New behavior in v6 when interface extends two incompatible interfaces under exactOptionalPropertyTypes #62569
Description
🔎 Search Terms
Partial, @types/node, exactOptionalPropertyTypes, interface
🕗 Version & Regression Information
- This changed between versions v5.9.3 and 6.0.0-dev.20251001
⏯ Playground Link
💻 Code
namespace http {
export interface TcpSocketConnectOpts {
port: number;
}
export interface AgentOptions extends Partial<TcpSocketConnectOpts> {
keepAlive?: boolean | undefined;
}
}
namespace tls {
export interface ConnectionOptions {
port?: number | undefined;
}
}
interface AgentOptions extends http.AgentOptions, tls.ConnectionOptions {
maxCachedSessions?: number | undefined;
}🙁 Actual behavior
This now fails to type check—I believe correctly, because Partial<{ port: number }> is { port?: number }, not { port?: number | undefined }. It’s surprising that this worked before.
🙂 Expected behavior
Actually, the new behavior is expected, so probably @types/node needs an update. I wanted to flag this in case/for when other folks hit it!
Additional information about the issue
- Happens on latest
@types/node. - Discovered via True Myth’s nightly TS@next CI job as well as dependabot upgrades that test. The semver-ts.org guidance to test against upcoming versions is: good!