Clang: Fallback to global completion if function call completion fails

We can not offer proper constructor completion with libclang <= 3.6, so
fall back to normal/global completion.

Change-Id: I90bb8d981ae20ed4c228f829ad4267221b92f8a1
Reviewed-by: Marco Bubke <marco.bubke@theqtcompany.com>

src/plugins/clangcodemodel/test/clang_tests_database.qrc

@@ -20,5 +20,6 @@
         <file>exampleIncludeDir/otherFile.h</file>
         <file>exampleIncludeDir/mylib/mylib.h</file>
         <file>globalCompletion.cpp</file>
+        <file>constructorCompletion.cpp</file>
     </qresource>
 </RCC>

src/plugins/clangcodemodel/test/clangcodecompletion_test.cpp

@@ -874,6 +874,15 @@ void ClangCodeCompletionTest::testCompleteFunctions()
     QVERIFY(hasItem(t.proposal, "TType<QString> f(bool)"));
 }
 
+void ClangCodeCompletionTest::testCompleteConstructorAndFallbackToGlobalCompletion()
+{
+    ProjectLessCompletionTest t("constructorCompletion.cpp");
+
+    QVERIFY(hasItem(t.proposal, "globalVariable"));
+    QVERIFY(hasItem(t.proposal, "GlobalClassWithCustomConstructor"));
+    QVERIFY(!hasSnippet(t.proposal, "class"));
+}
+
 void ClangCodeCompletionTest::testProjectDependentCompletion()
 {
     const TestDocument testDocument("completionWithProject.cpp");

src/plugins/clangcodemodel/test/clangcodecompletion_test.h

@@ -57,6 +57,7 @@ private slots:
     void testCompleteGlobals();
     void testCompleteMembers();
     void testCompleteFunctions();
+    void testCompleteConstructorAndFallbackToGlobalCompletion();
 
     void testProjectDependentCompletion();
     void testChangingProjectDependentCompletion();

src/plugins/clangcodemodel/test/constructorCompletion.cpp

@@ -0,0 +1,9 @@
+int globalVariable;
+
+struct GlobalClassWithCustomConstructor {
+    GlobalClassWithCustomConstructor(int) {}
+};
+
+void f() {
+    GlobalClassWithCustomConstructor foo( /* COMPLETE HERE */
+}