[Bug default/26998] New: abidiff --leaf-changes-only misreports array member changes

["gprocida+abigail at google dot com" <sourceware-bugzilla@sourceware.org>]

https://sourceware.org/bugzilla/show_bug.cgi?id=26998

            Bug ID: 26998
           Summary: abidiff --leaf-changes-only misreports array member
                    changes
           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: ---

We've seen various cases where abidiff --leaf-changes-only reporting falls off
the bottom of the represent helper resulting in the message "<member> has
*some* difference - please report as a bug".

The problem manifests itself in two different ways. Sometime this message just
appears (and I speculate anonymous type renumbering has something to do with
it). At other times, it's clear that there is a type change but abidiff has
already reported it.

I took a hour or so to dig deeper into one of the latter instances.

Note that extracting ABIs with abidw and then comparing them yields the same
results.

$ head -100 *.c
==> test.0.c <==
struct buzz {
  int a;
};

struct flexible {
  long count;
  struct buzz lightyear[0];
};

void impacted(const struct flexible * flex) { (void) flex; }

==> test.1.c <==
struct buzz {
  long a;
};

struct flexible {
  long count;
  struct buzz lightyear[0];
};

void impacted(const struct flexible * flex) { (void) flex; }
$ for x in test.{0,1}.c; do gcc -Wall -Wextra -g -c $x; done
$ abidiff --impacted-interfaces --leaf-changes-only test.{0,1}.o
Leaf changes summary: 2 artifacts changed
Changed leaf types summary: 2 leaf types changed
Removed/Changed/Added functions summary: 0 Removed, 0 Changed, 0 Added function
Removed/Changed/Added variables summary: 0 Removed, 0 Changed, 0 Added variable

'struct buzz at test.0.c:1:1' changed:
  type size changed from 32 to 64 (in bits)
  there are data member changes:
    type 'int' of 'buzz::a' changed:
      type name changed from 'int' to 'long int'
      type size changed from 32 to 64 (in bits)
  one impacted interface:
    function void impacted(const flexible*)

'struct flexible at test.0.c:5:1' changed:
  type size hasn't changed
  there are data member changes:
    'buzz flexible::lightyear[]' has *some* difference - please report as a bug
  one impacted interface:
    function void impacted(const flexible*)

Changing both array sizes from 0 to 1 results in actual (size) difference being
reported for struct flexible. However, this type should probably not be being
reported at all as it's not a leaf type (i.e., a changed type that is the root
cause of other changes).

I'll see if I can generate another test case where there's just a harmless
anonymous type rename and trigger the message that way as well.

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