LanguageClient: keep semantic tokens after receiving error

A usual error we receive for semantic request is that the request got
canceled. This can be due to external changes. But a server might still
be able to calculate a diff against a previous token set. So just keep
the previously reported tokens and rerequest a new highlight. If the
server is not able to calculate a diff it also might send a full
token set as a result for the delta request according to the protocol.

Fixes: QTCREATORBUG-26624
Change-Id: Ia91e599706519dbbf4cd22050484e4f36cecdab8
Reviewed-by: Christian Kandeler <christian.kandeler@qt.io>

src/plugins/languageclient/semantichighlightsupport.cpp

@@ -67,19 +67,33 @@ void SemanticTokenSupport::refresh()
 }
 
 void SemanticTokenSupport::reloadSemanticTokens(TextDocument *textDocument)
+{
+    reloadSemanticTokensImpl(textDocument);
+}
+
+void SemanticTokenSupport::reloadSemanticTokensImpl(TextDocument *textDocument,
+                                                    int remainingRerequests)
 {
     const SemanticRequestTypes supportedRequests = supportedSemanticRequests(textDocument);
     if (supportedRequests.testFlag(SemanticRequestType::None))
         return;
     const Utils::FilePath filePath = textDocument->filePath();
     const TextDocumentIdentifier docId(DocumentUri::fromFilePath(filePath));
-    auto responseCallback = [this, filePath, documentVersion = m_client->documentVersion(filePath)](
+    auto responseCallback = [this,
+                             remainingRerequests,
+                             filePath,
+                             documentVersion = m_client->documentVersion(filePath)](
                                 const SemanticTokensFullRequest::Response &response) {
         if (const auto error = response.error()) {
             qCDebug(LOGLSPHIGHLIGHT)
                 << "received error" << error->code() << error->message() << "for" << filePath;
+            if (remainingRerequests > 0) {
+                if (auto document = TextDocument::textDocumentForFilePath(filePath))
+                    reloadSemanticTokensImpl(document, remainingRerequests - 1);
             }
+        } else {
             handleSemanticTokens(filePath, response.result().value_or(nullptr), documentVersion);
+        }
     };
     /*if (supportedRequests.testFlag(SemanticRequestType::Range)) {
         const int start = widget->firstVisibleBlockNumber();
@@ -107,6 +121,12 @@ void SemanticTokenSupport::reloadSemanticTokens(TextDocument *textDocument)
 }
 
 void SemanticTokenSupport::updateSemanticTokens(TextDocument *textDocument)
+{
+    updateSemanticTokensImpl(textDocument);
+}
+
+void SemanticTokenSupport::updateSemanticTokensImpl(TextDocument *textDocument,
+                                                    int remainingRerequests)
 {
     const SemanticRequestTypes supportedRequests = supportedSemanticRequests(textDocument);
     if (supportedRequests.testFlag(SemanticRequestType::FullDelta)) {
@@ -122,15 +142,22 @@ void SemanticTokenSupport::updateSemanticTokens(TextDocument *textDocument)
             params.setPreviousResultId(previousResultId);
             SemanticTokensFullDeltaRequest request(params);
             request.setResponseCallback(
-                [this, filePath, documentVersion](
+                [this, filePath, documentVersion, remainingRerequests](
                     const SemanticTokensFullDeltaRequest::Response &response) {
                     if (const auto error = response.error()) {
                         qCDebug(LOGLSPHIGHLIGHT) << "received error" << error->code()
                                                  << error->message() << "for" << filePath;
+                        if (auto document = TextDocument::textDocumentForFilePath(filePath)) {
+                            if (remainingRerequests > 0)
+                                updateSemanticTokensImpl(document, remainingRerequests - 1);
+                            else
+                                reloadSemanticTokensImpl(document, 1); // try a full reload once
                         }
+                    } else {
                         handleSemanticTokensDelta(filePath,
                                                   response.result().value_or(nullptr),
                                                   documentVersion);
+                    }
                 });
             qCDebug(LOGLSPHIGHLIGHT)
                 << "Requesting delta for" << filePath << "with version" << documentVersion;
@@ -292,11 +319,6 @@ void SemanticTokenSupport::handleSemanticTokens(const Utils::FilePath &filePath,
     if (auto tokens = Utils::get_if<SemanticTokens>(&result)) {
         m_tokens[filePath] = {*tokens, documentVersion};
         highlight(filePath);
-    } else {
-        qCDebug(LOGLSPHIGHLIGHT)
-                << "no data in reply to full semantic tokens request, clearing tokens"
-                << m_client->name() << filePath;
-        m_tokens.remove(filePath);
     }
 }
 
@@ -363,12 +385,6 @@ void SemanticTokenSupport::handleSemanticTokensDelta(
         qCDebug(LOGLSPHIGHLIGHT) << "New Data " << newData;
         tokens.setData(newData);
         tokens.setResultId(tokensDelta->resultId());
-    } else {
-        qCDebug(LOGLSPHIGHLIGHT)
-                << "no data in reply to semantic tokens delta request, clearing tokens"
-                << m_client->name() << filePath;
-        m_tokens.remove(filePath);
-        return;
     }
     highlight(filePath);
 }

src/plugins/languageclient/semantichighlightsupport.h

@@ -83,6 +83,8 @@ public:
     void setTokensHandler(const SemanticTokensHandler &handler) { m_tokensHandler = handler; }
 
 private:
+    void reloadSemanticTokensImpl(TextEditor::TextDocument *doc, int remainingRerequests = 3);
+    void updateSemanticTokensImpl(TextEditor::TextDocument *doc, int remainingRerequests = 3);
     LanguageServerProtocol::SemanticRequestTypes supportedSemanticRequests(
         TextEditor::TextDocument *document) const;
     void handleSemanticTokens(const Utils::FilePath &filePath,