[Bug c++/100796] New: [11 Regression] GCC does not honor #pragma diagnostic ignored when using the integrated preprocessor

[Bug c++/100796] New: [11 Regression] GCC does not honor #pragma diagnostic ignored when using the integrated preprocessor

[dangelog at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=100796

            Bug ID: 100796
           Summary: [11 Regression] GCC does not honor #pragma diagnostic
                    ignored when using the integrated preprocessor
           Product: gcc
           Version: unknown
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: dangelog at gmail dot com
  Target Milestone: ---

Hi,

When building the qtbase `dev` branch with GCC 11, a bunch of warnings are
generated even in the presence of a ignoring pragma. 

For a bit of context, in Qt there's a macro called Q_OBJECT that users can add
to their classes; this macro expands to a series of declarations, including a
couple of virtuals. These may raise -Wsuggest-override warnings, in user code,
so such warnings are suppressed via pragmas (as part of the Q_OBJECT macro
itself).

GCC 10 honors the pragmas and doesn't raise warnings, but GCC 11 doesn't honor
them, resulting in warnings like

    include/QtCore/../../../src/corelib/kernel/qtmetamacros.h:159:32: error:
‘virtual const QMetaObject* QTextObject::metaObject() const’ can be marked
override [-Werror=suggest-override]
      159 |     virtual const QMetaObject *metaObject() const; \
          |                                ^~~~~~~~~~
    include/QtGui/../../../src/gui/text/qtextobject.h:62:5: note: in expansion
of macro ‘Q_OBJECT’
       62 |     Q_OBJECT
          |     ^~~~~~~~
    include/QtCore/../../../src/corelib/kernel/qtmetamacros.h:160:19: error:
‘virtual void* QTextObject::qt_metacast(const char*)’ can be marked override
[-Werror=suggest-override]
      160 |     virtual void *qt_metacast(const char *); \
          |                   ^~~~~~~~~~~
    include/QtGui/../../../src/gui/text/qtextobject.h:62:5: note: in expansion
of macro ‘Q_OBJECT’
       62 |     Q_OBJECT
          |     ^~~~~~~~

And so on and so forth.

Now, the peculiarity of this bug is that if you disable the integrated
preprocessor via -no-integrated-cpp then everything works fine. Similarly, if
you take a preprocessed output and compile *that*, then no warnings are raised.
I therefore suspect a regression in the integrated preprocessor.

For this reason I'm actually unable to attach a testcase: a preprocessed output
 compiles just fine. Please advise as of what kind of test I could do / provide
to help you track this one down. 



If you wish to try and compile Qt yourself, then it's relatively easy: 

1) clone git://code.qt.io/qt/qtbase.git , checkout dev
2) get a very recent CMake 
3) mkdir build
4) (with GCC 11 in PATH, or force it via CC/CXX env) cmake -GNinja
-DCMAKE_BUILD_TYPE=Debug -DQT_BUILD_EXAMPLES_BY_DEFAULT=OFF
-DQT_BUILD_TESTS_BY_DEFAULT=OFF -DFEATURE_developer_build=ON ../path/to/qtbase
5) ninja


Upstream bug: https://bugreports.qt.io/browse/QTBUG-93360

[Bug c++/100796] [11 Regression] GCC does not honor #pragma diagnostic ignored when using the integrated preprocessor

[redi at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=100796

--- Comment #1 from Jonathan Wakely <redi at gcc dot gnu.org> ---
This is not a 11 Regression, since it's exactly the same as previous releases,
isn't it?

I think it's a dup of PR 53431

[Bug c++/100796] [11 Regression] GCC does not honor #pragma diagnostic ignored when using the integrated preprocessor

[dangelog at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=100796

--- Comment #2 from Giuseppe D'Angelo <dangelog at gmail dot com> ---
Well, GCC 8-9-10 don't have this problem at all for us. This appeared only when
upgrading to 11.

Anyways, I'm not sure if it's the same issue. PR 53431 seems to be about the
preprocessor itself ignoring the pragmas -- like raising -Wundef even under a
pragma. 

Here is not quite about the preprocessor (in fact, the not-honored pragma can
only be honored by the compiler, it's about -Wsuggest-override). The compiler
seems to ignore that pragma in _random_ places (it's very inconsistent; the
majority of code is not flagged, except for a few occurrences).

