[interop] support 'default' mode for '-cxx-interoperability-mode' option

Default corresponds to the Swift language version used to compile the input. Swift-5.9 is still supported for now, but will be removed shortly

docs/CppInteroperability/GettingStartedWithC++Interop.md

@@ -32,7 +32,7 @@ module CxxTest {
 Add the C++ module to the include path and enable C++ interop:
 - Navigate to your project directory
 - In `Project` navigate to `Build Settings` -> `Swift Compiler`
-- Under `Custom Flags` -> `Other Swift Flags` add `-cxx-interoperability-mode=swift-5.9`
+- Under `Custom Flags` -> `Other Swift Flags` add `-cxx-interoperability-mode=default`
 - Under `Search Paths` -> `Import Paths` add your search path to the C++ module (i.e, `./ProjectName/CxxTest`). 
 
 - This should now allow your to import your C++ Module into any `.swift` file.
@@ -81,7 +81,7 @@ After creating your Swift package project, follow the steps [Creating a Module t
 - Swift code will be in `Sources/CxxInterop` called `main.swift`
 - C++ source code follows the example shown in [Creating a Module to contain your C++ source code](#creating-a-module-to-contain-your-c-source-code)
 - Under targets, add the name of your C++ module and the directory containing the Swift code as a target.
-- In the target defining your Swift target, add a`dependencies` to the C++ Module, the `path`, `source`, and `swiftSettings` with `unsafeFlags` with the source to the C++ Module, and enable `-cxx-interoperability-mode=swift-5.9`
+- In the target defining your Swift target, add a`dependencies` to the C++ Module, the `path`, `source`, and `swiftSettings` with `unsafeFlags` with the source to the C++ Module, and enable `-cxx-interoperability-mode=default`
 
 ```
 //In Package Manifest
@@ -111,7 +111,7 @@ let package = Package(
             sources: [ "main.swift" ],
             swiftSettings: [.unsafeFlags([
                 "-I", "Sources/CxxTest",
-                "-cxx-interoperability-mode=swift-5.9",
+                "-cxx-interoperability-mode=default",
             ])]
         ),
     ]
@@ -144,7 +144,7 @@ After creating your project follow the steps [Creating a Module to contain your
 - Create a `CMakeLists.txt` file and configure for your project
 - In`add_library` invoke `cxx-support` with the path to the C++ implementation file
 - Add the `target_include_directories` with `cxx-support` and path to the C++ Module `${CMAKE_SOURCE_DIR}/Sources/CxxTest`
-- Add the `add_executable` to the specific files/directory you would like to generate source, with`SHELL:-cxx-interoperability-mode=swift-5.9`.
+- Add the `add_executable` to the specific files/directory you would like to generate source, with`SHELL:-cxx-interoperability-mode=default`.
 - In the example below we will be following the file structure used in [Creating a Swift Package](#Creating-a-Swift-Package)
 
