While `TypedValueParser` will generally make it easier to reuse value
parsers, this was particularly written for flags. Besides having a
concrete API to document, an advantage over `fn(&str) -> Result<bool, E>`
value parsers is you get all of the benefits of the existing value
parsers for environment variable parsing.
Someone should not reasonably expect a coun flag to go up to billions,
millions, or even thousands. 255 should be sufficient for anyone,
right?
The original type was selected to be consistent with
`ArgMatches::occurrences_of` but that is also used for tracking how
many values appear which can be large with `xargs`.
I'm still conflicted on what the "right type" is an wish we could
support any numeric type. When I did a search on github though, every
case was for debug/quiet flags and only supported 2-3 occurrences,
making a `u8` overkill.
This came out of a discussion on #3792
This is the derive support for #3774 (see also #3775, #3777)
This combined with `value_parser` replaces `parser`. The main
frustration with this is that `ArgAction::Count` (the replacement for
`parse(from_occurrences)` must be a `u64`. We could come up with a
magic attribute that is meant to be the value parser's parsed type. We
could then use `TryFrom` to convert the parsed type to the user's type
to allow more. That is an exercise for the future. Alternatively, we
have #3792.
Prep for this included
- #3782
- #3783
- #3786
- #3789
- #3793
This will make it easier to divide off parser logic for adding in
actions.
This does mean we can't provide error reporting on bad values with
`bool` but
- We should have also been doing that for `from_flag`
- We'll be dropping this soon in clap4 anyways
