Make FunctionN into functional interfaces #15

retronym · 2015-07-15T04:52:02Z

No description provided.

Previously, implicit search would mark every import it touched as a lookup. Instead, let subsequent type check perform the lookup.

retronym · 2015-07-15T04:53:12Z

Part of https://gist.github.com/retronym/0178c212e4bacffed568#default-methods-for-traits

retronym · 2015-07-15T04:54:50Z

Validating with: https://scala-ci.typesafe.com/job/scala-2.12.x-validate-main/261/console

... 💚

Per review, adds a function that clarifies the purpose of the code path that collects imported implicits, namely, to examine qualifying imported implicits and then collect them. In the context of doing something with the import (besides importing), it's clear why we don't want to record that we used the import, that is, because we might be doing something other than using. That's clear, right?

SI-9383 Improved unused import warning

remove legacy bincompat stuff in two places

A DefDef owned by a trait may now have have a method body. Such a method must be emitted without ACC_ABSTRACT, and with the code attribute. Tested by intercepting the compile pipeline and adding the DEFAULTMETHOD flag and a method body before running the backend.

And do the same for the specialized variants. Tested by a Java source file that uses lambda syntax to create instances of generic and specialized `Function{0,1}`. Here's how the interfaces look now: ``` % javap -c -classpath /tmp/function 'scala.Function1' Compiled from "Function1.scala" public interface scala.Function1<T1, R> { public abstract R apply(T1); public <A> scala.Function1<A, R> compose(scala.Function1<A, T1>); Code: 0: aload_0 1: aload_1 2: invokestatic #18 // Method scala/Function1$class.compose:(Lscala/Function1;Lscala/Function1;)Lscala/Function1; 5: areturn public <A> scala.Function1<T1, A> andThen(scala.Function1<R, A>); Code: 0: aload_0 1: aload_1 2: invokestatic #24 // Method scala/Function1$class.andThen:(Lscala/Function1;Lscala/Function1;)Lscala/Function1; 5: areturn public abstract java.lang.String toString(); public int apply$mcII$sp(int); Code: 0: aload_0 1: iload_1 2: invokestatic #110 // Method scala/Function1$class.apply$mcII$sp:(Lscala/Function1;I)I 5: ireturn public long apply$mcJI$sp(int); Code: 0: aload_0 1: iload_1 2: invokestatic #115 // Method scala/Function1$class.apply$mcJI$sp:(Lscala/Function1;I)J 5: lreturn ... } % javap -c -classpath /tmp/function 'scala.Function1$mcII$sp' Compiled from "Function1.scala" public interface scala.Function1$mcII$sp extends scala.Function1<java.lang.Object, java.lang.Object> { public java.lang.Object apply(java.lang.Object); Code: 0: aload_0 1: aload_1 2: invokestatic #16 // Method scala/runtime/BoxesRunTime.unboxToInt:(Ljava/lang/Object;)I 5: invokeinterface #19, 2 // InterfaceMethod apply:(I)I 10: invokestatic #23 // Method scala/runtime/BoxesRunTime.boxToInteger:(I)Ljava/lang/Integer; 13: areturn public abstract int apply$mcII$sp(int); public int apply(int); Code: 0: aload_0 1: iload_1 2: invokeinterface #30, 2 // InterfaceMethod apply$mcII$sp:(I)I 7: ireturn } ```

