add proxy loader

Author: lobsterkatie

packages/nextjs/rollup.npm.config.js

@@ -42,12 +42,15 @@ export default [
   ...makeNPMConfigVariants(
     makeBaseNPMConfig({
       entrypoints: ['src/config/loaders/index.ts'],
+      // Needed in order to successfully import sucrase
+      esModuleInterop: true,
 
       packageSpecificConfig: {
         output: {
-          // make it so Rollup calms down about the fact that we're doing `export { loader as default }`
+          // make it so Rollup calms down about the fact that we're combining default and named exports
           exports: 'named',
         },
+        external: ['@rollup/plugin-sucrase', 'rollup'],
       },
     }),
   ),

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

@@ -1,2 +1,3 @@
 export { default as prefixLoader } from './prefixLoader';
 export { default as dataFetchersLoader } from './dataFetchersLoader';
+export { default as proxyLoader } from './proxyLoader';

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

@@ -0,0 +1,91 @@
+import { escapeStringForRegex } from '@sentry/utils';
+import * as fs from 'fs';
+import * as path from 'path';
+
+import { rollupize } from './rollup';
+import { LoaderThis } from './types';
+
+type LoaderOptions = {
+  pagesDir: string;
+};
+
+/**
+ * Replace the loaded file with a proxy module "wrapping" the original file. In the proxy, the original file is loaded,
+ * any data-fetching functions (`getInitialProps`, `getStaticProps`, and `getServerSideProps`) it contains are wrapped,
+ * and then everything is re-exported.
+ */
+export default async function proxyLoader(this: LoaderThis<LoaderOptions>, userCode: string): Promise<string> {
+  // We know one or the other will be defined, depending on the version of webpack being used
+  const { pagesDir } = 'getOptions' in this ? this.getOptions() : this.query;
+
+  // Get the parameterized route name from this page's filepath
+  const parameterizedRoute = path
+    // Get the path of the file insde of the pages directory
+    .relative(pagesDir, this.resourcePath)
+    // Add a slash at the beginning
+    .replace(/(.*)/, '/$1')
+    // Pull off the file extension
+    .replace(/\.(jsx?|tsx?)/, '')
+    // Any page file named `index` corresponds to root of the directory its in, URL-wise, so turn `/xyz/index` into
+    // just `/xyz`
+    .replace(/\/index$/, '')
+    // In case all of the above have left us with an empty string (which will happen if we're dealing with the
+    // homepage), sub back in the root route
+    .replace(/^$/, '/');
+
+  // TODO: For the moment we skip API routes. Those will need to be handled slightly differently because of the manual
+  // wrapping we've already been having people do using `withSentry`.
+  if (parameterizedRoute.startsWith('api')) {
+    return userCode;
+  }
+
+  // We don't want to wrap twice (or infinitely), so in the proxy we add this query string onto references to the
+  // wrapped file, so that we know that it's already been processed. (Adding this query string is also necessary to
+  // convince webpack that it's a different file than the one it's in the middle of loading now, so that the originals
+  // themselves will have a chance to load.)
+  if (this.resourceQuery.includes('__sentry_wrapped__')) {
+    return userCode;
+  }
+
+  const templatePath = path.resolve(__dirname, '../templates/proxyLoaderTemplate.js');
+  let templateCode = fs.readFileSync(templatePath).toString();
+  // Make sure the template is included when runing `webpack watch`
+  this.addDependency(templatePath);
+
+  // Inject the route 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.
+  let proxyCode = await rollupize(tempFilePath, this.resourcePath);
+  fs.unlinkSync(tempFilePath);
+
+  if (!proxyCode) {
+    // We will already have thrown a warning in `rollupize`, so no need to do it again here
+    return userCode;
+  }
+
+  // Add a query string onto all references to the wrapped file, so that webpack will consider it different from the
+  // non-query-stringged version (which we're already in the middle of loading as we speak), and load it separately from
+  // this. When the second load happens this loader will run again, but we'll be able to see the query string and will
+  // know to immediately return without processing. This avoids an infinite loop.
+  const resourceFilename = path.basename(this.resourcePath);
+  proxyCode = proxyCode.replace(
+    new RegExp(`/${escapeStringForRegex(resourceFilename)}'`, 'g'),
+    `/${resourceFilename}?__sentry_wrapped__'`,
+  );
+
+  return proxyCode;
+}