 ```
@@ -167,7 +167,7 @@ target_include_directories(cxx-support PUBLIC
 
 add_executable(CxxInterop ./Sources/CxxInterop/main.swift)
 target_compile_options(CxxInterop PRIVATE
-  "SHELL:-cxx-interoperability-mode=swift-5.9"
+  "SHELL:-cxx-interoperability-mode=default"
 target_link_libraries(CxxInterop PRIVATE cxx-support)
 
 ```

include/swift/AST/DiagnosticsFrontend.def

@@ -514,10 +514,9 @@ WARNING(compiler_plugin_not_loaded,none,
 ERROR(dont_enable_interop_and_compat,none,
       "do not pass both -enable-experimental-cxx-interop and "
       "-cxx-interoperability-mode. Remove -enable-experimental-cxx-interop.", ())
-      
-ERROR(invalid_interop_compat_mode,none,
-      "invalid option passed to -cxx-interoperability-mode. Please select either "
-      "'off' or 'swift-5.9'.", ())
+
+NOTE(valid_cxx_interop_modes,none,
+      "valid arguments to '-cxx-interoperability-mode=' are %0", (StringRef))
 NOTE(swift_will_maintain_compat,none,
      "Swift will maintain source compatibility for imported APIs based on the "
      "selected compatibility mode, so updating the Swift compiler will not "

lib/Frontend/CompilerInvocation.cpp

@@ -438,11 +438,26 @@ enum class CxxCompatMode {
 static CxxCompatMode validateCxxInteropCompatibilityMode(StringRef mode) {
   if (mode == "off")
     return CxxCompatMode::off;
+  if (mode == "default")
+    return CxxCompatMode::enabled;
+  // FIXME: Drop swift-5.9.
   if (mode == "swift-5.9")
     return CxxCompatMode::enabled;
   return CxxCompatMode::invalid;
 }
 
+static void diagnoseCxxInteropCompatMode(Arg *verArg, ArgList &Args,
+                                         DiagnosticEngine &diags) {
+  // General invalid argument error
+  diags.diagnose(SourceLoc(), diag::error_invalid_arg_value,
+                 verArg->getAsString(Args), verArg->getValue());
+
+  // Note valid C++ interoperability modes.
+  auto validVers = {llvm::StringRef("off"), llvm::StringRef("default")};
+  auto versStr = "'" + llvm::join(validVers, "', '") + "'";
+  diags.diagnose(SourceLoc(), diag::valid_cxx_interop_modes, versStr);
+}
+
 static bool ParseLangArgs(LangOptions &Opts, ArgList &Args,
                           DiagnosticEngine &Diags,
                           const FrontendOptions &FrontendOpts) {
@@ -940,10 +955,8 @@ static bool ParseLangArgs(LangOptions &Opts, ArgList &Args,
     auto interopCompatMode = validateCxxInteropCompatibilityMode(A->getValue());
     Opts.EnableCXXInterop |= (interopCompatMode == CxxCompatMode::enabled);
 
-    if (interopCompatMode == CxxCompatMode::invalid) {
-      Diags.diagnose(SourceLoc(), diag::invalid_interop_compat_mode);
-      Diags.diagnose(SourceLoc(), diag::swift_will_maintain_compat);
-    }
+    if (interopCompatMode == CxxCompatMode::invalid)
+      diagnoseCxxInteropCompatMode(A, Args, Diags);
   }
   
   if (Args.hasArg(OPT_enable_experimental_cxx_interop)) {

test/Interop/Cxx/driver/enable-interop-flag-depr.swift

@@ -1,6 +1,6 @@
 // RUN: rm -rf %t
 // RUN: split-file %s %t
-// RUN: not %target-swift-frontend -typecheck -I %t/Inputs  %t/test.swift  -enable-experimental-cxx-interop -cxx-interoperability-mode=swift-5.9 2>&1 | %FileCheck %s
+// RUN: not %target-swift-frontend -typecheck -I %t/Inputs  %t/test.swift  -enable-experimental-cxx-interop -cxx-interoperability-mode=default 2>&1 | %FileCheck %s
 
 //--- Inputs/module.modulemap
 module Test {

test/Interop/Cxx/driver/invalid-interop-compat-mode.swift

@@ -2,6 +2,9 @@
 // RUN: split-file %s %t
 // RUN: not %target-swift-frontend -typecheck -I %t/Inputs  %t/test.swift  -cxx-interoperability-mode=swift-5.8 2>&1 | %FileCheck %s
 
+// Note: swift-5.9 is still supported, but will be removed.
+// RUN: %target-swift-frontend -typecheck -I %t/Inputs  %t/test.swift  -cxx-interoperability-mode=swift-5.9
+
 //--- Inputs/module.modulemap
 module Test {
     header "test.h"
@@ -14,5 +17,5 @@ module Test {
 
 import Test
 
-// CHECK: error: invalid option passed to -cxx-interoperability-mode. Please select either 'off' or 'swift-5.9'.
-// CHECK: note: Swift will maintain source compatibility for imported APIs based on the selected compatibility mode, so updating the Swift compiler will not change how APIs are imported.
+// CHECK: error: invalid value 'swift-5.8' in '-cxx-interoperability-mode=swift-5.8'
+// CHECK: note: valid arguments to '-cxx-interoperability-mode=' are 'off', 'default'