Currently, these forward to the impl method in the impl class. Later (perhaps after bootstrapping dependencies like partest) we ought do away with the impl classes.

``` ⚡ cat sandbox/test.scala trait T { def m = v val v = 42 } class C extends T object Test { def main(args: Array[String]): Unit = { assert(new C().m == 42) } } /code/scala on topic/nuke-impl-classes* ⚡ qscalac -Xprint:fields,constructors,erasure,mixin sandbox/test.scala && qscala Test [[syntax trees at end of fields]] // test.scala package <empty> { abstract <sub_synth> trait T extends scala.AnyRef { <accessor> <sub_synth> def T$_setter_$v_=(x$1: Int): Unit; def /*T*/$init$(): Unit = { () }; def m: Int = T.this.v; <stable> <accessor> <sub_synth> def v: Int = 42 }; <sub_synth> class C extends AnyRef with T { override <stable> <accessor> def v: Int = C.this.v; private[this] val v: Int = _; override <accessor> def T$_setter_$v_=(x$1: Int): Unit = C.this.v = x$1; def <init>(): C = { C.super.<init>(); () } }; object Test extends scala.AnyRef { def <init>(): Test.type = { Test.super.<init>(); () }; def main(args: Array[String]): Unit = scala.Predef.assert(new C().m.==(42)) } } [[syntax trees at end of erasure]] // test.scala package <empty> { abstract <sub_synth> trait T extends Object { <accessor> <defaultmethod> <sub_synth> def T$_setter_$v_=(x$1: Int): Unit; def /*T*/$init$(): Unit = { () }; <defaultmethod> def m(): Int = T.this.v(); <stable> <accessor> <defaultmethod> <sub_synth> def v(): Int = 42 }; <sub_synth> class C extends Object with T { override <stable> <accessor> def v(): Int = C.this.v; private[this] val v: Int = _; override <accessor> def T$_setter_$v_=(x$1: Int): Unit = C.this.v = x$1; def <init>(): C = { C.super.<init>(); C.super./*T*/$init$(); () } }; <sub_synth> object Test extends Object { def <init>(): Test.type = { Test.super.<init>(); () }; def main(args: Array[String]): Unit = scala.Predef.assert(new C().m().==(42)) } } [[syntax trees at end of constructors]] // test.scala package <empty> { abstract <sub_synth> trait T extends Object { <accessor> <defaultmethod> <sub_synth> def T$_setter_$v_=(x$1: Int): Unit; <defaultmethod> def m(): Int = T.this.v(); <stable> <accessor> <defaultmethod> <sub_synth> def v(): Int; def /*T*/$init$(): Unit = { T.this.T$_setter_$v_=(42); () } }; <sub_synth> class C extends Object with T { override <stable> <accessor> def v(): Int = C.this.v; private[this] val v: Int = _; override <accessor> def T$_setter_$v_=(x$1: Int): Unit = C.this.v = x$1; def <init>(): C = { C.super.<init>(); C.super./*T*/$init$(); () } }; <sub_synth> object Test extends Object { def main(args: Array[String]): Unit = scala.Predef.assert(new C().m().==(42)); def <init>(): Test.type = { Test.super.<init>(); () } } } [[syntax trees at end of mixin]] // test.scala: tree is unchanged since constructors /code/scala on topic/nuke-impl-classes* ⚡ javap -c -classpath . T C Compiled from "test.scala" public interface T { public abstract void T$_setter_$v_$eq(int); public int m(); Code: 0: aload_0 1: invokeinterface #15, 1 // InterfaceMethod v:()I 6: ireturn public abstract int v(); public void $init$(); Code: 0: aload_0 1: bipush 42 3: invokeinterface #21, 2 // InterfaceMethod T$_setter_$v_$eq:(I)V 8: return } Compiled from "test.scala" public class C implements T { public int v(); Code: 0: aload_0 1: getfield #15 // Field v:I 4: ireturn public void T$_setter_$v_$eq(int); Code: 0: aload_0 1: iload_1 2: putfield #15 // Field v:I 5: return public C(); Code: 0: aload_0 1: invokespecial #24 // Method java/lang/Object."<init>":()V 4: aload_0 5: invokespecial #27 // Method T.$init$:()V 8: return } ```

``` cat sandbox/test1.scala && javap -c -classpath . T C trait T { def m = 42 } class C extends T object Test { def main(args: Array[String]): Unit = { val c = new C() assert(c.m == 42) } } Compiled from "test1.scala" public interface T { public int m(); Code: 0: bipush 42 2: ireturn public void $init$(); Code: 0: return } Compiled from "test1.scala" public class C implements T { public int m(); Code: 0: aload_0 1: invokespecial #14 // Method T.m:()I 4: ireturn public C(); Code: 0: aload_0 1: invokespecial #20 // Method java/lang/Object."<init>":()V 4: aload_0 5: invokespecial #23 // Method T.$init$:()V 8: return } ``` Here's another test that shows private methods working: ``` cat sandbox/test3.scala && qscalac sandbox/test3.scala && javap -private -classpath . -c T C && qscala Test trait T { private def foo = 0 def bar = foo } class C extends T object Test { def main(args: Array[String]): Unit = { new C().bar } } Compiled from "test3.scala" public interface T { private int foo(); Code: 0: iconst_0 1: ireturn public int bar(); Code: 0: aload_0 1: invokespecial #15 // Method foo:()I 4: ireturn public void $init$(); Code: 0: return } Compiled from "test3.scala" public class C implements T { public int bar(); Code: 0: aload_0 1: invokespecial #14 // Method T.bar:()I 4: ireturn public C(); Code: 0: aload_0 1: invokespecial #20 // Method java/lang/Object."<init>":()V 4: aload_0 5: invokespecial #23 // Method T.$init$:()V 8: return } ```

