[foreign-memaccess] RFR: 8252504: Add a method to MemoryLayout which returns a offset-computing method handle

[Chris Hegarty]

On Thu, 19 Nov 2020 17:26:56 GMT, Maurizio Cimadamore <mcimadamore at openjdk.org> wrote:

>> This PR adds two new methods: `bitOffsetHandle` and `byteOffsetHandle` to `MemoryLayout`, that can be used to create method handles that can compute the effective offset of a layout element given a set of additional `long` indexes.
>> 
>> I also cleaned up a leftover in the javadoc of bitOffset and byteOffset where an API note was stating that `sequenceElement()` layout path elements would be interpreted as `sequenceElement(0)`, but they were actually being rejected outright (as they should).
>> 
>> I also added some tests to cover the corner case where an UnsupportedOperationException was being thrown. (some of the churn in the tests is from introducing static imports. I hope it's not too noisy).
>
> Looks good - added some javadoc/test suggestions

This looks good.  It is true to say that `bitOffset`/`byteOffset` do not accept any path elements with free dimensions? If so, then it would be good to call this out explicitly - I cannot find it in the API.

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PR: https://git.openjdk.java.net/panama-foreign/pull/396