Emit trait method bodies in statics

And use this as the target of the default methods or
statically resolved super or $init calls.

The call-site change is predicated on `-Yuse-trait-statics`
as a stepping stone for experimentation / bootstrapping.

I have performed this transformation in the backend,
rather than trying to reflect this in the view from
Scala symbols + ASTs.

We also need to add an restriction related to invokespecial to Java
parents: to support a super call to one of these to implement a
super accessor, the interface must be listed as a direct parent
of the class.

The static method names has a trailing $ added to avoid duplicate
name and signature errors in classfiles.

7 files changed, 67 insertions, 28 deletions

diff --git a/test/junit/scala/lang/traits/BytecodeTest.scala b/test/junit/scala/lang/traits/BytecodeTest.scala
index f47fc9c127..ec8508df99 100644
--- a/test/junit/scala/lang/traits/BytecodeTest.scala
+++ b/test/junit/scala/lang/traits/BytecodeTest.scala
@@ -9,6 +9,7 @@ import scala.collection.JavaConverters._
 import scala.tools.asm.Opcodes
 import scala.tools.asm.Opcodes._
 import scala.tools.asm.tree.ClassNode
+import scala.tools.nsc.backend.jvm.opt.BytecodeUtils
 import scala.tools.partest.ASMConverters._
 import scala.tools.testing.BytecodeTesting
 import scala.tools.testing.BytecodeTesting._
@@ -18,8 +19,8 @@ class BytecodeTest extends BytecodeTesting {
   import compiler._
 
   def checkForwarder(classes: Map[String, ClassNode], clsName: Symbol, target: String) = {
-    val List(f) = getMethods(classes(clsName.name), "f")
-    assertSameCode(f, List(VarOp(ALOAD, 0), Invoke(INVOKESPECIAL, target, "f", "()I", false), Op(IRETURN)))
+    val f = getMethod(classes(clsName.name), "f")
+    assertSameCode(f, List(VarOp(ALOAD, 0), Invoke(INVOKESTATIC, target, "f$", s"(L$target;)I", true), Op(IRETURN)))
   }
 
   @Test
@@ -88,7 +89,7 @@ class BytecodeTest extends BytecodeTesting {
     assertSameSummary(getMethod(c("C18"), "f"), List(BIPUSH, IRETURN))
     checkForwarder(c, 'C19, "T7")
     assertSameCode(getMethod(c("C19"), "T7$$super$f"), List(VarOp(ALOAD, 0), Invoke(INVOKESPECIAL, "C18", "f", "()I", false), Op(IRETURN)))
-    assertInvoke(getMethod(c("C20"), "clone"), "T8", "clone") // mixin forwarder
+    assertInvoke(getMethod(c("C20"), "clone"), "T8", "clone$") // mixin forwarder
   }
 
   @Test
@@ -141,7 +142,7 @@ class BytecodeTest extends BytecodeTesting {
   def invocationReceivers(): Unit = {
     val List(c1, c2, t, u) = compileClasses(invocationReceiversTestCode.definitions("Object"))
     // mixin forwarder in C1
-    assertSameCode(getMethod(c1, "clone"), List(VarOp(ALOAD, 0), Invoke(INVOKESPECIAL, "T", "clone", "()Ljava/lang/Object;", false), Op(ARETURN)))
+    assertSameCode(getMethod(c1, "clone"), List(VarOp(ALOAD, 0), Invoke(INVOKESTATIC, "T", "clone$", "(LT;)Ljava/lang/Object;", true), Op(ARETURN)))
     assertInvoke(getMethod(c1, "f1"), "T", "clone")
     assertInvoke(getMethod(c1, "f2"), "T", "clone")
     assertInvoke(getMethod(c1, "f3"), "C1", "clone")
diff --git a/test/junit/scala/tools/nsc/backend/jvm/DefaultMethodTest.scala b/test/junit/scala/tools/nsc/backend/jvm/DefaultMethodTest.scala
index c9a958ee4f..841e850b49 100644
--- a/test/junit/scala/tools/nsc/backend/jvm/DefaultMethodTest.scala
+++ b/test/junit/scala/tools/nsc/backend/jvm/DefaultMethodTest.scala
@@ -5,6 +5,7 @@ import org.junit.Test
 
