Support Pick and other Mapped Types about ts-json-schema-generator HOT 17 CLOSED

Well, I've got an ugly(?) implementation working for Partial. Will test and do a pull request.

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Fixed in #ebad910

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That's awesome. I built this library to support schema generation in https://github.com/vega/vega-lite and it works really well. I don't have the time right now to look into the particular issue but I'm sure if you step through the execution and put breakpoints in the right spots, you can figure out how to fix this. It looks more complicated than it is.

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Simple example

export type MyObject = Part<B>;

type Part<T> = {
    [P in keyof T]?: T[P];
};

interface B {
    b: number;
    c: string;
}

The reason why it doesn't work is that we need to associate keys with values in Part. I didn't find an obvious way to do that and don't have time right now but will look at it in a few weeks.

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@robertdempsey it shouldn't take too long to fix this and I would love a PR for this. We could use this to fix an issue here: vega/vega-lite#3491 (comment)

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@domoritz sorry I haven't replied yet. We are a bit stretched for time too but will see if we can take a look. It might take a couple weeks if we do though and it'd be our first time working on this library. Will keep you updated on whether or not we get to take a look. Cheers!

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Thanks!

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Hi, I work with @robertdempsey. I've looked into this a little - it seems that because of the intentional limitation with the TS compiler to not know what is implementing a generic, we're going to have a hard time getting the information we need and fitting it into the way this project is set up.
eg see this issue

I debugged and stepped into MappedTypeNodeParser. getTypeFromTypeNode returns a type that doesn't have types in it, hence the 'undefined' error reported by @robertdempsey.

It ends up at getTypeFromTypeOperatorNode, where it does getTypeFromTypeNode on the T type, which is unknown. So the type we end up with is unknown and can't have any properties extracted from it.

We're keen to help, but I'm not really familiar with this code base, so any help in pointing me to the right direction to solve this kind of problem would be appreciated.

In the meantime I figure you must have solved something like this before in generics, so I'm studying that.

I've noticed that from this.getRootChildDefinitions(rootType), generics don't have baseTypes - it could be something to do with that.

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I looked a bit into it yesterday and I can’t say for sure whether this will work but my idea was to figure out all the possible values for P and then getting the type of each property of T. This way we should get Pick and Partial working. Sortify from your example at the top should be easy because the type on the right side does not depend on a key.

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https://astexplorer.net/ is super helpful to see what is different.

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I did had a look at that - still have a bit to learn to make it useful I think. Have you ever considered using simple-ast?

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Just putting notes here to help with dev - no need to respond unless you want to.

So the point at which we're losing the information is in the ExpressionWithTypeArgumentsNodeParser, when we call this.childNodeParser.createType, the node is passes through is exactly

type Partial<T> = {
    [P in keyof T]?: T[P];
};

and this has none of the type information that would allow the baseType to have properties.

UPDATE - it's actually available through the context. continuing...

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Have you ever considered using simple-ast?

No, I didn't know about it. Looks neat.

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In the MappedTypeGenerator the ObjectProperties can be extracted from the context.arguments like so:

context.getArguments().reduce((acc : ObjectProperty[], arg : any) => {
                acc = acc.concat(arg.getProperties())
                return acc;
            }, [])

however, they are still 'required'. I'm currently trying to figure out a nice way of ensuring the attributes of the parameters defined by the mapped type are used.

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Awesome. I'll review it once it's cleaned up.

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That's all linted.. Looking at Pick now.

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Fantastic. I'm really excited to have your contribution. There are a couple of pending refactorings that we couldn't do because of missing support for Partial. For instance vega/vega-lite#3502.

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