[Index] Index only system modules in the SDK

Indexing a module from the swiftinterface puts the swiftinterface
version in the cache. Subsequent builds don't see the adjacent
swiftmodule file. This can break test clients that need the adjacent
swiftmodule information. To avoid this scenario, ensure that we only
index system modules in the SDK, not local versions.

rdar://102207620

Author: xymus

include/swift/AST/Module.h

@@ -859,6 +859,10 @@ class ModuleDecl
   /// applicable.
   StringRef getModuleLoadedFilename() const;
 
+  /// \returns true if this module is defined under the SDK path.
+  /// If no SDK path is defined, this always returns false.
+  bool isSDKModule() const;
+
   /// \returns true if this module is the "swift" standard library module.
   bool isStdlibModule() const;
 

lib/AST/Module.cpp

@@ -1996,6 +1996,18 @@ StringRef ModuleDecl::getModuleLoadedFilename() const {
   return StringRef();
 }
 
+bool ModuleDecl::isSDKModule() const {
+  if (getASTContext().SearchPathOpts.getSDKPath().empty())
+    return false;
+
+  auto sdkPath = SmallString<8>(),
+       modulePath = SmallString<8>();
+  llvm::sys::path::native(getASTContext().SearchPathOpts.getSDKPath(), sdkPath);
+  llvm::sys::path::native(getModuleSourceFilename(), modulePath);
+
+  return modulePath.startswith(sdkPath);
+}
+
 bool ModuleDecl::isStdlibModule() const {
   return !getParent() && getName() == getASTContext().StdlibModuleName;
 }

lib/Index/IndexRecord.cpp

@@ -447,11 +447,12 @@ static void addModuleDependencies(ArrayRef<ImportedModule> imports,
             }
           } else {
             // Serialized AST file.
-            // Only index system modules (essentially stdlib and overlays).
+            // Only index system modules from the SDK, and the stdlib.
             // We don't officially support binary swift modules, so normally
             // the index data for user modules would get generated while
             // building them.
             if (mod->isSystemModule() && indexSystemModules &&
+                (mod->isSDKModule() || mod->isStdlibModule()) &&
                 (!skipStdlib || !mod->isStdlibModule())) {
               emitDataForSwiftSerializedModule(mod, indexStorePath,
                                                indexClangModules,

test/Index/index_only_sdk_system_modules.swift

@@ -0,0 +1,60 @@
+// RUN: %empty-directory(%t)
+// RUN: %empty-directory(%t/cache)
+// RUN: %empty-directory(%t/idx)
+// RUN: %empty-directory(%t/sdk)
+// RUN: split-file %s %t
+
+/// Create a Swift module to import.
+// RUN: cp %t/module.modulemap %t/sdk/
+// RUN: %target-swift-frontend -emit-module \
+// RUN:   -enable-library-evolution -swift-version 5 \
+// RUN:   -emit-module-path %t/sdk/LocalSystemModule.swiftmodule \
+// RUN:   -emit-module-interface-path %t/sdk/LocalSystemModule.swiftinterface \
+// RUN:   %t/LocalSystemModule.swift -I %t/sdk \
+// RUN:   -enable-testing
+
+/// Build a test client once with indexing, not setting an SDK.
+// RUN: %target-swift-frontend -typecheck %t/TestClient.swift \
+// RUN:   -I %t/sdk -module-cache-path %t/cache \
+// RUN:   -index-system-modules \
+// RUN:   -index-store-path %t/idx \
+// RUN:   -index-ignore-stdlib \
+// RUN:   -sdk %t/someothersdk -Rmodule-loading 2>&1 \
+// RUN:   | %FileCheck -check-prefix=CHECK-SWIFTMODULE %s
+// CHECK-SWIFTMODULE: source: '{{.*}}LocalSystemModule.swiftmodule'
+
+/// Build the test client again not setting an SDK, this one should still use
+/// the adjacent module that is built for testing.
+// RUN: %target-swift-frontend -typecheck %t/TestClient.swift \
+// RUN:   -I %t/sdk -module-cache-path %t/cache \
+// RUN:   -sdk %t/someothersdk -Rmodule-loading 2>&1 \
+// RUN:   | %FileCheck -check-prefix=CHECK-SWIFTMODULE %s
+
+/// @testable import of a module in the SDK works once but not after it's cached.
+// RUN: %empty-directory(%t/idx)
+// RUN: %target-swift-frontend -typecheck %t/TestClient.swift \
+// RUN:   -I %t/sdk -module-cache-path %t/cache \
+// RUN:   -index-system-modules \
+// RUN:   -index-store-path %t/idx \
+// RUN:   -index-ignore-stdlib \
+// RUN:   -sdk %t/sdk -Rmodule-loading 2>&1 \
+// RUN:   | %FileCheck -check-prefix=CHECK-SWIFTMODULE %s
+
+/// Failing case when building against the cached swiftmodule.
+// RUN: %target-swift-frontend -typecheck %t/TestClient.swift \
+// RUN:   -I %t/sdk -module-cache-path %t/cache \
+// RUN:   -sdk %t/sdk -Rmodule-loading \
+// RUN:   -verify -verify-ignore-unknown -show-diagnostics-after-fatal 2>&1
+
+//--- module.modulemap
+
+module LocalSystemModule [system] { }
+
+//--- LocalSystemModule.swift
+
+@_exported import LocalSystemModule
+
+//--- TestClient.swift
+
+@testable import LocalSystemModule // expected-error {{module 'LocalSystemModule' was not compiled for testing}}
+// expected-remark @-1 {{LocalSystemModule.swiftinterface}}