[clang] [clang][Dependency Scanning] Adding an API to Diagnose Invalid Negative Stat Cache Entries (PR #135703)

[Jan Svoboda via cfe-commits]

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@@ -108,6 +108,31 @@ DependencyScanningFilesystemSharedCache::getShardForUID(
   return CacheShards[Hash % NumShards];
 }
 
+void DependencyScanningFilesystemSharedCache::diagnoseNegativeStatCachedPaths(
+    llvm::raw_ostream &OS, llvm::vfs::FileSystem &UnderlyingFS) const {
+  // Iterate through all shards and look for cached stat errors.
+  for (unsigned i = 0; i < NumShards; i++) {
+    const CacheShard &Shard = CacheShards[i];
+    std::lock_guard<std::mutex> LockGuard(Shard.CacheLock);
+    for (const auto &[Path, CachedPair] : Shard.CacheByFilename) {
+      const CachedFileSystemEntry *Entry = CachedPair.first;
+
+      if (Entry->getError()) {
+        // Only examine cached errors.
+        llvm::ErrorOr<llvm::vfs::Status> Stat = UnderlyingFS.status(Path);
+        if (Stat) {
+          // This is the case where we have cached the non-existence
+          // of the file at Path, but the file is created but the cache is
+          // not invalidated. Report diagnostics.
+          OS << Path << " did not exist when it was first searched "
+             << "but was created later. This may have led to a build failure "
+                "due to missing files.\n";
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jansvoboda11 wrote:

This might get very busy with multiple files. Can we make this shorter?


https://github.com/llvm/llvm-project/pull/135703