[clangd] Publish config file errors over LSP

[sammccall]

Summary

We don't act as a language server for these files (e.g. don't get open/close
notifications for them), but just blindly publish diagnostics for them.

This works reasonably well in coc.nvim and vscode: they show up in the
workspace diagnostic list and when you open the file.
The only update after the file is reparsed, not as you type which is a bit
janky, but seems a lot better than nothing.

Fixes https://github.com/clangd/clangd/issues/614

[sammccall]

Handle diagnostics without a filename

[hokein]

The pre-merging bot seems to be failed on windows: https://reviews.llvm.org/harbormaster/unit/view/215879/.

clang-tools-extra/clangd/ClangdServer.cpp

833

I'd encode Config into names, DiagnosticHandler made me think this is a handler for clang diagnostics (without reading the context).

clang-tools-extra/clangd/ClangdServer.h

366

nit: = nullptr.

[thakis]

Looks like this breaks tests on windows: http://45.33.8.238/win/29315/step_9.txt

[cfe-commits]

Yep, thanks. This uncovered an existing error, so rather than reverting the
whole thing I've disabled the assert on windows while I fix
it. f1357264b8e3070bef5bb4ff35ececa4d6c76108

• msg-10998-26.txt160 BDownload

clang-tools-extra/clangd/ClangdServer.h

private:
   /// The empty string means no particular file is the target.
   /// Rather than called by each feature, this is exposed to the components
   /// that control worker threads, like TUScheduler and BackgroundIndex.
   /// This means it's OK to do some IO here, and it cuts across all features.
   Context createProcessingContext(PathRef) const;
   config::Provider *ConfigProvider = nullptr;
 
   const ThreadsafeFS &TFS;
+  Callbacks *ServerCallbacks = nullptr;
+  mutable std::mutex ConfigDiagnosticsMu;
 
   Path ResourceDir;
   // The index used to look up symbols. This could be:
   //   - null (all index functionality is optional)
   //   - the dynamic index owned by ClangdServer (DynamicIdx)
   //   - the static index passed to the constructor
   //   - a merged view of a static and dynamic index (MergedIndex)
   const SymbolIndex *Index = nullptr;

clang-tools-extra/clangd/ClangdServer.cpp

ClangdServer::Options::operator TUScheduler::Options() const {
   Opts.UpdateDebounce = UpdateDebounce;
   Opts.AsyncPreambleBuilds = AsyncPreambleBuilds;
   return Opts;
 }
 
 ClangdServer::ClangdServer(const GlobalCompilationDatabase &CDB,
                            const ThreadsafeFS &TFS, const Options &Opts,
                            Callbacks *Callbacks)
-    : ConfigProvider(Opts.ConfigProvider), TFS(TFS),
+    : ConfigProvider(Opts.ConfigProvider), TFS(TFS), ServerCallbacks(Callbacks),
       DynamicIdx(Opts.BuildDynamicSymbolIndex
                      ? new FileIndex(Opts.HeavyweightDynamicSymbolIndex,
                                      Opts.CollectMainFileRefs)
                      : nullptr),
       ClangTidyProvider(Opts.ClangTidyProvider),
       SuggestMissingIncludes(Opts.SuggestMissingIncludes),
       BuildRecoveryAST(Opts.BuildRecoveryAST),
       PreserveRecoveryASTType(Opts.PreserveRecoveryASTType),
Context ClangdServer::createProcessingContext(PathRef File) const {
   Params.FreshTime = std::chrono::steady_clock::now() - std::chrono::seconds(5);
   llvm::SmallString<256> PosixPath;
   if (!File.empty()) {
     assert(llvm::sys::path::is_absolute(File));
     llvm::sys::path::native(File, PosixPath, llvm::sys::path::Style::posix);
     Params.Path = PosixPath.str();
   }
 
