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From: "rs2740 at gmail dot com" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug c++/110164] New: Improve diagnostic for incomplete standard
 library types due to missing include
Date: Wed, 07 Jun 2023 21:49:36 +0000
X-Bugzilla-Reason: CC
X-Bugzilla-Type: new
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X-Bugzilla-Product: gcc
X-Bugzilla-Component: c++
X-Bugzilla-Version: 14.0
X-Bugzilla-Keywords: diagnostic
X-Bugzilla-Severity: normal
X-Bugzilla-Who: rs2740 at gmail dot com
X-Bugzilla-Status: UNCONFIRMED
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X-Bugzilla-Priority: P3
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D110164

            Bug ID: 110164
           Summary: Improve diagnostic for incomplete standard library
                    types due to missing include
           Product: gcc
           Version: 14.0
            Status: UNCONFIRMED
          Keywords: diagnostic
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: rs2740 at gmail dot com
  Target Milestone: ---

If I forget to include a header before using a sufficiently well-known stan=
dard
library type, GCC helpfully reminds me of the header:

$ echo 'std::array<int, 10> x;' | g++ -x c++ -

<stdin>:1:6: error: =E2=80=98array=E2=80=99 in namespace =E2=80=98std=E2=80=
=99 does not name a template type
<stdin>:1:1: note: =E2=80=98std::array=E2=80=99 is defined in header =E2=80=
=98<array>=E2=80=99; did you forget
to =E2=80=98#include <array>=E2=80=99?

But if I happen to have a different standard library header included that
happens to bring in a forward declaration of the type, the error message is
less helpful:

$ echo -e '#include <map>\nstd::array<int, 10> x;' | g++ -x c++ -

<stdin>:2:21: error: aggregate =E2=80=98std::array<int, 10> x=E2=80=99 has =
incomplete type and
cannot be defined

It would be nice if the latter case also has a hint about the potential mis=
sing
include.=