[cxx-interop] Always import cxx shim when cxx-interop is enabled (#60336)

Author: Huddie

include/swift/Frontend/Frontend.h

@@ -563,6 +563,10 @@ class CompilerInstance {
   /// i.e. if it can be found.
   bool canImportSwiftStringProcessing() const;
 
+  /// Whether the CxxShim library can be imported
+  /// i.e. if it can be found.
+  bool canImportCxxShim() const;
+
   /// Gets the SourceFile which is the primary input for this CompilerInstance.
   /// \returns the primary SourceFile, or nullptr if there is no primary input;
   /// if there are _multiple_ primary inputs, fails with an assertion.

include/swift/Strings.h

@@ -30,6 +30,8 @@ constexpr static const StringLiteral SWIFT_DISTRIBUTED_NAME = "Distributed";
 constexpr static const StringLiteral SWIFT_STRING_PROCESSING_NAME = "_StringProcessing";
 /// The name of the SwiftShims module, which contains private stdlib decls.
 constexpr static const StringLiteral SWIFT_SHIMS_NAME = "SwiftShims";
+/// The name of the CxxShim module, which contains a cxx casting utility.
+constexpr static const StringLiteral CXX_SHIM_NAME = "CxxShim";
 /// The name of the Builtin module, which contains Builtin functions.
 constexpr static const StringLiteral BUILTIN_NAME = "Builtin";
 /// The name of the clang imported header module.

lib/Frontend/Frontend.cpp

@@ -861,6 +861,14 @@ bool CompilerInstance::canImportSwiftStringProcessing() const {
   return getASTContext().canImportModule(modulePath);
 }
 
+bool CompilerInstance::canImportCxxShim() const {
+  ImportPath::Module::Builder builder(
+      getASTContext().getIdentifier(CXX_SHIM_NAME));
+  auto modulePath = builder.get();
+  return getASTContext().canImportModule(modulePath) &&
+         !Invocation.getFrontendOptions().InputsAndOutputs.hasModuleInterfaceOutputPath();
+}
+
 ImplicitImportInfo CompilerInstance::getImplicitImportInfo() const {
   auto &frontendOpts = Invocation.getFrontendOptions();
 
@@ -915,6 +923,10 @@ ImplicitImportInfo CompilerInstance::getImplicitImportInfo() const {
     }
   }
 
+  if (Invocation.getLangOptions().EnableCXXInterop && canImportCxxShim()) {
+    pushImport(CXX_SHIM_NAME);
+  }
+
   imports.ShouldImportUnderlyingModule = frontendOpts.ImportUnderlyingModule;
   imports.BridgingHeaderPath = frontendOpts.ImplicitObjCHeaderPath;
   return imports;

test/Interop/Cxx/class/inheritance/fields.swift

@@ -6,7 +6,6 @@
 // UNSUPPORTED: OS=windows-msvc
 
 import StdlibUnittest
-import CxxShim
 import Fields
 
 var FieldsTestSuite = TestSuite("Getting and setting fields in base classes")

test/Interop/Cxx/class/inheritance/functions.swift

@@ -5,7 +5,6 @@
 // XFAIL: OS=windows-msvc
 
 import StdlibUnittest
-import CxxShim
 import Functions
 
 var FunctionsTestSuite = TestSuite("Calling functions in base classes")

test/Interop/Cxx/foreign-reference/pod.swift

@@ -4,7 +4,6 @@
 // XFAIL: OS=windows-msvc
 
 import StdlibUnittest
-import CxxShim
 import POD
 
 extension IntPair {

test/Interop/Cxx/operators/member-inline.swift

@@ -5,7 +5,6 @@
 // XFAIL: OS=windows-msvc
 
 import MemberInline
-import CxxShim
 import StdlibUnittest
 
 var OperatorsTestSuite = TestSuite("Operators")

validation-test/ParseableInterface/verify_all_overlays.py

@@ -54,8 +54,6 @@
     output_path = os.path.join(output_dir, module_name + ".swiftmodule")
     compiler_args = ["-o", output_path, "-module-name", module_name,
                      interface_file]
-    if module_name == "std":
-        compiler_args += ["-enable-experimental-cxx-interop"]
 
     status = subprocess.call(compiler_invocation +
                              compiler_args)