Exclude RedirectingFileSystem with null OverlayFileDir in VFSUsage

[hjyamauchi]

This is to avoid assertion failures like the following when RedirectingFileSystem's are created and used outside createVFSFromOverlayFiles.

Assertion failed: VFSUsage.size() == getHeaderSearchOpts().VFSOverlayFiles.size() && "A different number of RedirectingFileSystem's were present than " "-ivfsoverlay options passed to Clang!", file S:\SourceCache\llvm-project\clang\lib\Lex\HeaderSearch.cpp, line 162

[hjyamauchi]

An assertion failure like the above was encountered in the swift toolchain in the context of this PR swiftlang/swift#78184 which uses a module map VFS overlay on top of the read-only Windows MSVC/ucrt include paths.

[hjyamauchi]

Note: This PR partially addresses the limitation described by this comment.

[llvmbot]

@llvm/pr-subscribers-clang

Author: Hiroshi Yamauchi (hjyamauchi)

Changes

This is to avoid assertion failures like the following when RedirectingFileSystem's are created and used outside createVFSFromOverlayFiles.

Assertion failed: VFSUsage.size() == getHeaderSearchOpts().VFSOverlayFiles.size() && "A different number of RedirectingFileSystem's were present than " "-ivfsoverlay options passed to Clang!", file S:\SourceCache\llvm-project\clang\lib\Lex\HeaderSearch.cpp, line 162

---

Full diff: https://github.com/llvm/llvm-project/pull/128267.diff

1 Files Affected:

• (modified) clang/lib/Lex/HeaderSearch.cpp (+8-3)

diff --git a/clang/lib/Lex/HeaderSearch.cpp b/clang/lib/Lex/HeaderSearch.cpp
index bf8fe44e4ca9c..f1e011627d499 100644
--- a/clang/lib/Lex/HeaderSearch.cpp
+++ b/clang/lib/Lex/HeaderSearch.cpp
@@ -149,11 +149,16 @@ std::vector<bool> HeaderSearch::collectVFSUsageAndClear() const {
 
   llvm::vfs::FileSystem &RootFS = FileMgr.getVirtualFileSystem();
   // TODO: This only works if the `RedirectingFileSystem`s were all created by
-  //       `createVFSFromOverlayFiles`.
+  //       `createVFSFromOverlayFiles`. But at least exclude the ones with null
+  //       OverlayFileDir.
   RootFS.visit([&](llvm::vfs::FileSystem &FS) {
     if (auto *RFS = dyn_cast<llvm::vfs::RedirectingFileSystem>(&FS)) {
-      VFSUsage.push_back(RFS->hasBeenUsed());
-      RFS->clearHasBeenUsed();
+      // Skip a `RedirectingFileSystem` with null OverlayFileDir which indicates
+      // that they aren't created by `createVFSFromOverlayFiles`.
+      if (!RFS->getOverlayFileDir().empty()) {
+        VFSUsage.push_back(RFS->hasBeenUsed());
+        RFS->clearHasBeenUsed();
+      }
     }
   });
   assert(VFSUsage.size() == getHeaderSearchOpts().VFSOverlayFiles.size() &&

[compnerd]

CC: @Bigcheese

[Bigcheese]

Hmm, I think this is fine, although it would be nice if there was a tighter connection between the -ivfsoverlay options and this. I don't think that needs to happen here though.