LanguageClient: update semantic highlighting only if server supports it

Task-number: QTCREATORBUG-23599
Change-Id: I76c804b51362ad6ab2aecf0631a16289a33e4810
Reviewed-by: Christian Stenger <christian.stenger@qt.io>

src/plugins/languageclient/client.cpp

@@ -392,8 +392,10 @@ void Client::deactivateDocument(TextEditor::TextDocument *document)
     hideDiagnostics(document);
     resetAssistProviders(document);
     document->setFormatter(nullptr);
+    if (m_serverCapabilities.semanticHighlighting().has_value()) {
         if (TextEditor::SyntaxHighlighter *highlighter = document->syntaxHighlighter())
             highlighter->clearAllExtraFormats();
+    }
     for (Core::IEditor *editor : Core::DocumentModel::editorsForDocument(document)) {
         if (auto textEditor = qobject_cast<TextEditor::BaseTextEditor *>(editor))
             textEditor->editorWidget()->removeHoverHandler(&m_hoverHandler);

src/plugins/languageclient/semantichighlightsupport.cpp

@@ -151,11 +151,13 @@ void applyHighlight(TextEditor::TextDocument *doc,
         }
     }
 
+    if (capabilities.semanticHighlighting().has_value()) {
         TextEditor::SemanticHighlighter::setExtraAdditionalFormats(
             doc->syntaxHighlighter(),
             results,
             scopesToFormatHash(highlightScopes(capabilities), doc->fontSettings()));
     }
+}
 
 } // namespace SemanticHighligtingSupport
 } // namespace LanguageClient