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fix: register createServerFn fetcher as serializable #5268

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Merged
merged 3 commits into from
Sep 28, 2025
Merged

fix: register createServerFn fetcher as serializable #5268

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d02c271
fix: createServerFn fetcher has TSS_SERVER_FUNCTION symbol prop
schiller-manuel Sep 27, 2025
0272efb
add serializer extension, register server functions to be serializable
schiller-manuel Sep 27, 2025
eca3de4
remove cast
schiller-manuel Sep 27, 2025
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2 changes: 1 addition & 1 deletion e2e/react-start/server-functions/src/routes/middleware/send-serverFn.tsx
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Original file line number Diff line number Diff line change
Expand Up @@ -6,7 +6,7 @@ const middleware = createMiddleware({ type: 'function' }).client(
async ({ next }) => {
return next({
sendContext: {
serverFn: barFn as any,
serverFn: barFn,
},
})
},
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3 changes: 3 additions & 0 deletions packages/router-core/src/index.ts
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Expand Up @@ -420,6 +420,9 @@ export type {
SerializerExtensions,
ValidateSerializable,
RegisteredSerializableInput,
SerializableExtensions,
DefaultSerializable,
Serializable,
} from './ssr/serializer/transformer'

export {
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21 changes: 13 additions & 8 deletions packages/router-core/src/ssr/serializer/transformer.ts
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Expand Up @@ -9,14 +9,19 @@ import type {
import type { LooseReturnType } from '../../utils'
import type { AnyRoute, ResolveAllSSR } from '../../route'

export type Serializable =
| number
| string
| boolean
| null
| undefined
| bigint
| Date
export interface DefaultSerializable {
number: number
string: string
boolean: boolean
null: null
undefined: undefined
bigint: bigint
Date: Date
}

export interface SerializableExtensions extends DefaultSerializable {}

export type Serializable = SerializableExtensions[keyof SerializableExtensions]

export function createSerializationAdapter<
TInput = unknown,
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2 changes: 2 additions & 0 deletions packages/start-client-core/src/createServerFn.ts
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Expand Up @@ -4,6 +4,7 @@ import { mergeHeaders } from '@tanstack/router-core/ssr/client'
import { TSS_SERVER_FUNCTION_FACTORY } from './constants'
import { getServerContextAfterGlobalMiddlewares } from './getServerContextAfterGlobalMiddlewares'
import { getStartOptions } from './getStartOptions'
import type { TSS_SERVER_FUNCTION } from './constants'
import type {
AnyValidator,
Constrain,
Expand Down Expand Up @@ -248,6 +249,7 @@ export type Fetcher<TRegister, TMiddlewares, TInputValidator, TResponse> =
: RequiredFetcher<TRegister, TMiddlewares, TInputValidator, TResponse>

export interface FetcherBase {
[TSS_SERVER_FUNCTION]: true
url: string
__executeServer: (opts: {
method: Method
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5 changes: 3 additions & 2 deletions packages/start-client-core/src/createStart.ts
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Original file line number Diff line number Diff line change
@@ -1,4 +1,5 @@
import { createMiddleware } from './createMiddleware'
import type { TSS_SERVER_FUNCTION } from './constants'
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⚠️ Potential issue | 🔴 Critical

Import TSS_SERVER_FUNCTION as a value so the computed property type-checks.

import type removes the runtime symbol, so when this module augmentation evaluates [TSS_SERVER_FUNCTION] there is no corresponding value and the file fails to compile ('TSS_SERVER_FUNCTION' only refers to a type, but is being used as a value here.). Pull the symbol in as a normal import (and keep using it in the ambient declaration) so the unique symbol is available.

-import type { TSS_SERVER_FUNCTION } from './constants'
+import { TSS_SERVER_FUNCTION } from './constants'

Also applies to: 120-122

🤖 Prompt for AI Agents 
In packages/start-client-core/src/createStart.ts around lines 2 and also lines
120-122, the symbol TSS_SERVER_FUNCTION is currently imported with "import type"
so it is erased at runtime and the module augmentation that uses
[TSS_SERVER_FUNCTION] fails to compile; change the import to a normal value
import (remove the "type" qualifier) so the unique symbol/value is present at
runtime and keep using that same identifier in the ambient declaration to allow
the computed property to type-check and compile.

import type {
AnyFunctionMiddleware,
AnyRequestMiddleware,
Expand Down Expand Up @@ -116,7 +117,7 @@ export type AnyStartInstance = StartInstance<any, any, any, any>
export type AnyStartInstanceOptions = StartInstanceOptions<any, any, any, any>

declare module '@tanstack/router-core' {
interface Register {
ssr: true
interface SerializableExtensions {
serverFn: { [TSS_SERVER_FUNCTION]: true }
}
}
12 changes: 12 additions & 0 deletions packages/start-client-core/src/tests/createServerFn.test-d.ts
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Original file line number Diff line number Diff line change
@@ -1,6 +1,7 @@
import { describe, expectTypeOf, test } from 'vitest'
import { createMiddleware } from '../createMiddleware'
import { createServerFn } from '../createServerFn'
import { TSS_SERVER_FUNCTION } from '../constants'
import type { Constrain, Register, Validator } from '@tanstack/router-core'
import type { ConstrainValidator } from '../createServerFn'

Expand Down Expand Up @@ -586,3 +587,14 @@ test('createServerFn with inputValidator and request middleware', () => {
Promise<string>
>()
})

test('createServerFn has TSS_SERVER_FUNCTION symbol set', () => {
const fn = createServerFn().handler(() => ({}))
expectTypeOf(fn).toHaveProperty(TSS_SERVER_FUNCTION)
expectTypeOf(fn[TSS_SERVER_FUNCTION]).toEqualTypeOf<true>()
})

test('createServerFn fetcher itself is serializable', () => {
const fn1 = createServerFn().handler(() => ({}))
const fn2 = createServerFn().handler(() => fn1)
})
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