Regression (7.0.0-dev.20260624.1): intersection type member dropped in generic position — TanStack Router stripSearchParams rejected (TS2322), clean in tsc + 20260623.1 #4462

Summary

Starting with @typescript/[email protected], tsgo reports a spurious TS2322 on valid TanStack Router code.

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 (here, 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.

The identical code compiles cleanly with stable tsc (6.0.3) and with tsgo 7.0.0-dev.20260623.1. It bisects to 20260624.1.

This is likely the same underlying regression as #4391 (also TanStack router-core, same build window) — there a const type parameter loses a string-literal property through Omit<...>, surfacing as TS2353. This report is a smaller, different surface (an intersection member dropped in a generic position, surfacing as TS2322).

Downstream report (same repro, library-user perspective): TanStack/router#7709.

Version matrix (same code, only the compiler changes)

Environment: macOS (darwin, arm64). @tanstack/[email protected], @tanstack/[email protected], [email protected].

Reproduction

src/
  routes/
    __root.tsx
    pricing.tsx
  routeTree.gen.ts   # generated by @tanstack/router-cli
tsconfig.json
tsr.config.json

src/routes/__root.tsx — root route validates a shared page search 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 route adds its own billing param and uses stripSearchParams:

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;
}

Steps:

npm install
npx tsr generate          # @tanstack/router-cli -> writes src/routeTree.gen.ts
npx tsgo --noEmit         # tsgo
# compare:  npx tsc --noEmit   (stable, clean)

Expected

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

Actual (tsgo >= 20260624.1)

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), this same root cause cascades widely: TS2322 on every stripSearchParams middleware, plus TS2339 on Route.useSearch().<ownField> and TS2353 on navigate({ search }) object literals, because the per-route resolved search schema everywhere falls back to the root-only schema. A single mid-size app surfaced ~156 such errors on 20260627.2, all clean on 20260623.1.