RFR: JDK-8025636 Hide lambda proxy frames in stacktraces

[Staffan Larsen]

Hi,

Please review this patch for hiding the lambda proxy frame in stack traces:

bug: https://bugs.openjdk.java.net/browse/JDK-8025636 <https://bugs.openjdk.java.net/browse/JDK-8025636>
webrev: http://cr.openjdk.java.net/~sla/8025636/webrev.00/ <http://cr.openjdk.java.net/~sla/8025636/webrev.00/>

This is a straightforward addition of the LambdaForm$Hidden annotation to the generated methods. What is surprising is that this works even if LambdaForm$Hidden is a package-private class in java.lang.invoke and thus not accessible from most of the generated classes. There is some discussion of and answers to this in the bug, but essentially this works because the annotation class is never resolved and the code in Hotspot that looks for the annotation amounts to nothing more than string comparisons.

Hidden stack frames can be shown by running with “-XX:+UnlockDiagnosticVMOptions -XX:+ShowHiddenFrames”.

For an example of what this patch does, consider this code:

       Runnable r = () -> { throw new RuntimeException(); };
       r.run();

Previously, this would output:

    java.lang.RuntimeException
	at pkg.Foo.lambda$main$0(Foo.java:5)
	at pkg.Foo$$Lambda$1/2001112025.run(<Unknown>:1000000)
	at pkg.Foo.main(Foo.java:15)

With the patch it looks like this:

    java.lang.RuntimeException
	at pkg.Foo.lambda$main$0(Foo.java:5)
	at pkg.Foo.main(Foo.java:15)


Thanks,
/Staffan

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