bisect--helper: reimplement `bisect_next` and `bisect_auto_next` shell functions in C

Reimplement the `bisect_next()` and the `bisect_auto_next()` shell functions
in C and add the subcommands to `git bisect--helper` to call them from
git-bisect.sh .

bisect_auto_next() function returns an enum bisect_error type as whole
`git bisect` can exit with an error code when bisect_next() does.

Return an error when `bisect_next()` fails, that fix a bug on shell script
version.

Using `--bisect-next` and `--bisect-auto-next` subcommands is a
temporary measure to port shell function to C so as to use the existing
test suite. As more functions are ported, `--bisect-auto-next`
subcommand will be retired and will be called by some other methods.

Mentored-by: Lars Schneider <larsxschneider@gmail.com>
Mentored-by: Christian Couder <chriscool@tuxfamily.org>
Mentored-by: Johannes Schindelin <Johannes.Schindelin@gmx.de>
Signed-off-by: Pranit Bauva <pranit.bauva@gmail.com>
Signed-off-by: Tanushree Tumane <tanushreetumane@gmail.com>
Signed-off-by: Miriam Rubio <mirucam@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

1 files changed, 9 insertions, 2 deletions

diff --git a/bisect.c b/bisect.c
index c6aba2b9f2..f5b1368128 100644
--- a/bisect.c
+++ b/bisect.c
@@ -988,8 +988,11 @@ void read_bisect_terms(const char **read_bad, const char **read_good)
  * the bisection process finished successfully.
  * In this case the calling function or command should not turn a
  * BISECT_INTERNAL_SUCCESS_1ST_BAD_FOUND return code into an error or a non zero exit code.
- * If no_checkout is non-zero, the bisection process does not
- * checkout the trial commit but instead simply updates BISECT_HEAD.
+ *
+ * Checking BISECT_INTERNAL_SUCCESS_1ST_BAD_FOUND
+ * in bisect_helper::bisect_next() and only transforming it to 0 at
+ * the end of bisect_helper::cmd_bisect__helper() helps bypassing
+ * all the code related to finding a commit to test.
  */
 enum bisect_error bisect_next_all(struct repository *r, const char *prefix)
 {
@@ -999,6 +1002,10 @@ enum bisect_error bisect_next_all(struct repository *r, const char *prefix)
 	enum bisect_error res = BISECT_OK;
 	struct object_id *bisect_rev;
 	char *steps_msg;
+	/*
+	 * If no_checkout is non-zero, the bisection process does not
+	 * checkout the trial commit but instead simply updates BISECT_HEAD.
+	 */
 	int no_checkout = ref_exists("BISECT_HEAD");
 	unsigned bisect_flags = 0;