swift-mirror/stdlib/private/OSLog/OSLogTestHelper.swift

//===----------------- OSLogTestHelper.swift ----------------------------------------===//
//
// This source file is part of the Swift.org open source project
//
// Copyright (c) 2014 - 2020 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 the list of Swift project authors
//
//===----------------------------------------------------------------------===//

// This file contains test helpers for testing the compiler diagnostics and optimizations
// of the new swift APIs for os log that accept string interpolations.

// Some functions defined in this file are marked @_optimize(none) to prevent inlining
// of string internals (such as String._StringGuts) which will interfere with
// constant evaluation and folding. Note that these functions will be inlined,
// constant evaluated, folded and optimized in the context of a caller. TODO:
// @_optimize(none) can be removed if (non-mandatory) inlining optimizations can be moved
// after serialization.

/// A function that acts like a check for whether logging is enabled in `_osLogTestHelper`.
@inline(never)
@usableFromInline
internal func isLoggingEnabled() -> Bool { true }

/// A closure that does nothing. Meant to be used as the default assertion of
/// `_osLogTestHelper`.
public let _noopClosure = { (x : String, y : UnsafeBufferPointer<UInt8>) in return }

/// A test helper that constructs a byte buffer and a format string from an
/// instance of `OSLogMessage` using the same logic as the new os log APIs,
/// and applies a given `assertion` to the constructed format string and
/// byte buffer. This function should be used only in tests.
/// - Parameters:
///   - message: An instance of `OSLogMessage` created from string interpolation
///   - assertion: A closure that takes a format string and a pointer to a
///     byte buffer and asserts a condition.
@_semantics("oslog.requires_constant_arguments")
@_transparent
@_optimize(none)
public // @testable
func _osLogTestHelper(
  _ message: OSLogMessage,
  assertion: (String, UnsafeBufferPointer<UInt8>) -> Void = _noopClosure
) {
  // Compute static constants first so that they can be folded by
  // OSLogOptimization pass.
  let formatString = message.interpolation.formatString
  let preamble = message.interpolation.preamble
  let argumentCount = message.interpolation.argumentCount
  let bufferSize = message.bufferSize
  let argumentClosures = message.interpolation.arguments.argumentClosures
  let formatStringPointer = _getGlobalStringTablePointer(formatString)

  // Code that will execute at runtime.
  if (!isLoggingEnabled()) {
    return
  }

  // Allocate a byte buffer to store the arguments. The buffer could be stack
  // allocated as it is local to this function and also its size is a
  // compile-time constant.
  let bufferMemory = UnsafeMutablePointer<UInt8>.allocate(capacity: bufferSize)
  // Array of references to auxiliary storage created during serialization of
  // strings. This array can be stack allocated.
  var stringStorageObjects: [AnyObject] = []

  var currentBufferPosition = bufferMemory
  serialize(preamble, at: &currentBufferPosition)
  serialize(argumentCount, at: &currentBufferPosition)
  argumentClosures.forEach { $0(&currentBufferPosition, &stringStorageObjects) }

  _os_log_impl_test(
    assertion,
    formatString,
    formatStringPointer,
    bufferMemory,
    UInt32(bufferSize))

  // The following operation extends the lifetime of argumentClosures,
  // stringStorageObjects, and also of the objects stored in them, till this
  // point. This is necessary because the assertion is passed internal pointers
  // to the objects/strings stored in these arrays, as in the actual os log
  // implementation.
  _fixLifetime(argumentClosures)
  _fixLifetime(stringStorageObjects)
  bufferMemory.deallocate()
}

/// A function that pretends to be _os_log_impl.
@inline(never)
@usableFromInline
internal func _os_log_impl_test(
  _ assertion: (String, UnsafeBufferPointer<UInt8>) -> Void,
  _ formatString: String,
  _ formatStringPointer: UnsafePointer<CChar>,
  _ bufferMemory: UnsafeMutablePointer<UInt8>,
  _ bufferSize: UInt32
) {
  assertion(
    formatString,
    UnsafeBufferPointer(
      start: UnsafePointer(bufferMemory),
      count: Int(bufferSize)))
}