Add scala.Dynamic language feature check.

Author: nicolasstucki

src/dotty/language.scala

@@ -13,4 +13,7 @@ object language {
   /** No auto tupling */
   val noAutoTupling = new Feature
 
+  /** Allow use of scala.Dynamic */
+  val dynamics = new Feature
+
 }

src/dotty/tools/dotc/core/Definitions.scala

@@ -424,8 +424,10 @@ class Definitions {
     def Product_productArity(implicit ctx: Context) = Product_productArityR.symbol
     lazy val Product_productPrefixR = ProductClass.requiredMethodRef(nme.productPrefix)
     def Product_productPrefix(implicit ctx: Context) = Product_productPrefixR.symbol
-  lazy val LanguageModuleRef          = ctx.requiredModule("dotty.language")
+  lazy val LanguageModuleRef = ctx.requiredModule("dotty.language")
   def LanguageModuleClass(implicit ctx: Context) = LanguageModuleRef.symbol.moduleClass.asClass
+  lazy val Scala2LanguageModuleRef = ctx.requiredModule("scala.language")
+  def Scala2LanguageModuleClass(implicit ctx: Context) = Scala2LanguageModuleRef.symbol.moduleClass.asClass
   lazy val NonLocalReturnControlType: TypeRef   = ctx.requiredClassRef("scala.runtime.NonLocalReturnControl")
 
   lazy val ClassTagType = ctx.requiredClassRef("scala.reflect.ClassTag")

src/dotty/tools/dotc/core/StdNames.scala

@@ -383,6 +383,7 @@ object StdNames {
     val delayedInit: N          = "delayedInit"
     val delayedInitArg: N       = "delayedInit$body"
     val drop: N                 = "drop"
+    val dynamics: N             = "dynamics"
     val dummyApply: N           = "<dummy-apply>"
     val elem: N                 = "elem"
     val emptyValDef: N          = "emptyValDef"

src/dotty/tools/dotc/core/TypeOps.scala

@@ -455,7 +455,8 @@ trait TypeOps { this: Context => // TODO: Make standalone object.
    */
   def featureEnabled(owner: ClassSymbol, feature: TermName): Boolean = {
     def toPrefix(sym: Symbol): String =
-      if (sym eq defn.LanguageModuleClass) "" else toPrefix(sym.owner) + sym.name + "."
+      if (!sym.exists || (sym eq defn.LanguageModuleClass) || (sym eq defn.Scala2LanguageModuleRef)) ""
+      else toPrefix(sym.owner) + sym.name + "."
     def featureName = toPrefix(owner) + feature
     def hasImport(implicit ctx: Context): Boolean = (
          ctx.importInfo != null
@@ -477,6 +478,11 @@ trait TypeOps { this: Context => // TODO: Make standalone object.
   def scala2Mode =
     featureEnabled(defn.LanguageModuleClass, nme.Scala2)
 
+  def dynamicsEnabled = {
+    featureEnabled(defn.Scala2LanguageModuleClass, nme.dynamics) ||
+    featureEnabled(defn.LanguageModuleClass, nme.dynamics)
+  }
+
   def testScala2Mode(msg: String, pos: Position) = {
     if (scala2Mode) migrationWarning(msg, pos)
     scala2Mode

src/dotty/tools/dotc/reporting/Reporter.scala

@@ -12,6 +12,7 @@ import config.Printers
 import java.lang.System.currentTimeMillis
 import core.Mode
 import interfaces.Diagnostic.{ERROR, WARNING, INFO}
+import dotty.tools.dotc.core.Symbols.Symbol
 
 object Reporter {
   class Error(msgFn: => String, pos: SourcePosition) extends Diagnostic(msgFn, pos, ERROR)
@@ -68,6 +69,29 @@ trait Reporting { this: Context =>
   def featureWarning(msg: => String, pos: SourcePosition = NoSourcePosition): Unit =
     reporter.report(new FeatureWarning(msg, pos))
 
+  private[this] var reportedFeatures = Set[Symbol]()
+  def featureWarning(pos: SourcePosition, feature: String, featureDescription: String, featureTrait: Symbol, required: Boolean): Unit = {
+    val req = if (required) "needs to" else "should"
+    val prefix = if (scala2Mode) "scala." else "dotty."
+    val fqname = prefix + "language." + feature
+
+    val explain = {
+      if (reportedFeatures.contains(featureTrait)) ""
+      else {
+        s"""|
+            |This can be achieved by adding the import clause 'import $fqname'
+            |or by setting the compiler option -language:$feature.
+            |See the Scala docs for value $fqname for a discussion
+            |why the feature $req be explicitly enabled.""".stripMargin
+      }
+    }
+    reportedFeatures += featureTrait
+
+    val msg = s"$featureDescription $req be enabled\nby making the implicit value $fqname visible.$explain"
+    if (required) error(msg, pos)
+    else featureWarning(msg, pos)
+  }
+
   def warning(msg: => String, pos: SourcePosition = NoSourcePosition): Unit =
     reporter.report(new Warning(msg, pos))
 

src/dotty/tools/dotc/typer/Typer.scala

@@ -1098,7 +1098,12 @@ class Typer extends Namer with TypeAssigner with Applications with Implicits wit
       .withType(dummy.nonMemberTermRef)
     checkVariance(impl1)
     if (!cls.is(AbstractOrTrait) && !ctx.isAfterTyper) checkRealizableBounds(cls.typeRef, cdef.pos)
-    assignType(cpy.TypeDef(cdef)(name, impl1, Nil), cls)
+    val cdef1 = assignType(cpy.TypeDef(cdef)(name, impl1, Nil), cls)
+    if (ctx.phase.isTyper && cdef1.tpe <:< defn.DynamicType && !ctx.dynamicsEnabled) {
+      val isRequired = parents1.exists(_.tpe =:= defn.DynamicType)
+      ctx.featureWarning(cdef.pos, nme.dynamics.toString, "extension of type scala.Dynamic", cls, isRequired)
+    }
+    cdef1
 
     // todo later: check that
     //  1. If class is non-abstract, it is instantiatable:

tests/neg/dynamicNoImport.scala

@@ -0,0 +1,3 @@
+class Foo extends scala.Dynamic // error
+trait Bar extends scala.Dynamic // error
+object Baz extends scala.Dynamic // error

tests/pos/dynamicExtendsNoImport.scala

@@ -0,0 +1,7 @@
+
+package foo {
+  import scala.language.dynamics
+  class Bar extends scala.Dynamic
+}
+
+class Baz extends foo.Bar