tests/pos/Map.scala does not produce idempotent bytecode

[nicolasstucki]

After compiling this file twice in #2272 the two bytecodes differed in the order of some bridges.

Printing the contents of the Map.classs with javap -c -v -p -s showed the following diff:

101c101
<    #92 = Utf8               ()Lscala/collection/Traversable;
---
>    #92 = Utf8               ()Lscala/collection/immutable/Traversable;
104,107c104,107
<    #95 = Utf8               ()Lscala/collection/immutable/Traversable;
<    #96 = Utf8               ()Lscala/collection/TraversableOnce;
<    #97 = Utf8               ()Lscala/collection/Iterable;
<    #98 = Utf8               ()Lscala/collection/immutable/Iterable;
---
>    #95 = Utf8               ()Lscala/collection/immutable/Iterable;
>    #96 = Utf8               ()Lscala/collection/Iterable;
>    #97 = Utf8               ()Lscala/collection/TraversableOnce;
>    #98 = Utf8               ()Lscala/collection/Traversable;
260,261c260,261
<   public scala.collection.Traversable seq();
<     descriptor: ()Lscala/collection/Traversable;
---
>   public scala.collection.immutable.Traversable seq();
>     descriptor: ()Lscala/collection/immutable/Traversable;
274,275c274,275
<   public scala.collection.immutable.Traversable seq();
<     descriptor: ()Lscala/collection/immutable/Traversable;
---
>   public scala.collection.immutable.Iterable seq();
>     descriptor: ()Lscala/collection/immutable/Iterable;
288,289c288,289
<   public scala.collection.TraversableOnce seq();
<     descriptor: ()Lscala/collection/TraversableOnce;
---
>   public scala.collection.Iterable seq();
>     descriptor: ()Lscala/collection/Iterable;
302,303c302,303
<   public scala.collection.Iterable seq();
<     descriptor: ()Lscala/collection/Iterable;
---
>   public scala.collection.Map seq();
>     descriptor: ()Lscala/collection/Map;
316,317c316,317
<   public scala.collection.Map seq();
<     descriptor: ()Lscala/collection/Map;
---
>   public scala.collection.TraversableOnce seq();
>     descriptor: ()Lscala/collection/TraversableOnce;
330,331c330,331
<   public scala.collection.immutable.Iterable seq();
<     descriptor: ()Lscala/collection/immutable/Iterable;
---
>   public scala.collection.Traversable seq();
>     descriptor: ()Lscala/collection/Traversable;

The same issue is present in the AbstractMap.classs.

[nicolasstucki]

Same issue is also present compiling tests/pos/t1203a.scala in NodeSeq.class

[smarter]

After compiling this file twice in #2272 the two bytecodes differed in the order of some bridges.

scalac has some infrastructure to dump bytecode with sorted members using ASM: https://github.com/scala/scala/blob/2.12.x/src/compiler/scala/tools/nsc/backend/jvm/AsmUtils.scala#L95 It's used to make better bytecode diffs.

[nicolasstucki]

If I understand correctly, that tool would hide the issue that I'm trying to show.

[smarter]

Yes, but since the order of members in the bytecode doesn't matter for anything, I think that's fine.

[nicolasstucki]

I would try to make this order idempotent as it is the only thing that has shown .class files that are not idempotent byte wise.

[nicolasstucki]

This can only be reproduced when recompiling classes that already exist in the standard library while also loading symbols from the scala2 compiled version.

[nicolasstucki]

This is just an artifact of the test framework loading classes compiled by scala2. It will disappear when we bootstrap.