Repl: emit warning for the :sh command

Fixes scala#21657

Author: bracevac

compiler/src/dotty/tools/repl/ParseResult.scala

@@ -100,6 +100,12 @@ object Reset {
   val command: String = ":reset"
 }
 
+/** `:sh <command line>` run a shell command (result is implicitly => List[String]) */
+case class Sh(expr: String) extends Command
+object Sh {
+  val command: String = ":sh"
+}
+
 /** Toggle automatic printing of results */
 case object Silent extends Command:
   val command: String = ":silent"
@@ -150,6 +156,7 @@ object ParseResult {
     TypeOf.command -> (arg => TypeOf(arg)),
     DocOf.command -> (arg => DocOf(arg)),
     Settings.command -> (arg => Settings(arg)),
+    Sh.command -> (arg => Sh(arg)),
     Silent.command -> (_ => Silent),
   )
 

compiler/src/dotty/tools/repl/ReplDriver.scala

@@ -538,6 +538,10 @@ class ReplDriver(settings: Array[String],
       }
       state
 
+    case Sh(expr) =>
+      out.println(s"""The :sh command is deprecated. Use `import scala.sys.process._` and `"command".!` instead.""")
+      state
+
     case Settings(arg) => arg match
       case "" =>
         given ctx: Context = state.context

compiler/test-resources/repl/i21657

@@ -0,0 +1,2 @@
+scala>:sh
+The :sh command is deprecated. Use `import scala.sys.process._` and `"command".!` instead.

compiler/test/dotty/tools/repl/TabcompleteTests.scala

@@ -218,6 +218,7 @@ class TabcompleteTests extends ReplTest {
         ":quit",
         ":reset",
         ":settings",
+        ":sh",
         ":silent",
         ":type"
       ),