There is no obvious reason why not to derive `Copy` and `Clone` for
types that use the `impl_newtype_macro`. Derives are less surprising so
deriving makes the code marginally easier to read.
Currently we rely on the inner bytes with types that are passed across
the FFI boundry when implementing comparison functions (e.g. `Ord`,
`PartialEq`), this is incorrect because the bytes are opaque, meaning
the byte layout is not guaranteed across versions of `libsecp26k1`.
Implement stable comparison functionality by doing:
- Implement `core::cmp` traits by first coercing the data into a stable
form e.g., by serializing it.
- Add fast comparison methods to `secp256k1-sys` types that wrap types
from libsecp, add similar methods to types in `secp256k1` that wrap
`secp256k1-sys` types (just call through to inner type).
- In `secp256k1-sys` feature gate the new `core::cmp` impls on
`not(fuzzing)`, when fuzzing just derive the impls instead.
Any additional methods added to `secp256k1-sys` types are private,
justified by the fact the -sys is meant to be just a thin wrapper around
libsecp256k1, we don't want to commit to supporting additional API
functions.
Please note, the solution presented in this patch is already present for
`secp256k1::PublicKey`, this PR removes that code in favour of deriving
traits that then call down to the same logic in `secp256k1-sys`.
An array in Rust has no concept of length, it is a fixed size data type.
Equally an array cannot be "empty", again since it is a fixed size data
type. These are methods/concepts seen in slices and vectors.
Remove the `len` and `is_empty` methods.
Clippy emits a warning since we define a method that has the same name
as a standard trait. Implement the trait `AsRef` instead of using a
custom method.