loc,  diag::err_pack_expansion_mismatch_unsupported);
-          return 0;
-        }
-        
+        assert(getSema().ArgumentPackSubstitutionIndex >= 0);        
         assert(getSema().ArgumentPackSubstitutionIndex < (int)Arg.pack_size());
         Arg = Arg.pack_begin()[getSema().ArgumentPackSubstitutionIndex];
       }
@@ -887,6 +886,60 @@ TemplateInstantiator::RebuildElaboratedType(SourceLocation KeywordLoc,
                                                                     NNS, T);
 }
 
+TemplateName TemplateInstantiator::TransformTemplateName(TemplateName Name,
+                                                         QualType ObjectType,
+                                             NamedDecl *FirstQualifierInScope) {
+  if (TemplateTemplateParmDecl *TTP
+       = dyn_cast_or_null<TemplateTemplateParmDecl>(Name.getAsTemplateDecl())) {
+    if (TTP->getDepth() < TemplateArgs.getNumLevels()) {
+      // If the corresponding template argument is NULL or non-existent, it's
+      // because we are performing instantiation from explicitly-specified
+      // template arguments in a function template, but there were some
+      // arguments left unspecified.
+      if (!TemplateArgs.hasTemplateArgument(TTP->getDepth(),
+                                            TTP->getPosition()))
+        return Name;
+      
+      TemplateArgument Arg = TemplateArgs(TTP->getDepth(), TTP->getPosition());
+      
+      if (TTP->isParameterPack()) {
+        assert(Arg.getKind() == TemplateArgument::Pack && 
+               "Missing argument pack");
+        
+        if (getSema().ArgumentPackSubstitutionIndex == -1) {
+          // We have the template argument pack to substitute, but we're not
+          // actually expanding the enclosing pack expansion yet. So, just
+          // keep the entire argument pack.
+          return getSema().Context.getSubstTemplateTemplateParmPack(TTP, Arg);
+        }
+        
+        assert(getSema().ArgumentPackSubstitutionIndex < (int)Arg.pack_size());
+        Arg = Arg.pack_begin()[getSema().ArgumentPackSubstitutionIndex];
+      }
+      
+      TemplateName Template = Arg.getAsTemplate();
+      assert(!Template.isNull() && Template.getAsTemplateDecl() &&
+             "Wrong kind of template template argument");
+      return Template;
+    }
+  }
+  
+  if (SubstTemplateTemplateParmPackStorage *SubstPack
+                                  = Name.getAsSubstTemplateTemplateParmPack()) {
+    if (getSema().ArgumentPackSubstitutionIndex == -1)
+      return Name;
+
+    const TemplateArgument &ArgPack = SubstPack->getArgumentPack();
+    assert(getSema().ArgumentPackSubstitutionIndex < (int)ArgPack.pack_size() &&
+           "Pack substitution index out-of-range");
+    return ArgPack.pack_begin()[getSema().ArgumentPackSubstitutionIndex]
+                                                               .getAsTemplate();
+  }
+  
+  return inherited::TransformTemplateName(Name, ObjectType, 
+                                          FirstQualifierInScope);
+}
+
 ExprResult 
 TemplateInstantiator::TransformPredefinedExpr(PredefinedExpr *E) {
   if (!E->isTypeDependent())