And use this as the target of the default methods or statically resolved super or $init calls. The call-site change is predicated on `-Yuse-trait-statics` as a stepping stone for experimentation / bootstrapping. I have performed this transformation in the backend, rather than trying to reflect this in the view from Scala symbols + ASTs. ``` > ;scalac sandbox/test.scala ; scala Test [info] Running scala.tools.nsc.MainGenericRunner -usejavacp Test T C [success] Total time: 2 s, completed 04/05/2016 11:07:13 AM > eval "javap -classpath . -c -private C".!! [info] ans: String = Compiled from "test.scala" [info] public class C implements T { [info] public C(); [info] Code: [info] 0: aload_0 [info] 1: invokespecial #14 // Method java/lang/Object."<init>":()V [info] 4: aload_0 [info] 5: invokespecial #17 // Method T.$init$:()V [info] 8: getstatic #23 // Field scala/Predef$.MODULE$:Lscala/Predef$; [info] 11: ldc #24 // String C [info] 13: invokevirtual #28 // Method scala/Predef$.println:(Ljava/lang/Object;)V [info] 16: aload_0 [info] 17: invokespecial #32 // Method T.foo:()I [info] 20: pop [info] 21: return [info] } > ;scalac -Yuse-trait-statics sandbox/test.scala ; scala Test [info] Running scala.tools.nsc.MainGenericRunner -usejavacp Test T C [success] Total time: 2 s, completed 04/05/2016 11:07:39 AM > eval "javap -classpath . -c -private C".!! [info] ans: String = Compiled from "test.scala" [info] public class C implements T { [info] public C(); [info] Code: [info] 0: aload_0 [info] 1: invokespecial #14 // Method java/lang/Object."<init>":()V [info] 4: aload_0 [info] 5: invokestatic #18 // Method T.$init$:(LT;)V [info] 8: getstatic #24 // Field scala/Predef$.MODULE$:Lscala/Predef$; [info] 11: ldc #25 // String C [info] 13: invokevirtual #29 // Method scala/Predef$.println:(Ljava/lang/Object;)V [info] 16: aload_0 [info] 17: invokestatic #33 // Method T.foo:(LT;)I [info] 20: pop [info] 21: return [info] } > eval "javap -classpath . -c -private T".!! [info] ans: String = Compiled from "test.scala" [info] public interface T { [info] public static int foo(T); [info] Code: [info] 0: iconst_0 [info] 1: ireturn [info] [info] public int foo(); [info] Code: [info] 0: aload_0 [info] 1: invokestatic #15 // Method foo:(LT;)I [info] 4: ireturn [info] [info] public static void $init$(T); [info] Code: [info] 0: getstatic #24 // Field scala/Predef$.MODULE$:Lscala/Predef$; [info] 3: ldc #25 // String T [info] 5: invokevirtual #29 // Method scala/Predef$.println:(Ljava/lang/Object;)V [info] 8: return [info] [info] public void $init$(); [info] Code: [info] 0: aload_0 [info] 1: invokestatic #32 // Method $init$:(LT;)V [info] 4: return [info] } ```

And use this as the target of the default methods or statically resolved super or $init calls. The call-site change is predicated on `-Yuse-trait-statics` as a stepping stone for experimentation / bootstrapping. I have performed this transformation in the backend, rather than trying to reflect this in the view from Scala symbols + ASTs. Once we commit to this change, we can remove the `lateInterfaces` bookkeeping from the backend, as we no long will need to add ancestor interfaces as direct parents to allow use of invokespecial for super calls. ``` > ;scalac sandbox/test.scala ; scala Test [info] Running scala.tools.nsc.MainGenericRunner -usejavacp Test T C [success] Total time: 2 s, completed 04/05/2016 11:07:13 AM > eval "javap -classpath . -c -private C".!! [info] ans: String = Compiled from "test.scala" [info] public class C implements T { [info] public C(); [info] Code: [info] 0: aload_0 [info] 1: invokespecial #14 // Method java/lang/Object."<init>":()V [info] 4: aload_0 [info] 5: invokespecial #17 // Method T.$init$:()V [info] 8: getstatic #23 // Field scala/Predef$.MODULE$:Lscala/Predef$; [info] 11: ldc #24 // String C [info] 13: invokevirtual #28 // Method scala/Predef$.println:(Ljava/lang/Object;)V [info] 16: aload_0 [info] 17: invokespecial #32 // Method T.foo:()I [info] 20: pop [info] 21: return [info] } > ;scalac -Yuse-trait-statics sandbox/test.scala ; scala Test [info] Running scala.tools.nsc.MainGenericRunner -usejavacp Test T C [success] Total time: 2 s, completed 04/05/2016 11:07:39 AM > eval "javap -classpath . -c -private C".!! [info] ans: String = Compiled from "test.scala" [info] public class C implements T { [info] public C(); [info] Code: [info] 0: aload_0 [info] 1: invokespecial #14 // Method java/lang/Object."<init>":()V [info] 4: aload_0 [info] 5: invokestatic #18 // Method T.$init$:(LT;)V [info] 8: getstatic #24 // Field scala/Predef$.MODULE$:Lscala/Predef$; [info] 11: ldc #25 // String C [info] 13: invokevirtual #29 // Method scala/Predef$.println:(Ljava/lang/Object;)V [info] 16: aload_0 [info] 17: invokestatic #33 // Method T.foo:(LT;)I [info] 20: pop [info] 21: return [info] } > eval "javap -classpath . -c -private T".!! [info] ans: String = Compiled from "test.scala" [info] public interface T { [info] public static int foo(T); [info] Code: [info] 0: iconst_0 [info] 1: ireturn [info] [info] public int foo(); [info] Code: [info] 0: aload_0 [info] 1: invokestatic #15 // Method foo:(LT;)I [info] 4: ireturn [info] [info] public static void $init$(T); [info] Code: [info] 0: getstatic #24 // Field scala/Predef$.MODULE$:Lscala/Predef$; [info] 3: ldc #25 // String T [info] 5: invokevirtual #29 // Method scala/Predef$.println:(Ljava/lang/Object;)V [info] 8: return [info] [info] public void $init$(); [info] Code: [info] 0: aload_0 [info] 1: invokestatic #32 // Method $init$:(LT;)V [info] 4: return [info] } ```

