[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 +561,25 @@ CXDiagnosticSet clang_experimental_DepGraph_getDiagnostics(CXDepGraph Graph) {
   return unwrap(Graph)->getDiagnosticSet();
 }
 
+CXStringSet *
+clang_experimental_DependencyScannerService_getInvalidNegStatCachedPaths(
+    CXDependencyScannerService S) {
+  DependencyScanningService *Service = unwrap(S);
+
+  // CASFS does not use the SharedCache, so there is nothing to diagnose.
+  if (Service->useCASFS())
+    return nullptr;
+
+  DependencyScanningFilesystemSharedCache &SharedCache =
+      Service->getSharedCache();
+  llvm::IntrusiveRefCntPtr<llvm::vfs::FileSystem> FS =
+      llvm::vfs::createPhysicalFileSystem();
+  auto InvaidNegStatCachedPaths =
+      SharedCache.getInvalidNegativeStatCachedPaths(*FS.get());
+  return cxstring::createSet(std::vector<std::string>(
+      InvaidNegStatCachedPaths.begin(), InvaidNegStatCachedPaths.end()));
+}
+
 static std::string
 lookupModuleOutput(const ModuleDeps &MD, ModuleOutputKind MOK, void *MLOContext,
                    std::variant<CXModuleLookupOutputCallback *,

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