[cats] add NonEmptyList arg parser (#225)

build.sbt

@@ -74,7 +74,7 @@ lazy val coreJS = core.js
 
 lazy val tests = crossProject(JSPlatform, JVMPlatform)
   .disablePlugins(MimaPlugin)
-  .dependsOn(cats, core)
+  .dependsOn(cats % "test", core)
   .settings(
     shared,
     caseAppPrefix,

cats/shared/src/main/scala/caseapp/cats/CatsArgParser.scala

@@ -0,0 +1,16 @@
+package caseapp.cats
+
+import caseapp.core.argparser.{AccumulatorArgParser, ArgParser}
+import cats.data.NonEmptyList
+
+object CatsArgParser {
+  implicit def nonEmptyListArgParser[T](
+    implicit parser: ArgParser[T]
+  ): AccumulatorArgParser[NonEmptyList[T]] =
+    AccumulatorArgParser.from(parser.description + "*") { (prevOpt, s) =>
+      parser(None, s).map { t =>
+        // inefficient for big lists
+        prevOpt.fold(NonEmptyList.one(t))(_ :+ t)
+      }
+    }
+}

tests/shared/src/test/scala/caseapp/CaseAppTests.scala

@@ -1,12 +1,14 @@
 package caseapp
 
+import _root_.cats.data.NonEmptyList
 import caseapp.core.Error
 import caseapp.core.Error.SeveralErrors
 import caseapp.core.help.{Help, WithHelp}
 import caseapp.demo._
 import shapeless.{Inl, Inr}
 import utest._
 import caseapp.core.util.Formatter
+import caseapp.cats.CatsArgParser._
 
 object CaseAppTests extends TestSuite {
 
@@ -105,6 +107,14 @@ object CaseAppTests extends TestSuite {
       assert(res == expectedRes)
     }
 
+    "parse nonEmptyList args" - {
+      val res =
+        Parser[WithNonEmptyList].parse(Seq("--nel", "2", "--nel", "5", "extra"))
+      val expectedRes =
+        Right((WithNonEmptyList(nel = NonEmptyList.of("2", "5")), Seq("extra")))
+      assert(res == expectedRes)
+    }
+
     "parse a user-defined argument type" - {
       val res = Parser[WithCustom].parse(Seq("--custom", "a"))
       val expectedRes = Right((WithCustom(custom = Custom("a")), Seq.empty))

tests/shared/src/test/scala/caseapp/Definitions.scala

@@ -2,6 +2,7 @@ package caseapp
 
 import caseapp.core.Error
 import caseapp.core.argparser.{ArgParser, SimpleArgParser}
+import _root_.cats.data.NonEmptyList
 
 object Definitions {
 
@@ -29,6 +30,7 @@ object Definitions {
   final case class WithTaggedList(
     list   : List[String]
   )
+  final case class WithNonEmptyList(nel: NonEmptyList[String])
 
   final case class OptBool(
     opt    : Option[Boolean]