Revert "[c++1z] P0195R2: Support pack-expansion of using-declarations."

This reverts commit r290080 as it leads to many Clang crashes, e.g.:
http://lab.llvm.org:8011/builders/clang-cmake-aarch64-quick/builds/1814

llvm-svn: 290092

6 files changed, 158 insertions, 292 deletions

diff --git a/clang/lib/Sema/SemaDeclCXX.cpp b/clang/lib/Sema/SemaDeclCXX.cpp
index 21bdd945f06..ac643af1490 100644
--- a/clang/lib/Sema/SemaDeclCXX.cpp
+++ b/clang/lib/Sema/SemaDeclCXX.cpp
@@ -8533,18 +8533,12 @@ void Sema::PushUsingDirective(Scope *S, UsingDirectiveDecl *UDir) {
 Decl *Sema::ActOnUsingDeclaration(Scope *S,
                                   AccessSpecifier AS,
                                   SourceLocation UsingLoc,
-                                  SourceLocation TypenameLoc,
                                   CXXScopeSpec &SS,
                                   UnqualifiedId &Name,
-                                  SourceLocation EllipsisLoc,
-                                  AttributeList *AttrList) {
+                                  AttributeList *AttrList,
+                                  SourceLocation TypenameLoc) {
   assert(S->getFlags() & Scope::DeclScope && "Invalid Scope.");
 
-  if (SS.isEmpty()) {
-    Diag(Name.getLocStart(), diag::err_using_requires_qualname);
-    return nullptr;
-  }
-
   switch (Name.getKind()) {
   case UnqualifiedId::IK_ImplicitSelfParam:
   case UnqualifiedId::IK_Identifier:
@@ -8590,23 +8584,14 @@ Decl *Sema::ActOnUsingDeclaration(Scope *S,
       << FixItHint::CreateInsertion(SS.getRange().getBegin(), "using ");
   }
 
-  if (EllipsisLoc.isInvalid()) {
-    if (DiagnoseUnexpandedParameterPack(SS, UPPC_UsingDeclaration) ||
-        DiagnoseUnexpandedParameterPack(TargetNameInfo, UPPC_UsingDeclaration))
-      return nullptr;
-  } else {
-    if (!SS.getScopeRep()->containsUnexpandedParameterPack() &&
-        !TargetNameInfo.containsUnexpandedParameterPack()) {
-      Diag(EllipsisLoc, diag::err_pack_expansion_without_parameter_packs)
-        << SourceRange(SS.getBeginLoc(), TargetNameInfo.getEndLoc());
-      EllipsisLoc = SourceLocation();
-    }
-  }
+  if (DiagnoseUnexpandedParameterPack(SS, UPPC_UsingDeclaration) ||
+      DiagnoseUnexpandedParameterPack(TargetNameInfo, UPPC_UsingDeclaration))
+    return nullptr;
 
-  NamedDecl *UD =
-      BuildUsingDeclaration(S, AS, UsingLoc, TypenameLoc.isValid(), TypenameLoc,
-                            SS, TargetNameInfo, EllipsisLoc, AttrList,
-                            /*IsInstantiation*/false);
+  NamedDecl *UD = BuildUsingDeclaration(S, AS, UsingLoc, SS,
+                                        TargetNameInfo, AttrList,
+                                        /* IsInstantiation */ false,
+                                        TypenameLoc.isValid(), TypenameLoc);
   if (UD)
     PushOnScopeChains(UD, S, /*AddToContext*/ false);
 
@@ -8669,7 +8654,6 @@ bool Sema::CheckUsingShadowDecl(UsingDecl *Using, NamedDecl *Orig,
              diag::err_using_decl_nested_name_specifier_is_current_class)
           << Using->getQualifierLoc().getSourceRange();
         Diag(Orig->getLocation(), diag::note_using_decl_target);
-        Using->setInvalidDecl();
         return true;
       }
 
@@ -8679,7 +8663,6 @@ bool Sema::CheckUsingShadowDecl(UsingDecl *Using, NamedDecl *Orig,
         << cast<CXXRecordDecl>(CurContext)
         << Using->getQualifierLoc().getSourceRange();
       Diag(Orig->getLocation(), diag::note_using_decl_target);
-      Using->setInvalidDecl();
       return true;
     }
   }
@@ -8703,7 +8686,7 @@ bool Sema::CheckUsingShadowDecl(UsingDecl *Using, NamedDecl *Orig,
     // We can have UsingDecls in our Previous results because we use the same
     // LookupResult for checking whether the UsingDecl itself is a valid
     // redeclaration.
-    if (isa<UsingDecl>(D) || isa<UsingPackDecl>(D))
+    if (isa<UsingDecl>(D))
       continue;
 
     if (IsEquivalentForUsingDecl(Context, D, Target)) {
@@ -8749,7 +8732,6 @@ bool Sema::CheckUsingShadowDecl(UsingDecl *Using, NamedDecl *Orig,
 
