fix(react-router): a lazy route follows a barrel that re-exports an import

[colbymchenry]

Problem

A lazily loaded folder whose index.ts passes on a page it imports linked nothing:

// Arshia76/DigiShop.Frontend, src/layout/index.ts
import { AdminLayout } from './AdminLayout'
import { UserLayout } from './UserLayout'

export { AdminLayout, UserLayout }

// src/App.tsx
lazy: async () => {
  const { UserLayout } = await import('@/layout')
  return { Component: UserLayout }
},

exportedComponent in src/resolution/frameworks/react.ts is the barrel walk behind lazy routes, React.lazy values and lazily loaded layouts (#2436, #2452, #2480). It reads the module's own export statement, then export … from and export *. For an export clause it looked for a declaration of that name in the barrel, but UserLayout there is an import binding, not a declaration, so it found nothing. The same happened for import Login from './Login'; export default Login, and for import { Page } from './page'; export { Page as Component }. All 27 lazy route refs in DigiShop's src/App.tsx stayed failed on main, and #2480's PR body listed this under "Not in this PR".

Fix

When the export names a binding with no declaration in the module, exportedComponent follows the module's import of that binding to the module it comes from. A default import continues as default, a named one by the name it imports. reads collects each file passed through, so lazyModules (#2452) still redraws the route when the page behind the import changes.

• A namespace import (import * as Tabs …; export { Tabs }) is no component, so it links nothing.
• A package's binding (import { Button } from '@mui/material'; export { Button }) doesn't resolve to a file, so it links nothing.
• export default withAuth(Page) hands over a call, not a binding. ownExport reads its first identifier (withAuth). That was harmless while only same-file declarations counted, but following imports would link the route to the imported HOC. So an export default X is followed only when the statement is the binding itself (exportsBinding), and the default stays unlinked, as on main.

Verification

Regression test. __tests__/react-router-barrel-imports.test.ts has 9 tests:

• 5 index cases: DigiShop's barrel, a barrel importing another barrel, export default of an imported binding, export { Page as Component }, and a React.lazy value through export { HelpPage as default }.
• 2 negative tests: a namespace and a package's binding link nothing, and so does export default withAuth(AccountPage).
• 2 sync cases: the page module appears later, and the imported page's default export moves.

On main, 7 of the 9 fail: every positive case and both sync cases. The 2 negative tests pass on main too, which is the point: they pin that the new step adds nothing there.

Checks.

• tsc --noEmit is clean, and so is a strict type-check of the test file.
• 16 related test files pass, 375 tests: React Router, lazy routes (fix(react-router): a lazy route links the page a barrel module forwards #2436, fix(react-router): a lazy route links the page its loader picks #2480), route sync (fix(sync): a route links the module it lazily loads when the module appears later #2422, fix(sync): a route rendering a same-file lazy value follows its module, and a new component gets its JSX edges #2452), import-binding sync, Vue/Angular routers, and frameworks.
• Full suite: 6,678 passed, 0 failed, 404 skipped (kernel-only and platform-gated).
• Mutation: dropping the export default binding check fails the withAuth case, which then links withAuth@src/hoc/withAuth.ts.

A/B on real repos (fresh codegraph init, main 5da4a41d vs this branch; only react.js differs between the builds)

50 repos:

• fix(react-router): a lazy route links the page a barrel module forwards #2436's 21-repo kit: milo/ui, medusa, outline, folo, bulletproof and others.
• The React apps from the JSX-route and import-first kits: refine's 281 examples, excalidraw, react.dev, binner, vanlife, proshop-v2, crwn-clothing, volun-mern and others.
• signoz's frontend and DigiShop.
• 7 apps from fix(react-router): a lazy route links the page its loader picks #2480's GitHub survey: qltt, toolbox, jotti, Serviceos, smartbook-system, prepify-frontend and Dreamer-UI.

Results:

• DigiShop.Frontend: 0 → 27 edges. These are the 13 pages behind @/pages and the 14 layout edges behind @/layout. Each lands on the declaration its barrel's import names; for example HomePage is in src/pages/Home/index.tsx, which src/pages/index.ts imports as { HomePage } from './Home'. No edge was retargeted or lost.
• 49 repos are byte-identical.

Sync. On DigiShop:

1. The 15 files the new edges land on were held out.
2. The app was indexed, the files put back, and codegraph sync run.
3. The 2 layouts relink: src/layout/UserLayout.tsx sits in the folder the route imports (@/layout), whose key the route's failed reference waits under.
4. The 13 pages don't. Each sits one folder below its barrel (src/pages/Home/index.tsx behind @/pages), and module:pages is not a key a file in pages/Home/ gives.

That is the limit #2436 recorded for export * barrels; see "Not in this PR". A fresh index links those pages, and so does a later edit of src/pages/index.ts.

Not in this PR

• A page added below its barrel's folder. A failed lazy-route reference is retried only by keys of the module it names, so a page that appears behind a nested barrel waits for a fresh index. The fix belongs in sync's failed-ref keying, for every barrel form, not in this walk.

Overlap

• fix(react): a JSX tag renders what the file imports under that name #2451 (open): adds the same step to the general import walk in import-resolver.ts, through clauseImports and exportedOrForwarded, for plain import { X } from './barrel'. This PR adds it to the lazy-route walk only, which fix(react): a JSX tag renders what the file imports under that name #2451 doesn't touch. The rule is the same: a clause name with no declaration is the module's import of it. Plain imports through such a barrel remain fix(react): a JSX tag renders what the file imports under that name #2451's to fix.
• fix(react): a component a file declares itself as a value is what its JSX renders #2420 (open, stale): its rewrite of lazyRouteComponent carried an import-forwarding step for import Login from './Login'; export default Login. exportedComponent (fix(react-router): a lazy route links the page a barrel module forwards #2436) superseded that walk, and this PR adds the step there, so fix(react): a component a file declares itself as a value is what its JSX renders #2420 can drop it when rebased.

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