This corrects an error in the change to the trait encoding in scala#5003: getters in traits should have empty bodies and be emitted as abstract. ``` % ~/scala/2.12.0-M4/bin/scalac sandbox/test.scala && javap -c T Compiled from "test.scala" public interface T { public abstract void T$_setter_$x_$eq(int); public int x(); Code: 0: aload_0 1: invokeinterface #15, 1 // InterfaceMethod x:()I 6: ireturn public int y(); Code: 0: aload_0 1: invokeinterface #20, 1 // InterfaceMethod y:()I 6: ireturn public void y_$eq(int); Code: 0: aload_0 1: iload_1 2: invokeinterface #24, 2 // InterfaceMethod y_$eq:(I)V 7: return public void $init$(); Code: 0: aload_0 1: bipush 42 3: invokeinterface #29, 2 // InterfaceMethod T$_setter_$x_$eq:(I)V 8: aload_0 9: bipush 24 11: invokeinterface #24, 2 // InterfaceMethod y_$eq:(I)V 16: return } % qscalac sandbox/test.scala && javap -c T Compiled from "test.scala" public interface T { public abstract void T$_setter_$x_$eq(int); public abstract int x(); public abstract int y(); public abstract void y_$eq(int); public static void $init$(T); Code: 0: aload_0 1: bipush 42 3: invokeinterface #21, 2 // InterfaceMethod T$_setter_$x_$eq:(I)V 8: aload_0 9: bipush 24 11: invokeinterface #23, 2 // InterfaceMethod y_$eq:(I)V 16: return public void $init$(); Code: 0: aload_0 1: invokestatic #27 // Method $init$:(LT;)V 4: return } ```

And use this as the target of the default methods or statically resolved super or $init calls. The call-site change is predicated on `-Yuse-trait-statics` as a stepping stone for experimentation / bootstrapping. I have performed this transformation in the backend, rather than trying to reflect this in the view from Scala symbols + ASTs. Once we commit to this change, we can remove the `lateInterfaces` bookkeeping from the backend, as we no long will need to add ancestor interfaces as direct parents to allow use of invokespecial for super calls. ``` > ;scalac sandbox/test.scala ; scala Test [info] Running scala.tools.nsc.MainGenericRunner -usejavacp Test T C [success] Total time: 2 s, completed 04/05/2016 11:07:13 AM > eval "javap -classpath . -c -private C".!! [info] ans: String = Compiled from "test.scala" [info] public class C implements T { [info] public C(); [info] Code: [info] 0: aload_0 [info] 1: invokespecial #14 // Method java/lang/Object."<init>":()V [info] 4: aload_0 [info] 5: invokespecial #17 // Method T.$init$:()V [info] 8: getstatic #23 // Field scala/Predef$.MODULE$:Lscala/Predef$; [info] 11: ldc #24 // String C [info] 13: invokevirtual #28 // Method scala/Predef$.println:(Ljava/lang/Object;)V [info] 16: aload_0 [info] 17: invokespecial #32 // Method T.foo:()I [info] 20: pop [info] 21: return [info] } > ;scalac -Yuse-trait-statics sandbox/test.scala ; scala Test [info] Running scala.tools.nsc.MainGenericRunner -usejavacp Test T C [success] Total time: 2 s, completed 04/05/2016 11:07:39 AM > eval "javap -classpath . -c -private C".!! [info] ans: String = Compiled from "test.scala" [info] public class C implements T { [info] public C(); [info] Code: [info] 0: aload_0 [info] 1: invokespecial #14 // Method java/lang/Object."<init>":()V [info] 4: aload_0 [info] 5: invokestatic #18 // Method T.$init$:(LT;)V [info] 8: getstatic #24 // Field scala/Predef$.MODULE$:Lscala/Predef$; [info] 11: ldc #25 // String C [info] 13: invokevirtual #29 // Method scala/Predef$.println:(Ljava/lang/Object;)V [info] 16: aload_0 [info] 17: invokestatic #33 // Method T.foo:(LT;)I [info] 20: pop [info] 21: return [info] } > eval "javap -classpath . -c -private T".!! [info] ans: String = Compiled from "test.scala" [info] public interface T { [info] public static int foo(T); [info] Code: [info] 0: iconst_0 [info] 1: ireturn [info] [info] public int foo(); [info] Code: [info] 0: aload_0 [info] 1: invokestatic #15 // Method foo:(LT;)I [info] 4: ireturn [info] [info] public static void $init$(T); [info] Code: [info] 0: getstatic #24 // Field scala/Predef$.MODULE$:Lscala/Predef$; [info] 3: ldc #25 // String T [info] 5: invokevirtual #29 // Method scala/Predef$.println:(Ljava/lang/Object;)V [info] 8: return [info] [info] public void $init$(); [info] Code: [info] 0: aload_0 [info] 1: invokestatic #32 // Method $init$:(LT;)V [info] 4: return [info] } ```

