[v3] var: add GIT_DEFAULT_BRANCH variable

Commit Message

Thomas Weißschuh Nov. 3, 2021, 6:53 p.m. UTC

Introduce the logical variable GIT_DEFAULT_BRANCH which represents the
the default branch name that will be used by "git init".

Currently this variable is equivalent to
    git config init.defaultbranch || 'master'

This however will break if at one point the default branch is changed as
indicated by `default_branch_name_advice` in `refs.c`.

By providing this command ahead of time users of git can make their
code forward-compatible.

Helped-by: Johannes Schindelin <[e-mail]>
Signed-off-by: Thomas Weißschuh <[e-mail]>
---

Changes from v1 ( https://lore.kernel.org/git/[e-mail]/ ):
* Replaced the custom subcommand with an internal variable
* Cleaned up the tests

Changes from v2 ( https://lore.kernel.org/git/[e-mail]/ ):
* Removed superfluous error handling
* Switched to better fitting function
* Reworded commit message to be more consistent with the rest of git

 Documentation/git-var.txt |  3 +++
 builtin/var.c             |  7 +++++++
 t/t0007-git-var.sh        | 19 +++++++++++++++++++
 3 files changed, 29 insertions(+)


base-commit: 0cddd84c9f3e9c3d793ec93034ef679335f35e49

Comments

Eric Sunshine Nov. 3, 2021, 7:57 p.m. UTC | #1

On Wed, Nov 3, 2021 at 2:53 PM Thomas Weißschuh <[e-mail]> wrote:
> Introduce the logical variable GIT_DEFAULT_BRANCH which represents the
> the default branch name that will be used by "git init".
> [...]
> Signed-off-by: Thomas Weißschuh <[e-mail]>
> ---
> diff --git a/t/t0007-git-var.sh b/t/t0007-git-var.sh
> @@ -27,6 +27,25 @@ test_expect_success !FAIL_PREREQS,!AUTOIDENT 'requested identities are strict' '
> +test_expect_success 'get GIT_DEFAULT_BRANCH without configuration' '
> +       (
> +               sane_unset GIT_TEST_DEFAULT_INITIAL_BRANCH_NAME &&
> +               echo master >expect &&
> +               git var GIT_DEFAULT_BRANCH >actual &&
> +               test_cmp expect actual
> +       )
> +'

So that we don't have to worry about this test breaking if the default
branch ever is changed, would it make sense to stop hard-coding
"master" here and instead employ the trick that Dscho mentioned
earlier in the thread (i.e. create a dummy repo and ask it for its
default branch)? Something like this (untested):

    (
        sane_unset GIT_TEST_... &&
        git init defbranch &&
        git -C defbranch symbolic-ref --short HEAD >expect &&
        git var GIT_DEFAULT_BRANCH >actual &&
        test_cmp expect actual
    )

> +test_expect_success 'get GIT_DEFAULT_BRANCH with configuration' '
> +       test_config init.defaultbranch foo &&
> +       (
> +               sane_unset GIT_TEST_DEFAULT_INITIAL_BRANCH_NAME &&
> +               echo foo >expect &&
> +               git var GIT_DEFAULT_BRANCH >actual &&
> +               test_cmp expect actual
> +       )
> +'

Junio C Hamano Nov. 3, 2021, 8:04 p.m. UTC | #2

Eric Sunshine <[e-mail]> writes:

> earlier in the thread (i.e. create a dummy repo and ask it for its
> default branch)? Something like this (untested):
>
>     (
>         sane_unset GIT_TEST_... &&
>         git init defbranch &&
>         git -C defbranch symbolic-ref --short HEAD >expect &&
>         git var GIT_DEFAULT_BRANCH >actual &&
>         test_cmp expect actual
>     )

So, the idea is to "observe" what the init command actually does,
and see if that matches the behaviour of the var command?

Sounds like a good way to ensure correctness to me.

Thanks.

Patch

diff --git a/Documentation/git-var.txt b/Documentation/git-var.txt
index 6072f936ab..387cc1b914 100644
--- a/Documentation/git-var.txt
+++ b/Documentation/git-var.txt
@@ -59,6 +59,9 @@  ifdef::git-default-pager[]
     The build you are using chose '{git-default-pager}' as the default.
 endif::git-default-pager[]
 
+GIT_DEFAULT_BRANCH::
+    The name of the first branch created in newly initialized repositories.
+
 SEE ALSO
 --------
 linkgit:git-commit-tree[1]
diff --git a/builtin/var.c b/builtin/var.c
index 6c6f46b4ae..491db27429 100644
--- a/builtin/var.c
+++ b/builtin/var.c
@@ -5,6 +5,7 @@ 
  */
 #include "builtin.h"
 #include "config.h"
+#include "refs.h"
 
 static const char var_usage[] = "git var (-l | <variable>)";
 
@@ -27,6 +28,11 @@  static const char *pager(int flag)
 	return pgm;
 }
 
+static const char *default_branch(int flag)
+{
+	return git_default_branch_name(1);
+}
+
 struct git_var {
 	const char *name;
 	const char *(*read)(int);
@@ -36,6 +42,7 @@  static struct git_var git_vars[] = {
 	{ "GIT_AUTHOR_IDENT",   git_author_info },
 	{ "GIT_EDITOR", editor },
 	{ "GIT_PAGER", pager },
+	{ "GIT_DEFAULT_BRANCH", default_branch },
 	{ "", NULL },
 };
 
diff --git a/t/t0007-git-var.sh b/t/t0007-git-var.sh
index 53af92d571..6b6852e35e 100755
--- a/t/t0007-git-var.sh
+++ b/t/t0007-git-var.sh
@@ -27,6 +27,25 @@  test_expect_success !FAIL_PREREQS,!AUTOIDENT 'requested identities are strict' '
 	)
 '
 
+test_expect_success 'get GIT_DEFAULT_BRANCH without configuration' '
+	(
+		sane_unset GIT_TEST_DEFAULT_INITIAL_BRANCH_NAME &&
+		echo master >expect &&
+		git var GIT_DEFAULT_BRANCH >actual &&
+		test_cmp expect actual
+	)
+'
+
+test_expect_success 'get GIT_DEFAULT_BRANCH with configuration' '
+	test_config init.defaultbranch foo &&
+	(
+		sane_unset GIT_TEST_DEFAULT_INITIAL_BRANCH_NAME &&
+		echo foo >expect &&
+		git var GIT_DEFAULT_BRANCH >actual &&
+		test_cmp expect actual
+	)
+'
+
 # For git var -l, we check only a representative variable;
 # testing the whole output would make our test too brittle with
 # respect to unrelated changes in the test suite's environment.