Re: [PATCH v7 06/13] bisect--helper: reimplement `bisect_next` and `bisect_auto_next` shell functions in C

[Johannes Schindelin <Johannes.Schindelin@gmx.de>]

Hi Miriam,

On Mon, 31 Aug 2020, Miriam Rubio wrote:

> From: Pranit Bauva <pranit.bauva@gmail.com>
>
> 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.
>
> 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>
> ---
>  bisect.c                 |  11 ++-
>  builtin/bisect--helper.c | 180 ++++++++++++++++++++++++++++++++++++++-
>  git-bisect.sh            |  47 +---------
>  3 files changed, 190 insertions(+), 48 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;
>
> diff --git a/builtin/bisect--helper.c b/builtin/bisect--helper.c
> index f71e8e54d2..e29e86142a 100644
> --- a/builtin/bisect--helper.c
> +++ b/builtin/bisect--helper.c
> @@ -8,6 +8,7 @@
>  #include "run-command.h"
>  #include "prompt.h"
>  #include "quote.h"
> +#include "revision.h"
>
>  static GIT_PATH_FUNC(git_path_bisect_terms, "BISECT_TERMS")
>  static GIT_PATH_FUNC(git_path_bisect_expected_rev, "BISECT_EXPECTED_REV")
> @@ -29,10 +30,17 @@ static const char * const git_bisect_helper_usage[] = {
>  	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] [--first-parent] [<bad> [<good>...]] [--] [<paths>...]"),
> +	N_("git bisect--helper --bisect-next"),
> +	N_("git bisect--helper --bisect-auto-next"),
>  	N_("git bisect--helper --bisect-autostart"),
>  	NULL
>  };
>
> +struct add_bisect_ref_data {
> +	struct rev_info *revs;
> +	unsigned int object_flags;
> +};
> +
>  struct bisect_terms {
>  	char *term_good;
>  	char *term_bad;
> @@ -56,6 +64,8 @@ static void set_terms(struct bisect_terms *terms, const char *bad,
>  static const char vocab_bad[] = "bad|new";
>  static const char vocab_good[] = "good|old";
>
> +static int bisect_autostart(struct bisect_terms *terms);
> +
>  /*
>   * Check whether the string `term` belongs to the set of strings
>   * included in the variable arguments.
> @@ -80,7 +90,7 @@ static int write_in_file(const char *path, const char *mode, const char *format,
>  	FILE *fp = NULL;
>  	int res = 0;
>
> -	if (strcmp(mode, "w"))
> +	if (strcmp(mode, "w") && strcmp(mode, "a"))
>  		BUG("write-in-file does not support '%s' mode", mode);
>  	fp = fopen(path, mode);
>  	if (!fp)
> @@ -109,6 +119,18 @@ static int write_to_file(const char *path, const char *format, ...)
>  	return res;
>  }
>
> +static int append_to_file(const char *path, const char *format, ...)
> +{
> +	int res;
> +	va_list args;
> +
> +	va_start(args, format);
> +	res = write_in_file(path, "a", format, args);
> +	va_end(args);
> +
> +	return res;
> +}
> +
>  static int check_term_format(const char *term, const char *orig_term)
>  {
>  	int res;
> @@ -451,6 +473,140 @@ static int bisect_append_log_quoted(const char **argv)
>  	return res;
>  }
>
> +static int add_bisect_ref(const char *refname, const struct object_id *oid,
> +			  int flags, void *cb)
> +{
> +	struct add_bisect_ref_data *data = cb;
> +
> +	add_pending_oid(data->revs, refname, oid, data->object_flags);
> +
> +	return 0;
> +}
> +
> +static int prepare_revs(struct bisect_terms *terms, struct rev_info *revs)
> +{
> +	int res = 0;
> +	struct add_bisect_ref_data cb = { revs };
> +	char *good = xstrfmt("%s-*", terms->term_good);
> +
> +	/*
> +	 * We cannot use terms->term_bad directly in
> +	 * for_each_glob_ref_in() and we have to append a '*' to it,
> +	 * otherwise for_each_glob_ref_in() will append '/' and '*'.
> +	 */
> +	char *bad = xstrfmt("%s*", terms->term_bad);
> +
> +	/*
> +	 * It is important to reset the flags used by revision walks
> +	 * as the previous call to bisect_next_all() in turn
> +	 * sets up a revision walk.
> +	 */
> +	reset_revision_walk();
> +	init_revisions(revs, NULL);
> +	setup_revisions(0, NULL, revs, NULL);
> +	for_each_glob_ref_in(add_bisect_ref, bad, "refs/bisect/", &cb);
> +	cb.object_flags = UNINTERESTING;
> +	for_each_glob_ref_in(add_bisect_ref, good, "refs/bisect/", &cb);
> +	if (prepare_revision_walk(revs))
> +		res = error(_("revision walk setup failed\n"));
> +
> +	free(good);
> +	free(bad);
> +	return res;
> +}
> +
> +static int bisect_skipped_commits(struct bisect_terms *terms)
> +{
> +	int res;
> +	FILE *fp = NULL;
> +	struct rev_info revs;
> +	struct commit *commit;
> +	struct pretty_print_context pp = {0};
> +	struct strbuf commit_name = STRBUF_INIT;
> +
> +	res = prepare_revs(terms, &revs);
> +	if (res)
> +		return res;
> +
> +	fp = fopen(git_path_bisect_log(), "a");
> +	if (!fp)
> +		return error_errno(_("could not open '%s' for appending"),
> +				  git_path_bisect_log());
> +
> +	if (fprintf(fp, "# only skipped commits left to test\n") < 0)
> +		return error_errno(_("failed to write to '%s'"), git_path_bisect_log());
> +
> +	while ((commit = get_revision(&revs)) != NULL) {
> +		strbuf_reset(&commit_name);
> +		format_commit_message(commit, "%s",
> +				      &commit_name, &pp);
> +		fprintf(fp, "# possible first %s commit: [%s] %s\n",
> +			terms->term_bad, oid_to_hex(&commit->object.oid),
> +			commit_name.buf);
> +	}
> +
> +	/*
> +	 * Reset the flags used by revision walks in case
> +	 * there is another revision walk after this one.
> +	 */
> +	reset_revision_walk();
> +
> +	strbuf_release(&commit_name);
> +	fclose(fp);
> +	return 0;
> +}
> +
> +static int bisect_successful(struct bisect_terms *terms)
> +{
> +	struct object_id oid;
> +	struct commit *commit;
> +	struct pretty_print_context pp = {0};
> +	struct strbuf commit_name = STRBUF_INIT;
> +	char *bad_ref = xstrfmt("refs/bisect/%s",terms->term_bad);
> +	int res;
> +
> +	read_ref(bad_ref, &oid);
> +	commit = lookup_commit_reference_by_name(bad_ref);
> +	format_commit_message(commit, "%s", &commit_name, &pp);
> +
> +	res = append_to_file(git_path_bisect_log(), "# first %s commit: [%s] %s\n",
> +			    terms->term_bad, oid_to_hex(&commit->object.oid),
> +			    commit_name.buf);
> +
> +	strbuf_release(&commit_name);
> +	free(bad_ref);
> +	return res;
> +}
> +
> +static enum bisect_error bisect_next(struct bisect_terms *terms, const char *prefix)
> +{
> +	enum bisect_error res;
> +
> +	bisect_autostart(terms);

