[PATCH 3/3] bisect: add --auto-reset to leave when done

["Harald Nordgren via GitGitGadget" <gitgitgadget@gmail.com>]

From: Harald Nordgren <haraldnordgren@gmail.com>

When a bisection finished, "git bisect" reported the first bad commit
but left the session active until "git bisect reset" was run by hand.

Add an "--auto-reset" option, accepted by both "git bisect start" and
"git bisect run", that resets as soon as the first bad commit is found,
returning to the commit checked out before "git bisect start". The flag
is persisted in a BISECT_AUTO_RESET state file and the restoring
checkout is done quietly.

Signed-off-by: Harald Nordgren <haraldnordgren@gmail.com>
---
 Documentation/git-bisect.adoc | 12 ++++++++++--
 bisect.c                      |  2 ++
 builtin/bisect.c              | 19 +++++++++++++++++--
 t/t6030-bisect-porcelain.sh   | 34 ++++++++++++++++++++++++++++++++++
 4 files changed, 63 insertions(+), 4 deletions(-)

diff --git a/Documentation/git-bisect.adoc b/Documentation/git-bisect.adoc
index d2115b2990..1b03dbba7a 100644
--- a/Documentation/git-bisect.adoc
+++ b/Documentation/git-bisect.adoc
@@ -10,7 +10,7 @@ SYNOPSIS
 --------
 [synopsis]
 git bisect start [--term-(bad|new)=<term-new> --term-(good|old)=<term-old>]
-		 [--no-checkout] [--first-parent] [<bad> [<good>...]] [--] [<pathspec>...]
+		 [--no-checkout] [--first-parent] [--auto-reset] [<bad> [<good>...]] [--] [<pathspec>...]
 git bisect (bad|new|<term-new>) [<rev>]
 git bisect (good|old|<term-old>) [<rev>...]
 git bisect terms [--term-(good|old) | --term-(bad|new)]
@@ -20,7 +20,7 @@ git bisect reset [<commit>]
 git bisect (visualize|view)
 git bisect replay <logfile>
 git bisect log
-git bisect run <cmd> [<arg>...]
+git bisect run [--auto-reset] <cmd> [<arg>...]
 git bisect help
 
 DESCRIPTION
@@ -385,6 +385,14 @@ ignored.
 This option is particularly useful in avoiding false positives when a merged
 branch contained broken or non-buildable commits, but the merge itself was OK.
 
+`--auto-reset`::
+	Once the first bad commit is found, clean up the bisection state and
+	return to the commit that was checked out before `git bisect start`,
+	as if `git bisect reset` had been run. The first bad commit is still
+	reported before resetting.
++
+This option may be given to `git bisect start` or to `git bisect run`.
+
 EXAMPLES
 --------
 
diff --git a/bisect.c b/bisect.c
index 94c7028d2a..a34309dd35 100644
--- a/bisect.c
+++ b/bisect.c
@@ -488,6 +488,7 @@ static GIT_PATH_FUNC(git_path_bisect_start, "BISECT_START")
 static GIT_PATH_FUNC(git_path_bisect_log, "BISECT_LOG")
 static GIT_PATH_FUNC(git_path_bisect_terms, "BISECT_TERMS")
 static GIT_PATH_FUNC(git_path_bisect_first_parent, "BISECT_FIRST_PARENT")
+static GIT_PATH_FUNC(git_path_bisect_auto_reset, "BISECT_AUTO_RESET")
 
 static void read_bisect_paths(struct strvec *array)
 {
@@ -1211,6 +1212,7 @@ int bisect_clean_state(void)
 	unlink_or_warn(git_path_bisect_run());
 	unlink_or_warn(git_path_bisect_terms());
 	unlink_or_warn(git_path_bisect_first_parent());
+	unlink_or_warn(git_path_bisect_auto_reset());
 	/*
 	 * Cleanup BISECT_START last to support the --no-checkout option
 	 * introduced in the commit 4796e823a.
diff --git a/builtin/bisect.c b/builtin/bisect.c
index 27d30b549e..b80eccb635 100644
--- a/builtin/bisect.c
+++ b/builtin/bisect.c
@@ -24,11 +24,12 @@ static GIT_PATH_FUNC(git_path_bisect_start, "BISECT_START")
 static GIT_PATH_FUNC(git_path_bisect_log, "BISECT_LOG")
 static GIT_PATH_FUNC(git_path_bisect_names, "BISECT_NAMES")
 static GIT_PATH_FUNC(git_path_bisect_first_parent, "BISECT_FIRST_PARENT")
+static GIT_PATH_FUNC(git_path_bisect_auto_reset, "BISECT_AUTO_RESET")
 static GIT_PATH_FUNC(git_path_bisect_run, "BISECT_RUN")
 
