clfilter: add actual repo filtering mechanism

clfilter: add actual repo filtering mechanism

We add a `filtered` method on repo. This method return an instance of `repoview`
that behaves exactly as the original repository but with a filtered changelog
attribute. Filters are identified by a "name". Planned filter are `unserved`,
`hidden` and `mutable`. Filtering the repository in place what out of question
as it wont not allows multiple thread to share the same repo. It would makes
control of the filtering scope harder too. See the `repoview` docstring for
details.

A mechanism to compute filtered revision is also installed. Some caches will be
installed in later commit.

--- a/mercurial/localrepo.py	Wed Dec 19 16:56:26 2012 -0800
+++ b/mercurial/localrepo.py	Thu Dec 20 15:32:42 2012 +0100
@@ -6,7 +6,7 @@
 # GNU General Public License version 2 or any later version.
 from node import bin, hex, nullid, nullrev, short
 from i18n import _
-import peer, changegroup, subrepo, discovery, pushkey, obsolete
+import peer, changegroup, subrepo, discovery, pushkey, obsolete, repoview
 import changelog, dirstate, filelog, manifest, context, bookmarks, phases
 import lock, transaction, store, encoding, base85
 import scmutil, util, extensions, hook, error, revset
@@ -303,6 +303,14 @@
         Intended to be ovewritten by filtered repo."""
         return self
 
+    def filtered(self, name):
+        """Return a filtered version of a repository"""
+        # build a new class with the mixin and the current class
+        # (possibily subclass of the repo)
+        class proxycls(repoview.repoview, self.unfiltered().__class__):
+            pass
+        return proxycls(self, name)
+
     @repofilecache('bookmarks')
     def _bookmarks(self):
         return bookmarks.bmstore(self)

--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/mercurial/repoview.py	Thu Dec 20 15:32:42 2012 +0100
@@ -0,0 +1,94 @@
+# repoview.py - Filtered view of a localrepo object
+#
+# Copyright 2012 Pierre-Yves David <[e-mail]>
+#                Logilab SA        <[e-mail]>
+#
+# This software may be used and distributed according to the terms of the
+# GNU General Public License version 2 or any later version.
+
+import copy
+
+# function to compute filtered set
+filtertable = {}
+
+def filteredrevs(repo, filtername):
+    """returns set of filtered revision for this filter name"""
+    return filtertable[filtername](repo.unfiltered())
+
+class repoview(object):
+    """Provide a read/write view of a repo through a filtered changelog
+
+    This object is used to access a filtered version of a repository without
+    altering the original repository object itself. We can not alter the
+    original object for two main reasons:
+    - It prevents the use of a repo with multiple filters at the same time. In
+      particular when multiple threads are involved.
+    - It makes scope of the filtering harder to control.
+
+    This object behaves very closely to the original repository. All attribute
+    operations are done on the original repository:
+    - An access to `repoview.someattr` actually returns `repo.someattr`,
+    - A write to `repoview.someattr` actually sets value of `repo.someattr`,
+    - A deletion of `repoview.someattr` actually drops `someattr`
+      from `repo.__dict__`.
+
+    The only exception is the `changelog` property. It is overridden to return
+    a (surface) copy of `repo.changelog` with some revisions filtered. The
+    `filtername` attribute of the view control the revisions that need to be
+    filtered.  (the fact the changelog is copied is an implementation detail).
+
+    Unlike attributes, this object intercepts all method calls. This means that
+    all methods are run on the `repoview` object with the filtered `changelog`
+    property. For this purpose the simple `repoview` class must be mixed with
+    the actual class of the repository. This ensures that the resulting
+    `repoview` object have the very same methods than the repo object. This
+    leads to the property below.
+
+        repoview.method() --> repo.__class__.method(repoview)
+
+    The inheritance has to be done dynamically because `repo` can be of any
+    subclasses of `localrepo`. Eg: `bundlerepo` or `httprepo`.
+    """
+
+    def __init__(self, repo, filtername):
+        object.__setattr__(self, '_unfilteredrepo', repo)
+        object.__setattr__(self, 'filtername', filtername)
+
+    # not a cacheproperty on purpose we shall implement a proper cache later
+    @property
+    def changelog(self):
+        """return a filtered version of the changeset
+
+        this changelog must not be used for writing"""
+        # some cache may be implemented later
+        cl = copy.copy(self._unfilteredrepo.changelog)
+        cl.filteredrevs = filteredrevs(self._unfilteredrepo, self.filtername)
+        return cl
+
+    def unfiltered(self):
+        """Return an unfiltered version of a repo"""
+        return self._unfilteredrepo
+
+    def filtered(self, name):
+        """Return a filtered version of a repository"""
+        if name == self.filtername:
+            return self
+        return self.unfiltered().filtered(name)
+
+    # everything access are forwarded to the proxied repo
+    def __getattr__(self, attr):
+        return getattr(self._unfilteredrepo, attr)
+
+    def __setattr__(self, attr, value):
+        return setattr(self._unfilteredrepo, attr, value)
+
+    def __delattr__(self, attr):
+        return delattr(self._unfilteredrepo, attr)
+
+    # The `requirement` attribut is initialiazed during __init__. But
+    # __getattr__ won't be called as it also exists on the class. We need
+    # explicit forwarding to main repo here
+    @property
+    def requirements(self):
+        return self._unfilteredrepo.requirements
+