[PATCH] checkout: automerge local changes while switching branches.

When switching branches from A to B, if the working tree has a
local modification at paths that are different between A and B,
we refused the operation saying "cannot merge."  This attempts
to do an automerge for such paths.

Signed-off-by: Junio C Hamano <redacted>

---

 Alex Riesen [off-list ref] writes:

 > On 1/9/06, Junio C Hamano [off-list ref] wrote:
 >> 2. Fix "git checkout <branch>" so that it does a reasonable thing
 >>    even when a dirty path is different in current HEAD and
 >>    destination branch.  Then I could:
 >>
 >>         $ git checkout symref ;# this would not work in the current git
 >>             # it would die like this:
 >>             # $ git checkout symref
 >>             # fatal: Entry 'gitweb.cgi' not uptodate. Cannot merge.
 >
 > That is actually very interesting. I already wished sometimes to be
 > able to switch branches with a dirty working directory (and usually
 > ended up with git diff+checkout+apply).
 > Even if it results in a merge and conflict markers in files it looks
 > like a very practical idea!

 This is still experimental and probably has rough edges, but I
 actually tested it once and it worked fine ;-).

 git-checkout.sh |   24 +++++++++++++++++++++++-
 1 files changed, 23 insertions(+), 1 deletions(-)

7929db987a9aac1d0370b64a8a00ffa13e6bab82

diff --git a/git-checkout.sh b/git-checkout.sh
index 3bbd111..1b2db91 100755
--- a/git-checkout.sh
+++ b/git-checkout.sh

@@ -121,7 +121,29 @@ then
 	git-checkout-index -q -f -u -a
 else
     git-update-index --refresh >/dev/null
-    git-read-tree -m -u $old $new
+    git-read-tree -m -u $old $new || (
+	echo >&2 -n "Try automerge [y/N]? "
+	read yesno
+	case "$yesno" in [yY]*) ;; *) exit 1 ;; esac
+
+	# NEEDSWORK: We may want to reset the index from the $new for
+	# these paths after the automerge happens, but it is not done
+	# yet.  Probably we need to leave unmerged ones alone, and
+	# yank the object name & mode from $new for cleanly merged
+	# paths and stuff them in the index.
+
+	names=`git diff-files --name-only`
+	echo "$names" | git update-index --remove --stdin
+
+	work=`git write-tree` &&
+	git read-tree -m -u $old $work $new || exit
+	if result=`git write-tree 2>/dev/null`
+	then
+	    echo >&2 "Trivially automerged." ;# can this even happen?
+	    exit 0
+	fi
+	git merge-index -o git-merge-one-file -a
+    )
 fi
 
 # 

-- 
1.1.1-g8ecb