Merge branch 'al/bisect-first-parent'

"git bisect" learns the "--first-parent" option to find the first
breakage along the first-parent chain.

* al/bisect-first-parent:
  bisect: combine args passed to find_bisection()
  bisect: introduce first-parent flag
  cmd_bisect__helper: defer parsing no-checkout flag
  rev-list: allow bisect and first-parent flags
  t6030: modernize "git bisect run" tests

Documentation/git-bisect.txt

@@ -17,7 +17,7 @@ The command takes various subcommands, and different options depending
 on the subcommand:
 
  git bisect start [--term-{old,good}=<term> --term-{new,bad}=<term>]
-		  [--no-checkout] [<bad> [<good>...]] [--] [<paths>...]
+		  [--no-checkout] [--first-parent] [<bad> [<good>...]] [--] [<paths>...]
  git bisect (bad|new|<term-new>) [<rev>]
  git bisect (good|old|<term-old>) [<rev>...]
  git bisect terms [--term-good | --term-bad]
@@ -365,6 +365,17 @@ does not require a checked out tree.
 +
 If the repository is bare, `--no-checkout` is assumed.
 
+--first-parent::
++
+Follow only the first parent commit upon seeing a merge commit.
++
+In detecting regressions introduced through the merging of a branch, the merge
+commit will be identified as introduction of the bug and its ancestors will be
+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.
+
 EXAMPLES
 --------
 

Documentation/rev-list-options.txt

@@ -128,8 +128,7 @@ parents) and `--max-parents=-1` (negative numbers denote no upper limit).
 	because merges into a topic branch tend to be only about
 	adjusting to updated upstream from time to time, and
 	this option allows you to ignore the individual commits
-	brought in to your history by such a merge. Cannot be
-	combined with --bisect.
+	brought in to your history by such a merge.
 
 --not::
 	Reverses the meaning of the '{caret}' prefix (or lack thereof)
@@ -207,7 +206,7 @@ ifndef::git-rev-list[]
 	Pretend as if the bad bisection ref `refs/bisect/bad`
 	was listed and as if it was followed by `--not` and the good
 	bisection refs `refs/bisect/good-*` on the command
-	line. Cannot be combined with --first-parent.
+	line.
 endif::git-rev-list[]
 
 --stdin::
@@ -743,7 +742,7 @@ outputs 'midpoint', the output of the two commands
 would be of roughly the same length.  Finding the change which
 introduces a regression is thus reduced to a binary search: repeatedly
 generate and test new 'midpoint's until the commit chain is of length
-one. Cannot be combined with --first-parent.
+one.
 
 --bisect-vars::
 	This calculates the same as `--bisect`, except that refs in

bisect.c

@@ -15,6 +15,7 @@
 #include "commit-slab.h"
 #include "commit-reach.h"
 #include "object-store.h"
+#include "dir.h"
 
 static struct oid_array good_revs;
 static struct oid_array skipped_revs;
@@ -88,15 +89,16 @@ static inline void weight_set(struct commit_list *elem, int weight)
 	**commit_weight_at(&commit_weight, elem->item) = weight;
 }
 
-static int count_interesting_parents(struct commit *commit)
+static int count_interesting_parents(struct commit *commit, unsigned bisect_flags)
 {
 	struct commit_list *p;
 	int count;
 
 	for (count = 0, p = commit->parents; p; p = p->next) {
-		if (p->item->object.flags & UNINTERESTING)
-			continue;
-		count++;
+		if (!(p->item->object.flags & UNINTERESTING))
+			count++;
+		if (bisect_flags & FIND_BISECTION_FIRST_PARENT_ONLY)
+			break;
 	}
 	return count;
 }
@@ -135,7 +137,7 @@ static void show_list(const char *debug, int counted, int nr,
 	for (p = list; p; p = p->next) {
 		struct commit_list *pp;
 		struct commit *commit = p->item;
-		unsigned flags = commit->object.flags;
+		unsigned commit_flags = commit->object.flags;
 		enum object_type type;
 		unsigned long size;
 		char *buf = read_object_file(&commit->object.oid, &type,
@@ -144,9 +146,9 @@ static void show_list(const char *debug, int counted, int nr,
 		int subject_len;
 
