CppEditor: Fix "insert def from decl" for template return types

Fixes: QTCREATORBUG-26397
Change-Id: Ia215f2c2b5da708b0fd7c894987683b305f4ccec
Reviewed-by: Christian Stenger <christian.stenger@qt.io>

src/libs/3rdparty/cplusplus/Control.cpp

@@ -844,3 +844,15 @@ void Control::addSymbol(Symbol *symbol)
 {
     d->symbols.push_back(symbol);
 }
+
+const Name *Control::toName(const QList<const Name *> &names)
+{
+    const Name *n = nullptr;
+    for (int i = names.size() - 1; i >= 0; --i) {
+        if (! n)
+            n = names.at(i);
+        else
+            n = qualifiedNameId(names.at(i), n);
+    }
+    return n;
+}

src/libs/3rdparty/cplusplus/Control.h

@@ -218,6 +218,8 @@ public:
     bool hasSymbol(Symbol *symbol) const;
     void addSymbol(Symbol *symbol);
 
+    const Name *toName(const QList<const Name *> &names);
+
 private:
     class Data;
     friend class Data;

src/libs/cplusplus/CppRewriter.cpp

@@ -283,8 +283,21 @@ public:
                                                                         number->size()));
                 }
             }
-            temps.append(control()->templateNameId(identifier(name->identifier()), name->isSpecialization(),
-                                                   args.data(), args.size()));
+
+            const FullySpecifiedType ty = rewrite->env->apply(name->identifier(), rewrite);
+            const Name * const minName = ty->isNamedType() ? ty->asNamedType()->name() : name;
+            const TemplateNameId * const newTemplateNameId = control()->templateNameId(
+                        identifier(minName->identifier()), name->isSpecialization(), args.data(),
+                        args.size());
+            const QList<const Name *> names = disassembledName(minName);
+            if (names.size() == 1) {
+                temps.append(newTemplateNameId);
+            } else {
+                const Name * const newBaseName = control()->toName(names.mid(0, names.size() - 1));
+                const Name * const fullName = control()->qualifiedNameId(newBaseName,
+                                                                         newTemplateNameId);
+                temps.append(fullName);
+            }
         }
 
         void visit(const DestructorNameId *name) override
@@ -317,6 +330,36 @@ public: // attributes
     SubstitutionEnvironment *env;
     RewriteType rewriteType;
     RewriteName rewriteName;
+
+private:
+    static QList<const Name *> disassembledName(const Name *name)
+    {
+        class NameDisassembler : public NameVisitor
+        {
+        public:
+            QList<const Name *> names() const { return m_names; }
+
+            void visit(const AnonymousNameId *n) override { m_names << n; }
+            virtual void visit(const Identifier *n) override { m_names << n; }
+            virtual void visit(const TemplateNameId *n) override { m_names << n; }
+            virtual void visit(const DestructorNameId *n) override { m_names << n; }
+            virtual void visit(const OperatorNameId *n) override { m_names << n; }
+            virtual void visit(const ConversionNameId *n) override { m_names << n; }
+            virtual void visit(const SelectorNameId *n) override { m_names << n; }
+            virtual void visit(const QualifiedNameId *n) override
+            {
+                if (n->base())
+                    n->base()->accept(this);
+                n->name()->accept(this);
+            }
+        private:
+            QList<const Name *> m_names;
+        };
+
+        NameDisassembler nd;
+        nd.accept(name);
+        return nd.names();
+    }
 };
 
 SubstitutionEnvironment::SubstitutionEnvironment()

src/libs/cplusplus/LookupContext.cpp

@@ -241,19 +241,6 @@ static bool symbolIdentical(Symbol *s1, Symbol *s2)
     return QByteArray(s1->fileName()) == QByteArray(s2->fileName());
 }
 
-static const Name *toName(const QList<const Name *> &names, Control *control)
-{
-    const Name *n = nullptr;
-    for (int i = names.size() - 1; i >= 0; --i) {
-        if (! n)
-            n = names.at(i);
-        else
-            n = control->qualifiedNameId(names.at(i), n);
-    }
-
-    return n;
-}
-
 static bool isInlineNamespace(ClassOrNamespace *con, const Name *name)
 {
     const QList<LookupItem> items = con->find(name);
@@ -282,12 +269,12 @@ const Name *LookupContext::minimalName(Symbol *symbol, ClassOrNamespace *target,
             // eliminate inline namespaces
             QList<const Name *> minimal = names;
             for (int i = minimal.size() - 2; i >= 0; --i) {
-                const Name *candidate = toName(minimal.mid(0, i + 1), control);
+                const Name *candidate = control->toName(minimal.mid(0, i + 1));
                 if (isInlineNamespace(target, candidate))
                     minimal.removeAt(i);
             }
 
-            return toName(minimal, control);
+            return control->toName(minimal);
         }
 
         return nullptr;

src/plugins/cppeditor/cppquickfix_test.cpp

@@ -4707,6 +4707,43 @@ N::S N::foo(const S &s)
     QuickFixOperationTest(testDocuments, &factory);
 }
 
+void QuickfixTest::testInsertDefFromDeclAliasTemplateAsReturnType()
+{
+    QList<TestDocumentPtr> testDocuments;
+
+    QByteArray original;
+    QByteArray expected;
+
+    // Header File
+    original = R"(
+struct foo {
+    struct foo2 {
+        template <typename T> using MyType = T;
+        MyType<int> @bar();
+    };
+};
+)";
+    expected = original;
+    testDocuments << CppTestDocument::create("file.h", original, expected);
+
+    // Source File
+    original = R"(
+#include "file.h"
+)";
+    expected = R"(
+#include "file.h"
+
+foo::foo2::MyType<int> foo::foo2::bar()
+{
+
+}
+)";
+    testDocuments << CppTestDocument::create("file.cpp", original, expected);
+
+    InsertDefFromDecl factory;
+    QuickFixOperationTest(testDocuments, &factory);
+}
+
 void QuickfixTest::testInsertDefsFromDecls_data()
 {
     QTest::addColumn<QByteArrayList>("headers");

src/plugins/cppeditor/cppquickfix_test.h

@@ -155,6 +155,7 @@ private slots:
     void testInsertDefFromDeclTemplateFunction();
     void testInsertDefFromDeclNotTriggeredForFriendFunc();
     void testInsertDefFromDeclMinimalFunctionParameterType();
+    void testInsertDefFromDeclAliasTemplateAsReturnType();
     void testInsertDefsFromDecls_data();
     void testInsertDefsFromDecls();