[clang][Modules] Adding C-API for Negative Stat Caching Diagnostics

clang/include/clang-c/Dependencies.h

@@ -585,6 +585,11 @@ const char *clang_experimental_DepGraph_getTUContextHash(CXDepGraph);
 CINDEX_LINKAGE
 CXDiagnosticSet clang_experimental_DepGraph_getDiagnostics(CXDepGraph);
 
+CINDEX_LINKAGE
+CXStringSet *
+    clang_experimental_DependencyScannerService_getInvalidNegStatCachedPaths(
+        CXDependencyScannerService);
+
 /**
  * @}
  */

clang/test/ClangScanDeps/error-c-api.cpp

@@ -4,3 +4,4 @@
 
 // CHECK: error: failed to get dependencies
 // CHECK-NEXT: 'missing.h' file not found
+// CHECk-NEXT: number of invalid negatively stat cached paths: 0

clang/tools/c-index-test/core_main.cpp

@@ -907,6 +907,16 @@ static int scanDeps(ArrayRef<const char *> Args, std::string WorkingDirectory,
     clang_disposeString(Spelling);
     clang_disposeDiagnostic(Diag);
   }
+
+  CXStringSet *InvalidNegativeStatCachedPaths =
+      clang_experimental_DependencyScannerService_getInvalidNegStatCachedPaths(
+          Service);
+  if (InvalidNegativeStatCachedPaths) {
+    llvm::errs() << "note: number of invalid negatively stat cached paths: "
+                 << InvalidNegativeStatCachedPaths->Count << "\n";
+    clang_disposeStringSet(InvalidNegativeStatCachedPaths);
+  }
+
   return 1;
 }
 

clang/tools/libclang/CDependencies.cpp

@@ -561,6 +561,29 @@ CXDiagnosticSet clang_experimental_DepGraph_getDiagnostics(CXDepGraph Graph) {
   return unwrap(Graph)->getDiagnosticSet();
 }
 
+CXStringSet *
+clang_experimental_DependencyScannerService_getInvalidNegStatCachedPaths(
+    CXDependencyScannerService S) {
+  DependencyScanningService *Service = unwrap(S);
+
+  // FIXME: CAS currently does not use the shared cache, and cannot produce
+  // the same diagnostics. We should add such a diagnostics to CAS as well.
+  if (Service->useCASFS())
+    return nullptr;
+
+  DependencyScanningFilesystemSharedCache &SharedCache =
+      Service->getSharedCache();
+
+  // Note that it is critical that this FS is the same as the default virtual
+  // file system we pass to the DependencyScanningWorkers.
+  llvm::IntrusiveRefCntPtr<llvm::vfs::FileSystem> FS =
+      llvm::vfs::createPhysicalFileSystem();
+
+  auto InvaidNegStatCachedPaths =
+      SharedCache.getInvalidNegativeStatCachedPaths(*FS);
+  return cxstring::createRefSet(InvaidNegStatCachedPaths);
+}
+
 static std::string
 lookupModuleOutput(const ModuleDeps &MD, ModuleOutputKind MOK, void *MLOContext,
                    std::variant<CXModuleLookupOutputCallback *,

clang/tools/libclang/CXString.cpp

@@ -107,31 +107,27 @@ CXString createCXString(CXStringBuf *buf) {
   return Str;
 }
 
-CXStringSet *createSet(const std::vector<std::string> &Strings) {
+template <typename StringTy, bool Copy>
+static CXStringSet *createSetImpl(ArrayRef<StringTy> Strings) {
   CXStringSet *Set = new CXStringSet;
   Set->Count = Strings.size();
   Set->Strings = new CXString[Set->Count];
-  for (unsigned SI = 0, SE = Set->Count; SI < SE; ++SI)
-    Set->Strings[SI] = createDup(Strings[SI]);
+  for (unsigned SI = 0, SE = Set->Count; SI < SE; ++SI) {
+    if constexpr (Copy) {
+      Set->Strings[SI] = createDup(Strings[SI]);
+    } else {
+      Set->Strings[SI] = createRef(Strings[SI]);
+    }
+  }
   return Set;
 }
 
-CXStringSet *createSet(const llvm::StringSet<> &StringsUnordered) {
-  std::vector<StringRef> Strings;
-
-  for (auto SI = StringsUnordered.begin(),
-            SE = StringsUnordered.end(); SI != SE; ++SI)
-    Strings.push_back(SI->getKey());
-
-  llvm::sort(Strings);
-
-  CXStringSet *Set = new CXStringSet;
-  Set->Count = Strings.size();
-  Set->Strings = new CXString[Set->Count];
-  int I = 0;
-  for (auto SI = Strings.begin(), SE = Strings.end(); SI != SE; ++SI)
-    Set->Strings[I++] = createDup(*SI);
-  return Set;
+CXStringSet *createSet(const std::vector<std::string> &Strings) {
+  return createSetImpl<std::string, true>(Strings);
+}
+
+CXStringSet *createRefSet(ArrayRef<StringRef> Strings) {
+  return createSetImpl<StringRef, false>(Strings);
 }
 
 //===----------------------------------------------------------------------===//

clang/tools/libclang/CXString.h

@@ -68,8 +68,14 @@ CXString createRef(std::string String) = delete;
 /// Create a CXString object that is backed by a string buffer.
 CXString createCXString(CXStringBuf *buf);
 
+/// Create a CXStringSet object that owns the strings. Such an object should be
+/// disposed with clang_disposeStringSet.
 CXStringSet *createSet(const std::vector<std::string> &Strings);
 
+/// Create a CXStringSet object that does not own the strings. Such an object
+/// should still be disposed with clang_disposeStringSet.
+CXStringSet *createRefSet(ArrayRef<StringRef> Strings);
+
 CXStringSet *createSet(const llvm::StringSet<> &Strings);
 
 /// A string pool used for fast allocation/deallocation of strings.
@@ -108,4 +114,3 @@ static inline StringRef getContents(const CXUnsavedFile &UF) {
 }
 
 #endif
-

clang/tools/libclang/libclang.map

@@ -577,6 +577,7 @@ LLVM_21 {
     clang_experimental_DepGraphModule_isCWDIgnored;
     clang_experimental_DepGraphModule_isInStableDirs; 
     clang_getFullyQualifiedName;
+    clang_experimental_DependencyScannerService_getInvalidNegStatCachedPaths;
 };
 
 # Example of how to add a new symbol version entry.  If you do add a new symbol