[foreign-memaccess+abi] RFR: Improve exception messages and simplify LayoutPath [v3]

[Jorn Vernee]

On Mon, 18 Sep 2023 11:23:46 GMT, Per Minborg <pminborg at openjdk.org> wrote:

>> This PR proposes to improve the exception messages in the internal `LayoutPath` class and also do some code simplifications.
>
> Per Minborg has updated the pull request incrementally with one additional commit since the last revision:
> 
>   Revert commit

I like the overall idea. I think improving the error messages can help tell a user from _where_ in a layout path an error occurs.

But, currently you are only printing out the inner-most enclosing layout. Another idea would be to print a kind of back trace, where each `enclosing` layout path is listed in the exception message, until we get to the root. That should, I think, give the full image of where in the layout path the error occurs.

src/java.base/share/classes/jdk/internal/foreign/LayoutPath.java line 285:

> 283:         if (!((AbstractMemorySegmentImpl) segment).isAlignedForElement(offset, constraint)) {
> 284:             throw new IllegalArgumentException(String.format(
> 285:                     "Target offset %d is incompatible with byteAlignment %d (of %s) for segment %s"

I think that this should still use 'alignment constraint' as that is the term that we use in the doc everywhere.
Suggestion:

                    "Target offset %d is incompatible with alignment constraint %d (of %s) for segment %s"

src/java.base/share/classes/jdk/internal/foreign/LayoutPath.java line 314:

> 312:     private <T extends MemoryLayout> T requireLayoutType(Class<T> layoutClass) {
> 313:         if (!layoutClass.isAssignableFrom(layout.getClass())) {
> 314:             throw badLayoutPath("unable to select a " + layoutClass.getSimpleName() + " from layout: " + layout);

This looks incorrect, it is not the `layoutClass` that is being selected. `layoutClass` should be the type of the current `layout`.

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PR Review: https://git.openjdk.org/panama-foreign/pull/886#pullrequestreview-1631272825
PR Review Comment: https://git.openjdk.org/panama-foreign/pull/886#discussion_r1328858014
PR Review Comment: https://git.openjdk.org/panama-foreign/pull/886#discussion_r1328861083