WIP migration to 0.8

[ThierryBerger]

This is actually me trying to learn rkyv 0.8 ; it's not working yet.

Current status

• hash_map is commented, let's focus on CustomPhantom first.

Fixing example code for CustomPhantom was not trivial, because:

• We have to use this non obvious #[rkyv(archive_bounds(CustomPhantom<T>: ArchiveWith<PhantomData<T>, Archived = PhantomData<T>>))] to make help rustc understand.
• I had to remove as = StructWithPhantom<T::Archived>, because it requires Self to be portable, and that i32 is not.
  • This is a bit unfortunate, I'd like to have generic field to be able to use as, but that might make the code more complex, maybe in another PR after discussion/validation?

Resolved

I keep these in the desription, even though it's been resolved.

Failing test when still using as = ...:

Details

   Doc-tests rkyv_wrappers

running 1 test
test rkyv_wrappers/src/custom_phantom.rs - custom_phantom::CustomPhantom (line 14) ... FAILED

failures:

---- rkyv_wrappers/src/custom_phantom.rs - custom_phantom::CustomPhantom (line 14) stdout ----
error[E0308]: mismatched types
   --> rkyv_wrappers/src/custom_phantom.rs:23:20
    |
12  | #[derive(Portable, Archive, Serialize, Deserialize, bytecheck::CheckBytes, Debug, PartialEq, Eq, Default)]
    |                    ^^^^^^^
    |                    |
    |                    expected `Place<<... as ArchiveWith<...>>::Archived>`, found `Place<PhantomData<T>>`
    |                    arguments to this function are incorrect
    |
    = note: expected struct `Place<<CustomPhantom<T> as ArchiveWith<PhantomData<T>>>::Archived>`
               found struct `Place<PhantomData<T>>`
    = help: consider constraining the associated type `<CustomPhantom<T> as ArchiveWith<PhantomData<T>>>::Archived` to `PhantomData<T>` or calling a method that returns `<CustomPhantom<T> as ArchiveWith<PhantomData<T>>>::Archived`
    = note: for more information, visit https://doc.rust-lang.org/book/ch19-03-advanced-traits.html
note: associated function defined here
   --> /home/tb/.cargo/registry/src/index.crates.io-1949cf8c6b5b557f/rkyv-0.8.10/src/with.rs:114:8
    |
114 |     fn resolve_with(
    |        ^^^^^^^^^^^^
    = note: this error originates in the derive macro `Archive` (in Nightly builds, run with -Z macro-backtrace for more info)

error[E0308]: mismatched types
   --> rkyv_wrappers/src/custom_phantom.rs:23:40
    |
12  | #[derive(Portable, Archive, Serialize, Deserialize, bytecheck::CheckBytes, Debug, PartialEq, Eq, Default)]
    |                                        ^^^^^^^^^^^
    |                                        |
    |                                        expected `&<CustomPhantom<T> as ArchiveWith<...>>::Archived`, found `&PhantomData<T>`
    |                                        arguments to this function are incorrect
    |
    = note: expected reference `&<CustomPhantom<T> as ArchiveWith<PhantomData<T>>>::Archived`
               found reference `&PhantomData<T>`
    = help: consider constraining the associated type `<CustomPhantom<T> as ArchiveWith<PhantomData<T>>>::Archived` to `PhantomData<T>` or calling a method that returns `<CustomPhantom<T> as ArchiveWith<PhantomData<T>>>::Archived`
    = note: for more information, visit https://doc.rust-lang.org/book/ch19-03-advanced-traits.html
note: associated function defined here
   --> /home/tb/.cargo/registry/src/index.crates.io-1949cf8c6b5b557f/rkyv-0.8.10/src/with.rs:139:8
    |
139 |     fn deserialize_with(field: &F, deserializer: &mut D)
    |        ^^^^^^^^^^^^^^^^
    = note: this error originates in the derive macro `Deserialize` (in Nightly builds, run with -Z macro-backtrace for more info)

error: aborting due to 2 previous errors

For more information about this error, try `rustc --explain E0308`.
Couldn't compile the test.

failures:
    rkyv_wrappers/src/custom_phantom.rs - custom_phantom::CustomPhantom (line 14)

test result: FAILED. 0 passed; 1 failed; 0 ignored; 0 measured; 0 filtered out; finished in 0.04s

[ThierryBerger]

This snippet doesn't compile, and errors are not too easy to read.

[ThierryBerger]

resolved it by adding:

• #[rkyv(archive_bounds(CustomPhantom<T>: ArchiveWith<PhantomData<T>, Archived = PhantomData<T>>))], to help rustc, suggested by @djkoloski .

I also removed as = StructWithPhantom<T::Archived>, because it requires to implement PartialEq and Debug manually. An example of a working as = would be great though.

[ThierryBerger]

There's only tests for hashmap, so I commented them as I commented hashmap too ; let's focus on phantomdata first.

[ThierryBerger]

I figured T doesn't really need to be Archive, as CustomPhantom is Archive ; it was there only for as = "StructWithPhantom<T::Archived>", which is not relevant because T is within CustomPhantom, which has no requirement on T being archived.

• I removed the as = because it would require manual implementation of rekyv(derive(Debug), compare(PartialEq)).
• We could also make this example using as if i32 were generic over aDifferentT: Archive, but that's controversial and I encountered errors.

I'd still like to see such examples (especially helpful in context of my nalgebra migration).