Problem:
The Lua-API bridge allows Dict params to be empty Lua (list) tables at
the function-signature level. But not for _nested_ Dicts, because they
are not modeled:
fae7540732/src/nvim/api/keysets.lua (L184)
Some API functions like nvim_cmd check for kObjectTypeDictionary and
don't handle the case of empty Lua tables (treated as "Array").
Solution:
Introduce VALIDATE_T_DICT and use it in places where
kObjectTypeDictionary was being checked directly.
fixes#21005
Problem:
Validation messages are not consistently formatted.
- Parameter names sometimes are NOT quoted.
- Descriptive names (non-parameters) sometimes ARE quoted.
Solution:
Always quote the `name` value passed to a VALIDATE macro _unless_ the
value has whitespace.
Problem:
- API validation involves too much boilerplate.
- API validation errors are not consistently worded.
Solution:
Introduce some macros. Currently these are clumsy, but they at least
help with consistency and avoid some nesting.
