TextEditor: always return a valid assist interface

It is required for updating currently visible proposals. Also guard
against potential null assist interfaces.

Amends 0bd6d7a69f

Fixes: QTCREATORBUG-29096
Change-Id: Ic34d70561b471e7e529f2fb7c239b49712aca502
Reviewed-by: Christian Kandeler <christian.kandeler@qt.io>
Reviewed-by: <github-actions-qt-creator@cristianadam.eu>

src/plugins/cppeditor/cppeditorwidget.cpp

@@ -1267,20 +1267,16 @@ std::unique_ptr<AssistInterface> CppEditorWidget::createAssistInterface(AssistKi
 
         if (cap)
             return cap->createAssistInterface(textDocument()->filePath(), this, getFeatures(), reason);
-        else {
-            if (isOldStyleSignalOrSlot())
+
+        if (isOldStyleSignalOrSlot()) {
             return CppModelManager::instance()
                 ->completionAssistProvider()
                 ->createAssistInterface(textDocument()->filePath(), this, getFeatures(), reason);
-            return TextEditorWidget::createAssistInterface(kind, reason);
         }
-    } else if (kind == QuickFix) {
-        if (isSemanticInfoValid())
+    }
+    if (kind == QuickFix && isSemanticInfoValid())
         return std::make_unique<CppQuickFixInterface>(const_cast<CppEditorWidget *>(this), reason);
-    } else {
     return TextEditorWidget::createAssistInterface(kind, reason);
-    }
-    return nullptr;
 }
 
 QSharedPointer<FunctionDeclDefLink> CppEditorWidget::declDefLink() const

src/plugins/cppeditor/cppquickfixassistant.cpp

@@ -149,7 +149,8 @@ QTextCursor CppQuickFixInterface::adjustedCursor()
 QuickFixOperations quickFixOperations(const TextEditor::AssistInterface *interface)
 {
     const auto cppInterface = dynamic_cast<const CppQuickFixInterface *>(interface);
-    QTC_ASSERT(cppInterface, return {});
+    if (!cppInterface)
+        return {};
     QuickFixOperations quickFixes;
     for (CppQuickFixFactory *factory : CppQuickFixFactory::cppQuickFixFactories())
         factory->match(*cppInterface, quickFixes);

src/plugins/qmljseditor/qmljseditor.cpp

@@ -1042,7 +1042,7 @@ std::unique_ptr<AssistInterface> QmlJSEditorWidget::createAssistInterface(
         return std::make_unique<Internal::QmlJSQuickFixAssistInterface>(
             const_cast<QmlJSEditorWidget *>(this), reason);
     }
-    return nullptr;
+    return TextEditorWidget::createAssistInterface(assistKind, reason);
 }
 
 QString QmlJSEditorWidget::foldReplacementText(const QTextBlock &block) const

src/plugins/texteditor/codeassist/codeassistant.cpp

@@ -175,8 +175,7 @@ void CodeAssistantPrivate::requestProposal(AssistReason reason,
 
     std::unique_ptr<AssistInterface> assistInterface =
             m_editorWidget->createAssistInterface(kind, reason);
-    if (!assistInterface)
-        return;
+    QTC_ASSERT(assistInterface, return);
 
     // We got an assist provider and interface so no need to reset the current context anymore
     earlyReturnContextClear.reset({});
@@ -395,8 +394,10 @@ void CodeAssistantPrivate::notifyChange()
         if (m_editorWidget->position() < m_proposalWidget->basePosition()) {
             destroyContext();
         } else {
-            m_proposalWidget->updateProposal(
-                m_editorWidget->createAssistInterface(m_assistKind, m_proposalWidget->reason()));
+            std::unique_ptr<AssistInterface> assistInterface
+                = m_editorWidget->createAssistInterface(m_assistKind, m_proposalWidget->reason());
+            QTC_ASSERT(assistInterface, destroyContext(); return);
+            m_proposalWidget->updateProposal(std::move(assistInterface));
             if (!isDisplayingProposal())
                 requestActivationCharProposal();
         }