We need to handle a negative value returned by `bisect_autostart()` by
aborting, e.g. `return BISECT_FAILED;`.

> +	if (bisect_next_check(terms, terms->term_good))
> +		return BISECT_FAILED;
> +
> +	/* Perform all bisection computation */
> +	res = bisect_next_all(the_repository, prefix);
> +
> +	if (res == BISECT_INTERNAL_SUCCESS_1ST_BAD_FOUND) {
> +		res = bisect_successful(terms);
> +		return res ? res : BISECT_INTERNAL_SUCCESS_1ST_BAD_FOUND;
> +	} else if (res == BISECT_ONLY_SKIPPED_LEFT) {
> +		res = bisect_skipped_commits(terms);
> +		return res ? res : BISECT_ONLY_SKIPPED_LEFT;
> +	}
> +	return res;
> +}
> +
> +static enum bisect_error bisect_auto_next(struct bisect_terms *terms, const char *prefix)
> +{
> +	if (bisect_next_check(terms, NULL))
> +		return BISECT_OK;
> +
> +	return bisect_next(terms, prefix);

This returns an error when `bisect_next()` failed, which is different from
what the shell script version did:

	git bisect--helper --bisect-next-check $TERM_GOOD $TERM_BAD && bisect_next || :

(note the trailing `|| :`, which will always return success).

I think this is a bug fix, though, so the change is good. But it probably
deserves to be called out in the commit message.

> +}
> +
>  static int bisect_start(struct bisect_terms *terms, const char **argv, int argc)
>  {
>  	int no_checkout = 0;
> @@ -699,7 +855,9 @@ int cmd_bisect__helper(int argc, const char **argv, const char *prefix)
>  		BISECT_NEXT_CHECK,
>  		BISECT_TERMS,
>  		BISECT_START,
> -		BISECT_AUTOSTART,
> +		BISECT_NEXT,
> +		BISECT_AUTO_NEXT,
> +		BISECT_AUTOSTART

I am curious: what is the reason not to use a trailing comma, and what is
the reason to force AUTOSTART to stay at the end (instead of appending the
new modes, which strikes me as more natural)?