 		fprintf(stderr, "%c%c%c ",
-			(flags & TREESAME) ? ' ' : 'T',
-			(flags & UNINTERESTING) ? 'U' : ' ',
-			(flags & COUNTED) ? 'C' : ' ');
+			(commit_flags & TREESAME) ? ' ' : 'T',
+			(commit_flags & UNINTERESTING) ? 'U' : ' ',
+			(commit_flags & COUNTED) ? 'C' : ' ');
 		if (*commit_weight_at(&commit_weight, p->item))
 			fprintf(stderr, "%3d", weight(p));
 		else
@@ -171,9 +173,9 @@ static struct commit_list *best_bisection(struct commit_list *list, int nr)
 	best = list;
 	for (p = list; p; p = p->next) {
 		int distance;
-		unsigned flags = p->item->object.flags;
+		unsigned commit_flags = p->item->object.flags;
 
-		if (flags & TREESAME)
+		if (commit_flags & TREESAME)
 			continue;
 		distance = weight(p);
 		if (nr - distance < distance)
@@ -212,9 +214,9 @@ static struct commit_list *best_bisection_sorted(struct commit_list *list, int n
 
 	for (p = list, cnt = 0; p; p = p->next) {
 		int distance;
-		unsigned flags = p->item->object.flags;
+		unsigned commit_flags = p->item->object.flags;
 
-		if (flags & TREESAME)
+		if (commit_flags & TREESAME)
 			continue;
 		distance = weight(p);
 		if (nr - distance < distance)
@@ -259,7 +261,7 @@ static struct commit_list *best_bisection_sorted(struct commit_list *list, int n
  */
 static struct commit_list *do_find_bisection(struct commit_list *list,
 					     int nr, int *weights,
-					     int find_all)
+					     unsigned bisect_flags)
 {
 	int n, counted;
 	struct commit_list *p;
@@ -268,12 +270,12 @@ static struct commit_list *do_find_bisection(struct commit_list *list,
 
 	for (n = 0, p = list; p; p = p->next) {
 		struct commit *commit = p->item;
-		unsigned flags = commit->object.flags;
+		unsigned commit_flags = commit->object.flags;
 
 		*commit_weight_at(&commit_weight, p->item) = &weights[n++];
-		switch (count_interesting_parents(commit)) {
+		switch (count_interesting_parents(commit, bisect_flags)) {
 		case 0:
-			if (!(flags & TREESAME)) {
+			if (!(commit_flags & TREESAME)) {
 				weight_set(p, 1);
 				counted++;
 				show_list("bisection 2 count one",
@@ -314,11 +316,13 @@ static struct commit_list *do_find_bisection(struct commit_list *list,
 			continue;
 		if (weight(p) != -2)
 			continue;
+		if (bisect_flags & FIND_BISECTION_FIRST_PARENT_ONLY)
+			BUG("shouldn't be calling count-distance in fp mode");
 		weight_set(p, count_distance(p));
 		clear_distance(list);
 
 		/* Does it happen to be at exactly half-way? */
-		if (!find_all && halfway(p, nr))
+		if (!(bisect_flags & FIND_BISECTION_ALL) && halfway(p, nr))
 			return p;
 		counted++;
 	}
@@ -328,11 +332,14 @@ static struct commit_list *do_find_bisection(struct commit_list *list,
 	while (counted < nr) {
 		for (p = list; p; p = p->next) {
 			struct commit_list *q;
-			unsigned flags = p->item->object.flags;
+			unsigned commit_flags = p->item->object.flags;
 
 			if (0 <= weight(p))
 				continue;
-			for (q = p->item->parents; q; q = q->next) {
+
+			for (q = p->item->parents;
+			     q;
+			     q = bisect_flags & FIND_BISECTION_FIRST_PARENT_ONLY ? NULL : q->next) {
 				if (q->item->object.flags & UNINTERESTING)
 					continue;
 				if (0 <= weight(q))
@@ -346,7 +353,7 @@ static struct commit_list *do_find_bisection(struct commit_list *list,
 			 * add one for p itself if p is to be counted,
 			 * otherwise inherit it from q directly.
 			 */
-			if (!(flags & TREESAME)) {
+			if (!(commit_flags & TREESAME)) {
 				weight_set(p, weight(q)+1);
 				counted++;
 				show_list("bisection 2 count one",
@@ -356,21 +363,21 @@ static struct commit_list *do_find_bisection(struct commit_list *list,
 				weight_set(p, weight(q));
 
