Compilation errors with rustc 1.64.0-nightly

[roper79]

Compiling 0.6.1 with current rustc 1.64.0-nightly (2643b1646 2022-07-27) results in multiple errors ambiguous associated type 'MetaData'.

[ashbeitz]

I saw the same issue and I believe that I managed to fix it. I am relatively new to Rust, so there may be a much better fix. To fix the ambiguity, for each of the places where there was ambiguity, I clarified that the item has the type generic_json::Json.

Here is an example of one of the changes that I made to src/compaction/mod.rs. I changed:

M: 'a + Send + Sync + Clone + Fn(Option<&J::MetaData>) -> K::MetaData;

to:

M: 'a + Send + Sync + Clone + Fn(Option<&J::MetaData>) -> <K as generic_json::Json>::MetaData;

Similar changes need to be made to all instances of the error.

[blast-hardcheese]

It almost seems like a bug in the compiler. Chasing the patch that you suggested, one of the suggestions from the compiler was

error[E0221]: ambiguous associated type `MetaData` in bounds of `K`
   --> src/indexed.rs:142:72
    |
142 |     fn as_json_with(&self, meta: impl Clone + Fn(Option<&J::MetaData>) -> K::MetaData) -> K {
    |                                                                           ^^^^^^^^^^^ ambiguous associated type `MetaData`
    |
    = note: associated type `K` could derive from `generic_json::Json`
    = note: associated type `K` could derive from `generic_json::Json`

I'd have expected duplicate identical derivations would unify

[blast-hardcheese]

Also, for those interested, the build that broke this was nightly release 7c4b47696 2022-04-30. Last known good version was e85edd9a8 2022-04-28

[timothee-haudebourg]

Yes this is a recurrent issue that keeps popping with new nightly releases. My goal is now to remove the trait_alias feature that causes a lot of problems and is not going to be stabilized soon. See #37 for more info. Once GATs are stabilized, then json_ld will be usable with stable Rust, and we won't have this kind of issues anymore.

[FrankReh]

Sorry, drive-by-er at the moment. The GATs that this blog says are stable in 1.65 coming Nov 3rd (tomorrow)?

https://blog.rust-lang.org/2022/10/28/gats-stabilization.html

[timothee-haudebourg]

@FrankReh that's right, and I already released a beta version on crates.io that works with this version. I have some more testing and documentation to write before I can safely remove the -beta label.

[timothee-haudebourg]

I've just release version 0.9.1, which work with stable Rust 1.65. The transition from the old architecture may be rough, please don't hesitate to ask if you need help transitioning.

This should solve this issue.