fix(remix-dev): make MDX builds deterministic

This is a fix along the lines of remix-run#2027; because the MDX virtual modules
resolve to absolute paths, the manifest/hashes/etc. differ based on the
parent directory structure.

Testing notes:
1. Expanded existing integration test to cover this scenario (fails without
   the fix). Also add other virtual module scenarios that weren't already
   covered
2. Validated in a real MDX Remix app that has split client / server builds
   (applied fix via patch-package)

.changeset/purple-ligers-drive.md

@@ -0,0 +1,5 @@
+---
+"@remix-run/dev": patch
+---
+
+Make MDX builds deterministic

integration/deterministic-build-output-test.ts

@@ -3,11 +3,35 @@ import globby from "globby";
 import fs from "fs";
 import path from "path";
 
-import { createFixtureProject } from "./helpers/create-fixture";
+import { createFixtureProject, js } from "./helpers/create-fixture";
 
 test("builds deterministically under different paths", async () => {
-  let dir1 = await createFixtureProject();
-  let dir2 = await createFixtureProject();
+  // This test validates various flavors of remix virtual modules to ensure
+  // we get identical builds regardless of the parent paths. If a virtual
+  // module resolves or imports from absolute paths (e.g. via `path.resolve`),
+  // the build hashes may change even though the output is identical. This
+  // can cause broken apps (i.e. manifest mismatch) if the server and client
+  // are built separately.
+
+  // Virtual modules tested:
+  //  * browserRouteModulesPlugin (implicitly tested by root route)
+  //  * emptyModulesPlugin (via app/routes/foo.tsx' server import)
+  //  * mdx (via app/routes/index.mdx)
+  //  * serverAssetsManifestPlugin (implicitly tested by build)
+  //  * serverEntryModulePlugin (implicitly tested by build)
+  //  * serverRouteModulesPlugin (implicitly tested by build)
+  let init = {
+    files: {
+      "app/routes/index.mdx": "# hello world",
+      "app/routes/foo.tsx": js`
+        export * from "~/foo/bar.server";
+        export default () => "YAY";
+      `,
+      "app/foo/bar.server.ts": "export const meta = () => []",
+    },
+  };
+  let dir1 = await createFixtureProject(init);
+  let dir2 = await createFixtureProject(init);
 
   expect(dir1).not.toEqual(dir2);
 

packages/remix-dev/compiler/plugins/mdx.ts

@@ -39,14 +39,15 @@ export function mdxPlugin(config: RemixConfig): esbuild.Plugin {
         let resolved = path.resolve(args.resolveDir, resolvedPath);
 
         return {
-          path: resolved,
+          path: path.relative(config.appDirectory, resolved),
           namespace: "mdx",
         };
       });
 
       build.onLoad({ filter: /\.mdx?$/ }, async (args) => {
+        let absolutePath = path.join(config.appDirectory, args.path);
         try {
-          let fileContents = await fsp.readFile(args.path, "utf-8");
+          let fileContents = await fsp.readFile(absolutePath, "utf-8");
 
           let rehypePlugins = [];
           let remarkPlugins = [
@@ -115,7 +116,7 @@ ${remixExports}`;
             errors: errors.length ? errors : undefined,
             warnings: warnings.length ? warnings : undefined,
             contents,
-            resolveDir: path.dirname(args.path),
+            resolveDir: path.dirname(absolutePath),
             loader: getLoaderForFile(args.path),
           };
         } catch (err: any) {