Support --help and --usage CLI options

Author: avdv

modules/core/src/main/scala/org/scalasteward/core/application/Cli.scala

@@ -17,7 +17,7 @@
 package org.scalasteward.core.application
 
 import caseapp._
-import caseapp.core.Error.MalformedValue
+import caseapp.core.Error.{MalformedValue, Other}
 import caseapp.core.argparser.{ArgParser, SimpleArgParser}
 import cats.syntax.all._
 import org.http4s.Uri
@@ -29,7 +29,15 @@ import scala.concurrent.duration._
 final class Cli[F[_]](implicit F: ApplicativeThrowable[F]) {
   def parseArgs(args: List[String]): F[Args] =
     F.fromEither {
-      CaseApp.parse[Args](args).bimap(e => new Throwable(e.message), { case (parsed, _) => parsed })
+      CaseApp
+        .parseWithHelp[Args](args)
+        .flatMap {
+          case (_, true, _, _)              => Left(Other(CaseApp.helpMessage[Args]))
+          case (_, _, true, _)              => Left(Other(CaseApp.usageMessage[Args]))
+          case (parsed @ Right(_), _, _, _) => parsed
+          case (e @ Left(_), _, _, _)       => e
+        }
+        .leftMap(e => new Throwable(e.message))
     }
 }
 

modules/core/src/test/scala/org/scalasteward/core/application/CliTest.scala

@@ -1,11 +1,13 @@
 package org.scalasteward.core.application
+
 import org.http4s.syntax.literals._
 import org.scalasteward.core.application.Cli.EnvVar
+import org.scalatest.EitherValues
 import org.scalatest.funsuite.AnyFunSuite
 import org.scalatest.matchers.should.Matchers
 import scala.concurrent.duration._
 
-class CliTest extends AnyFunSuite with Matchers {
+class CliTest extends AnyFunSuite with Matchers with EitherValues {
   type Result[A] = Either[Throwable, A]
   val cli: Cli[Result] = new Cli[Result]
 
@@ -66,6 +68,14 @@ class CliTest extends AnyFunSuite with Matchers {
     cli.parseArgs(Nil).isLeft shouldBe true
   }
 
+  test("parseArgs --help") {
+    cli.parseArgs(List("--help")).left.value.getMessage should include("--git-author-email")
+  }
+
+  test("parseArgs --usage") {
+    cli.parseArgs(List("--usage")).left.value.getMessage should startWith("Usage: args")
+  }
+
   test("env-var without equals sign") {
     Cli.envVarArgParser(None, "SBT_OPTS").isLeft shouldBe true
   }