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

This change introduces UsingPackDecl as a marker for the set of UsingDecls
produced by pack expansion of a single (unresolved) using declaration. This is
not strictly necessary (we just need to be able to map from the original using
declaration to its expansions somehow), but it's useful to maintain the
invariant that each declaration reference instantiates to refer to one
declaration.

This is a re-commit of r290080 (reverted in r290092) with a fix for a
use-after-lifetime bug.

llvm-svn: 290203

3 files changed, 28 insertions, 0 deletions

diff --git a/clang/lib/Serialization/ASTCommon.cpp b/clang/lib/Serialization/ASTCommon.cpp
index 79ccffc5abb..ecd249cc502 100644
--- a/clang/lib/Serialization/ASTCommon.cpp
+++ b/clang/lib/Serialization/ASTCommon.cpp
@@ -285,6 +285,7 @@ bool serialization::isRedeclarableDeclKind(unsigned Kind) {
   case Decl::NonTypeTemplateParm:
   case Decl::TemplateTemplateParm:
   case Decl::Using:
+  case Decl::UsingPack:
   case Decl::ObjCMethod:
   case Decl::ObjCCategory:
   case Decl::ObjCCategoryImpl:
diff --git a/clang/lib/Serialization/ASTReaderDecl.cpp b/clang/lib/Serialization/ASTReaderDecl.cpp
index 913a1419b3f..dc29a61c0a9 100644
--- a/clang/lib/Serialization/ASTReaderDecl.cpp
+++ b/clang/lib/Serialization/ASTReaderDecl.cpp
@@ -322,6 +322,7 @@ namespace clang {
     void VisitTemplateTemplateParmDecl(TemplateTemplateParmDecl *D);
     void VisitTypeAliasTemplateDecl(TypeAliasTemplateDecl *D);
     void VisitUsingDecl(UsingDecl *D);
+    void VisitUsingPackDecl(UsingPackDecl *D);
     void VisitUsingShadowDecl(UsingShadowDecl *D);
     void VisitConstructorUsingShadowDecl(ConstructorUsingShadowDecl *D);
     void VisitLinkageSpecDecl(LinkageSpecDecl *D);
@@ -1419,6 +1420,15 @@ void ASTDeclReader::VisitUsingDecl(UsingDecl *D) {
   mergeMergeable(D);
 }
 
+void ASTDeclReader::VisitUsingPackDecl(UsingPackDecl *D) {
+  VisitNamedDecl(D);
+  D->InstantiatedFrom = ReadDeclAs<NamedDecl>();
+  NamedDecl **Expansions = D->getTrailingObjects<NamedDecl*>();
+  for (unsigned I = 0; I != D->NumExpansions; ++I)
+    Expansions[I] = ReadDeclAs<NamedDecl>();
+  mergeMergeable(D);
+}
+
 void ASTDeclReader::VisitUsingShadowDecl(UsingShadowDecl *D) {
   RedeclarableResult Redecl = VisitRedeclarable(D);
   VisitNamedDecl(D);
@@ -1452,6 +1462,7 @@ void ASTDeclReader::VisitUnresolvedUsingValueDecl(UnresolvedUsingValueDecl *D) {
   D->setUsingLoc(ReadSourceLocation());
   D->QualifierLoc = Record.ReadNestedNameSpecifierLoc(Idx);
   ReadDeclarationNameLoc(D->DNLoc, D->getDeclName());
+  D->EllipsisLoc = ReadSourceLocation();
   mergeMergeable(D);
 }
 
@@ -1460,6 +1471,7 @@ void ASTDeclReader::VisitUnresolvedUsingTypenameDecl(
   VisitTypeDecl(D);
   D->TypenameLocation = ReadSourceLocation();
   D->QualifierLoc = Record.ReadNestedNameSpecifierLoc(Idx);
+  D->EllipsisLoc = ReadSourceLocation();
   mergeMergeable(D);
 }
 
@@ -3297,6 +3309,9 @@ Decl *ASTReader::ReadDeclRecord(DeclID ID) {
   case DECL_USING:
     D = UsingDecl::CreateDeserialized(Context, ID);
     break;
+  case DECL_USING_PACK:
+    D = UsingPackDecl::CreateDeserialized(Context, ID, Record[Idx++]);
+    break;
   case DECL_USING_SHADOW:
     D = UsingShadowDecl::CreateDeserialized(Context, ID);
     break;
diff --git a/clang/lib/Serialization/ASTWriterDecl.cpp b/clang/lib/Serialization/ASTWriterDecl.cpp
index 21468619dba..ee220f00a81 100644
--- a/clang/lib/Serialization/ASTWriterDecl.cpp
+++ b/clang/lib/Serialization/ASTWriterDecl.cpp
@@ -107,6 +107,7 @@ namespace clang {
     void VisitTemplateTemplateParmDecl(TemplateTemplateParmDecl *D);
     void VisitTypeAliasTemplateDecl(TypeAliasTemplateDecl *D);
     void VisitUsingDecl(UsingDecl *D);
+    void VisitUsingPackDecl(UsingPackDecl *D);
     void VisitUsingShadowDecl(UsingShadowDecl *D);
     void VisitConstructorUsingShadowDecl(ConstructorUsingShadowDecl *D);
     void VisitLinkageSpecDecl(LinkageSpecDecl *D);
@@ -1142,6 +1143,15 @@ void ASTDeclWriter::VisitUsingDecl(UsingDecl *D) {
   Code = serialization::DECL_USING;
 }
 
+void ASTDeclWriter::VisitUsingPackDecl(UsingPackDecl *D) {
+  Record.push_back(D->NumExpansions);
+  VisitNamedDecl(D);
+  Record.AddDeclRef(D->getInstantiatedFromUsingDecl());
+  for (auto *E : D->expansions())
+    Record.AddDeclRef(E);
+  Code = serialization::DECL_USING_PACK;
+}
+
 void ASTDeclWriter::VisitUsingShadowDecl(UsingShadowDecl *D) {
   VisitRedeclarable(D);
   VisitNamedDecl(D);
@@ -1175,6 +1185,7 @@ void ASTDeclWriter::VisitUnresolvedUsingValueDecl(UnresolvedUsingValueDecl *D) {
   Record.AddSourceLocation(D->getUsingLoc());
   Record.AddNestedNameSpecifierLoc(D->getQualifierLoc());
   Record.AddDeclarationNameLoc(D->DNLoc, D->getDeclName());
+  Record.AddSourceLocation(D->getEllipsisLoc());
   Code = serialization::DECL_UNRESOLVED_USING_VALUE;
 }
 
@@ -1183,6 +1194,7 @@ void ASTDeclWriter::VisitUnresolvedUsingTypenameDecl(
   VisitTypeDecl(D);
   Record.AddSourceLocation(D->getTypenameLoc());
   Record.AddNestedNameSpecifierLoc(D->getQualifierLoc());
+  Record.AddSourceLocation(D->getEllipsisLoc());
   Code = serialization::DECL_UNRESOLVED_USING_TYPENAME;
 }