rebase: add a config option for --no-fork-point

Some users (myself included) would prefer to have this feature off by
default because it can silently drop commits.

Signed-off-by: Alex Henrie <alexhenrie24@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Documentation/config/rebase.txt

@@ -68,3 +68,6 @@ rebase.rescheduleFailedExec::
 	Automatically reschedule `exec` commands that failed. This only makes
 	sense in interactive mode (or when an `--exec` option was provided).
 	This is the same as specifying the `--reschedule-failed-exec` option.
+
+rebase.forkPoint::
+	If set to false set `--no-fork-point` option by default.

builtin/rebase.c

@@ -102,6 +102,7 @@ struct rebase_options {
 	int reschedule_failed_exec;
 	int use_legacy_rebase;
 	int reapply_cherry_picks;
+	int fork_point;
 };
 
 #define REBASE_OPTIONS_INIT {			  	\
@@ -111,7 +112,8 @@ struct rebase_options {
 		.default_backend = "merge",	  	\
 		.flags = REBASE_NO_QUIET, 		\
 		.git_am_opts = STRVEC_INIT,		\
-		.git_format_patch_opt = STRBUF_INIT	\
+		.git_format_patch_opt = STRBUF_INIT,	\
+		.fork_point = -1,			\
 	}
 
 static struct replay_opts get_replay_opts(const struct rebase_options *opts)
@@ -1095,6 +1097,11 @@ static int rebase_config(const char *var, const char *value, void *data)
 		return 0;
 	}
 
+	if (!strcmp(var, "rebase.forkpoint")) {
+		opts->fork_point = git_config_bool(var, value) ? -1 : 0;
+		return 0;
+	}
+
 	if (!strcmp(var, "rebase.usebuiltin")) {
 		opts->use_legacy_rebase = !git_config_bool(var, value);
 		return 0;
@@ -1306,7 +1313,6 @@ int cmd_rebase(int argc, const char **argv, const char *prefix)
 	const char *gpg_sign = NULL;
 	struct string_list exec = STRING_LIST_INIT_NODUP;
 	const char *rebase_merges = NULL;
-	int fork_point = -1;
 	struct string_list strategy_options = STRING_LIST_INIT_NODUP;
 	struct object_id squash_onto;
 	char *squash_onto_name = NULL;
@@ -1406,7 +1412,7 @@ int cmd_rebase(int argc, const char **argv, const char *prefix)
 			N_("mode"),
 			N_("try to rebase merges instead of skipping them"),
 			PARSE_OPT_OPTARG, NULL, (intptr_t)""},
-		OPT_BOOL(0, "fork-point", &fork_point,
+		OPT_BOOL(0, "fork-point", &options.fork_point,
 			 N_("use 'merge-base --fork-point' to refine upstream")),
 		OPT_STRING('s', "strategy", &options.strategy,
 			   N_("strategy"), N_("use the given merge strategy")),
@@ -1494,7 +1500,7 @@ int cmd_rebase(int argc, const char **argv, const char *prefix)
 			die(_("cannot combine '--keep-base' with '--root'"));
 	}
 
-	if (options.root && fork_point > 0)
+	if (options.root && options.fork_point > 0)
 		die(_("cannot combine '--root' with '--fork-point'"));
 
 	if (action != ACTION_NONE && !in_progress)
@@ -1840,8 +1846,8 @@ int cmd_rebase(int argc, const char **argv, const char *prefix)
 								    NULL);
 			if (!options.upstream_name)
 				error_on_missing_default_upstream();
-			if (fork_point < 0)
-				fork_point = 1;
+			if (options.fork_point < 0)
+				options.fork_point = 1;
 		} else {
 			options.upstream_name = argv[0];
 			argc--;
@@ -1945,7 +1951,7 @@ int cmd_rebase(int argc, const char **argv, const char *prefix)
 	} else
 		BUG("unexpected number of arguments left to parse");
 
-	if (fork_point > 0) {
+	if (options.fork_point > 0) {
 		struct commit *head =
 			lookup_commit_reference(the_repository,
 						&options.orig_head);

t/t3431-rebase-fork-point.sh

@@ -26,19 +26,23 @@ test_expect_success setup '
 	test_commit G
 '
 
+do_test_rebase () {
+	expected="$1" &&
+	shift &&
+	git checkout master &&
+	git reset --hard E &&
+	git checkout side &&
+	git reset --hard G &&
+	git rebase $* &&
+	test_write_lines $expected >expect &&
+	git log --pretty=%s >actual &&
+	test_cmp expect actual
+}
+
 test_rebase () {
 	expected="$1" &&
 	shift &&
-	test_expect_success "git rebase $*" "
-		git checkout master &&
-		git reset --hard E &&
-		git checkout side &&
-		git reset --hard G &&
-		git rebase $* &&
-		test_write_lines $expected >expect &&
-		git log --pretty=%s >actual &&
-		test_cmp expect actual
-	"
+	test_expect_success "git rebase $*" "do_test_rebase '$expected' $*"
 }
 
 test_rebase 'G F E D B A'
@@ -74,4 +78,35 @@ test_expect_success 'git rebase --fork-point with ambigous refname' '
 	test_must_fail git rebase --fork-point --onto D one
 '
 
+test_expect_success '--fork-point and --root both given' '
+	test_must_fail git rebase --fork-point --root 2>err &&
+	test_i18ngrep "cannot combine" err
+'
+
+test_expect_success 'rebase.forkPoint set to false' '
+	test_config rebase.forkPoint false &&
+	do_test_rebase "G F C E D B A"
+'
+
+test_expect_success 'rebase.forkPoint set to false and then to true' '
+	test_config_global rebase.forkPoint false &&
+	test_config rebase.forkPoint true &&
+	do_test_rebase "G F E D B A"
+'
+
+test_expect_success 'rebase.forkPoint set to false and command line says --fork-point' '
+	test_config rebase.forkPoint false &&
+	do_test_rebase "G F E D B A" --fork-point
+'
+
+test_expect_success 'rebase.forkPoint set to true and command line says --no-fork-point' '
+	test_config rebase.forkPoint true &&
+	do_test_rebase "G F C E D B A" --no-fork-point
+'
+
+test_expect_success 'rebase.forkPoint set to true and --root given' '
+	test_config rebase.forkPoint true &&
+	git rebase --root
+'
+
 test_done