A recent change to witness matching in #32578 suddenly made the
following construction illegal:
// File1.swift
enum MyEnumInAnotherFile { /**/ }
// File2.swift
extension MyEnumInAnotherFile {
static var allCases: [MyEnumInAnotherFile] { /**/ }
}
Because it was no longer possible to derive the type witness for
`AllCases`. This is because, when inference ran before synthesis, we
would use the value witness to pick out the type witness and thus had no
need for synthesis. Now that we run synthesis first, we ought to just
allow deriving type witnesses across files, but still ban deriving value
witnesses. In general, if you can utter a type in a different file to
extend it, you should be able to see the requirements necessary to
derive a default type witness.
rdar://66279278, rdar://66279375, rdar://66279384, rdar://66279415, rdar://66279503
Add `AdditiveArithmetic` derived conformances for structs and classes, gated by
the `-enable-experimental-differentiable-programming` flag.
Structs and classes whose stored properties all conform to `Differentiable` can
derive `Differentiable`:
- `associatedtype TangentVector: Differentiable & AdditiveArithmetic`
- Member `TangentVector` structs are synthesized whose stored properties are
all `var` stored properties that conform to `Differentiable` and that are
not `@noDerivative`.
- `mutating func move(along: TangentVector)`
The `@noDerivative` attribute may be declared on stored properties to opt out of
inclusion in synthesized `TangentVector` structs.
Some stored properties cannot be used in `TangentVector` struct synthesis and
are implicitly marked as `@noDerivative`, with a warning:
- `let` stored properties.
- These cannot be updated by `mutating func move(along: TangentVector)`.
- Non-`Differentiable`-conforming stored properties.
`@noDerivative` also implies `@_semantics("autodiff.nonvarying")`, which is
relevant for differentiable activity analysis.
Add type-checking and SILGen tests.
Resolves TF-845.
Add `AdditiveArithmetic` derived conformances for structs, gated by the
`-enable-experimential-additive-arithmetic-derivation` flag.
Structs whose stored properties all conform to `AdditiveArithmetic` can derive
`AdditiveArithmetic`:
- `static var zero: Self`
- `static func +(lhs: Self, rhs: Self) -> Self`
- `static func -(lhs: Self, rhs: Self) -> Self`
- An "effective memberwise initializer":
- Either a synthesized memberwise initializer or a user-defined initializer
with the same type.
Effective memberwise initializers are used only by derived conformances for
`Self`-returning protocol requirements like `AdditiveArithmetic.+`, which
require memberwise initialization.
Resolves TF-844.
Unblocks TF-845: upstream `Differentiable` derived conformances.
