Merge pull request #8458 from dotty-staging/implicit-package-object

Always exclude package objects from the implicit scope

Author: odersky

compiler/src/dotty/tools/dotc/typer/Implicits.scala

@@ -507,10 +507,10 @@ trait ImplicitRunInfo {
     val incomplete: mutable.Set[Type] = mutable.Set()
 
     /** Is `sym` an anchor type for which givens may exist? Anchor types are classes,
-     *  opaque type aliases, and abstract types, but not type parameters
+     *  opaque type aliases, and abstract types, but not type parameters or package objects.
      */
     def isAnchor(sym: Symbol) =
-      sym.isClass && !sym.is(Package)
+      sym.isClass && !sym.is(Package) && (!sym.isPackageObject || ctx.scala2CompatMode)
       || sym.isOpaqueAlias
       || sym.is(Deferred, butNot = Param)
 
@@ -584,7 +584,7 @@ trait ImplicitRunInfo {
                 addPath(pre.prefix)
               }
             }
-            else {
+            else if (!pre.symbol.isPackageObject || ctx.scala2CompatMode)  {
               comps += pre
               addPath(pre.prefix)
             }

tests/neg/implicit-package-object.scala

@@ -0,0 +1,45 @@
+trait ToString[A] {
+  def print(a: A): Unit
+}
+
+package A {
+  case class AA(text: String)
+  given ToString[AA] = aa => println(aa.text)
+
+  opaque type AB = String
+  given ToString[AB] = ab => println(ab)
+
+  opaque type AC = String
+  given ToString[AC] {
+    def print(ac: AC): Unit = println(ac)
+  }
+}
+
+package B {
+  case class BA(text: String)
+  object BA {
+    given ToString[BA] = ba => println(ba.text)
+  }
+
+  opaque type BB = String
+  object BB {
+    given ToString[BB] = bb => println(bb)
+  }
+
+  opaque type BC = String
+  object BC {
+    given ToString[BC] {
+      def print(bc: BC): Unit = println(bc)
+    }
+  }
+}
+
+object Test {
+  val AA = summon[ToString[A.AA]] // error
+  val AB = summon[ToString[A.AB]] // error, used to compile
+  val AC = summon[ToString[A.AC]] // error
+
+  val BA = summon[ToString[B.BA]]
+  val BB = summon[ToString[B.BB]]
+  val BC = summon[ToString[B.BC]]
+}

tests/pos/toplevel-opaque-xm/Logarithm_1.scala

@@ -2,7 +2,7 @@ package logs
 
 opaque type Logarithm = Double
 
-implicit object Logarithm {
+object Logarithm {
 
   // These are the ways to lift to the logarithm type
   def apply(d: Double): Logarithm = math.log(d)
@@ -13,10 +13,11 @@ implicit object Logarithm {
   // This is the first way to unlift the logarithm type
   def exponent(l: Logarithm): Double = l
 
-  // Extension methods define opaque types' public APIs
 
-  // This is the second way to unlift the logarithm type
-  def (x: Logarithm).toDouble: Double = math.exp(x)
-  def (x: Logarithm) + (y: Logarithm) = Logarithm(math.exp(x) + math.exp(y))
-  def (x: Logarithm) * (y: Logarithm): Logarithm = Logarithm(x + y)
+  given AnyRef {
+    // This is the second way to unlift the logarithm type
+    def (x: Logarithm).toDouble: Double = math.exp(x)
+    def (x: Logarithm) + (y: Logarithm) = Logarithm(math.exp(x) + math.exp(y))
+    def (x: Logarithm) * (y: Logarithm): Logarithm = Logarithm(x + y)
+  }
 }

tests/pos/toplevel-opaque-xm/Test_2.scala

@@ -1,15 +1,10 @@
 package logs
 
-import Predef.{any2stringadd => _, _}
-
 object Test {
   val l = Logarithm(1.0)
   val l2 = Logarithm(2.0)
   val l3 = l * l2
-  val l4 = l + l2  // currently requires any2stringadd to be disabled because
-                   // as a contextual implicit this takes precedence over the
-                   // implicit scope implicit LogarithmOps.
-                   // TODO: Remove any2stringadd
-  val d = Logarithm.toDouble(l3)
+  val l4 = l + l2
+  val d = l3.toDouble
   val l5: Logarithm = (1.0).asInstanceOf[Logarithm]
 }