patchrevert: optionally refer to commit in the "reference" format

> A typical "git revert" commit uses the full title of the original
> commit in its title, and starts its body of the message with:
>
>     This reverts commit 8fa7f667cf61386257c00d6e954855cc3215ae91.
>
> This does not encourage the best practice of describing not just
> "what" (i.e. "Revert X" on the title says what we did) but "why"
> (i.e. and it does not say why X was undesirable).
>
> We can instead phrase this first line of the body to be more like
>
>     This reverts commit 8fa7f667 (do this and that, 2022-04-25)
>
> so that the title does not have to be
>
>     Revert "do this and that"
>
> We can instead use the title to describe "why" we are reverting the
> original commit.

> diff --git a/Documentation/git-revert.txt b/Documentation/git-revert.txt
> index bb92a4a451..8463fe9cf7 100644
> --- a/Documentation/git-revert.txt
> +++ b/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[]
> diff --git a/builtin/revert.c b/builtin/revert.c
> index 51776abea6..ada51e46b9 100644
> --- a/builtin/revert.c
> +++ b/builtin/revert.c
> @@ -116,6 +116,8 @@ static int run_sequencer(int argc, const char **argv, struct replay_opts *opts)
>  			N_("option for merge strategy"), option_parse_x),
>  		{ OPTION_STRING, 'S', "gpg-sign", &opts->gpg_sign, N_("key-id"),
>  		  N_("GPG sign commit"), PARSE_OPT_OPTARG, NULL, (intptr_t) "" },
> +		OPT_BOOL(0, "reference", &opts->commit_use_reference,
> +			 N_("use the 'reference' format to refer to commits")),
>  		OPT_END()
>  	};
>  	struct option *options = base_options;
> diff --git a/sequencer.c b/sequencer.c
> index a5f678f452..97abd5932b 100644
> --- a/sequencer.c
> +++ b/sequencer.c
> @@ -221,6 +221,9 @@ static int git_sequencer_config(const char *k, const char *v, void *cb)
>  		return ret;
>  	}
>
> +	if (!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 +2184,19 @@ static int do_pick_commit(struct repository *r,
>  		base_label = msg.label;
>  		next = parent;
>  		next_label = msg.parent_label;
> -		strbuf_addstr(&msgbuf, "Revert \"");
> -		strbuf_addstr(&msgbuf, msg.subject);
> -		strbuf_addstr(&msgbuf, "\"\n\nThis reverts commit ");
> -		strbuf_addstr(&msgbuf, oid_to_hex(&commit->object.oid));
> +		if (!opts->commit_use_reference) {
> +			strbuf_addstr(&msgbuf, "Revert \"");
> +			strbuf_addstr(&msgbuf, msg.subject);
> +			strbuf_addstr(&msgbuf, "\"");
> +		} else {
> +			strbuf_addstr(&msgbuf, "DESCRIBE WHY WE ARE REVERTING HERE");
> +		}

> +		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 {
> diff --git a/sequencer.h b/sequencer.h
> index da64473636..698599fe4e 100644
> --- a/sequencer.h
> +++ b/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;
>
> diff --git a/t/t3501-revert-cherry-pick.sh b/t/t3501-revert-cherry-pick.sh
> index 8617efaaf1..36f9565b92 100755
> --- a/t/t3501-revert-cherry-pick.sh
> +++ b/t/t3501-revert-cherry-pick.sh
> @@ -159,6 +159,7 @@ 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 &&
> @@ -174,4 +175,34 @@ 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 (vanilla)' '

> +	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 (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_done
> --
> 2.36.1-298-g81715a4e6d

>> +--reference::
>> ...
>> +	default.
>> +
>> +
>
> Is that extra empty line intentional?

>> +		if (!opts->commit_use_reference) {
>> +			strbuf_addstr(&msgbuf, "Revert \"");
>> +			strbuf_addstr(&msgbuf, msg.subject);
>> +			strbuf_addstr(&msgbuf, "\"");
>> +		} else {
>> +			strbuf_addstr(&msgbuf, "DESCRIBE WHY WE ARE REVERTING HERE");
>> +		}
>
> We often tell newcomers that we prefer the shorter conditional block to
> come first. Maybe you want to do that here, too? I don't mind the current
> form, though.

