Use parentheses and pipes to present alternatives in the argument help
for the --empty options of git am and git rebase, like in the rest of
the documentation.

While at it remove a stray use of the enum empty_action value
STOP_ON_EMPTY_COMMIT to indicate that no short option is present.
While it has a value of 0 and thus there is no user-visible change,
that enum is not meant to hold short option characters.  Hard-code 0,
like we do for other options without a short option.

Signed-off-by: René Scharfe <redacted>
---
 Documentation/git-rebase.txt | 4 ++--
 builtin/am.c                 | 2 +-
 builtin/rebase.c             | 2 +-
 3 files changed, 4 insertions(+), 4 deletions(-)

diff --git a/Documentation/git-rebase.txt b/Documentation/git-rebase.txt
index e7b39ad244..b4526ca246 100644
--- a/Documentation/git-rebase.txt
+++ b/Documentation/git-rebase.txt

@@ -289,7 +289,7 @@ See also INCOMPATIBLE OPTIONS below.
 +
 See also INCOMPATIBLE OPTIONS below.

---empty={drop,keep,ask}::
+--empty=(drop|keep|ask)::
        How to handle commits that are not empty to start and are not
        clean cherry-picks of any upstream commit, but which become
        empty after rebasing (because they contain a subset of already

@@ -695,7 +695,7 @@ be dropped automatically with `--no-keep-empty`).
 Similar to the apply backend, by default the merge backend drops
 commits that become empty unless `-i`/`--interactive` is specified (in
 which case it stops and asks the user what to do).  The merge backend
-also has an `--empty={drop,keep,ask}` option for changing the behavior
+also has an `--empty=(drop|keep|ask)` option for changing the behavior
 of handling commits that become empty.

 Directory rename detection

diff --git a/builtin/am.c b/builtin/am.c
index 6655059a57..9bb73d1671 100644
--- a/builtin/am.c
+++ b/builtin/am.c

@@ -2420,7 +2420,7 @@ int cmd_am(int argc, const char **argv, const char *prefix)
                { OPTION_STRING, 'S', "gpg-sign", &state.sign_commit, N_("key-id"),
                  N_("GPG-sign commits"),
                  PARSE_OPT_OPTARG, NULL, (intptr_t) "" },
-               OPT_CALLBACK_F(STOP_ON_EMPTY_COMMIT, "empty", &state.empty_type, "{stop,drop,keep}",
+               OPT_CALLBACK_F(0, "empty", &state.empty_type, "(stop|drop|keep)",
                  N_("how to handle empty patches"),
                  PARSE_OPT_NONEG, am_option_parse_empty),
                OPT_HIDDEN_BOOL(0, "rebasing", &state.rebasing,

diff --git a/builtin/rebase.c b/builtin/rebase.c
index f990811614..ad7baedd4a 100644
--- a/builtin/rebase.c
+++ b/builtin/rebase.c

@@ -1147,7 +1147,7 @@ int cmd_rebase(int argc, const char **argv, const char *prefix)
                                 "instead of ignoring them"),
                              1, PARSE_OPT_HIDDEN),
                OPT_RERERE_AUTOUPDATE(&options.allow_rerere_autoupdate),
-               OPT_CALLBACK_F(0, "empty", &options, "{drop,keep,ask}",
+               OPT_CALLBACK_F(0, "empty", &options, "(drop|keep|ask)",
                               N_("how to handle commits that become empty"),
                               PARSE_OPT_NONEG, parse_opt_empty),
                OPT_CALLBACK_F('k', "keep-empty", &options, NULL,
--

2.42.0