The null pattern semantics were terrible because I tried to match gnugrep,
but I got it wrong. Let's unwind that:
- The null pattern should match every line if neither -w nor -x.
- The null pattern should match empty lines if -x.
- The null pattern should not match any lines if -w.
The first two will stop processing (shortcut) even if additional patterns
are specified. In any other case, we will continue processing other
patterns. If no other patterns are specified beside a null pattern, then
we match if neither -w nor -x or set and do not match if either of those
are specified.
The justification for -w is that it should match on a whole word, but the
null pattern deos not have a whole word to match on.
Empty pattern files should never match anything, and more importantly, -v
should cause everything to be written.
PR: 253209
MFC-after: 4 days
f823c6dc73