-  auto DiagnosticHandler = [](const llvm::SMDiagnostic &Diag) {
-    if (Diag.getKind() == llvm::SourceMgr::DK_Error) {
-      elog("config error at {0}:{1}:{2}: {3}", Diag.getFilename(),
-           Diag.getLineNo(), Diag.getColumnNo(), Diag.getMessage());
-    } else {
-      log("config warning at {0}:{1}:{2}: {3}", Diag.getFilename(),
-          Diag.getLineNo(), Diag.getColumnNo(), Diag.getMessage());
+  llvm::StringMap<std::vector<Diag>> ReportableDiagnostics;
+  auto ConfigDiagnosticHandler = [&](const llvm::SMDiagnostic &D) {
+    // Ensure we create the map entry even for note diagnostics we don't report.
+    // This means that when the file is parsed with no warnings, we'll
+    // publish an empty set of diagnostics, clearing any the client has.
+    auto *Reportable = D.getFilename().empty()
+                           ? nullptr
+                           : &ReportableDiagnostics[D.getFilename()];
+    switch (D.getKind()) {
+    case llvm::SourceMgr::DK_Error:
+      elog("config error at {0}:{1}:{2}: {3}", D.getFilename(), D.getLineNo(),
+           D.getColumnNo(), D.getMessage());
+      if (Reportable)
+        Reportable->push_back(toDiag(D, Diag::ClangdConfig));
+      break;
+    case llvm::SourceMgr::DK_Warning:
+      log("config warning at {0}:{1}:{2}: {3}", D.getFilename(), D.getLineNo(),
+          D.getColumnNo(), D.getMessage());
+      if (Reportable)
+        Reportable->push_back(toDiag(D, Diag::ClangdConfig));
+      break;
+    case llvm::SourceMgr::DK_Note:
+    case llvm::SourceMgr::DK_Remark:
+      vlog("config note at {0}:{1}:{2}: {3}", D.getFilename(), D.getLineNo(),
+           D.getColumnNo(), D.getMessage());
+      break;
     }
   };
-  Config C = ConfigProvider->getConfig(Params, DiagnosticHandler);
+  Config C = ConfigProvider->getConfig(Params, ConfigDiagnosticHandler);
+  // Blindly publish diagnostics for the (unopened) parsed config files.
+  // We must avoid reporting diagnostics for *the same file* concurrently.
+  // Source file diags are published elsewhere, but those are different files.
+  if (!ReportableDiagnostics.empty()) {
+    std::lock_guard<std::mutex> Lock(ConfigDiagnosticsMu);
+    for (auto &Entry : ReportableDiagnostics)
+      ServerCallbacks->onDiagnosticsReady(Entry.first(), /*Version=*/"",
+                                          std::move(Entry.second));
+  }
   return Context::current().derive(Config::Key, std::move(C));
 }
 
 LLVM_NODISCARD bool
 ClangdServer::blockUntilIdleForTest(llvm::Optional<double> TimeoutSeconds) {
   return WorkScheduler.blockUntilIdle(timeoutSeconds(TimeoutSeconds)) &&
          (!BackgroundIdx ||
           BackgroundIdx->blockUntilIdleForTest(TimeoutSeconds));

clang-tools-extra/clangd/ConfigProvider.h

struct Params {
   /// By default, providers should validate caches against the data source.
   std::chrono::steady_clock::time_point FreshTime =
       std::chrono::steady_clock::time_point::max();
 };
 
 /// Used to report problems in parsing or interpreting a config.
 /// Errors reflect structurally invalid config that should be user-visible.
 /// Warnings reflect e.g. unknown properties that are recoverable.
+/// Notes are used to report files and fragments.
+/// (This can be used to track when previous warnings/errors have been "fixed").
 using DiagnosticCallback = llvm::function_ref<void(const llvm::SMDiagnostic &)>;
 
