[5.5] Do not build Swift interface files into binary modules when performing a canImport query.

include/swift/Frontend/ModuleInterfaceLoader.h

@@ -139,7 +139,8 @@ class ExplicitSwiftModuleLoader: public SerializedModuleLoaderBase {
                   std::unique_ptr<llvm::MemoryBuffer> *moduleBuffer,
                   std::unique_ptr<llvm::MemoryBuffer> *moduleDocBuffer,
                   std::unique_ptr<llvm::MemoryBuffer> *moduleSourceInfoBuffer,
-                  bool &isFramework, bool &isSystemModule) override;
+                  bool skipBuildingInterface, bool &isFramework,
+                  bool &isSystemModule) override;
 
   std::error_code findModuleFilesInDirectory(
                   ImportPath::Element ModuleID,
@@ -148,7 +149,7 @@ class ExplicitSwiftModuleLoader: public SerializedModuleLoaderBase {
                   std::unique_ptr<llvm::MemoryBuffer> *ModuleBuffer,
                   std::unique_ptr<llvm::MemoryBuffer> *ModuleDocBuffer,
                   std::unique_ptr<llvm::MemoryBuffer> *ModuleSourceInfoBuffer,
-                  bool IsFramework) override;
+                  bool skipBuildingInterface, bool IsFramework) override;
 
   bool canImportModule(ImportPath::Element mID) override;
 
@@ -385,7 +386,7 @@ class ModuleInterfaceLoader : public SerializedModuleLoaderBase {
      std::unique_ptr<llvm::MemoryBuffer> *ModuleBuffer,
      std::unique_ptr<llvm::MemoryBuffer> *ModuleDocBuffer,
      std::unique_ptr<llvm::MemoryBuffer> *ModuleSourceInfoBuffer,
-     bool IsFramework) override;
+     bool skipBuildingInterface, bool IsFramework) override;
 
   bool isCached(StringRef DepPath) override;
 public:

include/swift/Serialization/ModuleDependencyScanner.h

@@ -55,7 +55,7 @@ namespace swift {
           std::unique_ptr<llvm::MemoryBuffer> *ModuleBuffer,
           std::unique_ptr<llvm::MemoryBuffer> *ModuleDocBuffer,
           std::unique_ptr<llvm::MemoryBuffer> *ModuleSourceInfoBuffer,
-          bool IsFramework) override;
+          bool skipBuildingInterface, bool IsFramework) override;
 
       virtual void collectVisibleTopLevelModuleNames(
           SmallVectorImpl<Identifier> &names) const override {
@@ -117,7 +117,7 @@ namespace swift {
           std::unique_ptr<llvm::MemoryBuffer> *ModuleBuffer,
           std::unique_ptr<llvm::MemoryBuffer> *ModuleDocBuffer,
           std::unique_ptr<llvm::MemoryBuffer> *ModuleSourceInfoBuffer,
-                                                 bool IsFramework) override;
+          bool skipBuildingInterface, bool IsFramework) override;
 
       static bool classof(const ModuleDependencyScanner *MDS) {
         return MDS->getKind() == MDS_placeholder;

include/swift/Serialization/SerializedModuleLoader.h

@@ -77,7 +77,7 @@ class SerializedModuleLoaderBase : public ModuleLoader {
                           std::unique_ptr<llvm::MemoryBuffer> *moduleBuffer,
                           std::unique_ptr<llvm::MemoryBuffer> *moduleDocBuffer,
                           std::unique_ptr<llvm::MemoryBuffer> *moduleSourceInfoBuffer,
-                          bool &isFramework, bool &isSystemModule);
+                          bool skipBuildingInterface, bool &isFramework, bool &isSystemModule);
 
   /// Attempts to search the provided directory for a loadable serialized
   /// .swiftmodule with the provided `ModuleFilename`. Subclasses must
@@ -98,7 +98,7 @@ class SerializedModuleLoaderBase : public ModuleLoader {
       std::unique_ptr<llvm::MemoryBuffer> *ModuleBuffer,
       std::unique_ptr<llvm::MemoryBuffer> *ModuleDocBuffer,
       std::unique_ptr<llvm::MemoryBuffer> *ModuleSourceInfoBuffer,
-      bool IsFramework) = 0;
+      bool skipBuildingInterface, bool IsFramework) = 0;
 
   std::error_code
   openModuleFile(
@@ -218,7 +218,7 @@ class ImplicitSerializedModuleLoader : public SerializedModuleLoaderBase {
       std::unique_ptr<llvm::MemoryBuffer> *ModuleBuffer,
       std::unique_ptr<llvm::MemoryBuffer> *ModuleDocBuffer,
       std::unique_ptr<llvm::MemoryBuffer> *ModuleSourceInfoBuffer,
-      bool IsFramework) override;
+      bool skipBuildingInterface, bool IsFramework) override;
 
