[Bug c++/94830] New: Some concepts diagnostic messages are nondeterministic

[Bug c++/94830] New: Some concepts diagnostic messages are nondeterministic

[ppalka at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=94830

            Bug ID: 94830
           Summary: Some concepts diagnostic messages are nondeterministic
           Product: gcc
           Version: 10.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: ppalka at gcc dot gnu.org
  Target Milestone: ---

$ cat testcase.C
template<typename T, typename R>
  concept c = __is_same(T, R);

template<typename T, typename R>
  requires c<T,R>
void foo() { }

void bar()
{
  foo<int, char>();
}

$ g++ -std=c++2a testcase.C
testcase.C: In function ‘void bar()’:
testcase.C:10:18: error: use of function ‘void foo() [with T = int; R = char]’
with unsatisfied constraints
   10 |   foo<int, char>();
      |                  ^
testcase.C:6:6: note: declared here
    6 | void foo() { }
      |      ^~~
testcase.C:6:6: note: constraints not satisfied
testcase.C: In instantiation of ‘void foo() [with T = int; R = char]’:
testcase.C:10:18:   required from here
testcase.C:2:11:   required for the satisfaction of ‘c<T, R>’ [with T = int; R
= char]
testcase.C:2:15: note:   ‘int’ is not the same as ‘char’
    2 |   concept c = __is_same(T, R);
      |               ^~~~~~~~~~~~~~~


The diagnostic pointing to line 2:11 will on some invocations say "[with T =
int; R = char]" and on other invocations say "[with R = char; T = int]"

[Bug c++/94830] Some concepts diagnostic messages are nondeterministic

[ppalka at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=94830

Patrick Palka <ppalka at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Last reconfirmed|                            |2020-04-29
           Assignee|unassigned at gcc dot gnu.org      |ppalka at gcc dot gnu.org
     Ever confirmed|0                           |1
             Status|UNCONFIRMED                 |ASSIGNED

[Bug c++/94830] Some concepts diagnostic messages are nondeterministic

[cvs-commit at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=94830

--- Comment #1 from CVS Commits <cvs-commit at gcc dot gnu.org> ---
The master branch has been updated by Patrick Palka <ppalka@gcc.gnu.org>:

https://gcc.gnu.org/g:a7201a085cc30f89944931d8fb1d7936f02a169f

commit r10-8049-ga7201a085cc30f89944931d8fb1d7936f02a169f
Author: Patrick Palka <ppalka@redhat.com>
Date:   Wed Apr 29 09:04:58 2020 -0400

    c++: Nondeterministic concepts diagnostics [PR94830]

    This patch makes the order in which template parameters appear in the
    TREE_LIST returned by find_template_parameters deterministic between
    runs.

    The current nondeterminism is semantically harmless, but it has the
    undesirable effect of causing some concepts diagnostics which print a
    constraint's parameter mapping via pp_cxx_parameter_mapping to also be
    nondeterministic, as in the testcases below.

    gcc/cp/ChangeLog:

            PR c++/94830
            * pt.c (find_template_parameter_info::parm_list): New field.
            (keep_template_parm): Use the new field to build up the
            parameter list here instead of ...
            (find_template_parameters): ... here.  Return ftpi.parm_list.

    gcc/testsuite/ChangeLog:

            PR c++/94830
            * g++.dg/concepts/diagnostics12.C: Clarify the dg-message now
            that the corresponding diagnostic is deterministic.
            * g++.dg/concepts/diagnostics13.C: New test.

[Bug c++/94830] Some concepts diagnostic messages are nondeterministic

[ppalka at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=94830

Patrick Palka <ppalka at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
         Resolution|---                         |FIXED
   Target Milestone|---                         |10.0
             Status|ASSIGNED                    |RESOLVED

--- Comment #2 from Patrick Palka <ppalka at gcc dot gnu.org> ---
Fixed.