Allow JLine to fall back to a dumb terminal (#21330)

Set the `dumb` JLine option to `null` instead of `false` when a dumb
terminal is not forced. This allows JLine to fall back to a dumb
terminal if needed.

Fixes #11978.

Before:

```
➜ ~/dotty git:(mb/11978) ✗ echo 'object Example { def smth = "smth" }' | bin/scala
The `--offline` option is experimental
Please bear in mind that non-ideal user experience should be expected.
If you encounter any bugs or have feedback to share, make sure to reach out to the maintenance team at https://github.com/VirtusLab/scala-cli
Exception in thread "main" java.lang.IllegalStateException: Unable to create a terminal
        at org.jline.terminal.TerminalBuilder.doBuild(TerminalBuilder.java:394)
        at org.jline.terminal.TerminalBuilder.build(TerminalBuilder.java:362)
        at dotty.tools.repl.JLineTerminal.<init>(JLineTerminal.scala:34)
        at dotty.tools.repl.ReplDriver.runUntilQuit(ReplDriver.scala:145)
        at dotty.tools.repl.ReplDriver.tryRunning(ReplDriver.scala:136)
        at dotty.tools.repl.Main$.main(Main.scala:7)
        at dotty.tools.repl.Main.main(Main.scala)
        Suppressed: java.io.IOException: Unable to find terminal provider ffm
                at org.jline.terminal.spi.TerminalProvider.load(TerminalProvider.java:74)
                at org.jline.terminal.TerminalBuilder.checkProvider(TerminalBuilder.java:667)
                at org.jline.terminal.TerminalBuilder.getProviders(TerminalBuilder.java:632)
                at org.jline.terminal.TerminalBuilder.doBuild(TerminalBuilder.java:395)
                ... 6 more
        Suppressed: java.io.IOException: Unable to find terminal provider jni
                at org.jline.terminal.spi.TerminalProvider.load(TerminalProvider.java:74)
                at org.jline.terminal.TerminalBuilder.checkProvider(TerminalBuilder.java:667)
                at org.jline.terminal.TerminalBuilder.getProviders(TerminalBuilder.java:634)
                at org.jline.terminal.TerminalBuilder.doBuild(TerminalBuilder.java:395)
                ... 6 more
        Suppressed: java.io.IOException: Unable to find terminal provider jansi
                at org.jline.terminal.spi.TerminalProvider.load(TerminalProvider.java:74)
                at org.jline.terminal.TerminalBuilder.checkProvider(TerminalBuilder.java:667)
                at org.jline.terminal.TerminalBuilder.getProviders(TerminalBuilder.java:636)
                at org.jline.terminal.TerminalBuilder.doBuild(TerminalBuilder.java:395)
                ... 6 more
```

After:

```
➜  ~/dotty git:(mb/11978) echo 'object Example { def smth = "smth" }' | bin/scala
The `--offline` option is experimental
Please bear in mind that non-ideal user experience should be expected.
If you encounter any bugs or have feedback to share, make sure to reach out to the maintenance team at https://github.com/VirtusLab/scala-cli
Aug 05, 2024 3:53:49 PM org.jline.utils.Log logr
WARNING: Unable to create a system terminal, creating a dumb terminal (enable debug logging for more information)
Welcome to Scala 3.6.0-RC1-bin-SNAPSHOT-git-dce4377 (17.0.8, Java OpenJDK 64-Bit Server VM).
Type in expressions for evaluation. Or try :help.

scala> // defined object Example

scala> %                                                                                                                         
➜  ~/dotty 
```

Author: smarter

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

@@ -21,11 +21,16 @@ class JLineTerminal extends java.io.Closeable {
   // Logger.getLogger("org.jline").setLevel(Level.FINEST)
 
   private val terminal =
-    TerminalBuilder.builder()
-    .dumb(dumbTerminal) // fail early if not able to create a terminal
-    .build()
+    var builder = TerminalBuilder.builder()
+    if System.getenv("TERM") == "dumb" then
+      // Force dumb terminal if `TERM` is `"dumb"`.
+      // Note: the default value for the `dumb` option is `null`, which allows
+      // JLine to fall back to a dumb terminal. This is different than `true` or
+      // `false` and can't be set using the `dumb` setter.
+      // This option is used at https://github.com/jline/jline3/blob/894b5e72cde28a551079402add4caea7f5527806/terminal/src/main/java/org/jline/terminal/TerminalBuilder.java#L528.
+      builder.dumb(true)
+    builder.build()
   private val history = new DefaultHistory
-  def dumbTerminal = Option(System.getenv("TERM")) == Some("dumb")
 
