LanguageClient: improve clangd function hint

Add a Clangd specific function hint model that alwys highlights the
current parameter based on the number of commas in front of the cursor
position, like the builtin code model. It also correctly closes the
proposal after typing the closing parenthesis.

Fixes: QTCREATORBUG-26346
Fixes: QTCREATORBUG-30489
Change-Id: I09d3ac6856acfe5e0f206d8c3a96dbb561ea2ce7
Reviewed-by: Christian Kandeler <christian.kandeler@qt.io>

src/plugins/clangcodemodel/clangdcompletion.cpp

@@ -102,13 +102,52 @@ private:
     QElapsedTimer m_timer;
 };
 
+class ClangdFunctionHintProposalModel : public FunctionHintProposalModel
+{
+public:
+    using FunctionHintProposalModel::FunctionHintProposalModel;
+
+private:
+    int activeArgument(const QString &prefix) const override
+    {
+        const int arg = activeArgumenForPrefix(prefix);
+        if (arg < 0)
+            return -1;
+        m_currentArg = arg;
+        return arg;
+    }
+
+    QString text(int index) const override
+    {
+        using Parameters = QList<ParameterInformation>;
+        if (index < 0 || m_sigis.signatures().size() <= index)
+            return {};
+        const SignatureInformation signature = m_sigis.signatures().at(index);
+        QString label = signature.label();
+
+        const QList<QString> parameters = Utils::transform(signature.parameters().value_or(Parameters()),
+                                                           &ParameterInformation::label);
+        if (parameters.size() <= m_currentArg)
+            return label;
+
+        const QString &parameterText = parameters.at(m_currentArg);
+        const int start = label.indexOf(parameterText);
+        const int end = start + parameterText.length();
+        return label.mid(0, start).toHtmlEscaped() + "<b>" + parameterText.toHtmlEscaped() + "</b>"
+               + label.mid(end).toHtmlEscaped();
+    }
+
+    mutable int m_currentArg = 0;
+};
+
 class ClangdFunctionHintProcessor : public FunctionHintProcessor
 {
 public:
-    ClangdFunctionHintProcessor(ClangdClient *client);
+    ClangdFunctionHintProcessor(ClangdClient *client, int basePosition);
 
 private:
     IAssistProposal *perform() override;
+    IFunctionHintProposalModel *createModel(const SignatureHelp &signatureHelp) const override;
 
     ClangdClient * const m_client;
 };
@@ -138,7 +177,8 @@ IAssistProcessor *ClangdCompletionAssistProvider::createProcessor(
     switch (contextAnalyzer.completionAction()) {
     case ClangCompletionContextAnalyzer::PassThroughToLibClangAfterLeftParen:
         qCDebug(clangdLogCompletion) << "creating function hint processor";
-        return new ClangdFunctionHintProcessor(m_client);
+        return new ClangdFunctionHintProcessor(m_client,
+                                               contextAnalyzer.positionForProposal());
     case ClangCompletionContextAnalyzer::CompletePreprocessorDirective:
         qCDebug(clangdLogCompletion) << "creating macro processor";
         return new CustomAssistProcessor(m_client,
@@ -606,8 +646,8 @@ QList<AssistProposalItemInterface *> ClangdCompletionAssistProcessor::generateCo
     return itemGenerator(items);
 }
 
-ClangdFunctionHintProcessor::ClangdFunctionHintProcessor(ClangdClient *client)
-    : FunctionHintProcessor(client)
+ClangdFunctionHintProcessor::ClangdFunctionHintProcessor(ClangdClient *client, int basePosition)
+    : FunctionHintProcessor(client, basePosition)
     , m_client(client)
 {}
 
@@ -621,6 +661,12 @@ IAssistProposal *ClangdFunctionHintProcessor::perform()
     return FunctionHintProcessor::perform();
 }
 
+IFunctionHintProposalModel *ClangdFunctionHintProcessor::createModel(
+    const SignatureHelp &signatureHelp) const
+{
+    return new ClangdFunctionHintProposalModel(signatureHelp);
+}
+
 ClangdCompletionCapabilities::ClangdCompletionCapabilities(const JsonObject &object)
     : TextDocumentClientCapabilities::CompletionCapabilities(object)
 {
@@ -631,4 +677,18 @@ ClangdCompletionCapabilities::ClangdCompletionCapabilities(const JsonObject &obj
     }
 }
 
+ClangdFunctionHintProvider::ClangdFunctionHintProvider(ClangdClient *client)
+    : FunctionHintAssistProvider(client)
+    , m_client(client)
+{}
+
+IAssistProcessor *ClangdFunctionHintProvider::createProcessor(
+    const AssistInterface *interface) const
+{
+    ClangCompletionContextAnalyzer contextAnalyzer(interface->textDocument(),
+                                                   interface->position(), false, {});
+    contextAnalyzer.analyze();
+    return new ClangdFunctionHintProcessor(m_client, contextAnalyzer.positionForProposal());
+}
+
 } // namespace ClangCodeModel::Internal