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>

4 files changed, 29 insertions, 5 deletions

diff --git a/sw/inc/istype.hxx b/sw/inc/istype.hxx
new file mode 100644
index 000000000000..ec7dac428d61
--- /dev/null
+++ b/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: */
diff --git a/sw/source/core/access/accmap.cxx b/sw/source/core/access/accmap.cxx
index 7704b16f3e52..e8a106aa5892 100644
--- a/sw/source/core/access/accmap.cxx
+++ b/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;
     }
diff --git a/sw/source/core/doc/doclay.cxx b/sw/source/core/doc/doclay.cxx
index 7d3ad61e46b4..34bf4fabbcac 100644
--- a/sw/source/core/doc/doclay.cxx
+++ b/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 ) )
         {
diff --git a/sw/source/uibase/app/docsh2.cxx b/sw/source/uibase/app/docsh2.cxx
index 9e606f0b4095..208848bf9a05 100644
--- a/sw/source/uibase/app/docsh2.cxx
+++ b/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;