[PATCH] match: introduce nevermatcher for when no ignore files are present

[Augie Fackler]

On Thu, Jun 01, 2017 at 12:41:16AM -0700, Siddharth Agarwal wrote:
> # HG changeset patch
> # User Siddharth Agarwal <sid0 at fb.com>
> # Date 1496302852 25200
> #      Thu Jun 01 00:40:52 2017 -0700
> # Node ID 14f332c8fe10c498e7c35bef09e53b8b6c7e5f43
> # Parent  dbf330cadc5a3c0707c4611f2f4150be13cac02a
> match: introduce nevermatcher for when no ignore files are present

Queued, thanks.

> 952017471f93 introduced a deterministic `__repr__` for ignores. However, it
> didn't account for when ignore was `util.never`. This broke fsmonitor's ignore
> change detection -- with an empty hgignore, it would kick in all the time.
>
> Introduce `nevermatcher` and switch to it. This neatly parallels
> `alwaysmatcher`.
>
> diff --git a/mercurial/dirstate.py b/mercurial/dirstate.py
> --- a/mercurial/dirstate.py
> +++ b/mercurial/dirstate.py
> @@ -232,7 +232,7 @@ class dirstate(object):
>      def _ignore(self):
>          files = self._ignorefiles()
>          if not files:
> -            return util.never
> +            return matchmod.never(self._root, '')
>
>          pats = ['include:%s' % f for f in files]
>          return matchmod.match(self._root, '', [], pats, warn=self._ui.warn)
> diff --git a/mercurial/match.py b/mercurial/match.py
> --- a/mercurial/match.py
> +++ b/mercurial/match.py
> @@ -175,6 +175,9 @@ def exact(root, cwd, files, badfn=None):
>  def always(root, cwd):
>      return alwaysmatcher(root, cwd)
>
> +def never(root, cwd):
> +    return nevermatcher(root, cwd)
> +
>  def badmatch(match, badfn):
>      """Make a copy of the given matcher, replacing its bad method with the given
>      one.
> @@ -339,6 +342,25 @@ class alwaysmatcher(basematcher):
>      def __repr__(self):
>          return '<alwaysmatcher>'
>
> +class nevermatcher(basematcher):
> +    '''Matches nothing.'''
> +
> +    def __init__(self, root, cwd, badfn=None, relativeuipath=False):
> +        super(nevermatcher, self).__init__(root, cwd, badfn,
> +                                           relativeuipath=relativeuipath)
> +
> +    def always(self):
> +        return False
> +
> +    def matchfn(self, f):
> +        return False
> +
> +    def visitdir(self, dir):
> +        return False
> +
> +    def __repr__(self):
> +        return '<nevermatcher>'
> +
>  class patternmatcher(basematcher):
>
>      def __init__(self, root, cwd, kindpats, ctx=None, listsubrepos=False,
> diff --git a/tests/test-hgignore.t b/tests/test-hgignore.t
> --- a/tests/test-hgignore.t
> +++ b/tests/test-hgignore.t
> @@ -1,6 +1,10 @@
>    $ hg init ignorerepo
>    $ cd ignorerepo
>
> +debugignore with no hgignore should be deterministic:
> +  $ hg debugignore
> +  <nevermatcher>
> +
>  Issue562: .hgignore requires newline at end:
>
>    $ touch foo
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