Invoke Mercurial without loading global and user configs

Question

I'm writing some unit tests that call out to Mercurial, and I'd like to ensure the tests don't rely on any local state of the machine. I know I can override certain config values, e.g.:

hg --config ui.username='Test Account <not-a-real-address@example.com>' ...

However this still reads in the global and user .hgrc files on the machine, which could affect Mercurial's behavior in an unintended or undesirable way.

Is there a robust way to invoke hg without having it look at any config files except the .hg/hgrc file in the repo? For instance with Bash I can accomplish this with bash --noprofile --norc, but I don't see a similar flag for Mercurial.

NB: I'm aware of "heavyweight" options such as running the tests in an isolated virtual environment such as Docker. I'll certainly do something like that if necessary, but I'm wondering if there's a way to configure Mercurial itself.

Answer 1

A bit more poking found Issue 3147: command line option to disable ~/.hgrc, which was CLOSED WONTFIX, however the workaround suggested there appears to work as desired:

$ HGRCPATH= hg ...

This overrides the default search paths for hgrc files, though it isn't mentioned (as of this writing) in the hgrc docs (edit: it's mentioned on another page).

Example:

# lots of inherited config by default
$ hg showconfig | wc
     118     361    7232

$ HGRCPATH= hg showconfig
ui.formatted=True
ui.interactive=False

$ hg init foo && cd foo

$ HGRCPATH= hg showconfig
bundle.mainreporoot=/tmp/foo
ui.formatted=True
ui.interactive=False

Answer 2

In scripts you usually want to ensure that no local configuration and localisation breaks it. Mercurial provides the environment variable HGPLAIN= for that purpose. Thus in your scripts invoke mercurial always by setting it for that particular invocation of mercurial:

HGPLAIN= hg status

This makes sure that you see the output as produced by vanilla mercurial. See also https://www.mercurial-scm.org/repo/hg/help/environment and how to define exceptions to this rule, if needed.