[cxx-interop] serialize x-refs for class template specializations

lib/ClangImporter/ClangImporter.cpp

@@ -4837,13 +4837,19 @@ TinyPtrVector<ValueDecl *> CXXNamespaceMemberLookup::evaluate(
   auto &ctx = namespaceDecl->getASTContext();
 
   TinyPtrVector<ValueDecl *> result;
+  llvm::SmallPtrSet<clang::NamedDecl *, 8> importedDecls;
   for (auto redecl : clangNamespaceDecl->redecls()) {
     auto allResults = evaluateOrDefault(
         ctx.evaluator, ClangDirectLookupRequest({namespaceDecl, redecl, name}),
         {});
 
     for (auto found : allResults) {
       auto clangMember = found.get<clang::NamedDecl *>();
+      auto it = importedDecls.insert(clangMember);
+      // Skip over members already found during lookup in
+      // prior redeclarations.
+      if (!it.second)
+        continue;
       if (auto import =
               ctx.getClangModuleLoader()->importDeclDirectly(clangMember))
         result.push_back(cast<ValueDecl>(import));

lib/Serialization/CMakeLists.txt

@@ -18,6 +18,7 @@ target_link_libraries(swiftSerialization PRIVATE
   swiftClangImporter
   swiftOption
   swiftAST
-  swiftSIL)
+  swiftSIL
+  clangIndex)
 
 set_swift_llvm_is_available(swiftSerialization)

lib/Serialization/Deserialization.cpp

@@ -43,6 +43,7 @@
 #include "clang/AST/Attr.h"
 #include "clang/Basic/SourceManager.h"
 #include "clang/Basic/AttributeCommonInfo.h"
+#include "clang/Index/USRGeneration.h"
 #include "llvm/ADT/Statistic.h"
 #include "llvm/Support/Compiler.h"
 #include "llvm/Support/Debug.h"
@@ -2425,12 +2426,35 @@ ModuleFile::resolveCrossReference(ModuleID MID, uint32_t pathLen) {
       }
 
       if (!privateDiscriminator.empty()) {
-        ModuleDecl *searchModule = M;
-        if (!searchModule)
-          searchModule = nominal->getModuleContext();
-        searchModule->lookupMember(values, nominal, memberName,
-                                   privateDiscriminator);
-
+        if (importedFromClang) {
+          // This is a clang imported class template, that's
+          // serialized using original template name, and
+          // its USR that denotes the specific specialization.
+          auto members = nominal->lookupDirect(memberName);
+          for (const auto &m : members) {
+            if (!m->hasClangNode())
+              continue;
+            if (auto *ctd =
+                    dyn_cast<clang::ClassTemplateDecl>(m->getClangDecl())) {
+              for (const auto *spec : ctd->specializations()) {
+                llvm::SmallString<128> buffer;
+                clang::index::generateUSRForDecl(spec, buffer);
+                if (privateDiscriminator.str() == buffer) {
+                  if (auto import = getContext()
+                                        .getClangModuleLoader()
+                                        ->importDeclDirectly(spec))
+                    values.push_back(cast<ValueDecl>(import));
+                }
+              }
+            }
+          }
+        } else {
+          ModuleDecl *searchModule = M;
+          if (!searchModule)
+            searchModule = nominal->getModuleContext();
+          searchModule->lookupMember(values, nominal, memberName,
+                                     privateDiscriminator);
+        }
       } else {
         auto members = nominal->lookupDirect(memberName);
         values.append(members.begin(), members.end());

lib/Serialization/Serialization.cpp

@@ -55,6 +55,7 @@
 #include "swift/Strings.h"
 #include "clang/AST/DeclTemplate.h"
 #include "clang/Frontend/CompilerInstance.h"
+#include "clang/Index/USRGeneration.h"
 #include "clang/Serialization/ASTReader.h"
 #include "llvm/ADT/SmallSet.h"
 #include "llvm/ADT/SmallString.h"
@@ -2060,6 +2061,22 @@ getStableClangDeclPathComponentKind(
   llvm_unreachable("bad kind");
 }
 
+static Identifier getClangTemplateSpecializationXRefDiscriminator(
+    ASTContext &ctx, Identifier &name,
+    const clang::ClassTemplateSpecializationDecl *ctsd) {
+  auto it = name.str().find("<");
+  if (it == StringRef::npos)
+    return Identifier();
+  // Serialize a C++ class template specialization name as original
+  // class template name, and use its USR as the discriminator, that
+  // will let Swift find the correct specialization when this cross
+  // reference is deserialized.
+  name = ctx.getIdentifier(name.str().substr(0, it));
+  llvm::SmallString<128> buffer;
+  clang::index::generateUSRForDecl(ctsd, buffer);
+  return ctx.getIdentifier(buffer.str());
+}
+
 void Serializer::writeCrossReference(const DeclContext *DC, uint32_t pathLen) {
   using namespace decls_block;
 