>> @@ -174,4 +175,34 @@ 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 (vanilla)' '
>
> It might make sense to replace "vanilla" by "default format".

>> +	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 &&
>
> I was a bit puzzled about this dance, as I had expected this instead:
>
> 	grep "^This reverts commit $(git rev-parse HEAD^)\\.$" actual.raw
>
> but I guess you wanted to make sure that the file contents of `actual` are
> shown if no match was found?

>> +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
>> +'
>
> If it was up to me, I would combine these three test cases, if only to
> help the `--run=<single-number>` case (the latter two depend on the side
> effect of the first one to create a `to-ident` tag).

>> +test_expect_success 'identification of reverted commit (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_done

> A typical "git revert" commit uses the full title of the original
> commit in its title, and starts its body of the message with:
>
>     This reverts commit 8fa7f667cf61386257c00d6e954855cc3215ae91.
>
> This does not encourage the best practice of describing not just
> "what" (i.e. "Revert X" on the title says what we did) but "why"
> (i.e. and it does not say why X was undesirable).
>
> We can instead phrase this first line of the body to be more like
>
>     This reverts commit 8fa7f667 (do this and that, 2022-04-25)
>
> so that the title does not have to be
>
>     Revert "do this and that"
>
> We can instead use the title to describe "why" we are reverting the
> original commit.
>
> Introduce the "--reference" option to "git revert", and also the
> revert.reference configuration variable, which defaults to false, to
> tweak the title and the first line of the draft commit message for
> when creating a "revert" commit.
>
> When this option is in use, the first line of the pre-filled editor
> buffer becomes a comment line that tells the user to say _why_.  If
> the user exits the editor without touching this line by mistake,
> what we prepare to become the first line of the body, i.e. "This
> reverts commit 8fa7f667 (do this and that, 2022-04-25)", ends up to
> be the title of the resulting commit.  This behaviour is designed to
> help such a user to identify such a revert in "git log --oneline"
> easily so that it can be further reworded with "git rebase -i" later.
>
> Signed-off-by: Junio C Hamano <gitster@pobox.com>
> ---
>
>  * The only difference since the second one is that the first line of
>    the log message template is commented out and has asterisks to
>    draw more attention.  The last paragraph (new) in the proposed
>    log message explains the rationale behind this design.

