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fix(router-core): correct TypeScript param inference for routes nested inside _pathless directories (#6011) #6018

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fix(router-core): correct TypeScript param inference for routes nested inside _pathless directories (#6011) #6018

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12 changes: 11 additions & 1 deletion packages/router-core/src/typePrimitives.ts
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Original file line number Diff line number Diff line change
Expand Up @@ -11,6 +11,11 @@ import type { AnyRouter, RegisteredRouter } from './router'
import type { UseParamsResult } from './useParams'
import type { UseSearchResult } from './useSearch'
import type { Constrain, ConstrainLiteral } from './utils'
// Remove any `_pathless` folder segments for type extraction
export type StripPathless<T extends string> =
T extends `${infer A}/_pathless/${infer B}`
? `${A}/${B}`
: T;
Comment on lines +14 to +18
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@coderabbitai coderabbitai bot Dec 3, 2025

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⚠️ Potential issue | 🟡 Minor

StripPathless only removes the first _pathless segment; consider making it recursive

As written, StripPathless stops after stripping the first /_pathless/ occurrence, so paths with multiple _pathless folders (e.g. "/foo/_pathless/bar/_pathless/baz") will still contain a _pathless segment and won’t be fully normalized for param extraction.

You can make this handle all occurrences with a small recursive change:

-export type StripPathless<T extends string> =
-  T extends `${infer A}/_pathless/${infer B}`
-    ? `${A}/${B}`
-    : T;
+export type StripPathless<T extends string> =
+  T extends `${infer A}/_pathless/${infer B}`
+    ? StripPathless<`${A}/${B}`>
+    : T;

This preserves behavior for simple cases like "/_pathless/nested/$id" while correctly normalizing any deeper _pathless nesting. Based on learnings, this keeps the special handling scoped to the _pathless folder name without affecting other underscore semantics.

🤖 Prompt for AI Agents 
In packages/router-core/src/typePrimitives.ts around lines 14 to 18,
StripPathless currently only removes the first "/_pathless/" segment; change it
to be recursive so all occurrences are stripped. Replace the conditional branch
so that when T extends `${infer A}/_pathless/${infer B}` you return
StripPathless<`${A}/${B}`> (rather than just `${A}/${B}`) so nested/multiple
_pathless segments are normalized; keep the fallback as T.


export type ValidateFromPath<
TRouter extends AnyRouter = RegisteredRouter,
Expand All @@ -29,11 +34,16 @@ export type ValidateSearch<
TFrom extends string = string,
> = SearchParamOptions<TRouter, TFrom, TTo>


export type ValidateParams<
TRouter extends AnyRouter = RegisteredRouter,
TTo extends string | undefined = undefined,
TFrom extends string = string,
> = PathParamOptions<TRouter, TFrom, TTo>
> = PathParamOptions<
TRouter,
StripPathless<TFrom>,
TTo extends string ? StripPathless<TTo> : TTo
>

/**
* @private
Expand Down