Start implementing support for substitution into pack expansions that

involve template parameter packs at multiple template levels that
occur within the signatures members of class templates (and partial
specializations thereof). This is a work-in-progress that is deficient
in several ways, notably:
  - It only works for template type parameter packs, but we need to
  also support non-type template parameter packs and template template
  parameter packs.
  - It doesn't keep track of the lengths of the substituted argument
  packs in the expansion, so it can't properly diagnose length
  mismatches.

However, this is a concrete step in the right direction.


git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@123425 91177308-0d34-0410-b5e6-96231b3b80d8

4 files changed, 57 insertions, 4 deletions

diff --git a/lib/Sema/SemaTemplate.cpp b/lib/Sema/SemaTemplate.cpp
index 868458c2a9..6a37482d66 100644
--- a/lib/Sema/SemaTemplate.cpp
+++ b/lib/Sema/SemaTemplate.cpp
@@ -2713,6 +2713,11 @@ bool UnnamedLocalNoLinkageFinder::VisitTemplateTypeParmType(
   return false;
 }
 
+bool UnnamedLocalNoLinkageFinder::VisitSubstTemplateTypeParmPackType(
+                                        const SubstTemplateTypeParmPackType *) {
+  return false;
+}
+
 bool UnnamedLocalNoLinkageFinder::VisitTemplateSpecializationType(
                                             const TemplateSpecializationType*) {
   return false;
diff --git a/lib/Sema/SemaTemplateInstantiate.cpp b/lib/Sema/SemaTemplateInstantiate.cpp
index 5f181fb5e1..629dc58958 100644
--- a/lib/Sema/SemaTemplateInstantiate.cpp
+++ b/lib/Sema/SemaTemplateInstantiate.cpp
@@ -712,6 +712,12 @@ namespace {
     QualType TransformTemplateTypeParmType(TypeLocBuilder &TLB,
                                            TemplateTypeParmTypeLoc TL);
 
+    /// \brief Transforms an already-substituted template type parameter pack
+    /// into either itself (if we aren't substituting into its pack expansion)
+    /// or the appropriate substituted argument.
+    QualType TransformSubstTemplateTypeParmPackType(TypeLocBuilder &TLB,
+                                           SubstTemplateTypeParmPackTypeLoc TL);
+
     ExprResult TransformCallExpr(CallExpr *CE) {
       getSema().CallsUndergoingInstantiation.push_back(CE);
       ExprResult Result =
@@ -1024,10 +1030,15 @@ TemplateInstantiator::TransformTemplateTypeParmType(TypeLocBuilder &TLB,
              "Missing argument pack");
       
       if (getSema().ArgumentPackSubstitutionIndex == -1) {
-        // FIXME: Variadic templates fun case.
-        getSema().Diag(TL.getSourceRange().getBegin(), 
-                       diag::err_pack_expansion_mismatch_unsupported);
-        return QualType();
+        // We have the template argument pack, but we're not expanding the
+        // enclosing pack expansion yet. Just save the template argument
+        // pack for later substitution.
+        QualType Result
+          = getSema().Context.getSubstTemplateTypeParmPackType(T, Arg);
+        SubstTemplateTypeParmPackTypeLoc NewTL
+          = TLB.push<SubstTemplateTypeParmPackTypeLoc>(Result);
+        NewTL.setNameLoc(TL.getNameLoc());
+        return Result;
       }
       
       assert(getSema().ArgumentPackSubstitutionIndex < (int)Arg.pack_size());
@@ -1063,6 +1074,32 @@ TemplateInstantiator::TransformTemplateTypeParmType(TypeLocBuilder &TLB,
   return Result;
 }
 
+QualType 
+TemplateInstantiator::TransformSubstTemplateTypeParmPackType(
+                                                            TypeLocBuilder &TLB,
+                                         SubstTemplateTypeParmPackTypeLoc TL) {
+  if (getSema().ArgumentPackSubstitutionIndex == -1) {
+    // We aren't expanding the parameter pack, so just return ourselves.
+    SubstTemplateTypeParmPackTypeLoc NewTL
+      = TLB.push<SubstTemplateTypeParmPackTypeLoc>(TL.getType());
+    NewTL.setNameLoc(TL.getNameLoc());
+    return TL.getType();
+  }
+  
+  const TemplateArgument &ArgPack = TL.getTypePtr()->getArgumentPack();
+  unsigned Index = (unsigned)getSema().ArgumentPackSubstitutionIndex;
+  assert(Index < ArgPack.pack_size() && "Substitution index out-of-range");
+  
+  QualType Result = ArgPack.pack_begin()[Index].getAsType();
+  Result = getSema().Context.getSubstTemplateTypeParmType(
+                                      TL.getTypePtr()->getReplacedParameter(),
+                                                          Result);
+  SubstTemplateTypeParmTypeLoc NewTL
+    = TLB.push<SubstTemplateTypeParmTypeLoc>(Result);
+  NewTL.setNameLoc(TL.getNameLoc());
+  return Result;
+}
+
 /// \brief Perform substitution on the type T with a given set of template
 /// arguments.
 ///
diff --git a/lib/Sema/SemaTemplateVariadic.cpp b/lib/Sema/SemaTemplateVariadic.cpp
index 473dcb7d1f..dc5013c25d 100644
--- a/lib/Sema/SemaTemplateVariadic.cpp
+++ b/lib/Sema/SemaTemplateVariadic.cpp
@@ -456,6 +456,10 @@ bool Sema::CheckParameterPacksForExpansion(SourceLocation EllipsisLoc,
   std::pair<IdentifierInfo *, SourceLocation> FirstPack;
   bool HaveFirstPack = false;
   
+  // FIXME: Variadic templates. Even if we don't expand, we'd still like to
+  // return the number of expansions back to the caller, perhaps as an 
+  // llvm::Optional, so that it can be embedded in the pack expansion. This
+  // is important for the multi-level substitution case.
   for (unsigned I = 0; I != NumUnexpanded; ++I) {
     // Compute the depth and index for this parameter pack.
     unsigned Depth;
diff --git a/lib/Sema/TreeTransform.h b/lib/Sema/TreeTransform.h
index 43d89e2875..4127d5045a 100644
--- a/lib/Sema/TreeTransform.h
+++ b/lib/Sema/TreeTransform.h
@@ -3927,6 +3927,13 @@ QualType TreeTransform<Derived>::TransformSubstTemplateTypeParmType(
 }
 
 template<typename Derived>
+QualType TreeTransform<Derived>::TransformSubstTemplateTypeParmPackType(
+                                          TypeLocBuilder &TLB,
+                                          SubstTemplateTypeParmPackTypeLoc TL) {
+  return TransformTypeSpecType(TLB, TL);
+}
+
+template<typename Derived>
 QualType TreeTransform<Derived>::TransformTemplateSpecializationType(
                                                         TypeLocBuilder &TLB,
                                            TemplateSpecializationTypeLoc TL) {