Merge pull request swiftlang#25870 from pschuh/cpp-1

Add -enable-cxx-interop flag and support for extern "C" {}

Author: pschuh

include/swift/Basic/LangOptions.h

@@ -147,6 +147,12 @@ namespace swift {
     /// configuration options.
     bool EnableObjCInterop = true;
 
+    /// Enable C++ interop code generation and build configuration
+    /// options. Disabled by default because there is no way to control the
+    /// language mode of clang on a per-header or even per-module basis. Also
+    /// disabled because it is not complete.
+    bool EnableCXXInterop = false;
+
     /// On Darwin platforms, use the pre-stable ABI's mark bit for Swift
     /// classes instead of the stable ABI's bit. This is needed when
     /// targeting OSes prior to macOS 10.14.4 and iOS 12.2, where

include/swift/Option/FrontendOptions.td

@@ -500,6 +500,11 @@ def emit_sorted_sil : Flag<["-"], "emit-sorted-sil">,
 def emit_syntax : Flag<["-"], "emit-syntax">,
   HelpText<"Parse input file(s) and emit the Syntax tree(s) as JSON">, ModeOpt;
 
+def enable_cxx_interop :
+  Flag<["-"], "enable-cxx-interop">,
+  HelpText<"Enable C++ interop code generation and config directives">,
+  Flags<[FrontendOption, HelpHidden]>;
+
 def use_malloc : Flag<["-"], "use-malloc">,
   HelpText<"Allocate internal data structures using malloc "
            "(for memory debugging)">;

lib/ClangImporter/ClangImporter.cpp

@@ -498,8 +498,11 @@ getNormalInvocationArguments(std::vector<std::string> &invocationArgStrs,
         "-Werror=non-modular-include-in-framework-module");
 
   if (LangOpts.EnableObjCInterop) {
-    invocationArgStrs.insert(invocationArgStrs.end(),
-                             {"-x", "objective-c", "-std=gnu11", "-fobjc-arc"});
+    bool EnableCXXInterop = LangOpts.EnableCXXInterop;
+    invocationArgStrs.insert(
+        invocationArgStrs.end(),
+        {"-x", EnableCXXInterop ? "objective-c++" : "objective-c",
+         EnableCXXInterop ? "-std=gnu++17" : "-std=gnu11", "-fobjc-arc"});
     // TODO: Investigate whether 7.0 is a suitable default version.
     if (!triple.isOSDarwin())
       invocationArgStrs.insert(invocationArgStrs.end(),
@@ -518,7 +521,10 @@ getNormalInvocationArguments(std::vector<std::string> &invocationArgStrs,
       });
 
   } else {
-    invocationArgStrs.insert(invocationArgStrs.end(), {"-x", "c", "-std=gnu11"});
+    bool EnableCXXInterop = LangOpts.EnableCXXInterop;
+    invocationArgStrs.insert(invocationArgStrs.end(),
+                             {"-x", EnableCXXInterop ? "c++" : "c",
+                              EnableCXXInterop ? "-std=gnu++17" : "-std=gnu11"});
   }
 
   // Set C language options.

lib/ClangImporter/ImportDecl.cpp

@@ -8399,7 +8399,7 @@ bool ClangImporter::Implementation::addMemberAndAlternatesToExtension(
   // Quickly check the context and bail out if it obviously doesn't
   // belong here.
   if (auto *importDC = newName.getEffectiveContext().getAsDeclContext())
-    if (importDC->isTranslationUnit())
+    if (importDC->isFileContext())
       return true;
 
   // Then try to import the decl under the specified name.

lib/ClangImporter/ImportName.cpp

@@ -1404,8 +1404,8 @@ ImportedName NameImporter::importNameImpl(const clang::NamedDecl *D,
   case clang::DeclarationName::CXXOperatorName:
   case clang::DeclarationName::CXXUsingDirective:
   case clang::DeclarationName::CXXDeductionGuideName:
-    // Handling these is part of C++ interoperability.
-    llvm_unreachable("unhandled C++ interoperability");
+    // TODO: Handling these is part of C++ interoperability.
+    return ImportedName();
 
   case clang::DeclarationName::Identifier:
     // Map the identifier.

lib/ClangImporter/SwiftLookupTable.cpp

@@ -81,6 +81,9 @@ class SwiftLookupTableWriter : public clang::ModuleFileExtensionWriter {
                               llvm::BitstreamWriter &stream) override;
 
   void populateTable(SwiftLookupTable &table, NameImporter &);
+
+  void populateTableWithDecl(SwiftLookupTable &table,
+                             NameImporter &nameImporter, clang::Decl *decl);
 };
 
