Use mxcl/Chalk for terminal coloring

Replace in-house implementation with a relatively simple library.

Author: dduan

Package.swift

@@ -13,10 +13,12 @@ let package = Package(
   ],
   dependencies: [
     .package(url: "https://github.com/apple/swift-tools-support-core.git", .exact("0.0.1")),
+    .package(url: "https://github.com/mxcl/Chalk.git", from: "0.1.0"),
   ],
   targets: [
     .target(
-      name: "FileCheck"),
+      name: "FileCheck",
+      dependencies: ["Chalk"]),
     .target(
       name: "filecheck-tool",
       dependencies: ["FileCheck", "SwiftToolsSupport"]),

Sources/FileCheck/ColoredStream.swift

@@ -1,21 +1,17 @@
 import Foundation
+import Chalk
 
 func diagnose(_ kind : DiagnosticKind, at loc : CheckLocation, with message : String, options: FileCheckOptions) {
   let disableColors = options.contains(.disableColors) || isatty(fileno(stdout)) != 1
   if disableColors {
     print("\(kind): \(message)")
   } else {
-    diagnosticStream.write("\(kind): ", with: [.bold, kind.color])
-    diagnosticStream.write("\(message)\n", with: [.bold])
+      print("\(kind, color: kind.color, style: .bold): \(message, style: .bold)")
   }
 
   let msg = loc.message
   if !msg.isEmpty {
-    if disableColors {
-      print(msg)
-    } else {
-      diagnosticStream.write("\(msg)\n")
-    }
+    print(msg)
   }
 }
 
@@ -24,7 +20,7 @@ enum DiagnosticKind: String {
   case warning
   case note
 
-  var color: ANSIColor {
+  var color: Color {
     switch self {
     case .error: return .red
     case .warning: return .magenta
@@ -33,15 +29,6 @@ enum DiagnosticKind: String {
   }
 }
 
-struct StdOutStream: TextOutputStream {
-  mutating func write(_ string: String) {
-    print(string, terminator: "")
-  }
-}
-
-var stdoutStream = StdOutStream()
-var diagnosticStream = ColoredANSIStream(&stdoutStream)
-
 enum CheckLocation {
   case inBuffer(UnsafePointer<CChar>, UnsafeBufferPointer<CChar>)
   case string(String)