[Dependency Scanning] Batch Scanning: Update ClangImporter arguments when re-using a compiler instane.

Additional arguments that the compiler must pass to the Clang Importer (Clang dep scanner), incl. search paths, must come from the invocation that launched the scan in order to correctly match the specific target being scanned, instead of re-using those from a cached CompilerInstance.

Author: artemcm

lib/DependencyScan/ScanDependencies.cpp

@@ -916,6 +916,18 @@ using CompilerArgInstanceCacheMap =
     llvm::StringMap<std::pair<std::unique_ptr<CompilerInstance>,
                               std::unique_ptr<ModuleDependenciesCache>>>;
 
+static void
+updateCachedInstanceSearchPaths(CompilerInstance &cachedInstance,
+                                const CompilerInstance &invocationInstance) {
+  cachedInstance.getASTContext().SearchPathOpts =
+      invocationInstance.getASTContext().SearchPathOpts;
+  // The Clang Importer arguments must also match those of the current
+  // invocation instead of the cached one because they include search
+  // path directives for Clang.
+  cachedInstance.getASTContext().ClangImporterOpts =
+      invocationInstance.getASTContext().ClangImporterOpts;
+}
+
 static bool
 forEachBatchEntry(CompilerInstance &invocationInstance,
                   ModuleDependenciesCache &invocationCache,
@@ -950,13 +962,9 @@ forEachBatchEntry(CompilerInstance &invocationInstance,
       // before.
       pInstance = (*subInstanceMap)[entry.arguments].first.get();
       pCache = (*subInstanceMap)[entry.arguments].second.get();
-      // We must update the search paths of this instance to instead reflect those of the current
-      // invocation's.
-      for (auto &path : invocationInstance.getASTContext().SearchPathOpts.ImportSearchPaths)
-        pInstance->getASTContext().addSearchPath(path, false, false);
-      for (auto &path : invocationInstance.getASTContext().SearchPathOpts.FrameworkSearchPaths)
-        pInstance->getASTContext().addSearchPath(path.Path, true, path.IsSystem);
-
+      // We must update the search paths of this instance to instead reflect
+      // those of the current scanner invocation.
+      updateCachedInstanceSearchPaths(*pInstance, invocationInstance);
     } else {
       // Create a new instance by the arguments and save it in the map.
       subInstanceMap->insert(