Merge pull request scala#4121 from retronym/ticket/5938

SI-5938 Test for a FSC bug with mixin, duplicate static forwarders

Author: gkossakowski

test/files/run/t5938.scala

@@ -0,0 +1,35 @@
+import scala.tools.partest.DirectTest
+
+object Test extends DirectTest {
+
+  override def extraSettings: String =
+    s"-usejavacp -d ${testOutput.path}"
+
+  override def code = """
+object O extends C {
+  def main(args: Array[String]): Unit = {
+  }
+  // Static forwarder for foo and setter_foo_= added more once in a multi-run compile.
+}
+  """.trim
+
+  override def show(): Unit = {
+    val global = newCompiler()
+    Console.withErr(System.out) {
+      compileString(global)(code)
+      compileString(global)(code)
+      loadClass // was "duplicate name and signature in class X"
+    }
+  }
+
+  def loadClass: Class[_] = {
+    val cl = new java.net.URLClassLoader(Array(testOutput.toFile.toURL));
+    cl.loadClass("O")
+  }
+}
+
+trait T {
+  val foo: String = ""
+}
+class C extends T
+