 import scala.collection.JavaConverters
 import scala.collection.JavaConverters._
+import scala.reflect.internal.Flags
 import scala.tools.asm.Opcodes
 import scala.tools.asm.tree.ClassNode
 import scala.tools.testing.BytecodeTesting
@@ -21,7 +22,7 @@ class DefaultMethodTest extends BytecodeTesting {
       /** Transforms a single tree. */
       override def transform(tree: global.Tree): global.Tree = tree match {
         case dd @ DefDef(_, Foo, _, _, _, _) =>
-          dd.symbol.setFlag(reflect.internal.Flags.JAVA_DEFAULTMETHOD)
+          dd.symbol.setFlag(Flags.JAVA_DEFAULTMETHOD).resetFlag(Flags.DEFERRED)
           copyDefDef(dd)(rhs = Literal(Constant(1)).setType(definitions.IntTpe))
         case _ => super.transform(tree)
       }
@@ -31,6 +32,4 @@ class DefaultMethodTest extends BytecodeTesting {
     assertTrue("default method should not be abstract", (foo.access & Opcodes.ACC_ABSTRACT) == 0)
     assertTrue("default method body emitted", foo.instructions.size() > 0)
   }
-
-
 }
diff --git a/test/junit/scala/tools/nsc/backend/jvm/DirectCompileTest.scala b/test/junit/scala/tools/nsc/backend/jvm/DirectCompileTest.scala
index a28599cd92..38285fbce1 100644
--- a/test/junit/scala/tools/nsc/backend/jvm/DirectCompileTest.scala
+++ b/test/junit/scala/tools/nsc/backend/jvm/DirectCompileTest.scala
@@ -1,7 +1,9 @@
 package scala.tools.nsc.backend.jvm
 
+import java.nio.file.{Files, Paths}
+
 import org.junit.Assert._
-import org.junit.Test
+import org.junit.{Ignore, Test}
 import org.junit.runner.RunWith
 import org.junit.runners.JUnit4
 
diff --git a/test/junit/scala/tools/nsc/backend/jvm/opt/InlinerSeparateCompilationTest.scala b/test/junit/scala/tools/nsc/backend/jvm/opt/InlinerSeparateCompilationTest.scala
index a2513cacdc..85df42e069 100644
--- a/test/junit/scala/tools/nsc/backend/jvm/opt/InlinerSeparateCompilationTest.scala
+++ b/test/junit/scala/tools/nsc/backend/jvm/opt/InlinerSeparateCompilationTest.scala
@@ -97,7 +97,7 @@ class InlinerSeparateCompilationTest {
       """.stripMargin
 
     val List(a, t) = compileClassesSeparately(List(codeA, assembly), args)
-    assertNoInvoke(getMethod(t, "f"))
-    assertNoInvoke(getMethod(a, "n"))
+    assertNoInvoke(getMethod(t, "f$"))
+    assertNoInvoke(getMethod(a, "n$"))
   }
 }
diff --git a/test/junit/scala/tools/nsc/backend/jvm/opt/InlinerTest.scala b/test/junit/scala/tools/nsc/backend/jvm/opt/InlinerTest.scala
index 9173a1d189..f531ce9322 100644
--- a/test/junit/scala/tools/nsc/backend/jvm/opt/InlinerTest.scala
+++ b/test/junit/scala/tools/nsc/backend/jvm/opt/InlinerTest.scala
@@ -475,11 +475,9 @@ class InlinerTest extends BytecodeTesting {
         |  def t2 = this.f
         |}
       """.stripMargin
-    val warns = Set(
-      "C::f()I is annotated @inline but cannot be inlined: the method is not final and may be overridden",
-      "T::f()I is annotated @inline but cannot be inlined: the method is not final and may be overridden")
+    val warn = "T::f()I is annotated @inline but cannot be inlined: the method is not final and may be overridden"
     var count = 0
-    val List(c, t) = compile(code, allowMessage = i => {count += 1; warns.exists(i.msg contains _)})
+    val List(c, t) = compile(code, allowMessage = i => {count += 1; i.msg contains warn})
     assert(count == 2, count)
     assertInvoke(getMethod(c, "t1"), "T", "f")
     assertInvoke(getMethod(c, "t2"), "C", "f")
@@ -520,7 +518,7 @@ class InlinerTest extends BytecodeTesting {
     val List(c, oMirror, oModule, t) = compile(code, allowMessage = i => {count += 1; i.msg contains warn})
     assert(count == 1, count)
 
-    assertNoInvoke(getMethod(t, "f"))
+    assertNoInvoke(getMethod(t, "f$"))
 
     assertNoInvoke(getMethod(c, "t1"))
     assertNoInvoke(getMethod(c, "t2"))
@@ -546,9 +544,9 @@ class InlinerTest extends BytecodeTesting {
 
     val List(assembly, c, t) = compile(code)
 
-    assertNoInvoke(getMethod(t, "f"))
+    assertNoInvoke(getMethod(t, "f$"))
 
