[clang][ASTImporter] Add support for import of UsingPackDecl.

Reviewed By: martong

Differential Revision: https://reviews.llvm.org/D125986

clang/lib/AST/ASTImporter.cpp

@@ -548,6 +548,7 @@ namespace clang {
     ExpectedDecl VisitUsingDecl(UsingDecl *D);
     ExpectedDecl VisitUsingShadowDecl(UsingShadowDecl *D);
     ExpectedDecl VisitUsingDirectiveDecl(UsingDirectiveDecl *D);
+    ExpectedDecl VisitUsingPackDecl(UsingPackDecl *D);
     ExpectedDecl ImportUsingShadowDecls(BaseUsingDecl *D, BaseUsingDecl *ToSI);
     ExpectedDecl VisitUsingEnumDecl(UsingEnumDecl *D);
     ExpectedDecl VisitUnresolvedUsingValueDecl(UnresolvedUsingValueDecl *D);
@@ -4832,6 +4833,35 @@ ExpectedDecl ASTNodeImporter::VisitUsingDirectiveDecl(UsingDirectiveDecl *D) {
   return ToUsingDir;
 }
 
+ExpectedDecl ASTNodeImporter::VisitUsingPackDecl(UsingPackDecl *D) {
+  DeclContext *DC, *LexicalDC;
+  DeclarationName Name;
+  SourceLocation Loc;
+  NamedDecl *ToD = nullptr;
+  if (Error Err = ImportDeclParts(D, DC, LexicalDC, Name, ToD, Loc))
+    return std::move(Err);
+  if (ToD)
+    return ToD;
+
+  auto ToInstantiatedFromUsingOrErr =
+      Importer.Import(D->getInstantiatedFromUsingDecl());
+  if (!ToInstantiatedFromUsingOrErr)
+    return ToInstantiatedFromUsingOrErr.takeError();
+  SmallVector<NamedDecl *, 4> Expansions(D->expansions().size());
+  if (Error Err = ImportArrayChecked(D->expansions(), Expansions.begin()))
+    return std::move(Err);
+
+  UsingPackDecl *ToUsingPack;
+  if (GetImportedOrCreateDecl(ToUsingPack, D, Importer.getToContext(), DC,
+                              cast<NamedDecl>(*ToInstantiatedFromUsingOrErr),
+                              Expansions))
+    return ToUsingPack;
+
+  addDeclToContexts(D, ToUsingPack);
+
+  return ToUsingPack;
+}
+
 ExpectedDecl ASTNodeImporter::VisitUnresolvedUsingValueDecl(
     UnresolvedUsingValueDecl *D) {
   DeclContext *DC, *LexicalDC;

clang/unittests/AST/ASTImporterTest.cpp

@@ -910,6 +910,20 @@ TEST_P(ImportDecl, ImportUsingEnumDecl) {
              functionDecl(hasDescendant(usingEnumDecl(hasName("bar")))));
 }
 
+const internal::VariadicDynCastAllOfMatcher<Decl, UsingPackDecl> usingPackDecl;
+
+TEST_P(ImportDecl, ImportUsingPackDecl) {
+  MatchVerifier<Decl> Verifier;
+  testImport(
+      "struct A { int operator()() { return 1; } };"
+      "struct B { int operator()() { return 2; } };"
+      "template<typename ...T> struct C : T... { using T::operator()...; };"
+      "C<A, B> declToImport;",
+      Lang_CXX20, "", Lang_CXX20, Verifier,
+      varDecl(hasType(templateSpecializationType(hasDeclaration(
+          classTemplateSpecializationDecl(hasDescendant(usingPackDecl())))))));
+}
+
 /// \brief Matches shadow declarations introduced into a scope by a
 ///        (resolved) using declaration.
 ///
@@ -1022,6 +1036,31 @@ TEST_P(ImportExpr, DependentSizedArrayType) {
                  has(fieldDecl(hasType(dependentSizedArrayType())))))));
 }
 
+TEST_P(ASTImporterOptionSpecificTestBase, ImportUsingPackDecl) {
+  Decl *FromTU = getTuDecl(
+      "struct A { int operator()() { return 1; } };"
+      "struct B { int operator()() { return 2; } };"
+      "template<typename ...T> struct C : T... { using T::operator()...; };"
+      "C<A, B> Var;",
+      Lang_CXX20);
+
+  auto From = FirstDeclMatcher<UsingPackDecl>().match(FromTU, usingPackDecl());
+  ASSERT_TRUE(From);
+  auto To = cast<UsingPackDecl>(Import(From, Lang_CXX20));
+  ASSERT_TRUE(To);
+
+  ArrayRef<NamedDecl *> FromExpansions = From->expansions();
+  ArrayRef<NamedDecl *> ToExpansions = To->expansions();
+  ASSERT_EQ(FromExpansions.size(), ToExpansions.size());
+  for (unsigned int I = 0; I < FromExpansions.size(); ++I) {
+    auto ImportedExpansion = Import(FromExpansions[I], Lang_CXX20);
+    EXPECT_EQ(ImportedExpansion, ToExpansions[I]);
+  }
+
+  auto ImportedDC = cast<Decl>(Import(From->getDeclContext(), Lang_CXX20));
+  EXPECT_EQ(ImportedDC, cast<Decl>(To->getDeclContext()));
+}
+
 TEST_P(ASTImporterOptionSpecificTestBase, TemplateTypeParmDeclNoDefaultArg) {
   Decl *FromTU = getTuDecl("template<typename T> struct X {};", Lang_CXX03);
   auto From = FirstDeclMatcher<TemplateTypeParmDecl>().match(