Property ? is missing in wrong type

I’m seeing a regression where code that works in 3.1 does not work in tsnext. It seems like typescript is not looking at the right type (ContourTransform) and tried to match against a different type (WordcloudTransform).

TypeScript Version: @next (3.2) but not 3.1

Search Terms: Property ? is missing in type

Code

https://github.com/vega/vega-typings/blob/master/tests/spec/examples.ts#L3394

Expected behavior:

The tests should not fail and they work fine in ts 3.1.

Actual behavior:

https://travis-ci.org/vega/vega-typings/jobs/444180003

ERROR: 3394:3  expect  TypeScript@next compile error: 
Type '({ name: string; url: string; transform: { type: "filter"; expr: string; }[]; } | { name: string; source: string; transform: { type: "contour"; x: { expr: string; }; y: { expr: string; }; size: { signal: string; }[]; count: { ...; }; }[]; })[]' is not assignable to type 'Data[]'.
  Type '{ name: string; url: string; transform: { type: "filter"; expr: string; }[]; } | { name: string; source: string; transform: { type: "contour"; x: { expr: string; }; y: { expr: string; }; size: { signal: string; }[]; count: { ...; }; }[]; }' is not assignable to type 'Data'.
    Type '{ name: string; source: string; transform: { type: "contour"; x: { expr: string; }; y: { expr: string; }; size: { signal: string; }[]; count: { signal: string; }; }[]; }' is not assignable to type 'Data'.
      Type '{ name: string; source: string; transform: { type: "contour"; x: { expr: string; }; y: { expr: string; }; size: { signal: string; }[]; count: { signal: string; }; }[]; }' is not assignable to type '{ url: string | SignalRef; } & { name: string; on?: OnTrigger[] | undefined; format?: FormatJSON | FormatSV | FormatDSV | ({ type: "topojson"; property?: string | undefined; } & { ...; }) | ({ ...; } & { ...; }) | { ...; } | SignalRef | undefined; transform?: Transform[] | undefined; }'.
        Type '{ name: string; source: string; transform: { type: "contour"; x: { expr: string; }; y: { expr: string; }; size: { signal: string; }[]; count: { signal: string; }; }[]; }' is not assignable to type '{ url: string | SignalRef; }'.
          Property 'url' is missing in type '{ name: string; source: string; transform: { type: "contour"; x: { expr: string; }; y: { expr: string; }; size: { signal: string; }[]; count: { signal: string; }; }[]; }'.

[mattmccutchen]

Minimal example:

type Transform =
  ({ type: "contour"; size: [string]; } & ({ a?: number } | { b?: number }))
  | { type: "tree"; [k: string]: any; };

const transform: Transform = {
  type: 'contour',
  size: ['width'],
};

[weswigham]

In this case it just means that we need to investigate from the beginning to see what’s causing the problem - for most bugs it’s evident from the behavior, but I’m unsure here.