CodeAssist: Support asynchronous processing without threads

This is required for the CodemodelBackendIPC integration in the
ClangCodeModelPlugin. Since the heavy calculation happens in a separate
process, we only need to send appropriate requests and receive results
for a working completion. However, the CodeAssist API does not fit here
since it only provides means of caculating the results in the main
thread or a worker thread. We can't use the worker thread approach since
that would lead to threading issues regarding QLocalSocket in
CodemodelBackendIPC.

IAssistProcessor::setAsyncProposalAvailable() will hand the results
back to CodeAssist in order to display them.

Change-Id: I496192560fb406ec40fa8bcb7904f7a03d2eef50
Reviewed-by: David Schulz <david.schulz@theqtcompany.com>

src/plugins/texteditor/codeassist/iassistprocessor.h

@@ -33,6 +33,8 @@
 
 #include <texteditor/texteditor_global.h>
 
+#include <functional>
+
 namespace TextEditor {
 
 class IAssistProvider;
@@ -47,6 +49,15 @@ public:
 
     virtual IAssistProposal *immediateProposal(const AssistInterface *) { return 0; }
     virtual IAssistProposal *perform(const AssistInterface *interface) = 0;
+
+    void setAsyncProposalAvailable(IAssistProposal *proposal);
+
+    // Internal, used by CodeAssist
+    using AsyncCompletionsAvailableHandler = std::function<void (IAssistProposal *proposal)>;
+    void setAsyncCompletionAvailableHandler(const AsyncCompletionsAvailableHandler &finalizer);
+
+private:
+    AsyncCompletionsAvailableHandler m_asyncCompletionsAvailableHandler;
 };
 
 } // TextEditor