-    assertNoInvoke(getMethod(assembly, "n"))
+    assertNoInvoke(getMethod(assembly, "n$"))
 
     assertNoInvoke(getMethod(c, "t1"))
     assertNoInvoke(getMethod(c, "t2"))
@@ -624,8 +622,8 @@ class InlinerTest extends BytecodeTesting {
     val List(ca, cb, t1, t2a, t2b) = compile(code, allowMessage = i => {count += 1; i.msg contains warning})
     assert(count == 4, count) // see comments, f is not inlined 4 times
 
-    assertNoInvoke(getMethod(t2a, "g2a"))
-    assertInvoke(getMethod(t2b, "g2b"), "T1", "f")
+    assertNoInvoke(getMethod(t2a, "g2a$"))
+    assertInvoke(getMethod(t2b, "g2b$"), "T1", "f")
 
     assertInvoke(getMethod(ca, "m1a"), "T1", "f")
     assertNoInvoke(getMethod(ca, "m2a"))            // no invoke, see comment on def g2a
@@ -684,8 +682,8 @@ class InlinerTest extends BytecodeTesting {
         |}
       """.stripMargin
     val List(c, t) = compile(code)
-    val t1 = getMethod(t, "t1")
-    val t2 = getMethod(t, "t2")
+    val t1 = getMethod(t, "t1$")
+    val t2 = getMethod(t, "t2$")
     val cast = TypeOp(CHECKCAST, "C")
     Set(t1, t2).foreach(m => assert(m.instructions.contains(cast), m.instructions))
   }
@@ -1574,4 +1572,19 @@ class InlinerTest extends BytecodeTesting {
       Label(0), LineNumber(9, Label(0)), VarOp(ALOAD, 0), Invoke(INVOKEVIRTUAL, "C", "fx", "()V", false),
       Label(4), LineNumber(10, Label(4)), Op(ICONST_1), Op(IRETURN), Label(8)))
   }
+
+  @Test
+  def traitHO(): Unit = {
+    val code =
+      """trait T {
+        |  def foreach(f: Int => Unit): Unit = f(1)
+        |}
+        |final class C extends T {
+        |  def cons(x: Int): Unit = ()
+        |  def t1 = foreach(cons)
+        |}
+      """.stripMargin
+    val List(c, t) = compile(code)
+    assertNoIndy(getMethod(c, "t1"))
+  }
 }
diff --git a/test/junit/scala/tools/nsc/backend/jvm/opt/ScalaInlineInfoTest.scala b/test/junit/scala/tools/nsc/backend/jvm/opt/ScalaInlineInfoTest.scala
index 4791a29bfb..54f4c805c1 100644
--- a/test/junit/scala/tools/nsc/backend/jvm/opt/ScalaInlineInfoTest.scala
+++ b/test/junit/scala/tools/nsc/backend/jvm/opt/ScalaInlineInfoTest.scala
@@ -31,6 +31,14 @@ class ScalaInlineInfoTest extends BytecodeTesting {
     r.toString
   }
 
+  def assertSameMethods(c: ClassNode, nameAndSigs: Set[String]): Unit = {
+    val r = new StringBuilder
+    val inClass = c.methods.iterator.asScala.map(m => m.name + m.desc).toSet
+    for (m <- inClass.diff(nameAndSigs)) r.append(s"method in classfile found, but no inline info: $m")
+    for (m <- nameAndSigs.diff(inClass)) r.append(s"inline info found, but no method in classfile: $m")
+    assert(r.isEmpty, r.toString)
+  }
+
   @Test
   def traitMembersInlineInfo(): Unit = {
     val code =
@@ -79,26 +87,32 @@ class ScalaInlineInfoTest extends BytecodeTesting {
         ("T$$super$toString()Ljava/lang/String;",                     MethodInlineInfo(true ,false,false)),
         ("T$_setter_$x1_$eq(I)V",                                     MethodInlineInfo(false,false,false)),
         ("f1()I",                                                     MethodInlineInfo(false,false,false)),
-        ("f2()I",                                                     MethodInlineInfo(true, false,false)),
+        ("f1$(LT;)I",                                                  MethodInlineInfo(true ,false,false)),
+        ("f2()I",                                                     MethodInlineInfo(true ,false,false)), // no static impl method for private method f2
         ("f3()I",                                                     MethodInlineInfo(false,false,false)),
+        ("f3$(LT;)I",                                                  MethodInlineInfo(true ,false,false)),
         ("f4()Ljava/lang/String;",                                    MethodInlineInfo(false,true, false)),
+        ("f4$(LT;)Ljava/lang/String;",                                 MethodInlineInfo(true ,true, false)),
         ("f5()I",                                                     MethodInlineInfo(true ,false,false)),
-        ("f6()I",                                                     MethodInlineInfo(false,false,true )),
+        ("f5$(LT;)I",                                                  MethodInlineInfo(true ,false,false)),
+        ("f6()I",                                                     MethodInlineInfo(false,false,true )), // no static impl method for abstract method f6
         ("x1()I",                                                     MethodInlineInfo(false,false,false)),
         ("y2()I",                                                     MethodInlineInfo(false,false,false)),
         ("y2_$eq(I)V",                                                MethodInlineInfo(false,false,false)),
         ("x3()I",                                                     MethodInlineInfo(false,false,false)),
         ("x3_$eq(I)V",                                                MethodInlineInfo(false,false,false)),
         ("x4()I",                                                     MethodInlineInfo(false,false,false)),
+        ("x4$(LT;)I",                                                  MethodInlineInfo(true ,false,false)),
         ("x5()I",                                                     MethodInlineInfo(true, false,false)),
         ("L$lzycompute$1(Lscala/runtime/VolatileObjectRef;)LT$L$2$;", MethodInlineInfo(true, false,false)),
         ("L$1(Lscala/runtime/VolatileObjectRef;)LT$L$2$;",            MethodInlineInfo(true ,false,false)),
         ("nest$1()I",                                                 MethodInlineInfo(true, false,false)),
-        ("$init$()V",                                                 MethodInlineInfo(false,false,false))),
+        ("$init$(LT;)V",                                              MethodInlineInfo(true,false,false))),
       None // warning
     )
 