>
>    Third-time a charm, hopefully.
>
> Range-diff against v2:
> 1:  4152fc2092 ! 1:  f4325a503a revert: optionally refer to commit in the "reference" format
>     @@ Commit message
>          tweak the title and the first line of the draft commit message for
>          when creating a "revert" commit.
>
>     +    When this option is in use, the first line of the pre-filled editor
>     +    buffer becomes a comment line that tells the user to say _why_.  If
>     +    the user exits the editor without touching this line by mistake,
>     +    what we prepare to become the first line of the body, i.e. "This
>     +    reverts commit 8fa7f667 (do this and that, 2022-04-25)", ends up to
>     +    be the title of the resulting commit.  This behaviour is designed to
>     +    help such a user to identify such a revert in "git log --oneline"
>     +    easily so that it can be further reworded with "git rebase -i" later.
>     +
>          Signed-off-by: Junio C Hamano <gitster@pobox.com>
>
>       ## Documentation/config/revert.txt (new) ##
>     @@ sequencer.c: static int do_pick_commit(struct repository *r,
>      -		strbuf_addstr(&msgbuf, "\"\n\nThis reverts commit ");
>      -		strbuf_addstr(&msgbuf, oid_to_hex(&commit->object.oid));
>      +		if (opts->commit_use_reference) {
>     -+			strbuf_addstr(&msgbuf, "DESCRIBE WHY WE ARE REVERTING HERE");
>     ++			strbuf_addstr(&msgbuf,
>     ++				"# *** SAY WHY WE ARE REVERTING ON THE TITLE LINE ***");
>      +		} else {
>      +			strbuf_addstr(&msgbuf, "Revert \"");
>      +			strbuf_addstr(&msgbuf, msg.subject);
>
>  Documentation/config/revert.txt |  3 +++
>  Documentation/git-revert.txt    |  9 +++++++++
>  builtin/revert.c                |  2 ++
>  sequencer.c                     | 33 ++++++++++++++++++++++++++++-----
>  sequencer.h                     |  1 +
>  t/t3501-revert-cherry-pick.sh   | 31 +++++++++++++++++++++++++++++++
>  6 files changed, 74 insertions(+), 5 deletions(-)
>  create mode 100644 Documentation/config/revert.txt
>
> diff --git a/Documentation/config/revert.txt b/Documentation/config/revert.txt
> new file mode 100644
> index 0000000000..797bfb6d62
> --- /dev/null
> +++ b/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.
> diff --git a/Documentation/git-revert.txt b/Documentation/git-revert.txt
> index bb92a4a451..8463fe9cf7 100644
> --- a/Documentation/git-revert.txt
> +++ b/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[]
> diff --git a/builtin/revert.c b/builtin/revert.c
> index 51776abea6..ada51e46b9 100644
> --- a/builtin/revert.c
> +++ b/builtin/revert.c
> @@ -116,6 +116,8 @@ static int run_sequencer(int argc, const char **argv, struct replay_opts *opts)
>  			N_("option for merge strategy"), option_parse_x),
>  		{ OPTION_STRING, 'S', "gpg-sign", &opts->gpg_sign, N_("key-id"),
>  		  N_("GPG sign commit"), PARSE_OPT_OPTARG, NULL, (intptr_t) "" },
> +		OPT_BOOL(0, "reference", &opts->commit_use_reference,
> +			 N_("use the 'reference' format to refer to commits")),
>  		OPT_END()
>  	};
>  	struct option *options = base_options;
> diff --git a/sequencer.c b/sequencer.c
> index a5f678f452..96fec6ef6d 100644
> --- a/sequencer.c
> +++ b/sequencer.c
> @@ -221,6 +221,9 @@ static int git_sequencer_config(const char *k, const char *v, void *cb)
>  		return ret;
>  	}
>
> +	if (!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 \"");
> -		strbuf_addstr(&msgbuf, msg.subject);
> -		strbuf_addstr(&msgbuf, "\"\n\nThis reverts commit ");
> -		strbuf_addstr(&msgbuf, oid_to_hex(&commit->object.oid));
> +		if (opts->commit_use_reference) {
> +			strbuf_addstr(&msgbuf,
> +				"# *** SAY WHY WE ARE REVERTING ON THE TITLE LINE ***");
> +		} 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 {
> diff --git a/sequencer.h b/sequencer.h
> index da64473636..698599fe4e 100644
> --- a/sequencer.h
> +++ b/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;
>
> diff --git a/t/t3501-revert-cherry-pick.sh b/t/t3501-revert-cherry-pick.sh
> index 8617efaaf1..a386ae9e88 100755
> --- a/t/t3501-revert-cherry-pick.sh
> +++ b/t/t3501-revert-cherry-pick.sh
> @@ -159,6 +159,7 @@ 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 &&
> @@ -174,4 +175,34 @@ 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_done
> --
> 2.36.1-331-g1b5d92e060
>
>

> A typical "git revert" commit uses the full title of the original
> commit in its title, and starts its body of the message with:
> 
>      This reverts commit 8fa7f667cf61386257c00d6e954855cc3215ae91.
> 
> This does not encourage the best practice of describing not just
> "what" (i.e. "Revert X" on the title says what we did) but "why"
> (i.e. and it does not say why X was undesirable).
> 
> We can instead phrase this first line of the body to be more like
> 
>      This reverts commit 8fa7f667 (do this and that, 2022-04-25)
> 
> so that the title does not have to be
> 
>      Revert "do this and that"
> 
> We can instead use the title to describe "why" we are reverting the
> original commit.
> 
> Introduce the "--reference" option to "git revert", and also the
> revert.reference configuration variable, which defaults to false, to
> tweak the title and the first line of the draft commit message for
> when creating a "revert" commit.
> 
> When this option is in use, the first line of the pre-filled editor
> buffer becomes a comment line that tells the user to say _why_.  If
> the user exits the editor without touching this line by mistake,
> what we prepare to become the first line of the body, i.e. "This
> reverts commit 8fa7f667 (do this and that, 2022-04-25)", ends up to
> be the title of the resulting commit.  This behaviour is designed to
> help such a user to identify such a revert in "git log --oneline"
> easily so that it can be further reworded with "git rebase -i" later.
> 
> Signed-off-by: Junio C Hamano <gitster@pobox.com>
> ---
> 
>   * The only difference since the second one is that the first line of
>     the log message template is commented out and has asterisks to
>     draw more attention.  The last paragraph (new) in the proposed
>     log message explains the rationale behind this design.
> 
>     Third-time a charm, hopefully.

