Re: Sometimes unable to lock the index during pre-commit hook

[Junio C Hamano <gitster@pobox.com>]

Réda Housni Alaoui <reda.housnialaoui@gmail.com> writes:

> Are pre-commit hooks expected to be able to manipulate the index?

Hooks are described in githooks(5) manual pages; we may want to
clarify what is not allowed, but back when most of the entries were
written, the stance was that anything that is not explicitly allowed
there is forbidden.

In general, a pre-<something> hook is a way to inspect (i.e. look
but not touch) what is proposed to be done and veto it by exiting
with non-zero.  It is not expected to change the state of the
repository in any way.

The code does not necessarily enforce it, because it is costly to
take a snapshot of everything (including the index, the working tree
files, the files that are untracked, the objects in the object
database, etc.) before calling a hook and ensure that the hook did
not touch anything.

Thanks.