     Diag(Target->getLocation(), diag::note_using_decl_target);
     Diag(OldDecl->getLocation(), diag::note_using_decl_conflict);
-    Using->setInvalidDecl();
     return true;
   }
 
@@ -8762,7 +8744,6 @@ bool Sema::CheckUsingShadowDecl(UsingDecl *Using, NamedDecl *Orig,
     Diag(Using->getLocation(), diag::err_using_decl_conflict);
     Diag(Target->getLocation(), diag::note_using_decl_target);
     Diag(Tag->getLocation(), diag::note_using_decl_conflict);
-    Using->setInvalidDecl();
     return true;
   }
 
@@ -8772,7 +8753,6 @@ bool Sema::CheckUsingShadowDecl(UsingDecl *Using, NamedDecl *Orig,
   Diag(Using->getLocation(), diag::err_using_decl_conflict);
   Diag(Target->getLocation(), diag::note_using_decl_target);
   Diag(NonTag->getLocation(), diag::note_using_decl_conflict);
-  Using->setInvalidDecl();
   return true;
 }
 
@@ -8980,19 +8960,23 @@ private:
 ///   the lookup differently for these declarations.
 NamedDecl *Sema::BuildUsingDeclaration(Scope *S, AccessSpecifier AS,
                                        SourceLocation UsingLoc,
-                                       bool HasTypenameKeyword,
-                                       SourceLocation TypenameLoc,
                                        CXXScopeSpec &SS,
                                        DeclarationNameInfo NameInfo,
-                                       SourceLocation EllipsisLoc,
                                        AttributeList *AttrList,
-                                       bool IsInstantiation) {
+                                       bool IsInstantiation,
+                                       bool HasTypenameKeyword,
+                                       SourceLocation TypenameLoc) {
   assert(!SS.isInvalid() && "Invalid CXXScopeSpec.");
   SourceLocation IdentLoc = NameInfo.getLoc();
   assert(IdentLoc.isValid() && "Invalid TargetName location.");
 
   // FIXME: We ignore attributes for now.
 
+  if (SS.isEmpty()) {
+    Diag(IdentLoc, diag::err_using_requires_qualname);
+    return nullptr;
+  }
+
   // For an inheriting constructor declaration, the name of the using
   // declaration is the name of a constructor in this class, not in the
   // base class.
@@ -9058,17 +9042,16 @@ NamedDecl *Sema::BuildUsingDeclaration(Scope *S, AccessSpecifier AS,
   DeclContext *LookupContext = computeDeclContext(SS);
   NamedDecl *D;
   NestedNameSpecifierLoc QualifierLoc = SS.getWithLocInContext(Context);
-  if (!LookupContext || EllipsisLoc.isValid()) {
+  if (!LookupContext) {
     if (HasTypenameKeyword) {
       // FIXME: not all declaration name kinds are legal here
       D = UnresolvedUsingTypenameDecl::Create(Context, CurContext,
                                               UsingLoc, TypenameLoc,
                                               QualifierLoc,
-                                              IdentLoc, NameInfo.getName(),
-                                              EllipsisLoc);
+                                              IdentLoc, NameInfo.getName());
     } else {
       D = UnresolvedUsingValueDecl::Create(Context, CurContext, UsingLoc, 
-                                           QualifierLoc, NameInfo, EllipsisLoc);
+                                           QualifierLoc, NameInfo);
     }
     D->setAccess(AS);
     CurContext->addDecl(D);
@@ -9228,19 +9211,6 @@ NamedDecl *Sema::BuildUsingDeclaration(Scope *S, AccessSpecifier AS,
   return UD;
 }
 