> Range-diff against v2:
> 1:  4152fc2092 ! 1:  f4325a503a revert: optionally refer to commit in the "reference" format
>      @@ Commit message
>           tweak the title and the first line of the draft commit message for
>           when creating a "revert" commit.
>       
>      +    When this option is in use, the first line of the pre-filled editor
>      +    buffer becomes a comment line that tells the user to say _why_.  If
>      +    the user exits the editor without touching this line by mistake,
>      +    what we prepare to become the first line of the body, i.e. "This
>      +    reverts commit 8fa7f667 (do this and that, 2022-04-25)", ends up to
>      +    be the title of the resulting commit.  This behaviour is designed to
>      +    help such a user to identify such a revert in "git log --oneline"
>      +    easily so that it can be further reworded with "git rebase -i" later.
>      +
>           Signed-off-by: Junio C Hamano <gitster@pobox.com>
>       
>        ## Documentation/config/revert.txt (new) ##
>      @@ sequencer.c: static int do_pick_commit(struct repository *r,
>       -		strbuf_addstr(&msgbuf, "\"\n\nThis reverts commit ");
>       -		strbuf_addstr(&msgbuf, oid_to_hex(&commit->object.oid));
>       +		if (opts->commit_use_reference) {
>      -+			strbuf_addstr(&msgbuf, "DESCRIBE WHY WE ARE REVERTING HERE");
>      ++			strbuf_addstr(&msgbuf,
>      ++				"# *** SAY WHY WE ARE REVERTING ON THE TITLE LINE ***");
>       +		} else {
>       +			strbuf_addstr(&msgbuf, "Revert \"");
>       +			strbuf_addstr(&msgbuf, msg.subject);
> 
>   Documentation/config/revert.txt |  3 +++
>   Documentation/git-revert.txt    |  9 +++++++++
>   builtin/revert.c                |  2 ++
>   sequencer.c                     | 33 ++++++++++++++++++++++++++++-----
>   sequencer.h                     |  1 +
>   t/t3501-revert-cherry-pick.sh   | 31 +++++++++++++++++++++++++++++++
>   6 files changed, 74 insertions(+), 5 deletions(-)
>   create mode 100644 Documentation/config/revert.txt
> 
> diff --git a/Documentation/config/revert.txt b/Documentation/config/revert.txt
> new file mode 100644
> index 0000000000..797bfb6d62
> --- /dev/null
> +++ b/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.
> diff --git a/Documentation/git-revert.txt b/Documentation/git-revert.txt
> index bb92a4a451..8463fe9cf7 100644
> --- a/Documentation/git-revert.txt
> +++ b/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[]
> diff --git a/builtin/revert.c b/builtin/revert.c
> index 51776abea6..ada51e46b9 100644
> --- a/builtin/revert.c
> +++ b/builtin/revert.c
> @@ -116,6 +116,8 @@ static int run_sequencer(int argc, const char **argv, struct replay_opts *opts)
>   			N_("option for merge strategy"), option_parse_x),
>   		{ OPTION_STRING, 'S', "gpg-sign", &opts->gpg_sign, N_("key-id"),
>   		  N_("GPG sign commit"), PARSE_OPT_OPTARG, NULL, (intptr_t) "" },
> +		OPT_BOOL(0, "reference", &opts->commit_use_reference,
> +			 N_("use the 'reference' format to refer to commits")),
>   		OPT_END()
>   	};
>   	struct option *options = base_options;
> diff --git a/sequencer.c b/sequencer.c
> index a5f678f452..96fec6ef6d 100644
> --- a/sequencer.c
> +++ b/sequencer.c
> @@ -221,6 +221,9 @@ static int git_sequencer_config(const char *k, const char *v, void *cb)
>   		return ret;
>   	}
>   
> +	if (!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 \"");
> -		strbuf_addstr(&msgbuf, msg.subject);
> -		strbuf_addstr(&msgbuf, "\"\n\nThis reverts commit ");
> -		strbuf_addstr(&msgbuf, oid_to_hex(&commit->object.oid));
> +		if (opts->commit_use_reference) {
> +			strbuf_addstr(&msgbuf,
> +				"# *** SAY WHY WE ARE REVERTING ON THE TITLE LINE ***");
> +		} 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 {
> diff --git a/sequencer.h b/sequencer.h
> index da64473636..698599fe4e 100644
> --- a/sequencer.h
> +++ b/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;
>   
> diff --git a/t/t3501-revert-cherry-pick.sh b/t/t3501-revert-cherry-pick.sh
> index 8617efaaf1..a386ae9e88 100755
> --- a/t/t3501-revert-cherry-pick.sh
> +++ b/t/t3501-revert-cherry-pick.sh
> @@ -159,6 +159,7 @@ 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 &&
> @@ -174,4 +175,34 @@ 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_done

