Type ['instanceof', TimeStub] as Infer<TimeStub> is undefined

[mmailaender]

Report a bug

@ssalbdivad I have created a reproduction of yesterday's undefined problem Discord Discussion.

🧩 Context

• ArkType version: 1.0.29-alpha
• TypeScript version (4.8+): 5.4.2
• Other context you think may be relevant (Node version, OS, etc.):

🧑‍💻 Repro

https://github.com/mmailaender/svelte5/blob/arktype/src/lib/type.d.ts

GitPod: https://gitpod.io/?autostart=true#https://github.com/mmailaender/svelte5/blob/arktype/src/lib/type.d.ts

[ssalbdivad]

There are a couple problems:

1. this is defined in a .d.ts file. If you have skipLibCheck enabled (which you should), your tsconfig will not apply to these files and they will not be checked for errors.
2. (1) obfuscates issues like Infer not having been imported and const statements not being legal in .d.ts .

This is quite an unfortunate footgun TS built into the language when really what most people want is not to check files from node_modules. In general I'd recommend against using .d.ts files at all in your source. There's not really ever a good reason to use them instead of a standard .ts file and they create lots of problems.