[stdlib] encode/transcode => [encode/transcode]IfRepresentable...

...to make room for a more useful encode/transcode that inject replacement
characters when encoding fails.

stdlib/public/core/UTF16.swift

@@ -37,7 +37,9 @@ extension _Unicode.UTF16 : UnicodeEncoding {
     return UnicodeScalar(_unchecked: value)
   }
 
-  public static func encode(_ source: UnicodeScalar) -> EncodedScalar? {
+  public static func encodeIfRepresentable(
+    _ source: UnicodeScalar
+  ) -> EncodedScalar? {
     let x = source.value
     if _fastPath(x < (1 << 16)) {
       return EncodedScalar(_storage: x, _bitCount: 16)
@@ -50,7 +52,7 @@ extension _Unicode.UTF16 : UnicodeEncoding {
   }
 
   @inline(__always)
-  public static func transcode<FromEncoding : UnicodeEncoding>(
+  public static func transcodeIfRepresentable<FromEncoding : UnicodeEncoding>(
     _ content: FromEncoding.EncodedScalar, from _: FromEncoding.Type
   ) -> EncodedScalar? {
     if _fastPath(FromEncoding.self == UTF8.self) {
@@ -84,12 +86,12 @@ extension _Unicode.UTF16 : UnicodeEncoding {
       s &>>= 8
       r |= s & 0b0__11_1111
       r &= (1 &<< 21) - 1
-      return encode(UnicodeScalar(_unchecked: r))
+      return encodeIfRepresentable(UnicodeScalar(_unchecked: r))
     }
     else if _fastPath(FromEncoding.self == UTF16.self) {
       return unsafeBitCast(content, to: UTF16.EncodedScalar.self)
     }
-    return encode(FromEncoding.decode(content))
+    return encodeIfRepresentable(FromEncoding.decode(content))
   }
   
   public struct ForwardParser {

stdlib/public/core/UTF32.swift

@@ -34,7 +34,9 @@ extension _Unicode.UTF32 : UnicodeEncoding {
   }
 
   @inline(__always)
-  public static func encode(_ source: UnicodeScalar) -> EncodedScalar? {
+  public static func encodeIfRepresentable(
+    _ source: UnicodeScalar
+  ) -> EncodedScalar? {
     return EncodedScalar(source.value)
   }
   

stdlib/public/core/UTF8.swift

@@ -58,7 +58,9 @@ extension _Unicode.UTF8 : UnicodeEncoding {
   
   @inline(__always)
   @_inlineable
-  public static func encode(_ source: UnicodeScalar) -> EncodedScalar? {
+  public static func encodeIfRepresentable(
+    _ source: UnicodeScalar
+  ) -> EncodedScalar? {
     var c = source.value
     if _fastPath(c < (1&<<7)) {
       return EncodedScalar(_storage: c, _bitCount: 8)
@@ -86,7 +88,7 @@ extension _Unicode.UTF8 : UnicodeEncoding {
   }
 
   @inline(__always)
-  public static func transcode<FromEncoding : UnicodeEncoding>(
+  public static func transcodeIfRepresentable<FromEncoding : UnicodeEncoding>(
     _ content: FromEncoding.EncodedScalar, from _: FromEncoding.Type
   ) -> EncodedScalar? {
     if _fastPath(FromEncoding.self == UTF16.self) {
@@ -116,7 +118,7 @@ extension _Unicode.UTF8 : UnicodeEncoding {
     else if _fastPath(FromEncoding.self == UTF8.self) {
       return unsafeBitCast(content, to: UTF8.EncodedScalar.self)
     }
-    return encode(FromEncoding.decode(content))
+    return encodeIfRepresentable(FromEncoding.decode(content))
   }
 
