Enable qualified declaration names in `@derivative` attribute, just like
`@transpose` attribute.
`DerivativeAttr` now stores a base type `TypeRepr *`, which is non-null for
parsed attributes that reference a qualified original declaration.
Add `TypeResolutionFlags::AllowModule` flag to enable module lookup via
`TypeChecker::lookupMember` given a `ModuleType`.
Add tests for type-qualified and module-qualified declaration names.
Resolves TF-1058.
The new _Differentiable module is not available in any shipping OS release, but its public API currently doesn’t have availability, either.
Temporarily disable tests that import it when we’re testing with OS-provided libraries.
The typecheck test test/AutoDiff/stdlib/differentiable_protocol.swift imports _Differentable but still somehow succeeds in these configs, so leave that one enabled.
rdar://57975086
The `@derivative` attribute registers a function as a derivative of another
function-like declaration: a `func`, `init`, `subscript`, or `var` computed
property declaration.
The `@derivative` attribute also has an optional `wrt:` clause specifying the
parameters that are differentiated "with respect to", i.e. the differentiation
parameters. The differentiation parameters must conform to the `Differentiable`
protocol.
If the `wrt:` clause is unspecified, the differentiation parameters are inferred
to be all parameters that conform to `Differentiable`.
`@derivative` attribute type-checking verifies that the type of the derivative
function declaration is consistent with the type of the referenced original
declaration and the differentiation parameters.
The `@derivative` attribute is gated by the
`-enable-experimental-differentiable-programming` flag.
Resolves TF-829.
Adds parsing for a type attribute `@differentiable`, which is optionally allowed to have argument `@differentiable(linear)`.
The typechecker currently rejects all uses of `@differentiable` with "error: attribute does not apply to type". Future work (https://bugs.swift.org/browse/TF-871https://bugs.swift.org/browse/TF-873) will update the typechecker to allow this attribute in places where it is allowed.
Resolves https://bugs.swift.org/browse/TF-822.
