Per branch ignore exclusions

[John Arbash Meinel]

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John Whitley wrote:
> Martin Pool <mbp <at> canonical.com> writes:
>> Since we support Python regexps in ignore rules, it may already be
>> possible to use a negative-match regexp to do this.  If there is, it
>> should be documented as as recipe; if not it would be worth filing or
>> duping a bug.
> 
> I didn't see a dupe, so I filed as:
> https://bugs.launchpad.net/bugs/428031
> 
> Good idea, re: regexps.  Depending on the ignore implementation, a
> negative-match regexp may or may not work as the user expects.  It
> might require collapsing some or all ignore rules into a big ugly
> alternate-list regexp.  If the ignore engine already compiles the
> rules into a big regexp, a negative matcher might be ok.
> 
> In any event, I plan on starting by hacking out some (failing)
> exclusion tests and will use that time to see if a negative-match
> regexp approach will indeed work.
> 
> -- John

We turn globs into regexps and then put them all together in one big
match. Except it turned out that python's matcher had a limit of
something like 100 groups, so we limit it to 50 groups at a time.

Unfortunately this probably means that it will work for almost everyone,
except when it starts failing unpredictably...

John
=:->

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