This corrects an error in the change to the trait encoding in scala#5003: getters in traits should have empty bodies and be emitted as abstract. ``` % ~/scala/2.12.0-M4/bin/scalac sandbox/test.scala && javap -c T Compiled from "test.scala" public interface T { public abstract void T$_setter_$x_$eq(int); public int x(); Code: 0: aload_0 1: invokeinterface #15, 1 // InterfaceMethod x:()I 6: ireturn public int y(); Code: 0: aload_0 1: invokeinterface #20, 1 // InterfaceMethod y:()I 6: ireturn public void y_$eq(int); Code: 0: aload_0 1: iload_1 2: invokeinterface #24, 2 // InterfaceMethod y_$eq:(I)V 7: return public void $init$(); Code: 0: aload_0 1: bipush 42 3: invokeinterface #29, 2 // InterfaceMethod T$_setter_$x_$eq:(I)V 8: aload_0 9: bipush 24 11: invokeinterface #24, 2 // InterfaceMethod y_$eq:(I)V 16: return } % qscalac sandbox/test.scala && javap -c T Compiled from "test.scala" public interface T { public abstract void T$_setter_$x_$eq(int); public abstract int x(); public abstract int y(); public abstract void y_$eq(int); public static void $init$(T); Code: 0: aload_0 1: bipush 42 3: invokeinterface #21, 2 // InterfaceMethod T$_setter_$x_$eq:(I)V 8: aload_0 9: bipush 24 11: invokeinterface #23, 2 // InterfaceMethod y_$eq:(I)V 16: return public void $init$(); Code: 0: aload_0 1: invokestatic #27 // Method $init$:(LT;)V 4: return } ```

And use this as the target of the default methods or statically resolved super or $init calls. The call-site change is predicated on `-Yuse-trait-statics` as a stepping stone for experimentation / bootstrapping. I have performed this transformation in the backend, rather than trying to reflect this in the view from Scala symbols + ASTs. Once we commit to this change, we can remove the `lateInterfaces` bookkeeping from the backend, as we no long will need to add ancestor interfaces as direct parents to allow use of invokespecial for super calls. ``` > ;scalac sandbox/test.scala ; scala Test [info] Running scala.tools.nsc.MainGenericRunner -usejavacp Test T C [success] Total time: 2 s, completed 04/05/2016 11:07:13 AM > eval "javap -classpath . -c -private C".!! [info] ans: String = Compiled from "test.scala" [info] public class C implements T { [info] public C(); [info] Code: [info] 0: aload_0 [info] 1: invokespecial #14 // Method java/lang/Object."<init>":()V [info] 4: aload_0 [info] 5: invokespecial #17 // Method T.$init$:()V [info] 8: getstatic #23 // Field scala/Predef$.MODULE$:Lscala/Predef$; [info] 11: ldc #24 // String C [info] 13: invokevirtual #28 // Method scala/Predef$.println:(Ljava/lang/Object;)V [info] 16: aload_0 [info] 17: invokespecial #32 // Method T.foo:()I [info] 20: pop [info] 21: return [info] } > ;scalac -Yuse-trait-statics sandbox/test.scala ; scala Test [info] Running scala.tools.nsc.MainGenericRunner -usejavacp Test T C [success] Total time: 2 s, completed 04/05/2016 11:07:39 AM > eval "javap -classpath . -c -private C".!! [info] ans: String = Compiled from "test.scala" [info] public class C implements T { [info] public C(); [info] Code: [info] 0: aload_0 [info] 1: invokespecial #14 // Method java/lang/Object."<init>":()V [info] 4: aload_0 [info] 5: invokestatic #18 // Method T.$init$:(LT;)V [info] 8: getstatic #24 // Field scala/Predef$.MODULE$:Lscala/Predef$; [info] 11: ldc #25 // String C [info] 13: invokevirtual #29 // Method scala/Predef$.println:(Ljava/lang/Object;)V [info] 16: aload_0 [info] 17: invokestatic #33 // Method T.foo:(LT;)I [info] 20: pop [info] 21: return [info] } > eval "javap -classpath . -c -private T".!! [info] ans: String = Compiled from "test.scala" [info] public interface T { [info] public static int foo(T); [info] Code: [info] 0: iconst_0 [info] 1: ireturn [info] [info] public int foo(); [info] Code: [info] 0: aload_0 [info] 1: invokestatic #15 // Method foo:(LT;)I [info] 4: ireturn [info] [info] public static void $init$(T); [info] Code: [info] 0: getstatic #24 // Field scala/Predef$.MODULE$:Lscala/Predef$; [info] 3: ldc #25 // String T [info] 5: invokevirtual #29 // Method scala/Predef$.println:(Ljava/lang/Object;)V [info] 8: return [info] [info] public void $init$(); [info] Code: [info] 0: aload_0 [info] 1: invokestatic #32 // Method $init$:(LT;)V [info] 4: return [info] } ```

