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fix(types): fix the type definitions for factory models and config, a… #408

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fix(types): fix the type definitions for factory models and config, a…
Mar 29, 2026
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Mar 29, 2026
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31 changes: 13 additions & 18 deletions packages/typescript/ai/src/extend-adapter.ts
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Original file line number Diff line number Diff line change
Expand Up @@ -97,15 +97,6 @@ type InferFactoryModels<TFactory> = TFactory extends (
: string
: string

/**
* Infer the config parameter type from an adapter factory function.
*/
type InferConfig<TFactory> = TFactory extends (
model: any,
config?: infer TConfig,
) => any
? TConfig
: undefined

/**
* Infer the adapter return type from a factory function.
Expand All @@ -116,6 +107,12 @@ type InferAdapterReturn<TFactory> = TFactory extends (
? TReturn
: never

/**
* Extracts all parameter types after the first parameter from a function.
*/
type InferRestArgs<TFactory extends (...args: any) => any> =
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⚠️ Potential issue | 🔴 Critical

🧩 Analysis chain

🌐 Web query:

Does TypeScript allow a rest parameter type annotation of any(e.g.,(...args: any) => any), or must it be an array/tuple type like any[]?

💡 Result:

No, TypeScript does not allow a rest parameter type annotation of any like (...args: any) => any. The type annotation for rest parameters must be an array type like any[], a specific array type such as number[], or a tuple type.

Citations:

🏁 Script executed:

head -n 120 packages/typescript/ai/src/extend-adapter.ts | tail -n 20

Repository: TanStack/ai

Length of output: 541

Fix invalid rest-parameter typing in generic constraint.

Line 113 uses (...args: any), but TypeScript requires rest parameters to be array or tuple types (e.g., any[]). This will cause a TypeScript compilation error.

Suggested fix 
-type InferRestArgs<TFactory extends (...args: any) => any> =
+type InferRestArgs<TFactory extends (...args: any[]) => any> =
   Parameters<TFactory> extends [any, ...infer Rest] ? Rest : []
📝 Committable suggestion

‼️ IMPORTANT
Carefully review the code before committing. Ensure that it accurately replaces the highlighted code, contains no missing lines, and has no issues with indentation. Thoroughly test & benchmark the code to ensure it meets the requirements.

Suggested change
type InferRestArgs<TFactory extends (...args: any) => any> =
type InferRestArgs<TFactory extends (...args: any[]) => any> =
Parameters<TFactory> extends [any, ...infer Rest] ? Rest : []
🤖 Prompt for AI Agents 
Verify each finding against the current code and only fix it if needed.

In `@packages/typescript/ai/src/extend-adapter.ts` at line 113, The generic
constraint for InferRestArgs uses an invalid rest-parameter type; update the
constraint on TFactory from using (...args: any) to a valid rest tuple type such
as (...args: any[]) => any so TypeScript accepts it. Locate the type alias
InferRestArgs and change its constraint to TFactory extends (...args: any[]) =>
any (and if other similar generic constraints exist in the same file, apply the
same tuple/array rest fix).

Parameters<TFactory> extends [any, ...infer Rest] ? Rest : []

// ===========================
// extendAdapter Function
// ===========================
Expand Down Expand Up @@ -164,19 +161,17 @@ type InferAdapterReturn<TFactory> = TFactory extends (
* ```
*/
export function extendAdapter<
TFactory extends (...args: Array<any>) => any,
TFactory extends (model: any, ...args: Array<any>) => any,
const TDefs extends ReadonlyArray<ExtendedModelDef>,
>(
factory: TFactory,
_customModels: TDefs,
): (
model: InferFactoryModels<TFactory> | ExtractCustomModelNames<TDefs>,
...args: InferConfig<TFactory> extends undefined
? []
: [config?: InferConfig<TFactory>]
) => InferAdapterReturn<TFactory> {
) {
// At runtime, we simply pass through to the original factory.
// The _customModels parameter is only used for type inference.
// No runtime validation - users are trusted to pass valid model names.
return factory as any
}
return factory as unknown as (
model: InferFactoryModels<TFactory> | ExtractCustomModelNames<TDefs>,
...args: InferRestArgs<TFactory>
) => InferAdapterReturn<TFactory>
}