> Phillip Wood <phillip.wood123@gmail.com> writes:
> 
>> I think the changes to the template message are good. We're still
>> adding "--reference" as a valid option to cherry-pick though which I
>> don't think is a good idea (though in the future we may want to allow
>> "cherry-pick -x --reference")
> 
> I love when people notice mistakes that the original author and
> other people missed, many eyes making all bugs shallow.
> 
> I am inclined to apply the following on top.  How does it look?

> Thanks.
> 
> ----- >8 --------- >8 --------- >8 --------- >8 -----
> Subject: [PATCH] revert: --reference should apply only to 'revert', not 'cherry-pick'
> 
> As 'revert' and 'cherry-pick' share a lot of code, it is easy to
> modify the behaviour of one command and inadvertently affect the
> other.  An earlier change to teach the '--reference' option and the
> 'revert.reference' configuration variable to the former was not
> careful enough and 'cherry-pick --reference' wasn't rejected as an
> error.
> 
> It is possible to think 'cherry-pick -x' might benefit from the
> '--reference' option, but it is fundamentally different from
> 'revert' in at least two ways to make it questionable:
> 
>   - 'revert' names a commit that is ancestor of the resulting commit,
>     so an abbreviated object name with human readable title is
>     sufficient to identify the named commit uniquely without using
>     the full object name.  On the other hand, 'cherry-pick'
>     usually [*] picks a commit that is not an ancestor.  It might be
>     even picking a private commit that never becomes part of the
>     public history.
> 
>   - The whole commit message of 'cherry-pick' is a copy of the
>     original commit, and there is nothing gained to repeat only the
>     title part on 'cherry-picked from' message.
> 
> [*] well, you could revert and then you can pick the original that
>      was reverted to get back to where you were, but then you can
>      revert the revert to do the same thing.
> 
> Helped-by: Phillip Wood <phillip.wood@dunelm.org.uk>
> Signed-off-by: Junio C Hamano <gitster@pobox.com>
> ---
>   builtin/revert.c              | 9 +++++++--
>   sequencer.c                   | 2 +-
>   t/t3501-revert-cherry-pick.sh | 6 ++++++
>   3 files changed, 14 insertions(+), 3 deletions(-)
> 
> diff --git a/builtin/revert.c b/builtin/revert.c
> index ada51e46b9..f84c253f4c 100644
> --- a/builtin/revert.c
> +++ b/builtin/revert.c
> @@ -116,8 +116,6 @@ static int run_sequencer(int argc, const char **argv, struct replay_opts *opts)
>   			N_("option for merge strategy"), option_parse_x),
>   		{ OPTION_STRING, 'S', "gpg-sign", &opts->gpg_sign, N_("key-id"),
>   		  N_("GPG sign commit"), PARSE_OPT_OPTARG, NULL, (intptr_t) "" },
> -		OPT_BOOL(0, "reference", &opts->commit_use_reference,
> -			 N_("use the 'reference' format to refer to commits")),
>   		OPT_END()
>   	};
>   	struct option *options = base_options;
> @@ -132,6 +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,
> diff --git a/sequencer.c b/sequencer.c
> index 96fec6ef6d..4b66a1f79c 100644
> --- a/sequencer.c
> +++ b/sequencer.c
> @@ -221,7 +221,7 @@ static int git_sequencer_config(const char *k, const char *v, void *cb)
>   		return ret;
>   	}
>   
> -	if (!strcmp(k, "revert.reference"))
> +	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);
> diff --git a/t/t3501-revert-cherry-pick.sh b/t/t3501-revert-cherry-pick.sh
> index a386ae9e88..fb4466599b 100755
> --- a/t/t3501-revert-cherry-pick.sh
> +++ b/t/t3501-revert-cherry-pick.sh
> @@ -205,4 +205,10 @@ test_expect_success 'identification of reverted commit (revert.reference)' '
>   	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

