loplugin:cow_wrapper

check the classes that use o3tl::cow_wrapper so that they
don't unnecessarity trigger copies

Change-Id: I545e627598217f3e61ba2c384adb8d4f8b404829
Reviewed-on: https://gerrit.libreoffice.org/c/core/+/122030
Tested-by: Jenkins
Reviewed-by: Noel Grandin <noel.grandin@collabora.co.uk>

2 files changed, 121 insertions, 0 deletions

diff --git a/compilerplugins/clang/cow_wrapper.cxx b/compilerplugins/clang/cow_wrapper.cxx
new file mode 100644
index 000000000000..4c04674f65c1
--- /dev/null
+++ b/compilerplugins/clang/cow_wrapper.cxx
@@ -0,0 +1,88 @@
+/* -*- Mode: C++; tab-width: 4; indent-tabs-mode: nil; c-basic-offset: 4 -*- */
+/*
+ * This file is part of the LibreOffice project.
+ *
+ * Based on LLVM/Clang.
+ *
+ * This file is distributed under the University of Illinois Open Source
+ * License. See LICENSE.TXT for details.
+ *
+ */
+#ifndef LO_CLANG_SHARED_PLUGINS
+
+#include <cassert>
+#include <string>
+#include <iostream>
+#include <fstream>
+#include <set>
+#include <unordered_set>
+#include "plugin.hxx"
+#include "check.hxx"
+
+/*
+Look for places where we are using cow_wrapper, but we are calling a const method on the impl object
+with a non-const pointer, which means we will unnnecessarily trigger a copy.
+*/
+
+namespace
+{
+class Cow_Wrapper : public loplugin::FilteringPlugin<Cow_Wrapper>
+{
+public:
+    explicit Cow_Wrapper(loplugin::InstantiationData const& data)
+        : FilteringPlugin(data)
+    {
+    }
+
+    virtual bool preRun() override { return true; }
+
+    virtual void run() override
+    {
+        if (preRun())
+            TraverseDecl(compiler.getASTContext().getTranslationUnitDecl());
+    }
+
+    bool VisitCXXMemberCallExpr(const CXXMemberCallExpr*);
+};
+
+bool Cow_Wrapper::VisitCXXMemberCallExpr(const CXXMemberCallExpr* memberCallExpr)
+{
+    if (ignoreLocation(memberCallExpr))
+        return true;
+    auto methodDecl = memberCallExpr->getMethodDecl();
+    if (!methodDecl || !methodDecl->isConst())
+        return true;
+
+    auto operatorCallExpr = dyn_cast<CXXOperatorCallExpr>(
+        compat::IgnoreImplicit(memberCallExpr->getImplicitObjectArgument()));
+    if (!operatorCallExpr)
+        return true;
+    if (operatorCallExpr->getOperator() != OO_Arrow)
+        return true;
+    auto arrowMethodDecl = dyn_cast_or_null<CXXMethodDecl>(operatorCallExpr->getDirectCallee());
+    if (!arrowMethodDecl)
+        return true;
+    if (arrowMethodDecl->isConst())
+        return true;
+    auto dc = loplugin::DeclCheck(arrowMethodDecl->getParent())
+                  .Class("cow_wrapper")
+                  .Namespace("o3tl")
+                  .GlobalNamespace();
+    if (!dc)
+        return true;
+
+    report(DiagnosticsEngine::Warning,
+           "calling const method on o3tl::cow_wrapper impl class via non-const pointer, rather use "
+           "std::as_const to prevent triggering an unnecessary copy",
+           compat::getBeginLoc(memberCallExpr))
+        << memberCallExpr->getSourceRange();
+    return true;
+}
+
+loplugin::Plugin::Registration<Cow_Wrapper> cow_wrapper("cow_wrapper", true);
+
+} // namespace
+
+#endif // LO_CLANG_SHARED_PLUGINS
+
+/* vim:set shiftwidth=4 softtabstop=4 expandtab: */
diff --git a/compilerplugins/clang/test/cow_wrapper.cxx b/compilerplugins/clang/test/cow_wrapper.cxx
new file mode 100644
index 000000000000..705a4052ef66
--- /dev/null
+++ b/compilerplugins/clang/test/cow_wrapper.cxx
@@ -0,0 +1,33 @@
+/* -*- 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 "config_clang.h"
+#include "o3tl/cow_wrapper.hxx"
+
+struct ImplBitmapPalette
+{
+    void foo() const;
+};
+
+struct BitmapPalette
+{
+    void foo1()
+    {
+        // expected-error@+1 {{calling const method on o3tl::cow_wrapper impl class via non-const pointer, rather use std::as_const to prevent triggering an unnecessary copy [loplugin:cow_wrapper]}}
+        mpImpl->foo();
+    }
+    void foo2() const
+    {
+        // no error expected
+        mpImpl->foo();
+    }
+    o3tl::cow_wrapper<ImplBitmapPalette> mpImpl;
+};
+
+/* vim:set shiftwidth=4 softtabstop=4 expandtab cinoptions=b1,g0,N-s cinkeys+=0=break: */