new (but unused) refassign loplugin

which I wrote to check if there were any other cases where assigning to
a ref local var looks dodgy, after my fixes in
0b113d6ebb, but I didn't find anything, so
just leave this one in store

Change-Id: Ib820924c5e8aa85206730afeb06972ef48231ec5

compilerplugins/clang/store/refassign.cxx

@@ -0,0 +1,152 @@
+/* -*- Mode: C++; tab-width: 4; indent-tabs-mode: nil; c-basic-offset: 4 -*- */
+/*
+ * 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/.
+ */
+#ifndef LO_CLANG_SHARED_PLUGINS
+
+#include <cassert>
+#include <string>
+#include <iostream>
+#include <fstream>
+#include <set>
+
+#include <clang/AST/CXXInheritance.h>
+
+#include "check.hxx"
+#include "compat.hxx"
+#include "plugin.hxx"
+
+/**
+ * Look for a mistake I made (a lot) at one point where we assign a reference to a reference var, which
+ * does not do at all what I thought.
+ */
+
+namespace
+{
+class RefAssign : public loplugin::FilteringPlugin<RefAssign>
+{
+public:
+    explicit RefAssign(loplugin::InstantiationData const& data)
+        : FilteringPlugin(data)
+    {
+    }
+
+    virtual bool preRun() override
+    {
+        StringRef fn(handler.getMainFileName());
+        if (loplugin::isSamePathname(fn, SRCDIR "/comphelper/source/misc/syntaxhighlight.cxx"))
+            return false;
+        if (loplugin::isSamePathname(fn, SRCDIR "/svl/source/numbers/zformat.cxx"))
+            return false;
+        if (loplugin::isSamePathname(fn, SRCDIR "/tools/source/memtools/multisel.cxx"))
+            return false;
+        if (loplugin::isSamePathname(fn, SRCDIR "/tools/source/generic/point.cxx"))
+            return false;
+        if (loplugin::isSamePathname(fn, SRCDIR "/vcl/source/control/edit.cxx"))
+            return false;
+        if (loplugin::isSamePathname(fn, SRCDIR "/vcl/source/control/fmtfield.cxx"))
+            return false;
+        if (loplugin::isSamePathname(fn, SRCDIR "/vcl/source/control/field.cxx"))
+            return false;
+        if (loplugin::isSamePathname(fn, SRCDIR "/vcl/source/control/field2.cxx"))
+            return false;
+        if (loplugin::isSamePathname(fn, SRCDIR "/vcl/source/edit/textview.cxx"))
+            return false;
+        if (loplugin::isSamePathname(fn, SRCDIR "/vcl/source/edit/vclmedit.cxx"))
+            return false;
+        if (loplugin::isSamePathname(fn, SRCDIR "/editeng/source/editeng/editdoc.cxx"))
+            return false;
+        if (loplugin::isSamePathname(fn, SRCDIR "/editeng/source/editeng/impedit2.cxx"))
+            return false;
+        if (loplugin::isSamePathname(fn, SRCDIR "/svx/source/dialog/svxruler.cxx"))
+            return false;
+        if (loplugin::isSamePathname(fn, SRCDIR "/sw/source/uibase/ribbar/inputwin.cxx"))
+            return false;
+        if (loplugin::isSamePathname(fn, SRCDIR "/sw/source/core/text/txtftn.cxx"))
+            return false;
+
+        return true;
+    }
+
+    virtual void run() override
+    {
+        if (preRun())
+            TraverseDecl(compiler.getASTContext().getTranslationUnitDecl());
+    }
+
+    bool VisitBinaryOperator(BinaryOperator const*);
+    // causes crashes in CallExpr::getReturnType
+    bool TraverseFunctionTemplateDecl(FunctionTemplateDecl*) { return true; }
+    bool TraverseClassTemplateDecl(ClassTemplateDecl*) { return true; }
+
+private:
+    clang::QualType ExtractType(Expr const*);
+};
+
+bool RefAssign::VisitBinaryOperator(BinaryOperator const* binaryOp)
+{
+    if (ignoreLocation(binaryOp))
+        return true;
+    if (binaryOp->getOpcode() != BO_Assign)
+        return true;
+
+    // ignore assigning to/from an element of a collection
+    if (isa<CXXOperatorCallExpr>(binaryOp->getLHS()->IgnoreParenImpCasts()))
+        return true;
+    if (isa<CXXOperatorCallExpr>(binaryOp->getRHS()->IgnoreParenImpCasts()))
+        return true;
+
+    // if we are assigning to a parameter we probably mean it
+    if (auto declRefExpr = dyn_cast<DeclRefExpr>(binaryOp->getLHS()->IgnoreParenImpCasts()))
+        if (declRefExpr->getDecl() && isa<ParmVarDecl>(declRefExpr->getDecl()))
+            return true;
+
+    if (auto callExpr = dyn_cast<CallExpr>(binaryOp->getRHS()->IgnoreParenImpCasts()))
+        if (auto functionDecl = dyn_cast_or_null<FunctionDecl>(callExpr->getCalleeDecl()))
+            if (functionDecl->getIdentifier()
+                && (functionDecl->getName() == "min" || functionDecl->getName() == "max"))
+                return true;
+
+    auto lhsType = ExtractType(binaryOp->getLHS());
+    auto rhsType = ExtractType(binaryOp->getRHS());
+    if (!loplugin::TypeCheck(lhsType).LvalueReference())
+        return true;
+    if (!loplugin::TypeCheck(rhsType).LvalueReference())
+        return true;
+    binaryOp->dump();
+    report(DiagnosticsEngine::Warning,
+           "assigning a %0 to a var of type %1 probably does not do what you think",
+           compat::getBeginLoc(binaryOp))
+        << rhsType << lhsType << binaryOp->getSourceRange();
+    return true;
+}
+
+clang::QualType RefAssign::ExtractType(Expr const* expr)
+{
+    expr = expr->IgnoreParenImpCasts();
+    if (auto declReflExpr = dyn_cast<DeclRefExpr>(expr))
+    {
+        if (auto varDecl = dyn_cast<VarDecl>(declReflExpr->getDecl()))
+            return varDecl->getType();
+    }
+    else if (auto callExpr = dyn_cast<CallExpr>(expr))
+    {
+        if (callExpr->isTypeDependent())
+            return {};
+        //        callExpr->dump();
+        return callExpr->getCallReturnType(compiler.getASTContext());
+    }
+    return expr->getType();
+}
+
+loplugin::Plugin::Registration<RefAssign> refassign("refassign");
+
+} // namespace
+
+#endif // LO_CLANG_SHARED_PLUGINS
+
+/* vim:set shiftwidth=4 softtabstop=4 expandtab: */

compilerplugins/clang/test/refassign.cxx

@@ -0,0 +1,31 @@
+/* -*- 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 <sal/config.h>
+#include <vector>
+
+int& f1();
+int& f2();
+
+void test1()
+{
+    int& v1 = f1();
+    v1 = f2(); // expected-error {{assigning a 'int &' to a var of type 'int &' probably does not do what you think [loplugin:refassign]}}
+    f1()
+        = f2(); // expected-error {{assigning a 'int &' to a var of type 'int &' probably does not do what you think [loplugin:refassign]}}
+
+    // no warning expected
+    int x = 1;
+    x = f1();
+    std::vector<int> v;
+    v[0] = f1();
+    v1 = std::min(1, 2);
+};
+
+/* vim:set shiftwidth=4 softtabstop=4 expandtab cinoptions=b1,g0,N-s cinkeys+=0=break: */