[test] rebind byte types safely

Author: glessard

Tests/SystemTests/FilePathTests/FilePathTest.swift

@@ -22,7 +22,9 @@ func filePathFromUnterminatedBytes<S: Sequence>(_ bytes: S) -> FilePath where S.
   array += [0]
 
   return array.withUnsafeBufferPointer {
-    FilePath(platformString: $0.baseAddress!._asCChar)
+    $0.withMemoryRebound(to: CChar.self) {
+      FilePath(platformString: $0.baseAddress!)
+    }
   }
 }
 let invalidBytes: [UInt8] = [0x2F, 0x61, 0x2F, 0x62, 0x2F, 0x83]

Tests/SystemTests/SystemStringTests.swift

@@ -10,29 +10,6 @@
 // Tests for PlatformString, SystemString, and FilePath's forwarding APIs
 
 // TODO: Adapt test to Windows
-extension UnsafePointer where Pointee == UInt8 {
-  internal var _asCChar: UnsafePointer<CChar> {
-    UnsafeRawPointer(self).assumingMemoryBound(to: CChar.self)
-  }
-}
-extension UnsafePointer where Pointee == CChar {
-  internal var _asUInt8: UnsafePointer<UInt8> {
-    UnsafeRawPointer(self).assumingMemoryBound(to: UInt8.self)
-  }
-}
-extension UnsafeBufferPointer where Element == UInt8 {
-  internal var _asCChar: UnsafeBufferPointer<CChar> {
-    let base = baseAddress?._asCChar
-    return UnsafeBufferPointer<CChar>(start: base, count: self.count)
-  }
-}
-extension UnsafeBufferPointer where Element == CChar {
-  internal var _asUInt8: UnsafeBufferPointer<UInt8> {
-    let base = baseAddress?._asUInt8
-    return UnsafeBufferPointer<UInt8>(start: base, count: self.count)
-  }
-}
-
 
 import XCTest
 
@@ -46,7 +23,7 @@ private func makeRaw(
   _ str: String
 ) -> [CInterop.PlatformChar] {
   var str = str
-  var array = str.withUTF8 { Array($0._asCChar) }
+  var array = str.withUTF8 { $0.withMemoryRebound(to: CChar.self, Array.init) }
   array.append(0)
   return array
 }