[PATCH] branch: let inherit track a remote-tracking start point

[PATCH] branch: let inherit track a remote-tracking start point

[Harald Nordgren via GitGitGadget]

From: Harald Nordgren <haraldnordgren@gmail.com>

With branch.autoSetupMerge=inherit, "git switch topic" creates a local
topic branch from origin/topic with no upstream, and warns that no
remote is set. "git switch -c topic origin/topic" and an explicit
"--track=inherit" do the same.

A remote-tracking branch has no upstream of its own to copy. Make
inherit use it as the upstream directly, as the default "true" does,
so that inherit sets up tracking in every case the default does.

Signed-off-by: Harald Nordgren <haraldnordgren@gmail.com>
---
    branch: let inherit track a remote-tracking start point
    
    With branch.autoSetupMerge=inherit, make git switch -c new_branch
    upstream/master work without a warning, and sets the remote branch
    upstream/master as the upstream.

Published-As: https://github.com/gitgitgadget/git/releases/tag/pr-git-2450%2FHaraldNordgren%2Fhn%2Fbranch-inherit-remote-tracking-v1
Fetch-It-Via: git fetch https://github.com/gitgitgadget/git pr-git-2450/HaraldNordgren/hn/branch-inherit-remote-tracking-v1
Pull-Request: https://github.com/git/git/pull/2450

 Documentation/config/branch.adoc |  2 +-
 Documentation/git-branch.adoc    |  4 +++-
 branch.c                         |  3 +++
 t/t2060-switch.sh                | 17 +++++++++++++++++
 4 files changed, 24 insertions(+), 2 deletions(-)

diff --git a/Documentation/config/branch.adoc b/Documentation/config/branch.adoc
index c2acd89c99..6d9fbe5353 100644
--- a/Documentation/config/branch.adoc
+++ b/Documentation/config/branch.adoc
@@ -10,7 +10,7 @@
 `always`;; automatic setup is done when the starting point is either a
 	local branch or remote-tracking branch
 `inherit`;; if the starting point has a tracking configuration, it is copied to the new
-	branch
+	branch. A remote-tracking starting point is tracked directly, as with `true`.
 `simple`;; automatic setup is done only when the starting point
 	is a remote-tracking branch and the new branch has the same name as the
 	remote branch.
diff --git a/Documentation/git-branch.adoc b/Documentation/git-branch.adoc
index bfdf459329..238d99fd27 100644
--- a/Documentation/git-branch.adoc
+++ b/Documentation/git-branch.adoc
@@ -280,7 +280,9 @@ remove it anyway.
 The exact upstream branch is chosen depending on the optional argument:
 `-t`, `--track`, or `--track=direct` means to use the start-point branch
 itself as the upstream; `--track=inherit` means to copy the upstream
-configuration of the start-point branch.
+configuration of the start-point branch. A remote-tracking start-point
+has no upstream of its own, so `--track=inherit` uses it as the upstream
+directly.
 +
 The `branch.autoSetupMerge` configuration variable specifies how `git switch`,
 `git checkout` and `git branch` should behave when neither `--track` nor
diff --git a/branch.c b/branch.c
index 22f4f46b96..2c23179775 100644
--- a/branch.c
+++ b/branch.c
@@ -263,6 +263,9 @@ static void setup_tracking(const char *new_ref, const char *orig_ref,
 	if (!track)
 		BUG("asked to set up tracking, but tracking is disallowed");
 
+	if (track == BRANCH_TRACK_INHERIT && !starts_with(orig_ref, "refs/heads/"))
+		track = BRANCH_TRACK_REMOTE;
+
 	memset(&tracking, 0, sizeof(tracking));
 	tracking.spec.dst = (char *)orig_ref;
 	tracking.srcs = &tracking_srcs;
diff --git a/t/t2060-switch.sh b/t/t2060-switch.sh
index cec2fe6876..da9d01ab84 100755
--- a/t/t2060-switch.sh
+++ b/t/t2060-switch.sh
@@ -146,6 +146,23 @@ test_expect_success 'tracking info copied with autoSetupMerge=inherit' '
 	test_cmp_config "" --default "" branch.main2.merge
 '
 
+test_expect_success 'autoSetupMerge=inherit tracks a remote-tracking start point' '
+	git clone . downstream &&
+	(
+		cd downstream &&
+		git config branch.autoSetupMerge inherit &&
+		git switch -c new_branch origin/main &&
+		git status >../actual &&
+		cat >expect <<-EOF &&
+		On branch new_branch
+		Your branch is up to date with ${SQ}origin/main${SQ}.
+
+		nothing to commit, working tree clean
+		EOF
+		test_cmp expect ../actual
+	)
+'
+
 test_expect_success 'switch back when temporarily detached and checked out elsewhere ' '
 	test_when_finished "
 		git worktree remove wt1 ||:

base-commit: f57c9a73884400380bddd172acc88b569834f909
-- 
gitgitgadget

Re: [PATCH] branch: let inherit track a remote-tracking start point

[Junio C Hamano]

"Harald Nordgren via GitGitGadget" <gitgitgadget@gmail.com> writes:

>  `inherit`;; if the starting point has a tracking configuration, it is copied to the new
> -	branch
> +	branch. A remote-tracking starting point is tracked directly, as with `true`.

That is "A remote-tracking branch given as a starting point", not "A
remote-tracking starting point".  Don't abbreviate and drop "branch".

If a starting point is not a remote-tracking branch, shouldn't the
same thing happen, by the way?  IOW, shouldn't the updated text and
behaviour be more like

	`inherit`;; if the starting point has a tracking
	configuration, it is copied to the new branch.  Otherwise,
	the new branch is set to track the starting point itself.

I am not sure if it is the users of `inherit` want that forking a
new branch from something that they know is *not* tracking anything
suddenly starts to track the starting point (whether it is a
remote-tracking branch or something else).

Looking at the originating commit d3115660b4 (branch: add flags and
config to inherit tracking, 2021-12-20), it only talks about what
they want to do when the starting point does track something, and
forgets to say what they want when it does not track anything (the
author CC'ed in case he retains the memory of the motivation from 5
years ago), but if you ask me _now_, not doing anything, i.e., the
behaviour the old commit happened to have implemented without
explanation does sound like the right thing to do.

What we should do if this change of behaviour turns out to be
undesirable?

Perhaps `inherit` should gain a synonym `inherit-or-ignore` for
those who prefer the current behaviour, and we want two extra
behaviours, `inherit-or-fail` that complains and dies if the
specified starting point does not have anything for the new branch
to inherit, and `inherit-or-direct` that uses the fallback
definition, or something?