tests/test-config-env.py

nodemap: gate the feature behind a new requirement

Now that the feature is working smoothly, a question was still open, should we
gate the feature behind a new requirement or just treat it as a cache to be
warmed by those who can and ignored by other.

The advantage of using the cache approach is a transparent upgrade/downgrade
story, making the feature easier to move to. However having out of date cache
can come with a significant performance hit for process who expect an up to
date cache but found none. In this case the file needs to be stored under
`.hg/cache`.

The "requirement" approach guarantee that the persistent nodemap is up to date.
However, it comes with a less flexible activation story since an explicite
upgrade is required. In this case the file can be stored in `.hg/store`.

This wiki page is relevant to this questions:

  https://www.mercurial-scm.org/wiki/ComputedIndexPlan

So which one should we take? Another element came into plan, the persistent
nodemap use the `add` method of the transaction, it is used to keep track of a
file content before a transaction in case we need to rollback it back. It turns
out that the `transaction.add` API does not support file stored anywhere than
`.hg/store`. Making it support file stored elsewhere is possible, require a
change in on disk transaction format. Updating on disk file requires…
introducing a new requirements.

As a result, we pick the second option "gating the persistent nodemap behind a
new requirements".

Differential Revision: https://phab.mercurial-scm.org/D8417

# Test the config layer generated by environment variables

from __future__ import absolute_import, print_function

import os

from mercurial import (
    encoding,
    extensions,
    rcutil,
    ui as uimod,
    util,
)

from mercurial.utils import procutil

testtmp = encoding.environ[b'TESTTMP']

# prepare hgrc files
def join(name):
    return os.path.join(testtmp, name)


with open(join(b'sysrc'), 'wb') as f:
    f.write(b'[ui]\neditor=e0\n[pager]\npager=p0\n')

with open(join(b'userrc'), 'wb') as f:
    f.write(b'[ui]\neditor=e1')

# replace rcpath functions so they point to the files above
def systemrcpath():
    return [join(b'sysrc')]


def userrcpath():
    return [join(b'userrc')]


extensions.wrapfunction(rcutil, 'default_rc_resources', lambda orig: [])

rcutil.systemrcpath = systemrcpath
rcutil.userrcpath = userrcpath

# utility to print configs
def printconfigs(env):
    encoding.environ = env
    rcutil._rccomponents = None  # reset cache
    ui = uimod.ui.load()
    for section, name, value in ui.walkconfig():
        source = ui.configsource(section, name)
        procutil.stdout.write(
            b'%s.%s=%s # %s\n' % (section, name, value, util.pconvert(source))
        )
    procutil.stdout.write(b'\n')


# environment variable overrides
printconfigs({})
printconfigs({b'EDITOR': b'e2', b'PAGER': b'p2'})