tuple validation

[marcoqu]

Hi,
when generating a schema for a tuple-like structure, I noticed some issues:

type Test = [number, number]

generates a schema that allows for additional values, while it shouldn't.

{
    "$schema": "http://json-schema.org/draft-06/schema#",
    "definitions": {
        "Test": {
            "type": "array",
            "items": [
                {
                    "type": "number"
                },
                {
                    "type": "number"
                }
            ],
            "minItems": 2,
            "additionalItems": {
                "anyOf": [
                    {
                        "type": "number"
                    },
                    {
                        "type": "number"
                    }
                ]
            }
        }
    },
    "$ref": "#/definitions/Test"
}

also,

type Test = [number, number, number|undefined]

requires at least three values, while it should require at least 2 and at most three.

Anyways, great project.

[domoritz]

Yes, that's a bug. I don't know how easy it is to get this information from the AST but I'd love to get a PR for this.

[marcoqu]

I could have a look, but it looks like the additionalItems property was explicitely added, while I think tuples should not allow additionalItems. But maybe there's something I'm missing.

return {
    type: "array",
    items: tupleDefinitions,
    minItems: tupleDefinitions.length,
    ...(tupleDefinitions.length > 1 ? {additionalItems: {anyOf: tupleDefinitions}} : {}),
};

could become

return {
    type: "array",
    items: tupleDefinitions,
    minItems: tupleDefinitions.length,
    maxItems: tupleDefinitions.length,
};

And then one would need to look into the undefined items in the tail of the tuple to lower the minItems count?

[marcoqu]

I looked into it.
Apparently "When accessing an element outside the set of known indices, a union type is used instead".

So, while this const tuple:[string, number] = ["", 1, 2] gives an error. This tuple[4] = 99 is valid. Link

Still, I believe it goes against the expected behavior of a schema generator. Maybe you could want an option for this? --strictTuples?

With regard to the lowering the value of minItems if the trailing elements of the tuple include undefined, it appears the in typescript there is no way of having optional arguments to a tuple. Nonetheless, lowering the value of minItems would have the expected effect of getting undefined if the item is not set...

Not sure how you want to go about this.

[domoritz]

Thanks for looking into this!

In this library, I chose not to add many options and have the most correct defaults. If you want more options, they could be added to https://github.com/YousefED/typescript-json-schema. I hope that makes sense.

[marcoqu]

Ok, thanks!
Since I see you are involved in both, can i ask you what's the difference between this project and YousefED/typescript-json-schema?

[domoritz]

Good question! YousefED/typescript-json-schema uses typeAtLocation while this project uses the AST itself. Using the AST is more complicated but tracks aliases better. I use this project for Vega-Lite and that's my main use case. I'm not going to fix anything unless it is relevant for Vega-Lite. YousefED/typescript-json-schema has a lot more customization options and the code is much shorter. However, since it is less complex, it sometimes does not work as well. Both projects benefit from each other. For instance, I try to share test cases where I can and if there is a fix that applies to both projects, I usually copy it over.

[marcoqu]

Got it.
I'm using this for a vscode extension for generating json schemas from types. I believe for the moment I'll maintain a close fork of your version since it seems to be the most complete.

Thanks!

[domoritz]

I see. Well, let me ask then, would you be willing to help me maintain this library? that is, respond to issues about tuples and help resolve issues around tuples when there is a new typescript version? The changes you made could be useful in Vega-Lite as well.

[marcoqu]

Sure, to the best of my abilities... ;)

…

On Thu, Jun 7, 2018 at 7:21 PM Dominik Moritz ***@***.***> wrote: I see. Well, let me ask then, would you be willing to help me maintain this library? that is, respond to issues about tuples and help resolve issues around tuples when there is a new typescript version? The changes you made could be useful in Vega-Lite as well. — You are receiving this because you authored the thread. Reply to this email directly, view it on GitHub <#28 (comment)>, or mute the thread <https://github.com/notifications/unsubscribe-auth/AA7VrchDQg_e7LdEWBlXz8nXM97kiBZeks5t6WEqgaJpZM4UabOI> .

[domoritz]

Sweet. Can you send a PR with --strictTuples? Make sure to add some tests and update the docs. I will test it against Vega-Lite and if it makes sense, I'm happy to make strictTuples the default. Sounds good?