Generic type information for classes within closures not emitted by javac 11.0.15

[Dawid Weiss]

Just FYI - I did a little bisecting archeology and it's this issue:
https://bugs.openjdk.org/browse/JDK-8215470

The signatures from the nested class are fine after that commit and erased/
missing before. So the bug is present in anything up to jdk-13-ga.

Dawid

On Wed, Jun 8, 2022 at 10:08 PM Dawid Weiss <dawid.weiss at gmail.com> wrote:

>
> Good evening,
>
> I've spent an interesting day debugging a very awkward error in Google
> Guice: a binding would work in JDK17 but would result in an odd (and
> misleading) error information under JDK11. This turns out to be a problem
> with generic signatures emitted by the corresponding compilers.
>
> I narrowed it down to essentially something like this [full source at 1]:
>
> Callable<Void> r =
>         () -> {
>           class Foo1 {
>             public Map<String, Integer> field;
>           }
>
>           System.out.println("Foo1.field type: " +
> Foo1.class.getField("field").getGenericType());
>           return null;
>         };
>     r.call();
>
> When I compile and run this snippet under java 11.0.15, I get only the
> following signatures for generic types:
>
> Foo1.field type: interface java.util.Map
>
> if you move the inner class declaration outside of the closure, proper
> generic info is stored and then loaded/ printed:
>
> Foo2.field type: java.util.Map<java.lang.String, java.lang.Integer>
>
> In Java 17.0.3, this compiles and works fine and I can't find any issue
> where this was fixed. Is this a class bytecode constraint somewhere? My
> reading of the JLS [2] would suggest the signature is mandatory, even if
> emitted from within that nested class Foo1?
>
> Any pointers would be appreciated!
> Dawid
>
> [1] https://gist.github.com/dweiss/d77452c52daa178e041adce145c2e86a
> [2]
> https://docs.oracle.com/javase/specs/jvms/se11/html/jvms-4.html#jvms-4.7.9.1
>
>
>
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