Typesafe useRouteLoaderData behind future flag

.changeset/eleven-insects-tickle.md

@@ -0,0 +1,6 @@
+---
+"@react-router/dev": minor
+"react-router": minor
+---
+
+Add a new `typesafeUseRouteLoaderData` future flag, which, when enabled, improves the type of `useRouteLoaderData` with inference and errors.

contributors.yml

@@ -136,6 +136,7 @@
 - jenseng
 - JeraldVin
 - JesusTheHun
+- jeyj0
 - jimniels
 - jmargeta
 - johnpangalos

packages/react-router-dev/config/config.ts

@@ -85,6 +85,7 @@ type ServerModuleFormat = "esm" | "cjs";
 
 interface FutureConfig {
   unstable_optimizeDeps: boolean;
+  typesafeUseRouteLoaderData: boolean;
 }
 
 export type BuildManifest = DefaultBuildManifest | ServerBundlesBuildManifest;
@@ -482,6 +483,8 @@ async function resolveConfig({
   let future: FutureConfig = {
     unstable_optimizeDeps:
       reactRouterUserConfig.future?.unstable_optimizeDeps ?? false,
+    typesafeUseRouteLoaderData:
+      reactRouterUserConfig.future?.typesafeUseRouteLoaderData ?? false,
   };
 
   let reactRouterConfig: ResolvedReactRouterConfig = deepFreeze({

packages/react-router-dev/typegen/generate.ts

@@ -4,7 +4,7 @@ import * as Pathe from "pathe/utils";
 
 import { type RouteManifest, type RouteManifestEntry } from "../config/routes";
 import { type Context } from "./context";
-import { getTypesPath } from "./paths";
+import { getTypesDir, getTypesPath } from "./paths";
 
 export function generate(ctx: Context, route: RouteManifestEntry): string {
   const lineage = getRouteLineage(ctx.config.routes, route);
@@ -120,3 +120,44 @@ function parseParams(urlpath: string) {
   if (hasSplat) result["*"] = [false];
   return result;
 }
+
+export function generateRouteManifest(ctx: Context) {
+  return ts`
+    export type RouteManifest = {
+      ${Object.entries(ctx.config.routes)
+        .map(([routeId, routeEntry], i) => {
+          const indent = i === 0 ? "" : "  ".repeat(3);
+          const routeTypeFile = Path.relative(
+            getTypesDir(ctx),
+            getTypesPath(ctx, routeEntry)
+          );
+          return `${indent}"${routeId}": import("./${routeTypeFile}").Info,`;
+        })
+        .join("\n")}
+    };
+
+    export type RouteId = keyof RouteManifest;
+  `;
+}
+
+export function generateUseRouteLoaderDataType(ctx: Context) {
+  if (ctx.config.future.typesafeUseRouteLoaderData) {
+    return ts`
+      import type { RouteId, RouteManifest } from "./routeManifest";
+
+      declare module "react-router" {
+        export function useRouteLoaderData<RI extends RouteId>(
+          id: RI,
+        ): RouteManifest[RI]["loaderData"] | undefined;
+      }
+    `;
+  }
+
+  return ts`
+    declare module "react-router" {
+      export function useRouteLoaderData<T = any>(
+        routeId: string
+      ): SerializeFrom<T> | undefined;
+    }
+  `;
+}

packages/react-router-dev/typegen/index.ts

@@ -6,9 +6,13 @@ import type vite from "vite";
 
 import { createConfigLoader } from "../config/config";
 
-import { generate } from "./generate";
+import {
+  generate,
+  generateRouteManifest,
+  generateUseRouteLoaderDataType,
+} from "./generate";
 import type { Context } from "./context";
-import { getTypesDir, getTypesPath } from "./paths";
+import { getTypesDir, getTypesPath, getGlobalTypesFilePath } from "./paths";
 
 export async function run(rootDirectory: string) {
   const ctx = await createContext({ rootDirectory, watch: false });
@@ -81,4 +85,17 @@ async function writeAll(ctx: Context): Promise<void> {
     fs.mkdirSync(Path.dirname(typesPath), { recursive: true });
     fs.writeFileSync(typesPath, content);
   });
+
+  const useRouteLoaderDataContent = generateUseRouteLoaderDataType(ctx);
+  const useRouteLoaderDataTypesPath = getGlobalTypesFilePath(
+    ctx,
+    "useRouteLoaderData"
+  );
+  fs.writeFileSync(useRouteLoaderDataTypesPath, useRouteLoaderDataContent);
+
+  if (ctx.config.future.typesafeUseRouteLoaderData) {
+    const routeManifestContent = generateRouteManifest(ctx);
+    const routeManifestPath = getGlobalTypesFilePath(ctx, "routeManifest");
+    fs.writeFileSync(routeManifestPath, routeManifestContent);
+  }
 }

packages/react-router-dev/typegen/paths.ts

@@ -16,3 +16,7 @@ export function getTypesPath(ctx: Context, route: RouteManifestEntry) {
     "+types/" + Pathe.filename(route.file) + ".ts"
   );
 }
+
+export function getGlobalTypesFilePath(ctx: Context, fileName: string) {
+  return Path.join(getTypesDir(ctx), Pathe.filename(fileName) + ".d.ts");
+}

packages/react-router/lib/hooks.tsx

@@ -1117,7 +1117,7 @@ export function useLoaderData<T = any>(): SerializeFrom<T> {
   @category Hooks
  */
 export function useRouteLoaderData<T = any>(
-  routeId: string
+  routeId: never // actually string after typegen; never allows typesafeUseRouteLoaderData future flag to work
 ): SerializeFrom<T> | undefined {
   let state = useDataRouterState(DataRouterStateHook.UseRouteLoaderData);
   return state.loaderData[routeId] as SerializeFrom<T> | undefined;