Add Sequence._withRawContiguousStorageIfAvailable

Author: karwa

stdlib/public/core/Sequence.swift

@@ -366,6 +366,10 @@ public protocol Sequence {
   func withContiguousStorageIfAvailable<R>(
     _ body: (UnsafeBufferPointer<Element>) throws -> R
   ) rethrows -> R?  
+
+  func _withRawContiguousStorageIfAvailable<R>(
+    _ body: (UnsafeRawBufferPointer) throws -> R
+  ) rethrows -> R?  
 }
 
 // Provides a default associated type witness for Iterator when the
@@ -1111,6 +1115,15 @@ extension Sequence {
   ) rethrows -> R? {
     return nil
   }  
+  
+  @inlinable
+  public func _withRawContiguousStorageIfAvailable<R>(
+    _ body: (UnsafeRawBufferPointer) throws -> R
+  ) rethrows -> R?  {
+    return try withContiguousStorageIfAvailable { 
+      try body(UnsafeRawBufferPointer($0)) 
+    }
+  }
 }
 
 // FIXME(ABI)#182

stdlib/public/core/UnsafeRawBufferPointer.swift.gyb

@@ -145,6 +145,17 @@ extension Unsafe${Mutable}RawBufferPointer: Sequence {
   public func makeIterator() -> Iterator {
     return Iterator(_position: _position, _end: _end)
   }
+
+  @inlinable @inline(__always)
+  public func _withRawContiguousStorageIfAvailable<R>(
+    _ body: (UnsafeRawBufferPointer) throws -> R
+  ) rethrows -> R? {
+% if not mutable:
+      return try body(self)
+% else:
+      return try body(UnsafeRawBufferPointer(self))
+% end
+  }
 }
 
 extension Unsafe${Mutable}RawBufferPointer: ${Mutable}Collection {

test/api-digester/Outputs/stability-stdlib-abi.swift.expected

@@ -95,3 +95,4 @@ Struct String has removed conformance to _HasContiguousBytes
 Struct Substring has removed conformance to _HasContiguousBytes
 Var String._providesContiguousBytesNoCopy has been removed
 Var Substring._providesContiguousBytesNoCopy has been removed
+Func Sequence._withRawContiguousStorageIfAvailable(_:) has been added as a protocol requirement