RFR: 7903878: jextract should derive struct field offsets from struct layouts

[Maurizio Cimadamore]

On Fri, 6 Dec 2024 23:03:47 GMT, Nizar Benalla <nbenalla at openjdk.org> wrote:

> Please read the JBS issue for more details.
> 
> Currently jextract emits hardwired offsets, it would be better if the offsets could be computed dynamically from the struct layouts.
> 
> Passes all tests, unsure if this patch requires new tests.
> Note: I used `fieldElementPaths(field.name())))` instead of the `javaName` to deal with nested structs.
> 
> 
> It seems like GitHub actions are broken for Ubuntu? will look into this next week if necessary.

Looks good. In principle we could save the construction of `fieldElementPaths`, as we use that both in the offset and in the layout accessor (e.g. `emitOffsetFieldDecl` and `emitLayoutFieldDecl`) but I'm not sure how much that matters in practice, as I'd expect most layout paths to be a simple call to `groupElement(String)`.

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Marked as reviewed by mcimadamore (Reviewer).

PR Review: https://git.openjdk.org/jextract/pull/262#pullrequestreview-2488573097