ref(nextjs): Use virtual rather than temporary file for proxy module

packages/nextjs/package.json

@@ -18,6 +18,7 @@
   },
   "dependencies": {
     "@rollup/plugin-sucrase": "4.0.4",
+    "@rollup/plugin-virtual": "3.0.0",
     "@sentry/core": "7.16.0",
     "@sentry/integrations": "7.16.0",
     "@sentry/node": "7.16.0",

packages/nextjs/src/config/loaders/proxyLoader.ts

@@ -50,34 +50,21 @@ export default async function proxyLoader(this: LoaderThis<LoaderOptions>, userC
   // Make sure the template is included when runing `webpack watch`
   this.addDependency(templatePath);
 
-  // Inject the route into the template
+  // Inject the route and the path to the file we're wrapping into the template
   templateCode = templateCode.replace(/__ROUTE__/g, parameterizedRoute);
-
-  // Fill in the path to the file we're wrapping and save the result as a temporary file in the same folder (so that
-  // relative imports and exports are calculated correctly).
-  //
-  // TODO: We're saving the filled-in template to disk, however temporarily, because Rollup expects a path to a code
-  // file, not code itself. There is a rollup plugin which can fake this (`@rollup/plugin-virtual`) but the virtual file
-  // seems to be inside of a virtual directory (in other words, one level down from where you'd expect it) and that
-  // messes up relative imports and exports. Presumably there's a way to make it work, though, and if we can, it would
-  // be cleaner than having to first write and then delete a temporary file each time we run this loader.
   templateCode = templateCode.replace(/__RESOURCE_PATH__/g, this.resourcePath);
-  const tempFilePath = path.resolve(path.dirname(this.resourcePath), `temp${Math.random()}.js`);
-  fs.writeFileSync(tempFilePath, templateCode);
 
   // Run the proxy module code through Rollup, in order to split the `export * from '<wrapped file>'` out into
-  // individual exports (which nextjs seems to require), then delete the tempoary file.
+  // individual exports (which nextjs seems to require).
   let proxyCode;
   try {
-    proxyCode = await rollupize(tempFilePath, this.resourcePath);
+    proxyCode = await rollupize(templateCode, this.resourcePath);
   } catch (err) {
     __DEBUG_BUILD__ &&
       logger.warn(
         `Could not wrap ${this.resourcePath}. An error occurred while processing the proxy module template:\n${err}`,
       );
     return userCode;
-  } finally {
-    fs.unlinkSync(tempFilePath);
   }
 
   // Add a query string onto all references to the wrapped file, so that webpack will consider it different from the

packages/nextjs/src/config/loaders/rollup.ts

@@ -1,12 +1,20 @@
 import sucrase from '@rollup/plugin-sucrase';
+import virtual from '@rollup/plugin-virtual';
+import { escapeStringForRegex } from '@sentry/utils';
 import * as path from 'path';
 import type { InputOptions as RollupInputOptions, OutputOptions as RollupOutputOptions } from 'rollup';
 import { rollup } from 'rollup';
 
-const getRollupInputOptions = (proxyPath: string, userModulePath: string): RollupInputOptions => ({
-  input: proxyPath,
+const SENTRY_PROXY_MODULE_NAME = 'sentry-proxy-module';
+
+const getRollupInputOptions = (templateCode: string, userModulePath: string): RollupInputOptions => ({
+  input: SENTRY_PROXY_MODULE_NAME,
 
   plugins: [
+    virtual({
+      [SENTRY_PROXY_MODULE_NAME]: templateCode,
+    }),
+
     sucrase({
       transforms: ['jsx', 'typescript'],
     }),
@@ -17,7 +25,7 @@ const getRollupInputOptions = (proxyPath: string, userModulePath: string): Rollu
   // otherwise they won't be processed. (We need Rollup to process the former so that we can use the code, and we need
   // it to process the latter so it knows what exports to re-export from the proxy module.) Past that, we don't care, so
   // don't bother to process anything else.
-  external: importPath => importPath !== proxyPath && importPath !== userModulePath,
+  external: importPath => importPath !== SENTRY_PROXY_MODULE_NAME && importPath !== userModulePath,
 
   // Prevent rollup from stressing out about TS's use of global `this` when polyfilling await. (TS will polyfill if the
   // user's tsconfig `target` is set to anything before `es2017`. See https://stackoverflow.com/a/72822340 and
@@ -53,34 +61,44 @@ const rollupOutputOptions: RollupOutputOptions = {
 };
 