-NamedDecl *Sema::BuildUsingPackDecl(NamedDecl *InstantiatedFrom,
-                                    ArrayRef<NamedDecl *> Expansions) {
-  assert(isa<UnresolvedUsingValueDecl>(InstantiatedFrom) ||
-         isa<UnresolvedUsingTypenameDecl>(InstantiatedFrom) ||
-         isa<UsingPackDecl>(InstantiatedFrom));
-
-  auto *UPD =
-      UsingPackDecl::Create(Context, CurContext, InstantiatedFrom, Expansions);
-  UPD->setAccess(InstantiatedFrom->getAccess());
-  CurContext->addDecl(UPD);
-  return UPD;
-}
-
 /// Additional checks for a using declaration referring to a constructor name.
 bool Sema::CheckInheritingConstructorUsingDecl(UsingDecl *UD) {
   assert(!UD->hasTypename() && "expecting a constructor name");
@@ -9294,7 +9264,7 @@ bool Sema::CheckUsingDeclRedeclaration(SourceLocation UsingLoc,
     // scope?
     if (Qual->isDependent() && !HasTypenameKeyword) {
       for (auto *D : Prev) {
-        if (!isa<TypeDecl>(D) && !isa<UsingDecl>(D) && !isa<UsingPackDecl>(D)) {
+        if (!isa<TypeDecl>(D) && !isa<UsingDecl>(D)) {
           bool OldCouldBeEnumerator =
               isa<UnresolvedUsingValueDecl>(D) || isa<EnumConstantDecl>(D);
           Diag(NameLoc,
diff --git a/clang/lib/Sema/SemaExprCXX.cpp b/clang/lib/Sema/SemaExprCXX.cpp
index 5c3900adbde..74beeac7244 100644
--- a/clang/lib/Sema/SemaExprCXX.cpp
+++ b/clang/lib/Sema/SemaExprCXX.cpp
@@ -7462,11 +7462,17 @@ Sema::CheckMicrosoftIfExistsSymbol(Scope *S, SourceLocation KeywordLoc,
                                    UnqualifiedId &Name) {
   DeclarationNameInfo TargetNameInfo = GetNameFromUnqualifiedId(Name);
 
-  // Check for an unexpanded parameter pack.
-  auto UPPC = IsIfExists ? UPPC_IfExists : UPPC_IfNotExists;
-  if (DiagnoseUnexpandedParameterPack(SS, UPPC) ||
-      DiagnoseUnexpandedParameterPack(TargetNameInfo, UPPC))
+  // Check for unexpanded parameter packs.
+  SmallVector<UnexpandedParameterPack, 4> Unexpanded;
+  collectUnexpandedParameterPacks(SS, Unexpanded);
+  collectUnexpandedParameterPacks(TargetNameInfo, Unexpanded);
+  if (!Unexpanded.empty()) {
+    DiagnoseUnexpandedParameterPacks(KeywordLoc,
+                                     IsIfExists? UPPC_IfExists
+                                               : UPPC_IfNotExists,
+                                     Unexpanded);
     return IER_Error;
+  }
 
   return CheckMicrosoftIfExistsSymbol(S, SS, TargetNameInfo);
 }
diff --git a/clang/lib/Sema/SemaOverload.cpp b/clang/lib/Sema/SemaOverload.cpp
index 2129729dab9..d49142b8d85 100644
--- a/clang/lib/Sema/SemaOverload.cpp
+++ b/clang/lib/Sema/SemaOverload.cpp
@@ -981,7 +981,7 @@ Sema::CheckOverload(Scope *S, FunctionDecl *New, const LookupResult &Old,
         Match = *I;
         return Ovl_Match;
       }
-    } else if (isa<UsingDecl>(OldD) || isa<UsingPackDecl>(OldD)) {
+    } else if (isa<UsingDecl>(OldD)) {
       // We can overload with these, which can show up when doing
       // redeclaration checks for UsingDecls.
       assert(Old.getLookupKind() == LookupUsingDeclName);
@@ -11420,12 +11420,6 @@ BuildRecoveryCallExpr(Sema &SemaRef, Scope *S, Expr *Fn,
 
   assert(!R.empty() && "lookup results empty despite recovery");
 
-  // If recovery created an ambiguity, just bail out.
-  if (R.isAmbiguous()) {
-    R.suppressDiagnostics();
-    return ExprError();
-  }
-
   // Build an implicit member call if appropriate.  Just drop the
   // casts and such from the call, we don't really care.
   ExprResult NewFn = ExprError();
diff --git a/clang/lib/Sema/SemaTemplateInstantiateDecl.cpp b/clang/lib/Sema/SemaTemplateInstantiateDecl.cpp
index dbc322ebfdc..0956a1cc502 100644
--- a/clang/lib/Sema/SemaTemplateInstantiateDecl.cpp
+++ b/clang/lib/Sema/SemaTemplateInstantiateDecl.cpp
@@ -2495,76 +2495,35 @@ Decl *TemplateDeclInstantiator::VisitConstructorUsingShadowDecl(
   return nullptr;
 }
 
