Exclude phantom parameters from methods signatures

Author: Duhemm

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

@@ -980,7 +980,8 @@ object Erasure {
           methodResultSig(restpe)
 
         case mtpe: MethodType =>
-          val params = mtpe.paramInfos
+          // phantom method parameters do not make it to the bytecode.
+          val params = mtpe.paramInfos.filterNot(_.isPhantom)
           val restpe = mtpe.resultType
           builder.append('(')
           // TODO: Update once we support varargs

tests/generic-java-signatures/phantom.check

@@ -0,0 +1,3 @@
+public <U,T> T MyOtherPhantom$.f1(int,int)
+U <: java.lang.Object
+T <: dotty.runtime.ErasedPhantom

tests/generic-java-signatures/phantom.scala

@@ -0,0 +1,21 @@
+object MyOtherPhantom extends Phantom {
+  type MyPhantom[V] <: this.Any
+  def myPhantom[X]: MyPhantom[X] = assume
+
+  def f1[U, T <: MyPhantom[U]](a: Int, b: T,  c: Int): T = b
+
+  def f2 = {
+    f1(3, myPhantom[Int], 2)
+  }
+}
+
+object Test {
+  def main(args: Array[String]): Unit = {
+    val f1 = MyOtherPhantom.getClass.getMethods.find(_.getName.endsWith("f1")).get
+    val tParams = f1.getTypeParameters
+    println(f1.toGenericString)
+    tParams.foreach { tp =>
+      println(tp.getName + " <: " + tp.getBounds.map(_.getTypeName).mkString(", "))
+    }
+  }
+}