Implement command aliases

[tbidne]

This implements the "command aliases" portion of #484 (the other part, default commands, is left for another day). My motivation is presumably similar to the OP of that issue i.e. I sometimes want shorter aliases for commands, much like we can do with options. For example:

-- options
long "file"
  <> short 'f'

-- new, for commands
-- commandAliases :: NonEmpty String -> ParserInfo a -> Mod CommandFields a
commandAliases
  ("print" :| ["p"])
  (info (pure Print) (progDesc "Runs print"))

I chose to implement this as a companion to the normal function:

command :: String -> ParserInfo a -> Mod CommandFields a

since CommandFields is a modifier for the command group, not an individual command, so we cannot monoidally combine names for an individual command, like we can for options.

This is technically a breaking change as Options.Applicative.Builder.Internal exports the CommandFields constructor:

diff --git a/src/Options/Applicative/Builder/Internal.hs b/src/Options/Applicative/Builder/Internal.hs
index 2110067..68984c2 100644
--- a/src/Options/Applicative/Builder/Internal.hs
+++ b/src/Options/Applicative/Builder/Internal.hs
 data CommandFields a = CommandFields
-  { cmdCommands :: [(String, ParserInfo a)]
+  { cmdCommands :: [(NonEmpty String, ParserInfo a)]
   , cmdGroup :: Maybe String }

Incidentally, it would be great to have #367, as imo this should really only require a minor bump, not a major one. I would be happy to investigate that, though there is less need for it wrt this PR, since we are already on a new major bump.

Thanks!

[tbidne]

Some bikeshedding notes:

1. Currently, this differs from the proposed rendering in the issue i.e. we have no whitespace between aliases:

   Usage: prop_cmd_aliases (COMMAND | COMMAND)
   
   Available options:
     -h,--help                Show this help text
   
   Available commands:
     hello,hi                 Print greeting
     goodbye                  Say goodbye
   
   French commands:
     bonjour                  Print greeting
     au-revoir,adieu,ciao     Say goodbye
   
   Other commands:
     health                   Check health
     aux                      Auxiliary
   

   This is for consistency with options (e.g. see -h,--help above), though it is arguably busy compared to the variant with a single space:

   Usage: prop_cmd_aliases (COMMAND | COMMAND)
   
   Available options:
     -h,--help                Show this help text
   
   Available commands:
     hello, hi                Print greeting
     goodbye                  Say goodbye
   
   French commands:
     bonjour                  Print greeting
     au-revoir, adieu, ciao   Say goodbye
   
   Other commands:
     health                   Check health
     aux                      Auxiliary
   

2. There is no normalizing wrt repeated aliases, for instance, duplicate aliases will be listed in completions multiple times. This is consistent with how commands currently work e.g.

   command "cmd" (info (pure Cmd1) ...)
     <> command "cmd" (info (pure Cmd2) ...)

   Both will be listed and CLI cmd will choose Cmd2.

[tbidne]

The microhs error is baffling me:

mhs: uncaught exception: error: "src/Options/Applicative/Common.hs": line 200, col 48: Cannot satisfy constraint: ([] ~ NonEmpty)
     fully qualified: (Primitives.~ Data.List_Type.[] Data.List.NonEmpty_Type.NonEmpty)

It is complaining here:

    cmdMatches cs
      | prefDisambiguate prefs = snd <$> filter (any (isPrefixOf arg) . fst) cs
      --                                 HERE: vvv
      | otherwise = maybeToList (lookupCmd arg cs)

The types are:

cs :: [(NonEmpty String, ParserInfo r)]
lookupCmd :: String -> [(NonEmpty String, a)] -> Maybe a

🤷

[HuwCampbell]

Pretty sure that error is because micro haskell has a different type for any.

any :: forall a . (a -> Bool) -> [a] -> Bool

As opposed to it being over Foldable.

any :: Foldable t -> (a -> Bool) -> t a -> Bool

[HuwCampbell]

Excellent as usual. Thanks.

I'll do some tyre kicking, but I see no current issues.

[tbidne]

Pretty sure that error is because micro haskell has a different type for any.

Bang on, fixed now.

Thanks for the review and kind words!

[tbidne]

Thanks for the merge!