[AutoDiff] Peel off @sendable implicit conversion when checking for unsupported differentiable function conversion

[asl]

No description provided.

[asl]

It is a bit non-trivial to craft a standalone testcase for this as it happens within Testing context, where such conversions are added by a Framework.

The testcase is essentially:

import Testing
import _Differentiation

@inlinable
@derivative(of: min)
public func _vjpMin<T: Comparable & Differentiable>(
    _ lhs: T,
    _ rhs: T
) -> (value: T, pullback: (T.TangentVector) -> (T.TangentVector, T.TangentVector)) {
    func pullback(_ tangentVector: T.TangentVector) -> (T.TangentVector, T.TangentVector) {
        if lhs <= rhs {
            return (tangentVector, .zero)
        }
        else {
            return (.zero, tangentVector)
        }
    }
    return (value: min(lhs, rhs), pullback: pullback)
}

@Test
func testMin() {
    let vwgLessThan = valueWithGradient(at: 2.0, 3.0, of: min(_:_:))
    print(vwgLessThan.value == 2.0)
    print(vwgLessThan.gradient == (1.0, 0.0))
}

Here Testing creates an implicit conversion for min from (Double, Double) -> Double to @sendable (Double, Double) -> Double`

[asl]

@swift-ci please test

[asl]

Tagging @JaapWijnen

[xedin]

There is also ABISafeConversionExpr which does the same thing for l-value types, in case that matters in some other case.

[asl]

Noted, thanks! I just do not have example in hand, but we'll see.