feat(eslint-plugin): [no-type-alias] support tuples

[ankeetmaini]

Fixes #720

[typescript-eslint]

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[bradzacher]

good idea but not quite right.
the reason that the cases failed is because we never added handling for TSTupleType.

What we will want to do instead is:

• add back the undhandled case error.
• add a new option allowTupleTypes, which follows the same schema as allowMappedTypes.
• add in a new clause in validateTypeAliases which handles TSTupleType

[ankeetmaini]

Thanks @bradzacher, updated the PR :)

[bradzacher]

awesome! code lgtm. nice work covering everything well.
thanks for doing this.

[ckknight]

Can we also have a test for readonly tuples?

[bradzacher]

that's actually an interesting point - this rule doesn't support TSTypeOperator at all.

Considering the existence of readonly [tuple], this should also add support for that.

Wouldn't be a huge change to also support the keyof operator too.

[ankeetmaini]

if (type.node.type === AST_NODE_TYPES.TSTypeOperator) {
  if (
    (['keyof', 'readonly'].includes(type.node.operator) &&
    type.node.typeAnnotation &&
    type.node.typeAnnotation.type === 'TSTupleType'
  ) {
    return true;
  }
}

type.node.typeAnnotation.type === 'TSTupleType'

TS is throwing on this line This condition will always return 'false' since the types 'AST_NODE_TYPES.TSTypeAnnotation' and '"TSTupleType"' have no overlap.ts(2367)

How else can I ascertain that TSTypeOperator contains a tuple type? I checked the AST too, it seems valid https://astexplorer.net/#/gist/149c54ba8d9a45dace62a4aac639f613/79446ea665c469c0e03fe7a74fdeb35ac7bbcde5

[bradzacher]

try AST_NODE_TYPES.TSTupleType

[ankeetmaini]

It fails with that too. :(

[bradzacher]

It's part of the type union, so it should work:
https://github.com/typescript-eslint/typescript-eslint/blob/master/packages/typescript-estree/src/ts-estree/ts-estree.ts#L399-L435

[bradzacher]

The types were wrong for TSTypeOperator. I fixed them for you on this branch.

[ankeetmaini]

@bradzacher thanks, I've updated the tests and rebased with master.

[bradzacher]

LGTM. Thanks for doing this