Fix #21242: Add REPL flag to quit after evaluating init script (#22636)

Adding a new REPL flag `--repl-quit-after-init`: evaluate the init
script and skip the interactive mode.

Fix the remaining part of #21242

Test with flag at REPL startup:

```scala
> ./bin/replQ --repl-quit-after-init --repl-init-script 'println("Hello from init script!"); val i = 2 * 2' 
Hello from init script!
val i: Int = 4
>
```

Author: noti0na1

bin/replQ

@@ -0,0 +1,6 @@
+#!/usr/bin/env bash
+
+ROOT="$(cd "$(dirname "${BASH_SOURCE[0]}")" >& /dev/null && pwd)/.."
+. $ROOT/bin/commonQ
+
+java -Dscala.usejavacp=true -cp $cp dotty.tools.repl.Main -usejavacp "$@"

compiler/src/dotty/tools/dotc/config/ScalaSettings.scala

@@ -128,6 +128,7 @@ trait CommonScalaSettings:
   val usejavacp: Setting[Boolean] = BooleanSetting(RootSetting, "usejavacp", "Utilize the java.class.path in classpath resolution.", aliases = List("--use-java-class-path"))
   val scalajs: Setting[Boolean] = BooleanSetting(RootSetting, "scalajs", "Compile in Scala.js mode (requires scalajs-library.jar on the classpath).", aliases = List("--scalajs"))
   val replInitScript: Setting[String] = StringSetting(RootSetting, "repl-init-script", "code", "The code will be run on REPL startup.", "", aliases = List("--repl-init-script"))
+  val replQuitAfterInit: Setting[Boolean] = BooleanSetting(RootSetting, "repl-quit-after-init", "Quit REPL after evaluating the init script.", aliases = List("--repl-quit-after-init"))
 end CommonScalaSettings
 
 /** -P "plugin" settings. Various tools might support plugins. */

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

@@ -153,7 +153,9 @@ class ReplDriver(settings: Array[String],
    *
    *  Possible reason for unsuccessful run are raised flags in CLI like --help or --version
    */
-  final def tryRunning = if shouldStart then runUntilQuit()
+  final def tryRunning = if shouldStart then
+    if rootCtx.settings.replQuitAfterInit.value(using rootCtx) then initialState
+    else runUntilQuit()
 
   /** Run REPL with `state` until `:quit` command found
    *

compiler/test/dotty/tools/scripting/BashExitCodeTests.scala

@@ -32,10 +32,11 @@ class BashExitCodeTests:
         s"expected $expectedExitCode but got $exitCode${pp("out", stdout)}${pp("err", stderr)}"
       }, expectedExitCode, exitCode)
 
-  // Helpers for running scala, scalac, and scalac without the output directory ("raw")
+  // Helpers for running scala, scalac and repl without the output directory ("raw")
   def scala(args: String*)     = verifyExit(scalaPath, ("--power" +: args :+ "--offline" :+ "--server=false")*)
   def scalacRaw(args: String*) = verifyExit(scalacPath, args*)
   def scalac(args: String*)    = scalacRaw(("-d" +: tmpDir +: args)*)
+  def repl(args: String*)      = verifyExit(scalaPath, ("--power" +: "repl" +: "--offline" +: "--" +: args)*)
 
   /** The path to the test file for this class. */
   def f(body: String, suffix: String = ".scala"): String =
@@ -72,6 +73,8 @@ class BashExitCodeTests:
   @Test def xPluginList   = scala("-Xplugin-list")(0)
   @Test def vPhases       = scala("-Vphases")(0)
 
+  @Test def replEval      = repl("--repl-quit-after-init", "--repl-init-script", "\'println(\"Hello from init script!\"); val i = 2 * 2\'")(0)
+
   /** A utility for running two commands in a row, like you do in bash. */
   extension (inline u1: Unit) inline def & (inline u2: Unit): Unit = { u1; u2 }
 end BashExitCodeTests