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//
// This source file is part of the Swift.org open source project
//
// Copyright (c) 2024 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
//
/// A protocol describing a type that can be attached to a test report or
/// written to disk when a test is run.
///
/// To attach an attachable value to a test report or test run output, use it to
/// initialize a new instance of ``Attachment``, then call
/// ``Attachment/attach(sourceLocation:)``. An attachment can only be attached
/// once.
///
/// The testing library provides default conformances to this protocol for a
/// variety of standard library types. Most user-defined types do not need to
/// conform to this protocol.
///
/// A type should conform to this protocol if it can be represented as a
/// sequence of bytes that would be diagnostically useful if a test fails. If a
/// type cannot conform directly to this protocol (such as a non-final class or
/// a type declared in a third-party module), you can create a container type
/// that conforms to ``AttachableContainer`` to act as a proxy.
@_spi(Experimental)
public protocol Attachable: ~Copyable {
/// An estimate of the number of bytes of memory needed to store this value as
/// an attachment.
///
/// The testing library uses this property to determine if an attachment
/// should be held in memory or should be immediately persisted to storage.
/// Larger attachments are more likely to be persisted, but the algorithm the
/// testing library uses is an implementation detail and is subject to change.
///
/// The value of this property is approximately equal to the number of bytes
/// that will actually be needed, or `nil` if the value cannot be computed
/// efficiently. The default implementation of this property returns `nil`.
///
/// - Complexity: O(1) unless `Self` conforms to `Collection`, in which case
/// up to O(_n_) where _n_ is the length of the collection.
var estimatedAttachmentByteCount: Int? { get }
/// Call a function and pass a buffer representing this instance to it.
///
/// - Parameters:
/// - attachment: The attachment that is requesting a buffer (that is, the
/// attachment containing this instance.)
/// - body: A function to call. A temporary buffer containing a data
/// representation of this instance is passed to it.
///
/// - Returns: Whatever is returned by `body`.
///
/// - Throws: Whatever is thrown by `body`, or any error that prevented the
/// creation of the buffer.
///
/// The testing library uses this function when writing an attachment to a
/// test report or to a file on disk. The format of the buffer is
/// implementation-defined, but should be "idiomatic" for this type: for
/// example, if this type represents an image, it would be appropriate for
/// the buffer to contain an image in PNG format, JPEG format, etc., but it
/// would not be idiomatic for the buffer to contain a textual description of
/// the image.
borrowing func withUnsafeBufferPointer<R>(for attachment: borrowing Attachment<Self>, _ body: (UnsafeRawBufferPointer) throws -> R) throws -> R
}
// MARK: - Default implementations
extension Attachable where Self: ~Copyable {
public var estimatedAttachmentByteCount: Int? {
nil
}
}
extension Attachable where Self: Collection, Element == UInt8 {
public var estimatedAttachmentByteCount: Int? {
count
}
// We do not provide an implementation of withUnsafeBufferPointer(for:_:) here
// because there is no way in the standard library to statically detect if a
// collection can provide contiguous storage (_HasContiguousBytes is not API.)
// If withContiguousStorageIfAvailable(_:) fails, we don't want to make a
// (potentially expensive!) copy of the collection.
}
extension Attachable where Self: StringProtocol {
public var estimatedAttachmentByteCount: Int? {
// NOTE: utf8.count may be O(n) for foreign strings.
// SEE: https://github.com/swiftlang/swift/blob/main/stdlib/public/core/StringUTF8View.swift
utf8.count
}
}
// MARK: - Default conformances
// Implement the protocol requirements for byte arrays and buffers so that
// developers can attach raw data when needed.
@_spi(Experimental)
extension Array<UInt8>: Attachable {
public func withUnsafeBufferPointer<R>(for attachment: borrowing Attachment<Self>, _ body: (UnsafeRawBufferPointer) throws -> R) throws -> R {
try withUnsafeBytes(body)
}
}
@_spi(Experimental)
extension ContiguousArray<UInt8>: Attachable {
public func withUnsafeBufferPointer<R>(for attachment: borrowing Attachment<Self>, _ body: (UnsafeRawBufferPointer) throws -> R) throws -> R {
try withUnsafeBytes(body)
}
}
@_spi(Experimental)
extension ArraySlice<UInt8>: Attachable {
public func withUnsafeBufferPointer<R>(for attachment: borrowing Attachment<Self>, _ body: (UnsafeRawBufferPointer) throws -> R) throws -> R {
try withUnsafeBytes(body)
}
}
@_spi(Experimental)
extension String: Attachable {
public func withUnsafeBufferPointer<R>(for attachment: borrowing Attachment<Self>, _ body: (UnsafeRawBufferPointer) throws -> R) throws -> R {
var selfCopy = self
return try selfCopy.withUTF8 { utf8 in
try body(UnsafeRawBufferPointer(utf8))
}
}
}
@_spi(Experimental)
extension Substring: Attachable {
public func withUnsafeBufferPointer<R>(for attachment: borrowing Attachment<Self>, _ body: (UnsafeRawBufferPointer) throws -> R) throws -> R {
var selfCopy = self
return try selfCopy.withUTF8 { utf8 in
try body(UnsafeRawBufferPointer(utf8))
}
}
}
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