Add help to choices

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

@@ -11,6 +11,7 @@ import SourceVersion.*
 import reporting.Message
 import NameKinds.QualifiedName
 import Annotations.ExperimentalAnnotation
+import Settings.Setting.ChoiceWithHelp
 
 object Feature:
 
@@ -35,14 +36,31 @@ object Feature:
   val into = experimental("into")
 
   val values = List(
-    nme.help,
-    nme.noAutoTupling, nme.dynamics, nme.unsafeNulls, nme.postfixOps, nme.strictEquality,
-    nme.implicitConversions, nme.adhocExtensions,
-    namedTypeArguments, genericNumberLiterals, scala2macros,
-    dependent, erasedDefinitions, symbolLiterals, fewerBraces, saferExceptions,
-    clauseInterleaving, pureFunctions, captureChecking, into
+    (nme.help, "Display all available features"),
+    (nme.noAutoTupling, "Disable automatic tupling"),
+    (nme.dynamics, "Allow direct or indirect subclasses of scala.Dynamic"),
+    (nme.unsafeNulls, "Enable unsafe nulls for explicit nulls"),
+    (nme.postfixOps, "Allow postfix operator notation"),
+    (nme.strictEquality, "Enable strict equality (=== and !==)"),
+    (nme.implicitConversions, "Allow implicit conversions without warnings"),
+    (nme.adhocExtensions, "Allow ad-hoc extension methods"),
+    (namedTypeArguments, "Allow named type arguments"),
+    (genericNumberLiterals, "Allow generic number literals"),
+    (scala2macros, "Allow Scala 2 macros"),
+    (dependent, "Allow dependent method types"),
+    (erasedDefinitions, "Allow erased definitions"),
+    (symbolLiterals, "Allow symbol literals"),
+    (fewerBraces, "Allow fewer braces"),
+    (saferExceptions, "Enable safer exceptions"),
+    (clauseInterleaving, "Enable clause interleaving"),
+    (pureFunctions, "Enable pure functions"),
+    (captureChecking, "Enable experimental capture checking"),
+    (into, "Allow into clauses in pattern matches")
   )
 
+  private def enabledLanguageFeaturesBySetting(using Context): List[String] =
+    ctx.settings.language.value.asInstanceOf
+
   /** Is `feature` enabled by by a command-line setting? The enabling setting is
    *
    *       -language:<prefix>feature
@@ -51,7 +69,7 @@ object Feature:
    *  but subtracting the prefix `scala.language.` at the front.
    */
   def enabledBySetting(feature: TermName)(using Context): Boolean =
-    ctx.base.settings.language.value.contains(feature.toString)
+    enabledLanguageFeaturesBySetting.contains(feature.toString)
 
   /** Is `feature` enabled by by an import? This is the case if the feature
    *  is imported by a named import
@@ -172,7 +190,7 @@ object Feature:
 
   /** Check that experimental compiler options are only set for snapshot or nightly compiler versions. */
   def checkExperimentalSettings(using Context): Unit =
-    for setting <- ctx.settings.language.value
+    for setting <- enabledLanguageFeaturesBySetting
         if setting.startsWith("experimental.") && setting != "experimental.macros"
     do checkExperimentalFeature(s"feature $setting", NoSourcePosition)
 

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

@@ -114,7 +114,7 @@ trait CommonScalaSettings:
   val explainTypes: Setting[Boolean] = BooleanSetting(RootSetting, "explain-types", "Explain type errors in more detail (deprecated, use -explain instead).", aliases = List("--explain-types", "-explaintypes"))
   val explainCyclic: Setting[Boolean] = BooleanSetting(RootSetting, "explain-cyclic", "Explain cyclic reference errors in more detail.", aliases = List("--explain-cyclic"))
   val unchecked: Setting[Boolean] = BooleanSetting(RootSetting, "unchecked", "Enable additional warnings where generated code depends on assumptions.", initialValue = true, aliases = List("--unchecked"))
-  val language: Setting[List[String]] = MultiChoiceSetting(RootSetting, "language", "feature", "Enable one or more language features.", choices = ScalaSettingsProperties.supportedLanguageFeatures, aliases = List("--language"))
+  val language: Setting[List[ChoiceWithHelp[String]]] = MultiChoiceHelpSetting(RootSetting, "language", "feature", "Enable one or more language features.", choices = ScalaSettingsProperties.supportedLanguageFeatures, default = Nil, aliases = List("--language"))
   val experimental: Setting[Boolean] = BooleanSetting(RootSetting, "experimental", "Annotate all top-level definitions with @experimental. This enables the use of experimental features anywhere in the project.")
 
   /* Coverage settings */
@@ -448,3 +448,4 @@ private sealed trait YSettings:
   val YearlyTastyOutput: Setting[AbstractFile] = OutputSetting(ForkSetting, "Yearly-tasty-output", "directory|jar", "Destination to write generated .tasty files to for use in pipelined compilation.", NoAbstractFile, aliases = List("-Ypickle-write"), preferPrevious = true)
   val YallowOutlineFromTasty: Setting[Boolean] = BooleanSetting(ForkSetting, "Yallow-outline-from-tasty", "Allow outline TASTy to be loaded with the -from-tasty option.")
 end YSettings
+

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

@@ -1,6 +1,7 @@
 package dotty.tools.dotc
 package config
 
+import Settings.Setting.ChoiceWithHelp
 import dotty.tools.backend.jvm.BackendUtils.classfileVersionMap
 import dotty.tools.io.{AbstractFile, Directory, JDK9Reflectors, PlainDirectory, NoAbstractFile}
 import scala.language.unsafeNulls
@@ -26,8 +27,8 @@ object ScalaSettingsProperties:
   def supportedSourceVersions: List[String] =
     SourceVersion.values.toList.map(_.toString)
 
-  def supportedLanguageFeatures: List[String] =
-    Feature.values.toList.map(_.toString)
+  def supportedLanguageFeatures: List[ChoiceWithHelp[String]] =
+    Feature.values.map((n, d) => ChoiceWithHelp(n.toString, d))
 
   def defaultClasspath: String = sys.env.getOrElse("CLASSPATH", ".")