swap structopt for bpaf

[pacak]

Clean build is a bit faster and a bit smaller

before:
cargo build --release  70.39s user 3.50s system 823% cpu 8.976 total
% ls -lha target/release/choose                                                                  
-rwxrwxr-x 2 pacak pacak 6.1M Nov 28 20:42 target/release/choose
                                                                    
after:
cargo build --release  45.35s user 1.96s system 611% cpu 7.731 total
% ls -lha target/release/choose                                                                  
-rwxrwxr-x 2 pacak pacak 5.7M Nov 28 20:43 target/release/choose

I also removed vector allocation from tests - should be faster since bpaf can take them as a reference and dropped the program name from all the arguments - it is handled automagically.

Also added FromStr impl for Choice and replaced ToString for ParseError with std::fmt::Display.

You might want to expose bpaf's bright-color / dull-color for cosmetic reasons. And maybe autocomplete.

It should be possible to speed up the compilation a bit more if we replace derive API with combinatoric one.

[lukehsiao]

I notice the help generates a strange warning.

❯ cargo run -- --help
    Finished dev [unoptimized + debuginfo] target(s) in 0.01s
     Running `target/debug/choose --help`
failed to parse choice argument: --help
`choose` sections from each line of files

Usage: [-c] [-d] [-x] [-f ARG] [-i INPUT] [-n] [--one-indexed] [-o SEP] <CHOICE>...

Available positional items:
    <CHOICE>  Fields to print. Either a, a:b, a..b, or a..=b, where a and b are integers. The beginning
              or end of a range can be omitted, resulting in including the beginning or end of the line,
              respectively. a:b is inclusive of b (unless overridden by -x). a..b is
              exclusive of b and a..=b is inclusive of b.

Available options:
    -c, --character-wise                Choose fields by character number
    -d, --debug                         Activate debug mode
    -x, --exclusive                     Use exclusive ranges, similar to array indexing in many programming languages
    -f, --field-separator <ARG>         Specify field separator other than whitespace, using Rust `regex` syntax
    -i, --input <INPUT>                 Input file
    -n, --non-greedy                    Use non-greedy field separators
        --one-indexed                   Index from 1 instead of 0
    -o, --output-field-separator <SEP>  Specify output field separator
    -h, --help                          Prints help information

Specifically, the

failed to parse choice argument: --help

But besides that, this seems awesome!

This PR is very educational just for me to see the derive API implemented in this way from the author themselves. I took a swing with bpaf earlier, but couldn't get it quite working out.

[pacak]

failed to parse choice argument: --help

Hmm.... choice function shouldn't really print anything to stderr if it also wants to return an error, bpaf will print whatever error it returns.

[pacak]

I took a swing with bpaf earlier, but couldn't get it quite working out.

I would really like to see some of that along with the comments of what you tried to do, how and why so I can improve the documentation or maybe the library. Here or there's a ticket in bpaf repo with "feedback wanted" label.