fix(vite): preserve names for exports from .client imports

.changeset/rude-keys-heal.md

@@ -0,0 +1,15 @@
+---
+"@remix-run/dev": patch
+---
+
+Vite: Preserve names for exports from .client imports
+
+Unlike `.server` modules, the main idea is not to prevent code from leaking into the server build
+since the client build is already public. Rather, the goal is to isolate the SSR render from client-only code.
+Routes need to import code from `.client` modules without compilation failing and then rely on runtime checks 
+to determine if the code is running on the server or client.
+
+Replacing `.client` modules with empty modules would cause the build to fail as ESM named imports are statically analyzed.
+So instead, we preserve the named export but replace each exported value with an empty object.
+That way, the import is valid at build time and the standard runtime checks can be used to determine if then
+code is running on the server or client.

integration/helpers/vite.ts

@@ -9,6 +9,8 @@ import resolveBin from "resolve-bin";
 import stripIndent from "strip-indent";
 import waitOn from "wait-on";
 import getPort from "get-port";
+import shell from "shelljs";
+import glob from "glob";
 
 const __dirname = url.fileURLToPath(new URL(".", import.meta.url));
 
@@ -249,3 +251,17 @@ export function createEditor(projectDir: string) {
     await fs.writeFile(filepath, transform(contents), "utf8");
   };
 }
+
+export function grep(cwd: string, pattern: RegExp): string[] {
+  let assetFiles = glob.sync("**/*.@(js|jsx|ts|tsx)", {
+    cwd,
+    absolute: true,
+  });
+
+  let lines = shell
+    .grep("-l", pattern, assetFiles)
+    .stdout.trim()
+    .split("\n")
+    .filter((line) => line.length > 0);
+  return lines;
+}

integration/vite-dot-client-test.ts

@@ -0,0 +1,48 @@
+import * as path from "node:path";
+import { test, expect } from "@playwright/test";
+
+import { createProject, grep, viteBuild } from "./helpers/vite.js";
+
+let files = {
+  "app/utils.client.ts": String.raw`
+    export const dotClientFile = "CLIENT_ONLY_FILE";
+    export default dotClientFile;
+  `,
+  "app/.client/utils.ts": String.raw`
+    export const dotClientDir = "CLIENT_ONLY_DIR";
+    export default dotClientDir;
+  `,
+};
+
+test("Vite / client code excluded from server bundle", async () => {
+  let cwd = await createProject({
+    ...files,
+    "app/routes/dot-client-imports.tsx": String.raw`
+      import { dotClientFile } from "../utils.client";
+      import { dotClientDir } from "../.client/utils";
+
+      export default function() {
+        const [mounted, setMounted] = useState(false);
+
+        useEffect(() => {
+          setMounted(true);
+        }, []);
+
+        return (
+          <>
+            <h2>Index</h2>
+            <p>{mounted ? dotClientFile + dotClientDir : ""}</p>
+          </>
+        );
+      }
+    `,
+  });
+  let [client, server] = viteBuild({ cwd });
+  expect(client.status).toBe(0);
+  expect(server.status).toBe(0);
+  let lines = grep(
+    path.join(cwd, "build/server"),
+    /CLIENT_ONLY_FILE|CLIENT_ONLY_DIR/
+  );
+  expect(lines).toHaveLength(0);
+});

integration/vite-dot-server-test.ts

@@ -1,9 +1,7 @@
 import * as path from "node:path";
 import { test, expect } from "@playwright/test";
-import shell from "shelljs";
-import glob from "glob";
 
-import { createProject, viteBuild } from "./helpers/vite.js";
+import { createProject, grep, viteBuild } from "./helpers/vite.js";
 
 let files = {
   "app/utils.server.ts": String.raw`
@@ -198,17 +196,3 @@ test("Vite / dead-code elimination for server exports", async () => {
   );
   expect(lines).toHaveLength(0);
 });
-
-function grep(cwd: string, pattern: RegExp): string[] {
-  let assetFiles = glob.sync("**/*.@(js|jsx|ts|tsx)", {
-    cwd,
-    absolute: true,
-  });
-
-  let lines = shell
-    .grep("-l", pattern, assetFiles)
-    .stdout.trim()
-    .split("\n")
-    .filter((line) => line.length > 0);
-  return lines;
-}

packages/remix-dev/vite/plugin.ts

@@ -938,14 +938,21 @@ export const remixVitePlugin: RemixVitePlugin = (options = {}) => {
     },
     {
       name: "remix-empty-client-modules",
-      enforce: "pre",
-      async transform(_code, id, options) {
+      enforce: "post",
+      async transform(code, id, options) {
         if (!options?.ssr) return;
         let clientFileRE = /\.client(\.[cm]?[jt]sx?)?$/;
         let clientDirRE = /\/\.client\//;
         if (clientFileRE.test(id) || clientDirRE.test(id)) {
+          let exports = esModuleLexer(code)[1];
           return {
-            code: "export {}",
+            code: exports
+              .map(({ n: name }) =>
+                name === "default"
+                  ? "export default {};"
+                  : `export const ${name} = {};`
+              )
+              .join("\n"),
             map: null,
           };
         }