json: better support for "type" unions (e.g. nullable arrays w/ typed items)

[ochafik]

Adds support for the following nullable syntax I've seen in the wild (also checked properly by https://www.jsonschemavalidator.net/):

{
  "type": ["array", "null"],
  "items": { "type": "string" }
}

Before this PR, the grammar above was treated like {"anyOf": [{"type": "array"}, {"type": "null"}]} (meaning it would accept to generate [123]).

With this PR, it ensures the array is typed, e.g. ["123"] is possible but not [123]

[HanClinto]

Updating the integration tests with pass/fail cases for this one would help me understand better what's going on with this.

[ochafik]

Updating the integration tests with pass/fail cases for this one would help me understand better what's going on with this.

I think we need #7790 for that ;-) In the meantime added an example to the PR's description, sorry it was a bit cryptic :-D

[HanClinto]

Updating the integration tests with pass/fail cases for this one would help me understand better what's going on with this.

I think we need #7790 for that ;-) In the meantime added an example to the PR's description, sorry it was a bit cryptic :-D

haha, thanks. :) Noted -- I've been a bit slow on that one. It's finally updated and I think it's ready for review / merge.

[HanClinto]

Looks like one of the tests is failing:

Assertion failed: (false), function verify, file test-json-schema-to-grammar.cpp, line 38.

[ochafik]

Looks like one of the tests is failing:

Assertion failed: (false), function verify, file test-json-schema-to-grammar.cpp, line 38.

Fixed, thanks!

[HanClinto]

Super, super clean.

To test I reverted the change to json-schema-to-grammar.cpp and the integration test failed. Brought the changes in, and the integration test passed.

The changes are small and discrete and self-contained. Love it! ❤️❤️❤️ Enthusiastic approval -- very well done!!