 /// A chunk of configuration that has been fully analyzed and is ready to apply.
 /// Typically this is obtained from a Fragment by calling Fragment::compile().
 ///
 /// Calling it updates the configuration to reflect settings from the fragment.
 /// Returns true if the condition was met and the settings were used.
 using CompiledFragment = std::function<bool(const Params &, Config &)>;

clang-tools-extra/clangd/ConfigYAML.cpp

SM->setDiagHandler(
       },
       &Diags);
   std::vector<Fragment> Result;
   for (auto &Doc : llvm::yaml::Stream(*Buf, *SM)) {
     if (Node *N = Doc.getRoot()) {
       Fragment Fragment;
       Fragment.Source.Manager = SM;
       Fragment.Source.Location = N->getSourceRange().Start;
+      SM->PrintMessage(Fragment.Source.Location, llvm::SourceMgr::DK_Note,
+                       "Parsing config fragment");
       if (Parser(*SM).parse(Fragment, *N))
         Result.push_back(std::move(Fragment));
     }
   }
+  SM->PrintMessage(SM->FindLocForLineAndColumn(SM->getMainFileID(), 0, 0),
+                   llvm::SourceMgr::DK_Note,
+                   "Parsed " + llvm::Twine(Result.size()) +
+                       " fragments from file");
   // Hack: stash the buffer in the SourceMgr to keep it alive.
   // SM has two entries: "main" non-owning buffer, and ignored owning buffer.
   SM->AddNewSourceBuffer(std::move(Buf), llvm::SMLoc());
   return Result;
 }
 
 } // namespace config
 } // namespace clangd
 } // namespace clang

clang-tools-extra/clangd/Diagnostics.h

 #include "clang/Basic/LangOptions.h"
 #include "clang/Basic/SourceLocation.h"
 #include "llvm/ADT/ArrayRef.h"
 #include "llvm/ADT/DenseSet.h"
 #include "llvm/ADT/None.h"
 #include "llvm/ADT/Optional.h"
 #include "llvm/ADT/STLExtras.h"
 #include "llvm/ADT/StringSet.h"
+#include "llvm/Support/SourceMgr.h"
 #include <cassert>
 #include <string>
 
 namespace clang {
 namespace tidy {
 class ClangTidyContext;
 } // namespace tidy
 namespace clangd {

 /// Represents a note for the diagnostic. Severity of notes can only be 'note'
 /// or 'remark'.
 struct Note : DiagBase {};
 
 /// A top-level diagnostic that may have Notes and Fixes.
 struct Diag : DiagBase {
   std::string Name; // if ID was recognized.
   // The source of this diagnostic.
-  enum {
+  enum DiagSource {
     Unknown,
     Clang,
     ClangTidy,
+    ClangdConfig,
   } Source = Unknown;
   /// Elaborate on the problem, usually pointing to a related piece of code.
   std::vector<Note> Notes;
   /// *Alternative* fixes for this diagnostic, one should be chosen.
   std::vector<Fix> Fixes;
 };
 llvm::raw_ostream &operator<<(llvm::raw_ostream &OS, const Diag &D);
 
+Diag toDiag(const llvm::SMDiagnostic &, Diag::DiagSource Source);
+
 /// Conversion to LSP diagnostics. Formats the error message of each diagnostic
 /// to include all its notes. Notes inside main file are also provided as
 /// separate diagnostics with their corresponding fixits. Notes outside main
 /// file do not have a corresponding LSP diagnostic, but can still be included
 /// as part of their main diagnostic's message.
 void toLSPDiags(
     const Diag &D, const URIForFile &File, const ClangdDiagnosticOptions &Opts,
     llvm::function_ref<void(clangd::Diagnostic, llvm::ArrayRef<Fix>)> OutFn);

clang-tools-extra/clangd/Diagnostics.cpp

CodeAction toCodeAction(const Fix &F, const URIForFile &File) {
   Action.title = F.Message;
   Action.kind = std::string(CodeAction::QUICKFIX_KIND);
   Action.edit.emplace();
   Action.edit->changes.emplace();
   (*Action.edit->changes)[File.uri()] = {F.Edits.begin(), F.Edits.end()};
   return Action;
 }
 
