CAP-52 XDR

[jonjove]

What

Add the XDR for CAP-52, specifically InvokeHostFunctionOp.

Why

Required to support CAP-52 in stellar/rs-stellar-contract-env and stellar/stellar-core.

Known limitations

N/A

[leighmcculloch]

@jonjove Are you wanting to have this merged to the main branch? It looks like the XDR contained within isn't in stellar-core, because when I run make clean build the changes disappear. If you're not wanting this to be merged, could you convert the PR to be a draft?

[jonjove]

@leighmcculloch it took me a while to get all the PRs open, but it corresponds to changes in stellar/stellar-core#3450 and stellar/rs-soroban-env#112. I don't know how we want to sequence these merges.

[leighmcculloch]

@jonjove I think if you want to be strict about it, you should break up stellar/stellar-core#3450 to be two PRs, one that modifies the XDR first, and then one that makes any changes that are dependent on the stellar-env-host crate having that XDR. Then the process would be:

• Modify XDR.
• Update rs-stellar-xdr.
• Update rs-stellar-env-host.
• Update stellar-core.

We may as well have the XDR in its own repo. cc @MonsieurNicolas

@graydon How did you do this recently?

[leighmcculloch]

Until we figure this out I think it's fine if you merge this just before merging the stellar-core PR, assuming the .x files are identical.

[graydon]

I left a comment in the accompanying core XDR change that I think the return from the function should have an SCVal and so this would need to be regenerated to match if so. Otherwise ok.

[jonjove]

@graydon I left a long comment explaining why I don't think we should have the SCVal.