 			/* Does it happen to be at exactly half-way? */
-			if (!find_all && halfway(p, nr))
+			if (!(bisect_flags & FIND_BISECTION_ALL) && halfway(p, nr))
 				return p;
 		}
 	}
 
 	show_list("bisection 2 counted all", counted, nr, list);
 
-	if (!find_all)
+	if (!(bisect_flags & FIND_BISECTION_ALL))
 		return best_bisection(list, nr);
 	else
 		return best_bisection_sorted(list, nr);
 }
 
 void find_bisection(struct commit_list **commit_list, int *reaches,
-		    int *all, int find_all)
+		    int *all, unsigned bisect_flags)
 {
 	int nr, on_list;
 	struct commit_list *list, *p, *best, *next, *last;
@@ -386,16 +393,16 @@ void find_bisection(struct commit_list **commit_list, int *reaches,
 	for (nr = on_list = 0, last = NULL, p = *commit_list;
 	     p;
 	     p = next) {
-		unsigned flags = p->item->object.flags;
+		unsigned commit_flags = p->item->object.flags;
 
 		next = p->next;
-		if (flags & UNINTERESTING) {
+		if (commit_flags & UNINTERESTING) {
 			free(p);
 			continue;
 		}
 		p->next = last;
 		last = p;
-		if (!(flags & TREESAME))
+		if (!(commit_flags & TREESAME))
 			nr++;
 		on_list++;
 	}
@@ -406,9 +413,9 @@ void find_bisection(struct commit_list **commit_list, int *reaches,
 	weights = xcalloc(on_list, sizeof(*weights));
 
 	/* Do the real work of finding bisection commit. */
-	best = do_find_bisection(list, nr, weights, find_all);
+	best = do_find_bisection(list, nr, weights, bisect_flags);
 	if (best) {
-		if (!find_all) {
+		if (!(bisect_flags & FIND_BISECTION_ALL)) {
 			list->item = best->item;
 			free_commit_list(list->next);
 			best = list;
@@ -454,6 +461,7 @@ static GIT_PATH_FUNC(git_path_bisect_run, "BISECT_RUN")
 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_head_name, "head-name")
 
 static void read_bisect_paths(struct strvec *array)
@@ -983,7 +991,7 @@ void read_bisect_terms(const char **read_bad, const char **read_good)
  * If no_checkout is non-zero, the bisection process does not
  * checkout the trial commit but instead simply updates BISECT_HEAD.
  */
-enum bisect_error bisect_next_all(struct repository *r, const char *prefix, int no_checkout)
+enum bisect_error bisect_next_all(struct repository *r, const char *prefix)
 {
 	struct rev_info revs;
 	struct commit_list *tried;
@@ -991,21 +999,31 @@ enum bisect_error bisect_next_all(struct repository *r, const char *prefix, int
 	enum bisect_error res = BISECT_OK;
 	struct object_id *bisect_rev;
 	char *steps_msg;
+	int no_checkout = ref_exists("BISECT_HEAD");
+	unsigned bisect_flags = 0;
 
 	read_bisect_terms(&term_bad, &term_good);
 	if (read_bisect_refs())
 		die(_("reading bisect refs failed"));
 
+	if (file_exists(git_path_bisect_first_parent()))
+		bisect_flags |= FIND_BISECTION_FIRST_PARENT_ONLY;
+
+	if (skipped_revs.nr)
+		bisect_flags |= FIND_BISECTION_ALL;
+
 	res = check_good_are_ancestors_of_bad(r, prefix, no_checkout);
 	if (res)
 		return res;
 
 	bisect_rev_setup(r, &revs, prefix, "%s", "^%s", 1);
+
+	revs.first_parent_only = !!(bisect_flags & FIND_BISECTION_FIRST_PARENT_ONLY);
 	revs.limited = 1;
 
 	bisect_common(&revs);
 
