From ec313e741d2f57d51785a1a64e5ede29be17174c Mon Sep 17 00:00:00 2001
From: Jan Svoboda <jan_svoboda@apple.com>
Date: Fri, 12 Sep 2025 14:30:06 -0700
Subject: [PATCH] [clang] Avoid reparsing VFS overlay files for module dep
 collector

---
 clang/lib/Frontend/CompilerInstance.cpp       | 15 ++++-----------
 clang/test/VFS/broken-vfs-module-dep.c        |  1 -
 llvm/include/llvm/Support/VirtualFileSystem.h | 10 +++-------
 llvm/lib/Support/VirtualFileSystem.cpp        | 16 +++-------------
 4 files changed, 10 insertions(+), 32 deletions(-)

diff --git a/clang/lib/Frontend/CompilerInstance.cpp b/clang/lib/Frontend/CompilerInstance.cpp
index 31a8d75fec4bd..3e67cf157cb1c 100644
--- a/clang/lib/Frontend/CompilerInstance.cpp
+++ b/clang/lib/Frontend/CompilerInstance.cpp
@@ -271,19 +271,12 @@ static void collectIncludePCH(CompilerInstance &CI,
 
 static void collectVFSEntries(CompilerInstance &CI,
                               std::shared_ptr<ModuleDependencyCollector> MDC) {
-  if (CI.getHeaderSearchOpts().VFSOverlayFiles.empty())
-    return;
-
   // Collect all VFS found.
   SmallVector<llvm::vfs::YAMLVFSEntry, 16> VFSEntries;
-  for (const std::string &VFSFile : CI.getHeaderSearchOpts().VFSOverlayFiles) {
-    llvm::ErrorOr<std::unique_ptr<llvm::MemoryBuffer>> Buffer =
-        llvm::MemoryBuffer::getFile(VFSFile);
-    if (!Buffer)
-      return;
-    llvm::vfs::collectVFSFromYAML(std::move(Buffer.get()),
-                                  /*DiagHandler*/ nullptr, VFSFile, VFSEntries);
-  }
+  CI.getVirtualFileSystem().visit([&](llvm::vfs::FileSystem &VFS) {
+    if (auto *RedirectingVFS = dyn_cast<llvm::vfs::RedirectingFileSystem>(&VFS))
+      llvm::vfs::collectVFSEntries(*RedirectingVFS, VFSEntries);
+  });
 
   for (auto &E : VFSEntries)
     MDC->addFile(E.VPath, E.RPath);
diff --git a/clang/test/VFS/broken-vfs-module-dep.c b/clang/test/VFS/broken-vfs-module-dep.c
index 2336306de8c6d..1c371a13e85c9 100644
--- a/clang/test/VFS/broken-vfs-module-dep.c
+++ b/clang/test/VFS/broken-vfs-module-dep.c
@@ -2,6 +2,5 @@
 // RUN: mkdir -p %t
 // RUN: not %clang_cc1 -module-dependency-dir %t -ivfsoverlay %S/Inputs/invalid-yaml.yaml %s 2>&1 | FileCheck %s
 
-// CHECK: error: Unexpected token
 // CHECK: error: Unexpected token
 // CHECK: 1 error generated
diff --git a/llvm/include/llvm/Support/VirtualFileSystem.h b/llvm/include/llvm/Support/VirtualFileSystem.h
index d97677305a39f..8007f3c853f20 100644
--- a/llvm/include/llvm/Support/VirtualFileSystem.h
+++ b/llvm/include/llvm/Support/VirtualFileSystem.h
@@ -1114,14 +1114,10 @@ class LLVM_ABI RedirectingFileSystem
 };
 
 /// Collect all pairs of <virtual path, real path> entries from the
-/// \p YAMLFilePath. This is used by the module dependency collector to forward
+/// \p VFS. This is used by the module dependency collector to forward
 /// the entries into the reproducer output VFS YAML file.
-LLVM_ABI void collectVFSFromYAML(
-    std::unique_ptr<llvm::MemoryBuffer> Buffer,
-    llvm::SourceMgr::DiagHandlerTy DiagHandler, StringRef YAMLFilePath,
-    SmallVectorImpl<YAMLVFSEntry> &CollectedEntries,
-    void *DiagContext = nullptr,
-    IntrusiveRefCntPtr<FileSystem> ExternalFS = getRealFileSystem());
+void collectVFSEntries(RedirectingFileSystem &VFS,
+                       SmallVectorImpl<YAMLVFSEntry> &CollectedEntries);
 
 class YAMLVFSWriter {
   std::vector<YAMLVFSEntry> Mappings;
diff --git a/llvm/lib/Support/VirtualFileSystem.cpp b/llvm/lib/Support/VirtualFileSystem.cpp
index 5d4248819f1fb..cf784595c2f1c 100644
--- a/llvm/lib/Support/VirtualFileSystem.cpp
+++ b/llvm/lib/Support/VirtualFileSystem.cpp
@@ -2707,19 +2707,9 @@ static void getVFSEntries(RedirectingFileSystem::Entry *SrcE,
   Entries.push_back(YAMLVFSEntry(VPath.c_str(), FE->getExternalContentsPath()));
 }
 
-void vfs::collectVFSFromYAML(std::unique_ptr<MemoryBuffer> Buffer,
-                             SourceMgr::DiagHandlerTy DiagHandler,
-                             StringRef YAMLFilePath,
-                             SmallVectorImpl<YAMLVFSEntry> &CollectedEntries,
-                             void *DiagContext,
-                             IntrusiveRefCntPtr<FileSystem> ExternalFS) {
-  std::unique_ptr<RedirectingFileSystem> VFS = RedirectingFileSystem::create(
-      std::move(Buffer), DiagHandler, YAMLFilePath, DiagContext,
-      std::move(ExternalFS));
-  if (!VFS)
-    return;
-  ErrorOr<RedirectingFileSystem::LookupResult> RootResult =
-      VFS->lookupPath("/");
+void vfs::collectVFSEntries(RedirectingFileSystem &VFS,
+                            SmallVectorImpl<YAMLVFSEntry> &CollectedEntries) {
+  ErrorOr<RedirectingFileSystem::LookupResult> RootResult = VFS.lookupPath("/");
   if (!RootResult)
     return;
   SmallVector<StringRef, 8> Components;