swift

5accda22 - [AutoDiff upstream] Introduce @differentiable attribute to mark functions as differentiable. (#27506)

[AutoDiff upstream] Introduce @differentiable attribute to mark functions as differentiable. (#27506) This PR introduces `@differentiable` attribute to mark functions as differentiable. This PR only contains changes related to parsing the attribute. Type checking and other changes will be added in subsequent patches. See https://github.com/apple/swift/pull/27506/files#diff-f3216f4188fd5ed34e1007e5a9c2490f for examples and tests for the new attribute.