[Dependency Scanning] Treat resource-directory-discovered modules as stable and make them use the SDK-specific module cache path

Author: artemcm

lib/Frontend/ModuleInterfaceLoader.cpp

@@ -2890,13 +2890,18 @@ void setOutputPath(ResultTy &resolvedOutputPath, const StringRef &moduleName,
                    const CompilerInvocation &CI, const ArgListTy &extraArgs) {
   auto &outputPath = resolvedOutputPath.outputPath;
   outputPath = CI.getClangModuleCachePath();
+  auto isPrefixedWith = [interfacePath](StringRef path) {
+    return !path.empty() &&
+        hasPrefix(llvm::sys::path::begin(interfacePath.str()),
+                  llvm::sys::path::end(interfacePath.str()),
+                  llvm::sys::path::begin(path), llvm::sys::path::end(path));
+  };
 
   // Dependency-scanner-specific module output path handling
   if ((CI.getFrontendOptions().RequestedAction ==
        FrontendOptions::ActionType::ScanDependencies)) {
-    if (!sdkPath.empty() &&
-        hasPrefix(llvm::sys::path::begin(interfacePath.str()), llvm::sys::path::end(interfacePath.str()),
-                  llvm::sys::path::begin(sdkPath), llvm::sys::path::end(sdkPath)))
+    auto runtimeResourcePath = CI.getSearchPathOptions().RuntimeResourcePath;
+    if (isPrefixedWith(sdkPath) || isPrefixedWith(runtimeResourcePath))
       outputPath = CI.getFrontendOptions().ExplicitSDKModulesOutputPath;
     else
       outputPath = CI.getFrontendOptions().ExplicitModulesOutputPath;