Add an option to disable ClangImporter imports form source. …

include/swift/ClangImporter/ClangImporterOptions.h

@@ -99,6 +99,10 @@ class ClangImporterOptions {
   /// When set, don't enforce warnings with -Werror.
   bool DebuggerSupport = false;
 
+  /// When set, ClangImporter is disabled, and all requests go to the
+  /// DWARFImporter delegate.
+  bool DisableSourceImport = false;
+
   /// Return a hash code of any components from these options that should
   /// contribute to a Swift Bridging PCH hash.
   llvm::hash_code getPCHHashComponents() const {

include/swift/Option/FrontendOptions.td

@@ -268,6 +268,10 @@ def debug_crash_after_parse : Flag<["-"], "debug-crash-after-parse">,
 def debugger_support : Flag<["-"], "debugger-support">,
   HelpText<"Process swift code as if running in the debugger">;
 
+def disable_clangimporter_source_import : Flag<["-"],
+  "disable-clangimporter-source-import">,
+  HelpText<"Disable ClangImporter and forward all requests straight the DWARF importer.">;
+
 def disable_arc_opts : Flag<["-"], "disable-arc-opts">,
   HelpText<"Don't run SIL ARC optimization passes.">;
 def disable_ossa_opts : Flag<["-"], "disable-ossa-opts">,

lib/ClangImporter/ClangImporter.cpp

@@ -1757,18 +1757,24 @@ ModuleDecl *ClangImporter::Implementation::loadModuleClang(
   return finishLoadingClangModule(clangModule, /*preferOverlay=*/false);
 }
 
-ModuleDecl *ClangImporter::loadModule(
-    SourceLoc importLoc,
-    ArrayRef<std::pair<Identifier, SourceLoc>> path) {
-  ModuleDecl *MD = Impl.loadModuleClang(importLoc, path);
+ModuleDecl *
+ClangImporter::loadModule(SourceLoc importLoc,
+                          ArrayRef<std::pair<Identifier, SourceLoc>> path) {
+  return Impl.loadModule(importLoc, path);
+}
+
+ModuleDecl *ClangImporter::Implementation::loadModule(
+    SourceLoc importLoc, ArrayRef<std::pair<Identifier, SourceLoc>> path) {
+  ModuleDecl *MD = nullptr;
+  if (!DisableSourceImport)
+    MD = loadModuleClang(importLoc, path);
   if (!MD)
-    MD = Impl.loadModuleDWARF(importLoc, path);
+    MD = loadModuleDWARF(importLoc, path);
   return MD;
 }
 
 ModuleDecl *ClangImporter::Implementation::finishLoadingClangModule(
-    const clang::Module *clangModule,
-    bool findOverlay) {
+    const clang::Module *clangModule, bool findOverlay) {
   assert(clangModule);
 
   // Bump the generation count.
@@ -1954,6 +1960,7 @@ ClangImporter::Implementation::Implementation(
       BridgingHeaderLookupTable(new SwiftLookupTable(nullptr)),
       BuffersForDiagnostics(ctx.SourceMgr),
       platformAvailability(ctx.LangOpts), nameImporter(),
+      DisableSourceImport(opts.DisableSourceImport),
       DWARFImporter(dwarfImporterDelegate) {}
 
 ClangImporter::Implementation::~Implementation() {
@@ -2613,7 +2620,8 @@ void ClangImporter::lookupTypeDecl(
   clang::LookupResult lookupResult(sema, clangName, clang::SourceLocation(),
                                    lookupKind);
   bool foundViaClang = false;
-  if (sema.LookupName(lookupResult, /*Scope=*/nullptr)) {
+  if (!Impl.DisableSourceImport &&
+      sema.LookupName(lookupResult, /*Scope=*/nullptr)) {
     for (auto clangDecl : lookupResult) {
       if (!isa<clang::TypeDecl>(clangDecl) &&
           !isa<clang::ObjCContainerDecl>(clangDecl) &&

lib/ClangImporter/ImporterImpl.h

@@ -605,6 +605,10 @@ class LLVM_LIBRARY_VISIBILITY ClangImporter::Implementation
   bool shouldIgnoreBridgeHeaderTopLevelDecl(clang::Decl *D);
 
 private:
+  /// When set, ClangImporter is disabled, and all requests go to the
+  /// DWARFImporter delegate.
+  bool DisableSourceImport;
+
   /// The DWARF importer delegate, if installed.
   DWARFImporterDelegate *DWARFImporter = nullptr;
 public:
@@ -614,7 +618,7 @@ class LLVM_LIBRARY_VISIBILITY ClangImporter::Implementation
 private:
   /// The list of Clang modules found in the debug info.
   llvm::DenseMap<Identifier, LoadedFile *> DWARFModuleUnits;
-public:
+
   /// Load a module using the clang::CompilerInstance.
   ModuleDecl *loadModuleClang(SourceLoc importLoc,
                               ArrayRef<std::pair<Identifier, SourceLoc>> path);
@@ -624,7 +628,11 @@ class LLVM_LIBRARY_VISIBILITY ClangImporter::Implementation
   ModuleDecl *loadModuleDWARF(SourceLoc importLoc,
                               ArrayRef<std::pair<Identifier, SourceLoc>> path);
 
-
+public:
+  /// Load a module using either method.
+  ModuleDecl *loadModule(SourceLoc importLoc,
+                         ArrayRef<std::pair<Identifier, SourceLoc>> path);
+
   void recordImplicitUnwrapForDecl(ValueDecl *decl, bool isIUO) {
     if (!isIUO)
       return;

lib/Frontend/CompilerInvocation.cpp

@@ -638,7 +638,12 @@ static bool ParseClangImporterArgs(ClangImporterOptions &Opts,
 
   if (Args.hasArg(OPT_warnings_as_errors))
     Opts.ExtraArgs.push_back("-Werror");
+
   Opts.DebuggerSupport |= Args.hasArg(OPT_debugger_support);
+
+  Opts.DisableSourceImport |=
+      Args.hasArg(OPT_disable_clangimporter_source_import);
+
   return false;
 }
 

test/ClangImporter/disable-source-import.swift

@@ -0,0 +1,18 @@
+// RUN: %empty-directory(%t.mcp)
+
+// This should fail only if -disable-clangimporter-source-import is present.
+
+// RUN: %target-swift-frontend(mock-sdk: %clang-importer-sdk) \
+// RUN:    -enable-objc-interop -typecheck -I %S/Inputs/custom-modules \
+// RUN:    -module-cache-path %t.mcp %s | %FileCheck --allow-empty %s
+
+// RUN: not %target-swift-frontend(mock-sdk: %clang-importer-sdk) \
+// RUN:    -enable-objc-interop -typecheck -o - -I %S/Inputs/custom-modules \
+// RUN:    -module-cache-path %t.mcp -disable-clangimporter-source-import %s \
+// RUN:    2>&1 | %FileCheck --check-prefix=ERROR %s
+
+import ExternIntX
+
+public let y = x // ERROR: error
+
+// CHECK-NOT: error