Re: [PATCH 2/4] dir.c::match_basename(): pay attention to the length of string parameters

On Tue, Mar 26, 2013 at 11:39:29AM -0700, Junio C Hamano wrote:

The function takes two counted strings (<basename, basenamelen> and
<pattern, patternlen>) as parameters, together with prefix (the
length of the prefix in pattern that is to be matched literally
without globbing against the basename) and EXC_* flags that tells it
how to match the pattern against the basename.

However, it did not pay attention to the length of these counted
strings.  Update them to do the following:

 * When the entire pattern is to be matched literally, the pattern
   matches the basename only when the lengths of them are the same,
   and they match up to that length.

 * When the pattern is "*" followed by a string to be matched
   literally, make sure that the basenamelen is equal or longer than
   the "literal" part of the pattern, and the tail of the basename
   string matches that literal part.

 * Otherwise, make sure we use only the counted part of the strings
   when calling fnmatch_icase().  Because these counted strings are
   full strings most of the time, avoid unnecessary allocation.

I think this is OK, with the intention that we would eventually drop the
allocations from your third bullet point in favor of using a
byte-counted version of fnmatch (i.e., nwildmatch). But until then we're
going to see a performance drop.

The pattern is usually going to be NUL-terminated at the length counter,
but every time we feed a directory, it's going to run into this
allocation. And we do it once for _every_ directory against _every_
wildcard gitignore pattern. So I think it is probably going to be
measurable. I guess we can try measuring it on something like WebKit,
which has plenty of both directories and gitattributes.

-Peff