>  	} cmdmode = 0;
>  	int res = 0, nolog = 0;
>  	struct option options[] = {
> @@ -723,6 +881,10 @@ int cmd_bisect__helper(int argc, const char **argv, const char *prefix)
>  			 N_("print out the bisect terms"), BISECT_TERMS),
>  		OPT_CMDMODE(0, "bisect-start", &cmdmode,
>  			 N_("start the bisect session"), BISECT_START),
> +		OPT_CMDMODE(0, "bisect-next", &cmdmode,
> +			 N_("find the next bisection commit"), BISECT_NEXT),
> +		OPT_CMDMODE(0, "bisect-auto-next", &cmdmode,
> +			 N_("verify the next bisection state then checkout the next bisection commit"), BISECT_AUTO_NEXT),
>  		OPT_CMDMODE(0, "bisect-autostart", &cmdmode,
>  			 N_("start the bisection if it has not yet been started"), BISECT_AUTOSTART),
>  		OPT_BOOL(0, "no-log", &nolog,
> @@ -784,6 +946,18 @@ int cmd_bisect__helper(int argc, const char **argv, const char *prefix)
>  		set_terms(&terms, "bad", "good");
>  		res = bisect_start(&terms, argv, argc);
>  		break;
> +	case BISECT_NEXT:
> +		if (argc)
> +			return error(_("--bisect-next requires 0 arguments"));
> +		get_terms(&terms);
> +		res = bisect_next(&terms, prefix);
> +		break;
> +	case BISECT_AUTO_NEXT:
> +		if (argc)
> +			return error(_("--bisect-auto-next requires 0 arguments"));
> +		get_terms(&terms);
> +		res = bisect_auto_next(&terms, prefix);
> +		break;
>  	case BISECT_AUTOSTART:
>  		if (argc)
>  			return error(_("--bisect-autostart does not accept arguments"));
> @@ -799,7 +973,7 @@ int cmd_bisect__helper(int argc, const char **argv, const char *prefix)
>  	 * Handle early success
>  	 * From check_merge_bases > check_good_are_ancestors_of_bad > bisect_next_all
>  	 */
> -	if (res == BISECT_INTERNAL_SUCCESS_MERGE_BASE)
> +	if ((res == BISECT_INTERNAL_SUCCESS_MERGE_BASE) || (res == BISECT_INTERNAL_SUCCESS_1ST_BAD_FOUND))
>  		res = BISECT_OK;
>
>  	return -res;
> diff --git a/git-bisect.sh b/git-bisect.sh
> index 9ca583d964..59424f5b37 100755
> --- a/git-bisect.sh
> +++ b/git-bisect.sh
> @@ -65,8 +65,7 @@ bisect_start() {
>  	#
>  	# Check if we can proceed to the next bisect state.
>  	#
> -	get_terms
> -	bisect_auto_next
> +	git bisect--helper --bisect-auto-next || exit
>
>  	trap '-' 0
>  }
> @@ -119,45 +118,7 @@ bisect_state() {
>  	*)
>  		usage ;;
>  	esac
> -	bisect_auto_next
> -}
> -
> -bisect_auto_next() {
> -	git bisect--helper --bisect-next-check $TERM_GOOD $TERM_BAD && bisect_next || :
> -}
> -
> -bisect_next() {
> -	case "$#" in 0) ;; *) usage ;; esac
> -	git bisect--helper --bisect-autostart
> -	git bisect--helper --bisect-next-check $TERM_GOOD $TERM_BAD $TERM_GOOD|| exit
> -
> -	# Perform all bisection computation, display and checkout
> -	git bisect--helper --next-all
> -	res=$?
> -
> -	# Check if we should exit because bisection is finished
> -	if test $res -eq 10
> -	then
> -		bad_rev=$(git show-ref --hash --verify refs/bisect/$TERM_BAD)
> -		bad_commit=$(git show-branch $bad_rev)
> -		echo "# first $TERM_BAD commit: $bad_commit" >>"$GIT_DIR/BISECT_LOG"
> -		exit 0
> -	elif test $res -eq 2
> -	then
> -		echo "# only skipped commits left to test" >>"$GIT_DIR/BISECT_LOG"
> -		good_revs=$(git for-each-ref --format="%(objectname)" "refs/bisect/$TERM_GOOD-*")
> -		for skipped in $(git rev-list refs/bisect/$TERM_BAD --not $good_revs)
> -		do
> -			skipped_commit=$(git show-branch $skipped)
> -			echo "# possible first $TERM_BAD commit: $skipped_commit" >>"$GIT_DIR/BISECT_LOG"
> -		done
> -		exit $res
> -	fi
> -
> -	# Check for an error in the bisection process
> -	test $res -ne 0 && exit $res
> -
> -	return 0
> +	git bisect--helper --bisect-auto-next
>  }
>
>  bisect_visualize() {
> @@ -213,7 +174,7 @@ bisect_replay () {
>  		esac
>  	done <"$file"
>  	IFS="$oIFS"
> -	bisect_auto_next
> +	git bisect--helper --bisect-auto-next

We probably need to append `|| exit` here.

Thank you,
Johannes

>  }
>
>  bisect_run () {
> @@ -310,7 +271,7 @@ case "$#" in
>  		bisect_skip "$@" ;;
>  	next)
>  		# Not sure we want "next" at the UI level anymore.
> -		bisect_next "$@" ;;
> +		git bisect--helper --bisect-next "$@" || exit ;;
>  	visualize|view)
>  		bisect_visualize "$@" ;;
>  	reset)
> --
> 2.25.0
>
>