Re: [PATCH] checkout -d: explicitly detach HEAD even when switching to the tip of a branch

Xavier Maillard [off-list ref] writes:

   > You cannot currently checkout the tip of an existing branch
   > without moving to the branch.
   > 
   > This allows you to detach your HEAD and place it at such a
   > commit, with:
   > 
   >     $ git checkout -d master

   What about

	 $ git checkout master^0

   trick to force detaching?

I love this idea.

Could anybody remind me why we have the "new != old" check here?

diff --git a/git-checkout.sh b/git-checkout.sh
index a7390e8..573a3c0 100755
--- a/git-checkout.sh
+++ b/git-checkout.sh

@@ -170,7 +170,7 @@ describe_detached_head () {
 	}
 }
 
-if test -z "$branch$newbranch" && test "$new" != "$old"
+if test -z "$branch$newbranch"
 then
 	detached="$new"
 	if test -n "$oldbranch" && test -z "$quiet"

I think I do not need an explicit -d option if we just remove
that second test.  It is coming from an ancient commit 91dcdfd3,
and I _think_ it was to prevent something like:

	git-checkout-script v2.6.12^0

from succeeding, while allowing

	git-checkout-script HEAD^0

to be a no-op (as it happens to be naming the same commit).

commit 91dcdfd3b5331d955cfb60edf8930f1b5c142905
Author: Linus Torvalds [off-list ref]
Date:   Mon Jul 11 20:44:20 2005 -0700

    Make "git checkout" create new branches on demand

diff --git a/git-checkout-script b/git-checkout-script
index 48e1da9..7e70338 100755
--- a/git-checkout-script
+++ b/git-checkout-script

@@ -5,10 +5,19 @@ old=$(git-rev-parse HEAD)
 ...

@@ -32,6 +41,16 @@ while [ "$#" != "0" ]; do
 done
 [ -z "$new" ] && new=$old
 
+#
+# If we don't have an old branch that we're switching to,
+# and we don't have a new branch name for the target we
+# are switching to, then we'd better just be checking out
+# what we already had
+#
+[ -z "$branch$newbranch" ] &&
+	[ "$new" != "$old" ] &&
+	die "git checkout: you need to specify a new branch name"
+
 if [ "$force" ]
 then
     git-read-tree --reset $new &&

@@ -47,6 +66,10 @@ fi
 ...