RFR: JDK-8266670: Better modeling of access flags in core reflection [v11]

[Joe Darcy]

On Wed, 23 Feb 2022 00:40:44 GMT, Joe Darcy <darcy at openjdk.org> wrote:

>> This is an early review of changes to better model JVM access flags, that is "modifiers" like public, protected, etc. but explicitly at a VM level.
>> 
>> Language level modifiers and JVM level access flags are closely related, but distinct. There are concepts that overlap in the two domains (public, private, etc.), others that only have a language-level modifier (sealed), and still others that only have an access flag (synthetic).
>> 
>> The existing java.lang.reflect.Modifier class is inadequate to model these subtleties. For example, the bit positions used by access flags on different kinds of elements overlap (such as "volatile" for fields and "bridge" for methods. Just having a raw integer does not provide sufficient context to decode the corresponding language-level string. Methods like Modifier.methodModifiers() were introduced to cope with this situation.
>> 
>> With additional modifiers and flags on the horizon with projects like Valhalla, addressing the existent modeling deficiency now ahead of time is reasonable before further strain is introduced.
>> 
>> This PR in its current form is meant to give the overall shape of the API. It is missing implementations to map from, say, method modifiers to access flags, taking into account overlaps in bit positions.
>> 
>> The CSR https://bugs.openjdk.java.net/browse/JDK-8281660 will be filled in once the API is further along.
>
> Joe Darcy has updated the pull request incrementally with one additional commit since the last revision:
> 
>   Add mask to access flag functionality.

I've pushed an initial version of functionality to map from an integer mask to a set of access flags based on location.

I suspect this will be refined and changed a bit before the code goes back. Potential changes I see now:

* an ANY_CLASS location allowing the union of the flags for CLASS and INNER_CLASS (or a method providing equivalent functionality)
*  simple maskToAccessFlags(int mask) method that worked if all the bit positions were unambiguous.

@asotona , how does this API look for your use cases?

I'll start wiring up the various accessFlag methods on java.lang.Class, java.lang.reflect.* etc.

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PR: https://git.openjdk.java.net/jdk/pull/7445