-template <typename T>
-Decl *TemplateDeclInstantiator::instantiateUnresolvedUsingDecl(
-    T *D, bool InstantiatingPackElement) {
-  // If this is a pack expansion, expand it now.
-  if (D->isPackExpansion() && !InstantiatingPackElement) {
-    SmallVector<UnexpandedParameterPack, 2> Unexpanded;
-    SemaRef.collectUnexpandedParameterPacks(D->getQualifierLoc(), Unexpanded);
-    SemaRef.collectUnexpandedParameterPacks(D->getNameInfo(), Unexpanded);
-
-    // Determine whether the set of unexpanded parameter packs can and should
-    // be expanded.
-    bool Expand = true;
-    bool RetainExpansion = false;
-    Optional<unsigned> NumExpansions;
-    if (SemaRef.CheckParameterPacksForExpansion(
-          D->getEllipsisLoc(), D->getSourceRange(), Unexpanded, TemplateArgs,
-            Expand, RetainExpansion, NumExpansions))
-      return nullptr;
-
-    // This declaration cannot appear within a function template signature,
-    // so we can't have a partial argument list for a parameter pack.
-    assert(!RetainExpansion &&
-           "should never need to retain an expansion for UsingPackDecl");
-
-    if (!Expand) {
-      // We cannot fully expand the pack expansion now, so substitute into the
-      // pattern and create a new pack expansion.
-      Sema::ArgumentPackSubstitutionIndexRAII SubstIndex(SemaRef, -1);
-      return instantiateUnresolvedUsingDecl(D, true);
-    }
-
-    // Within a function, we don't have any normal way to check for conflicts
-    // between shadow declarations from different using declarations in the
-    // same pack expansion, but this is always ill-formed because all expansions
-    // must produce (conflicting) enumerators.
-    //
-    // Sadly we can't just reject this in the template definition because it
-    // could be valid if the pack is empty or has exactly one expansion.
-    if (D->getDeclContext()->isFunctionOrMethod() && *NumExpansions > 1) {
-      SemaRef.Diag(D->getEllipsisLoc(),
-                   diag::err_using_decl_redeclaration_expansion);
-      return nullptr;
-    }
+Decl * TemplateDeclInstantiator
+    ::VisitUnresolvedUsingTypenameDecl(UnresolvedUsingTypenameDecl *D) {
+  NestedNameSpecifierLoc QualifierLoc
+    = SemaRef.SubstNestedNameSpecifierLoc(D->getQualifierLoc(),
+                                          TemplateArgs);
+  if (!QualifierLoc)
+    return nullptr;
 
-    // Instantiate the slices of this pack and build a UsingPackDecl.
-    SmallVector<NamedDecl*, 8> Expansions;
-    for (unsigned I = 0; I != *NumExpansions; ++I) {
-      Sema::ArgumentPackSubstitutionIndexRAII SubstIndex(SemaRef, I);
-      Decl *Slice = instantiateUnresolvedUsingDecl(D, true);
-      if (!Slice)
-        return nullptr;
-      // Note that we can still get unresolved using declarations here, if we
-      // had arguments for all packs but the pattern also contained other
-      // template arguments (this only happens during partial substitution, eg
-      // into the body of a generic lambda in a function template).
-      Expansions.push_back(cast<NamedDecl>(Slice));
-    }
+  CXXScopeSpec SS;
+  SS.Adopt(QualifierLoc);
 
-    auto *NewD = SemaRef.BuildUsingPackDecl(D, Expansions);
-    if (isDeclWithinFunction(D))
-      SemaRef.CurrentInstantiationScope->InstantiatedLocal(D, NewD);
-    return NewD;
-  }
+  // Since NameInfo refers to a typename, it cannot be a C++ special name.
+  // Hence, no transformation is required for it.
+  DeclarationNameInfo NameInfo(D->getDeclName(), D->getLocation());
+  NamedDecl *UD =
+    SemaRef.BuildUsingDeclaration(/*Scope*/ nullptr, D->getAccess(),
+                                  D->getUsingLoc(), SS, NameInfo, nullptr,
+                                  /*instantiation*/ true,
+                                  /*typename*/ true, D->getTypenameLoc());
+  if (UD)
+    SemaRef.Context.setInstantiatedFromUsingDecl(UD, D);
 
-  UnresolvedUsingTypenameDecl *TD = dyn_cast<UnresolvedUsingTypenameDecl>(D);
-  SourceLocation TypenameLoc = TD ? TD->getTypenameLoc() : SourceLocation();
+  return UD;
+}
 
+Decl * TemplateDeclInstantiator
+    ::VisitUnresolvedUsingValueDecl(UnresolvedUsingValueDecl *D) {
   NestedNameSpecifierLoc QualifierLoc
-    = SemaRef.SubstNestedNameSpecifierLoc(D->getQualifierLoc(),
-                                          TemplateArgs);
+      = SemaRef.SubstNestedNameSpecifierLoc(D->getQualifierLoc(), TemplateArgs);
   if (!QualifierLoc)
     return nullptr;
 
@@ -2574,48 +2533,17 @@ Decl *TemplateDeclInstantiator::instantiateUnresolvedUsingDecl(
   DeclarationNameInfo NameInfo
     = SemaRef.SubstDeclarationNameInfo(D->getNameInfo(), TemplateArgs);
 
