[PATCH v3 2/4] bisect: introduce first-parent flag

From: Aaron Lipman <alipman88@gmail.com>
To: git@vger.kernel.org
Cc: Aaron Lipman <alipman88@gmail.com>
Subject: [PATCH v3 2/4] bisect: introduce first-parent flag
Date: Sat,  1 Aug 2020 13:58:38 -0400	[thread overview]
Message-ID: <20200801175840.1877-3-alipman88@gmail.com> (raw)
In-Reply-To: <20200801175840.1877-1-alipman88@gmail.com>

Upon seeing a merge commit when bisecting, this option may be used to
follow only the first parent.

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.

Signed-off-by: Aaron Lipman <alipman88@gmail.com>
---
 Documentation/git-bisect.txt | 13 ++++++++++++-
 bisect.c                     | 10 +++++++++-
 builtin/bisect--helper.c     | 14 ++++++++++----
 t/t6030-bisect-porcelain.sh  | 18 ++++++++++++++++++
 4 files changed, 49 insertions(+), 6 deletions(-)

diff --git a/Documentation/git-bisect.txt b/Documentation/git-bisect.txt
index 7586c5a843..0e993e4587 100644
--- a/Documentation/git-bisect.txt
+++ b/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
 --------
 
diff --git a/bisect.c b/bisect.c
index a11fdb1473..afbb5aea32 100644
--- a/bisect.c
+++ b/bisect.c
@@ -460,6 +460,7 @@ 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 argv_array *array)
@@ -981,6 +982,12 @@ void read_bisect_terms(const char **read_bad, const char **read_good)
 	fclose(fp);
 }
 
+static int read_first_parent_option(void)
+{
+	const char *filename = git_path_bisect_first_parent();
+	return !access(filename, F_OK);
+}
+
 /*
  * We use the convention that return BISECT_INTERNAL_SUCCESS_1ST_BAD_FOUND (-10) means
  * the bisection process finished successfully.
@@ -997,7 +1004,7 @@ 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 first_parent_only = 0; /* TODO: pass --first-parent flag from git bisect start */
+	int first_parent_only = read_first_parent_option();
 
 	read_bisect_terms(&term_bad, &term_good);
 	if (read_bisect_refs())
@@ -1141,6 +1148,7 @@ 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());
 	/*
diff --git a/builtin/bisect--helper.c b/builtin/bisect--helper.c
index ec4996282e..9273140f0b 100644
--- a/builtin/bisect--helper.c
+++ b/builtin/bisect--helper.c
@@ -17,6 +17,7 @@ static GIT_PATH_FUNC(git_path_bisect_head, "BISECT_HEAD")
 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]"),
@@ -28,7 +29,7 @@ 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
 };
 
@@ -422,7 +423,7 @@ static int bisect_append_log_quoted(const char **argv)
 }
 
 static int bisect_start(struct bisect_terms *terms, int no_checkout,
-			const char **argv, int argc)
+			int first_parent_only, const char **argv, int argc)
 {
 	int i, has_double_dash = 0, must_write_terms = 0, bad_seen = 0;
 	int flags, pathspec_pos, res = 0;
@@ -577,6 +578,9 @@ 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);
@@ -632,7 +636,7 @@ 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 no_checkout = 0, first_parent_only = 0, res = 0, nolog = 0;
 	struct option options[] = {
 		OPT_CMDMODE(0, "next-all", &cmdmode,
 			 N_("perform 'git bisect next'"), NEXT_ALL),
@@ -656,6 +660,8 @@ int cmd_bisect__helper(int argc, const char **argv, const char *prefix)
 			 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, "first-parent", &first_parent_only,
+			 N_("only trace the first parent of merge commits")),
 		OPT_BOOL(0, "no-log", &nolog,
 			 N_("no log for BISECT_WRITE")),
 		OPT_END()
@@ -713,7 +719,7 @@ 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, no_checkout, first_parent_only, argv, argc);
 		break;
 	default:
 		return error("BUG: unknown subcommand '%d'", cmdmode);
diff --git a/t/t6030-bisect-porcelain.sh b/t/t6030-bisect-porcelain.sh
index 36d9b2b2e4..51f5eb6ea3 100755
--- a/t/t6030-bisect-porcelain.sh
+++ b/t/t6030-bisect-porcelain.sh
@@ -458,6 +458,24 @@ 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 &&
-- 
2.24.3 (Apple Git-128)

