SIP-23 Account for literal types in varargs translation #13
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Before: sandbox/test.scala:2: error: type mismatch; found : Array[1] required: Array[Int]
adriaanm
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Oct 28, 2014
SIP-23 Account for literal types in varargs translation
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
adriaanm
pushed a commit
that referenced
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Jun 10, 2017
Non local returns aren't eliminated after inlined in 2.11 or 2.12
```
⚡ scala
Welcome to Scala 2.12.1 (Java HotSpot(TM) 64-Bit Server VM, Java 1.8.0_112).
Type in expressions for evaluation. Or try :help.
scala> @inlune def foo(a: => Any) = if ("".isEmpty) a else ""
<console>:11: error: not found: type inlune
@inlune def foo(a: => Any) = if ("".isEmpty) a else ""
^
scala> @inline def foo(a: => Any) = if ("".isEmpty) a else ""
foo: (a: => Any)Any
scala> class InlineReturn { def test: Any = foo(return "") }
defined class InlineReturn
scala> :javap -c InlineReturn#test
public java.lang.Object test();
Code:
0: new #4 // class java/lang/Object
3: dup
4: invokespecial scala#32 // Method java/lang/Object."<init>":()V
7: astore_1
8: getstatic scala#36 // Field $line4/$read$$iw$$iw$.MODULE$:L$line4/$read$$iw$$iw$;
11: aload_1
12: invokedynamic scala#59, 0 // InvokeDynamic #0:apply:(Ljava/lang/Object;)Lscala/Function0;
17: invokevirtual scala#63 // Method $line4/$read$$iw$$iw$.foo:(Lscala/Function0;)Ljava/lang/Object;
20: goto 44
23: astore_2
24: aload_2
25: invokevirtual scala#66 // Method scala/runtime/NonLocalReturnControl.key:()Ljava/lang/Object;
28: aload_1
29: if_acmpne 39
32: aload_2
33: invokevirtual scala#69 // Method scala/runtime/NonLocalReturnControl.value:()Ljava/lang/Object;
36: goto 41
39: aload_2
40: athrow
41: goto 44
44: areturn
Exception table:
from to target type
8 20 23 Class scala/runtime/NonLocalReturnControl
```
```
⚡ ~/scala/2.11.8/bin/scala
Welcome to Scala 2.11.8 (Java HotSpot(TM) 64-Bit Server VM, Java 1.8.0_112).
Type in expressions for evaluation. Or try :help.
scala> @inline def foo(a: => Any) = if ("".isEmpty) a else ""
foo: (a: => Any)Any
scala> class InlineReturn { def test: Any = foo(return "") }
defined class InlineReturn
scala> :javap -c InlineReturn#test
public java.lang.Object test();
Code:
0: new #4 // class java/lang/Object
3: dup
4: invokespecial #13 // Method java/lang/Object."<init>":()V
7: astore_1
8: getstatic #19 // Field .MODULE$:L;
11: new #21 // class InlineReturn$$anonfun$test$1
14: dup
15: aload_0
16: aload_1
17: invokespecial #24 // Method InlineReturn$$anonfun$test$1."<init>":(LInlineReturn;Ljava/lang/Object;)V
20: invokevirtual scala#28 // Method .foo:(Lscala/Function0;)Ljava/lang/Object;
23: goto 39
26: astore_2
27: aload_2
28: invokevirtual scala#31 // Method scala/runtime/NonLocalReturnControl.key:()Ljava/lang/Object;
31: aload_1
32: if_acmpne 40
35: aload_2
36: invokevirtual scala#34 // Method scala/runtime/NonLocalReturnControl.value:()Ljava/lang/Object;
39: areturn
40: aload_2
41: athrow
Exception table:
from to target type
8 26 26 Class scala/runtime/NonLocalReturnControl
scala> :quit
```
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