Implement "git stash branch <newbranch> <stash>"

Restores the stashed state on a new branch rooted at the commit on which
the stash was originally created, so that conflicts caused by subsequent
changes on the original branch can be dealt with.

(Thanks to Junio for this nice idea.)
Signed-off-by: NAbhijit Menon-Sen <ams@toroid.org>
Signed-off-by: NJunio C Hamano <gitster@pobox.com>

Documentation/git-stash.txt

@@ -8,8 +8,11 @@ git-stash - Stash the changes in a dirty working directory away
 SYNOPSIS
 --------
 [verse]
-'git stash' (list | show [<stash>] | apply [<stash>] | clear | drop [<stash>] | pop [<stash>])
+'git stash' list
+'git stash' (show | apply | drop | pop ) [<stash>]
+'git stash' branch <branchname> [<stash>]
 'git stash' [save [<message>]]
+'git stash' clear
 
 DESCRIPTION
 -----------
@@ -81,6 +84,20 @@ tree's changes, but also the index's ones. However, this can fail, when you
 have conflicts (which are stored in the index, where you therefore can no
 longer apply the changes as they were originally).
 
+branch <branchname> [<stash>]::
+
+	Creates and checks out a new branch named `<branchname>` starting from
+	the commit at which the `<stash>` was originally created, applies the
+	changes recorded in `<stash>` to the new working tree and index, then
+	drops the `<stash>` if that completes successfully. When no `<stash>`
+	is given, applies the latest one.
++
+This is useful if the branch on which you ran `git stash save` has
+changed enough that `git stash apply` fails due to conflicts. Since
+the stash is applied on top of the commit that was HEAD at the time
+`git stash` was run, it restores the originally stashed state with
+no conflicts.
+
 clear::
 	Remove all the stashed states. Note that those states will then
 	be subject to pruning, and may be difficult or impossible to recover.

git-stash.sh

@@ -218,6 +218,23 @@ drop_stash () {
 	git rev-parse --verify "$ref_stash@{0}" > /dev/null 2>&1 || clear_stash
 }
 
+apply_to_branch () {
+	have_stash || die 'Nothing to apply'
+
+	test -n "$1" || die 'No branch name specified'
+	branch=$1
+
+	if test -z "$2"
+	then
+		set x "$ref_stash@{0}"
+	fi
+	stash=$2
+
+	git-checkout -b $branch $stash^ &&
+	apply_stash --index $stash &&
+	drop_stash $stash
+}
+
 # Main command set
 case "$1" in
 list)
@@ -264,6 +281,10 @@ pop)
 		drop_stash "$@"
 	fi
 	;;
+branch)
+	shift
+	apply_to_branch "$@"
+	;;
 *)
 	if test $# -eq 0
 	then