 /// Module file extension reader for the Swift lookup tables.
@@ -1793,21 +1796,35 @@ void importer::finalizeLookupTable(SwiftLookupTable &table,
   }
 }
 
+void SwiftLookupTableWriter::populateTableWithDecl(SwiftLookupTable &table,
+                                                   NameImporter &nameImporter,
+                                                   clang::Decl *decl) {
+  // Skip anything from an AST file.
+  if (decl->isFromASTFile())
+    return;
+
+  // Iterate into extern "C" {} type declarations.
+  if (auto linkageDecl = dyn_cast<clang::LinkageSpecDecl>(decl)) {
+    for (auto *decl : linkageDecl->noload_decls()) {
+      populateTableWithDecl(table, nameImporter, decl);
+    }
+    return;
+  }
+
+  // Skip non-named declarations.
+  auto named = dyn_cast<clang::NamedDecl>(decl);
+  if (!named)
+    return;
+
+  // Add this entry to the lookup table.
+  addEntryToLookupTable(table, named, nameImporter);
+}
+
 void SwiftLookupTableWriter::populateTable(SwiftLookupTable &table,
                                            NameImporter &nameImporter) {
   auto &sema = nameImporter.getClangSema();
   for (auto decl : sema.Context.getTranslationUnitDecl()->noload_decls()) {
-    // Skip anything from an AST file.
-    if (decl->isFromASTFile())
-      continue;
-
-    // Skip non-named declarations.
-    auto named = dyn_cast<clang::NamedDecl>(decl);
-    if (!named)
-      continue;
-
-    // Add this entry to the lookup table.
-    addEntryToLookupTable(table, named, nameImporter);
+    populateTableWithDecl(table, nameImporter, decl);
   }
 
   // Add macros to the lookup table.

lib/ClangImporter/SwiftLookupTable.h

@@ -196,6 +196,8 @@ class EffectiveClangContext {
       DC = omDecl->getCanonicalDecl();
     } else if (auto fDecl = dyn_cast<clang::FunctionDecl>(dc)) {
       DC = fDecl->getCanonicalDecl();
+    } else if (auto nsDecl = dyn_cast<clang::NamespaceDecl>(dc)) {
+      DC = nsDecl->getCanonicalDecl();
     } else {
       assert(isa<clang::TranslationUnitDecl>(dc) ||
              isa<clang::ObjCContainerDecl>(dc) &&

lib/Driver/ToolChains.cpp

@@ -194,6 +194,7 @@ static void addCommonFrontendArgs(const ToolChain &TC, const OutputInfo &OI,
   inputArgs.AddLastArg(arguments, options::OPT_enable_library_evolution);
   inputArgs.AddLastArg(arguments, options::OPT_enable_testing);
   inputArgs.AddLastArg(arguments, options::OPT_enable_private_imports);
+  inputArgs.AddLastArg(arguments, options::OPT_enable_cxx_interop);
   inputArgs.AddLastArg(arguments, options::OPT_g_Group);
   inputArgs.AddLastArg(arguments, options::OPT_debug_info_format);
   inputArgs.AddLastArg(arguments, options::OPT_import_underlying_module);

lib/Frontend/CompilerInvocation.cpp

@@ -499,6 +499,7 @@ static bool ParseLangArgs(LangOptions &Opts, ArgList &Args,
     TargetArg = A->getValue();
   }
 
+  Opts.EnableCXXInterop |= Args.hasArg(OPT_enable_cxx_interop);
   Opts.EnableObjCInterop =
       Args.hasFlag(OPT_enable_objc_interop, OPT_disable_objc_interop,
                    Target.isOSDarwin());

stdlib/public/SwiftShims/GlobalObjects.h

@@ -24,7 +24,10 @@
 #include "Visibility.h"
 
 #ifdef __cplusplus
-namespace swift { extern "C" {
+#ifndef __swift__
+namespace swift {
+#endif
+extern "C" {
 #endif
 
 struct _SwiftArrayBodyStorage {
@@ -102,7 +105,10 @@ static_assert(
     4 * sizeof(__swift_intptr_t) + sizeof(__swift_int64_t),
   "_SwiftSetBodyStorage has unexpected size");
 
-}} // extern "C", namespace swift
+} // extern "C"
+#ifndef __swift__
+} // namespace swift
+#endif
 #endif
 
 #endif