20     grep as grepmod,

   997 @predicate(b'diff(pattern)', weight=110)

   998 def diff(repo, subset, x):

   999     """Search revision differences for when the pattern was added or removed.

  1000 

  1001     The pattern may be a substring literal or a regular expression. See

  1002     :hg:`help revisions.patterns`.

  1003     """

  1004     args = getargsdict(x, b'diff', b'pattern')

  1005     if b'pattern' not in args:

  1006         # i18n: "diff" is a keyword

  1007         raise error.ParseError(_(b'diff takes at least 1 argument'))

  1008 

  1009     pattern = getstring(args[b'pattern'], _(b'diff requires a string pattern'))

  1010     regexp = stringutil.substringregexp(pattern, re.M)

  1011 

  1012     # TODO: add support for file pattern and --follow. For example,

  1013     # diff(pattern[, set]) where set may be file(pattern) or follow(pattern),

  1014     # and we'll eventually add a support for narrowing files by revset?

  1015     fmatch = matchmod.always()

  1016 

  1017     def makefilematcher(ctx):

  1018         return fmatch

  1019 

  1020     # TODO: search in a windowed way

  1021     searcher = grepmod.grepsearcher(repo.ui, repo, regexp, diff=True)

  1022 

  1023     def testdiff(rev):

  1024         # consume the generator to discard revfiles/matches cache

  1025         found = False

  1026         for fn, ctx, pstates, states in searcher.searchfiles(

  1027             baseset([rev]), makefilematcher

  1028         ):

  1029             if next(grepmod.difflinestates(pstates, states), None):

  1030                 found = True

  1031         return found

  1032 

  1033     return subset.filter(testdiff, condrepr=(b'<diff %r>', pattern))

  1034 

  1035