bisect: libify exit_if_skipped_commits to error_if_skipped* and its dependents

Since we want to get rid of git-bisect.sh, it would be necessary to
convert those exit() calls to return statements so that errors can be
reported.

Emulate try catch in C by converting `exit(<positive-value>)` to
`return <negative-value>`. Follow POSIX conventions to return
<negative-value> to indicate error.

Update all callers to handle the error returns.

Mentored-by: Christian Couder <[email protected]>
Mentored-by: Johannes Schindelin <[email protected]>
Signed-off-by: Pranit Bauva <[email protected]>
Signed-off-by: Tanushree Tumane <[email protected]>
Signed-off-by: Miriam Rubio <[email protected]>
Signed-off-by: Junio C Hamano <[email protected]>

Author: pranitbauva1997

bisect.c

@@ -661,11 +661,11 @@ static void bisect_common(struct rev_info *revs)
 		mark_edges_uninteresting(revs, NULL, 0);
 }
 
-static void exit_if_skipped_commits(struct commit_list *tried,
+static enum bisect_error error_if_skipped_commits(struct commit_list *tried,
 				    const struct object_id *bad)
 {
 	if (!tried)
-		return;
+		return BISECT_OK;
 
 	printf("There are only 'skip'ped commits left to test.\n"
 	       "The first %s commit could be any of:\n", term_bad);
@@ -676,7 +676,8 @@ static void exit_if_skipped_commits(struct commit_list *tried,
 	if (bad)
 		printf("%s\n", oid_to_hex(bad));
 	printf(_("We cannot bisect more!\n"));
-	exit(2);
+
+	return BISECT_ONLY_SKIPPED_LEFT;
 }
 
 static int is_expected_rev(const struct object_id *oid)
@@ -950,6 +951,7 @@ enum bisect_error bisect_next_all(struct repository *r, const char *prefix, int
 	struct rev_info revs;
 	struct commit_list *tried;
 	int reaches = 0, all = 0, nr, steps;
+	enum bisect_error res = BISECT_OK;
 	struct object_id *bisect_rev;
 	char *steps_msg;
 
@@ -972,8 +974,9 @@ enum bisect_error bisect_next_all(struct repository *r, const char *prefix, int
 		 * We should exit here only if the "bad"
 		 * commit is also a "skip" commit.
 		 */
-		exit_if_skipped_commits(tried, NULL);
-
+		res = error_if_skipped_commits(tried, NULL);
+		if (res < 0)
+			exit(-res);
 		printf(_("%s was both %s and %s\n"),
 		       oid_to_hex(current_bad_oid),
 		       term_good,
@@ -990,7 +993,9 @@ enum bisect_error bisect_next_all(struct repository *r, const char *prefix, int
 	bisect_rev = &revs.commits->item->object.oid;
 
 	if (oideq(bisect_rev, current_bad_oid)) {
-		exit_if_skipped_commits(tried, current_bad_oid);
+		res = error_if_skipped_commits(tried, current_bad_oid);
+		if (res)
+			exit(-res);
 		printf("%s is the first %s commit\n", oid_to_hex(bisect_rev),
 			term_bad);
 		show_diff_tree(r, prefix, revs.commits->item);

bisect.h

@@ -37,10 +37,13 @@ struct rev_list_info {
  * commit has been found (and possibly checked out) and it
  * should be tested.
  * BISECT_FAILED error code: default error code.
+ * BISECT_ONLY_SKIPPED_LEFT error code: only skipped
+ * commits left to be tested.
  */
 enum bisect_error {
 	BISECT_OK = 0,
-	BISECT_FAILED = -1
+	BISECT_FAILED = -1,
+	BISECT_ONLY_SKIPPED_LEFT = -2
 };
 
 enum bisect_error bisect_next_all(struct repository *r,