bisect: add support for bisecting bare repositories

This enhances the support for bisecting history in bare repositories.

The "git bisect" command no longer needs to be run inside a repository
with a working tree; it defaults to --no-checkout when run in a bare
repository.

Two tests are included to demonstrate this behaviour.

Suggested-by: Junio C Hamano <gitster@pobox.com>
Reviewed-by: Jonathan Nieder <jrnieder@gmail.com>
Signed-off-by: Jon Seymour <jon.seymour@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Documentation/git-bisect.txt

@@ -273,6 +273,8 @@ it point to the commit that should be tested.
 +
 This option may be useful when the test you would perform in each step
 does not require a checked out tree.
++
+If the repository is bare, `--no-checkout` is assumed.
 
 EXAMPLES
 --------

git-bisect.sh

@@ -29,7 +29,6 @@ Please use "git help bisect" to get the full man page.'
 OPTIONS_SPEC=
 . git-sh-setup
 . git-sh-i18n
-require_work_tree
 
 _x40='[0-9a-f][0-9a-f][0-9a-f][0-9a-f][0-9a-f]'
 _x40="$_x40$_x40$_x40$_x40$_x40$_x40$_x40$_x40"
@@ -79,7 +78,12 @@ bisect_start() {
 	orig_args=$(git rev-parse --sq-quote "$@")
 	bad_seen=0
 	eval=''
-	mode=''
+	if test "z$(git rev-parse --is-bare-repository)" != zfalse
+	then
+		mode=--no-checkout
+	else
+		mode=''
+	fi
 	while [ $# -gt 0 ]; do
 		arg="$1"
 		case "$arg" in

git.c

@@ -320,7 +320,7 @@ static void handle_internal_command(int argc, const char **argv)
 		{ "annotate", cmd_annotate, RUN_SETUP },
 		{ "apply", cmd_apply, RUN_SETUP_GENTLY },
 		{ "archive", cmd_archive },
-		{ "bisect--helper", cmd_bisect__helper, RUN_SETUP | NEED_WORK_TREE },
+		{ "bisect--helper", cmd_bisect__helper, RUN_SETUP },
 		{ "blame", cmd_blame, RUN_SETUP },
 		{ "branch", cmd_branch, RUN_SETUP },
 		{ "bundle", cmd_bundle, RUN_SETUP_GENTLY },

t/t6030-bisect-porcelain.sh

@@ -592,6 +592,37 @@ test_expect_success 'erroring out when using bad path parameters' '
 	grep "bad path parameters" error.txt
 '
 
+test_expect_success 'test bisection on bare repo - --no-checkout specified' '
+	git clone --bare . bare.nocheckout &&
+	(
+		cd bare.nocheckout &&
+		git bisect start --no-checkout &&
+		git bisect good $HASH1 &&
+		git bisect bad $HASH4 &&
+		git bisect run eval \
+			"test \$(git rev-list BISECT_HEAD ^$HASH2 --max-count=1 | wc -l) = 0" \
+			>../nocheckout.log &&
+		git bisect reset
+	) &&
+	grep "$HASH3 is the first bad commit" nocheckout.log
+'
+
+
+test_expect_success 'test bisection on bare repo - --no-checkout defaulted' '
+	git clone --bare . bare.defaulted &&
+	(
+		cd bare.defaulted &&
+		git bisect start &&
+		git bisect good $HASH1 &&
+		git bisect bad $HASH4 &&
+		git bisect run eval \
+			"test \$(git rev-list BISECT_HEAD ^$HASH2 --max-count=1 | wc -l) = 0" \
+			>../defaulted.log &&
+		git bisect reset
+	) &&
+	grep "$HASH3 is the first bad commit" defaulted.log
+'
+
 #
 # This creates a broken branch which cannot be checked out because
 # the tree created has been deleted.