-	find_bisection(&revs.commits, &reaches, &all, !!skipped_revs.nr);
+	find_bisection(&revs.commits, &reaches, &all, bisect_flags);
 	revs.commits = managed_skipped(revs.commits, &tried);
 
 	if (!revs.commits) {
@@ -1133,6 +1151,7 @@ int bisect_clean_state(void)
 	unlink_or_warn(git_path_bisect_names());
 	unlink_or_warn(git_path_bisect_run());
 	unlink_or_warn(git_path_bisect_terms());
+	unlink_or_warn(git_path_bisect_first_parent());
 	/* Cleanup head-name if it got left by an old version of git-bisect */
 	unlink_or_warn(git_path_head_name());
 	/*

bisect.h

@@ -12,7 +12,7 @@ struct repository;
  * best commit, as chosen by `find_all`.
  */
 void find_bisection(struct commit_list **list, int *reaches, int *all,
-		    int find_all);
+		    unsigned bisect_flags);
 
 struct commit_list *filter_skipped(struct commit_list *list,
 				   struct commit_list **tried,
@@ -23,6 +23,9 @@ struct commit_list *filter_skipped(struct commit_list *list,
 #define BISECT_SHOW_ALL		(1<<0)
 #define REV_LIST_QUIET		(1<<1)
 
+#define FIND_BISECTION_ALL			(1u<<0)
+#define FIND_BISECTION_FIRST_PARENT_ONLY	(1u<<1)
+
 struct rev_list_info {
 	struct rev_info *revs;
 	int flags;
@@ -58,9 +61,7 @@ enum bisect_error {
 	BISECT_INTERNAL_SUCCESS_MERGE_BASE = -11
 };
 
-enum bisect_error bisect_next_all(struct repository *r,
-		    const char *prefix,
-		    int no_checkout);
+enum bisect_error bisect_next_all(struct repository *r, const char *prefix);
 
 int estimate_bisect_steps(int all);
 

builtin/bisect--helper.c

@@ -16,9 +16,10 @@ 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_head_name, "head-name")
 static GIT_PATH_FUNC(git_path_bisect_names, "BISECT_NAMES")
+static GIT_PATH_FUNC(git_path_bisect_first_parent, "BISECT_FIRST_PARENT")
 
 static const char * const git_bisect_helper_usage[] = {
-	N_("git bisect--helper --next-all [--no-checkout]"),
+	N_("git bisect--helper --next-all"),
 	N_("git bisect--helper --write-terms <bad_term> <good_term>"),
 	N_("git bisect--helper --bisect-clean-state"),
 	N_("git bisect--helper --bisect-reset [<commit>]"),
@@ -27,7 +28,7 @@ static const char * const git_bisect_helper_usage[] = {
 	N_("git bisect--helper --bisect-next-check <good_term> <bad_term> [<term>]"),
 	N_("git bisect--helper --bisect-terms [--term-good | --term-old | --term-bad | --term-new]"),
 	N_("git bisect--helper --bisect-start [--term-{old,good}=<term> --term-{new,bad}=<term>]"
-					     "[--no-checkout] [<bad> [<good>...]] [--] [<paths>...]"),
+					    " [--no-checkout] [--first-parent] [<bad> [<good>...]] [--] [<paths>...]"),
 	NULL
 };
 
@@ -420,9 +421,10 @@ finish:
 	return res;
 }
 
-static int bisect_start(struct bisect_terms *terms, int no_checkout,
-			const char **argv, int argc)
+static int bisect_start(struct bisect_terms *terms, const char **argv, int argc)
 {
+	int no_checkout = 0;
+	int first_parent_only = 0;
 	int i, has_double_dash = 0, must_write_terms = 0, bad_seen = 0;
 	int flags, pathspec_pos, res = 0;
 	struct string_list revs = STRING_LIST_INIT_DUP;
@@ -452,6 +454,8 @@ static int bisect_start(struct bisect_terms *terms, int no_checkout,
 			break;
 		} else if (!strcmp(arg, "--no-checkout")) {
 			no_checkout = 1;
+		} else if (!strcmp(arg, "--first-parent")) {
+			first_parent_only = 1;
 		} else if (!strcmp(arg, "--term-good") ||
 			 !strcmp(arg, "--term-old")) {
 			i++;
@@ -576,6 +580,9 @@ static int bisect_start(struct bisect_terms *terms, int no_checkout,
 	 */
 	write_file(git_path_bisect_start(), "%s\n", start_head.buf);
 