+Diag toDiag(const llvm::SMDiagnostic &D, Diag::DiagSource Source) {
+  Diag Result;
+  Result.Message = D.getMessage().str();
+  switch (D.getKind()) {
+  case llvm::SourceMgr::DK_Error:
+    Result.Severity = DiagnosticsEngine::Error;
+    break;
+  case llvm::SourceMgr::DK_Warning:
+    Result.Severity = DiagnosticsEngine::Warning;
+    break;
+  default:
+    break;
+  }
+  Result.Source = Source;
+  Result.AbsFile = D.getFilename().str();
+  Result.InsideMainFile = D.getSourceMgr()->FindBufferContainingLoc(
+                              D.getLoc()) == D.getSourceMgr()->getMainFileID();
+  if (D.getRanges().empty())
+    Result.Range = {{D.getLineNo() - 1, D.getColumnNo()},
+                    {D.getLineNo() - 1, D.getColumnNo()}};
+  else
+    Result.Range = {{D.getLineNo() - 1, (int)D.getRanges().front().first},
+                    {D.getLineNo() - 1, (int)D.getRanges().front().second}};
+  return Result;
+}
+
 void toLSPDiags(
     const Diag &D, const URIForFile &File, const ClangdDiagnosticOptions &Opts,
     llvm::function_ref<void(clangd::Diagnostic, llvm::ArrayRef<Fix>)> OutFn) {
   clangd::Diagnostic Main;
   Main.severity = getSeverity(D.Severity);
 
   // Main diagnostic should always refer to a range inside main file. If a
   // diagnostic made it so for, it means either itself or one of its notes is
void toLSPDiags(
   Main.code = D.Name;
   switch (D.Source) {
   case Diag::Clang:
     Main.source = "clang";
     break;
   case Diag::ClangTidy:
     Main.source = "clang-tidy";
     break;
+  case Diag::ClangdConfig:
+    Main.source = "clangd-config";
+    break;
   case Diag::Unknown:
     break;
   }
   if (Opts.EmbedFixesInDiagnostics) {
     Main.codeActions.emplace();
     for (const auto &Fix : D.Fixes)
       Main.codeActions->push_back(toCodeAction(Fix, File));
     if (Main.codeActions->size() == 1)

