build -i doesn't accept multiple arguments since 0.12.7

[hombit]

Bug Description

Parsing of an arguments list doesn't supported since 0.12.7, but it looks like a breaking change. I also have found no information about this change in the changelog

# maturin build -i python3.7 python3.8 python3.9 python3.10
error: Found argument 'python3.8' which wasn't expected, or isn't valid in this context

USAGE:
    maturin build [OPTIONS]

For more information try --help

maturin build -i python3.7 -i python3.8 works as expected

Your Python version (python -V)

python 3.9.9

Your pip version (pip -V)

21.3.1

What bindings you're using

pyo3

Does cargo build work?

• Yes, it works

If on windows, have you checked that you aren't accidentally using unix path (those with the forward slash /)?

• Yes

Steps to Reproduce

1. Install maturin >= 0.12.7
2. maturin build -i python3.7 python3.8

[messense]

I think it's a side effect of upgrading to clap 3.0. Clap 3.0 has splitted the meaning of multiple to multiple_values and multiple_occurrences and it recommended to use multiple_occurrences when upgrading. See https://docs.rs/clap/latest/clap/struct.Arg.html#method.multiple_values

We can certainly bring multiple value support back, but it does leave a question how do we deal with other options that can appear multiple times?

[hombit]

I'm not sure if it is not too late to fix it in 0.12.x, but fixing Changelog and readme could help other people