Improved TypeScript ergonomics

[bennypowers]

This issue tracks some nice-to-have enhancements for type detection.

The analyzer does great picking up on explicitly typed members:

function XMixin<B extends Constructor<{ b: B }>(superclass: B) {
  return class XL<A> extends superclass {
    x: X<A> = new X<A>(this.b);
    bool: boolean = true;
  }
}

Here,

• the mixin parameter will be correctly typed as B
• the x field will be correctly typed as X<A>
• the bool field will be typed as boolean

However, it would be nice if for the following code:

function XMixin<B extends Constructor>(superclass: B) {
  return class XL<A> extends superclass {
    x = new X<A>();
    bool = true;
  }
}

Would give:

• the parameter as B extends Constructor<{ b: B }>
• the x field as X<A> (even without an explicit typing)
• the bool field as boolean (even without an explicit typing)

I'm guessing that the TypeScript API has the chops to infer those things, given a SourceFile AST, but I haven't looked into it just yet.

[bennypowers]

I've got a plugin for boolean types, want that in core @thepassle ?

[thepassle]

What does the plugin do exactly? Assign the type of bool to be {type: {text: boolean}} by inferring the type from its default value?

I think we could add some type inference behavior for fields, (and variables?), but we'd need to make sure to keep the correct 'priority' of type systems. Currently JSDoc will overrule TS types, so the priority should probably be (from least prio to highest prio):

• inferred type
• TS type (overrules inferred)
• JSDoc type (overrules TS)

[bennypowers]

Since op i updated the plugin to handle

• boolean initializers
• number initializers
• string initializers
• T as const initializers

        if (isBoolean(node))
          memberDoc.type = { text: 'boolean' };
        else if (isAsConst(node.initializer, api))
          memberDoc.type = { text: node.initializer.expression.getText() };
        else if (api.isStringLiteral(node.initializer))
          memberDoc.type = { text: 'string' };
        else if (api.isNumericLiteral(node.initializer))
          memberDoc.type = { text: 'number' };

[bennypowers]

I'll open a draft PR and we can go over it there 🙂

[thepassle]

I think we should make a new handler for this, something like handleTypeInference and add it here: https://github.com/open-wc/custom-elements-manifest/blob/master/packages/analyzer/src/features/analyse-phase/creators/createClassField.js#L18

fieldTemplate = handleTypeInference(fieldDoc, node);

That way we can easily add it for variables as well

[thepassle]

type inference was added, ill close this for now