This corrects an error in the change to the trait encoding in scala#5003: getters in traits should have empty bodies and be emitted as abstract. ``` % ~/scala/2.12.0-M4/bin/scalac sandbox/test.scala && javap -c T Compiled from "test.scala" public interface T { public abstract void T$_setter_$x_$eq(int); public int x(); Code: 0: aload_0 1: invokeinterface #15, 1 // InterfaceMethod x:()I 6: ireturn public int y(); Code: 0: aload_0 1: invokeinterface #20, 1 // InterfaceMethod y:()I 6: ireturn public void y_$eq(int); Code: 0: aload_0 1: iload_1 2: invokeinterface #24, 2 // InterfaceMethod y_$eq:(I)V 7: return public void $init$(); Code: 0: aload_0 1: bipush 42 3: invokeinterface #29, 2 // InterfaceMethod T$_setter_$x_$eq:(I)V 8: aload_0 9: bipush 24 11: invokeinterface #24, 2 // InterfaceMethod y_$eq:(I)V 16: return } % qscalac sandbox/test.scala && javap -c T Compiled from "test.scala" public interface T { public abstract void T$_setter_$x_$eq(int); public abstract int x(); public abstract int y(); public abstract void y_$eq(int); public static void $init$(T); Code: 0: aload_0 1: bipush 42 3: invokeinterface #21, 2 // InterfaceMethod T$_setter_$x_$eq:(I)V 8: aload_0 9: bipush 24 11: invokeinterface #23, 2 // InterfaceMethod y_$eq:(I)V 16: return public void $init$(); Code: 0: aload_0 1: invokestatic #27 // Method $init$:(LT;)V 4: return } ```