-  // Produce a pack expansion only if we're not instantiating a particular
-  // slice of a pack expansion.
-  bool InstantiatingSlice = D->getEllipsisLoc().isValid() &&
-                            SemaRef.ArgumentPackSubstitutionIndex != -1;
-  SourceLocation EllipsisLoc =
-      InstantiatingSlice ? SourceLocation() : D->getEllipsisLoc();
-
-  NamedDecl *UD = SemaRef.BuildUsingDeclaration(
-      /*Scope*/ nullptr, D->getAccess(), D->getUsingLoc(),
-      /*HasTypename*/ TD, TypenameLoc, SS, NameInfo, EllipsisLoc, nullptr,
-      /*IsInstantiation*/ true);
+  NamedDecl *UD =
+    SemaRef.BuildUsingDeclaration(/*Scope*/ nullptr, D->getAccess(),
+                                  D->getUsingLoc(), SS, NameInfo, nullptr,
+                                  /*instantiation*/ true,
+                                  /*typename*/ false, SourceLocation());
   if (UD)
     SemaRef.Context.setInstantiatedFromUsingDecl(UD, D);
 
   return UD;
 }
 
-Decl *TemplateDeclInstantiator::VisitUnresolvedUsingTypenameDecl(
-    UnresolvedUsingTypenameDecl *D) {
-  return instantiateUnresolvedUsingDecl(D);
-}
-
-Decl *TemplateDeclInstantiator::VisitUnresolvedUsingValueDecl(
-    UnresolvedUsingValueDecl *D) {
-  return instantiateUnresolvedUsingDecl(D);
-}
-
-Decl *TemplateDeclInstantiator::VisitUsingPackDecl(UsingPackDecl *D) {
-  SmallVector<NamedDecl*, 8> Expansions;
-  for (auto *UD : D->expansions()) {
-    if (auto *NewUD =
-            SemaRef.FindInstantiatedDecl(D->getLocation(), UD, TemplateArgs))
-      Expansions.push_back(cast<NamedDecl>(NewUD));
-    else
-      return nullptr;
-  }
-
-  auto *NewD = SemaRef.BuildUsingPackDecl(D, Expansions);
-  if (isDeclWithinFunction(D))
-    SemaRef.CurrentInstantiationScope->InstantiatedLocal(D, NewD);
-  return NewD;
-}
 
 Decl *TemplateDeclInstantiator::VisitClassScopeFunctionSpecializationDecl(
                                      ClassScopeFunctionSpecializationDecl *Decl) {
@@ -4585,36 +4513,22 @@ static bool isInstantiationOf(UsingShadowDecl *Pattern,
                             Pattern);
 }
 
-static bool isInstantiationOf(UsingDecl *Pattern, UsingDecl *Instance,
+static bool isInstantiationOf(UsingDecl *Pattern,
+                              UsingDecl *Instance,
                               ASTContext &C) {
   return declaresSameEntity(C.getInstantiatedFromUsingDecl(Instance), Pattern);
 }
 
-template<typename T>
-static bool isInstantiationOfUnresolvedUsingDecl(T *Pattern, Decl *Other,
-                                                 ASTContext &Ctx) {
-  // An unresolved using declaration can instantiate to an unresolved using
-  // declaration, or to a using declaration or a using declaration pack.
-  //
-  // Multiple declarations can claim to be instantiated from an unresolved
-  // using declaration if it's a pack expansion. We want the UsingPackDecl
-  // in that case, not the individual UsingDecls within the pack.
-  bool OtherIsPackExpansion;
-  NamedDecl *OtherFrom;
-  if (auto *OtherUUD = dyn_cast<T>(Other)) {
-    OtherIsPackExpansion = OtherUUD->isPackExpansion();
-    OtherFrom = Ctx.getInstantiatedFromUsingDecl(OtherUUD);
-  } else if (auto *OtherUPD = dyn_cast<UsingPackDecl>(Other)) {
-    OtherIsPackExpansion = true;
-    OtherFrom = OtherUPD->getInstantiatedFromUsingDecl();
-  } else if (auto *OtherUD = dyn_cast<UsingDecl>(Other)) {
-    OtherIsPackExpansion = false;
-    OtherFrom = Ctx.getInstantiatedFromUsingDecl(OtherUD);
-  } else {
-    return false;
-  }
-  return Pattern->isPackExpansion() == OtherIsPackExpansion &&
-         declaresSameEntity(OtherFrom, Pattern);
+static bool isInstantiationOf(UnresolvedUsingValueDecl *Pattern,
+                              NamedDecl *Instance,
+                              ASTContext &C) {
+  return declaresSameEntity(C.getInstantiatedFromUsingDecl(Instance), Pattern);
+}
+
+static bool isInstantiationOf(UnresolvedUsingTypenameDecl *Pattern,
+                              NamedDecl *Instance,
+                              ASTContext &C) {
+  return declaresSameEntity(C.getInstantiatedFromUsingDecl(Instance), Pattern);
 }
 
