Re: [PR] RFC: proposal for declarative VDUs [couchdb]

["janl (via GitHub)" <gi...@apache.org>]

janl commented on PR #5792:
URL: https://github.com/apache/couchdb/pull/5792#issuecomment-3714914366

   I’m trying to consolidate the discussions so we don’t have to retread a lot of text to move forward. These are (let me know if I missed any) the open discussion items:
   
   1. Scope
   
   The brief for the design was to be able to model even complex VDUs statically. This was accomplished by adding if/then/else-like behaviour as well as allowing custom error messages.
   
   Things could be significantly simplified if we reduced the scope to exclude these more complicated constructs and trade-off that not everything a JS VDU can do can be done statically.
   
   I’m not listing all the smaller sub-issues that would follow from this.
   
   The main question to answer here is whether the resulting functionality is useful enough so that people would adopt them?
   
   
   2. Error Reporting
   
   The proposal anticipates it being used interactively. That is, a user is doing an action that should result in saving a document, but a validation rejects the write. It would be a tedious software to be used if only the first of multiple possible validation error were to be returned and fixing each one would require a validation roundtrip.
   
   Hence the proposal suggests to report _all_ validation errors in one response instead of just the first one.
   
   This would mean a substantial code change to the selector code, as now a list of errors must be carried through it and logic-shortcut returns need to be skipped. This leads to more complex selector code that encodes two different behaviours, one for Mango indexing and one for validation. There are concerns about this complexity both in implementation and mental-model for the end-user.
   


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