> When this option is in use, the first line of the pre-filled editor
> buffer becomes a comment line that tells the user to say _why_.  If
> the user exits the editor without touching this line by mistake,
> what we prepare to become the first line of the body, i.e. "This
> reverts commit 8fa7f667 (do this and that, 2022-04-25)", ends up to
> be the title of the resulting commit.  This behaviour is designed to
> help such a user to identify such a revert in "git log --oneline"
> easily so that it can be further reworded with "git rebase -i" later.

> @@ -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 \"");
> -		strbuf_addstr(&msgbuf, msg.subject);
> -		strbuf_addstr(&msgbuf, "\"\n\nThis reverts commit ");
> -		strbuf_addstr(&msgbuf, oid_to_hex(&commit->object.oid));
> +		if (opts->commit_use_reference) {
> +			strbuf_addstr(&msgbuf,
> +				"# *** SAY WHY WE ARE REVERTING ON THE TITLE LINE ***");
> +		} 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);
>  		}

> +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_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

> I think a good solution to that would be to e.g. emit:
>
>     # *** SAY WHY WE ARE REVERTING ON THE TITLE LINE ***
>
>     Reverts commit <git reference>
>
>     This revert of a merge reverts changes made to <git reference 2>.
>
> Instead of what you have, which is:
>
>     # *** SAY WHY WE ARE REVERTING ON THE TITLE LINE ***
>
>     This reverts commit <git reference>, reversing
>     changes made to <git reference 2>.
>
> It's sharing a bit less code between the two, but I think the message is
> suffering for it now.

>> +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
>
> Also (probably mentioned) I'd find this much easier to read/review if it
> was using test_cmp, now you need to carefully parse the code to see what
> the outputs are like exactly, but if we compared the full output...

> Johannes Schindelin <Johannes.Schindelin@gmx.de> writes:
>
> >> +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
> >> +'
> >
> > If it was up to me, I would combine these three test cases, if only to
> > help the `--run=<single-number>` case (the latter two depend on the
> > side effect of the first one to create a `to-ident` tag).
>
> I wonder if our prereq infrastructure is lightweight and scalable enough
> so that we can easily add a support a pseudo-prerequisite PREVIOUS that
> lets us say
>
> 	test_expect_success PREVIOUS "identification ..." '
> 		...
> 	'
>
> to mean that this test requires the previous test has not been
> skipped.

> Hi Junio,
>
> On Mon, 23 May 2022, Junio C Hamano wrote:
>
>> Johannes Schindelin <Johannes.Schindelin@gmx.de> writes:
>>
>> >> +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
>> >> +'
>> >
>> > If it was up to me, I would combine these three test cases, if only to
>> > help the `--run=<single-number>` case (the latter two depend on the
>> > side effect of the first one to create a `to-ident` tag).
>>
>> I wonder if our prereq infrastructure is lightweight and scalable enough
>> so that we can easily add a support a pseudo-prerequisite PREVIOUS that
>> lets us say
>>
>> 	test_expect_success PREVIOUS "identification ..." '
>> 		...
>> 	'
>>
>> to mean that this test requires the previous test has not been
>> skipped.
>
> In theory, this sounds good to me.
>
> In practice, however, side effects are awful and make everything harder,
> from developing code to debugging to helping new contributors. I wish we
> would do away with them altogether and have something more akin to the
> before/after constructs known from e.g. TestNG (think `@BeforeTest` and
> `@BeforeClass`).
>
> One option would be to mark `setup` steps completely differently, sort of
> imitating the prereq infrastructure instead of using
> `test_expect_success`. Kind of prereqs, but required to pass.

