next.js/packages/next/src/client/components/router-reducer/handle-segment-mismatch.ts

import type { FlightRouterState } from '../../../server/app-render/types'
import { handleExternalUrl } from './reducers/navigate-reducer'
import type {
  ReadonlyReducerState,
  ReducerActions,
} from './router-reducer-types'

/**
 * Handles the case where the client router attempted to patch the tree but, due to a mismatch, the patch failed.
 * This will perform an MPA navigation to return the router to a valid state.
 */
export function handleSegmentMismatch(
  state: ReadonlyReducerState,
  action: ReducerActions,
  treePatch: FlightRouterState
) {
  if (process.env.NODE_ENV === 'development') {
    console.warn(
      'Performing hard navigation because your application experienced an unrecoverable error. If this keeps occurring, please file a Next.js issue.\n\n' +
        'Reason: Segment mismatch\n' +
        `Last Action: ${action.type}\n\n` +
        `Current Tree: ${JSON.stringify(state.tree)}\n\n` +
        `Tree Patch Payload: ${JSON.stringify(treePatch)}`
    )
  }

  return handleExternalUrl(state, {}, state.canonicalUrl, true)
}