Fix utf8 decode (swiftlang#145)

* remove Error

* replace to String(decoding:as) from String(data: encoding)

Author: zunda-pixel

Tools/markdown-tool/Commands/FormatCommand.swift

@@ -138,10 +138,8 @@ extension MarkdownCommand {
             }
             which.waitUntilExit()
 
-            guard which.terminationStatus == 0,
-                let output = String(data: standardOutput.fileHandleForReading.readDataToEndOfFile(), encoding: .utf8) else {
-                    return nil
-            }
+            guard which.terminationStatus == 0 else { return nil }
+            let output = String(decoding: standardOutput.fileHandleForReading.readDataToEndOfFile(), as: UTF8.self)
 
             return output.trimmingCharacters(in: CharacterSet(charactersIn: "\n"))
         }

Tools/markdown-tool/MarkdownCommand.swift

@@ -14,27 +14,14 @@ import Markdown
 
 @main
 struct MarkdownCommand: ParsableCommand {
-    enum Error: LocalizedError {
-        case couldntDecodeInputAsUTF8
-
-        var errorDescription: String? {
-            switch self {
-            case .couldntDecodeInputAsUTF8:
-                return "Couldn't decode input as UTF-8"
-            }
-        }
-    }
-
     static let configuration = CommandConfiguration(commandName: "markdown", shouldDisplay: false, subcommands: [
         DumpTree.self,
         Format.self,
     ])
 
     static func parseFile(at path: String, options: ParseOptions) throws -> (source: String, parsed: Document) {
         let data = try Data(contentsOf: URL(fileURLWithPath: path))
-        guard let inputString = String(data: data, encoding: .utf8) else {
-            throw Error.couldntDecodeInputAsUTF8
-        }
+        let inputString = String(decoding: data, as: UTF8.self)
         return (inputString, Document(parsing: inputString, options: options))
     }
 
@@ -45,9 +32,7 @@ struct MarkdownCommand: ParsableCommand {
         } else {
             stdinData = FileHandle.standardInput.readDataToEndOfFile()
         }
-        guard let stdinString = String(data: stdinData, encoding: .utf8) else {
-            throw Error.couldntDecodeInputAsUTF8
-        }
+        let stdinString = String(decoding: stdinData, as: UTF8.self)
         return (stdinString, Document(parsing: stdinString, options: options))
     }
 }