[clang] [clang][deps] Overload `Filesystem::exists` in `DependencyScanningFilesystem` to have it use cached `status` (PR #88152)

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llvmbot wrote:


<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-clang

Author: Artem Chikin (artemcm)

<details>
<summary>Changes</summary>

As-is, calls to `exists()` fallback on the implementation in `ProxyFileSystem::exists` which explicitly calls out to the underlying `FS`, which for the `DependencyScanningFilesystem` (overlay) is the real underlying filesystem.

Instead, directly overloading `exists` allows us to have it rely on the cached `status` behavior used elsewhere by the `DependencyScanningFilesystem`.

---
Full diff: https://github.com/llvm/llvm-project/pull/88152.diff


2 Files Affected:

- (modified) clang/include/clang/Tooling/DependencyScanning/DependencyScanningFilesystem.h (+4) 
- (modified) clang/lib/Tooling/DependencyScanning/DependencyScanningFilesystem.cpp (+6) 


``````````diff
diff --git a/clang/include/clang/Tooling/DependencyScanning/DependencyScanningFilesystem.h b/clang/include/clang/Tooling/DependencyScanning/DependencyScanningFilesystem.h
index 9a522a3e2fe252..4fdfebada5b7f7 100644
--- a/clang/include/clang/Tooling/DependencyScanning/DependencyScanningFilesystem.h
+++ b/clang/include/clang/Tooling/DependencyScanning/DependencyScanningFilesystem.h
@@ -365,6 +365,10 @@ class DependencyScanningWorkerFilesystem
     return LocalCache.insertEntryForFilename(Filename, Entry);
   }
 
+  /// Check whether \p Path exists. By default checks cached result of \c status(),
+  /// and falls back on FS if unable to do so.
+  bool exists(const Twine &Path) override;
+
   /// Returns entry associated with the filename in the shared cache if there is
   /// some. Otherwise, constructs new one with the given error code, associates
   /// it with the filename and returns the result.
diff --git a/clang/lib/Tooling/DependencyScanning/DependencyScanningFilesystem.cpp b/clang/lib/Tooling/DependencyScanning/DependencyScanningFilesystem.cpp
index 9b7812a1adb9e3..174edc98da5877 100644
--- a/clang/lib/Tooling/DependencyScanning/DependencyScanningFilesystem.cpp
+++ b/clang/lib/Tooling/DependencyScanning/DependencyScanningFilesystem.cpp
@@ -270,6 +270,12 @@ DependencyScanningWorkerFilesystem::status(const Twine &Path) {
   return Result->getStatus();
 }
 
+bool
+DependencyScanningWorkerFilesystem::exists(const Twine &Path) {
+  auto Status = status(Path);
+  return Status && Status->exists();
+}
+
 namespace {
 
 /// The VFS that is used by clang consumes the \c CachedFileSystemEntry using

``````````

</details>


https://github.com/llvm/llvm-project/pull/88152