Build lalrpop without lalrpop binary

[moreal]

When I started to work on RustPython project today, I met compile error about python.rs. I guess it occurred because the python.rs, generated lalrpop file, was removed and it became to generate the file every compile. And the error message guided me to install lalrpop by using cargo install lalrpop command.

This pull request makes the parser/build.rs uses lalrpop crates instead of lalrpop binary.

You can test with the below commands:

# Remove lalrpop if it was installed already
cargo uninstall lalrpop

# Remove generated python.rs
rm -rf ./target

cargo build

[youknowone]

maybe i'd better to find a better way to do it.

[moreal]

maybe i'd better to find a better way to do it.

@youknowone With more research, I know it can run the lalrpop in Rust code directly, instead of binary. I made it always use lalrpop in Rust code directly. Is there a case to require using lalrpop binary, that I don't know?

[youknowone]

No, actually I recently added it as an optional dependency. @coolreader18 wanted to avoid lalrpop dependency from CI side.

[moreal]

No, actually I recently added it as an optional dependency. @coolreader18 wanted to avoid lalrpop dependency from CI side.

Ok, I see. Then I think it'll be the best if lalrpop is used in default and the CI excludes the lalrpop with some args.

rust-lang/cargo#3126 seems able to implement my thought but it seems not resolved yet.

At now, I'll make this pull request as draft because I'm not sure what is the solution 🤔

Current my thought is:

• Add rustpython-parser/lalrpop feature into /Cargo.toml default feature.
• Make CI to use an option to exclude the feature like --features=-rustpython-parser/lalrpop. (Ability to disable individual default features rust-lang/cargo#3126)

[moreal]

I opened again because @youknowone pushed ca256d3 commit and the CI seems passed well.

[youknowone]

thank you for good idea