ClangCodeModel: Request clangd quickfix for -Wswitch warning

This way, a warning about missing switch cases will be accompanied by a
matching code action, which allows the user to fix it right away by
clicking on the lightbulb.
Requires clangd >= 15; see https://reviews.llvm.org/D118976.

Change-Id: I11e82264c41e4154f979d28a5e44e72c8158595b
Reviewed-by: David Schulz <david.schulz@qt.io>

src/plugins/clangcodemodel/clangdclient.cpp

@@ -1544,8 +1544,18 @@ void ClangdClient::handleDiagnostics(const PublishDiagnosticsParams &params)
         return;
     for (const Diagnostic &diagnostic : params.diagnostics()) {
         const ClangdDiagnostic clangdDiagnostic(diagnostic);
-        for (const CodeAction &action : clangdDiagnostic.codeActions().value_or(QList<CodeAction>{}))
+        const auto codeActions = clangdDiagnostic.codeActions();
+        if (codeActions && !codeActions->isEmpty()) {
+            for (const CodeAction &action : *codeActions)
                 LanguageClient::updateCodeActionRefactoringMarker(this, action, uri);
+        } else {
+            // We know that there's only one kind of diagnostic for which clangd has
+            // a quickfix tweak, so let's not be wasteful.
+            const Diagnostic::Code code = diagnostic.code().value_or(Diagnostic::Code());
+            const QString * const codeString = Utils::get_if<QString>(&code);
+            if (codeString && *codeString == "-Wswitch")
+                requestCodeActions(uri, diagnostic);
+        }
     }
 }
 

src/plugins/languageclient/client.cpp

@@ -866,7 +866,19 @@ SymbolSupport &Client::symbolSupport()
     return m_symbolSupport;
 }
 
+void Client::requestCodeActions(const LanguageServerProtocol::DocumentUri &uri,
+                                const LanguageServerProtocol::Diagnostic &diagnostic)
+{
+    requestCodeActions(uri, diagnostic.range(), {diagnostic});
+}
+
 void Client::requestCodeActions(const DocumentUri &uri, const QList<Diagnostic> &diagnostics)
+{
+    requestCodeActions(uri, {}, diagnostics);
+}
+
+void Client::requestCodeActions(const DocumentUri &uri, const Range &range,
+                                const QList<Diagnostic> &diagnostics)
 {
     const Utils::FilePath fileName = uri.toFilePath();
     TextEditor::TextDocument *doc = TextEditor::TextDocument::textDocumentForFilePath(fileName);
@@ -878,10 +890,14 @@ void Client::requestCodeActions(const DocumentUri &uri, const QList<Diagnostic>
     context.setDiagnostics(diagnostics);
     codeActionParams.setContext(context);
     codeActionParams.setTextDocument(TextDocumentIdentifier(uri));
+    if (range.isEmpty()) {
         Position start(0, 0);
         const QTextBlock &lastBlock = doc->document()->lastBlock();
         Position end(lastBlock.blockNumber(), lastBlock.length() - 1);
         codeActionParams.setRange(Range(start, end));
+    } else {
+        codeActionParams.setRange(range);
+    }
     CodeActionRequest request(codeActionParams);
     request.setResponseCallback(
         [uri, self = QPointer<Client>(this)](const CodeActionRequest::Response &response) {

src/plugins/languageclient/client.h

@@ -168,6 +168,8 @@ public:
     void updateConfiguration(const QJsonValue &configuration);
 
     // commands
+    void requestCodeActions(const LanguageServerProtocol::DocumentUri &uri,
+                            const LanguageServerProtocol::Diagnostic &diagnostic);
     void requestCodeActions(const LanguageServerProtocol::DocumentUri &uri,
                             const QList<LanguageServerProtocol::Diagnostic> &diagnostics);
     void requestCodeActions(const LanguageServerProtocol::CodeActionRequest &request);
@@ -253,6 +255,9 @@ private:
     void requestDocumentHighlightsNow(TextEditor::TextEditorWidget *widget);
     LanguageServerProtocol::SemanticRequestTypes supportedSemanticRequests(TextEditor::TextDocument *document) const;
     void handleSemanticTokens(const LanguageServerProtocol::SemanticTokens &tokens);
+    void requestCodeActions(const LanguageServerProtocol::DocumentUri &uri,
+                            const LanguageServerProtocol::Range &range,
+                            const QList<LanguageServerProtocol::Diagnostic> &diagnostics);
     void documentClosed(Core::IDocument *document);
 
     virtual void handleDocumentClosed(TextEditor::TextDocument *) {}