Re: [PATCH 1/9] init: allow overriding the default branch name for new repositories

[Johannes Schindelin <Johannes.Schindelin@gmx.de>]

Hi Phillip,

On Thu, 11 Jun 2020, Phillip Wood wrote:

> On 10/06/2020 22:19, Don Goodman-Wilson via GitGitGadget wrote:
> > From: Don Goodman-Wilson <don@goodman-wilson.com>
> >
> > There is a growing number of projects trying to avoid the non-inclusive
> > name `master` in their repositories.
>
> I think it would be helpful to explain why 'master' is no-inclusive even
> if it originates from the concept of a master copy. i.e. it suggests
> master/slave even if git is not based on that concept.

Unfortunately, we do not even have that defense: the term `master` was
copied from BitKeeper, which firmly uses it in the `master/slave` context.
See e.g.
https://mail.gnome.org/archives/desktop-devel-list/2019-May/msg00066.html

I added a _brief_ extension to the context to the first commit's commit
message. However, I do not want to go into details here because _this_
patch series is only about empowering users to change their default main
branch name.

> Have you got some examples of projects that have changed and the names
> that they are using?

Yes, there are plenty examples, and I do not want to pick a tiny subset to
demonstrate that. A more useful resource is probably this post:
https://www.hanselman.com/blog/EasilyRenameYourGitDefaultBranchFromMasterToMain.aspx

> I think it would be helpful if we can agree on a replacement for master
> - if every repository uses a different name for its main branch it adds
> an extra complication for new contributors to those projects.

Sure, and that's what I thought we'd discuss, too, maybe at the meeting I
proposed elsewhere (Emily started a new thread about it:
https://lore.kernel.org/git/20200610222719.GE148632@google.com/).

> >  For existing repositories, this
> > requires manual work. For new repositories, the only way to do that
> > automatically is by copying all of Git's template directory, then
> > hard-coding the desired default branch name into the `.git/HEAD` file,
> > and then configuring `init.templateDir` to point to those copied
> > template files.
> >
> > To make this process much less cumbersome, let's introduce support for
> > `core.defaultBranchName`. That way, users won't need to keep their
> > copied template files up to date, and won't interfere with default hooks
> > installed by their administrators.
> >
> > While at it, also let users set the default branch name via the
> > environment variable `GIT_TEST_DEFAULT_BRANCH_NAME`,
>
> I'm not sure we usually promote the use of GIT_TEST_... environment
> variables outside of the test suite.

True. Together with Alban's suggestion to make this purely work in the
test suite (i.e. not even adjust the C code to respect that environment
variable), you convinced me to (re-)move that part of the commit.

> > diff --git a/refs.c b/refs.c
> > index 224ff66c7bb..8499b3865cb 100644
> > --- a/refs.c
> > +++ b/refs.c
> > @@ -560,6 +560,40 @@ void expand_ref_prefix(struct argv_array *prefixes, const char *prefix)
> >  		argv_array_pushf(prefixes, *p, len, prefix);
> >  }
> >
> > +char *git_default_branch_name(int short_name)
> > +{
> > +	const char *branch_name = getenv("GIT_TEST_DEFAULT_BRANCH_NAME");
> > +	char *from_config = NULL, *prefixed;
> > +
> > +	/*
> > +	 * If the default branch name was not specified via the environment
> > +	 * variable GIT_TEST_DEFAULT_BRANCH_NAME, retrieve it from the config
> > +	 * setting core.defaultBranchName. If neither are set, fall back to the
> > +	 * hard-coded default.
> > +	 */
> > +	if (!branch_name || !*branch_name) {
> > +		if (git_config_get_string("core.defaultbranchname",
> > +					  &from_config) < 0)
> > +			die(_("Could not retrieve `core.defaultBranchName`"));
> > +
> > +		if (from_config)
> > +			branch_name = from_config;
> > +		else
> > +			branch_name = "master";
> > +	}
> > +
> > +	if (short_name)
> > +		return from_config ? from_config : xstrdup(branch_name);
>
> If short_name is set we return without validating the name is that
> intentional?

No, unintentional. Thank you for pointing this out. It will be fixed in v2
(still working on it).

> > +
> > +	/* prepend "refs/heads/" to the branch name */
> > +	prefixed = xstrfmt("refs/heads/%s", branch_name);
> > +	if (check_refname_format(prefixed, 0))
> > +		die(_("invalid default branch name: '%s'"), branch_name);
> > +
> > +	free(from_config);
> > +	return prefixed;
> > +}
> > +
> >  /*
> >   * *string and *len will only be substituted, and *string returned (for
> >   * later free()ing) if the string passed in is a magic short-hand form
> > diff --git a/refs.h b/refs.h
> > index a92d2c74c83..e8d4f6e2f13 100644
> > --- a/refs.h
> > +++ b/refs.h
> > @@ -154,6 +154,12 @@ int repo_dwim_log(struct repository *r, const char *str, int len, struct object_
> >  int dwim_ref(const char *str, int len, struct object_id *oid, char **ref);
> >  int dwim_log(const char *str, int len, struct object_id *oid, char **ref);
> >
> > +/*
> > + * Retrieves the name of the default branch. If `short_name` is non-zero, the
> > + * branch name will be prefixed with "refs/heads/".
>
> Isn't the other way around - the branch name is prefixed with
> "refs/heads/" if short is zero.

Absolutely. Thank you for your careful review, I read past this at least
half a dozen times.

> > + */
> > +char *git_default_branch_name(int short_name);
> > +
> >  /*
> >   * A ref_transaction represents a collection of reference updates that
> >   * should succeed or fail together.
> > diff --git a/t/t0001-init.sh b/t/t0001-init.sh
> > index 1edd5aeb8f0..b144cd8f46b 100755
> > --- a/t/t0001-init.sh
> > +++ b/t/t0001-init.sh
> > @@ -464,4 +464,24 @@ test_expect_success MINGW 'redirect std handles' '
> >  	grep "Needed a single revision" output.txt
> >  '
> >
> > +test_expect_success 'custom default branch name from config' '
> > +	git config --global core.defaultbranchname nmb &&
>
> In tests we usually use 'test_config' rather than 'git config' as the
> former automatically cleans up the config at the end of the test.

Right, and in this instance it is `test_config_global`.

> > +	GIT_TEST_DEFAULT_BRANCH_NAME= git init custom-config &&
> > +	git config --global --unset core.defaultbranchname &&
> > +	git -C custom-config symbolic-ref HEAD >actual &&
> > +	grep nmb actual
> > +'
> > +
> > +test_expect_success 'custom default branch name from env' '
> > +	GIT_TEST_DEFAULT_BRANCH_NAME=nmb git init custom-env &&
>
> It would be good to test that this overrides the config setting

Except that we'll make this a thing that is internal to the test suite
now. So this test case can go.

Thank you for helping me improve the patch series!
Dscho