   private def blue(str: String)(using Context) =
     if (ctx.settings.color.value != "never") Console.BLUE + str + Console.RESET

compiler/test-coursier/dotty/tools/coursier/CoursierScalaTests.scala

@@ -75,8 +75,8 @@ class CoursierScalaTests:
     version()
 
     def emptyArgsEqualsRepl() =
-      val output = CoursierScalaTests.csScalaCmd()
-      assertTrue(output.mkString("\n").contains("Unable to create a terminal")) // Scala attempted to create REPL so we can assume it is working
+      val output = CoursierScalaTests.csScalaCmdWithStdin(Seq.empty, Some("println(\"Hello World\")\n:quit"))
+      assertTrue(output.mkString("\n").contains("Hello World"))
     emptyArgsEqualsRepl()
 
     def run() =
@@ -132,8 +132,8 @@ class CoursierScalaTests:
     compileFilesToJarAndRun()
 
     def replWithArgs() =
-      val output = CoursierScalaTests.csScalaCmd("-source", "3.0-migration")
-      assertTrue(output.mkString("\n").contains("Unable to create a terminal")) // Scala attempted to create REPL so we can assume it is working
+      val output = CoursierScalaTests.csScalaCmdWithStdin(Seq("-source", "3.0-migration"), Some("println(\"Hello World\")\n:quit"))
+      assertTrue(output.mkString("\n").contains("Hello World"))
     replWithArgs()
 
     def argumentFile() =
@@ -148,25 +148,31 @@ class CoursierScalaTests:
 
 object CoursierScalaTests:
 
-  def execCmd(command: String, options: String*): (Int, List[String]) =
+  private def execCmd(command: String, options: Seq[String] = Seq.empty, stdin: Option[String] = None): (Int, List[String]) =
     val cmd = (command :: options.toList).toSeq.mkString(" ")
     val out = new ListBuffer[String]
-    val code = cmd.!(ProcessLogger(out += _, out += _))
+    val process = stdin match
+      case Some(input) => Process(cmd) #< new java.io.ByteArrayInputStream(input.getBytes)
+      case None => Process(cmd)
+    val code = process.!(ProcessLogger(out += _, out += _))
     (code, out.toList)
 
   def csScalaCmd(options: String*): List[String] =
-    csCmd("dotty.tools.MainGenericRunner", options*)
+    csScalaCmdWithStdin(options, None)
+  
+  def csScalaCmdWithStdin(options: Seq[String], stdin: Option[String]): List[String] =
+    csCmd("dotty.tools.MainGenericRunner", options, stdin)
 
   def csScalaCompilerCmd(options: String*): List[String] =
-    csCmd("dotty.tools.dotc.Main", options*)
+    csCmd("dotty.tools.dotc.Main", options)
 
-  private def csCmd(entry: String, options: String*): List[String] =
+  private def csCmd(entry: String, options: Seq[String], stdin: Option[String] = None): List[String] =
     val (jOpts, args) = options.partition(_.startsWith("-J"))
     val newOptions = args match
       case Nil => args
       case _ => "--" +: args
     val newJOpts = jOpts.map(s => s"--java-opt ${s.stripPrefix("-J")}").mkString(" ")
-    execCmd("./cs", (s"""launch "org.scala-lang:scala3-compiler_3:${sys.env("DOTTY_BOOTSTRAPPED_VERSION")}" $newJOpts --main-class "$entry" --property "scala.usejavacp=true" --property "scala.use_legacy_launcher=true"""" +: newOptions)*)._2
+    execCmd("./cs", (s"""launch "org.scala-lang:scala3-compiler_3:${sys.env("DOTTY_BOOTSTRAPPED_VERSION")}" $newJOpts --main-class "$entry" --property "scala.usejavacp=true" --property "scala.use_legacy_launcher=true"""" +: newOptions), stdin)._2
 
   /** Get coursier script */
   @BeforeClass def setup(): Unit =
@@ -177,7 +183,7 @@ object CoursierScalaTests:
       case other => fail(s"Unsupported OS for coursier launcher: $other")
 
     def runAndCheckCmd(cmd: String, options: String*): Unit =
-      val (code, out) = execCmd(cmd, options*)
+      val (code, out) = execCmd(cmd, options)
       if code != 0 then
         fail(s"Failed to run $cmd ${options.mkString(" ")}, exit code: $code, output: ${out.mkString("\n")}")