From d8922070c507c3d59bca9db831a30fd6d8e19eec Mon Sep 17 00:00:00 2001
From: Alexandre Archambault <alexarchambault@users.noreply.github.com>
Date: Thu, 26 Jan 2023 10:37:33 +0100
Subject: [PATCH] Make Parser covariant in Scala 3 (#453)

---
 .../src/main/scala-2/caseapp/core/parser/Internal.scala      | 5 +++++
 .../src/main/scala-3/caseapp/core/parser/Internal.scala      | 5 +++++
 .../shared/src/main/scala-3/caseapp/core/parser/Parser.scala | 2 +-
 .../src/main/scala/caseapp/core/complete/Completer.scala     | 2 +-
 .../src/main/scala/caseapp/core/help/WithFullHelp.scala      | 2 +-
 core/shared/src/main/scala/caseapp/core/help/WithHelp.scala  | 2 +-
 .../src/main/scala/caseapp/core/parser/ParserMethods.scala   | 3 ++-
 7 files changed, 16 insertions(+), 5 deletions(-)
 create mode 100644 core/shared/src/main/scala-2/caseapp/core/parser/Internal.scala
 create mode 100644 core/shared/src/main/scala-3/caseapp/core/parser/Internal.scala

diff --git a/core/shared/src/main/scala-2/caseapp/core/parser/Internal.scala b/core/shared/src/main/scala-2/caseapp/core/parser/Internal.scala
new file mode 100644
index 00000000..65cdc092
--- /dev/null
+++ b/core/shared/src/main/scala-2/caseapp/core/parser/Internal.scala
@@ -0,0 +1,5 @@
+package caseapp.core.parser
+
+private[parser] object Internal {
+  type uncheckedVarianceScala2 = scala.annotation.unchecked.uncheckedVariance
+}
diff --git a/core/shared/src/main/scala-3/caseapp/core/parser/Internal.scala b/core/shared/src/main/scala-3/caseapp/core/parser/Internal.scala
new file mode 100644
index 00000000..fa3f7131
--- /dev/null
+++ b/core/shared/src/main/scala-3/caseapp/core/parser/Internal.scala
@@ -0,0 +1,5 @@
+package caseapp.core.parser
+
+private[parser] object Internal {
+  final class uncheckedVarianceScala2 extends scala.annotation.StaticAnnotation
+}
diff --git a/core/shared/src/main/scala-3/caseapp/core/parser/Parser.scala b/core/shared/src/main/scala-3/caseapp/core/parser/Parser.scala
index 4b27cf14..aabc8660 100644
--- a/core/shared/src/main/scala-3/caseapp/core/parser/Parser.scala
+++ b/core/shared/src/main/scala-3/caseapp/core/parser/Parser.scala
@@ -12,7 +12,7 @@ import scala.language.implicitConversions
   * @tparam T:
   *   success result type
   */
-abstract class Parser[T] extends ParserMethods[T] {
+abstract class Parser[+T] extends ParserMethods[T] {
 
   import Parser.Step
 
diff --git a/core/shared/src/main/scala/caseapp/core/complete/Completer.scala b/core/shared/src/main/scala/caseapp/core/complete/Completer.scala
index cf879e18..78a98f99 100644
--- a/core/shared/src/main/scala/caseapp/core/complete/Completer.scala
+++ b/core/shared/src/main/scala/caseapp/core/complete/Completer.scala
@@ -3,7 +3,7 @@ package caseapp.core.complete
 import caseapp.core.Arg
 import caseapp.core.help.{WithFullHelp, WithHelp}
 
-trait Completer[T] { self =>
+trait Completer[-T] { self =>
   def optionName(prefix: String, state: Option[T]): List[CompletionItem]
   def optionValue(arg: Arg, prefix: String, state: Option[T]): List[CompletionItem]
   def argument(prefix: String, state: Option[T]): List[CompletionItem]
diff --git a/core/shared/src/main/scala/caseapp/core/help/WithFullHelp.scala b/core/shared/src/main/scala/caseapp/core/help/WithFullHelp.scala
index 9a2c6ca6..9cc21462 100644
--- a/core/shared/src/main/scala/caseapp/core/help/WithFullHelp.scala
+++ b/core/shared/src/main/scala/caseapp/core/help/WithFullHelp.scala
@@ -4,7 +4,7 @@ import caseapp.core.Error
 import caseapp.{ExtraName, Group, HelpMessage, Recurse}
 import caseapp.core.parser.Parser
 
-final case class WithFullHelp[T](
+final case class WithFullHelp[+T](
   @Recurse
   withHelp: WithHelp[T],
   @Group("Help")
diff --git a/core/shared/src/main/scala/caseapp/core/help/WithHelp.scala b/core/shared/src/main/scala/caseapp/core/help/WithHelp.scala
index 08c58475..d66e210e 100644
--- a/core/shared/src/main/scala/caseapp/core/help/WithHelp.scala
+++ b/core/shared/src/main/scala/caseapp/core/help/WithHelp.scala
@@ -14,7 +14,7 @@ import caseapp.core.Error
   * @tparam T:
   *   type to which usage and help options are added
   */
-final case class WithHelp[T](
+final case class WithHelp[+T](
   @Group("Help")
   @HelpMessage("Print usage and exit")
   usage: Boolean = false,
diff --git a/core/shared/src/main/scala/caseapp/core/parser/ParserMethods.scala b/core/shared/src/main/scala/caseapp/core/parser/ParserMethods.scala
index b2a2a021..3bf7d225 100644
--- a/core/shared/src/main/scala/caseapp/core/parser/ParserMethods.scala
+++ b/core/shared/src/main/scala/caseapp/core/parser/ParserMethods.scala
@@ -6,9 +6,10 @@ import caseapp.core.util.Formatter
 import caseapp.Name
 import caseapp.core.complete.Completer
 import caseapp.core.complete.CompletionItem
+
 import scala.annotation.tailrec
 
-trait ParserMethods[T] { parser: Parser[T] =>
+trait ParserMethods[+T] { parser: Parser[T @Internal.uncheckedVarianceScala2] =>
 
   import Parser.Step