[Bug default/27161] New: enumerator additions can be harmful

[Bug default/27161] New: enumerator additions can be harmful

[gprocida+abigail at google dot com]

https://sourceware.org/bugzilla/show_bug.cgi?id=27161

            Bug ID: 27161
           Summary: enumerator additions can be harmful
           Product: libabigail
           Version: unspecified
            Status: UNCONFIRMED
          Severity: normal
          Priority: P2
         Component: default
          Assignee: dodji at redhat dot com
          Reporter: gprocida+abigail at google dot com
                CC: libabigail at sourceware dot org
  Target Milestone: ---

libabigail has an asymmetrical definition of "harmless" when it comes to
enumerator additions and removals.

Consider two *library* functions.

int contravariant(enum foo x);
enum foo covariant(int y);

Enumerator additions are safe for users of contravariant but unsafe for users
of covariant, and vice versa with removals.

More generally if a client is expected to consume the enum, removals are safe;
produce the enum, additions are safe. Working out which is happening is general
is impossible.

It really does not make sense to favour one direction over the other. We should
be conservative and treat both as harmful.

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