clang-tools-extra/clangd/test/config.test

+# We specify a custom path in XDG_CONFIG_HOME, which only works on some systems.
+# UNSUPPORTED: system-windows
+# UNSUPPORTED: system-darwin
+
+# RUN: rm -rf %t
+# RUN: mkdir -p %t/clangd
+
+# Create a config file that injects a flag we can observe, and has an error.
+# RUN: echo 'Foo: bar' > %t/clangd/config.yaml
+# RUN: echo 'CompileFlags: {Add: -DFOO=BAR}' >> %t/clangd/config.yaml
+
+# RUN: env XDG_CONFIG_HOME=%t clangd -lit-test -enable-config < %s | FileCheck -strict-whitespace %s
+
+{"jsonrpc":"2.0","id":0,"method":"initialize","params":{"processId":123,"rootPath":"clangd","capabilities":{},"trace":"off"}}
+---
+{"jsonrpc":"2.0","method":"textDocument/didOpen","params":{"textDocument":{"uri":"test:///foo.c","languageId":"c","text":"int x = FOO;"}}}
+# First, the errors from the config file.
+#      CHECK:  "method": "textDocument/publishDiagnostics",
+# CHECK-NEXT:  "params": {
+# CHECK-NEXT:    "diagnostics": [
+# CHECK-NEXT:      {
+# CHECK-NEXT:        "message": "Unknown Config key Foo",
+# CHECK-NEXT:        "range": {
+# CHECK-NEXT:          "end": {
+# CHECK-NEXT:            "character": 3,
+# CHECK-NEXT:            "line": 0
+# CHECK-NEXT:          },
+# CHECK-NEXT:          "start": {
+# CHECK-NEXT:            "character": 0,
+# CHECK-NEXT:            "line": 0
+# CHECK-NEXT:          }
+# CHECK-NEXT:        },
+# CHECK-NEXT:        "severity": 2,
+# CHECK-NEXT:        "source": "clangd-config"
+# CHECK-NEXT:      }
+# CHECK-NEXT:    ],
+# CHECK-NEXT:    "uri": "file://{{.*}}/config.yaml"
+# CHECK-NEXT:  }
+# Next, the error from the main file. BAR rather than FOO means we used config.
+#      CHECK:  "method": "textDocument/publishDiagnostics",
+# CHECK-NEXT:  "params": {
+# CHECK-NEXT:    "diagnostics": [
+# CHECK-NEXT:      {
+# CHECK-NEXT:        "code": "undeclared_var_use",
+# CHECK-NEXT:        "message": "Use of undeclared identifier 'BAR'",
+# CHECK-NEXT:        "range": {
+# CHECK-NEXT:          "end": {
+# CHECK-NEXT:            "character": 11,
+# CHECK-NEXT:            "line": 0
+# CHECK-NEXT:          },
+# CHECK-NEXT:          "start": {
+# CHECK-NEXT:            "character": 8,
+# CHECK-NEXT:            "line": 0
+# CHECK-NEXT:          }
+# CHECK-NEXT:        },
+# CHECK-NEXT:        "severity": 1,
+# CHECK-NEXT:        "source": "clang"
+# CHECK-NEXT:      }
+# CHECK-NEXT:    ],
+# CHECK-NEXT:    "uri": "file://{{.*}}/foo.c",
+# CHECK-NEXT:    "version": 0
+# CHECK-NEXT:  }
+---
+{"jsonrpc":"2.0","id":4,"method":"shutdown"}
+---
+{"jsonrpc":"2.0","method":"exit"}

clang-tools-extra/clangd/unittests/ConfigProviderTests.cpp

TEST(ProviderTest, FromYAMLFile) {
   MockFS FS;
   FS.Files["foo.yaml"] = AddFooWithErr;
 
   CapturedDiags Diags;
   auto P = Provider::fromYAMLFile(testPath("foo.yaml"), /*Directory=*/"", FS);
   auto Cfg = P->getConfig(Params(), Diags.callback());
   EXPECT_THAT(Diags.Diagnostics,
               ElementsAre(DiagMessage("Unknown CompileFlags key Unknown")));
+  EXPECT_THAT(Diags.Files, ElementsAre(testPath("foo.yaml")));
   EXPECT_THAT(getAddedArgs(Cfg), ElementsAre("foo"));
-  Diags.Diagnostics.clear();
+  Diags.clear();
 
   Cfg = P->getConfig(Params(), Diags.callback());
   EXPECT_THAT(Diags.Diagnostics, IsEmpty()) << "Cached, not re-parsed";
+  EXPECT_THAT(Diags.Files, IsEmpty());
   EXPECT_THAT(getAddedArgs(Cfg), ElementsAre("foo"));
 
   FS.Files["foo.yaml"] = AddBarBaz;
   Cfg = P->getConfig(Params(), Diags.callback());
   EXPECT_THAT(Diags.Diagnostics, IsEmpty()) << "New config, no errors";
+  EXPECT_THAT(Diags.Files, ElementsAre(testPath("foo.yaml")));
   EXPECT_THAT(getAddedArgs(Cfg), ElementsAre("bar", "baz"));
+  Diags.clear();
 
   FS.Files.erase("foo.yaml");
   Cfg = P->getConfig(Params(), Diags.callback());
   EXPECT_THAT(Diags.Diagnostics, IsEmpty()) << "Missing file is not an error";
+  EXPECT_THAT(Diags.Files, IsEmpty());
   EXPECT_THAT(getAddedArgs(Cfg), IsEmpty());
 }
 
