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Type alias circularly references itself (5.4 regression) #58302
Description
🔎 Search Terms
Type alias circularly references itself (5.4 regression)
🕗 Version & Regression Information
- This changed between versions 5.3.3 and 5.4.5
⏯ Playground Link
💻 Code
type BooleanPaths<T> = string &
{
[K in keyof T]: T[K] extends boolean
? K
: T[K] extends object
? K extends number | string
? `${K}.${BooleanPaths<T[K]>}`
: never
: never;
}[keyof T];🙁 Actual behavior
This code fails with two errors:
Type alias 'BooleanPaths' circularly references itself.
Type 'BooleanPaths' is not generic.
🙂 Expected behavior
The compilation should pass, as it has in previous versions.
Additional information about the issue
No response
Activity
RyanCavanaugh commentedon Apr 24, 2024
Bisects to #56515
ahejlsberg commentedon May 6, 2024
The issue is that following #56515 we perform constraint reduction on intersection types
T & PorP & T, where T is a type parameter or indexed access type andPis a primitive type, theobjecttype, or{}, reducing the intersection type to justTwhen the constraint ofTfully encompassesP. For example, for aT extends string, the intersectionT & stringis reduced to justT. In the repro, we attempt to reduce the intersectionstring & {...}[keyof T], but resolving the constraint of{...}[keyof T]causes a circularity. It's unfortunate, but the price we have to pay to get the benefits of the feature.I'd suggest rewriting the
BooleanPathstype to this simpler formulation:No circularity and handles both object and tuple types.
typescript-bot commentedon May 9, 2024
This issue has been marked as "Design Limitation" and has seen no recent activity. It has been automatically closed for house-keeping purposes.