[Bug default/23700] Wrong propagation of private type suppression category

["dodji at redhat dot com" <sourceware-bugzilla@sourceware.org>]

https://sourceware.org/bugzilla/show_bug.cgi?id=23700

dodji at redhat dot com changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |ASSIGNED
   Last reconfirmed|                            |2018-10-01
            Summary|Surprising abidiff report   |Wrong propagation of
                   |on IBus                     |private type suppression
                   |                            |category
     Ever confirmed|0                           |1

--- Comment #4 from dodji at redhat dot com ---
Here is my analysis of the second part of the issue reported here.

Conceptually, there are two kinds of type suppression specifications:

1/ a generic user-provided suppression specification that is meant to suppress
changes on types specified by the user

2/ a private type suppression specification that is automatically generated
from the path to public header files provided by the user.

Technically, one difference between 1 and 2 lays in the way we propagate
categories of changes matched by those suppression specifications.

If a class type change of category SUPPRESSED_CATEGORY is referenced in a
typedef change, then the typedef change is also considered to be of category
SUPPRESSED_CATEGORY.  In other words, the SUPPRESSED_CATEGORY category is
propagated to the typedef change.  That means that if a change to a class type
is suppressed, a (changed) typedef to that class is considered to be suppressed
too.

But then that is not true if the class type was changed because it's private. 
In that, a typedef to that class can be *public*, because the said typedef is
defined in a public header.  In that case the typedef change should *NOT* be
considered suppressed just because the class type change was suppressed.

The problem we have here is that we don't make any difference between 1/ and
2/.  So we need to introduce different propagation rules for 1/ and 2/.

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