[PATCH 07/26] bisect.c: libify `check_good_are_ancestors_of_bad` and its dependents

["Pranit Bauva via GitGitGadget" <gitgitgadget@gmail.com>]

From: Pranit Bauva <pranit.bauva@gmail.com>

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 <negetive-value>`. Follow POSIX conventions to return
<negative-value> to indicate error.

Turn `exit()` to `return` calls in `check_good_are_ancestors_of_bad()`.

In `check_merge_bases()` there is an early success special case,
so we have introduced special error code `-11` which indicates early
success. This `-11` is converted back to `0` in `cmd_bisect_helper()`.

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>
---
 bisect.c                 | 41 +++++++++++++++++++++++++---------------
 builtin/bisect--helper.c | 12 ++++++++++--
 2 files changed, 36 insertions(+), 17 deletions(-)

diff --git a/bisect.c b/bisect.c
index 1134854fe2..87db1cc4be 100644
--- a/bisect.c
+++ b/bisect.c
@@ -859,17 +859,24 @@ static int check_ancestors(int rev_nr, struct commit **rev, const char *prefix)
  *
  * If that's not the case, we need to check the merge bases.
  * If a merge base must be tested by the user, its source code will be
- * checked out to be tested by the user and we will exit.
+ * checked out to be tested by the user and we will return.
  */
-static void check_good_are_ancestors_of_bad(const char *prefix, int no_checkout)
+static int check_good_are_ancestors_of_bad(const char *prefix, int no_checkout)
 {
 	char *filename = git_pathdup("BISECT_ANCESTORS_OK");
 	struct stat st;
 	int fd, rev_nr, res = 0;
 	struct commit **rev;
 
-	if (!current_bad_oid)
-		die(_("a %s revision is needed"), term_bad);
+	/*
+	 * We don't want to clean the bisection state
+	 * as we need to get back to where we started
+	 * by using `git bisect reset`.
+	 */
+	if (!current_bad_oid) {
+		res = error(_("a %s revision is needed"), term_bad);
+		goto done;
+	}
 
 	/* Check if file BISECT_ANCESTORS_OK exists. */
 	if (!stat(filename, &st) && S_ISREG(st.st_mode))
@@ -884,18 +891,20 @@ static void check_good_are_ancestors_of_bad(const char *prefix, int no_checkout)
 	if (check_ancestors(rev_nr, rev, prefix))
 		res = check_merge_bases(rev_nr, rev, no_checkout);
 	free(rev);
-	if(res)
-		exit(res == -11 ? 0 : -res);
-
-	/* Create file BISECT_ANCESTORS_OK. */
-	fd = open(filename, O_CREAT | O_TRUNC | O_WRONLY, 0600);
-	if (fd < 0)
-		warning_errno(_("could not create file '%s'"),
-			      filename);
-	else
-		close(fd);
+	
+	if (!res)
+	{
+		/* Create file BISECT_ANCESTORS_OK. */
+		fd = open(filename, O_CREAT | O_TRUNC | O_WRONLY, 0600);
+		if (fd < 0)
+			warning_errno(_("could not create file '%s'"),
+				      filename);
+		else
+			close(fd);
+	}
  done:
 	free(filename);
+	return res;
 }
 
 /*
@@ -973,7 +982,9 @@ int bisect_next_all(const char *prefix, int no_checkout)
 	if (read_bisect_refs())
 		die(_("reading bisect refs failed"));
 
-	check_good_are_ancestors_of_bad(prefix, no_checkout);
+	res = check_good_are_ancestors_of_bad(prefix, no_checkout);
+	if (res)
+		return res;
 
 	bisect_rev_setup(&revs, prefix, "%s", "^%s", 1);
 	revs.limited = 1;
diff --git a/builtin/bisect--helper.c b/builtin/bisect--helper.c
index f441ea85ff..ffb5dbe4b3 100644
--- a/builtin/bisect--helper.c
+++ b/builtin/bisect--helper.c
@@ -663,7 +663,8 @@ int cmd_bisect__helper(int argc, const char **argv, const char *prefix)
 
 	switch (cmdmode) {
 	case NEXT_ALL:
-		return bisect_next_all(prefix, no_checkout);
+		res = bisect_next_all(prefix, no_checkout);
+		break;
 	case WRITE_TERMS:
 		if (argc != 2)
 			return error(_("--write-terms requires two arguments"));
@@ -710,5 +711,12 @@ int cmd_bisect__helper(int argc, const char **argv, const char *prefix)
 		return error("BUG: unknown subcommand '%d'", cmdmode);
 	}
 	free_terms(&terms);
-	return !!res;
+	/* 
+	 * Handle early success
+	 * From check_merge_bases > check_good_are_ancestors_of_bad > bisect_next_all
+	 */
+	if (res == -11)
+		res = 0;
+
+	return res < 0 ? -res : res;
 }
-- 
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