Fix some tautological std::type_info (in-)equality comparisons

...which could never succeed.

I became aware of this when Clang 15 trunk -std=c++2b, implementing
<http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2021/p1328r1.html> "Making
std::type_info::operator== constexpr", pointed at two of the broken comparisons
with

> sw/source/uibase/app/docsh2.cxx:478:25: error: code will never be executed [-Werror,-Wunreachable-code]
>                         pTmpFrame->GetFrame().Appear();
>                         ^~~~~~~~~
> sw/source/uibase/app/docsh2.cxx:475:33: error: code will never be executed [-Werror,-Wunreachable-code]
>                         bOnly = false;
>                                 ^~~~~

(It didn't emit warnings pointing at any of the other broken comparisons,
though.)

All of these broken comparisons were regressions introduced with
89d39bc100aabf5dccbe77c0b5c0c85736e85b39 "tdf#94559: 4th step to remove
rtti.hxx", replacing uses of the IS_TYPE macro (from include/tools/rtti.hxx,
meanwhile removed with d64e535fe9a00b671cf1be3eb5632c0d5f4b8bea "Remove unused
rtti.hxx").

I now added loplugin:typeidcomparison to also find the other broken comparisons
introduced by that commit.  (The remaining cases where that commit replaced uses
of TYPE_INFO with typeid comparisons were correct and/or have meanwhile been
replaced with code not using typeid, see
553ee72041d6f66e26156eb1ad0d9e3c13457f7a "simplify some use of typeid" and
d656da9bc4f2df0bb99c65a288847e3fdd43a37c "~SwModify: do not silently tolerate
clients registered past death".)

The original IS_TYPE macro made sure not to dereference null pointers,

> #define IS_TYPE(T,pObj) \
>         ( pObj && (pObj)->Type() == TYPE(T) )

I don't know if any of the pointers now dereferenced in those typeid expressions
can legitimately be null.  But to be on the safe side, I replicated that check
in the newly introduced isType (sw/inc/istype.hxx).

(It is interesting to note that none of the static analysis that we routinely
employ seems to have noticed these broken comparisons.)

Change-Id: I65baffdd27bac1abf744283ff98c2dc864fa63b4
Reviewed-on: https://gerrit.libreoffice.org/c/core/+/129865
Tested-by: Jenkins
Reviewed-by: Stephan Bergmann <sbergman@redhat.com>

compilerplugins/clang/test/typeidcomparison.cxx

@@ -0,0 +1,41 @@
+/* -*- 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 <typeinfo>
+
+struct Base
+{
+    virtual ~Base();
+};
+
+struct Derived : Base
+{
+};
+
+void good(Base* p)
+{
+    (void)(typeid(*p) == typeid(Derived));
+    (void)(typeid(Derived) == typeid(*p));
+    (void)(typeid(*p) != typeid(Derived));
+    (void)(typeid(Derived) != typeid(*p));
+}
+
+void bad(Base* p)
+{
+    // expected-error@+1 {{comparison of type info of mixed pointer and non-pointer types 'Base *' and 'Derived' can never succeed [loplugin:typeidcomparison]}}
+    (void)(typeid(p) == typeid(Derived));
+    // expected-error@+1 {{comparison of type info of mixed pointer and non-pointer types 'Derived' and 'Base *' can never succeed [loplugin:typeidcomparison]}}
+    (void)(typeid(Derived) == typeid(p));
+    // expected-error@+1 {{comparison of type info of mixed pointer and non-pointer types 'Base *' and 'Derived' can never succeed [loplugin:typeidcomparison]}}
+    (void)(typeid(p) != typeid(Derived));
+    // expected-error@+1 {{comparison of type info of mixed pointer and non-pointer types 'Derived' and 'Base *' can never succeed [loplugin:typeidcomparison]}}
+    (void)(typeid(Derived) != typeid(p));
+}
+
+/* vim:set shiftwidth=4 softtabstop=4 expandtab cinoptions=b1,g0,N-s cinkeys+=0=break: */

compilerplugins/clang/typeidcomparison.cxx

@@ -0,0 +1,90 @@
+/* -*- 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/.
+ */
+
+// Find (in-)equality comparisons between typeid expressions that can never succeed.  For now, just
+// detects cases where the two involved types are structurally different, one a pointer type and the
+// other a non-pointer type.
+
+#ifndef LO_CLANG_SHARED_PLUGINS
+
+#include "plugin.hxx"
+
+namespace
+{
+class TypeidComparison final : public loplugin::FilteringPlugin<TypeidComparison>
+{
+public:
+    explicit TypeidComparison(loplugin::InstantiationData const& data)
+        : FilteringPlugin(data)
+    {
+    }
+
+    // For CXXRewrittenBinaryOperator `typeid(...) != typeid(...)`:
+    bool shouldVisitImplicitCode() const { return true; }
+
+    bool preRun() override { return compiler.getLangOpts().CPlusPlus; }
+
+    void run() override
+    {
+        if (preRun())
+        {
+            TraverseDecl(compiler.getASTContext().getTranslationUnitDecl());
+        }
+    }
+
+    bool VisitCXXOperatorCallExpr(CXXOperatorCallExpr const* expr)
+    {
+        if (ignoreLocation(expr))
+        {
+            return true;
+        }
+        auto const op = expr->getOperator();
+        if (op != OO_EqualEqual && op != OO_ExclaimEqual)
+        {
+            return true;
+        }
+        assert(expr->getNumArgs() == 2);
+        auto const e1 = dyn_cast<CXXTypeidExpr>(expr->getArg(0)->IgnoreParenImpCasts());
+        if (e1 == nullptr)
+        {
+            return true;
+        }
+        auto const e2 = dyn_cast<CXXTypeidExpr>(expr->getArg(1)->IgnoreParenImpCasts());
+        if (e2 == nullptr)
+        {
+            return true;
+        }
+        auto const t1 = getOperandType(e1);
+        auto const t2 = getOperandType(e2);
+        if (t1->isPointerType() == t2->isPointerType())
+        {
+            return true;
+        }
+        report(DiagnosticsEngine::Warning,
+               "comparison of type info of mixed pointer and non-pointer types %0 and %1 can never "
+               "succeed",
+               expr->getExprLoc())
+            << t1 << t2 << expr->getSourceRange();
+        return true;
+    }
+
+private:
+    QualType getOperandType(CXXTypeidExpr const* expr)
+    {
+        return expr->isTypeOperand() ? expr->getTypeOperand(compiler.getASTContext())
+                                     : expr->getExprOperand()->getType();
+    }
+};
+
+static loplugin::Plugin::Registration<TypeidComparison> typeidcomparison("typeidcomparison");
+}
+
+#endif
+
+/* vim:set shiftwidth=4 softtabstop=4 expandtab cinoptions=b1,g0,N-s cinkeys+=0=break: */

