[stdlib/private][os log] Simplify the OSLogPrototype stdlib-private

module to contain only code necessary for testing the compiler
optimizations and diagnostics. This commit comprises the following changes:

1. Rename the OSLogPrototype module to OSLogTestHelper and rename the files.
2. Make the private module: OSLogTestHelper independent of os overlay.
3. Simplify the os log test suites and make them not perform logging.
4. Enable the os log test suites on all platforms.

<rdar://problem/60542172>

Author: ravikandhadai

stdlib/private/OSLog/CMakeLists.txt

@@ -1,8 +1,8 @@
-add_swift_target_library(swiftOSLogPrototype
+add_swift_target_library(swiftOSLogTestHelper
   IS_SDK_OVERLAY
   SHARED
 
-  OSLog.swift
+  OSLogTestHelper.swift
   OSLogMessage.swift
   OSLogIntegerFormatting.swift
   OSLogStringAlignment.swift
@@ -11,10 +11,10 @@ add_swift_target_library(swiftOSLogPrototype
   OSLogNSObjectType.swift
   OSLogFloatingPointTypes.swift
 
-  SWIFT_MODULE_DEPENDS_IOS Darwin os ObjectiveC
-  SWIFT_MODULE_DEPENDS_OSX Darwin os ObjectiveC
-  SWIFT_MODULE_DEPENDS_TVOS Darwin os ObjectiveC
-  SWIFT_MODULE_DEPENDS_WATCHOS Darwin os ObjectiveC
+  SWIFT_MODULE_DEPENDS_IOS Darwin ObjectiveC
+  SWIFT_MODULE_DEPENDS_OSX Darwin ObjectiveC
+  SWIFT_MODULE_DEPENDS_TVOS Darwin ObjectiveC
+  SWIFT_MODULE_DEPENDS_WATCHOS Darwin ObjectiveC
   TARGET_SDKS ALL_APPLE_PLATFORMS
   SWIFT_COMPILE_FLAGS ${SWIFT_STANDARD_LIBRARY_SWIFT_FLAGS}
   INSTALL_IN_COMPONENT never_install

stdlib/private/OSLog/OSLog.swift

@@ -0,0 +1,106 @@
+//===----------------- 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.
+@_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)))
+}