@@ -2116,11 +2133,19 @@ void Serializer::writeCrossReference(const DeclContext *DC, uint32_t pathLen) {
 
     bool isProtocolExt = DC->getParent()->getExtendedProtocolDecl();
 
+    Identifier name = generic->getName();
+    if (generic->hasClangNode()) {
+      if (auto *ctsd = dyn_cast_or_null<clang::ClassTemplateSpecializationDecl>(
+              generic->getClangDecl())) {
+        assert(discriminator.empty());
+        discriminator = getClangTemplateSpecializationXRefDiscriminator(
+            getASTContext(), name, ctsd);
+      }
+    }
     XRefTypePathPieceLayout::emitRecord(Out, ScratchRecord, abbrCode,
-                                        addDeclBaseNameRef(generic->getName()),
+                                        addDeclBaseNameRef(name),
                                         addDeclBaseNameRef(discriminator),
-                                        isProtocolExt,
-                                        generic->hasClangNode());
+                                        isProtocolExt, generic->hasClangNode());
     break;
   }
 
@@ -2290,10 +2315,19 @@ void Serializer::writeCrossReference(const Decl *D) {
       discriminator = containingFile->getDiscriminatorForPrivateDecl(type);
     }
 
-    XRefTypePathPieceLayout::emitRecord(Out, ScratchRecord, abbrCode,
-                                        addDeclBaseNameRef(type->getName()),
-                                        addDeclBaseNameRef(discriminator),
-                                        isProtocolExt, D->hasClangNode());
+    Identifier name = type->getName();
+    if (type->hasClangNode()) {
+      if (auto *ctsd = dyn_cast_or_null<clang::ClassTemplateSpecializationDecl>(
+              type->getClangDecl())) {
+        assert(discriminator.empty());
+        discriminator = getClangTemplateSpecializationXRefDiscriminator(
+            getASTContext(), name, ctsd);
+      }
+    }
+
+    XRefTypePathPieceLayout::emitRecord(
+        Out, ScratchRecord, abbrCode, addDeclBaseNameRef(name),
+        addDeclBaseNameRef(discriminator), isProtocolExt, D->hasClangNode());
     return;
   }
 

test/Interop/Cxx/templates/swift-class-template-specialization-module-xref.swift

@@ -0,0 +1,78 @@
+// RUN: %empty-directory(%t)
+// RUN: split-file %s %t
+// RUN: %target-swiftxx-frontend -emit-module %t/Inputs/test.swift -module-name TestA -I %t/Inputs -o %t/test-part.swiftmodule
+// RUN: %target-swiftxx-frontend -merge-modules -emit-module %t/test-part.swiftmodule -module-name TestA -I %t/Inputs -o %t/TestA.swiftmodule -sil-verify-none
+// RUN: %target-swift-ide-test -print-module -module-to-print=TestA -I %t/ -source-filename=test -enable-experimental-cxx-interop | %FileCheck %s
+
+//--- Inputs/module.modulemap
+module CxxHeader {
+    header "header.h"
+    requires cplusplus
+}
+
+//--- Inputs/header.h
+
+#include <stddef.h>
+
+namespace std2 {
+
+template<class T>
+class vec {
+public:
+  using Element = T;
+  using RawIterator = const T  * _Nonnull;
+  vec() {}
+  vec(const vec<T> &other) : items(other.items) { }
+  ~vec() {}
+
+  T * _Nonnull begin() {
+    return items;
+  }
+  T * _Nonnull end() {
+    return items + 10;
+  }
+  RawIterator begin() const {
+    return items;
+  }
+  RawIterator end() const {
+    return items + 10;
+  }
+  size_t size() const {
+    return 10;
+  }
+
+private:
+  T items[10];
+};
+
+} // namespace std2
+
+namespace ns2 {
+
+class App {
+public:
+
+  inline std2::vec<App> getApps() const {
+    return {};
+  }
+  int x  = 0;
+};
+
+} // namespace ns2
+
+using vec2Apps = std2::vec<ns2::App>;
+
+//--- Inputs/test.swift
+
+import Cxx
+import CxxHeader
+
+extension vec2Apps : CxxSequence {
+}
+
+public func testFunction() -> [Int] {
+  let applications = ns2.App().getApps()
+  return applications.map { Int($0.x) }
+}
+
+// CHECK: func testFunction() -> [Int]