The `CollectionDifference` type has a few different invariants
that were not being validated when initializing using the type's
`Decodable` conformance, since the type was using the
autogenerated `Codable` implementation. This change provides
manual implementations of the `Encodable` and `Decodable`
requirements, and adds tests that validate the failure when trying
to decode invalid JSON for CollectionDifference (and a few other
types).
Restore (un-revert) sting comparison, with fixes
More exhaustive testing of opaque strings, which consistently reproduces prior sporadic failure. Shims fixups. Some test tweaking.
At the cost of slight test readability, improve the diagnostics on test failure by pointing to the specific test case which failed on round-trip failure.
One of the limitations of not having conditional conformance at the
moment is that the implementation of `init(from:)` and `encode(to:)` on
types which require it is that failure to cast dependent types to
`Encodable` or `Decodable` is a runtime failure. There is no way to
statically guarantee that the wrapped type is `Encodable` or
`Decodable`.
As such, in those implementations, at best we can directly call
`(element as! Encodable).encode(to: encoder)`, or similar. However, this
encodes the element directly into an encoder, without giving the encoder
a chance to intercept the type. This is problematic for `JSONEncoder`
because it cannot apply a strategy if it doesn't get to intercept the
type.
This gives a temporary workaround for JSON strategies because of
internal Foundation knowledge.
