[Bug c++/112293] New: Enhance error reporting with fix-it for missing <algorithm> in gcc 14

[Bug c++/112293] New: Enhance error reporting with fix-it for missing <algorithm> in gcc 14

[arkamar at atlas dot cz]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=112293

            Bug ID: 112293
           Summary: Enhance error reporting with fix-it for missing
                    <algorithm> in gcc 14
           Product: gcc
           Version: 14.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: arkamar at atlas dot cz
  Target Milestone: ---
              Host: x86_64-pc-linux-gnu
             Build: x86_64-pc-linux-gnu

We encountered an issue while attempting to build the rspamd package using
gcc-14 on Gentoo Linux. The build process fails with a somewhat ambiguous error
message [1]. However, the same package compiles successfully with gcc-13.

The issue appears to arise from internal changes in libstdc++ that now require
the explicit inclusion of the <algorithm> header (this part is likely a bug
within rspamd). Is it possible to enhance the error messaging, perhaps with a
fix-it hint, to suggest that <algorithm> needs to be explicitly included for
clarity?

Here is the minimized snippet to reproduce the issue:

#include <functional>
#include <stdexcept>
struct test;
std::vector<test *> v;
auto f(test *t) {
  auto it = std::remove(begin(v), end(v), t);
}

which currently fails with the following error message:

test.cxx: In function _auto f(test*)_:
test.cxx:6:30: error: cannot convert _std::vector<test*>::iterator_ to _const
char*_
    6 |   auto it = std::remove(begin(v), end(v), t);
      |                         ~~~~~^~~
      |                              |
      |                              std::vector<test*>::iterator
In file included from
/usr/lib/gcc/x86_64-pc-linux-gnu/14/include/g++-v14/cstdio:42,
                 from
/usr/lib/gcc/x86_64-pc-linux-gnu/14/include/g++-v14/ext/string_conversions.h:45,
                 from
/usr/lib/gcc/x86_64-pc-linux-gnu/14/include/g++-v14/bits/basic_string.h:4158,
                 from
/usr/lib/gcc/x86_64-pc-linux-gnu/14/include/g++-v14/string:54,
                 from
/usr/lib/gcc/x86_64-pc-linux-gnu/14/include/g++-v14/stdexcept:39,
                 from test.cxx:2:
/usr/include/stdio.h:157:32: note:   initializing argument 1 of _int
remove(const char*)_
  157 | extern int remove (const char *__filename) __THROW;
      |

I tested this with: gcc version 14.0.0 20231022 (experimental) (Gentoo
14.0.0_pre20231022-r1 p7)

[1] https://bugs.gentoo.org/916438

[Bug c++/112293] Enhance error reporting with fix-it for missing <algorithm> in gcc 14

[redi at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=112293

--- Comment #1 from Jonathan Wakely <redi at gcc dot gnu.org> ---
(In reply to Petr Vaněk from comment #0)
> The issue appears to arise from internal changes in libstdc++ that now
> require the explicit inclusion of the <algorithm> header (this part is
> likely a bug within rspamd).

The C++ standard always required the explicit inclusion of <algorithm> for the
std::remove algorithm. This is definitely a bug in rspamd.

> Is it possible to enhance the error messaging,
> perhaps with a fix-it hint, to suggest that <algorithm> needs to be
> explicitly included for clarity?

That would be difficult, because std::remove is overloaded and another overload
was found here (the one declared in <cstdio>). Usually we only provide fix-it
hints when name lookup doesn't find anything.

> Here is the minimized snippet to reproduce the issue:
> 
> #include <functional>
> #include <stdexcept>
> struct test;
> std::vector<test *> v;
> auto f(test *t) {
>   auto it = std::remove(begin(v), end(v), t);
> }

This is broken in two ways, you need to include both <algorithm> *and* <vector>
for this program.

[Bug c++/112293] Enhance error reporting with fix-it for missing <algorithm> in gcc 14

[redi at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=112293

--- Comment #2 from Jonathan Wakely <redi at gcc dot gnu.org> ---
(In reply to Jonathan Wakely from comment #1)
> This is broken in two ways, you need to include both <algorithm> *and*
> <vector> for this program.

Actually three ways. There is no guarantee that std::vector's iterators have
namespace std as an associated namespace, so begin(v) and end(v) are not
guaranteed to find std::begin and std::end. You should qualify them or add
using declarations.

[Bug c++/112293] Enhance error reporting with fix-it for missing <algorithm> in gcc 14

[redi at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=112293

--- Comment #3 from Jonathan Wakely <redi at gcc dot gnu.org> ---
As I wrote in PR 82594, the error should say that the number of arguments is
wrong instead of the irrelevant error about converting to const char*.

I don't think a fix-it is likely here though.

[Bug c++/112293] Enhance error reporting with fix-it for missing <algorithm> in gcc 14

[redi at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=112293

--- Comment #4 from Jonathan Wakely <redi at gcc dot gnu.org> ---
FWIW the change in transitive includes was r14-1459-g940645cec500ab

[Bug c++/112293] Enhance error reporting with fix-it for missing <algorithm> in gcc 14

[arkamar at atlas dot cz]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=112293

--- Comment #5 from Petr Vaněk <arkamar at atlas dot cz> ---
Thank you for the quick response and clarifications. I'll work on patching
rspamd to adhere to these requirements.

As for std::begin and std::end, rspamd uses them correctly, the std:: was
actually reduced by cvise in this case.

[Bug c++/112293] Enhance error reporting with fix-it for missing <algorithm> in gcc 14

[redi at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=112293

--- Comment #6 from Jonathan Wakely <redi at gcc dot gnu.org> ---
(In reply to Jonathan Wakely from comment #1)
> That would be difficult, because std::remove is overloaded and another
> overload was found here (the one declared in <cstdio>). Usually we only
> provide fix-it hints when name lookup doesn't find anything.

This is also a very unusual case. Most C++ std::lib functions are not
overloaded in C stdlib headers. Any change here would be quite specific to
std::remove, possibly even unique. There's std::bind which collides with POSIX
::bind. There are also std::isalnum etc. but I don't think it's possible to get
the problem there, since they're declared in the same header as the std::locale
type that you call them with.

[Bug c++/112293] Enhance error reporting with fix-it for missing <algorithm> in gcc 14

[sjames at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=112293

Sam James <sjames at gcc dot gnu.org> changed:

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

--- Comment #7 from Sam James <sjames at gcc dot gnu.org> ---
I think this has come up with chromium/nodejs v8 as well, in both cases with
people being confused about the stdio remove candidate at the end.

[Bug c++/112293] Enhance error reporting with fix-it for missing <algorithm> in gcc 14

[redi at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=112293

--- Comment #8 from Jonathan Wakely <redi at gcc dot gnu.org> ---
And here too: https://bugzilla.redhat.com/show_bug.cgi?id=2259394

[Bug c++/112293] Enhance error reporting with fix-it for missing <algorithm> in gcc 14

[fw at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=112293

Florian Weimer <fw at gcc dot gnu.org> changed:

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

--- Comment #9 from Florian Weimer <fw at gcc dot gnu.org> ---
Could we change the C++ standard not to declare std::remove in <cstdio>?