[Bug default/31513] abidiff wrongly considers data members moved to base class as harmful

["quic_jiafan at quicinc dot com" <sourceware-bugzilla@sourceware.org>]

https://sourceware.org/bugzilla/show_bug.cgi?id=31513

Jianfeng Fan <quic_jiafan at quicinc dot com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |quic_jiafan at quicinc dot com

--- Comment #14 from Jianfeng Fan <quic_jiafan at quicinc dot com> ---
Hi,
There may be an issue in the commit
https://sourceware.org/git/?p=libabigail.git;a=commit;h=338394f5454990c715b52bb4bc2ed47b39d6528b

in abg-comp-filter.cc
https://sourceware.org/git/?p=libabigail.git;a=blobdiff;f=src/abg-comp-filter.cc;h=caea9d0c5308264b40f9b07f5d1bdfebef5caae4;hp=63716775ee8ebe482a7b2f0c504e42372979d77e;hb=338394f5454990c715b52bb4bc2ed47b39d6528b;hpb=a917072c12449cfea03e79a6e82e286e0f54f57b

Added inline comments
static bool
has_subtype_changes(const string_decl_base_sptr_map& f_data_members,
                    const string_decl_base_sptr_map& s_data_members,
                    diff_context_sptr ctxt)
{
  // Now compare the offsets of the data members collected.
  var_decl_sptr s_member;
  for (auto entry : f_data_members)
    {
      var_decl_sptr f_member = is_var_decl(entry.second);
      ABG_ASSERT(f_member);

      auto i = s_data_members.find(entry.first);
      if (i == s_data_members.end())
        {
          unsigned offset = get_data_member_offset(f_member);
          s_member = find_data_member_at_offset(s_data_members, offset);
          if (!s_member)
            // A data member was suppressed; that's bad; let's consider
            // that as a sub-type change.
            return true;
        }

      if (!s_member) <<<<<<<<< we never reset s_member, so it will only be
assigned once, each f_member compare to the first s_member.
        s_member = is_var_decl(i->second);
      ABG_ASSERT(s_member);
      diff_sptr d =compute_diff(f_member->get_type(), s_member->get_type(),
ctxt);
      <<<<<<<<< we can add s_member.reset(); here, s_member can be updated next
time.
      if (d->has_changes())
        return true;
    }
  return false;
}

With this change, the result for test case report1.txt can be changed to
Functions changes summary: 0 Removed, 0 Changed (1 filtered out), 0 Added
function
Variables changes summary: 0 Removed, 0 Changed, 0 Added variable

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