FilterMatcher: turn into metaconfig-parsable type

scalafmt-core/shared/src/main/scala/org/scalafmt/config/FilterMatcher.scala

@@ -4,13 +4,38 @@ import org.scalafmt.sysops.AbsoluteFile
 
 import scala.util.matching.Regex
 
+import metaconfig._
+
 case class FilterMatcher(include: Regex, exclude: Regex) {
   def matchesFile(file: AbsoluteFile): Boolean = matches(file.toString())
   def matches(input: String): Boolean = include.pattern.matcher(input).find() &&
     !exclude.pattern.matcher(input).find()
 }
 
 object FilterMatcher {
+  val default = FilterMatcher(".*".r, "^$".r)
+
+  implicit val filterMatcherSurface: generic.Surface[FilterMatcher] = generic
+    .deriveSurface[FilterMatcher]
+  implicit val filterMatcherEncoder: ConfEncoder[FilterMatcher] = generic
+    .deriveEncoder[FilterMatcher]
+  implicit val filterMatcherDecoder: ConfDecoderEx[FilterMatcher] = generic
+    .deriveDecoderEx(default)
+
+  implicit val regexEncoder: ConfEncoder[Regex] = ConfEncoder.StringEncoder
+    .contramap[Regex](_.regex)
+  implicit val regexDecoder: ConfDecoderEx[Regex] = {
+    val seqStringDecoder = implicitly[ConfDecoderEx[Seq[String]]]
+    (state, conf) =>
+      seqStringDecoder.read(state.map(x => Seq(x.regex)), conf) match {
+        case Configured.Ok(x) => Configured.Ok(mkRegexp(x))
+        case x: Configured.NotOk => conf match {
+            case Conf.Str(s) => Configured.Ok(s.r)
+            case _ => x
+          }
+      }
+  }
+
   def mkRegexp(filters: Seq[String], strict: Boolean = false): Regex =
     filters match {
       case Nil => "$a".r // will never match anything