 static bool isInstantiationOfStaticDataMember(VarDecl *Pattern,
@@ -4635,14 +4549,21 @@ static bool isInstantiationOfStaticDataMember(VarDecl *Pattern,
 // Other is the prospective instantiation
 // D is the prospective pattern
 static bool isInstantiationOf(ASTContext &Ctx, NamedDecl *D, Decl *Other) {
-  if (auto *UUD = dyn_cast<UnresolvedUsingTypenameDecl>(D))
-    return isInstantiationOfUnresolvedUsingDecl(UUD, Other, Ctx);
+  if (D->getKind() != Other->getKind()) {
+    if (auto *UUD = dyn_cast<UnresolvedUsingTypenameDecl>(D)) {
+      if (UsingDecl *UD = dyn_cast<UsingDecl>(Other)) {
+        return isInstantiationOf(UUD, UD, Ctx);
+      }
+    }
 
-  if (auto *UUD = dyn_cast<UnresolvedUsingValueDecl>(D))
-    return isInstantiationOfUnresolvedUsingDecl(UUD, Other, Ctx);
+    if (auto *UUD = dyn_cast<UnresolvedUsingValueDecl>(D)) {
+      if (UsingDecl *UD = dyn_cast<UsingDecl>(Other)) {
+        return isInstantiationOf(UUD, UD, Ctx);
+      }
+    }
 
-  if (D->getKind() != Other->getKind())
     return false;
+  }
 
   if (auto *Record = dyn_cast<CXXRecordDecl>(Other))
     return isInstantiationOf(cast<CXXRecordDecl>(D), Record);
@@ -4679,6 +4600,12 @@ static bool isInstantiationOf(ASTContext &Ctx, NamedDecl *D, Decl *Other) {
   if (auto *Using = dyn_cast<UsingDecl>(Other))
     return isInstantiationOf(cast<UsingDecl>(D), Using, Ctx);
 
+  if (auto *Using = dyn_cast<UnresolvedUsingValueDecl>(Other))
+    return isInstantiationOf(cast<UnresolvedUsingValueDecl>(D), Using, Ctx);
+
+  if (auto *Using = dyn_cast<UnresolvedUsingTypenameDecl>(Other))
+    return isInstantiationOf(cast<UnresolvedUsingTypenameDecl>(D), Using, Ctx);
+
   if (auto *Shadow = dyn_cast<UsingShadowDecl>(Other))
     return isInstantiationOf(cast<UsingShadowDecl>(D), Shadow, Ctx);
 
@@ -4919,8 +4846,6 @@ NamedDecl *Sema::FindInstantiatedDecl(SourceLocation Loc, NamedDecl *D,
     }
 
     NamedDecl *Result = nullptr;
-    // FIXME: If the name is a dependent name, this lookup won't necessarily
-    // find it. Does that ever matter?
     if (D->getDeclName()) {
       DeclContext::lookup_result Found = ParentDC->lookup(D->getDeclName());
       Result = findInstantiationOf(Context, D, Found.begin(), Found.end());
diff --git a/clang/lib/Sema/SemaTemplateVariadic.cpp b/clang/lib/Sema/SemaTemplateVariadic.cpp
index 54556b505ee..c8bc2c38809 100644
--- a/clang/lib/Sema/SemaTemplateVariadic.cpp
+++ b/clang/lib/Sema/SemaTemplateVariadic.cpp
@@ -390,18 +390,21 @@ void Sema::collectUnexpandedParameterPacks(QualType T,
 void Sema::collectUnexpandedParameterPacks(TypeLoc TL,
                    SmallVectorImpl<UnexpandedParameterPack> &Unexpanded) {
   CollectUnexpandedParameterPacksVisitor(Unexpanded).TraverseTypeLoc(TL);  
-}
+}  
 
-void Sema::collectUnexpandedParameterPacks(
-    NestedNameSpecifierLoc NNS,
-    SmallVectorImpl<UnexpandedParameterPack> &Unexpanded) {
+void Sema::collectUnexpandedParameterPacks(CXXScopeSpec &SS,
+                                           SmallVectorImpl<UnexpandedParameterPack> &Unexpanded) {
+  NestedNameSpecifier *Qualifier = SS.getScopeRep();
+  if (!Qualifier)
+    return;
+  
+  NestedNameSpecifierLoc QualifierLoc(Qualifier, SS.location_data());
   CollectUnexpandedParameterPacksVisitor(Unexpanded)
-      .TraverseNestedNameSpecifierLoc(NNS);
+    .TraverseNestedNameSpecifierLoc(QualifierLoc);
 }
 