+	if (first_parent_only)
+		write_file(git_path_bisect_first_parent(), "\n");
+
 	if (no_checkout) {
 		if (get_oid(start_head.buf, &oid) < 0) {
 			res = error(_("invalid ref: '%s'"), start_head.buf);
@@ -631,7 +638,7 @@ int cmd_bisect__helper(int argc, const char **argv, const char *prefix)
 		BISECT_TERMS,
 		BISECT_START
 	} cmdmode = 0;
-	int no_checkout = 0, res = 0, nolog = 0;
+	int res = 0, nolog = 0;
 	struct option options[] = {
 		OPT_CMDMODE(0, "next-all", &cmdmode,
 			 N_("perform 'git bisect next'"), NEXT_ALL),
@@ -653,8 +660,6 @@ int cmd_bisect__helper(int argc, const char **argv, const char *prefix)
 			 N_("print out the bisect terms"), BISECT_TERMS),
 		OPT_CMDMODE(0, "bisect-start", &cmdmode,
 			 N_("start the bisect session"), BISECT_START),
-		OPT_BOOL(0, "no-checkout", &no_checkout,
-			 N_("update BISECT_HEAD instead of checking out the current commit")),
 		OPT_BOOL(0, "no-log", &nolog,
 			 N_("no log for BISECT_WRITE")),
 		OPT_END()
@@ -670,7 +675,7 @@ int cmd_bisect__helper(int argc, const char **argv, const char *prefix)
 
 	switch (cmdmode) {
 	case NEXT_ALL:
-		res = bisect_next_all(the_repository, prefix, no_checkout);
+		res = bisect_next_all(the_repository, prefix);
 		break;
 	case WRITE_TERMS:
 		if (argc != 2)
@@ -712,7 +717,7 @@ int cmd_bisect__helper(int argc, const char **argv, const char *prefix)
 		break;
 	case BISECT_START:
 		set_terms(&terms, "bad", "good");
-		res = bisect_start(&terms, no_checkout, argv, argc);
+		res = bisect_start(&terms, argv, argc);
 		break;
 	default:
 		return error("BUG: unknown subcommand '%d'", cmdmode);

builtin/rev-list.c

@@ -637,8 +637,15 @@ int cmd_rev_list(int argc, const char **argv, const char *prefix)
 
 	if (bisect_list) {
 		int reaches, all;
+		unsigned bisect_flags = 0;
 
-		find_bisection(&revs.commits, &reaches, &all, bisect_find_all);
+		if (bisect_find_all)
+			bisect_flags |= FIND_BISECTION_ALL;
+
+		if (revs.first_parent_only)
+			bisect_flags |= FIND_BISECTION_FIRST_PARENT_ONLY;
+
+		find_bisection(&revs.commits, &reaches, &all, bisect_flags);
 
 		if (bisect_show_vars)
 			return show_bisect_vars(&info, reaches, all);

git-bisect.sh

@@ -153,7 +153,7 @@ bisect_next() {
 	git bisect--helper --bisect-next-check $TERM_GOOD $TERM_BAD $TERM_GOOD|| exit
 
 	# Perform all bisection computation, display and checkout
-	git bisect--helper --next-all $(git rev-parse --verify -q BISECT_HEAD > /dev/null && echo --no-checkout)
+	git bisect--helper --next-all
 	res=$?
 
 	# Check if we should exit because bisection is finished

revision.c

@@ -2889,9 +2889,6 @@ int setup_revisions(int argc, const char **argv, struct rev_info *revs, struct s
 	if (!revs->reflog_info && revs->grep_filter.use_reflog_filter)
 		die("cannot use --grep-reflog without --walk-reflogs");
 
-	if (revs->first_parent_only && revs->bisect)
-		die(_("--first-parent is incompatible with --bisect"));
-
 	if (revs->line_level_traverse &&
 	    (revs->diffopt.output_format & ~(DIFF_FORMAT_PATCH | DIFF_FORMAT_NO_OUTPUT)))
 		die(_("-L does not yet support diff formats besides -p and -s"));

t/t6000-rev-list-misc.sh

@@ -128,8 +128,8 @@ test_expect_success 'rev-list can negate index objects' '
 	test_cmp expect actual
 '
 
-test_expect_success '--bisect and --first-parent can not be combined' '
-	test_must_fail git rev-list --bisect --first-parent HEAD
+test_expect_success '--bisect and --first-parent can be combined' '
+	git rev-list --bisect --first-parent HEAD
 '
 
 test_expect_success '--header shows a NUL after each commit' '

t/t6002-rev-list-bisect.sh

@@ -263,4 +263,49 @@ test_expect_success 'rev-parse --bisect can default to good/bad refs' '
 	test_cmp expect.sorted actual.sorted
 '
 
