CplusPlus: Fix minimal name construction

... when using declarations are involved.

Fixes: QTCREATORBUG-14524
Change-Id: I0c391b88628f40973b6f601e60c64263f62a88a0
Reviewed-by: Christian Stenger <christian.stenger@qt.io>

src/libs/cplusplus/LookupContext.cpp

@@ -216,7 +216,14 @@ LookupContext &LookupContext::operator=(const LookupContext &other)
 QList<const Name *> LookupContext::fullyQualifiedName(Symbol *symbol, InlineNamespacePolicy policy)
 {
     QList<const Name *> qualifiedName = path(symbol->enclosingScope(), policy);
-    addNames(symbol->name(), &qualifiedName, /*add all names*/ true);
+    QList<const Name *> symbolNames;
+    addNames(symbol->name(), &symbolNames, /*add all names*/ true);
+    if (const UsingDeclaration * const usingDecl = symbol->asUsingDeclaration()) {
+        if (!symbolNames.isEmpty())
+            qualifiedName << symbolNames.last();
+    } else {
+        qualifiedName << symbolNames;
+    }
     return qualifiedName;
 }
 
@@ -811,7 +818,7 @@ void CreateBindings::lookupInScope(const Name *name, Scope *scope,
                 continue; // skip using namespace directives
             else if (! id->match(s->identifier()))
                 continue;
-            else if (s->name() && s->name()->isQualifiedNameId())
+            else if (s->name() && s->name()->isQualifiedNameId() && !s->asUsingDeclaration())
                 continue; // skip qualified ids.
 
             if (Q_UNLIKELY(debug)) {

src/plugins/cppeditor/cppeditorplugin.h

@@ -155,6 +155,7 @@ private slots:
     void test_quickfix_InsertDefFromDecl_erroneousStatementAtEndOfFile();
     void test_quickfix_InsertDefFromDecl_rvalueReference();
     void test_quickfix_InsertDefFromDecl_functionTryBlock();
+    void test_quickfix_InsertDefFromDecl_usingDecl();
     void test_quickfix_InsertDefFromDecl_findImplementationFile();
     void test_quickfix_InsertDefFromDecl_unicodeIdentifier();
     void test_quickfix_InsertDefFromDecl_templateClass();

src/plugins/cppeditor/cppquickfix_test.cpp

@@ -4322,6 +4322,41 @@ void Foo::otherFunc()
     QuickFixOperationTest(testDocuments, &factory);
 }
 
+void CppEditorPlugin::test_quickfix_InsertDefFromDecl_usingDecl()
+{
+    QList<QuickFixTestDocument::Ptr> testDocuments;
+
+    QByteArray original;
+    QByteArray expected;
+
+    // Header File
+    original = R"(
+namespace N { struct S; }
+using N::S;
+
+void @func(const S &s);
+)";
+    expected = original;
+    testDocuments << QuickFixTestDocument::create("file.h", original, expected);
+
+    // Source File
+    original = R"(
+#include "file.h"
+)";
+    expected = R"(
+#include "file.h"
+
+void func(const S &s)
+{
+
+}
+)";
+    testDocuments << QuickFixTestDocument::create("file.cpp", original, expected);
+
+    InsertDefFromDecl factory;
+    QuickFixOperationTest(testDocuments, &factory);
+}
+
 /// Find right implementation file. (QTCREATORBUG-10728)
 void CppEditorPlugin::test_quickfix_InsertDefFromDecl_findImplementationFile()
 {