Merge branch 'jc/revert-show-parent-info'

"git revert" learns "--reference" option to use more human-readable
reference to the commit it reverts in the message template it
prepares for the user.

* jc/revert-show-parent-info:
  revert: --reference should apply only to 'revert', not 'cherry-pick'
  revert: optionally refer to commit in the "reference" format

Documentation/config/revert.txt

@@ -0,0 +1,3 @@
+revert.reference::
+	Setting this variable to true makes `git revert` to behave
+	as if the `--reference` option is given.

Documentation/git-revert.txt

@@ -117,6 +117,15 @@ effect to your index in a row.
 	Allow the rerere mechanism to update the index with the
 	result of auto-conflict resolution if possible.
 
+--reference::
+	Instead of starting the body of the log message with "This
+	reverts <full object name of the commit being reverted>.",
+	refer to the commit using "--pretty=reference" format
+	(cf. linkgit:git-log[1]).  The `revert.reference`
+	configuration variable can be used to enable this option by
+	default.
+
+
 SEQUENCER SUBCOMMANDS
 ---------------------
 include::sequencer.txt[]

builtin/revert.c

@@ -130,6 +130,13 @@ static int run_sequencer(int argc, const char **argv, struct replay_opts *opts)
 			OPT_END(),
 		};
 		options = parse_options_concat(options, cp_extra);
+	} else if (opts->action == REPLAY_REVERT) {
+		struct option cp_extra[] = {
+			OPT_BOOL(0, "reference", &opts->commit_use_reference,
+				 N_("use the 'reference' format to refer to commits")),
+			OPT_END(),
+		};
+		options = parse_options_concat(options, cp_extra);
 	}
 
 	argc = parse_options(argc, argv, NULL, options, usage_str,

sequencer.c

@@ -221,6 +221,9 @@ static int git_sequencer_config(const char *k, const char *v, void *cb)
 		return ret;
 	}
 
+	if (opts->action == REPLAY_REVERT && !strcmp(k, "revert.reference"))
+		opts->commit_use_reference = git_config_bool(k, v);
+
 	status = git_gpg_config(k, v, NULL);
 	if (status)
 		return status;
@@ -2059,6 +2062,20 @@ static int should_edit(struct replay_opts *opts) {
 	return opts->edit;
 }
 
+static void refer_to_commit(struct replay_opts *opts,
+			    struct strbuf *msgbuf, struct commit *commit)
+{
+	if (opts->commit_use_reference) {
+		struct pretty_print_context ctx = {
+			.abbrev = DEFAULT_ABBREV,
+			.date_mode.type = DATE_SHORT,
+		};
+		format_commit_message(commit, "%h (%s, %ad)", msgbuf, &ctx);
+	} else {
+		strbuf_addstr(msgbuf, oid_to_hex(&commit->object.oid));
+	}
+}
+
 static int do_pick_commit(struct repository *r,
 			  struct todo_item *item,
 			  struct replay_opts *opts,
@@ -2167,14 +2184,20 @@ static int do_pick_commit(struct repository *r,
 		base_label = msg.label;
 		next = parent;
 		next_label = msg.parent_label;
-		strbuf_addstr(&msgbuf, "Revert \"");
+		if (opts->commit_use_reference) {
-		strbuf_addstr(&msgbuf, msg.subject);
+			strbuf_addstr(&msgbuf,
-		strbuf_addstr(&msgbuf, "\"\n\nThis reverts commit ");
+				"# *** SAY WHY WE ARE REVERTING ON THE TITLE LINE ***");
-		strbuf_addstr(&msgbuf, oid_to_hex(&commit->object.oid));
+		} else {
+			strbuf_addstr(&msgbuf, "Revert \"");
+			strbuf_addstr(&msgbuf, msg.subject);
+			strbuf_addstr(&msgbuf, "\"");
+		}
+		strbuf_addstr(&msgbuf, "\n\nThis reverts commit ");
+		refer_to_commit(opts, &msgbuf, commit);
 
 		if (commit->parents && commit->parents->next) {
 			strbuf_addstr(&msgbuf, ", reversing\nchanges made to ");
-			strbuf_addstr(&msgbuf, oid_to_hex(&parent->object.oid));
+			refer_to_commit(opts, &msgbuf, parent);
 		}
 		strbuf_addstr(&msgbuf, ".\n");
 	} else {

sequencer.h

@@ -49,6 +49,7 @@ struct replay_opts {
 	int reschedule_failed_exec;
 	int committer_date_is_author_date;
 	int ignore_date;
+	int commit_use_reference;
 
 	int mainline;
 

t/t3501-revert-cherry-pick.sh

@@ -158,6 +158,7 @@ test_expect_success 'cherry-pick works with dirty renamed file' '
 '
 
 test_expect_success 'advice from failed revert' '
+	test_when_finished "git reset --hard" &&
 	test_commit --no-tag "add dream" dream dream &&
 	dream_oid=$(git rev-parse --short HEAD) &&
 	cat <<-EOF >expected &&
@@ -173,4 +174,40 @@ test_expect_success 'advice from failed revert' '
 	test_must_fail git revert HEAD^ 2>actual &&
 	test_cmp expected actual
 '
+
+test_expect_success 'identification of reverted commit (default)' '
+	test_commit to-ident &&
+	test_when_finished "git reset --hard to-ident" &&
+	git checkout --detach to-ident &&
+	git revert --no-edit HEAD &&
+	git cat-file commit HEAD >actual.raw &&
+	grep "^This reverts " actual.raw >actual &&
+	echo "This reverts commit $(git rev-parse HEAD^)." >expect &&
+	test_cmp expect actual
+'
+
+test_expect_success 'identification of reverted commit (--reference)' '
+	git checkout --detach to-ident &&
+	git revert --reference --no-edit HEAD &&
+	git cat-file commit HEAD >actual.raw &&
+	grep "^This reverts " actual.raw >actual &&
+	echo "This reverts commit $(git show -s --pretty=reference HEAD^)." >expect &&
+	test_cmp expect actual
+'
+
+test_expect_success 'identification of reverted commit (revert.reference)' '
+	git checkout --detach to-ident &&
+	git -c revert.reference=true revert --no-edit HEAD &&
+	git cat-file commit HEAD >actual.raw &&
+	grep "^This reverts " actual.raw >actual &&
+	echo "This reverts commit $(git show -s --pretty=reference HEAD^)." >expect &&
+	test_cmp expect actual
+'
+
+test_expect_success 'cherry-pick is unaware of --reference (for now)' '
+	test_when_finished "git reset --hard" &&
+	test_must_fail git cherry-pick --reference HEAD 2>actual &&
+	grep "^usage: git cherry-pick" actual
+'
+
 test_done