Support re-export of derive_builder

[ryo33]

Background

parol generates code that has several external crates, including derive_builder. And, parol_runtime re-exports the crates for ease of use.

Problem

I know derive_builder doesn't support crate renaming, but it also seems not to support re-exporting.
So we need a user-confusing workaround in lib.rs or main.rs as below:

use parol_runtime::derive_builder;

Solution

Replace `::derive_builder" with "derive_builder" in generated code.

It may break projects in Rust 2015 edition, and we may need a feature toggle for this behavior.

[TedDriggs]

I think I'm reading that parol is generating structs that are then trying to derive a builder, without requiring the user of parol to directly depend on derive_builder; does that accurately describe the issue?

[ryo33]

Yes, it does.

[TedDriggs]

It seems that the common solution for this is to expose a crate attribute, e.g.

#[derive(Builder)]
#[builder(crate = "parol_runtime::derive_builder")]

That's how serde does it, and that seems like that should not have any backwards compatibility risks. Would parol_runtime be able to use such a solution?

[ryo33]

Yeah, it seems nice.

[TedDriggs]

Okay, that seems doable though some help on tests will be appreciated.

[TedDriggs]

This is published as part of 0.12.0