Helper type to narrow route props

README.md

@@ -261,6 +261,16 @@ The difference between `/:id*` and `/:id/*` is that in the former, the `id` para
   - `/profile/:id/*`, with `/profile/123/abc`
     - `id` is `123`
 
+You can narrow prop types for your routes using `RoutePropsForPath<path>`:
+```js
+import type { RoutePropsForPath } from 'preact-iso/router'
+
+function User(props: RoutePropsForPath<'/user/:id'>) {
+	props.user.id2 // type error
+	props.user.id // no type error
+}
+```
+
 ### `useLocation`
 
 A hook to work with the `LocationProvider` to access location context.

src/router.d.ts

@@ -59,6 +59,32 @@ type RoutableProps =
 
 export type RouteProps<Props> = RoutableProps & { component: AnyComponent<Props> };
 
+export type RoutePropsForPath<Path extends string> = Path extends '*'
+	? { params: {}; rest: string }
+
+	: Path extends `:${infer placeholder}?/${infer rest}`
+	? { [k in placeholder]?: string } & { params: RoutePropsForPath<rest>['params'] & { [k in placeholder]?: string } } & Omit<RoutePropsForPath<rest>, 'params'>
+
+	: Path extends `:${infer placeholder}/${infer rest}`
+	? { [k in placeholder]: string } & { params: RoutePropsForPath<rest>['params'] & { [k in placeholder]: string } } & Omit<RoutePropsForPath<rest>, 'params'>
+
+	: Path extends `:${infer placeholder}?`
+	? { [k in placeholder]?: string } & { params: { [k in placeholder]?: string } }
+
+	: Path extends `:${infer placeholder}*`
+	? { [k in placeholder]?: string } & { params: { [k in placeholder]?: string } }
+
+	: Path extends `:${infer placeholder}+`
+	? { [k in placeholder]: string } & { params: { [k in placeholder]: string } }
+
+	: Path extends `:${infer placeholder}`
+	? { [k in placeholder]: string } & { params: { [k in placeholder]: string } }
+
+	: Path extends (`/${infer rest}` | `${infer _}/${infer rest}`)
+	? RoutePropsForPath<rest>
+
+	: { params: {} };
+
 export function Route<Props>(props: RouteProps<Props> & Partial<Props>): VNode;
 
 declare module 'preact' {

test/node/pattern-match.types.ts

@@ -0,0 +1,103 @@
+// Test this file by running:
+// npx tsc --noEmit test/node/pattern-match.types.ts
+
+import type { RoutePropsForPath } from '../../src/router.js';
+
+// Test utils
+
+type isEqualsType<T, U> = T extends U ? U extends T ? true : false : false;
+type isWeakEqualsType<T, U> = T extends U ? true : false;
+
+// Type tests based on router-match.test.js cases
+
+// Base route test
+const test1: isEqualsType<
+  RoutePropsForPath<'/'> ,
+	{ params: {} }
+> = true;
+
+const test1_1: isEqualsType<
+  RoutePropsForPath<'/'> ,
+	{ arbitrary: {} }
+> = false;
+
+// Param route test
+const test2: isEqualsType<
+  RoutePropsForPath<'/user/:id'> ,
+  { params: { id: string }, id: string }
+> = true;
+
+const test2_weak: isWeakEqualsType<
+  RoutePropsForPath<'/user/:id'> ,
+  { params: { id: string } }
+> = true;
+
+// Param rest segment test
+const test3: isEqualsType<
+  RoutePropsForPath<'/user/*'> ,
+  { params: {}, rest: string }
+> = true;
+
+const test3_1: isEqualsType<
+  RoutePropsForPath<'/*'> ,
+  { params: {}, rest: string }
+> = true;
+
+const test3_2: isEqualsType<
+  RoutePropsForPath<'*'> ,
+  { params: {}, rest: string }
+> = true;
+
+// Param route with rest segment test
+const test4: isEqualsType<
+  RoutePropsForPath<'/user/:id/*'> ,
+  { params: { id: string }, id: string, rest: string }
+> = true;
+
+// Optional param route test
+const test5: isEqualsType<
+  RoutePropsForPath<'/user/:id?'> ,
+	{ params: { id?: string }, id?: string }
+> = true;
+
+// Optional rest param route "/:x*" test
+const test6: isEqualsType<
+  RoutePropsForPath<'/user/:id*'> ,
+  { params: { id?: string }, id?: string }
+> = true;
+
+// rest param should not be present
+const test6_error: isEqualsType<
+  RoutePropsForPath<'/user/:id*'> ,
+  { params: { id: string }, rest: string }
+> = false;
+
+// Rest param route "/:x+" test
+const test7: isEqualsType<
+  RoutePropsForPath<'/user/:id+'> ,
+  { params: { id: string }, id: string }
+> = true;
+
+// rest param should not be present
+const test7_error: isEqualsType<
+  RoutePropsForPath<'/user/:id+'>,
+  { params: { id: string }, id: string, rest: string }
+> = false;
+
+// Handles leading/trailing slashes test
+const test8: isEqualsType<
+  RoutePropsForPath<'/about-late/:seg1/:seg2/'> ,
+  { params: { seg1: string; seg2: string }, seg1: string, seg2: string }
+> = true;
+
+// Multiple params test (from overwrite properties test)
+const test9: isEqualsType<
+  RoutePropsForPath<'/:path/:query'> ,
+  { params: { path: string; query: string }, path: string, query: string }
+> = true;
+
+// Empty route test
+const test10: isEqualsType<
+  RoutePropsForPath<''> ,
+  { params: {} }
+> = true;