derive macro for Arbitrary is hard to find

[lolbinarycat]

probably the biggest hurdle to using proptest is the need to manually implement Arbitrary for a type. the ability to have a derive macro, even if it was really limited (eg. only unit enums) would be incredibly useful.

obviously this derive macro couldn't figure out the best methods for shrinking a value and such, but often it wouldn't need to, as a lot of types (like unit enums) don't have any meaningful way they can be shrunk.

[matthew-russo]

Hi, this already exists:

https://proptest-rs.github.io/proptest/proptest-derive/index.html

https://crates.io/crates/proptest-derive

Let us know if this addresses your use case or if there are improvements you'd like to see

[lolbinarycat]

is there a reason for burying this all the way at the end? personally i would have reexported this gated under a derive feature flag like most other crates, but at the very least it should be referenced in the api docs for Arbitrary.

[matthew-russo]

The two crates are documented separately so first we document the proptest crate and then we document the proptest-derive crate. We can embed some more mention of the derive macro earlier on in the book and in the api docs

[matthew-russo]

It is mentioned in this area of the book about defining a canonical strategy:
https://proptest-rs.github.io/proptest/proptest/tutorial/arbitrary.html?highlight=derive#defining-a-canonical-strategy-for-a-type

I'll add a note in the doc comments of Arbitrary.