-void Sema::collectUnexpandedParameterPacks(
-    const DeclarationNameInfo &NameInfo,
-    SmallVectorImpl<UnexpandedParameterPack> &Unexpanded) {
+void Sema::collectUnexpandedParameterPacks(const DeclarationNameInfo &NameInfo,
+                         SmallVectorImpl<UnexpandedParameterPack> &Unexpanded) {
   CollectUnexpandedParameterPacksVisitor(Unexpanded)
     .TraverseDeclarationNameInfo(NameInfo);
 }
diff --git a/clang/lib/Sema/TreeTransform.h b/clang/lib/Sema/TreeTransform.h
index 849fdac7ec6..a76a078fd00 100644
--- a/clang/lib/Sema/TreeTransform.h
+++ b/clang/lib/Sema/TreeTransform.h
@@ -457,10 +457,6 @@ public:
     return cast_or_null<NamedDecl>(getDerived().TransformDecl(Loc, D));
   }
 
-  /// Transform the set of declarations in an OverloadExpr.
-  bool TransformOverloadExprDecls(OverloadExpr *Old, bool RequiresADL,
-                                  LookupResult &R);
-
   /// \brief Transform the given nested-name-specifier with source-location
   /// information.
   ///
@@ -825,7 +821,7 @@ public:
 
   /// \brief Rebuild an unresolved typename type, given the decl that
   /// the UnresolvedUsingTypenameDecl was transformed to.
-  QualType RebuildUnresolvedUsingType(SourceLocation NameLoc, Decl *D);
+  QualType RebuildUnresolvedUsingType(Decl *D);
 
   /// \brief Build a new typedef type.
   QualType RebuildTypedefType(TypedefNameDecl *Typedef) {
@@ -5165,7 +5161,7 @@ TreeTransform<Derived>::TransformUnresolvedUsingType(TypeLocBuilder &TLB,
 
   QualType Result = TL.getType();
   if (getDerived().AlwaysRebuild() || D != T->getDecl()) {
-    Result = getDerived().RebuildUnresolvedUsingType(TL.getNameLoc(), D);
+    Result = getDerived().RebuildUnresolvedUsingType(D);
     if (Result.isNull())
       return QualType();
   }
@@ -9798,71 +9794,44 @@ TreeTransform<Derived>::TransformCXXPseudoDestructorExpr(
                                                      Destroyed);
 }
 
-template <typename Derived>
-bool TreeTransform<Derived>::TransformOverloadExprDecls(OverloadExpr *Old,
-                                                        bool RequiresADL,
-                                                        LookupResult &R) {
+template<typename Derived>
+ExprResult
+TreeTransform<Derived>::TransformUnresolvedLookupExpr(
+                                                  UnresolvedLookupExpr *Old) {
+  LookupResult R(SemaRef, Old->getName(), Old->getNameLoc(),
+                 Sema::LookupOrdinaryName);
+
   // Transform all the decls.
-  bool AllEmptyPacks = true;
-  for (auto *OldD : Old->decls()) {
-    Decl *InstD = getDerived().TransformDecl(Old->getNameLoc(), OldD);
+  for (UnresolvedLookupExpr::decls_iterator I = Old->decls_begin(),
+         E = Old->decls_end(); I != E; ++I) {
+    NamedDecl *InstD = static_cast<NamedDecl*>(
+                                 getDerived().TransformDecl(Old->getNameLoc(),
+                                                            *I));
     if (!InstD) {
       // Silently ignore these if a UsingShadowDecl instantiated to nothing.
       // This can happen because of dependent hiding.
-      if (isa<UsingShadowDecl>(OldD))
+      if (isa<UsingShadowDecl>(*I))
         continue;
       else {
         R.clear();
-        return true;
+        return ExprError();
       }
     }
 
-    // Expand using pack declarations.
-    ArrayRef<NamedDecl*> Decls = cast<NamedDecl>(InstD);
-    if (auto *UPD = dyn_cast<UsingPackDecl>(InstD))
-      Decls = UPD->expansions();
-
     // Expand using declarations.
-    for (auto *D : Decls) {
-      if (auto *UD = dyn_cast<UsingDecl>(D)) {
-        for (auto *SD : UD->shadows())
-          R.addDecl(SD);
-      } else {
-        R.addDecl(D);
-      }
+    if (isa<UsingDecl>(InstD)) {
+      UsingDecl *UD = cast<UsingDecl>(InstD);
+      for (auto *I : UD->shadows())
+        R.addDecl(I);
+      continue;
     }
 
-    AllEmptyPacks &= Decls.empty();
-  };
-
-  // C++ [temp.res]/8.4.2:
-  //   The program is ill-formed, no diagnostic required, if [...] lookup for
-  //   a name in the template definition found a using-declaration, but the
-  //   lookup in the corresponding scope in the instantiation odoes not find
-  //   any declarations because the using-declaration was a pack expansion and
-  //   the corresponding pack is empty
-  if (AllEmptyPacks && !RequiresADL) {
-    getSema().Diag(Old->getNameLoc(), diag::err_using_pack_expansion_empty)
-        << isa<UnresolvedMemberExpr>(Old) << Old->getNameInfo().getName();
-    return true;
+    R.addDecl(InstD);
   }
 
