refactor: collect all isThenable/isPromise definitions (#70293)

This collects the few different isThenable and isPromise definitions
into one shared function

packages/next/src/client/components/router-reducer/router-reducer-types.ts

@@ -272,15 +272,3 @@ export type ReducerActions = Readonly<
   | HmrRefreshAction
   | ServerActionAction
 >
-
-export function isThenable(value: any): value is Promise<AppRouterState> {
-  // TODO: We don't gain anything from this abstraction. It's unsound, and only
-  // makes sense in the specific places where we use it. So it's better to keep
-  // the type coercion inline, instead of leaking this to other places in
-  // the codebase.
-  return (
-    value &&
-    (typeof value === 'object' || typeof value === 'function') &&
-    typeof value.then === 'function'
-  )
-}

packages/next/src/client/components/use-reducer-with-devtools.ts

@@ -1,13 +1,13 @@
 import type { Dispatch } from 'react'
 import React, { use } from 'react'
 import { useRef, useEffect, useCallback } from 'react'
-import {
-  isThenable,
-  type AppRouterState,
-  type ReducerActions,
-  type ReducerState,
+import type {
+  AppRouterState,
+  ReducerActions,
+  ReducerState,
 } from './router-reducer/router-reducer-types'
 import type { AppRouterActionQueue } from '../../shared/lib/router/action-queue'
+import { isThenable } from '../../shared/lib/is-thenable'
 
 export type ReduxDevtoolsSyncFn = (state: AppRouterState) => void
 

packages/next/src/server/after/after-context.ts

@@ -7,6 +7,7 @@ import { ResponseCookies } from '../web/spec-extension/cookies'
 import type { RequestLifecycleOpts } from '../base-server'
 import type { AfterCallback, AfterTask } from './after'
 import { InvariantError } from '../../shared/lib/invariant-error'
+import { isThenable } from '../../shared/lib/is-thenable'
 
 export type AfterContextOpts = {
   waitUntil: RequestLifecycleOpts['waitUntil'] | undefined
@@ -36,7 +37,7 @@ export class AfterContext {
   }
 
   public after(task: AfterTask): void {
-    if (isPromise(task)) {
+    if (isThenable(task)) {
       task.catch(() => {}) // avoid unhandled rejection crashes
       if (!this.waitUntil) {
         errorWaitUntilNotAvailable()
@@ -141,12 +142,3 @@ function wrapRequestStoreForAfterCallbacks(
     serverComponentsHmrCache: requestStore.serverComponentsHmrCache,
   }
 }
-
-function isPromise(p: unknown): p is Promise<unknown> {
-  return (
-    p !== null &&
-    typeof p === 'object' &&
-    'then' in p &&
-    typeof p.then === 'function'
-  )
-}

packages/next/src/server/lib/trace/tracer.ts

@@ -11,6 +11,7 @@ import type {
   AttributeValue,
   TextMapGetter,
 } from 'next/dist/compiled/@opentelemetry/api'
+import { isThenable } from '../../../shared/lib/is-thenable'
 
 let api: typeof import('next/dist/compiled/@opentelemetry/api')
 
@@ -34,10 +35,6 @@ if (process.env.NEXT_RUNTIME === 'edge') {
 const { context, propagation, trace, SpanStatusCode, SpanKind, ROOT_CONTEXT } =
   api
 
-const isPromise = <T>(p: any): p is Promise<T> => {
-  return p !== null && typeof p === 'object' && typeof p.then === 'function'
-}
-
 export class BubbledError extends Error {
   constructor(
     public readonly bubble?: boolean,
@@ -352,7 +349,7 @@ class NextTracerImpl implements NextTracer {
             }
 
             const result = fn(span)
-            if (isPromise(result)) {
+            if (isThenable(result)) {
               // If there's error make sure it throws
               return result
                 .then((res) => {

packages/next/src/shared/lib/is-thenable.ts

@@ -0,0 +1,16 @@
+/**
+ * Check to see if a value is Thenable.
+ *
+ * @param promise the maybe-thenable value
+ * @returns true if the value is thenable
+ */
+export function isThenable<T = unknown>(
+  promise: Promise<T> | T
+): promise is Promise<T> {
+  return (
+    promise !== null &&
+    typeof promise === 'object' &&
+    'then' in promise &&
+    typeof promise.then === 'function'
+  )
+}

packages/next/src/shared/lib/router/action-queue.ts

@@ -1,5 +1,4 @@
 import {
-  isThenable,
   type AppRouterState,
   type ReducerActions,
   type ReducerState,
@@ -11,6 +10,7 @@ import {
 import type { ReduxDevToolsInstance } from '../../../client/components/use-reducer-with-devtools'
 import { reducer } from '../../../client/components/router-reducer/router-reducer'
 import { startTransition } from 'react'
+import { isThenable } from '../is-thenable'
 
 export type DispatchStatePromise = React.Dispatch<ReducerState>