[clangd] Send empty diagnostics when a file is closed

[ilya-biryukov]

Summary

The LSP clients cannot know clangd will not send diagnostic updates
for closed files, so we send them an empty list of diagnostics to
avoid showing stale diagnostics for closed files in the UI, e.g. in the
"Problems" pane of VSCode.

Fixes PR41217.

[hokein]

clang-tools-extra/clangd/ClangdLSPServer.cpp

1000 ↗

(On Diff #192057)

IIUC, it seems that we might have race condition here, considering:

• open a file which will take a long time to get diagnostic
• the file gets closed, we publish an empty diagnostic
• we get the diagnostics of the file, and we cache them, and emit them to clients

[ilya-biryukov]

clang-tools-extra/clangd/ClangdLSPServer.cpp

1000 ↗

(On Diff #192057)

We should be fine there, TUScheduler won't send diagnostics after the call to remove returns.
This is ensured by calling ASTWorker::stop(), which sets the ASTWorker::ReportDiagnostics flag to false.

[hokein]

clang-tools-extra/clangd/ClangdLSPServer.cpp

1000 ↗

(On Diff #192057)

That makes sense, thanks for the clarification. Maybe add a comment in onDocumentDidClose for future readers.

[ilya-biryukov]

• Added a comment that races are not possible

clang-tools-extra/clangd/ClangdLSPServer.cpp

1000 ↗

(On Diff #192057)

Added a comment. Thanks!

clangd/ClangdLSPServer.h

private:
   bool shouldRunCompletion(const CompletionParams &Params) const;
 
   /// Forces a reparse of all currently opened files.  As a result, this method
   /// may be very expensive.  This method is normally called when the
   /// compilation database is changed.
   void reparseOpenedFiles();
   void applyConfiguration(const ConfigurationSettings &Settings);
 
+  /// Sends a "publishDiagnostics" notification to the LSP client.
+  void publishDiagnostics(const URIForFile &File,
+                          std::vector<clangd::Diagnostic> Diagnostics);
+
   /// Used to indicate that the 'shutdown' request was received from the
   /// Language Server client.
   bool ShutdownRequestReceived = false;
 
   std::mutex FixItsMutex;
   typedef std::map<clangd::Diagnostic, std::vector<Fix>, LSPDiagnosticCompare>
       DiagnosticToReplacementMap;
   /// Caches FixIts per file and diagnostics

clangd/ClangdLSPServer.cpp

Server->rename(
           std::move(Reply)));
 }
 
 void ClangdLSPServer::onDocumentDidClose(
     const DidCloseTextDocumentParams &Params) {
   PathRef File = Params.textDocument.uri.file();
   DraftMgr.removeDraft(File);
   Server->removeDocument(File);
+
+  {
+    std::lock_guard<std::mutex> Lock(FixItsMutex);
+    FixItsMap.erase(File);
+  }
+  // clangd will not send updates for this file anymore, so we empty out the
+  // list of diagnostics shown on the client (e.g. in the "Problems" pane of
+  // VSCode). Note that this cannot race with actual diagnostics responses
+  // because removeDocument() guarantees no diagnostic callbacks will be
+  // executed after it returns.
+  publishDiagnostics(URIForFile::canonicalize(File, /*TUPath=*/File), {});
 }
 
 void ClangdLSPServer::onDocumentOnTypeFormatting(
     const DocumentOnTypeFormattingParams &Params,
     Callback<std::vector<TextEdit>> Reply) {
   auto File = Params.textDocument.uri.file();
   auto Code = DraftMgr.getDraft(File);
   if (!Code)
if (Old != New) {
       CDB->setCompileCommand(File, std::move(New));
       ShouldReparseOpenFiles = true;
     }
   }
   if (ShouldReparseOpenFiles)
     reparseOpenedFiles();
 }
 
+void ClangdLSPServer::publishDiagnostics(
+    const URIForFile &File, std::vector<clangd::Diagnostic> Diagnostics) {
+  // Publish diagnostics.
+  notify("textDocument/publishDiagnostics",
+         llvm::json::Object{
+             {"uri", File},
+             {"diagnostics", std::move(Diagnostics)},
+         });
+}
+
 // FIXME: This function needs to be properly tested.
 void ClangdLSPServer::onChangeConfiguration(
     const DidChangeConfigurationParams &Params) {
   applyConfiguration(Params.settings);
 }
 
 void ClangdLSPServer::onReference(const ReferenceParams &Params,
                                   Callback<std::vector<Location>> Reply) {
toLSPDiags(Diag, URI, DiagOpts,
                  auto &FixItsForDiagnostic = LocalFixIts[Diag];
                  llvm::copy(Fixes, std::back_inserter(FixItsForDiagnostic));
                  LSPDiagnostics.push_back(std::move(Diag));
                });
   }
 
   // Cache FixIts
   {
-    // FIXME(ibiryukov): should be deleted when documents are removed
     std::lock_guard<std::mutex> Lock(FixItsMutex);
     FixItsMap[File] = LocalFixIts;
   }
 
-  // Publish diagnostics.
-  notify("textDocument/publishDiagnostics",
-         llvm::json::Object{
-             {"uri", URI},
-             {"diagnostics", std::move(LSPDiagnostics)},
-         });
+  // Send a notification to the LSP client.
+  publishDiagnostics(URI, std::move(LSPDiagnostics));
 }
 
 void ClangdLSPServer::onFileUpdated(PathRef File, const TUStatus &Status) {
   if (!SupportFileStatus)
     return;
   // FIXME: we don't emit "BuildingFile" and `RunningAction`, as these
   // two statuses are running faster in practice, which leads the UI constantly
   // changing, and doesn't provide much value. We may want to emit status at a

test/clangd/diagnostics.test

 # CHECK-NEXT:          }
 # CHECK-NEXT:        },
 # CHECK-NEXT:        "severity": 2
 # CHECK-NEXT:      }
 # CHECK-NEXT:    ],
 # CHECK-NEXT:    "uri": "file://{{.*}}/foo.c"
 # CHECK-NEXT:  }
 ---
+{"jsonrpc":"2.0","id":2,"method":"sync","params":null}
+---
+{"jsonrpc":"2.0","method":"textDocument/didClose","params":{"textDocument":{"uri":"test:///foo.c"}}}
+#      CHECK:  "method": "textDocument/publishDiagnostics",
+# CHECK-NEXT:  "params": {
+# CHECK-NEXT:    "diagnostics": [],
+# CHECK-NEXT:    "uri": "file://{{.*}}/foo.c"
+# CHECK-NEXT:  }
+---
 {"jsonrpc":"2.0","id":5,"method":"shutdown"}
 ---
 {"jsonrpc":"2.0","method":"exit"}