If I run the preprocessor manually, the pragma is still correctly present in
the preprocessed output. However: running the compiler over that preprocessed
output does NOT raise the warning. That leads to the fact that adding
-no-integrated-cpp is a successful workaround; this makes me think something
broke in there...?

[Bug c++/100796] [11 Regression] GCC does not honor #pragma diagnostic ignored when using the integrated preprocessor

[rguenth at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=100796

Richard Biener <rguenth at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Keywords|                            |diagnostic
            Version|unknown                     |11.1.1
   Target Milestone|---                         |11.2

[Bug c++/100796] [11 Regression] GCC does not honor #pragma diagnostic ignored when using the integrated preprocessor

[jason at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=100796

Jason Merrill <jason at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |jason at gcc dot gnu.org

--- Comment #3 from Jason Merrill <jason at gcc dot gnu.org> ---
(In reply to Giuseppe D'Angelo from comment #0)
> Please advise as of what kind of test I could do
> / provide to help you track this one down. 

The testcase doesn't really need to be reduced, just separated from the Qt
build system: some source files and a compiler command line would be fine.

[Bug c++/100796] [11 Regression] GCC does not honor #pragma diagnostic ignored when using the integrated preprocessor

[dangelog at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=100796

--- Comment #4 from Giuseppe D'Angelo <dangelog at gmail dot com> ---
Created attachment 51011
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=51011&action=edit
testcase

Hi,

I've tried to "carve" a subset of files that show the problem. Apologies for
not really being minimal.

How to reproduce: 
1) uncompress
2) cd $dir/home/peppe/projects/src/qt5/qtbase/build
3) (with c++ = GCC 11) run

c++ -DQT_CONCURRENT_LIB -DQT_CORE_LIB
-DQT_TESTCASE_BUILDDIR=\"/home/peppe/projects/src/qt5/qtbase/build/tests/auto/corelib/io/qurl\"
-DQT_TESTCASE_SOURCEDIR=\"/home/peppe/projects/src/qt5/qtbase/tests/auto/corelib/io/qurl\"
-D_LARGEFILE64_SOURCE -D_LARGEFILE_SOURCE
-Itests/auto/corelib/io/qurl/tst_qurl_autogen/include
-I../tests/auto/corelib/io/qurl -Itests/auto/corelib/io/qurl -Iinclude
-Iinclude/QtCore -I../mkspecs/linux-g++ -Iinclude/QtTest -Iinclude/QtConcurrent
-Isrc/testlib -Iinclude/QtTest/6.2.0 -Iinclude/QtTest/6.2.0/QtTest
-Isrc/corelib -Iinclude/QtCore/6.2.0 -Iinclude/QtCore/6.2.0/QtCore -g -fPIE
-fvisibility=hidden -fvisibility-inlines-hidden -Wall -Wextra -fPIC -pthread
-Wsuggest-override -std=gnu++2a -o /dev/null  -c
../tests/auto/corelib/io/qurl/tst_qurl.cpp


That for me generates a bunch of false warnings such as

> include/QtCore/../../../src/corelib/kernel/qtmetamacros.h:159:32: warning: ‘virtual const QMetaObject* QSocketNotifier::metaObject() const’ can be marked override [-Wsuggest-override]
>   159 |     virtual const QMetaObject *metaObject() const; \
>       |                                ^~~~~~~~~~
> include/QtCore/../../../src/corelib/kernel/qsocketnotifier.h:51:5: note: in expansion of macro ‘Q_OBJECT’
>    51 |     Q_OBJECT
>       |     ^~~~~~~~


and many more.

As mentioned before: adding -no-integrated-cpp to the command line, and/or
splitting the compilation in explicit preprocessing+compilation, makes the
warnings disappear.

Please let me know if the testcase works or if I forgot to add something
(hoping that system headers don't make a difference, anyways, I'm testing under
Ubuntu 20.04).

[Bug c++/100796] [11 Regression] GCC does not honor #pragma diagnostic ignored when using the integrated preprocessor

[jason at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=100796

--- Comment #5 from Jason Merrill <jason at gcc dot gnu.org> ---
Created attachment 51012
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=51012&action=edit
fix

Testing this fix now.  Making a suitable testcase for the testsuite will be a
bit tricky...