 TEST(ProviderTest, FromAncestorRelativeYAMLFiles) {
   MockFS FS;
   FS.Files["a/b/c/foo.yaml"] = AddBarBaz;
   FS.Files["a/foo.yaml"] = AddFooWithErr;
 
   std::string ABCPath =
       testPath("a/b/c/d/test.cc", llvm::sys::path::Style::posix);
   Params ABCParams;
   ABCParams.Path = ABCPath;
   std::string APath =
       testPath("a/b/e/f/test.cc", llvm::sys::path::Style::posix);
   Params AParams;
   AParams.Path = APath;
 
   CapturedDiags Diags;
   auto P = Provider::fromAncestorRelativeYAMLFiles("foo.yaml", FS);
 
   auto Cfg = P->getConfig(Params(), Diags.callback());
   EXPECT_THAT(Diags.Diagnostics, IsEmpty());
+  EXPECT_THAT(Diags.Files, IsEmpty());
   EXPECT_THAT(getAddedArgs(Cfg), IsEmpty());
 
   Cfg = P->getConfig(ABCParams, Diags.callback());
   EXPECT_THAT(Diags.Diagnostics,
               ElementsAre(DiagMessage("Unknown CompileFlags key Unknown")));
+  EXPECT_THAT(Diags.Files,
+              ElementsAre(testPath("a/foo.yaml"), testPath("a/b/c/foo.yaml")));
   EXPECT_THAT(getAddedArgs(Cfg), ElementsAre("foo", "bar", "baz"));
-  Diags.Diagnostics.clear();
+  Diags.clear();
 
   Cfg = P->getConfig(AParams, Diags.callback());
   EXPECT_THAT(Diags.Diagnostics, IsEmpty()) << "Cached config";
+  EXPECT_THAT(Diags.Files, IsEmpty());
   EXPECT_THAT(getAddedArgs(Cfg), ElementsAre("foo"));
 
   FS.Files.erase("a/foo.yaml");
   Cfg = P->getConfig(ABCParams, Diags.callback());
   EXPECT_THAT(Diags.Diagnostics, IsEmpty());
+  EXPECT_THAT(Diags.Files, IsEmpty());
   EXPECT_THAT(getAddedArgs(Cfg), ElementsAre("bar", "baz"));
 }
 
 // FIXME: delete this test, it's covered by FileCacheTests.
 TEST(ProviderTest, Staleness) {
   MockFS FS;
 
   auto StartTime = std::chrono::steady_clock::now();
   Params StaleOK;
   StaleOK.FreshTime = StartTime;
   Params MustBeFresh;
   MustBeFresh.FreshTime = StartTime + std::chrono::hours(1);
   CapturedDiags Diags;
   auto P = Provider::fromYAMLFile(testPath("foo.yaml"), /*Directory=*/"", FS);
 
   // Initial query always reads, regardless of policy.
   FS.Files["foo.yaml"] = AddFooWithErr;
   auto Cfg = P->getConfig(StaleOK, Diags.callback());
   EXPECT_THAT(Diags.Diagnostics,
               ElementsAre(DiagMessage("Unknown CompileFlags key Unknown")));
   EXPECT_THAT(getAddedArgs(Cfg), ElementsAre("foo"));
-  Diags.Diagnostics.clear();
+  Diags.clear();
 
   // Stale value reused by policy.
   FS.Files["foo.yaml"] = AddBarBaz;
   Cfg = P->getConfig(StaleOK, Diags.callback());
   EXPECT_THAT(Diags.Diagnostics, IsEmpty()) << "Cached, not re-parsed";
   EXPECT_THAT(getAddedArgs(Cfg), ElementsAre("foo"));
 
   // Cache revalidated by policy.
)yaml";
 
