SI-9832 -Xlint:help shows default

Conclude help method with the default list.

Extra words are supplied for underscore.

2 files changed, 76 insertions, 5 deletions

diff --git a/src/compiler/scala/tools/nsc/settings/MutableSettings.scala b/src/compiler/scala/tools/nsc/settings/MutableSettings.scala
index b4987e1240..11cde935f2 100644
--- a/src/compiler/scala/tools/nsc/settings/MutableSettings.scala
+++ b/src/compiler/scala/tools/nsc/settings/MutableSettings.scala
@@ -744,11 +744,19 @@ class MutableSettings(val errorFn: String => Unit)
     def isHelping: Boolean = sawHelp
 
     def help: String = {
-      val choiceLength = choices.map(_.length).max + 1
-      val formatStr = s"  %-${choiceLength}s %s"
-      choices.zipAll(descriptions, "", "").map {
-        case (arg, descr) => formatStr.format(arg, descr)
-      } mkString (f"$descr%n", f"%n", "")
+      val describe: ((String, String)) => String = {
+        val choiceWidth = choices.map(_.length).max + 1
+        val formatStr   = s"  %-${choiceWidth}s %s"
+        locally {
+          case (choice, description) => formatStr.format(choice, description)
+        }
+      }
+      val verboseDefault = default match {
+        case Some("_" :: Nil) => Some("All choices are enabled by default." :: Nil)
+        case _ => default
+      }
+      val orelse = verboseDefault.map(_.mkString(f"%nDefault: ", ", ", f"%n")).getOrElse("")
+      choices.zipAll(descriptions, "", "").map(describe).mkString(f"${descr}%n", f"%n", orelse)
     }
 
     def clear(): Unit         = {
diff --git a/test/junit/scala/tools/nsc/settings/SettingsTest.scala b/test/junit/scala/tools/nsc/settings/SettingsTest.scala
index 96f83c4c2f..3fdf758619 100644
--- a/test/junit/scala/tools/nsc/settings/SettingsTest.scala
+++ b/test/junit/scala/tools/nsc/settings/SettingsTest.scala
@@ -180,4 +180,67 @@ class SettingsTest {
     assertThrows[IllegalArgumentException](check(expected = "2.11", "-Xsource", "2.11"), _ == "-Xsource requires an argument, the syntax is -Xsource:<version>")
     assertThrows[IllegalArgumentException](check(expected = "2.11", "-Xsource:2.invalid"), _ contains "There was a problem parsing 2.invalid")
   }
+
+  @Test def helpHasDefault(): Unit = {
+    val s = new MutableSettings(msg => throw new IllegalArgumentException(msg))
+    object mChoices extends s.MultiChoiceEnumeration {
+      val a = Choice("a", "help a")
+      val b = Choice("b", "help b")
+      val c = Choice("c", "help c")
+    }
+    val m = s.MultiChoiceSetting("-m", "args", "magic sauce", mChoices, Some(List("b")))
+
+    def check(args: String*)(t: s.MultiChoiceSetting[mChoices.type] => Boolean): Boolean = {
+      m.clear()
+      val (ok, rest) = s.processArguments(args.toList, processAll = true)
+      assert(rest.isEmpty)
+      t(m)
+    }
+
+    import mChoices._
+
+    assertTrue(check("-m")(_.value == Set(b)))
+    assertTrue(check("-m") { _ =>
+      assertEquals(
+      """magic sauce
+        |  a  help a
+        |  b  help b
+        |  c  help c
+        |Default: b
+        |""".stripMargin,
+        m.help)
+      true
+    })
+  }
+  @Test def helpHasDefaultAll(): Unit = {
+    val s = new MutableSettings(msg => throw new IllegalArgumentException(msg))
+    object mChoices extends s.MultiChoiceEnumeration {
+      val a = Choice("a", "help a")
+      val b = Choice("b", "help b")
+      val c = Choice("c", "help c")
+    }
+    val m = s.MultiChoiceSetting("-m", "args", "magic sauce", mChoices, Some(List("_")))
+
+    def check(args: String*)(t: s.MultiChoiceSetting[mChoices.type] => Boolean): Boolean = {
+      m.clear()
+      val (ok, rest) = s.processArguments(args.toList, processAll = true)
+      assert(rest.isEmpty)
+      t(m)
+    }
+
+    import mChoices._
+
+    assertTrue(check("-m")(_.value == Set(a, b, c)))
+    assertTrue(check("-m") { _ =>
+      assertEquals(
+      """magic sauce
+        |  a  help a
+        |  b  help b
+        |  c  help c
+        |Default: All choices are enabled by default.
+        |""".stripMargin,
+        m.help)
+      true
+    })
+  }
 }