   // Resolve a kind, but don't do any further analysis.  If it's
   // ambiguous, the callee needs to deal with it.
   R.resolveKind();
-  return false;
-}
-
-template<typename Derived>
-ExprResult
-TreeTransform<Derived>::TransformUnresolvedLookupExpr(
-                                                  UnresolvedLookupExpr *Old) {
-  LookupResult R(SemaRef, Old->getName(), Old->getNameLoc(),
-                 Sema::LookupOrdinaryName);
-
-  // Transform the declaration set.
-  if (TransformOverloadExprDecls(Old, Old->requiresADL(), R))
-    return ExprError();
 
   // Rebuild the nested-name qualifier, if present.
   CXXScopeSpec SS;
@@ -10730,9 +10699,35 @@ TreeTransform<Derived>::TransformUnresolvedMemberExpr(UnresolvedMemberExpr *Old)
   LookupResult R(SemaRef, Old->getMemberNameInfo(),
                  Sema::LookupOrdinaryName);
 
-  // Transform the declaration set.
-  if (TransformOverloadExprDecls(Old, /*RequiresADL*/false, R))
-    return ExprError();
+  // Transform all the decls.
+  for (UnresolvedMemberExpr::decls_iterator I = Old->decls_begin(),
+         E = Old->decls_end(); I != E; ++I) {
+    NamedDecl *InstD = static_cast<NamedDecl*>(
+                                getDerived().TransformDecl(Old->getMemberLoc(),
+                                                           *I));
+    if (!InstD) {
+      // Silently ignore these if a UsingShadowDecl instantiated to nothing.
+      // This can happen because of dependent hiding.
+      if (isa<UsingShadowDecl>(*I))
+        continue;
+      else {
+        R.clear();
+        return ExprError();
+      }
+    }
+
+    // Expand using declarations.
+    if (isa<UsingDecl>(InstD)) {
+      UsingDecl *UD = cast<UsingDecl>(InstD);
+      for (auto *I : UD->shadows())
+        R.addDecl(I);
+      continue;
+    }
+
+    R.addDecl(InstD);
+  }
+
+  R.resolveKind();
 
   // Determine the naming class.
   if (Old->getNamingClass()) {
@@ -11847,48 +11842,21 @@ QualType TreeTransform<Derived>::RebuildFunctionNoProtoType(QualType T) {
 }
 
 template<typename Derived>
-QualType TreeTransform<Derived>::RebuildUnresolvedUsingType(SourceLocation Loc,
-                                                            Decl *D) {
+QualType TreeTransform<Derived>::RebuildUnresolvedUsingType(Decl *D) {
   assert(D && "no decl found");
   if (D->isInvalidDecl()) return QualType();
 
   // FIXME: Doesn't account for ObjCInterfaceDecl!
   TypeDecl *Ty;
-  if (auto *UPD = dyn_cast<UsingPackDecl>(D)) {
-    // A valid resolved using typename pack expansion decl can have multiple
-    // UsingDecls, but they must each have exactly one type, and it must be
-    // the same type in every case. But we must have at least one expansion!
-    if (UPD->expansions().empty()) {
-      getSema().Diag(Loc, diag::err_using_pack_expansion_empty)
-          << UPD->isCXXClassMember() << UPD;
-      return QualType();
-    }
-
-    // We might still have some unresolved types. Try to pick a resolved type
-    // if we can. The final instantiation will check that the remaining
-    // unresolved types instantiate to the type we pick.
-    QualType FallbackT;
-    QualType T;
-    for (auto *E : UPD->expansions()) {
-      QualType ThisT = RebuildUnresolvedUsingType(Loc, E);
-      if (ThisT.isNull())
-        continue;
-      else if (ThisT->getAs<UnresolvedUsingType>())
-        FallbackT = ThisT;
-      else if (T.isNull())
-        T = ThisT;
-      else
-        assert(getSema().Context.hasSameType(ThisT, T) &&
-               "mismatched resolved types in using pack expansion");
-    }
-    return T.isNull() ? FallbackT : T;
-  } else if (auto *Using = dyn_cast<UsingDecl>(D)) {
+  if (isa<UsingDecl>(D)) {
+    UsingDecl *Using = cast<UsingDecl>(D);
     assert(Using->hasTypename() &&
            "UnresolvedUsingTypenameDecl transformed to non-typename using");
 
     // A valid resolved using typename decl points to exactly one type decl.
     assert(++Using->shadow_begin() == Using->shadow_end());
     Ty = cast<TypeDecl>((*Using->shadow_begin())->getTargetDecl());
+
   } else {
     assert(isa<UnresolvedUsingTypenameDecl>(D) &&
            "UnresolvedUsingTypenameDecl transformed to non-using decl");