   // This should be an absolute match/exclude hence baz/bar.h should not be
   // excluded.
   auto P =
       Provider::fromYAMLFile(testPath("baz/foo.yaml"), /*Directory=*/"", FS);
   auto Cfg = P->getConfig(Bar, Diags.callback());
   ASSERT_THAT(Diags.Diagnostics, IsEmpty());
   EXPECT_THAT(getAddedArgs(Cfg), ElementsAre("bar"));
-  Diags.Diagnostics.clear();
+  Diags.clear();
 
   // This should be a relative match/exclude hence baz/bar.h should be excluded.
   P = Provider::fromAncestorRelativeYAMLFiles("foo.yaml", FS);
   Cfg = P->getConfig(Bar, Diags.callback());
   ASSERT_THAT(Diags.Diagnostics, IsEmpty());
   EXPECT_THAT(getAddedArgs(Cfg), IsEmpty());
-  Diags.Diagnostics.clear();
+  Diags.clear();
 }
 } // namespace
 } // namespace config
 } // namespace clangd
 } // namespace clang

clang-tools-extra/clangd/unittests/ConfigTesting.h

 namespace clangd {
 namespace config {
 
 // Provides a DiagnosticsCallback that records diganostics.
 // Unlike just pushing them into a vector, underlying storage need not survive.
 struct CapturedDiags {
   std::function<void(const llvm::SMDiagnostic &)> callback() {
     return [this](const llvm::SMDiagnostic &D) {
+      if (Files.empty() || Files.back() != D.getFilename())
+        Files.push_back(D.getFilename().str());
+
+      if (D.getKind() > llvm::SourceMgr::DK_Warning)
+        return;
+
       Diagnostics.emplace_back();
       Diag &Out = Diagnostics.back();
       Out.Message = D.getMessage().str();
       Out.Kind = D.getKind();
       Out.Pos.line = D.getLineNo() - 1;
       Out.Pos.character = D.getColumnNo(); // Zero-based - bug in SourceMgr?
       if (!D.getRanges().empty()) {
         const auto &R = D.getRanges().front();
struct Diag {
     Position Pos;
     llvm::Optional<Range> Rng;
 
     friend void PrintTo(const Diag &D, std::ostream *OS) {
       *OS << (D.Kind == llvm::SourceMgr::DK_Error ? "error: " : "warning: ")
           << D.Message << "@" << llvm::to_string(D.Pos);
     }
   };
-  std::vector<Diag> Diagnostics;
+  std::vector<Diag> Diagnostics;  // Warning or higher.
+  std::vector<std::string> Files; // Filename from diagnostics including notes.
+
+  void clear() {
+    Diagnostics.clear();
+    Files.clear();
+  }
 };
 
 MATCHER_P(DiagMessage, M, "") { return arg.Message == M; }
 MATCHER_P(DiagKind, K, "") { return arg.Kind == K; }
 MATCHER_P(DiagPos, P, "") { return arg.Pos == P; }
 MATCHER_P(DiagRange, R, "") { return arg.Rng == R; }
 
 inline Position toPosition(llvm::SMLoc L, const llvm::SourceMgr &SM) {

clang-tools-extra/clangd/unittests/ConfigYAMLTests.cpp

 ---
 ClangTidy: 
   CheckOptions: 
     IgnoreMacros: true
     example-check.ExampleOption: 0
   )yaml";
   auto Results = Fragment::parseYAML(YAML, "config.yaml", Diags.callback());
   EXPECT_THAT(Diags.Diagnostics, IsEmpty());
+  EXPECT_THAT(Diags.Files, ElementsAre("config.yaml"));
   ASSERT_EQ(Results.size(), 4u);
   EXPECT_FALSE(Results[0].If.HasUnrecognizedCondition);
   EXPECT_THAT(Results[0].If.PathMatch, ElementsAre(Val("abc")));
   EXPECT_THAT(Results[0].CompileFlags.Add, ElementsAre(Val("foo"), Val("bar")));
 
   EXPECT_THAT(Results[1].CompileFlags.Add, ElementsAre(Val("b\naz\n")));
 
   ASSERT_TRUE(Results[2].Index.Background);