solenv/CompilerTest_compilerplugins_clang.mk

@@ -95,6 +95,7 @@ $(eval $(call gb_CompilerTest_add_exception_objects,compilerplugins_clang, \
     compilerplugins/clang/test/stringview \
     compilerplugins/clang/test/stringviewparam \
     compilerplugins/clang/test/typedefparam \
+    compilerplugins/clang/test/typeidcomparison \
     compilerplugins/clang/test/unnecessarycatchthrow \
     compilerplugins/clang/test/unnecessaryoverride \
     compilerplugins/clang/test/unnecessaryoverride-dtor \

sw/inc/istype.hxx

@@ -0,0 +1,21 @@
+/* -*- 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/.
+ */
+
+#pragma once
+
+#include <sal/config.h>
+
+#include <typeinfo>
+
+template <typename T1, typename T2> bool isType(T2* p)
+{
+    return p != nullptr && typeid(*p) == typeid(T1);
+}
+
+/* vim:set shiftwidth=4 softtabstop=4 expandtab cinoptions=b1,g0,N-s cinkeys+=0=break: */

sw/source/core/access/accmap.cxx

@@ -42,6 +42,7 @@
 #include "acccell.hxx"
 #include "acctable.hxx"
 #include <fesh.hxx>
+#include <istype.hxx>
 #include <rootfrm.hxx>
 #include <txtfrm.hxx>
 #include <hffrm.hxx>
@@ -198,7 +199,7 @@ void SwDrawModellListener_Impl::Notify( SfxBroadcaster& /*rBC*/,
     if (pSdrHint->GetObject() &&
            ( dynamic_cast< const SwFlyDrawObj* >(pSdrHint->GetObject()) !=  nullptr ||
               dynamic_cast< const SwVirtFlyDrawObj* >(pSdrHint->GetObject()) !=  nullptr ||
-             typeid(SdrObject) == typeid(pSdrHint->GetObject()) ) )
+             isType<SdrObject>(pSdrHint->GetObject()) ) )
     {
         return;
     }

sw/source/core/doc/doclay.cxx

@@ -30,6 +30,7 @@
 #include <osl/diagnose.h>
 #include <svx/svdouno.hxx>
 #include <editeng/frmdiritem.hxx>
+#include <istype.hxx>
 #include <swmodule.hxx>
 #include <modcfg.hxx>
 #include <com/sun/star/beans/XPropertySet.hpp>
@@ -139,7 +140,7 @@ SdrObject* SwDoc::CloneSdrObj( const SdrObject& rObj, bool bMoveWithinDoc,
     SdrLayerID nLayerIdForClone = rObj.GetLayer();
     if ( dynamic_cast<const SwFlyDrawObj*>( pObj) ==  nullptr &&
          dynamic_cast<const SwVirtFlyDrawObj*>( pObj) ==  nullptr &&
-         typeid(SdrObject) != typeid(pObj) )
+         !isType<SdrObject>(pObj) )
     {
         if ( getIDocumentDrawModelAccess().IsVisibleLayerId( nLayerIdForClone ) )
         {

sw/source/uibase/app/docsh2.cxx

@@ -66,6 +66,7 @@
 #include <basic/basmgr.hxx>
 #include <comphelper/classids.hxx>
 #include <fmtcol.hxx>
+#include <istype.hxx>
 #include <view.hxx>
 #include <docsh.hxx>
 #include <docary.hxx>
@@ -467,13 +468,13 @@ void SwDocShell::Execute(SfxRequest& rReq)
                 SfxViewFrame *pTmpFrame = SfxViewFrame::GetFirst(this);
                 SfxViewShell* pViewShell = SfxViewShell::Current();
                 SwView* pCurrView = dynamic_cast< SwView *> ( pViewShell );
-                bool bCurrent = typeid(SwPagePreview) == typeid( pViewShell );
+                bool bCurrent = isType<SwPagePreview>( pViewShell );
 
                 while( pTmpFrame )    // search Preview
                 {
-                    if( typeid(SwView) == typeid( pTmpFrame->GetViewShell()) )
+                    if( isType<SwView>( pTmpFrame->GetViewShell()) )
                         bOnly = false;
-                    else if( typeid(SwPagePreview) == typeid( pTmpFrame->GetViewShell()))
+                    else if( isType<SwPagePreview>( pTmpFrame->GetViewShell()))
                     {
                         pTmpFrame->GetFrame().Appear();
                         bFound = true;