And use this as the target of the default methods or statically resolved super or $init calls. The call-site change is predicated on `-Yuse-trait-statics` as a stepping stone for experimentation / bootstrapping. I have performed this transformation in the backend, rather than trying to reflect this in the view from Scala symbols + ASTs. Once we commit to this change, we can remove the `lateInterfaces` bookkeeping from the backend, as we no long will need to add ancestor interfaces as direct parents to allow use of invokespecial for super calls. ``` > ;scalac sandbox/test.scala ; scala Test [info] Running scala.tools.nsc.MainGenericRunner -usejavacp Test T C [success] Total time: 2 s, completed 04/05/2016 11:07:13 AM > eval "javap -classpath . -c -private C".!! [info] ans: String = Compiled from "test.scala" [info] public class C implements T { [info] public C(); [info] Code: [info] 0: aload_0 [info] 1: invokespecial #14 // Method java/lang/Object."<init>":()V [info] 4: aload_0 [info] 5: invokespecial #17 // Method T.$init$:()V [info] 8: getstatic #23 // Field scala/Predef$.MODULE$:Lscala/Predef$; [info] 11: ldc #24 // String C [info] 13: invokevirtual #28 // Method scala/Predef$.println:(Ljava/lang/Object;)V [info] 16: aload_0 [info] 17: invokespecial #32 // Method T.foo:()I [info] 20: pop [info] 21: return [info] } > ;scalac -Yuse-trait-statics sandbox/test.scala ; scala Test [info] Running scala.tools.nsc.MainGenericRunner -usejavacp Test T C [success] Total time: 2 s, completed 04/05/2016 11:07:39 AM > eval "javap -classpath . -c -private C".!! [info] ans: String = Compiled from "test.scala" [info] public class C implements T { [info] public C(); [info] Code: [info] 0: aload_0 [info] 1: invokespecial #14 // Method java/lang/Object."<init>":()V [info] 4: aload_0 [info] 5: invokestatic #18 // Method T.$init$:(LT;)V [info] 8: getstatic #24 // Field scala/Predef$.MODULE$:Lscala/Predef$; [info] 11: ldc #25 // String C [info] 13: invokevirtual #29 // Method scala/Predef$.println:(Ljava/lang/Object;)V [info] 16: aload_0 [info] 17: invokestatic #33 // Method T.foo:(LT;)I [info] 20: pop [info] 21: return [info] } > eval "javap -classpath . -c -private T".!! [info] ans: String = Compiled from "test.scala" [info] public interface T { [info] public static int foo(T); [info] Code: [info] 0: iconst_0 [info] 1: ireturn [info] [info] public int foo(); [info] Code: [info] 0: aload_0 [info] 1: invokestatic #15 // Method foo:(LT;)I [info] 4: ireturn [info] [info] public static void $init$(T); [info] Code: [info] 0: getstatic #24 // Field scala/Predef$.MODULE$:Lscala/Predef$; [info] 3: ldc #25 // String T [info] 5: invokevirtual #29 // Method scala/Predef$.println:(Ljava/lang/Object;)V [info] 8: return [info] [info] public void $init$(); [info] Code: [info] 0: aload_0 [info] 1: invokestatic #32 // Method $init$:(LT;)V [info] 4: return [info] } ```

This corrects an error in the change to the trait encoding in scala#5003: getters in traits should have empty bodies and be emitted as abstract. ``` % ~/scala/2.12.0-M4/bin/scalac sandbox/test.scala && javap -c T Compiled from "test.scala" public interface T { public abstract void T$_setter_$x_$eq(int); public int x(); Code: 0: aload_0 1: invokeinterface #15, 1 // InterfaceMethod x:()I 6: ireturn public int y(); Code: 0: aload_0 1: invokeinterface #20, 1 // InterfaceMethod y:()I 6: ireturn public void y_$eq(int); Code: 0: aload_0 1: iload_1 2: invokeinterface #24, 2 // InterfaceMethod y_$eq:(I)V 7: return public void $init$(); Code: 0: aload_0 1: bipush 42 3: invokeinterface #29, 2 // InterfaceMethod T$_setter_$x_$eq:(I)V 8: aload_0 9: bipush 24 11: invokeinterface #24, 2 // InterfaceMethod y_$eq:(I)V 16: return } % qscalac sandbox/test.scala && javap -c T Compiled from "test.scala" public interface T { public abstract void T$_setter_$x_$eq(int); public abstract int x(); public abstract int y(); public abstract void y_$eq(int); public static void $init$(T); Code: 0: aload_0 1: bipush 42 3: invokeinterface #21, 2 // InterfaceMethod T$_setter_$x_$eq:(I)V 8: aload_0 9: bipush 24 11: invokeinterface #23, 2 // InterfaceMethod y_$eq:(I)V 16: return public void $init$(); Code: 0: aload_0 1: invokestatic #27 // Method $init$:(LT;)V 4: return } ```