+test_output_expect_success '--bisect --first-parent' 'git rev-list --bisect --first-parent E ^F' <<EOF
+e4
+EOF
+
+test_output_expect_success '--first-parent' 'git rev-list --first-parent E ^F' <<EOF
+E
+e1
+e2
+e3
+e4
+e5
+e6
+e7
+e8
+EOF
+
+test_output_expect_success '--bisect-vars --first-parent' 'git rev-list --bisect-vars --first-parent E ^F' <<EOF
+bisect_rev='e5'
+bisect_nr=4
+bisect_good=4
+bisect_bad=3
+bisect_all=9
+bisect_steps=2
+EOF
+
+test_expect_success '--bisect-all --first-parent' '
+	cat >expect.unsorted <<-EOF &&
+	$(git rev-parse E) (tag: E, dist=0)
+	$(git rev-parse e1) (tag: e1, dist=1)
+	$(git rev-parse e2) (tag: e2, dist=2)
+	$(git rev-parse e3) (tag: e3, dist=3)
+	$(git rev-parse e4) (tag: e4, dist=4)
+	$(git rev-parse e5) (tag: e5, dist=4)
+	$(git rev-parse e6) (tag: e6, dist=3)
+	$(git rev-parse e7) (tag: e7, dist=2)
+	$(git rev-parse e8) (tag: e8, dist=1)
+	EOF
+
+	# expect results to be ordered by distance (descending),
+	# commit hash (ascending)
+	sort -k4,4r -k1,1 expect.unsorted >expect &&
+	git rev-list --bisect-all --first-parent E ^F >actual &&
+	test_cmp expect actual
+'
+
 test_done

t/t6030-bisect-porcelain.sh

@@ -243,32 +243,30 @@ test_expect_success 'bisect skip: with commit both bad and skipped' '
 '
 
 # We want to automatically find the commit that
-# introduced "Another" into hello.
-test_expect_success \
-    '"git bisect run" simple case' \
-    'echo "#"\!"/bin/sh" > test_script.sh &&
-     echo "grep Another hello > /dev/null" >> test_script.sh &&
-     echo "test \$? -ne 0" >> test_script.sh &&
-     chmod +x test_script.sh &&
-     git bisect start &&
-     git bisect good $HASH1 &&
-     git bisect bad $HASH4 &&
-     git bisect run ./test_script.sh > my_bisect_log.txt &&
-     grep "$HASH3 is the first bad commit" my_bisect_log.txt &&
-     git bisect reset'
+# added "Another" into hello.
+test_expect_success '"git bisect run" simple case' '
+	write_script test_script.sh <<-\EOF &&
+	! grep Another hello >/dev/null
+	EOF
+	git bisect start &&
+	git bisect good $HASH1 &&
+	git bisect bad $HASH4 &&
+	git bisect run ./test_script.sh >my_bisect_log.txt &&
+	grep "$HASH3 is the first bad commit" my_bisect_log.txt &&
+	git bisect reset
+'
 
 # We want to automatically find the commit that
-# introduced "Ciao" into hello.
-test_expect_success \
-    '"git bisect run" with more complex "git bisect start"' \
-    'echo "#"\!"/bin/sh" > test_script.sh &&
-     echo "grep Ciao hello > /dev/null" >> test_script.sh &&
-     echo "test \$? -ne 0" >> test_script.sh &&
-     chmod +x test_script.sh &&
-     git bisect start $HASH4 $HASH1 &&
-     git bisect run ./test_script.sh > my_bisect_log.txt &&
-     grep "$HASH4 is the first bad commit" my_bisect_log.txt &&
-     git bisect reset'
+# added "Ciao" into hello.
+test_expect_success '"git bisect run" with more complex "git bisect start"' '
+	write_script test_script.sh <<-\EOF &&
+	! grep Ciao hello >/dev/null
+	EOF
+	git bisect start $HASH4 $HASH1 &&
+	git bisect run ./test_script.sh >my_bisect_log.txt &&
+	grep "$HASH4 is the first bad commit" my_bisect_log.txt &&
+	git bisect reset
+'
 
