Fix generatePath when passed a zero value param

.changeset/purple-islands-cough.md

@@ -0,0 +1,5 @@
+---
+"react-router": patch
+---
+
+Fix `generatePath` when passed a numeric `0` value parameter

packages/react-router/__tests__/generatePath-test.tsx

@@ -44,6 +44,14 @@ describe("generatePath", () => {
         })
       ).toBe("/courses/foo*");
     });
+    it("handles a 0 parameter", () => {
+      // @ts-expect-error
+      // incorrect usage but worked in 6.3.0 so keep it to avoid the regression
+      expect(generatePath("/courses/:id", { id: 0 })).toBe("/courses/0");
+      // @ts-expect-error
+      // incorrect usage but worked in 6.3.0 so keep it to avoid the regression
+      expect(generatePath("/courses/*", { "*": 0 })).toBe("/courses/0");
+    });
   });
 
   describe("with extraneous params", () => {

packages/router/utils.ts

@@ -762,6 +762,9 @@ export function generatePath<Path extends string>(
   // ensure `/` is added at the beginning if the path is absolute
   const prefix = path.startsWith("/") ? "/" : "";
 
+  const stringify = (p: any) =>
+    p == null ? "" : typeof p === "string" ? p : String(p);
+
   const segments = path
     .split(/\/+/)
     .map((segment, index, array) => {
@@ -770,26 +773,16 @@ export function generatePath<Path extends string>(
       // only apply the splat if it's the last segment
       if (isLastSegment && segment === "*") {
         const star = "*" as PathParam<Path>;
-        const starParam = params[star];
-
         // Apply the splat
-        return starParam;
+        return stringify(params[star]);
       }
 
       const keyMatch = segment.match(/^:(\w+)(\??)$/);
       if (keyMatch) {
         const [, key, optional] = keyMatch;
         let param = params[key as PathParam<Path>];
-
-        if (optional === "?") {
-          return param == null ? "" : param;
-        }
-
-        if (param == null) {
-          invariant(false, `Missing ":${key}" param`);
-        }
-
-        return param;
+        invariant(optional === "?" || param != null, `Missing ":${key}" param`);
+        return stringify(param);
       }
 
       // Remove any optional markers from optional static segments