And use this as the target of the default methods or statically resolved super or $init calls. The call-site change is predicated on `-Yuse-trait-statics` as a stepping stone for experimentation / bootstrapping. I have performed this transformation in the backend, rather than trying to reflect this in the view from Scala symbols + ASTs. Once we commit to this change, we can remove the `lateInterfaces` bookkeeping from the backend, as we no long will need to add ancestor interfaces as direct parents to allow use of invokespecial for super calls. ``` > ;scalac sandbox/test.scala ; scala Test [info] Running scala.tools.nsc.MainGenericRunner -usejavacp Test T C [success] Total time: 2 s, completed 04/05/2016 11:07:13 AM > eval "javap -classpath . -c -private C".!! [info] ans: String = Compiled from "test.scala" [info] public class C implements T { [info] public C(); [info] Code: [info] 0: aload_0 [info] 1: invokespecial #14 // Method java/lang/Object."<init>":()V [info] 4: aload_0 [info] 5: invokespecial #17 // Method T.$init$:()V [info] 8: getstatic #23 // Field scala/Predef$.MODULE$:Lscala/Predef$; [info] 11: ldc #24 // String C [info] 13: invokevirtual #28 // Method scala/Predef$.println:(Ljava/lang/Object;)V [info] 16: aload_0 [info] 17: invokespecial #32 // Method T.foo:()I [info] 20: pop [info] 21: return [info] } > ;scalac -Yuse-trait-statics sandbox/test.scala ; scala Test [info] Running scala.tools.nsc.MainGenericRunner -usejavacp Test T C [success] Total time: 2 s, completed 04/05/2016 11:07:39 AM > eval "javap -classpath . -c -private C".!! [info] ans: String = Compiled from "test.scala" [info] public class C implements T { [info] public C(); [info] Code: [info] 0: aload_0 [info] 1: invokespecial #14 // Method java/lang/Object."<init>":()V [info] 4: aload_0 [info] 5: invokestatic #18 // Method T.$init$:(LT;)V [info] 8: getstatic #24 // Field scala/Predef$.MODULE$:Lscala/Predef$; [info] 11: ldc #25 // String C [info] 13: invokevirtual #29 // Method scala/Predef$.println:(Ljava/lang/Object;)V [info] 16: aload_0 [info] 17: invokestatic #33 // Method T.foo:(LT;)I [info] 20: pop [info] 21: return [info] } > eval "javap -classpath . -c -private T".!! [info] ans: String = Compiled from "test.scala" [info] public interface T { [info] public static int foo(T); [info] Code: [info] 0: iconst_0 [info] 1: ireturn [info] [info] public int foo(); [info] Code: [info] 0: aload_0 [info] 1: invokestatic #15 // Method foo:(LT;)I [info] 4: ireturn [info] [info] public static void $init$(T); [info] Code: [info] 0: getstatic #24 // Field scala/Predef$.MODULE$:Lscala/Predef$; [info] 3: ldc #25 // String T [info] 5: invokevirtual #29 // Method scala/Predef$.println:(Ljava/lang/Object;)V [info] 8: return [info] [info] public void $init$(); [info] Code: [info] 0: aload_0 [info] 1: invokestatic #32 // Method $init$:(LT;)V [info] 4: return [info] } ```

And use this as the target of the default methods or statically resolved super or $init calls. The call-site change is predicated on `-Yuse-trait-statics` as a stepping stone for experimentation / bootstrapping. I have performed this transformation in the backend, rather than trying to reflect this in the view from Scala symbols + ASTs. ``` > ;scalac sandbox/test.scala ; scala Test [info] Running scala.tools.nsc.MainGenericRunner -usejavacp Test T C [success] Total time: 2 s, completed 04/05/2016 11:07:13 AM > eval "javap -classpath . -c -private C".!! [info] ans: String = Compiled from "test.scala" [info] public class C implements T { [info] public C(); [info] Code: [info] 0: aload_0 [info] 1: invokespecial #14 // Method java/lang/Object."<init>":()V [info] 4: aload_0 [info] 5: invokespecial #17 // Method T.$init$:()V [info] 8: getstatic #23 // Field scala/Predef$.MODULE$:Lscala/Predef$; [info] 11: ldc #24 // String C [info] 13: invokevirtual #28 // Method scala/Predef$.println:(Ljava/lang/Object;)V [info] 16: aload_0 [info] 17: invokespecial #32 // Method T.foo:()I [info] 20: pop [info] 21: return [info] } > ;scalac -Yuse-trait-statics sandbox/test.scala ; scala Test [info] Running scala.tools.nsc.MainGenericRunner -usejavacp Test T C [success] Total time: 2 s, completed 04/05/2016 11:07:39 AM > eval "javap -classpath . -c -private C".!! [info] ans: String = Compiled from "test.scala" [info] public class C implements T { [info] public C(); [info] Code: [info] 0: aload_0 [info] 1: invokespecial #14 // Method java/lang/Object."<init>":()V [info] 4: aload_0 [info] 5: invokestatic #18 // Method T.$init$:(LT;)V [info] 8: getstatic #24 // Field scala/Predef$.MODULE$:Lscala/Predef$; [info] 11: ldc #25 // String C [info] 13: invokevirtual #29 // Method scala/Predef$.println:(Ljava/lang/Object;)V [info] 16: aload_0 [info] 17: invokestatic #33 // Method T.foo:(LT;)I [info] 20: pop [info] 21: return [info] } > eval "javap -classpath . -c -private T".!! [info] ans: String = Compiled from "test.scala" [info] public interface T { [info] public static int foo(T); [info] Code: [info] 0: iconst_0 [info] 1: ireturn [info] [info] public int foo(); [info] Code: [info] 0: aload_0 [info] 1: invokestatic #15 // Method foo:(LT;)I [info] 4: ireturn [info] [info] public static void $init$(T); [info] Code: [info] 0: getstatic #24 // Field scala/Predef$.MODULE$:Lscala/Predef$; [info] 3: ldc #25 // String T [info] 5: invokevirtual #29 // Method scala/Predef$.println:(Ljava/lang/Object;)V [info] 8: return [info] [info] } ```