Clang: Do not show global completions after comma

Handle the case when we try to show the function hint but
do not find any completion. Do not fall back to the normal
code completion in such case.

Fixes: QTCREATORBUG-21624
Change-Id: I147d71b8970c18d49947f68786347a9db97736bb
Reviewed-by: Marco Bubke <marco.bubke@qt.io>

src/plugins/clangcodemodel/clangcompletionassistprocessor.cpp

@@ -214,6 +214,9 @@ void ClangCompletionAssistProcessor::handleAvailableCompletions(const CodeComple
             setAsyncProposalAvailable(createFunctionHintProposal(completions));
             return;
         }
+
+        if (!m_fallbackToNormalCompletion)
+            return;
         // else: Proceed with a normal completion in case:
         // 1) it was not a function call, but e.g. a function declaration like "void f("
         // 2) '{' meant not a constructor call.
@@ -286,6 +289,14 @@ static QByteArray modifyInput(QTextDocument *doc, int endOfExpression) {
     return modifiedInput;
 }
 
+static QChar lastPrecedingNonWhitespaceChar(const ClangCompletionAssistInterface *interface)
+{
+    int pos = interface->position();
+    while (pos >= 0 && interface->characterAt(pos).isSpace())
+        --pos;
+    return pos >= 0 ? interface->characterAt(pos) : QChar::Null;
+}
+
 IAssistProposal *ClangCompletionAssistProcessor::startCompletionHelper()
 {
     ClangCompletionContextAnalyzer analyzer(m_interface.data(), m_interface->languageFeatures());
@@ -323,6 +334,8 @@ IAssistProposal *ClangCompletionAssistProcessor::startCompletionHelper()
     }
     case ClangCompletionContextAnalyzer::PassThroughToLibClangAfterLeftParen: {
         m_sentRequestType = FunctionHintCompletion;
+        if (lastPrecedingNonWhitespaceChar(m_interface.data()) == ',')
+            m_fallbackToNormalCompletion = false;
         m_requestSent = sendCompletionRequest(analyzer.positionForClang(), QByteArray(),
                                               analyzer.functionNameStart());
         break;