fix: TypeScript compatibility with exactOptionalPropertyTypes: true

[0372hoanghoccode]

Fixes #14734

Summary

This PR fixes TypeScript compatibility when exactOptionalPropertyTypes: true is enabled in tsconfig.json.

Problem

When exactOptionalPropertyTypes is enabled, TypeScript requires optional properties to explicitly allow undefined. The generated types from react-router typegen were causing type errors:

Type 'undefined' is not assignable to type 'Func'

This occurred because:

• Route modules have optional exports like action?: () => {...}
• When importing: typeof import('./root') → { action: (() => ...) | undefined }
• With exactOptionalPropertyTypes: true: action?: Func ≠ action: Func | undefined

Solution

1. Added StrictOptionals type helper in packages/react-router/lib/types/utils.ts

   • Converts { action: Func | undefined } to { action?: Func }

2. Runtime detection in packages/react-router-dev/typegen/generate.ts

   • Detects exactOptionalPropertyTypes setting in tsconfig.json

3. Conditional type wrapping in generated code

   • When exactOptionalPropertyTypes: true: type Module = StrictOptionals<typeof import(...)>
   • Otherwise: type Module = typeof import(...)

4. Exported StrictOptionals via react-router/internal for generated code to use

Testing

• Added integration test exactOptionalPropertyTypes compatibility in integration/typegen-test.ts
• Verifies type inference works correctly with exactOptionalPropertyTypes: true

Changes

• packages/react-router/lib/types/utils.ts - Added StrictOptionals type
• packages/react-router/lib/types/internal.ts - Exported StrictOptionals
• packages/react-router-dev/typegen/generate.ts - Detection and conditional wrapping
• integration/typegen-test.ts - Integration test
• .changeset/fix-exact-optional-property-types.md - Changeset

[changeset-bot]

🦋 Changeset detected

Latest commit: 08d06ec

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 11 packages

Name	Type
react-router	Patch
@react-router/dev	Patch
@react-router/architect	Patch
@react-router/cloudflare	Patch
react-router-dom	Patch
@react-router/express	Patch
@react-router/node	Patch
@react-router/serve	Patch
@react-router/fs-routes	Patch
@react-router/remix-routes-option-adapter	Patch
create-react-router	Patch

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[remix-cla-bot]

Thank you for signing the Contributor License Agreement. Let's get this merged! 🥳

[0372hoanghoccode]

I've fixed the Windows test failure in flatRoutes-test.ts by using path.posix.join for cross-platform compatibility.

The remaining CI failures (route-config-test.ts, data-browser-router-test.tsx, special-characters-test.tsx) are pre-existing issues in the dev branch - they also fail when testing dev directly on Windows. These failures are not related to my TypeScript changes for exactOptionalPropertyTypes.

My changes only modified:

• TypeScript type definitions to support exactOptionalPropertyTypes: true
• Fixed Windows path issue in flatRoutes-test.ts