LSP: rerequest completion if contents change while processing

Task-number: QTCREATORBUG-21108
Change-Id: I6ca7920e7099dba0ba1bc953a2e6296bd86c1dc1
Reviewed-by: Eike Ziller <eike.ziller@qt.io>

src/plugins/languageclient/languageclientcodeassist.cpp

@@ -219,6 +219,7 @@ public:
     LanguageClientCompletionAssistProcessor(BaseClient *client);
     TextEditor::IAssistProposal *perform(const TextEditor::AssistInterface *interface) override;
     bool running() override;
+    bool needsRestart() const override { return true; }
 
 private:
     void handleCompletionResponse(const Response<CompletionResult, LanguageClientNull> &response);

src/plugins/texteditor/codeassist/codeassistant.cpp

@@ -245,10 +245,17 @@ void CodeAssistantPrivate::requestProposal(AssistReason reason,
     case IAssistProvider::Asynchronous: {
         processor->setAsyncCompletionAvailableHandler(
             [this, reason](IAssistProposal *newProposal){
+                if (m_asyncProcessor && m_asyncProcessor->needsRestart() && m_receivedContentWhileWaiting) {
+                    delete newProposal;
+                    m_receivedContentWhileWaiting = false;
+                    invalidateCurrentRequestData();
+                    requestProposal(reason, m_assistKind, m_requestProvider);
+                } else {
                     invalidateCurrentRequestData();
                     displayProposal(newProposal, reason);
 
                     emit q->finished();
+                }
         });
 
         // If there is a proposal, nothing asynchronous happened...

src/plugins/texteditor/codeassist/iassistprocessor.h

@@ -50,6 +50,7 @@ public:
     void setAsyncCompletionAvailableHandler(const AsyncCompletionsAvailableHandler &finalizer);
 
     virtual bool running() { return false; }
+    virtual bool needsRestart() const { return false; }
 
 private:
     AsyncCompletionsAvailableHandler m_asyncCompletionsAvailableHandler;