json: Add json.ParseWithStartPos function

[wata727]

Similar to hclsyntax.ParseConfig, this PR changes the start position to be passed to the json.Parse function.

This feature is necessary to transfer hcl.Block via RPC. We need to be able to specify the start position when we take a partial JSON and parse it on the other side. See also #332 #381

However, I understand that this change breaks backward compatibility. I propose this change for interface consistency, but if you care about compatibility, I could add a parsing function that accepts positions (e.g. json.ParseWithPos). Please tell me your opinion.

[apparentlymart]

Hi @wata727! Thanks for working on this and sorry for the slow response.

There are many callers of this function outside of the HCL codebase, so I think unfortunately we must retain API compatibility here, even though indeed the json package API is inconsistent with the others.

I like your proposed compromise of adding a new function. I'd suggest to call it ParseWithStartPos, to make it more obvious that the position argument is the starting position; I've seen some people be confused about the purpose of the pos argument in hclsyntax.ParseConfig so I think this is a good opportunity to learn from that feedback and make this new function name more explicit. We can make json.Parse be a wrapper around json.ParseWithStartPos using the default start position, so that there will still be only one real implementation of the function.

Does that sound reasonable to you? Thanks again!

[wata727]

@apparentlymart Thank you for your review. Agreed with your suggestion.
Instead, I added the json.ParseWithStartPos function. Could you review it again?

[apparentlymart]

Thanks @wata727! I've merged it.

I'm going to wait a little while before tagging a new release because I'm currently in the review process for some other PRs and so I'd ideally like to include them all into the same release tag.

[freddd]

Hi @apparentlymart, sorry to ping you in an old PR. Do you have any ETA on when you will be tagging a new release?