Replace derive_builder with bon

[Turbo87]

bon uses the type system to ensure all required fields have been set, which means that we can catch issues at compile time. The necessary attributes are also less verbose due to better defaults inside bon.

The only downside I've found is that custom builder fns like dummy_checksum() don't appear easy to implement at the moment, which is why I've inlined the two custom builder fns that we had. (/cc @Veetaha)

[codecov]

Codecov Report

Attention: Patch coverage is 75.00000% with 5 lines in your changes missing coverage. Please review.

Project coverage is 88.91%. Comparing base (6347fbb) to head (523aa4d).
Report is 8 commits behind head on main.

Files with missing lines	Patch %	Lines
src/bin/background-worker.rs	0.00%	5 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #9712      +/-   ##
==========================================
- Coverage   88.93%   88.91%   -0.02%     
==========================================
  Files         288      288              
  Lines       29630    29609      -21     
==========================================
- Hits        26350    26326      -24     
- Misses       3280     3283       +3     

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

[Veetaha]

@Turbo87 regarding the custom dummy checksum finishing function (method on the builder that consumes the builder and returns the result).

It should be possible to add custom methods to the builder itself in the next release. It will be a 3.0 release, but breaking changes there won't touch 99% of the users since they break some rare obscure cases and rarely used apis such as #[builder(expose_positional_fn)], so the upgrade will probably require just a bump in Cargo.toml in this case.

The builder type state API will be stabilized (the PR for that was recently merged into master elastio/bon#145).
There is an example in that PR that shows how one could add methods to the builder. The documentation for this feature is not ready at the moment though.

Thank you for the feedback!

[Veetaha]

Regarding the usage in test fixtures. In 3.0 it will be possible to annotate the type of the builder, so test fixtures could benefit from this by returning a builder with (potentially partially) filled values like so:

#[derive(bon::Builder)]
#[cfg_attr(test, builder(on(_, overwritable)))]
struct User {
    login: String,
    name: String,
    level: u32,
}

#[cfg(test)]
mod tests {
    use super::*;
    use user_builder::{SetLevel, SetLogin, SetName};

    // Base fixture that has dummy values for all or maybe just part of the fields
    fn user() -> UserBuilder<SetLevel<SetName<SetLogin>>> {
        User::builder()
            .level(24)
            .name("Bon Bon".to_owned())
            .login("@bonbon".to_owned())
    }

    #[test]
    fn test_with_empty_name() {
        // Build user with an empty name, and all other fields filled with dummy data
        let user = user()
            .name("".to_owned())
            .build();

        // ...
    }

    #[test]
    fn test_with_zero_level_and_admin_login() {
        let admin = user()
            .level(0)
            .login("@admin".to_owned())
            .build();

        // ...
    }
}

Although, I'm not sure if there will be big demand for this. Notice the #[builder(overwritable)] attribute that is also discussed (elastio/bon#149) to allow for overwrites of already set values that is useful in case of fixtures.

[Veetaha]

FYI there will be a new attribute in 3.0. that will allow expressing this setter as this (apart from defining the custom method on the builder directly):

#[builder(with = |features: &BTreeMap<...>| -> serde_json::Result<_> { 
  serde_json::to_value(features) 
})]
features: serde_json::Value,

Yes it's possible to have a fallible setter this way if you annotate the return type of the closure with a type that has Result suffix. The lack of return type annotation implies the closure passed to with is infallible.

[Turbo87]

awesome, thanks for the quick feedback :)