Handling empty lists and empty maps with Minimal NestedText

[jonjanisch]

Hi, I'm the maintainer of nestedtext-min-java - a Java impl of Minimal Nested Text. I'm using it for an internal authorization library currently and hit a bit of an embarrassing snag.

How should I dump a dictionary item in which the value is an empty list? I have a policy that dumps out to Minimal NestedText like this:

name: SomePolicy
rules:
  -
    actions:
      - CREATE
      - UPDATE
    roles:
      - ROLE_1
      - ROLE_2
  -
    actions:
      - READ
      - LIST
    roles:
      - USER

When testing, I deleted the rules for this policy and it persisted it dumped out the nested text like this:

name: SomePolicy
rules:

This seems to be consistent with how NestedText dumps empty lists with the dialect i and I see these notes in the docs:

If “i” is included in dialect, support for inline lists and dictionaries is dropped. The default is “I”, which enables support for inlines. The main effect of disabling inlines in the dump functions is that empty lists and dictionaries are output using an empty value, which is normally interpreted by NestedText as an empty string.

But this makes it difficult to round-trip a Minimal NestedText file since the empty list is lost and it's trying to load it as a String. I can certainly handle this in my authorization library level, but if possible I would like to add some workaround in nestedtext-min-java. Any thoughts?

[jonjanisch]

I hastily wrote this last night. But I think I can easily solve this in my lib by providing Java class deserializing which I've been putting off, e.g. load("someNestedText", MyClass.class). For the current load method that loads into a String, List, or Map, I can provide some warnings in the docs about this edge case.

When I originally posted this, I thought the Minimal NestedText format should possibly be augmented by allowing inline list and inline map specifically for the case of representing empty list or empty map, e.g.:

name: SomePolicy
rules:
  []

But I no longer think it's necessary.

[LewisGaul]

NestedText does already support inline lists and maps though?

[jonjanisch]

The subset Minimal NestedText does not though.

[KenKundert]

Yes, with Minimal NestedText it is not possible to represent an empty list or dictionary. I recommend instead using an empty end-of-line string and using a Schema to do the conversion where it makes sense to do so. It sounds like you came to a similar conclusion. If that is not adequate, then I recommend implementing full NestedText.

[jonjanisch]

Thanks, I've updated the library with data binding and it's working great.

Team team = new NestedText().load(data, Team.class);