 #define BUILTIN_GIT_BISECT_START_USAGE \
 	N_("git bisect start [--term-(bad|new)=<term-new> --term-(good|old)=<term-old>]\n" \
-	   "                 [--no-checkout] [--first-parent] [<bad> [<good>...]] [--] [<pathspec>...]")
+	   "                 [--no-checkout] [--first-parent] [--auto-reset] [<bad> [<good>...]] [--] [<pathspec>...]")
 #define BUILTIN_GIT_BISECT_BAD_USAGE \
 	N_("git bisect (bad|new|<term-new>) [<rev>]")
 #define BUILTIN_GIT_BISECT_GOOD_USAGE \
@@ -48,7 +49,7 @@ static GIT_PATH_FUNC(git_path_bisect_run, "BISECT_RUN")
 #define BUILTIN_GIT_BISECT_LOG_USAGE \
 	"git bisect log"
 #define BUILTIN_GIT_BISECT_RUN_USAGE \
-	N_("git bisect run <cmd> [<arg>...]")
+	N_("git bisect run [--auto-reset] <cmd> [<arg>...]")
 #define BUILTIN_GIT_BISECT_HELP_USAGE \
 	"git bisect help"
 
@@ -688,6 +689,8 @@ static enum bisect_error bisect_next(struct bisect_terms *terms, const char *pre
 
 	if (res == BISECT_INTERNAL_SUCCESS_1ST_BAD_FOUND) {
 		res = bisect_successful(terms);
+		if (!res && !is_empty_or_missing_file(git_path_bisect_auto_reset()))
+			res = bisect_reset(NULL, 1);
 		return res ? res : BISECT_INTERNAL_SUCCESS_1ST_BAD_FOUND;
 	} else if (res == BISECT_ONLY_SKIPPED_LEFT) {
 		res = bisect_skipped_commits(terms);
@@ -711,6 +714,7 @@ static enum bisect_error bisect_start(struct bisect_terms *terms, int argc,
 {
 	int no_checkout = 0;
 	int first_parent_only = 0;
+	int auto_reset = 0;
 	int i, has_double_dash = 0, must_write_terms = 0, bad_seen = 0;
 	int flags, pathspec_pos;
 	enum bisect_error res = BISECT_OK;
@@ -743,6 +747,8 @@ static enum bisect_error bisect_start(struct bisect_terms *terms, int argc,
 			no_checkout = 1;
 		} else if (!strcmp(arg, "--first-parent")) {
 			first_parent_only = 1;
+		} else if (!strcmp(arg, "--auto-reset")) {
+			auto_reset = 1;
 		} else if (!strcmp(arg, "--term-good") ||
 			 !strcmp(arg, "--term-old")) {
 			i++;
@@ -857,6 +863,9 @@ static enum bisect_error bisect_start(struct bisect_terms *terms, int argc,
 	if (first_parent_only)
 		write_file(git_path_bisect_first_parent(), "\n");
 
+	if (auto_reset)
+		write_file(git_path_bisect_auto_reset(), "\n");
+
 	if (no_checkout) {
 		if (repo_get_oid(the_repository, start_head.buf, &oid) < 0) {
 			res = error(_("invalid ref: '%s'"), start_head.buf);
@@ -1242,6 +1251,12 @@ static int bisect_run(struct bisect_terms *terms, int argc, const char **argv)
 	if (bisect_next_check(terms, NULL))
 		return BISECT_FAILED;
 
+	if (argc && !strcmp(argv[0], "--auto-reset")) {
+		write_file(git_path_bisect_auto_reset(), "\n");
+		argc--;
+		argv++;
+	}
+
 	if (!argc) {
 		error(_("bisect run failed: no command provided."));
 		return BISECT_FAILED;
diff --git a/t/t6030-bisect-porcelain.sh b/t/t6030-bisect-porcelain.sh
index 081116220a..5389ba388c 100755
--- a/t/t6030-bisect-porcelain.sh
+++ b/t/t6030-bisect-porcelain.sh
@@ -453,6 +453,40 @@ test_expect_success '"git bisect run" simple case' '
 	git bisect reset
 '
 
+test_expect_success '"git bisect start --auto-reset" leaves the bisection' '
+	test_when_finished "git bisect reset" &&
+	git bisect start --auto-reset $HASH4 $HASH2 &&
+	git bisect bad &&
+	test_path_is_missing "$(git rev-parse --git-path BISECT_START)"
+'
+
+test_expect_success '"git bisect run --auto-reset" leaves the bisection' '
+	test_when_finished "git bisect reset" &&
+	write_script test_script.sh <<-\EOF &&
+	! grep Another hello >/dev/null
+	EOF
+	git bisect start $HASH4 $HASH2 &&
+	git bisect run --auto-reset ./test_script.sh >my_bisect_log.txt &&
+	grep "$HASH3 is the first .bad. commit" my_bisect_log.txt &&
+	test_path_is_missing "$(git rev-parse --git-path BISECT_START)"
+'
+
+test_expect_success 'without --auto-reset the bisection state is kept' '
+	test_when_finished "git bisect reset" &&
+	git bisect start $HASH4 $HASH2 &&
+	git bisect bad &&
+	test_path_is_file "$(git rev-parse --git-path BISECT_START)"
+'
+
+test_expect_success '--auto-reset does not leak into a later bisection' '
+	test_when_finished "git bisect reset" &&
+	git bisect start --auto-reset $HASH4 $HASH2 &&
+	git bisect bad &&
+	git bisect start $HASH4 $HASH2 &&
+	git bisect bad &&
+	test_path_is_file "$(git rev-parse --git-path BISECT_START)"
+'
+
 # We want to automatically find the commit that
 # added "Ciao" into hello.
 test_expect_success '"git bisect run" with more complex "git bisect start"' '
-- 
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