[clang] [clang Dependency Scanning] Enhance File Caching Diagnostics (PR #144105)

[Qiongsi Wu via cfe-commits]

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@@ -220,13 +220,41 @@ class DependencyScanningFilesystemSharedCache {
   CacheShard &getShardForFilename(StringRef Filename) const;
   CacheShard &getShardForUID(llvm::sys::fs::UniqueID UID) const;
 
-  /// Visits all cached entries and re-stat an entry using FS if
-  /// it is negatively stat cached. If re-stat succeeds on a path,
-  /// the path is added to InvalidPaths, indicating that the cache
-  /// may have erroneously negatively cached it. The caller can then
-  /// use InvalidPaths to issue diagnostics.
-  std::vector<StringRef>
-  getInvalidNegativeStatCachedPaths(llvm::vfs::FileSystem &UnderlyingFS) const;
+  struct InvalidEntryDiagInfo {
+    // A null terminated string that contains a path.
+    const char *Path = nullptr;
+
+    enum class Type : unsigned char { NegativeCaching = 1, SizeChanged = 2 };
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qiongsiwu wrote:

This enum class is redundant here, because we can check if `SizeInfo` below exists to tell which kind of diagnostics we are producing. However, it feels opaque to do that. Additionally, having a enum will allow us to easily add more kinds of diagnostics. Are we in favor of keeping the enum? 

https://github.com/llvm/llvm-project/pull/144105