[Schema Inaccuracy] GET /repos/{owner}/{repo}/issues/{issue_number}/timeline" events union is not discriminating

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Assessment

Difficulty
4/5
Estimated time
3-5 days
Newbie friendliness
45/100
Issue type
Bug
Clarity
Mostly clear
Activity status
Stale
Tech stack
openapi, typescript
Domain
api

Research direction

Start with the OpenAPI schema for GET /repos/{owner}/{repo}/issues/{issue_number}/timeline and inspect how its event response union is defined. Check how the event field is represented across variants, then verify that event values discriminate the payload so timelineEvent.created_at is available for merged events.

Written by the indexing model from the issue text.

Description

feature
What happened?

const timelinePages = octokit.paginate.iterator(
  octokit.issues.listEventsForTimeline,
  { repo, owner, issue_number },
);

(async function () {
  for await (const page of timelinePages) {
    for (const timelineEvent of page.data) {
      if (timelineEvent.event === "merged") timelineEvent.created_at;
    }
  }
})().catch((e) => console.log(e));

gives an error

Property 'created_at' does not exist on type '{ id: number; node_id: string; url: string; actor: { name?: string | null | undefined; email?: string | null | undefined; login: string; id: number; node_id: string; avatar_url: string; gravatar_id: string | null; ... 14 more ...; user_view_type?: string | undefined; }; ... 5 more ...; label: { ...; }; } | ... 20 mo...'.
Property 'created_at' does not exist on type '{ event?: string | undefined; sha: string; node_id: string; url: string; author: { date: string; email: string; name: string; }; committer: { date: string; email: string; name: string; }; message: string; tree: { ...; }; parents: { ...; }[]; verification: { ...; }; html_url: string; }'. (ts 2339)

because TypeScript doesn't seem to have a way to discriminate the values in the union of event types.

It's basically impossible to inspect any of the event payload in a typed way due to this union being overlapping.

I think the fix would be to use the event field as a discriminator.

Versions

Octokit 22.0

Relevant log output
Code of Conduct
  • I agree to follow this project's Code of Conduct

The told me to reopen this issue here: https://github.com/octokit/types.ts/issues/676#issuecomment-3135915038

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