From d6ca91ea42455453d08a7922e96fa6685827028d Mon Sep 17 00:00:00 2001
From: Balazs Benics <balazs.benics@sigmatechnology.se>
Date: Sat, 4 Sep 2021 10:19:57 +0200
Subject: [PATCH] [clang][AST] Add support for SubstTemplateTypeParmPackType to
 ASTImporter

Thank you @martong for acquiring a suitable test case!

Reviewed By: shafik, martong

Differential Revision: https://reviews.llvm.org/D109237
---
 clang/lib/AST/ASTImporter.cpp           | 18 ++++++++++++
 clang/unittests/AST/ASTImporterTest.cpp | 51 +++++++++++++++++++++++++++++++++
 2 files changed, 69 insertions(+)

diff --git a/clang/lib/AST/ASTImporter.cpp b/clang/lib/AST/ASTImporter.cpp
index e7d02b6..c30d35a 100644
--- a/clang/lib/AST/ASTImporter.cpp
+++ b/clang/lib/AST/ASTImporter.cpp
@@ -383,6 +383,8 @@ namespace clang {
     ExpectedType VisitTemplateTypeParmType(const TemplateTypeParmType *T);
     ExpectedType VisitSubstTemplateTypeParmType(
         const SubstTemplateTypeParmType *T);
+    ExpectedType
+    VisitSubstTemplateTypeParmPackType(const SubstTemplateTypeParmPackType *T);
     ExpectedType VisitTemplateSpecializationType(
         const TemplateSpecializationType *T);
     ExpectedType VisitElaboratedType(const ElaboratedType *T);
@@ -1486,6 +1488,22 @@ ExpectedType ASTNodeImporter::VisitSubstTemplateTypeParmType(
         Replaced, (*ToReplacementTypeOrErr).getCanonicalType());
 }
 
+ExpectedType ASTNodeImporter::VisitSubstTemplateTypeParmPackType(
+    const SubstTemplateTypeParmPackType *T) {
+  ExpectedType ReplacedOrErr = import(QualType(T->getReplacedParameter(), 0));
+  if (!ReplacedOrErr)
+    return ReplacedOrErr.takeError();
+  const TemplateTypeParmType *Replaced =
+      cast<TemplateTypeParmType>(ReplacedOrErr->getTypePtr());
+
+  Expected<TemplateArgument> ToArgumentPack = import(T->getArgumentPack());
+  if (!ToArgumentPack)
+    return ToArgumentPack.takeError();
+
+  return Importer.getToContext().getSubstTemplateTypeParmPackType(
+      Replaced, *ToArgumentPack);
+}
+
 ExpectedType ASTNodeImporter::VisitTemplateSpecializationType(
                                        const TemplateSpecializationType *T) {
   auto ToTemplateOrErr = import(T->getTemplateName());
diff --git a/clang/unittests/AST/ASTImporterTest.cpp b/clang/unittests/AST/ASTImporterTest.cpp
index d49e7c0..556f206 100644
--- a/clang/unittests/AST/ASTImporterTest.cpp
+++ b/clang/unittests/AST/ASTImporterTest.cpp
@@ -4693,6 +4693,57 @@ TEST_P(ASTImporterOptionSpecificTestBase,
       ToD2->getDeclContext(), ToD2->getTemplateParameters()->getParam(0)));
 }
 
+const AstTypeMatcher<SubstTemplateTypeParmPackType>
+    substTemplateTypeParmPackType;
+
+TEST_P(ASTImporterOptionSpecificTestBase, ImportSubstTemplateTypeParmPackType) {
+  constexpr auto Code = R"(
+    template<typename ...T> struct D {
+      template<typename... U> using B = int(int (*...p)(T, U));
+      template<typename U1, typename U2> D(B<U1, U2>*);
+    };
+    int f(int(int, int), int(int, int));
+
+    using asd = D<float, double, float>::B<int, long, int>;
+    )";
+  Decl *FromTU = getTuDecl(Code, Lang_CXX11, "input.cpp");
+  auto *FromClass = FirstDeclMatcher<ClassTemplateSpecializationDecl>().match(
+      FromTU, classTemplateSpecializationDecl());
+
+  {
+    ASTContext &FromCtx = FromTU->getASTContext();
+    const auto *FromSubstPack = selectFirst<SubstTemplateTypeParmPackType>(
+        "pack", match(substTemplateTypeParmPackType().bind("pack"), FromCtx));
+
+    ASSERT_TRUE(FromSubstPack);
+    ASSERT_EQ(FromSubstPack->getIdentifier()->getName(), "T");
+    ArrayRef<TemplateArgument> FromArgPack =
+        FromSubstPack->getArgumentPack().pack_elements();
+    ASSERT_EQ(FromArgPack.size(), 3u);
+    ASSERT_EQ(FromArgPack[0].getAsType(), FromCtx.FloatTy);
+    ASSERT_EQ(FromArgPack[1].getAsType(), FromCtx.DoubleTy);
+    ASSERT_EQ(FromArgPack[2].getAsType(), FromCtx.FloatTy);
+  }
+  {
+    // Let's do the import.
+    ClassTemplateSpecializationDecl *ToClass = Import(FromClass, Lang_CXX11);
+    ASTContext &ToCtx = ToClass->getASTContext();
+
+    const auto *ToSubstPack = selectFirst<SubstTemplateTypeParmPackType>(
+        "pack", match(substTemplateTypeParmPackType().bind("pack"), ToCtx));
+
+    // Check if it meets the requirements.
+    ASSERT_TRUE(ToSubstPack);
+    ASSERT_EQ(ToSubstPack->getIdentifier()->getName(), "T");
+    ArrayRef<TemplateArgument> ToArgPack =
+        ToSubstPack->getArgumentPack().pack_elements();
+    ASSERT_EQ(ToArgPack.size(), 3u);
+    ASSERT_EQ(ToArgPack[0].getAsType(), ToCtx.FloatTy);
+    ASSERT_EQ(ToArgPack[1].getAsType(), ToCtx.DoubleTy);
+    ASSERT_EQ(ToArgPack[2].getAsType(), ToCtx.FloatTy);
+  }
+}
+
 struct ASTImporterLookupTableTest : ASTImporterOptionSpecificTestBase {};
 
 TEST_P(ASTImporterLookupTableTest, OneDecl) {
-- 
2.7.4