ls: check fts_children() for errors that may not surface otherwise

[kevans]

Summary

In particular, if one simply does a non-recursive ls on a directory
that is not accessible, there are some classes of errors that may cause
it to fail that wouldn't be surfaced unless we do an fts_read() that
will recurse into the inaccessible directory. Catch those kinds of
errors here since we cannot expect to an FTS_ERR/FTS_DNR entry to follow
up on them.

PR: 287451

[des]

bin/ls/ls.c

710

The errno check is redundant, chp == NULL && errno == 0 can only happen if a) ftsp is not of type FTS_D or b) FTS_STOP is set on ftsp. Neither is possible here.

bin/ls/tests/ls_tests.sh

505

why not simply use -o match and -e match here?

[kevans]

bin/ls/ls.c

710

The manpage claims it returns NULL and errno will be set to 0 if the directory is empty. I don't see how that is falls within your two cases, because an empty directory would otherwise get an FTS_D + FTD_DP pair just like a non-empty.

[des]

bin/ls/ls.c

710

Ah, I failed to consider that the directory might be empty.

[kevans]

bin/ls/tests/ls_tests.sh

505

Incorporated along with other discussed improvements