   bool maybeDiagnoseTargetMismatch(
       SourceLoc sourceLocation,
@@ -264,7 +264,7 @@ class MemoryBufferSerializedModuleLoader : public SerializedModuleLoaderBase {
       std::unique_ptr<llvm::MemoryBuffer> *ModuleBuffer,
       std::unique_ptr<llvm::MemoryBuffer> *ModuleDocBuffer,
       std::unique_ptr<llvm::MemoryBuffer> *ModuleSourceInfoBuffer,
-      bool IsFramework) override;
+      bool skipBuildingInterface, bool IsFramework) override;
 
   bool maybeDiagnoseTargetMismatch(
       SourceLoc sourceLocation,

lib/Frontend/ModuleInterfaceLoader.cpp

@@ -972,7 +972,7 @@ std::error_code ModuleInterfaceLoader::findModuleFilesInDirectory(
   std::unique_ptr<llvm::MemoryBuffer> *ModuleBuffer,
   std::unique_ptr<llvm::MemoryBuffer> *ModuleDocBuffer,
   std::unique_ptr<llvm::MemoryBuffer> *ModuleSourceInfoBuffer,
-  bool IsFramework) {
+  bool skipBuildingInterface, bool IsFramework) {
 
   // If running in OnlySerialized mode, ModuleInterfaceLoader
   // should not have been constructed at all.
@@ -1000,6 +1000,16 @@ std::error_code ModuleInterfaceLoader::findModuleFilesInDirectory(
     InPath = PrivateInPath;
   }
 
+  // If we've been told to skip building interfaces, we are done here and do
+  // not need to have the module actually built. For example, if we are
+  // currently answering a `canImport` query, it is enough to have found
+  // the interface.
+  if (skipBuildingInterface) {
+    if (ModuleInterfacePath)
+      *ModuleInterfacePath = InPath;
+    return std::error_code();
+  }
+
   // Create an instance of the Impl to do the heavy lifting.
   auto ModuleName = ModuleID.Item.str();
   ModuleInterfaceLoaderImpl Impl(
@@ -1571,7 +1581,7 @@ bool ExplicitSwiftModuleLoader::findModule(ImportPath::Element ModuleID,
            std::unique_ptr<llvm::MemoryBuffer> *ModuleBuffer,
            std::unique_ptr<llvm::MemoryBuffer> *ModuleDocBuffer,
            std::unique_ptr<llvm::MemoryBuffer> *ModuleSourceInfoBuffer,
-           bool &IsFramework, bool &IsSystemModule) {
+           bool skipBuildingInterface, bool &IsFramework, bool &IsSystemModule) {
   StringRef moduleName = ModuleID.Item.str();
   auto it = Impl.ExplicitModuleMap.find(moduleName);
   // If no explicit module path is given matches the name, return with an
@@ -1648,7 +1658,7 @@ std::error_code ExplicitSwiftModuleLoader::findModuleFilesInDirectory(
   std::unique_ptr<llvm::MemoryBuffer> *ModuleBuffer,
   std::unique_ptr<llvm::MemoryBuffer> *ModuleDocBuffer,
   std::unique_ptr<llvm::MemoryBuffer> *ModuleSourceInfoBuffer,
-  bool IsFramework) {
+  bool skipBuildingInterface, bool IsFramework) {
   llvm_unreachable("Not supported in the Explicit Swift Module Loader.");
   return std::make_error_code(std::errc::not_supported);
 }

lib/Serialization/ModuleDependencyScanner.cpp

@@ -32,7 +32,7 @@ std::error_code ModuleDependencyScanner::findModuleFilesInDirectory(
                                       std::unique_ptr<llvm::MemoryBuffer> *ModuleBuffer,
                                       std::unique_ptr<llvm::MemoryBuffer> *ModuleDocBuffer,
                                       std::unique_ptr<llvm::MemoryBuffer> *ModuleSourceInfoBuffer,
-                                      bool IsFramework) {
+                                      bool skipBuildingInterface, bool IsFramework) {
   using namespace llvm::sys;
 
   auto &fs = *Ctx.SourceMgr.getFileSystem();
@@ -76,7 +76,7 @@ std::error_code PlaceholderSwiftModuleScanner::findModuleFilesInDirectory(
     std::unique_ptr<llvm::MemoryBuffer> *ModuleBuffer,
     std::unique_ptr<llvm::MemoryBuffer> *ModuleDocBuffer,
     std::unique_ptr<llvm::MemoryBuffer> *ModuleSourceInfoBuffer,
-    bool IsFramework) {
+    bool skipBuildingInterface, bool IsFramework) {
   StringRef moduleName = ModuleID.Item.str();
   auto it = PlaceholderDependencyModuleMap.find(moduleName);
   // If no placeholder module stub path is given matches the name, return with an

