[RFC PATCH] bisect: Honor log.date

[Peter Krefting <peter@softwolves.pp.se>]

When bisect finds the target commit to display, it calls git diff-tree
to do so. This is a plumbing command that is not affected by the user's
log.date setting. Switch to instead use "git show", which does honor
it.

Reported-by: Michael Osipov <michael.osipov@innomotics.com>
Signed-off-By: Peter Krefting <peter@softwolves.pp.se>
---
  bisect.c | 26 +++++++++++---------------
  1 file changed, 11 insertions(+), 15 deletions(-)

Junio C Hamano:

> Instead of focusing too narrowly on the log.date option, that would 
> only tweak the date format, it may be a more fruitful way to invest 
> brainwaves in to consider the feasibility of switching to use "git 
> show" there.

Indeed.

Here is a patch that does exactly that.

This is my first patch to the actual codebase in Git, so it might be 
bit rough; improvements are welcome. I might need to change something 
in the test suite as well?

With this patch applied, running with log.date=iso and 
log.decorate=short, I get this output:

  $ ./git-bisect start
  [...]
  $ ./git-bisect good v2.43.2
  [...]
  $ ./git-bisect bad v2.43.3
  [...]
  $ ./git-bisect good
  0d464a4e6a5a19bd8fbea1deae22d48d14dccb01 is the first bad commit
  commit 0d464a4e6a5a19bd8fbea1deae22d48d14dccb01 (tag: v2.43.3)
  Author: Junio C Hamano <gitster@pobox.com>
  Date:   2024-02-22 16:13:38 -0800

      Git 2.43.3

  Signed-off-by: Junio C Hamano <gitster@pobox.com>

which is the format I expect.

diff --git a/bisect.c b/bisect.c
index 8487f8cd1b..0f7126c32b 100644
--- a/bisect.c
+++ b/bisect.c
@@ -959,23 +959,19 @@ static enum bisect_error check_good_are_ancestors_of_bad(struct repository *r,
  }

  /*
- * This does "git diff-tree --pretty COMMIT" without one fork+exec.
+ * Runs "git show" to display a commit
   */
-static void show_diff_tree(struct repository *r,
-			   const char *prefix,
-			   struct commit *commit)
+static void show_commit(struct commit *commit)
  {
-	const char *argv[] = {
-		"diff-tree", "--pretty", "--stat", "--summary", "--cc", NULL
-	};
-	struct rev_info opt;
+	struct child_process show = CHILD_PROCESS_INIT;

-	git_config(git_diff_ui_config, NULL);
-	repo_init_revisions(r, &opt, prefix);
-
-	setup_revisions(ARRAY_SIZE(argv) - 1, argv, &opt, NULL);
-	log_tree_commit(&opt, commit);
-	release_revisions(&opt);
+	/* Invoke "git show --pretty=medium --shortstat --no-abbrev-commit --no-patch $object" */
+	strvec_pushl(&show.args, "show", "--pretty=medium", "--shortstat", "--no-abbrev-commit", "--no-patch",
+		     oid_to_hex(&commit->object.oid), NULL);
+	show.git_cmd = 1;
+	if (run_command(&show))
+		die(_("unable to start 'show' for object '%s'"),
+		    oid_to_hex(&commit->object.oid));
  }

  /*
@@ -1092,7 +1088,7 @@ enum bisect_error bisect_next_all(struct repository *r, const char *prefix)
  		printf("%s is the first %s commit\n", oid_to_hex(bisect_rev),
  			term_bad);

-		show_diff_tree(r, prefix, revs.commits->item);
+		show_commit(revs.commits->item);
  		/*
  		 * This means the bisection process succeeded.
  		 * Using BISECT_INTERNAL_SUCCESS_1ST_BAD_FOUND (-10)
-- 
2.39.2