 # $HASH1 is good, $HASH5 is bad, we skip $HASH3
 # but $HASH4 is good,
@@ -295,24 +293,17 @@ HASH6=
 test_expect_success 'bisect run & skip: cannot tell between 2' '
 	add_line_into_file "6: Yet a line." hello &&
 	HASH6=$(git rev-parse --verify HEAD) &&
-	echo "#"\!"/bin/sh" > test_script.sh &&
-	echo "sed -ne \\\$p hello | grep Ciao > /dev/null && exit 125" >> test_script.sh &&
-	echo "grep line hello > /dev/null" >> test_script.sh &&
-	echo "test \$? -ne 0" >> test_script.sh &&
-	chmod +x test_script.sh &&
+	write_script test_script.sh <<-\EOF &&
+	sed -ne \$p hello | grep Ciao >/dev/null && exit 125
+	! grep line hello >/dev/null
+	EOF
 	git bisect start $HASH6 $HASH1 &&
-	if git bisect run ./test_script.sh > my_bisect_log.txt
-	then
-		echo Oops, should have failed.
-		false
-	else
-		test $? -eq 2 &&
-		grep "first bad commit could be any of" my_bisect_log.txt &&
-		! grep $HASH3 my_bisect_log.txt &&
-		! grep $HASH6 my_bisect_log.txt &&
-		grep $HASH4 my_bisect_log.txt &&
-		grep $HASH5 my_bisect_log.txt
-	fi
+	test_expect_code 2 git bisect run ./test_script.sh >my_bisect_log.txt &&
+	grep "first bad commit could be any of" my_bisect_log.txt &&
+	! grep $HASH3 my_bisect_log.txt &&
+	! grep $HASH6 my_bisect_log.txt &&
+	grep $HASH4 my_bisect_log.txt &&
+	grep $HASH5 my_bisect_log.txt
 '
 
 HASH7=
@@ -320,14 +311,13 @@ test_expect_success 'bisect run & skip: find first bad' '
 	git bisect reset &&
 	add_line_into_file "7: Should be the last line." hello &&
 	HASH7=$(git rev-parse --verify HEAD) &&
-	echo "#"\!"/bin/sh" > test_script.sh &&
-	echo "sed -ne \\\$p hello | grep Ciao > /dev/null && exit 125" >> test_script.sh &&
-	echo "sed -ne \\\$p hello | grep day > /dev/null && exit 125" >> test_script.sh &&
-	echo "grep Yet hello > /dev/null" >> test_script.sh &&
-	echo "test \$? -ne 0" >> test_script.sh &&
-	chmod +x test_script.sh &&
+	write_script test_script.sh <<-\EOF &&
+	sed -ne \$p hello | grep Ciao >/dev/null && exit 125
+	sed -ne \$p hello | grep day >/dev/null && exit 125
+	! grep Yet hello >/dev/null
+	EOF
 	git bisect start $HASH7 $HASH1 &&
-	git bisect run ./test_script.sh > my_bisect_log.txt &&
+	git bisect run ./test_script.sh >my_bisect_log.txt &&
 	grep "$HASH6 is the first bad commit" my_bisect_log.txt
 '
 
@@ -458,6 +448,24 @@ test_expect_success 'many merge bases creation' '
 	grep "$SIDE_HASH5" merge_bases.txt
 '
 
+# We want to automatically find the merge that
+# added "line" into hello.
+test_expect_success '"git bisect run --first-parent" simple case' '
+	git rev-list --first-parent $B_HASH ^$HASH4 >first_parent_chain.txt &&
+	write_script test_script.sh <<-\EOF &&
+	grep $(git rev-parse HEAD) first_parent_chain.txt || exit -1
+	! grep line hello >/dev/null
+	EOF
+	git bisect start --first-parent &&
+	test_path_is_file ".git/BISECT_FIRST_PARENT" &&
+	git bisect good $HASH4 &&
+	git bisect bad $B_HASH &&
+	git bisect run ./test_script.sh >my_bisect_log.txt &&
+	grep "$B_HASH is the first bad commit" my_bisect_log.txt &&
+	git bisect reset &&
+	test_path_is_missing .git/BISECT_FIRST_PARENT
+'
+
 test_expect_success 'good merge bases when good and bad are siblings' '
 	git bisect start "$B_HASH" "$A_HASH" > my_bisect_log.txt &&
 	test_i18ngrep "merge base must be tested" my_bisect_log.txt &&