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//
// This source file is part of the Swift.org open source project
//
// Copyright (c) 2023–2025 Apple Inc. and the Swift project authors
// Licensed under Apache License v2.0 with Runtime Library Exception
//
// See https://swift.org/LICENSE.txt for license information
// See https://swift.org/CONTRIBUTORS.txt for Swift project authors
//
private import _TestingInternals
@_spi(Experimental) @_spi(ForToolsIntegrationOnly)
#if SWT_NO_EXIT_TESTS
@available(*, unavailable, message: "Exit tests are not available on this platform.")
#endif
extension ExitTest {
/// A type representing a value captured by an exit test's body.
///
/// An instance of this type may represent the actual value that was captured
/// when the exit test was invoked. In the child process created by the
/// current exit test handler, instances will initially only have the type of
/// the value, but not the value itself.
///
/// Instances of this type are created automatically by the testing library
/// for all elements in an exit test body's capture list and are stored in the
/// exit test's ``capturedValues`` property. For example, given the following
/// exit test:
///
/// ```swift
/// await #expect(processExitsWith: .failure) { [a = a as T, b = b as U, c = c as V] in
/// ...
/// }
/// ```
///
/// There are three captured values in its ``capturedValues`` property. These
/// values are captured at the time the exit test is called, as they would be
/// if the closure were called locally.
///
/// The current exit test handler is responsible for encoding and decoding
/// instances of this type. When the handler is called, it is passed an
/// instance of ``ExitTest``. The handler encodes the values in that
/// instance's ``capturedValues`` property, then passes the encoded forms of
/// those values to the child process. The encoding format and message-passing
/// interface are implementation details of the exit test handler.
///
/// When the child process calls ``ExitTest/find(identifiedBy:)``, it receives
/// an instance of ``ExitTest`` whose ``capturedValues`` property contains
/// type information but no values. The child process decodes the values it
/// encoded in the parent process and then updates the ``wrappedValue``
/// property of each element in the array before calling the exit test's body.
public struct CapturedValue: Sendable {
#if !SWT_NO_EXIT_TESTS
/// An enumeration of the different states a captured value can have.
private enum _Kind: Sendable {
/// The runtime value of the captured value is known.
case wrappedValue(any Codable & Sendable)
/// Only the type of the captured value is known.
case typeOnly(any (Codable & Sendable).Type)
}
/// The current state of this instance.
private var _kind: _Kind
init(wrappedValue: some Codable & Sendable) {
_kind = .wrappedValue(wrappedValue)
}
init(typeOnly type: (some Codable & Sendable).Type) {
_kind = .typeOnly(type)
}
#endif
/// The underlying value captured by this instance at runtime.
///
/// In a child process created by the current exit test handler, the value
/// of this property is `nil` until the entry point sets it.
public var wrappedValue: (any Codable & Sendable)? {
get {
#if !SWT_NO_EXIT_TESTS
if case let .wrappedValue(wrappedValue) = _kind {
return wrappedValue
}
return nil
#else
swt_unreachable()
#endif
}
set {
#if !SWT_NO_EXIT_TESTS
let type = typeOfWrappedValue
func validate<T, U>(_ newValue: T, is expectedType: U.Type) {
assert(newValue is U, "Attempted to set a captured value to an instance of '\(String(describingForTest: T.self))', but an instance of '\(String(describingForTest: U.self))' was expected.")
}
validate(newValue, is: type)
if let newValue {
_kind = .wrappedValue(newValue)
} else {
_kind = .typeOnly(type)
}
#else
swt_unreachable()
#endif
}
}
/// The type of the underlying value captured by this instance.
///
/// This type is known at compile time and is always available, even before
/// this instance's ``wrappedValue`` property is set.
public var typeOfWrappedValue: any (Codable & Sendable).Type {
#if !SWT_NO_EXIT_TESTS
switch _kind {
case let .wrappedValue(wrappedValue):
type(of: wrappedValue)
case let .typeOnly(type):
type
}
#else
swt_unreachable()
#endif
}
}
}
#if !SWT_NO_EXIT_TESTS
// MARK: - Collection conveniences
extension Array where Element == ExitTest.CapturedValue {
init<each T>(_ wrappedValues: repeat each T) where repeat each T: Codable & Sendable {
self.init()
repeat self.append(ExitTest.CapturedValue(wrappedValue: each wrappedValues))
}
init<each T>(_ typesOfWrappedValues: repeat (each T).Type) where repeat each T: Codable & Sendable {
self.init()
repeat self.append(ExitTest.CapturedValue(typeOnly: (each typesOfWrappedValues).self))
}
}
extension Collection where Element == ExitTest.CapturedValue {
/// Cast the elements in this collection to a tuple of their wrapped values.
///
/// - Returns: A tuple containing the wrapped values of the elements in this
/// collection.
///
/// - Throws: If an expected value could not be found or was not of the
/// type the caller expected.
///
/// This function assumes that the entry point function has already set the
/// ``wrappedValue`` property of each element in this collection.
func takeCapturedValues<each T>() throws -> (repeat each T) {
func nextValue<U>(
as type: U.Type,
from capturedValues: inout SubSequence
) throws -> U {
// Get the next captured value in the collection. If we run out of values
// before running out of parameter pack elements, then something in the
// exit test handler or entry point is likely broken.
guard let wrappedValue = capturedValues.first?.wrappedValue else {
let actualCount = self.count
let expectedCount = parameterPackCount(repeat (each T).self)
fatalError("Found fewer captured values (\(actualCount)) than expected (\(expectedCount)) when passing them to the current exit test.")
}
// Next loop, get the next element. (We're mutating a subsequence, not
// self, so this is generally an O(1) operation.)
capturedValues = capturedValues.dropFirst()
// Make sure the value is of the correct type. If it's not, that's also
// probably a problem with the exit test handler or entry point.
guard let wrappedValue = wrappedValue as? U else {
fatalError("Expected captured value at index \(capturedValues.startIndex) with type '\(String(describingForTest: U.self))', but found an instance of '\(String(describingForTest: Swift.type(of: wrappedValue)))' instead.")
}
return wrappedValue
}
var capturedValues = self[...]
return (repeat try nextValue(as: (each T).self, from: &capturedValues))
}
}
#endif
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