[AutoDiff upstream] Upstream @transpose attribute type-checking. (swiftlang#30664)

The `@transpose` attribute registers a function as the transpose of another
function-like declaration: a `func`, `init`, `subscript`, or `var` computed
property declaration.

The `@transpose` attribute also has an optional `wrt:` clause specifying the
linearity parameters, i.e. the parameters that are transposed with respect to.
The linearity parameters must conform to the `Differentiable` protocol and
satisfy `Self == TangentVector`.

If the `wrt:` clause is unspecified, the linearity parameters are inferred to be
all parameters that conform to `Differentiable` and that satisfy
`Self == TangentVector`.

`@transpose` attribute type-checking verifies that the type of the transpose
function declaration is consistent with the type of the referenced original
declaration and the linearity parameters.

Resolves TF-830.

Author: ematejska

include/swift/AST/DiagnosticsSema.def

@@ -3024,6 +3024,23 @@ ERROR(derivative_attr_original_already_has_derivative,none,
 NOTE(derivative_attr_duplicate_note,none,
      "other attribute declared here", ())
 
+// @transpose
+ERROR(transpose_attr_invalid_linearity_parameter_or_result,none,
+      "cannot transpose with respect to original %select{result|parameter}1 "
+      "'%0' that does not conform to 'Differentiable' and satisfy "
+      "'%0 == %0.TangentVector'", (StringRef, /*isParameter*/ bool))
+ERROR(transpose_attr_overload_not_found,none,
+      "could not find function %0 with expected type %1", (DeclName, Type))
+ERROR(transpose_attr_cannot_use_named_wrt_params,none,
+      "cannot use named 'wrt' parameters in '@transpose(of:)' attribute, found "
+      "%0", (Identifier))
+ERROR(transpose_attr_wrt_self_must_be_static,none,
+     "the transpose of an instance method must be a 'static' method in the "
+     "same type when 'self' is a linearity parameter", ())
+NOTE(transpose_attr_wrt_self_self_type_mismatch_note,none,
+     "the transpose is declared in %0 but the original function is declared in "
+     "%1", (Type, Type))
+
 // Automatic differentiation attributes
 ERROR(autodiff_attr_original_decl_invalid_kind,none,
       "%0 is not a 'func', 'init', 'subscript', or 'var' computed property "