new loplugin: constmethod

parked in store/ for now, because, as I worked my way up the layers of
modules, the higher I got, the more false+ I got when trying to only
make changes that preserved logical-constness.

Change-Id: I4acd2c4416775f7c6a3d91eb0bce048630ccaff5

compilerplugins/clang/test/constmethod.cxx

+/* -*- Mode: C++; tab-width: 4; indent-tabs-mode: nil; c-basic-offset: 4; fill-column: 100 -*- */
+/*
+ * This file is part of the LibreOffice project.
+ *
+ * This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/.
+ */
+
+#include <memory>
+#include <vcl/vclptr.hxx>
+
+class OutputDevice;
+
+struct Class1
+{
+    struct Impl {
+        void foo_notconst();
+        void foo_const() const;
+        int & foo_both();
+        int const & foo_both() const;
+    };
+    std::unique_ptr<Impl> pImpl;
+    int* m_pint;
+    VclPtr<OutputDevice> m_pvcl;
+
+    void foo1() {
+        pImpl->foo_notconst();
+    }
+    void foo2() { // expected-error {{this method can be const [loplugin:constmethod]}}
+        pImpl->foo_const();
+    }
+    // TODO this should trigger a warning, but doesn't
+    void foo3() {
+        pImpl->foo_both();
+    }
+    Impl* foo4() {
+        return pImpl.get(); // no warning expected
+    }
+    int* foo5() {
+        return m_pint; // no warning expected
+    }
+    OutputDevice* foo6() {
+        return m_pvcl; // no warning expected
+    }
+};