Description
Concerns have been raised about Z18 as the type of Z516's 'argument' key; in particular, an instance of Z18 can be resolved, whereas we wouldn't want resolution to happen inside an error object.
Based on comments in this merge request and also a recent voice conversation, Z39 appears to be a good candidate for the type of this key. Z516 is only used in a few places, and changing the type of this key from Z18 to Z39 should require only a smallish effort. Z516 has no uses in WikiLambda and none in function-evaluator.
Note that Z511 and Z526 both use keys of type Z39 to refer to other arbitrary keys, similarly to how Z516's 'argument' key is used.
Desired behavior/Acceptance criteria (returned value, expected error, performance expectations, etc.)
- All tests involving Z516 should continue to work (after being modified appropriately).
Completion checklist
- Before closing this task, review one by one the checklist available here: https://www.mediawiki.org/wiki/Abstract_Wikipedia_team/Definition_of_Done#Back-end_Task/Bug_completion_checklist