clangbackend: Fix lexicographical sorting of completions

Utf8String has a weird operator<, so we did not get the expected results
from our string comparisons.

Task-number: QTCREATORBUG-6242
Change-Id: I0e94dc42d6e04ab833efcce41463b7024455b6d8
Reviewed-by: Cristian Adam <cristian.adam@qt.io>

src/tools/clangbackend/source/codecompletionsextractor.cpp

@@ -146,8 +146,14 @@ static void sortCodeCompletions(CodeCompletions &codeCompletions)
         if (first.requiredFixIts.empty() != second.requiredFixIts.empty())
             return first.requiredFixIts.empty() > second.requiredFixIts.empty();
 
-        return std::tie(first.priority, first.text, first.completionKind)
+        if (first.priority != second.priority)
-                < std::tie(second.priority, second.text, second.completionKind);
+            return first.priority < second.priority;
+
+        const int textCmp = first.text.toString().compare(second.text);
+        if (textCmp != 0)
+            return textCmp < 0;
+
+        return first.completionKind < second.completionKind;
     };
 
     // Keep the order for the items with the same priority and name.

tests/unit/unittest/codecompleter-test.cpp

@@ -647,6 +647,26 @@ TEST_F(CodeCompleterSlowTest, FunctionOverloadsWithoutDotOrArrowOrder)
     ASSERT_THAT(abs(firstIndex - secondIndex), 1);
 }
 
+TEST_F(CodeCompleterSlowTest, LexicographicalSorting)
+{
+    auto myCompleter = setupCompleter(completionsOrder);
+    const ClangBackEnd::CodeCompletions completions = myCompleter.complete(40, 18);
+
+    const int funcAIndex = Utils::indexOf(completions, [](const CodeCompletion &codeCompletion) {
+        return codeCompletion.text == "memberFuncAAA";
+    });
+    const int funcBIndex = Utils::indexOf(completions, [](const CodeCompletion &codeCompletion) {
+        return codeCompletion.text == "memberFuncBB";
+    });
+    const int funcCIndex = Utils::indexOf(completions, [](const CodeCompletion &codeCompletion) {
+        return codeCompletion.text == "memberFuncC";
+    });
+
+    ASSERT_NE(funcAIndex, -1);
+    ASSERT_EQ(funcBIndex, funcAIndex + 1);
+    ASSERT_EQ(funcCIndex, funcAIndex + 2);
+}
+
 ClangBackEnd::CodeCompleter CodeCompleter::setupCompleter(
         const ClangBackEnd::FileContainer &fileContainer)
 {

tests/unit/unittest/data/completions_order.cpp

@@ -26,3 +26,16 @@ void testPriorities() {
     DifferentPriorities d;
     d.
 }
+
+class LexicographicalSorting
+{
+public:
+    void memberFuncBB();
+    void memberFuncC();
+    void memberFuncAAA();
+};
+
+void testLexicographicalSorting() {
+    LexicographicalSorting ls;
+    ls.memberFunc
+}