 /**
- * Use Rollup to process the proxy module file (located at `tempProxyFilePath`) in order to split its `export * from
- * '<wrapped file>'` call into individual exports (which nextjs seems to need).
+ * Use Rollup to process the proxy module code, in order to split its `export * from '<wrapped file>'` call into
+ * individual exports (which nextjs seems to need).
  *
  * Note: Any errors which occur are handled by the proxy loader which calls this function.
  *
- * @param tempProxyFilePath The path to the temporary file containing the proxy module code
+ * @param templateCode The proxy module code
  * @param userModulePath The path to the file being wrapped
  * @returns The processed proxy module code
  */
-export async function rollupize(tempProxyFilePath: string, userModulePath: string): Promise<string> {
-  const intermediateBundle = await rollup(getRollupInputOptions(tempProxyFilePath, userModulePath));
+export async function rollupize(templateCode: string, userModulePath: string): Promise<string> {
+  const intermediateBundle = await rollup(getRollupInputOptions(templateCode, userModulePath));
   const finalBundle = await intermediateBundle.generate(rollupOutputOptions);
 
   // The module at index 0 is always the entrypoint, which in this case is the proxy module.
   let { code } = finalBundle.output[0];
 
-  // Rollup does a few things to the code we *don't* want. Undo those changes before returning the code.
+  // In addition to doing the desired work, Rollup also does a few things we *don't* want. Specifically, in messes up
+  // the path in both `import * as origModule from '<userModulePath>'` and `export * from '<userModulePath>'`.
   //
-  // Nextjs uses square brackets surrounding a path segment to denote a parameter in the route, but Rollup turns those
-  // square brackets into underscores. Further, Rollup adds file extensions to bare-path-type import and export sources.
-  // Because it assumes that everything will have already been processed, it always uses `.js` as the added extension.
-  // We need to restore the original name and extension so that Webpack will be able to find the wrapped file.
-  const userModuleFilename = path.basename(userModulePath);
-  const mutatedUserModuleFilename = userModuleFilename
-    // `[\\[\\]]` is the character class containing `[` and `]`
-    .replace(new RegExp('[\\[\\]]', 'g'), '_')
-    .replace(/(jsx?|tsx?)$/, 'js');
-  code = code.replace(new RegExp(mutatedUserModuleFilename, 'g'), userModuleFilename);
+  // - It turns the square brackets surrounding each parameterized path segment into underscores.
+  // - It always adds `.js` to the end of the filename.
+  // - It converts the path from aboslute to relative, which would be fine except that when used with the virual plugin,
+  //   it uses an incorrect (and not entirely predicable) base for that relative path.
+  //
+  // To fix this, we overwrite the messed up path with what we know it should be: `./<userModulePathBasename>`. (We can
+  // find the value of the messed up path by looking at what `import * as origModule from '<userModulePath>'` becomes.
+  // Because it's the first line of the template, it's also the first line of the result, and is therefore easy to
+  // find.)
+
+  const importStarStatement = code.split('\n')[0];
+  // This regex should always match (we control both the input and the process which generates it, so we can guarantee
+  // the outcome of that processing), but just in case it somehow doesn't, we need it to throw an error so that the
+  // proxy loader will know to return the user's code untouched rather than returning proxy module code including a
+  // broken path. The non-null assertion asserts that a match has indeed been found.
+  // eslint-disable-next-line @typescript-eslint/no-non-null-assertion
+  const messedUpPath = /^import \* as .* from '(.*)';$/.exec(importStarStatement)![1];
+
+  code = code.replace(new RegExp(escapeStringForRegex(messedUpPath), 'g'), `./${path.basename(userModulePath)}`);
 
   return code;
 }

yarn.lock

@@ -4231,6 +4231,11 @@
     "@rollup/pluginutils" "^4.1.1"
     sucrase "^3.20.0"
 
+"@rollup/[email protected]":
+  version "3.0.0"
+  resolved "https://registry.yarnpkg.com/@rollup/plugin-virtual/-/plugin-virtual-3.0.0.tgz#8c3f54b4ab4b267d9cd3dcbaedc58d4fd1deddca"
+  integrity sha512-K9KORe1myM62o0lKkNR4MmCxjwuAXsZEtIHpaILfv4kILXTOrXt/R2ha7PzMcCHPYdnkWPiBZK8ed4Zr3Ll5lQ==
+
 "@rollup/pluginutils@^3.0.8", "@rollup/pluginutils@^3.0.9", "@rollup/pluginutils@^3.1.0":
   version "3.1.0"
   resolved "https://registry.yarnpkg.com/@rollup/pluginutils/-/pluginutils-3.1.0.tgz#706b4524ee6dc8b103b3c995533e5ad680c02b9b"