     assert(infoT == expectT, mapDiff(expectT.methodInfos, infoT.methodInfos) + infoT)
+    assertSameMethods(t, expectT.methodInfos.keySet)
 
     val infoC = inlineInfo(c)
     val expectC = InlineInfo(false, None, Map(
@@ -119,6 +133,7 @@ class ScalaInlineInfoTest extends BytecodeTesting {
       None)
 
     assert(infoC == expectC, mapDiff(expectC.methodInfos, infoC.methodInfos) + infoC)
+    assertSameMethods(c, expectC.methodInfos.keySet)
   }
 
   @Test
@@ -156,7 +171,6 @@ class ScalaInlineInfoTest extends BytecodeTesting {
         ("F",None),
         ("T",Some("h(Ljava/lang/String;)I")),
         ("U",None)))
-
   }
 
   @Test
@@ -169,5 +183,6 @@ class ScalaInlineInfoTest extends BytecodeTesting {
       "O$lzycompute()LC$O$;" -> MethodInlineInfo(true,false,false),
       "O()LC$O$;"            -> MethodInlineInfo(true,false,false))
     assert(infoC.methodInfos == expected, mapDiff(infoC.methodInfos, expected))
+    assertSameMethods(c, expected.keySet)
   }
 }
diff --git a/test/junit/scala/tools/testing/BytecodeTesting.scala b/test/junit/scala/tools/testing/BytecodeTesting.scala
index 4ddb6580df..c0fdb8010f 100644
--- a/test/junit/scala/tools/testing/BytecodeTesting.scala
+++ b/test/junit/scala/tools/testing/BytecodeTesting.scala
@@ -12,6 +12,7 @@ import scala.tools.asm.tree.{AbstractInsnNode, ClassNode, MethodNode}
 import scala.tools.cmd.CommandLineParser
 import scala.tools.nsc.backend.jvm.AsmUtils
 import scala.tools.nsc.backend.jvm.AsmUtils._
+import scala.tools.nsc.backend.jvm.opt.BytecodeUtils
 import scala.tools.nsc.io.AbstractFile
 import scala.tools.nsc.reporters.StoreReporter
 import scala.tools.nsc.{Global, Settings}
@@ -247,11 +248,19 @@ object BytecodeTesting {
 
   def getAsmMethod(c: ClassNode, name: String): MethodNode = {
     val methods = getAsmMethods(c, name)
+    def fail() = {
+      val allNames = getAsmMethods(c, _ => true).map(_.name)
+      throw new AssertionFailedError(s"Could not find method named $name among ${allNames}")
+    }
     methods match {
       case List(m) => m
-      case ms =>
-        val allNames = getAsmMethods(c, _ => true).map(_.name)
-        throw new AssertionFailedError(s"Could not find method named $name among ${allNames}")
+      case ms @ List(m1, m2) if BytecodeUtils.isInterface(c) =>
+        val (statics, nonStatics) = ms.partition(BytecodeUtils.isStaticMethod)
+        (statics, nonStatics) match {
+          case (List(staticMethod), List(_)) => m1 // prefer the static method of the pair if methods in traits
+          case _ => fail()
+        }
+      case ms => fail()
     }
   }