Subject: Re: [PATCH] parse-options: don't complete option aliases by default

From: Ævar Arnfjörð Bjarmason <[email-masked]>
Date: Thu, 15 Jul 2021 18:16:26 +0200

On Thu, Jul 15 2021, Philippe Blain via GitGitGadget wrote:

> From: Philippe Blain <[email-masked]>
>
> Since 'OPT_ALIAS' was created in 5c387428f1 (parse-options: don't emit
> "ambiguous option" for aliases, 2019-04-29), 'git clone
> --git-completion-helper', which is used by the Bash completion script to
> list options accepted by clone (via '__gitcomp_builtin'), lists both
> '--recurse-submodules' and its alias '--recursive', which was not the
> case before since '--recursive' had the PARSE_OPT_HIDDEN flag set, and
> options with this flag are skipped by 'parse-options.c::show_gitcomp',
> which implements 'git <cmd> --git-completion-helper'.
>
> At the point where 'show_gitcomp' is called in 'parse_options_step',
> 'preprocess_options' was already called in 'parse_options', so any
> aliases are now copies of the original options with a modified help text
> indicating they are aliases.
>
> Helpfully, since 64cc539fd2 (parse-options: don't leak alias help
> messages, 2021-03-21) these copies have the PARSE_OPT_FROM_ALIAS flag
> set, so check that flag early in 'show_gitcomp' and do not print them,
> unless the user explicitely requested that *all* completion be shown (by
> setting 'GIT_COMPLETION_SHOW_ALL'). After all, if we want to encourage
> the use of '--recurse-submodules' over '--recursive', we'd better just
> suggest the former.
>
> The only other options alias is 'log' and friends' '--mailmap', which is
> an alias for '--use-mailmap', but the Bash completion helpers for these
> commands do not use '__gitcomp_builtin', and thus are unnaffected by
> this change.
>
> Test the new behaviour in t9902-completion.sh. As a side effect, this
> also tests the correct behaviour of GIT_COMPLETION_SHOW_ALL, which was
> not tested before. Note that since '__gitcomp_builtin' caches the
> options it shows, we need to re-source the completion script to clear
> that cache for the second test.
>
> Signed-off-by: Philippe Blain <[email-masked]>
> ---
>     parse-options: don't complete option aliases by default
>
> Published-As: https://github.com/gitgitgadget/git/releases/tag/pr-996%2Fphil-blain%2Fclone-recurse-completion-v1
> Fetch-It-Via: git fetch https://github.com/gitgitgadget/git pr-996/phil-blain/clone-recurse-completion-v1
> Pull-Request: https://github.com/gitgitgadget/git/pull/996
>
>  parse-options.c       |  2 +-
>  t/t9902-completion.sh | 13 +++++++++++++
>  2 files changed, 14 insertions(+), 1 deletion(-)
>
> diff --git a/parse-options.c b/parse-options.c
> index e6f56768ca5..2abff136a17 100644
> --- a/parse-options.c
> +++ b/parse-options.c
> @@ -585,7 +585,7 @@ static int show_gitcomp(const struct option *opts, int show_all)
>  		if (!opts->long_name)
>  			continue;
>  		if (!show_all &&
> -			(opts->flags & (PARSE_OPT_HIDDEN | PARSE_OPT_NOCOMPLETE)))
> +			(opts->flags & (PARSE_OPT_HIDDEN | PARSE_OPT_NOCOMPLETE | PARSE_OPT_FROM_ALIAS)))
>  			continue;
>  
>  		switch (opts->type) {
> diff --git a/t/t9902-completion.sh b/t/t9902-completion.sh
> index cb057ef1613..11573936d58 100755
> --- a/t/t9902-completion.sh
> +++ b/t/t9902-completion.sh
> @@ -2404,6 +2404,19 @@ test_expect_success 'sourcing the completion script clears cached --options' '
>  	verbose test -z "$__gitcomp_builtin_notes_edit"
>  '
>  
> +test_expect_success 'option aliases are not shown by default' '
> +	test_completion "git clone --recurs" "--recurse-submodules "
> +'

I'm a bit biased here since I like --recursive better, but let's not
drag that whole argument up again. I don't find the argument in
bb62e0a99fc (clone: teach --recurse-submodules to optionally take a
pathspec, 2017-03-17) convincing enough to have moved such a prominent
use-case to a longer option name.

But, water under the bridge. Aside from that:

For me a Google search for "git clone --recursive" is ~40k results, but
"git clone --recurse-submodules". The former links to various
discussions/docs/stackoverflow answers, often --recurse-submodules isn't
mentioned at all or as an aside.

I think it's unfortunate that we:

 1. Conflate whether something shows up in completion v.s. the
    help. Given its prominence and that "git clone -h" is ~50 lines why
    not note --recursive there.

 2. Don't have the completion aware of these aliases, i.e. "git clone
    --rec<TAB>" before your chance offers a completion of both, that sucks,
    we should fully complete the non-alias instead.

 3. Making it PARSE_OPT_HIDDEN "solves" #2 at the cost of hiding it in
    "git help -h", and now this won't work, but did before:

        git clone --recursi<TAB>

    I.e. even if we didn't want to do #2 *and* wanted to hide it in the
    usage output surely completing an unmbigous prefix is better, even
    if it's a hidden option?

Per-se none of this is a blocker or "we must fix this first" for this
particular change, we have this in many existing cases.

I daresay there's no other alias that's in as wide a use in the wild, so
we should think about this one particularly carefully though.

It's not fully clear from your commit message which of 1-3 you're aiming
for, I think it's more of the "discourage its use". 

Sure, fair enough, but PARSE_OPT_HIDDEN is not a 1=1 mapping to that,
and can often lead to more user confusion.

E.g. the user has used --recursive for years, but can't even find it in
-h (I also think it's a mistake to have entirely removed it from the
docs, even if one agrees with its "deprecation" I'd say we should keep
some "used to be called --recursive" note there).