fix(plugin-vite): register co-located islands added while dev server runs

packages/plugin-vite/src/plugins/client_snapshot.ts

@@ -163,19 +163,25 @@ if (import.meta.hot) {
   ];
 }
 
-function isIslandPath(
+/**
+ * A `(_islands)` path segment marks a local island folder, the same
+ * convention the initial route crawl uses.
+ */
+const LOCAL_ISLAND_REG = /[/\\]\(_islands\)[/\\]/;
+
+export function isIslandPath(
   options: ResolvedFreshViteConfig,
   filePath: string,
 ): boolean {
   const relIsland = path.relative(options.islandsDir, filePath);
   if (!relIsland.startsWith("..")) return true;
 
   const relRoutes = path.relative(options.routeDir, filePath);
+  if (relRoutes.startsWith("..")) return false;
 
-  if (!relIsland.startsWith("..") && relRoutes.includes("(_islands)")) {
-    return true;
-  }
-  return false;
+  // Leading separator so that a `(_islands)` folder sitting directly in the
+  // route dir matches too.
+  return LOCAL_ISLAND_REG.test(`${path.SEPARATOR}${relRoutes}`);
 }
 
 function invalidateSnapshots(server: ViteDevServer) {

packages/plugin-vite/src/plugins/client_snapshot_test.ts

@@ -0,0 +1,58 @@
+import { expect } from "@std/expect/expect";
+import * as path from "@std/path";
+import { isIslandPath } from "./client_snapshot.ts";
+import type { ResolvedFreshViteConfig } from "../utils.ts";
+
+const ROOT = path.join(path.SEPARATOR, "project");
+
+const options = {
+  islandsDir: path.join(ROOT, "islands"),
+  routeDir: path.join(ROOT, "routes"),
+} as ResolvedFreshViteConfig;
+
+Deno.test("client snapshot - isIslandPath detects the islands dir", () => {
+  expect(isIslandPath(options, path.join(ROOT, "islands", "Counter.tsx")))
+    .toBe(true);
+  expect(
+    isIslandPath(options, path.join(ROOT, "islands", "nested", "Counter.tsx")),
+  ).toBe(true);
+});
+
+Deno.test("client snapshot - isIslandPath detects local island folders", () => {
+  expect(
+    isIslandPath(options, path.join(ROOT, "routes", "(_islands)", "Foo.tsx")),
+  ).toBe(true);
+  // Inside a route group.
+  expect(
+    isIslandPath(
+      options,
+      path.join(ROOT, "routes", "(marketing)", "(_islands)", "Foo.tsx"),
+    ),
+  ).toBe(true);
+  // And inside a plain route folder.
+  expect(
+    isIslandPath(
+      options,
+      path.join(ROOT, "routes", "shop", "(_islands)", "Cart.tsx"),
+    ),
+  ).toBe(true);
+});
+
+Deno.test("client snapshot - isIslandPath ignores everything else", () => {
+  expect(isIslandPath(options, path.join(ROOT, "routes", "index.tsx")))
+    .toBe(false);
+  // Another route group is not an island folder.
+  expect(
+    isIslandPath(
+      options,
+      path.join(ROOT, "routes", "(_components)", "Head.tsx"),
+    ),
+  ).toBe(false);
+  // `(_islands)` has to be a path segment, not a substring.
+  expect(
+    isIslandPath(options, path.join(ROOT, "routes", "(_islands)x", "Foo.tsx")),
+  ).toBe(false);
+  // Outside both dirs, even when the name matches.
+  expect(isIslandPath(options, path.join(ROOT, "(_islands)", "Foo.tsx")))
+    .toBe(false);
+});