Unit-test LUBs. #15
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Unit-test LUBs. #15
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This requires -Xexperimental in 2.11.x. Update spec. TODO: - test! - include SIP as spec addendum - don't predicate on -Xexperimental -- introduce -Xsip:23? Notes: - `()` is not a literal, neither are `Symbol`s
`LiteralType` is a `SingleType` with a literal for its path. With an example: `1` is to `p.type`, as `1` is to `p`. `lit` is the most precise type for an expression known to evaluate to `lit`. Note that we cannot constant fold the expression to `lit`, since it may have a side effect. `ConstantType(c)` is the type of an expression that can be constant folded to `c`. When an expressions should not be constant folded, the corresponding `LiteralType` is created: `ConstantType(c).deconst == LiteralType(c)` (this is where all `LiteralType`s originate, except for unpickling). `typedLiteral` always infers a `ConstantType`, which is subsequently `deconst`ed or `widen`ed where necessary (see `widenIfNecessary`). In short, only `final val`s may have `ConstantType`s, and `widen`ing is required to ensure that a path is stable and accessible (roughly speaking). When checking subtyping, this invariant is useful: `LiteralType(c).widen == c.tpe`. TODO: - test! (subtyping, type inference, type tests, patmat, dependent method types) - fully predicate implementation on -Xsip:23 - is it safe to reduce LITERAL in pickler?
test case:
```
val y: 5 = 5
def g(x: Int) = x match {
case _: y.type => 0
}
```
Before: sandbox/test.scala:2: error: type mismatch; found : Array[1] required: Array[Int]
e.g., val x : -1 => -1 = ???
TODO: deriving this from type param bounds is not the best way,
should consider all constraints that we encounter
scala> def stable[T <: 1](x: T): T = x
stable: [T <: 1](x: T)T
scala> stable(1)
res0: 1 = 1
scala> stable(2)
<console>:9: error: inferred type arguments [2] do not conform to method stable's type parameter bounds [T <: 1]
stable(2)
^
<console>:9: error: type mismatch;
found : Int(2)
required: T
stable(2)
^
scala> def stable[T <: Singleton](x: T): T = x
stable: [T <: Singleton](x: T)T
scala> val x: Int = 2
x: Int = 2
scala> val y: x.type = x
y: x.type = 2
scala> stable(y)
res3: x.type = 2
this bootstraps
``` scala> val x = "a" x: "a" = a scala> x.asInstanceOf["a"] res1: "a" = a scala> "1".asInstanceOf["2"] x asInstanceOf Throwable java.lang.ClassCastException ... 33 elided scala> "1".asInstanceOf["1"] res3: "1" = 1 scala> 1.asInstanceOf[1] res4: 1 = 1 scala> 1.asInstanceOf[2] x asInstanceOf Throwable java.lang.ClassCastException ... 33 elided ```
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Thanks, @folone! I'll have a look tomorrow. Just moved back to SF ;-) |
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Oh, get un jet lagged first then! |
|
Thanks! Good start! I added some comments over at 8ae5c19. |
adriaanm
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adriaanm
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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 scala#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 scala#27 // Method $init$:(LT;)V 4: return } ```
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@folone any chance you could rebase against https://github.com/milessabin/scala/commits/topic/sip-23-redux and send those tests my way as a PR? |
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@milessabin will do tonight! |
adriaanm
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Jun 28, 2016
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 scala#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 scala#27 // Method $init$:(LT;)V 4: return } ```
adriaanm
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Aug 22, 2016
Top level modules in Scala currently desugar as:
```
class C; object O extends C { toString }
```
```
public final class O$ extends C {
public static final O$ MODULE$;
public static {};
Code:
0: new #2 // class O$
3: invokespecial #12 // Method "<init>":()V
6: return
private O$();
Code:
0: aload_0
1: invokespecial #13 // Method C."<init>":()V
4: aload_0
5: putstatic #15 // Field MODULE$:LO$;
8: aload_0
9: invokevirtual #21 // Method java/lang/Object.toString:()Ljava/lang/String;
12: pop
13: return
}
```
The static initalizer `<clinit>` calls the constructor `<init>`, which
invokes superclass constructor, assigns `MODULE$= this`, and then runs
the remainder of the object's constructor (`toString` in the example
above.)
It turns out that this relies on a bug in the JVM's verifier: assignment to a
static final must occur lexically within the <clinit>, not from within `<init>`
(even if the latter is happens to be called by the former).
I'd like to move the assignment to <clinit> but that would
change behaviour of "benign" cyclic references between modules.
Example:
```
package p1; class CC { def foo = O.bar}; object O {new CC().foo; def bar = println(1)};
// Exiting paste mode, now interpreting.
scala> p1.O
1
```
This relies on the way that we assign MODULE$ field after the super class constructors
are finished, but before the rest of the module constructor is called.
Instead, this commit removes the ACC_FINAL bit from the field. It actually wasn't
behaving as final at all, precisely the issue that the stricter verifier
now alerts us to.
```
scala> :paste -raw
// Entering paste mode (ctrl-D to finish)
package p1; object O
// Exiting paste mode, now interpreting.
scala> val O1 = p1.O
O1: p1.O.type = p1.O$@ee7d9f1
scala> scala.reflect.ensureAccessible(p1.O.getClass.getDeclaredConstructor()).newInstance()
res0: p1.O.type = p1.O$@64cee07
scala> O1 eq p1.O
res1: Boolean = false
```
We will still achieve safe publication of the assignment to other threads
by virtue of the fact that `<clinit>` is executed within the scope of
an initlization lock, as specified by:
https://docs.oracle.com/javase/specs/jvms/se8/html/jvms-5.html#jvms-5.5
Fixes scala/scala-dev#SD-194
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Here are some unit tests. @adriaanm is this something you had in mind for this?