8380567: DynamicCallSiteDesc.bootstrapMethod should return DirectMethodHandleDesc

[liach]

We should fix the return type of DynamicCallSiteDesc.bootstrapMethod; luckily we can do this without breaking binary compatibility.

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Issues

• JDK-8380567: DynamicCallSiteDesc.bootstrapMethod should return DirectMethodHandleDesc (Bug - P4)
• JDK-8380568: DynamicCallSiteDesc.bootstrapMethod should return DirectMethodHandleDesc (CSR)

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[bridgekeeper]

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[mlbridge]

Webrevs

• 00: Full (1af86fcb)

[ExE-Boss]

I wish there was a way to declare required bridge overloads without needing interfaces such as these (which only works for public instance methods), or needing some sort of post‑compilation bytecode rewriting (which works for any method, but significantly complicates the build steps).

[liach]

Don't think it's in the interest of us to expand the language here. This trick actually should be perfectly legal to avoid NoSuchMethodError for all compliant Java SE implementations (see the CSR for details)

[Marcono1234]

Would it make sense to add a comment here though to make the purpose of this BootstrapMethodHook clearer?

[liach]

I think the notes in DynamicCllSiteDesc.bootstrapMethod() is sufficient to explain this situation.

[ExE-Boss]

I believe that this might’ve been originally declared as a MethodHandleDesc with the expectation that the bootstrap method could potentially use a constant dynamic in some future JVM.

[liach]

Unlikely, an entry in the BootstrapMethods table most likely will stay a MH constant plus a list of argument constants. Such a refactor would also hurt DynmicConstantDesc.

[Marcono1234]

Are these @implSpec and @implNote tags really needed? For users they will be quite confusing.

And DynamicCallSiteDesc is final, so this would mostly be relevant for re-implementations of the JDK (?) or rewrites of this class?

[liach]

Yes, implSpec and implNote are for implementations of the Java SE Platform. Rules concerning subclasses in public are part of the regular API specifications.