7.1 regression: TS5115 for import("cloudflare:workers") with @cloudflare/workers-types #65445

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1. maschwenk commented on Nov 11, 2026

   

   Max Schwenk (maschwenk)

   on Nov 11, 2026

   Last edited by maschwenk

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   bisected from source: it starts at microsoft/typescript-go#4687 (ee860ff3d7ed), which reports TS2589, and its parent 351840bc5add is clean. #64372 later turned the TS2589 into TS5115

   microsoft/typescript-go#4687 added anonymousSymbol.SetDeclarations(originalSymbol.Declarations()) in getTypeWithSyntheticDefaultImportType. deleting that line on main at 1b54f27457a7 makes the workers-types repro check clean, along with this reduction that needs no package (target: es2022, module: esnext, moduleResolution: bundler):

   declare module "x" {
     type Stubable = (...args: any[]) => any;
     type Result<R> = R extends Stubable ? Provider<R> : Promise<R>;
     type MethodOrProperty<V> = V extends (...args: infer P) => infer R ? (...args: P) => Result<R> : Result<V>;
     type Provider<T> = T extends Stubable ? MethodOrProperty<T> : unknown;
     export function stub<T extends Stubable>(value: T): Provider<T>;
   }
   
   const a = import("x").then((m) => 1);

   with declarations, the synthetic default type of import("x") passes the anonymous type check in couldContainTypeVariables, so inference from the .then callback walks into its members and getErasedSignature erases stub's type parameter to any. Provider<any> is infinite (declare const x: Provider<any> reports TS2589 back to 5.9.3), and p.then((m) => 1) on a Promise<{ stub<T extends Stubable>(value: T): Provider<T> }> already reports TS2589 on 5.9.3, 6.0.3 and 7.0.2. what's new is that the import() type takes that path