[Bug c++/113360] New: Truncated constexpr error messages with -std=c++23/26

["mpolacek at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=113360

            Bug ID: 113360
           Summary: Truncated constexpr error messages with -std=c++23/26
           Product: gcc
           Version: unknown
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: mpolacek at gcc dot gnu.org
  Target Milestone: ---

Test by Paul Keir:

constexpr bool init_list()
{
  int total{};
  for (int x : {1, 2, 3})
    total += x;
  return total == 6;
}

static_assert(init_list(), "");

Using -std=c++23, the error message is:

<source>: In function 'constexpr bool init_list()':
<source>:6:24: error: deducing from brace-enclosed initializer list requires
'#include <initializer_list>'
  +++ |+#include <initializer_list>
    1 | // #include <initializer_list>
......
    6 |   for (int x : {1, 2, 3})
      |                        ^
<source>: At global scope:
<source>:11:24: error: non-constant condition for static assertion
   11 | static_assert(init_list(), "");
      |               ~~~~~~~~~^~
<source>:11:24: error: 'constexpr bool init_list()' called in a constant
expression
<source>:3:16: note: 'constexpr bool init_list()' is not usable as a
'constexpr' function because:
    3 | constexpr bool init_list()
      |                ^~~~~~~~~