[PATCH v2] parse-options: don't complete option aliases by default

From: Philippe Blain <levraiphilippeblain@gmail.com>

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'.

This means that typing 'git clone --recurs<TAB>' will yield both '--recurse-submodules' and '--recursive', which is not ideal since both do the same thing, and so the completion should directly complete the canonical option.

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 <levraiphilippeblain@gmail.com>
---
    parse-options: don't complete option aliases by default
    
    Changes since v1:
    
     * Added a paragraph to the commit message to clarify that the goal of
       this patch is to have the completion show only the canonical option
       and not its alias.

Published-As: https://github.com/gitgitgadget/git/releases/tag/pr-996%2Fphil-blain%2Fclone-recurse-completion-v2
Fetch-It-Via: git fetch https://github.com/gitgitgadget/git pr-996/phil-blain/clone-recurse-completion-v2
Pull-Request: https://github.com/gitgitgadget/git/pull/996

Range-diff vs v1:

 1:  091a59323b7 ! 1:  9ae43e17e0c parse-options: don't complete option aliases by default
     @@ Commit message
          options with this flag are skipped by 'parse-options.c::show_gitcomp',
          which implements 'git <cmd> --git-completion-helper'.
      
     +    This means that typing 'git clone --recurs<TAB>' will yield both
     +    '--recurse-submodules' and '--recursive', which is not ideal since both
     +    do the same thing, and so the completion should directly complete the
     +    canonical option.
     +
          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

 parse-options.c       |  2 +-
 t/t9902-completion.sh | 13 +++++++++++++
 2 files changed, 14 insertions(+), 1 deletion(-)