lib/Serialization/SerializedModuleLoader.cpp

@@ -421,7 +421,7 @@ std::error_code ImplicitSerializedModuleLoader::findModuleFilesInDirectory(
     std::unique_ptr<llvm::MemoryBuffer> *ModuleBuffer,
     std::unique_ptr<llvm::MemoryBuffer> *ModuleDocBuffer,
     std::unique_ptr<llvm::MemoryBuffer> *ModuleSourceInfoBuffer,
-    bool IsFramework) {
+    bool skipBuildingInterface, bool IsFramework) {
   assert(((ModuleBuffer && ModuleDocBuffer) ||
           (!ModuleBuffer && !ModuleDocBuffer)) &&
          "Module and Module Doc buffer must both be initialized or NULL");
@@ -514,7 +514,7 @@ SerializedModuleLoaderBase::findModule(ImportPath::Element moduleID,
            std::unique_ptr<llvm::MemoryBuffer> *moduleBuffer,
            std::unique_ptr<llvm::MemoryBuffer> *moduleDocBuffer,
            std::unique_ptr<llvm::MemoryBuffer> *moduleSourceInfoBuffer,
-           bool &isFramework, bool &isSystemModule) {
+           bool skipBuildingInterface, bool &isFramework, bool &isSystemModule) {
   SmallString<32> moduleName(moduleID.Item.str());
   SerializedModuleBaseName genericBaseName(moduleName);
 
@@ -552,6 +552,7 @@ SerializedModuleLoaderBase::findModule(ImportPath::Element moduleID,
                         moduleInterfacePath,
                         moduleBuffer, moduleDocBuffer,
                         moduleSourceInfoBuffer,
+                        skipBuildingInterface,
                         IsFramework);
       if (!result) {
         return true;
@@ -609,7 +610,8 @@ SerializedModuleLoaderBase::findModule(ImportPath::Element moduleID,
 
           auto result = findModuleFilesInDirectory(
               moduleID, absoluteBaseName, moduleInterfacePath,
-              moduleBuffer, moduleDocBuffer, moduleSourceInfoBuffer, isFramework);
+              moduleBuffer, moduleDocBuffer, moduleSourceInfoBuffer,
+              skipBuildingInterface, isFramework);
           if (!result)
             return true;
           else if (result == std::errc::not_supported)
@@ -998,9 +1000,10 @@ bool SerializedModuleLoaderBase::canImportModule(
   std::unique_ptr<llvm::MemoryBuffer> *unusedModuleSourceInfoBuffer = nullptr;
   bool isFramework = false;
   bool isSystemModule = false;
+  bool skipBuildingInterface = true;
   return findModule(mID, unusedModuleInterfacePath, unusedModuleBuffer,
                     unusedModuleDocBuffer, unusedModuleSourceInfoBuffer,
-                    isFramework, isSystemModule);
+                    skipBuildingInterface, isFramework, isSystemModule);
 }
 
 bool MemoryBufferSerializedModuleLoader::canImportModule(
@@ -1028,7 +1031,7 @@ SerializedModuleLoaderBase::loadModule(SourceLoc importLoc,
   // Look on disk.
   if (!findModule(moduleID, &moduleInterfacePath, &moduleInputBuffer,
                   &moduleDocInputBuffer, &moduleSourceInfoInputBuffer,
-                  isFramework, isSystemModule)) {
+                  /* skipBuildingInterface */ false, isFramework, isSystemModule)) {
     return nullptr;
   }
 
@@ -1142,7 +1145,7 @@ std::error_code MemoryBufferSerializedModuleLoader::findModuleFilesInDirectory(
     std::unique_ptr<llvm::MemoryBuffer> *ModuleBuffer,
     std::unique_ptr<llvm::MemoryBuffer> *ModuleDocBuffer,
     std::unique_ptr<llvm::MemoryBuffer> *ModuleSourceInfoBuffer,
-    bool IsFramework) {
+    bool skipBuildingInterface, bool IsFramework) {
   // This is a soft error instead of an llvm_unreachable because this API is
   // primarily used by LLDB which makes it more likely that unwitting changes to
   // the Swift compiler accidentally break the contract.

test/ScanDependencies/Inputs/Swift/Foo.swiftinterface

@@ -0,0 +1,4 @@
+// swift-interface-format-version: 1.0
+// swift-module-flags: -module-name Foo
+import Swift
+

test/ScanDependencies/can_import_no_build.swift

@@ -0,0 +1,9 @@
+// RUN: %target-swift-frontend -c -primary-file %s -Rmodule-interface-rebuild -I %S/Inputs/Swift/
+
+#if canImport(Foo)
+print("Can indeed import Foo!")
+#else
+print("Cannot import Foo!")
+#endif
+
+// CHECK-NOT: rebuilding module 'Foo' from interface

unittests/FrontendTool/ModuleLoadingTests.cpp

@@ -128,7 +128,8 @@ class ModuleInterfaceLoaderTest : public testing::Test {
       loader->findModuleFilesInDirectory({moduleName, SourceLoc()},
         SerializedModuleBaseName(tempDir, SerializedModuleBaseName("Library")),
         /*ModuleInterfacePath*/nullptr,
-        &moduleBuffer, &moduleDocBuffer, &moduleSourceInfoBuffer, /*IsFramework*/false);
+        &moduleBuffer, &moduleDocBuffer, &moduleSourceInfoBuffer,
+        /*skipBuildingInterface*/ false, /*IsFramework*/false);
     ASSERT_FALSE(error);
     ASSERT_FALSE(diags.hadAnyError());