   @_fixed_layout

stdlib/public/core/Unicode.swift

@@ -265,7 +265,7 @@ extension _Unicode.UTF8 : UnicodeCodec {
     _ input: UnicodeScalar,
     into processCodeUnit: (CodeUnit) -> Void
   ) {
-    var s = encode(input)!._storage
+    var s = encodeIfRepresentable(input)!._storage
     processCodeUnit(UInt8(extendingOrTruncating: s))
     s &>>= 8
     if _fastPath(s == 0) { return }
@@ -414,7 +414,7 @@ extension _Unicode.UTF16 : UnicodeCodec {
     _ input: UnicodeScalar,
     into processCodeUnit: (CodeUnit) -> Void
   ) {
-    var s = encode(input)!._storage
+    var s = encodeIfRepresentable(input)!._storage
     processCodeUnit(UInt16(extendingOrTruncating: s))
     s &>>= 16
     if _fastPath(s == 0) { return }

stdlib/public/core/UnicodeEncoding.swift

@@ -26,11 +26,11 @@ public protocol _UnicodeEncoding {
 
   /// Converts from encoding-independent to encoded representation, returning
   /// `nil` if the scalar can't be represented in this encoding.
-  static func encode(_ content: UnicodeScalar) -> EncodedScalar?
+  static func encodeIfRepresentable(_ content: UnicodeScalar) -> EncodedScalar?
 
   /// Converts a scalar from another encoding's representation, returning
   /// `nil` if the scalar can't be represented in this encoding.
-  static func transcode<FromEncoding : UnicodeEncoding>(
+  static func transcodeIfRepresentable<FromEncoding : UnicodeEncoding>(
     _ content: FromEncoding.EncodedScalar, from _: FromEncoding.Type
   ) -> EncodedScalar?
 
@@ -55,7 +55,7 @@ public protocol UnicodeEncoding : _UnicodeEncoding
 where ForwardParser.Encoding == Self, ReverseParser.Encoding == Self {}
 
 extension _UnicodeEncoding {
-  public static func transcode<FromEncoding : UnicodeEncoding>(
+  public static func transcodeIfRepresentable<FromEncoding : UnicodeEncoding>(
     _ content: FromEncoding.EncodedScalar, from _: FromEncoding.Type
   ) -> EncodedScalar? {
     return encode(FromEncoding.decode(content))

test/Prototypes/UnicodeDecoders.swift

@@ -221,12 +221,12 @@ func checkDecodeUTF<Codec : UnicodeCodec & UnicodeEncoding>(
     decoded.append(scalar)
     expectEqual(
       UnicodeScalar(scalar),
-      Codec.decode(Codec.encode(UnicodeScalar(scalar)!)!))
+      Codec.decode(Codec.encodeIfRepresentable(UnicodeScalar(scalar)!)!))
   }
   
   func output1(_ scalar: UnicodeScalar) {
     decoded.append(scalar.value)
-    expectEqual(scalar, Codec.decode(Codec.encode(scalar)!))
+    expectEqual(scalar, Codec.decode(Codec.encodeIfRepresentable(scalar)!))
   }
   
   var result = assertionSuccess()
@@ -307,16 +307,17 @@ func checkDecodeUTF<Codec : UnicodeCodec & UnicodeEncoding>(
   //===--- Transcoded Scalars ---------------------------------------------===//
   for x in decoded.lazy.map({ UnicodeScalar($0)! }) {
     expectEqualSequence(
-      UTF8.encode(x)!,
-      UTF8.transcode(Codec.encode(x)!, from: Codec.self)!
+      UTF8.encodeIfRepresentable(x)!,
+      UTF8.transcode(Codec.encodeIfRepresentable(x)!, from: Codec.self)!
     )
     expectEqualSequence(
-      UTF16.encode(x)!,
-      UTF16.transcode(Codec.encode(x)!, from: Codec.self)!
+      UTF16.encodeIfRepresentable(x)!,
+      UTF16.transcodeIfRepresentable(
+        Codec.encodeIfRepresentable(x)!, from: Codec.self)!
     )
     expectEqualSequence(
-      UTF32.encode(x)!,
-      UTF32.transcode(Codec.encode(x)!, from: Codec.self)!
+      UTF32.encodeIfRepresentable(x)!,
+      UTF32.transcodeIfRepresentable(Codec.encode(x)!, from: Codec.self)!
     )
   }