Merge pull request #2713 from dotty-staging/fix-phantom-assume

Make Phantom.assume return type an ExprType

Author: odersky

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

@@ -1010,7 +1010,7 @@ class Definitions {
 
     val any = enterCompleteClassSymbol(cls, tpnme.Any, Protected | Final | NoInitsTrait, Nil)
     val nothing = enterCompleteClassSymbol(cls, tpnme.Nothing, Protected | Final | NoInitsTrait, List(any.typeRef))
-    enterMethod(cls, nme.assume_, MethodType(Nil, nothing.typeRef), Protected | Final | Method)
+    enterMethod(cls, nme.assume_, ExprType(nothing.typeRef), Protected | Final | Method)
 
     cls
   }

compiler/src/dotty/tools/dotc/transform/Erasure.scala

@@ -411,9 +411,14 @@ object Erasure extends TypeTestsCasts{
         }
       }
 
-      recur(typed(tree.qualifier, AnySelectionProto))
+      if (tree.symbol eq defn.Phantom_assume) PhantomErasure.erasedAssume
+      else recur(typed(tree.qualifier, AnySelectionProto))
     }
 
+    override def typedIdent(tree: untpd.Ident, pt: Type)(implicit ctx: Context): tpd.Tree =
+      if (tree.symbol eq defn.Phantom_assume) PhantomErasure.erasedAssume
+      else super.typedIdent(tree, pt)
+
     override def typedThis(tree: untpd.This)(implicit ctx: Context): Tree =
       if (tree.symbol == ctx.owner.lexicallyEnclosingClass || tree.symbol.isStaticOwner) promote(tree)
       else {
@@ -456,8 +461,6 @@ object Erasure extends TypeTestsCasts{
       val Apply(fun, args) = tree
       if (fun.symbol == defn.cbnArg)
         typedUnadapted(args.head, pt)
-      else if (fun.symbol eq defn.Phantom_assume)
-        PhantomErasure.erasedAssume
       else typedExpr(fun, FunProto(args, pt, this)) match {
         case fun1: Apply => // arguments passed in prototype were already passed
           fun1

tests/neg/phantom-assume-1.scala

@@ -0,0 +1,4 @@
+object Boo extends Phantom {
+  type BooAny = this.Any
+  def assume1: BooAny = assume() // error:  method assume in trait Phantom does not take parameters
+}

tests/run/phantom-assume-1.check

@@ -0,0 +1,17 @@
+
+object Test {
+  import Boo._
+
+  def main(args: Array[String]): Unit = {
+    Boo.assume1
+    Boo.assume2
+    Boo.assume3
+  }
+}
+
+object Boo extends Phantom {
+  type BooAny = this.Any
+  def assume1: BooAny = assume
+  def assume2: BooAny = this.assume
+  def assume3: BooAny = Boo.assume
+}