tests/revnamesext.py

tags: validate nodes in _getfnodes() and update cache in case of unknown nodes

`hgtagsfnodescache` can contain unknown nodes due to cache corruption and this
lead to a traceback on operations like `hg tags` as we don't validate nodes.

This patch validates that all filenodes returned after `hgtagsfnodescache` are
known to the repository. If there exists any unknown filenode, we force
recompute it and update the cache.

The test change demonstrates the fix.

Differential Revision: https://phab.mercurial-scm.org/D10083

# Dummy extension to define a namespace containing revision names

from __future__ import absolute_import

from mercurial import namespaces


def reposetup(ui, repo):
    names = {b'r%d' % rev: repo[rev].node() for rev in repo}
    namemap = lambda r, name: names.get(name)
    nodemap = lambda r, node: [b'r%d' % repo[node].rev()]

    ns = namespaces.namespace(
        b'revnames',
        templatename=b'revname',
        logname=b'revname',
        listnames=lambda r: names.keys(),
        namemap=namemap,
        nodemap=nodemap,
    )
    repo.names.addnamespace(ns)