[Bug c++/100796] [11 Regression] GCC does not honor #pragma diagnostic ignored when using the integrated preprocessor

[dangelog at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=100796

--- Comment #6 from Giuseppe D'Angelo <dangelog at gmail dot com> ---
Hi,

Wow, that was quick!

I can't really judge the merit of the patch, but I've picked it on top of the
GCC 11.1.0 tarball and can confirm that it seems to fix all the warnings for
us. Thank you very much!

[Bug c++/100796] [11 Regression] GCC does not honor #pragma diagnostic ignored when using the integrated preprocessor

[cvs-commit at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=100796

--- Comment #7 from CVS Commits <cvs-commit at gcc dot gnu.org> ---
The master branch has been updated by Jason Merrill <jason@gcc.gnu.org>:

https://gcc.gnu.org/g:9e64426dae129cca5b62355ef6c5a3bd6137e830

commit r12-1538-g9e64426dae129cca5b62355ef6c5a3bd6137e830
Author: Jason Merrill <jason@redhat.com>
Date:   Mon Jun 14 17:37:43 2021 -0400

    libcpp: location comparison within macro [PR100796]

    The patch for 96391 changed linemap_compare_locations to give up on
    comparing locations from macro expansions if we don't have column
    information.  But in this testcase, the BOILERPLATE macro is multiple lines
    long, so we do want to compare locations within the macro.  So this patch
    moves the LINE_MAP_MAX_LOCATION_WITH_COLS check inside the block, to use it
    for failing gracefully.

            PR c++/100796
            PR preprocessor/96391

    libcpp/ChangeLog:

            * line-map.c (linemap_compare_locations): Only use comparison with
            LINE_MAP_MAX_LOCATION_WITH_COLS to avoid abort.

    gcc/testsuite/ChangeLog:

            * g++.dg/plugin/location-overflow-test-pr100796.c: New test.
            * g++.dg/plugin/plugin.exp: Run it.

[Bug c++/100796] [11 Regression] GCC does not honor #pragma diagnostic ignored when using the integrated preprocessor

[cvs-commit at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=100796

--- Comment #8 from CVS Commits <cvs-commit at gcc dot gnu.org> ---
The releases/gcc-11 branch has been updated by Jason Merrill
<jason@gcc.gnu.org>:

https://gcc.gnu.org/g:bb2e908638758097e261bca1a4825d171a18af9c

commit r11-8583-gbb2e908638758097e261bca1a4825d171a18af9c
Author: Jason Merrill <jason@redhat.com>
Date:   Mon Jun 14 17:37:43 2021 -0400

    libcpp: location comparison within macro [PR100796]

    The patch for 96391 changed linemap_compare_locations to give up on
    comparing locations from macro expansions if we don't have column
    information.  But in this testcase, the BOILERPLATE macro is multiple lines
    long, so we do want to compare locations within the macro.  So this patch
    moves the LINE_MAP_MAX_LOCATION_WITH_COLS check inside the block, to use it
    for failing gracefully.

            PR c++/100796
            PR preprocessor/96391

    libcpp/ChangeLog:

            * line-map.c (linemap_compare_locations): Only use comparison with
            LINE_MAP_MAX_LOCATION_WITH_COLS to avoid abort.

    gcc/testsuite/ChangeLog:

            * g++.dg/plugin/location-overflow-test-pr100796.c: New test.
            * g++.dg/plugin/plugin.exp: Run it.

[Bug c++/100796] [11 Regression] GCC does not honor #pragma diagnostic ignored when using the integrated preprocessor

[jason at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=100796

Jason Merrill <jason at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
         Resolution|---                         |FIXED
             Status|UNCONFIRMED                 |RESOLVED

--- Comment #9 from Jason Merrill <jason at gcc dot gnu.org> ---
Fixed for 11.2

[Bug c++/100796] [11 Regression] GCC does not honor #pragma diagnostic ignored when using the integrated preprocessor

[dangelog at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=100796

--- Comment #10 from Giuseppe D'Angelo <dangelog at gmail dot com> ---
Thank you very much.