feat: allow Link's "to" prop to accept external urls

.changeset/silent-oranges-pay.md

@@ -0,0 +1,11 @@
+---
+"react-router": patch
+"react-router-dom": patch
+---
+
+allow using `<Link>` with external URLs
+
+```tsx
+<Link to="//example.com/some/path">
+<Link to="https://www.currentorigin.com/path">
+```

package.json

@@ -120,7 +120,7 @@
       "none": "11 kB"
     },
     "packages/react-router-dom/dist/umd/react-router-dom.production.min.js": {
-      "none": "16.5 kB"
+      "none": "16.7 kB"
     }
   }
 }

packages/react-router-dom/__tests__/link-href-test.tsx

@@ -89,6 +89,45 @@ describe("<Link> href", () => {
         ["/about", "/about"]
       );
     });
+
+    test('<Link to="https://remix.run"> is treated as external link', () => {
+      let renderer: TestRenderer.ReactTestRenderer;
+      TestRenderer.act(() => {
+        renderer = TestRenderer.create(
+          <MemoryRouter initialEntries={["/inbox/messages"]}>
+            <Routes>
+              <Route path="inbox">
+                <Route
+                  path="messages"
+                  element={<Link to="https://remix.run" />}
+                />
+              </Route>
+            </Routes>
+          </MemoryRouter>
+        );
+      });
+
+      expect(renderer.root.findByType("a").props.href).toEqual(
+        "https://remix.run"
+      );
+    });
+
+    test('<Link to="//remix.run"> is treated as external link', () => {
+      let renderer: TestRenderer.ReactTestRenderer;
+      TestRenderer.act(() => {
+        renderer = TestRenderer.create(
+          <MemoryRouter initialEntries={["/inbox/messages"]}>
+            <Routes>
+              <Route path="inbox">
+                <Route path="messages" element={<Link to="//remix.run" />} />
+              </Route>
+            </Routes>
+          </MemoryRouter>
+        );
+      });
+
+      expect(renderer.root.findByType("a").props.href).toEqual("//remix.run");
+    });
   });
 
   describe("in a dynamic route", () => {

packages/react-router-dom/index.tsx

@@ -391,6 +391,11 @@ export interface LinkProps
   to: To;
 }
 
+const isBrowser =
+  typeof window !== "undefined" &&
+  typeof window.document !== "undefined" &&
+  typeof window.document.createElement !== "undefined";
+
 /**
  * The public API for rendering a history-aware <a>.
  */
@@ -409,8 +414,32 @@ export const Link = React.forwardRef<HTMLAnchorElement, LinkProps>(
     },
     ref
   ) {
-    let href = useHref(to, { relative });
-    let internalOnClick = useLinkClickHandler(to, {
+    // `location` is the unaltered href we will render in the <a> tag for absolute URLs
+    let location = typeof to === "string" ? to : createPath(to);
+    let isAbsolute =
+      /^[a-z+]+:\/\//i.test(location) || location.startsWith("//");
+
+    // Location to use in the click handler
+    let navigationLocation = location;
+    let isExternal = false;
+    if (isBrowser && isAbsolute) {
+      let currentUrl = new URL(window.location.href);
+      let targetUrl = location.startsWith("//")
+        ? new URL(currentUrl.protocol + location)
+        : new URL(location);
+      if (targetUrl.origin === currentUrl.origin) {
+        // Strip the protocol/origin for same-origin absolute URLs
+        navigationLocation =
+          targetUrl.pathname + targetUrl.search + targetUrl.hash;
+      } else {
+        isExternal = true;
+      }
+    }
+
+    // `href` is what we render in the <a> tag for relative URLs
+    let href = useHref(navigationLocation, { relative });
+
+    let internalOnClick = useLinkClickHandler(navigationLocation, {
       replace,
       state,
       target,
@@ -430,8 +459,8 @@ export const Link = React.forwardRef<HTMLAnchorElement, LinkProps>(
       // eslint-disable-next-line jsx-a11y/anchor-has-content
       <a
         {...rest}
-        href={href}
-        onClick={reloadDocument ? onClick : handleClick}
+        href={isAbsolute ? location : href}
+        onClick={isExternal || reloadDocument ? onClick : handleClick}
         ref={ref}
         target={target}
       />