[PATCH] scripts: Fix git-checkout.sh to work with non-master branches (take 2)

[Andrew Cooper <andrew.cooper3@xxxxxxxxxx>]

First, rename $TAG to $COMMITTISH.  We already pass tags, branches (well, only
master) and full SHAs into this script.

Xen uses master for QEMU_UPSTREAM_REVISION, and has done for other trees too
in the path.  Apparently we've never specified a different branch, because the
git-clone rune only pulls in the master branch; it does not pull in diverging
branches.

Fix this by performing an explicit fetch of the $COMMITTISH, then checking out
the dummy branch from the FETCH_HEAD.

Suggested-by: Jason Andryuk <jason.andryuk@xxxxxxx>
Signed-off-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
---
CC: Anthony PERARD <anthony.perard@xxxxxxxxxx>
CC: Michal Orzel <michal.orzel@xxxxxxx>
CC: Jan Beulich <jbeulich@xxxxxxxx>
CC: Julien Grall <julien@xxxxxxx>
CC: Roger Pau Monné <roger.pau@xxxxxxxxxx>
CC: Stefano Stabellini <sstabellini@xxxxxxxxxx>
CC: Jason Andryuk <jason.andryuk@xxxxxxx>

A second attempt, given that c554ec124b12 ended up having to be reverted.

https://gitlab.com/xen-project/people/andyhhp/xen/-/pipelines/1683296906
---
 scripts/git-checkout.sh | 9 +++++----
 1 file changed, 5 insertions(+), 4 deletions(-)

diff --git a/scripts/git-checkout.sh b/scripts/git-checkout.sh
index fd4425ac4ee8..a22540a2a5bb 100755
--- a/scripts/git-checkout.sh
+++ b/scripts/git-checkout.sh
@@ -1,12 +1,12 @@
 #!/bin/sh
 
 if test $# -lt 3; then
-       echo "Usage: $0 <tree> <tag> <dir>"
+       echo "Usage: $0 <tree> <committish> <dir>"
        exit 1
 fi
 
 TREE=$1
-TAG=$2
+COMMITTISH=$2
 DIR=$3
 
 set -e
@@ -15,10 +15,11 @@ if test \! -d $DIR-remote; then
        rm -rf $DIR-remote $DIR-remote.tmp
        mkdir -p $DIR-remote.tmp; rmdir $DIR-remote.tmp
        $GIT clone $TREE $DIR-remote.tmp
-       if test "$TAG" ; then
+       if test "$COMMITTISH" ; then
                cd $DIR-remote.tmp
+               $GIT fetch origin $COMMITTISH
                $GIT branch -D dummy >/dev/null 2>&1 ||:
-               $GIT checkout -b dummy $TAG
+               $GIT checkout -b dummy FETCH_HEAD
                cd -
        fi
        mv $DIR-remote.tmp $DIR-remote
-- 
2.39.5