> A typical "git revert" commit uses the full title of the original
> commit in its title, and starts its body of the message with:
>
>     This reverts commit 8fa7f667cf61386257c00d6e954855cc3215ae91.
>
> This does not encourage the best practice of describing not just
> "what" (i.e. "Revert X" on the title says what we did) but "why"
> (i.e. and it does not say why X was undesirable).
>
> We can instead phrase this first line of the body to be more like
>
>     This reverts commit 8fa7f667 (do this and that, 2022-04-25)
>
> so that the title does not have to be
>
>     Revert "do this and that"
>
> We can instead use the title to describe "why" we are reverting the
> original commit.
>
> Introduce the "--reference" option to "git revert", and also the
> revert.reference configuration variable, which defaults to false, to
> tweak the title and the first line of the draft commit message for
> when creating a "revert" commit.

> +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 +2184,19 @@ static int do_pick_commit(struct repository *r,
>  		base_label = msg.label;
>  		next = parent;
>  		next_label = msg.parent_label;
> -		strbuf_addstr(&msgbuf, "Revert \"");
> -		strbuf_addstr(&msgbuf, msg.subject);
> -		strbuf_addstr(&msgbuf, "\"\n\nThis reverts commit ");
> -		strbuf_addstr(&msgbuf, oid_to_hex(&commit->object.oid));
> +		if (!opts->commit_use_reference) {
> +			strbuf_addstr(&msgbuf, "Revert \"");
> +			strbuf_addstr(&msgbuf, msg.subject);
> +			strbuf_addstr(&msgbuf, "\"");
> +		} else {
> +			strbuf_addstr(&msgbuf, "DESCRIBE WHY WE ARE REVERTING HERE");

> +		}
> +		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 {

> diff --git a/sequencer.h b/sequencer.h
> index da64473636..698599fe4e 100644
> --- a/sequencer.h
> +++ b/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;
>  
> diff --git a/t/t3501-revert-cherry-pick.sh b/t/t3501-revert-cherry-pick.sh
> index 8617efaaf1..36f9565b92 100755
> --- a/t/t3501-revert-cherry-pick.sh
> +++ b/t/t3501-revert-cherry-pick.sh
> @@ -159,6 +159,7 @@ 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 &&
> @@ -174,4 +175,34 @@ 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 (vanilla)' '
> +	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 (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_done

>> +		if (!opts->commit_use_reference) {
>> +			strbuf_addstr(&msgbuf, "Revert \"");
>> +			strbuf_addstr(&msgbuf, msg.subject);
>> +			strbuf_addstr(&msgbuf, "\"");
>> +		} else {
>> +			strbuf_addstr(&msgbuf, "DESCRIBE WHY WE ARE REVERTING HERE");
>
> Having seen how people use git in the wild, this *WILL* result in a
> bunch of history where people don't edit that at all.

> Ævar Arnfjörð Bjarmason <avarab@gmail.com> writes:
>
>>> +		if (!opts->commit_use_reference) {
>>> +			strbuf_addstr(&msgbuf, "Revert \"");
>>> +			strbuf_addstr(&msgbuf, msg.subject);
>>> +			strbuf_addstr(&msgbuf, "\"");
>>> +		} else {
>>> +			strbuf_addstr(&msgbuf, "DESCRIBE WHY WE ARE REVERTING HERE");
>>
>> Having seen how people use git in the wild, this *WILL* result in a
>> bunch of history where people don't edit that at all.
>
> It was done very much on purpose.  A pressure from other project
> participants against the ugly all caps content-free message will
> help instill better behaviour.

> A solo developer also will learn
> after making reverts with content-free titles (and if they do not
> find it inconvenient for their development purpose that their
> history is full of content-free titles shouting in all caps, then
> more power to them---if they are happy, we are happy, too).

> If we leave something like
>
> 	# Add one line above and explain not *what* this revert did,
> 	# but *why* you decided to revert in 50-70 chars.  Did it
> 	# break something? Was it premature?
>
> 	This reverts commit 8aa3f0dc (CI: set CC in MAKEFLAGS directly, 2022-04-21)
>
> presumably, stripspace will make the "This reverts commit ..." the
> title of the reverted commit.  It would invite people not to edit it
> out out of laziness.  Since the whole point of this change is to
> encourage people to describe the reason behind the revert on the
> subject line, such an invitation is counter-productive.

