libctf, include: support unnamed structure members better

libctf, include: support unnamed structure members better

libctf has no intrinsic support for the GCC unnamed structure member
extension.  This principally means that you can't look up named members
inside unnamed struct or union members via ctf_member_info: you have to
tiresomely find out the type ID of the unnamed members via iteration,
then look in each of these.

This is ridiculous.  Fix it by extending ctf_member_info so that it
recurses into unnamed members for you: this is still unambiguous because
GCC won't let you create ambiguously-named members even in the presence
of this extension.

For consistency, and because the release hasn't happened and we can
still do this, break the ctf_member_next API and add flags: we specify
one flag, CTF_MN_RECURSE, which if set causes ctf_member_next to
automatically recurse into unnamed members for you, returning not only
the members themselves but all their contained members, so that you can
use ctf_member_next to identify every member that it would be valid to
call ctf_member_info with.

New lookup tests are added for all of this.

include/ChangeLog
2021-01-05  Nick Alcock  <nick.alcock@oracle.com>

	* ctf-api.h (CTF_MN_RECURSE): New.
	(ctf_member_next): Add flags argument.

libctf/ChangeLog
2021-01-05  Nick Alcock  <nick.alcock@oracle.com>

	* ctf-impl.h (struct ctf_next) <u.ctn_next>: Move to...
	<ctn_next>: ... here.
	* ctf-util.c (ctf_next_destroy): Unconditionally destroy it.
	* ctf-lookup.c (ctf_symbol_next): Adjust accordingly.
	* ctf-types.c (ctf_member_iter): Reimplement in terms of...
	(ctf_member_next): ... this.  Support recursive unnamed member
	iteration (off by default).
	(ctf_member_info): Look up members in unnamed sub-structs.
	* ctf-dedup.c (ctf_dedup_rhash_type): Adjust ctf_member_next call.
	(ctf_dedup_emit_struct_members): Likewise.
	* testsuite/libctf-lookup/struct-iteration-ctf.c: Test empty unnamed
	members, and a normal member after the end.
	* testsuite/libctf-lookup/struct-iteration.c: Verify that
	ctf_member_count is consistent with the number of successful returns
	from a non-recursive ctf_member_next.
	* testsuite/libctf-lookup/struct-iteration-*: New, test iteration
	over struct members.
	* testsuite/libctf-lookup/struct-lookup.c: New test.
	* testsuite/libctf-lookup/struct-lookup.lk: New test.