2 files changed, 39 insertions, 0 deletions

diff --git a/clang/lib/AST/ASTImporter.cpp b/clang/lib/AST/ASTImporter.cpp
index 1ac4870cabe..da0d68900af 100644
--- a/clang/lib/AST/ASTImporter.cpp
+++ b/clang/lib/AST/ASTImporter.cpp
@@ -419,6 +419,8 @@ namespace clang {
     Expected<FunctionTemplateAndArgsTy>
     ImportFunctionTemplateWithTemplateArgsFromSpecialization(
         FunctionDecl *FromFD);
+    Error ImportTemplateParameterLists(const DeclaratorDecl *FromD,
+                                       DeclaratorDecl *ToD);
 
     Error ImportTemplateInformation(FunctionDecl *FromFD, FunctionDecl *ToFD);
 
@@ -2780,6 +2782,22 @@ ExpectedDecl ASTNodeImporter::VisitEnumConstantDecl(EnumConstantDecl *D) {
   return ToEnumerator;
 }
 
+Error ASTNodeImporter::ImportTemplateParameterLists(const DeclaratorDecl *FromD,
+                                                    DeclaratorDecl *ToD) {
+  unsigned int Num = FromD->getNumTemplateParameterLists();
+  if (Num == 0)
+    return Error::success();
+  SmallVector<TemplateParameterList *, 2> ToTPLists(Num);
+  for (unsigned int I = 0; I < Num; ++I)
+    if (Expected<TemplateParameterList *> ToTPListOrErr =
+            import(FromD->getTemplateParameterList(I)))
+      ToTPLists[I] = *ToTPListOrErr;
+    else
+      return ToTPListOrErr.takeError();
+  ToD->setTemplateParameterListsInfo(Importer.ToContext, ToTPLists);
+  return Error::success();
+}
+
 Error ASTNodeImporter::ImportTemplateInformation(
     FunctionDecl *FromFD, FunctionDecl *ToFD) {
   switch (FromFD->getTemplatedKind()) {
@@ -2826,6 +2844,9 @@ Error ASTNodeImporter::ImportTemplateInformation(
     if (!POIOrErr)
       return POIOrErr.takeError();
 
+    if (Error Err = ImportTemplateParameterLists(FromFD, ToFD))
+      return Err;
+
     TemplateSpecializationKind TSK = FTSInfo->getTemplateSpecializationKind();
     ToFD->setFunctionTemplateSpecialization(
         std::get<0>(*FunctionAndArgsOrErr), ToTAList, /* InsertPos= */ nullptr,
diff --git a/clang/unittests/AST/ASTImporterTest.cpp b/clang/unittests/AST/ASTImporterTest.cpp
index 7cac2b57036..952e6f92db8 100644
--- a/clang/unittests/AST/ASTImporterTest.cpp
+++ b/clang/unittests/AST/ASTImporterTest.cpp
@@ -5083,6 +5083,24 @@ TEST_P(ASTImporterOptionSpecificTestBase,
   EXPECT_FALSE(ImportedD->getUnderlyingType()->isIncompleteType());
 }
 
+TEST_P(ASTImporterOptionSpecificTestBase, ImportTemplateParameterLists) {
+  auto Code =
+      R"(
+      template<class T>
+      int f() { return 0; }
+      template <> int f<int>() { return 4; }
+      )";
+
+  Decl *FromTU = getTuDecl(Code, Lang_CXX);
+  auto *FromD = FirstDeclMatcher<FunctionDecl>().match(FromTU,
+      functionDecl(hasName("f"), isExplicitTemplateSpecialization()));
+  ASSERT_EQ(FromD->getNumTemplateParameterLists(), 1);
+
+  auto *ToD = Import(FromD, Lang_CXX);
+  // The template parameter list should exist.
+  EXPECT_EQ(ToD->getNumTemplateParameterLists(), 1);
+}
+
 struct ASTImporterLookupTableTest : ASTImporterOptionSpecificTestBase {};
 
 TEST_P(ASTImporterLookupTableTest, OneDecl) {