> Doing the first two lines like so:
>
> 	Revert 8aa3f0dc (CI: set CC in MAKEFLAGS directly, 2022-04-21)
> 	# Edit the above line to explain not *what* this revert did,
>
> would have pretty much the same effect, I am afraid.
>
> So...

>
>> If we leave something like
>>
>> 	# Add one line above and explain not *what* this revert did,
>> 	# but *why* you decided to revert in 50-70 chars.  Did it
>> 	# break something? Was it premature?
>>
>> 	This reverts commit 8aa3f0dc (CI: set CC in MAKEFLAGS directly, 2022-04-21)
>>
>> presumably, stripspace will make the "This reverts commit ..." the
>> title of the reverted commit.  It would invite people not to edit it
>> out out of laziness.  Since the whole point of this change is to
>> encourage people to describe the reason behind the revert on the
>> subject line, such an invitation is counter-productive.
>
> If that's the concern we could also comment the "This reverts" line.

> A typical "git revert" commit uses the full title of the original
> commit in its title, and starts its body of the message with:
> 
>      This reverts commit 8fa7f667cf61386257c00d6e954855cc3215ae91.
> 
> This does not encourage the best practice of describing not just
> "what" (i.e. "Revert X" on the title says what we did) but "why"
> (i.e. and it does not say why X was undesirable).
> 
> We can instead phrase this first line of the body to be more like
> 
>      This reverts commit 8fa7f667 (do this and that, 2022-04-25)
> 
> so that the title does not have to be
> 
>      Revert "do this and that"
> 
> We can instead use the title to describe "why" we are reverting the
> original commit.
> 
> Introduce the "--reference" option to "git revert", and also the
> revert.reference configuration variable, which defaults to false, to
> tweak the title and the first line of the draft commit message for
> when creating a "revert" commit.

> diff --git a/builtin/revert.c b/builtin/revert.c
> index 51776abea6..ada51e46b9 100644
> --- a/builtin/revert.c
> +++ b/builtin/revert.c
> @@ -116,6 +116,8 @@ static int run_sequencer(int argc, const char **argv, struct replay_opts *opts)
>   			N_("option for merge strategy"), option_parse_x),
>   		{ OPTION_STRING, 'S', "gpg-sign", &opts->gpg_sign, N_("key-id"),
>   		  N_("GPG sign commit"), PARSE_OPT_OPTARG, NULL, (intptr_t) "" },
> +		OPT_BOOL(0, "reference", &opts->commit_use_reference,
> +			 N_("use the 'reference' format to refer to commits")),

>   static int do_pick_commit(struct repository *r,
>   			  struct todo_item *item,
>   			  struct replay_opts *opts,
> @@ -2167,14 +2184,19 @@ static int do_pick_commit(struct repository *r,
>   		base_label = msg.label;
>   		next = parent;
>   		next_label = msg.parent_label;
> -		strbuf_addstr(&msgbuf, "Revert \"");
> -		strbuf_addstr(&msgbuf, msg.subject);
> -		strbuf_addstr(&msgbuf, "\"\n\nThis reverts commit ");
> -		strbuf_addstr(&msgbuf, oid_to_hex(&commit->object.oid));
> +		if (!opts->commit_use_reference) {
> +			strbuf_addstr(&msgbuf, "Revert \"");
> +			strbuf_addstr(&msgbuf, msg.subject);
> +			strbuf_addstr(&msgbuf, "\"");
> +		} else {
> +			strbuf_addstr(&msgbuf, "DESCRIBE WHY WE ARE REVERTING HERE");

> ---
>  Documentation/config/revert.txt |  3 +++
>  Documentation/git-revert.txt    |  9 +++++++++
>  builtin/revert.c                |  2 ++
>  sequencer.c                     | 32 +++++++++++++++++++++++++++-----
>  sequencer.h                     |  1 +
>  t/t3501-revert-cherry-pick.sh   | 31 +++++++++++++++++++++++++++++++
>  6 files changed, 73 insertions(+), 5 deletions(-)
>  create mode 100644 Documentation/config/revert.txt
>
> diff --git a/Documentation/config/revert.txt b/Documentation/config/revert.txt
> new file mode 100644
> index 0000000000..797bfb6d62
> --- /dev/null
> +++ b/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.