stash: introduce 'stash save --keep-index' option

'git stash save' saves local modifications to a new stash, and runs 'git
reset --hard' to revert them to a clean index and work tree.  When the
'--keep-index' option is specified, after that 'git reset --hard' the
previous contents of the index is restored and the work tree is updated
to match the index.  This option is useful if the user wants to commit
only parts of his local modifications, but wants to test those parts
before committing.

Also add support for the completion of the new option, and add an
example use case to the documentation.

Signed-off-by: SZEDER Gábor <szeder@ira.uka.de>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

3 files changed, 51 insertions, 6 deletions

diff --git a/Documentation/git-stash.txt b/Documentation/git-stash.txt
index 23ac33129..8f331ee7d 100644
--- a/Documentation/git-stash.txt
+++ b/Documentation/git-stash.txt
@@ -36,12 +36,15 @@ is also possible).
 OPTIONS
 -------
 
-save [<message>]::
+save [--keep-index] [<message>]::
 
 	Save your local modifications to a new 'stash', and run `git reset
 	--hard` to revert them.  This is the default action when no
 	subcommand is given. The <message> part is optional and gives
 	the description along with the stashed state.
++
+If the `--keep-index` option is used, all changes already added to the
+index are left intact.
 
 list [<options>]::
 
@@ -169,6 +172,23 @@ $ git stash apply
 ... continue hacking ...
 ----------------------------------------------------------------
 
+Testing partial commits::
+
+You can use `git stash save --keep-index` when you want to make two or
+more commits out of the changes in the work tree, and you want to test
+each change before committing:
++
+----------------------------------------------------------------
+... hack hack hack ...
+$ git add --patch foo
+$ git stash save --keep-index
+$ build && run tests
+$ git commit -m 'First part'
+$ git stash apply
+$ build && run tests
+$ git commit -a -m 'Second part'
+----------------------------------------------------------------
+
 SEE ALSO
 --------
 linkgit:git-checkout[1],
diff --git a/contrib/completion/git-completion.bash b/contrib/completion/git-completion.bash
index 3f4614985..595de80ea 100755
--- a/contrib/completion/git-completion.bash
+++ b/contrib/completion/git-completion.bash
@@ -1137,8 +1137,19 @@ _git_show ()
 _git_stash ()
 {
 	local subcommands='save list show apply clear drop pop create'
-	if [ -z "$(__git_find_subcommand "$subcommands")" ]; then
+	local subcommand="$(__git_find_subcommand "$subcommands")"
+	if [ -z "$subcommand" ]; then
 		__gitcomp "$subcommands"
+	else
+		local cur="${COMP_WORDS[COMP_CWORD]}"
+		case "$subcommand,$cur" in
+		save,--*)
+			__gitcomp "--keep-index"
+			;;
+		*)
+			COMPREPLY=()
+			;;
+		esac
 	fi
 }
 
diff --git a/git-stash.sh b/git-stash.sh
index 4938ade58..92531a295 100755
--- a/git-stash.sh
+++ b/git-stash.sh
@@ -86,6 +86,13 @@ create_stash () {
 }
 
 save_stash () {
+	keep_index=
+	case "$1" in
+	--keep-index)
+		keep_index=t
+		shift
+	esac
+
 	stash_msg="$1"
 
 	if no_changes
@@ -104,6 +111,13 @@ save_stash () {
 	git update-ref -m "$stash_msg" $ref_stash $w_commit ||
 		die "Cannot save the current status"
 	printf 'Saved working directory and index state "%s"\n' "$stash_msg"
+
+	git reset --hard
+
+	if test -n "$keep_index" && test -n $i_tree
+	then
+		git read-tree --reset -u $i_tree
+	fi
 }
 
 have_stash () {
@@ -153,7 +167,8 @@ apply_stash () {
 		die "$*: no valid stashed state found"
 
 	unstashed_index_tree=
-	if test -n "$unstash_index" && test "$b_tree" != "$i_tree"
+	if test -n "$unstash_index" && test "$b_tree" != "$i_tree" &&
+			test "$c_tree" != "$i_tree"
 	then
 		git diff-tree --binary $s^2^..$s^2 | git apply --cached
 		test $? -ne 0 &&
@@ -235,7 +250,7 @@ show)
 	;;
 save)
 	shift
-	save_stash "$*" && git-reset --hard
+	save_stash "$*"
 	;;
 apply)
 	shift
@@ -268,8 +283,7 @@ pop)
 	if test $# -eq 0
 	then
 		save_stash &&
-		echo '(To restore them type "git stash apply")' &&
-		git-reset --hard
+		echo '(To restore them type "git stash apply")'
 	else
 		usage
 	fi