checkout & worktree: introduce checkout.defaultRemote

Introduce a checkout.defaultRemote setting which can be used to
designate a remote to prefer (via checkout.defaultRemote=origin) when
running e.g. "git checkout master" to mean origin/master, even though
there's other remotes that have the "master" branch.

I want this because it's very handy to use this workflow to checkout a
repository and create a topic branch, then get back to a "master" as
retrieved from upstream:

    (
        cd /tmp &&
        rm -rf tbdiff &&
        git clone git@github.com:trast/tbdiff.git &&
        cd tbdiff &&
        git branch -m topic &&
        git checkout master
    )

That will output:

    Branch 'master' set up to track remote branch 'master' from 'origin'.
    Switched to a new branch 'master'

But as soon as a new remote is added (e.g. just to inspect something
from someone else) the DWIMery goes away:

    (
        cd /tmp &&
        rm -rf tbdiff &&
        git clone git@github.com:trast/tbdiff.git &&
        cd tbdiff &&
        git branch -m topic &&
        git remote add avar git@github.com:avar/tbdiff.git &&
        git fetch avar &&
        git checkout master
    )

Will output (without the advice output added earlier in this series):

    error: pathspec 'master' did not match any file(s) known to git.

The new checkout.defaultRemote config allows me to say that whenever
that ambiguity comes up I'd like to prefer "origin", and it'll still
work as though the only remote I had was "origin".

Also adjust the advice.checkoutAmbiguousRemoteBranchName message to
mention this new config setting to the user, the full output on my
git.git is now (the last paragraph is new):

    $ ./git --exec-path=$PWD checkout master
    error: pathspec 'master' did not match any file(s) known to git.
    hint: 'master' matched more than one remote tracking branch.
    hint: We found 26 remotes with a reference that matched. So we fell back
    hint: on trying to resolve the argument as a path, but failed there too!
    hint:
    hint: If you meant to check out a remote tracking branch on, e.g. 'origin',
    hint: you can do so by fully qualifying the name with the --track option:
    hint:
    hint:     git checkout --track origin/<name>
    hint:
    hint: If you'd like to always have checkouts of an ambiguous <name> prefer
    hint: one remote, e.g. the 'origin' remote, consider setting
    hint: checkout.defaultRemote=origin in your config.

I considered splitting this into checkout.defaultRemote and
worktree.defaultRemote, but it's probably less confusing to break our
own rules that anything shared between config should live in core.*
than have two config settings, and I couldn't come up with a short
name under core.* that made sense (core.defaultRemoteForCheckout?).

See also 70c9ac2f19 ("DWIM "git checkout frotz" to "git checkout -b
frotz origin/frotz"", 2009-10-18) which introduced this DWIM feature
to begin with, and 4e85333197 ("worktree: make add <path> <branch>
dwim", 2017-11-26) which added it to git-worktree.

Signed-off-by: Ævar Arnfjörð Bjarmason <avarab@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

1 files changed, 9 insertions, 3 deletions

diff --git a/builtin/checkout.c b/builtin/checkout.c
index baa0274..5b357e9 100644
--- a/builtin/checkout.c
+++ b/builtin/checkout.c
@@ -912,8 +912,10 @@ static int parse_branchname_arg(int argc, const char **argv,
 	 *   (b) If <something> is _not_ a commit, either "--" is present
 	 *       or <something> is not a path, no -t or -b was given, and
 	 *       and there is a tracking branch whose name is <something>
-	 *       in one and only one remote, then this is a short-hand to
-	 *       fork local <something> from that remote-tracking branch.
+	 *       in one and only one remote (or if the branch exists on the
+	 *       remote named in checkout.defaultRemote), then this is a
+	 *       short-hand to fork local <something> from that
+	 *       remote-tracking branch.
 	 *
 	 *   (c) Otherwise, if "--" is present, treat it like case (1).
 	 *
@@ -1277,7 +1279,11 @@ int cmd_checkout(int argc, const char **argv, const char *prefix)
 				 "If you meant to check out a remote tracking branch on, e.g. 'origin',\n"
 				 "you can do so by fully qualifying the name with the --track option:\n"
 				 "\n"
-				 "    git checkout --track origin/<name>"),
+				 "    git checkout --track origin/<name>\n"
+				 "\n"
+				 "If you'd like to always have checkouts of an ambiguous <name> prefer\n"
+				 "one remote, e.g. the 'origin' remote, consider setting\n"
+				 "checkout.defaultRemote=origin in your config."),
 			       argv[0],
 			       dwim_remotes_matched);
 		return ret;