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

@@ -0,0 +1,103 @@
+import type { RollupSucraseOptions } from '@rollup/plugin-sucrase';
+import sucrase from '@rollup/plugin-sucrase';
+import { logger } 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, resourcePath: string) => RollupInputOptions = (
+  proxyPath,
+  resourcePath,
+) => ({
+  input: proxyPath,
+  plugins: [
+    // For some reason, even though everything in `RollupSucraseOptions` besides `transforms` is supposed to be
+    // optional, TS complains that there are a bunch of missing properties (hence the typecast). Similar to
+    // https://github.com/microsoft/TypeScript/issues/20722, though that's been fixed. (In this case it's an interface
+    // exporting a `Pick` picking optional properties which is turning them required somehow.)'
+    sucrase({
+      transforms: ['jsx', 'typescript'],
+    } as unknown as RollupSucraseOptions),
+  ],
+
+  // We want to process as few files as possible, so as not to slow down the build any more than we have to. We need the
+  // proxy module (living in the temporary file we've created) and the file we're wrapping not to be external, because
+  // 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 !== resourcePath,
+
+  // 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
+  // https://stackoverflow.com/a/60347490.)
+  context: 'this',
+
+  // Rollup's path-resolution logic when handling re-exports can go wrong when wrapping pages which aren't at the root
+  // level of the `pages` directory. This may be a bug, as it doesn't match the behavior described in the docs, but what
+  // seems to happen is this:
+  //
+  //   - We try to wrap `pages/xyz/userPage.js`, which contains `export { helperFunc } from '../../utils/helper'`
+  //   - Rollup converts '../../utils/helper' into an absolute path
+  //   - We mark the helper module as external
+  //   - Rollup then converts it back to a relative path, but relative to `pages/` rather than `pages/xyz/`. (This is
+  //     the part which doesn't match the docs. They say that Rollup will use the common ancestor of all modules in the
+  //     bundle as the basis for the relative path calculation, but both our temporary file and the page being wrapped
+  //     live in `pages/xyz/`, and they're the only two files in the bundle, so `pages/xyz/`` should be used as the
+  //     root. Unclear why it's not.)
+  //   - As a result of the miscalculation, our proxy module will include `export { helperFunc } from '../utils/helper'`
+  //     rather than the expected `export { helperFunc } from '../../utils/helper'`, thereby causing a build error in
+  //     nextjs..
+  //
+  // It's not 100% clear why, but telling it not to do the conversion back from absolute to relative (by setting
+  // `makeAbsoluteExternalsRelative` to `false`) seems to also prevent it from going from relative to absolute in the
+  // first place, with the result that the path remains untouched (which is what we want.)
+  makeAbsoluteExternalsRelative: false,
+});
+
+const rollupOutputOptions: RollupOutputOptions = {
+  format: 'esm',
+
+  // Don't create a bundle - we just want the transformed entrypoint file
+  preserveModules: true,
+};
+
+/**
+ * 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).
+ *
+ * @param tempProxyFilePath The path to the temporary file containing the proxy module code
+ * @param resourcePath The path to the file being wrapped
+ * @returns The processed proxy module code, or undefined if an error occurs
+ */
+export async function rollupize(tempProxyFilePath: string, resourcePath: string): Promise<string | undefined> {
+  let finalBundle;
+
+  try {
+    const intermediateBundle = await rollup(getRollupInputOptions(tempProxyFilePath, resourcePath));
+    finalBundle = await intermediateBundle.generate(rollupOutputOptions);
+  } catch (err) {
+    __DEBUG_BUILD__ &&
+      logger.warn(
+        `Could not wrap ${resourcePath}. An error occurred while processing the proxy module template:\n${err}`,
+      );
+    return undefined;
+  }
+
+  // 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.
+  //
+  // 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 resourceFilename = path.basename(resourcePath);
+  const mutatedResourceFilename = resourceFilename
+    // `[\\[\\]]` is the character class containing `[` and `]`
+    .replace(new RegExp('[\\[\\]]', 'g'), '_')
+    .replace(/(jsx?|tsx?)$/, 'js');
+  code = code.replace(new RegExp(mutatedResourceFilename, 'g'), resourceFilename);
+
+  return code;
+}