Fix erasure of implicit functions

and check at runtime that it works

Author: odersky

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

@@ -44,7 +44,7 @@ object TypeErasure {
       val sym = tp.symbol
       sym.isClass &&
       sym != defn.AnyClass && sym != defn.ArrayClass &&
-      !defn.isUnimplementedFunctionClass(sym)
+      !defn.isUnimplementedFunctionClass(sym) && !defn.isImplicitFunctionClass(sym)
     case _: TermRef =>
       true
     case JavaArrayType(elem) =>

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

@@ -345,21 +345,23 @@ object Erasure extends TypeTestsCasts{
     override def typedSelect(tree: untpd.Select, pt: Type)(implicit ctx: Context): Tree = {
 
       def mapOwner(sym: Symbol): Symbol = {
-        val owner = sym.owner
-        if ((owner eq defn.AnyClass) || (owner eq defn.AnyValClass)) {
-          assert(sym.isConstructor, s"${sym.showLocated}")
-          defn.ObjectClass
-        }
-        else if (defn.isUnimplementedFunctionClass(owner))
-          defn.FunctionXXLClass
-        else
-          owner
+        def recur(owner: Symbol): Symbol =
+          if ((owner eq defn.AnyClass) || (owner eq defn.AnyValClass)) {
+            assert(sym.isConstructor, s"${sym.showLocated}")
+            defn.ObjectClass
+          } else if (defn.isUnimplementedFunctionClass(owner))
+            defn.FunctionXXLClass
+          else if (defn.isImplicitFunctionClass(owner))
+            recur(defn.FunctionClass(owner.name.functionArity))
+          else
+            owner
+        recur(sym.owner)
       }
 
-      var sym = tree.symbol
-      val owner = mapOwner(sym)
-      if (owner ne sym.owner) sym = owner.info.decl(sym.name).symbol
-      assert(sym.exists, owner)
+      val origSym = tree.symbol
+      val owner = mapOwner(origSym)
+      val sym = if (owner eq origSym.owner) origSym else owner.info.decl(origSym.name).symbol
+      assert(sym.exists, origSym.showLocated)
 
       def select(qual: Tree, sym: Symbol): Tree = {
         val name = tree.typeOpt match {

tests/pending/run/implicitFuns.scala

@@ -0,0 +1,32 @@
+object Test {
+  def main(args: Array[String]) = {
+
+    implicit val world: String = "world!"
+
+    val i1 = (implicit (s: String) => s.length > 2)
+    val i2 = {implicit (s: String) => s.length > 2}
+
+    assert(i1)
+    assert(i2)
+
+    val x: implicit String => Boolean = { implicit (s: String) => s.length > 2 }
+
+    val xx: implicit (String, Int) => Int = implicit (x: String, y: Int) => x.length + y
+
+    val y: String => Boolean = x
+
+    val yy: (String, Int) => Any = xx
+
+    val b = x("hello")
+
+    val b1: Boolean = b
+
+    val bi = x
+
+    val bi1: Boolean = bi
+
+    val c = xx("hh", 22)
+
+    val c1: Int = c
+  }
+}