Update LegacyABI.swift

Author: benrimmington

stdlib/public/core/LegacyABI.swift

@@ -2,46 +2,48 @@
 //
 // This source file is part of the Swift.org open source project
 //
-// Copyright (c) 2014 - 2019 Apple Inc. and the Swift project authors
+// 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 non-API (or underscored) declarations that are needed to
 // be kept around for ABI compatibility
+//
+//===----------------------------------------------------------------------===//
 
 extension Unicode.UTF16 {
   @available(*, unavailable, renamed: "Unicode.UTF16.isASCII")
-  @inlinable
-  public static func _isASCII(_ x: CodeUnit) -> Bool  {
+  @usableFromInline
+  internal static func _isASCII(_ x: CodeUnit) -> Bool {
     return Unicode.UTF16.isASCII(x)
   }
 }
 
 @available(*, unavailable, renamed: "Unicode.UTF8.isASCII")
-@inlinable
+@usableFromInline
 internal func _isASCII(_ x: UInt8) -> Bool {
   return Unicode.UTF8.isASCII(x)
 }
 
 @available(*, unavailable, renamed: "Unicode.UTF8.isContinuation")
-@inlinable
+@usableFromInline
 internal func _isContinuation(_ x: UInt8) -> Bool {
   return UTF8.isContinuation(x)
 }
 
 extension Substring {
-@available(*, unavailable, renamed: "Substring.base")
-  @inlinable
+  @available(*, unavailable, renamed: "Substring.base")
+  @usableFromInline
   internal var _wholeString: String { return base }
 }
 
 extension String {
   @available(*, unavailable, renamed: "String.withUTF8")
-  @inlinable
+  @usableFromInline
   internal func _withUTF8<R>(
     _ body: (UnsafeBufferPointer<UInt8>) throws -> R
   ) rethrows -> R {
@@ -52,7 +54,7 @@ extension String {
 
 extension Substring {
   @available(*, unavailable, renamed: "Substring.withUTF8")
-  @inlinable
+  @usableFromInline
   internal func _withUTF8<R>(
     _ body: (UnsafeBufferPointer<UInt8>) throws -> R
   ) rethrows -> R {
@@ -63,6 +65,7 @@ extension Substring {
 
 // This function is no longer used but must be kept for ABI compatibility
 // because references to it may have been inlined.
+@available(*, unavailable)
 @usableFromInline
 internal func _branchHint(_ actual: Bool, expected: Bool) -> Bool {
   // The LLVM intrinsic underlying int_expect_Int1 now requires an immediate
@@ -73,6 +76,7 @@ internal func _branchHint(_ actual: Bool, expected: Bool) -> Bool {
 }
 
 extension String {
+  @available(*, unavailable)
   @usableFromInline // Never actually used in inlinable code...
   internal func _nativeCopyUTF16CodeUnits(
     into buffer: UnsafeMutableBufferPointer<UInt16>,
@@ -84,6 +88,7 @@ extension String.UTF16View {
   // Swift 5.x: This was accidentally shipped as inlinable, but was never used
   // from an inlinable context. The definition is kept around for techincal ABI
   // compatibility (even though it shouldn't matter), but is unused.
-  @inlinable @inline(__always)
+  @available(*, unavailable)
+  @usableFromInline
   internal var _shortHeuristic: Int { return 32 }
 }