test/Interop/SwiftToCxx/cross-module-refs/imported-struct-refs-in-cxx.swift

@@ -6,7 +6,7 @@
 // RUN: %FileCheck %s < %t/uses-structs.h
 // RUN: %check-interop-cxx-header-in-clang(-I %t %t/uses-structs.h)
 
-// RUN: %target-swift-frontend %s -typecheck -module-name UsesStructs -I %t -cxx-interoperability-mode=swift-5.9 -emit-clang-header-path %t/uses-structs-default.h -clang-header-expose-module Structs=structs.h
+// RUN: %target-swift-frontend %s -typecheck -module-name UsesStructs -I %t -cxx-interoperability-mode=default -emit-clang-header-path %t/uses-structs-default.h -clang-header-expose-module Structs=structs.h
 // RUN: %check-interop-cxx-header-in-clang(-I %t %t/uses-structs-default.h)
 
 import Structs

test/SourceKit/InterfaceGen/gen_clang_cxx_module.swift

@@ -2,7 +2,7 @@
 // RUN: split-file %s %t
 
 // RUN: %sourcekitd-test -req=interface-gen -module CxxModule -- -Xfrontend -disable-implicit-concurrency-module-import -Xfrontend -disable-implicit-string-processing-module-import -I %t/Inputs -target %target-triple %clang-importer-sdk-nosource | %FileCheck %s
-// RUN: %sourcekitd-test -req=interface-gen -module CxxModule -- -Xfrontend -disable-implicit-concurrency-module-import -Xfrontend -disable-implicit-string-processing-module-import -cxx-interoperability-mode=swift-5.9 -I %t/Inputs -target %target-triple %clang-importer-sdk-nosource | %FileCheck %s
+// RUN: %sourcekitd-test -req=interface-gen -module CxxModule -- -Xfrontend -disable-implicit-concurrency-module-import -Xfrontend -disable-implicit-string-processing-module-import -cxx-interoperability-mode=default -I %t/Inputs -target %target-triple %clang-importer-sdk-nosource | %FileCheck %s
 
 
 // RUN: not %sourcekitd-test -req=interface-gen -module CxxModule -- -Xfrontend -disable-implicit-concurrency-module-import -Xfrontend -disable-implicit-string-processing-module-import -Xcc -DERROR  -I %t/Inputs -target %target-triple %clang-importer-sdk-nosource 2>&1 | %FileCheck --check-prefix=NOLOAD %s

test/SourceKit/InterfaceGen/gen_clang_libcxx_sdk_module.swift

@@ -1,4 +1,4 @@
-// RUN: %sourcekitd-test -req=interface-gen -module CxxStdlib -- -Xfrontend -disable-implicit-concurrency-module-import -Xfrontend -disable-implicit-string-processing-module-import -cxx-interoperability-mode=swift-5.9 -target %target-triple -sdk %sdk | %FileCheck %s
+// RUN: %sourcekitd-test -req=interface-gen -module CxxStdlib -- -Xfrontend -disable-implicit-concurrency-module-import -Xfrontend -disable-implicit-string-processing-module-import -cxx-interoperability-mode=default -target %target-triple -sdk %sdk | %FileCheck %s
 
 // REQUIRES: OS=macosx
 

test/lit.cfg

@@ -744,8 +744,8 @@ elif swift_test_mode == 'with_cxx_interop':
     config.available_features.add("nonexecutable_test")
     config.available_features.add("executable_test")
     config.available_features.add("with_cxx_interop")
-    config.swift_frontend_test_options += ' -cxx-interoperability-mode=swift-5.9'
-    config.swift_driver_test_options += ' -cxx-interoperability-mode=swift-5.9'
+    config.swift_frontend_test_options += ' -cxx-interoperability-mode=default'
+    config.swift_driver_test_options += ' -cxx-interoperability-mode=default'
 else:
     lit_config.fatal("Unknown test mode %r" % swift_test_mode)
 
@@ -2400,7 +2400,7 @@ config.substitutions.insert(0, ('%check-cxx-header-in-clang',
 config.substitutions.append(('%env-', config.target_env_prefix))
 
 config.substitutions.append(('%target-clangxx', '%s -std=c++11' % config.target_clang))
-config.substitutions.append(('%target-swiftxx-frontend', '%s -cxx-interoperability-mode=swift-5.9' % config.target_swift_frontend))
+config.substitutions.append(('%target-swiftxx-frontend', '%s -cxx-interoperability-mode=default' % config.target_swift_frontend))
 
 config.substitutions.append(('%target-runtime', config.target_runtime))
 

tools/SourceKit/lib/SwiftLang/SwiftEditorInterfaceGen.cpp

@@ -724,7 +724,7 @@ void SwiftLangSupport::editorOpenInterface(EditorConsumer &Consumer,
       }
       if (retryWithCxxEnabled) {
           std::vector<const char *> AdjustedArgs(Args.begin(), Args.end());
-          AdjustedArgs.push_back("-cxx-interoperability-mode=swift-5.9");
+          AdjustedArgs.push_back("-cxx-interoperability-mode=default");
           return editorOpenInterface(Consumer, Name, ModuleName, Group, AdjustedArgs,
                                      SynthesizedExtensions, InterestedUSR);
       }