tsgo (`@typescript/native-preview` ≥ 20260624.1) drops route search intersection member — `stripSearchParams` rejected with TS2322 (clean in tsc + tsgo 20260623.1)

[meabed]

Which project does this relate to?

Router

Describe the bug

A regression in the TypeScript 7 native compiler (@typescript/native-preview / tsgo), starting in 7.0.0-dev.20260624.1, makes valid TanStack Router code fail type-checking.

A route's resolved search schema is the intersection of its parent's search schema and the route's own validateSearch output. When that schema is used as a type argument — e.g. for the stripSearchParams search middleware — tsgo drops the route's own member from the intersection, leaving only the parent's. The middleware, correctly typed SearchMiddleware<Parent & Own>, is then checked against SearchMiddleware<Parent> and rejected with TS2322.

This is not a Router defect — the types are valid. Stable tsc (6.0.3) and tsgo 7.0.0-dev.20260623.1 both accept the exact same code; only tsgo >= 20260624.1 rejects it. Filing here because it breaks Router users who run the native-preview compiler, and you may want to track it or add a type-level workaround. Root cause is upstream and appears related to microsoft/typescript-go#4391 (also router-core, same build window, different surface — there a const type parameter loses a string-literal through Omit<...>, surfacing as TS2353).

Version matrix (same code, only the compiler changes)

Compiler	Result
stable tsc 6.0.3	no errors
tsgo 7.0.0-dev.20260623.1	no errors
tsgo 7.0.0-dev.20260624.1 (first bad)	TS2322
tsgo 7.0.0-dev.20260627.2 (latest)	TS2322

@tanstack/react-router@1.170.16, @tanstack/zod-adapter@1.167.0, zod@4.4.3, macOS arm64.

Actual error

src/routes/pricing.tsx(10,27): error TS2322: Type 'SearchMiddleware<{ billing: "monthly" | "yearly"; } & { page: number; }>' is not assignable to type 'SearchMiddleware<{ page: number; }>'.

The expected type has collapsed to the parent-only { page: number } — the route's own { billing } member is dropped from the intersection in this generic position.

Real-world impact

In a full app (root validateSearch + many file routes) the same root cause cascades widely: TS2322 on every stripSearchParams middleware, plus TS2339 on Route.useSearch().<ownField> and TS2353 on navigate({ search }) literals, because each route's resolved search schema falls back to the root-only schema. A mid-size app surfaced ~156 errors on 20260627.2, all clean on 20260623.1.

Your Example Website or App

Minimal reproduction (two route files) inlined below.

Steps to Reproduce the Bug or Issue

src/routes/__root.tsx — root validates a shared page param:

import { createRootRoute, Outlet } from '@tanstack/react-router';
import { zodValidator } from '@tanstack/zod-adapter';
import { z } from 'zod';

export const Route = createRootRoute({
  validateSearch: zodValidator(z.object({ page: z.coerce.number().default(1) })),
  component: () => <Outlet />,
});

src/routes/pricing.tsx — leaf adds billing + a stripSearchParams middleware:

import { createFileRoute, stripSearchParams } from '@tanstack/react-router';
import { zodValidator } from '@tanstack/zod-adapter';
import { z } from 'zod';

const defaults = { billing: 'monthly' } as const;

export const Route = createFileRoute('/pricing')({
  validateSearch: zodValidator(z.object({ billing: z.enum(['monthly', 'yearly']).default('monthly') })),
  search: { middlewares: [stripSearchParams(defaults)] },
  component: Page,
});

function Page() {
  return Route.useSearch().billing;
}

Then:

npm install
npx tsr generate        # @tanstack/router-cli -> src/routeTree.gen.ts
npx tsgo --noEmit       # TS2322 on tsgo >= 20260624.1
npx tsc  --noEmit       # clean (stable TypeScript)

Expected behavior

No error. The route's search schema is { page: number } & { billing: 'monthly' | 'yearly' }, and stripSearchParams({ billing: 'monthly' }) yields a SearchMiddleware for exactly that type — as stable tsc and tsgo 20260623.1 both confirm.

Screenshots or Videos

N/A

Platform

• TanStack Router: 1.170.16
• tsgo (@typescript/native-preview): 7.0.0-dev.20260624.1+ (clean on 20260623.1)
• OS: macOS (arm64)

Additional context

Bisected to 7.0.0-dev.20260624.1. Likely the same upstream tsgo regression as microsoft/typescript-go#4391.

[meabed]

Filed upstream as the root cause: microsoft/typescript-go#4462 (same minimal repro, compiler-focused).

[meabed]

Runnable reproduction repo: https://github.com/meabed/tsgo-tanstack-router-search-repro

git clone https://github.com/meabed/tsgo-tanstack-router-search-repro
cd tsgo-tanstack-router-search-repro
npm install
npx tsgo --noEmit   # TS2322 on @typescript/native-preview >= 7.0.0-dev.20260624.1
npx tsc  --noEmit   # clean

(src/routeTree.gen.ts is committed, so no generate step needed; re-run npx tsr generate if you change the routes.)