let's use "0.1.x" versioning until we have some confidence in this #12
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(I'll merge this myself once the 0.1.0 release is done and I've made sure it seems to work) |
I've already tagged 0.1.0, so 0.1.1 is next I also threw in using scalaOrganization.value instead of hardcoding "org.scala-lang" since that's the new hotness
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maybe we could go 1.0.0 when 2.13.0-M1 comes out? or wait for 2.13.0-RC1? I don't have a strong feeling about it |
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I'd prefer to wait until RC1 so we can guarantee binary compatibility. |
SethTisue
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Mar 20, 2017
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$;
public static {};
Code:
0: new scala#2 // class O$
3: invokespecial scala#12 // Method "<init>":()V
6: return
private O$();
Code:
0: aload_0
1: invokespecial scala#13 // Method C."<init>":()V
4: aload_0
5: putstatic scala#15 // Field MODULE$:LO$;
8: aload_0
9: invokevirtual scala#21 // Method java/lang/Object.toString:()Ljava/lang/String;
12: pop
13: return
}
```
The static initalizer `<clinit>` calls the constructor `<init>`, which
invokes superclass constructor, assigns `MODULE$= 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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I've already tagged 0.1.0, so 0.1.1 is next
I also threw in using scalaOrganization.value instead of
hardcoding "org.scala-lang" since that's the new hotness