Add ES Module loader initial implementation #1348

jmartin4563 · 2022-09-09T15:16:57Z

Proposed Release Notes

Added loader hook to support instrumentation of CommonJS dependencies in ES Module applications

Links

Closes NEWRELIC-3121

Details

Created esm-loader.mjs with resolve hook, based on prototype by @michaelgoin (h/t)
Added new npm script for running our ESM flavored unit tests (npm run unit:esm), and updated CI to run this script
Introduced testdouble, a library that allows us to fake out import statements like proxyquire does for require
Updated eslint configuration to allow for import(), and updated linting commands to run on .mjs files

Proxyquire doesn't work in an import setting, it only works with require

CLAassistant · 2022-09-09T15:17:03Z

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CLAassistant · 2022-09-09T15:17:03Z

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michaelgoin

Very clean implementation, nice work!

A few comments around doing unnecessary work. You/the team can decide if you want to care or not this early. My main thing is they are easily identifiable and I'm not sure how easy to track down if problems do come up with customers.

I'd normally look for an integration test with this sort of thing to confirm actual functionality but I believe that is intended to be tackled in a separate story. So given that, the unit testing looks legit.

michaelgoin · 2022-09-09T16:15:24Z

esm-loader.mjs

+  }
+
+  const instrumentationApi = newrelic.shim
+  const logger = instrumentationApi.logger.child({ component: 'esm-loader' })


One thing to note is via this approach, we'll be instantiating a child logger every single invocation of resolve... so once per every import. This is probably pretty cheap / not noticeable but might recommend avoiding any extra work we can, that is obvious, that can add to startup times for customer applications.

Updated to use the logging module directly, as that is a pattern applied by basically everything else in this repo

michaelgoin · 2022-09-09T16:20:01Z

.eslintrc.js

@@ -8,6 +8,9 @@
 module.exports = {
  extends: ['@newrelic', 'plugin:jsdoc/recommended'],
  plugins: ['jsdoc'],
+  parserOptions: {
+    ecmaVersion: '2020'


I think ideally when we bump allowed versions based on what's allowed (deprecating older node versions), we update the shared definition so all projects are consistent. Fine to land this sort of thing in the project but might follow-up with updating the shared eslint module and then removing here.

Also, I'm not sure what was needed to bump that version but calling out that this will probably allow "spread parameters after optional chaining" which is not available in Node 14. So there's a small risk of introducing something that won't work. Hopefully that would get caught by tests but noting we have been burned at least once since I've been involved with the Node team.

The reason I introduced this is that doing await import() without it caused a parsing error on my unit test file, causing eslint to fail completely on the file (which would then fail CI). Fixing that is not worth the risk of potentially allowing introduction of bugs for v14 IMO, so what do you think about undoing this change and then adding my ESM unit test to .eslintignore?

We have at times had to have a config specific to the tests folder to bump the ecmascript version earlier than the code base for testing newer features. For example, async-await while still supporting very old node versions.

It looks like we still have a file in there, so I might just bump that one to start: test/.eslintrc.js.

for future posterity 16.3.0 is when es2020 spec is 100% implemented: see https://node.green/

michaelgoin · 2022-09-09T16:23:51Z

esm-loader.mjs

+    logger.debug(`${specifier} is not a CommonJS module, skipping for now`)
+  }
+
+  return { url, format }


This would only matter for large projects, or may never matter, but the destructuring to later create an object to return the exact elements does result in an unnecessary allocation on a potentially hot startup path (application with many import statements). It may be negligible in this case but calling out as that is something to consider with agent development that often has less of an impact in CRUD/traditional development. Allocating too much on heavily invoked paths can start impacting GC, even when objects are short lived, which can have non-obvious impacts to perf sometimes (or obvious other times). A more obvious case where this might come up is instrumenting a database "read" method.

Better to be cautious now than have to try and track down these GC thrashes in the wild

michaelgoin · 2022-09-09T16:26:27Z

esm-loader.mjs

+      )
+    }
+
+    logger.debug(`${specifier} is not a CommonJS module, skipping for now`)


Since the 'commonjs' if block does not return, I believe this log message will be logged regardless. Seems like it may not happen anyways as we are unlikely to have anything registered unless one of these projects converts (or does hybrid support? maybe?) but probably want to clean up anyways.

whoops! that's my bad, will fix :)

esm-loader.mjs

michaelgoin · 2022-09-09T16:41:52Z

THIRD_PARTY_NOTICES.md

+This product includes source derived from [testdouble](https://github.com/testdouble/testdouble.js) ([v3.16.6](https://github.com/testdouble/testdouble.js/tree/v3.16.6)), distributed under the [MIT License](https://github.com/testdouble/testdouble.js/blob/v3.16.6/LICENSE.txt):
+
+```
+The MIT License (MIT)


MIT license ✔️

I only added that parserOptions stanza to fix a parsing issue in my unit test file, but configuring it in the top-level eslintrc.js meant that I updated eslint to allow things that would have broken in node14. By configuring in the test-only eslint config, we limit the blast radius of this potential issue

…h debug statements

jordigh · 2022-09-12T14:11:45Z

esm-loader.mjs

+ * @returns {Promise} Promise object representing the resolution of a given specifier
+ */
+export async function resolve(specifier, context, nextResolve) {
+  if (!newrelic.shim) {


I hadn't seen this idiom before. Other than being shorter, is it better than newrelic.agent.config.agent_enabled?

Checking for that would only cover the case where the configuration explicitly disables the agent, it doesn't cover the case where the agent errors out on bootstrap (like if the configuration file is invalid). Checking for the shim or agent property covers both cases in one if, because those properties get added as this very last portion of initialize(https://github.com/newrelic/node-newrelic/blob/main/index.js#L101)

Can we check for the agent itself, then? That seems a little more intentional than checking to see if the shim API is there.

Sure! Will update to assert newrelic.agent

jordigh · 2022-09-12T14:17:00Z

esm-loader.mjs

+    }
+  }
+
+  return resolvedModule


Dumb n00b javascript question but is there a difference between returning the actual module here vs returning the promise given by nextResolve above in case there's no instrumentation?

we need to await the parent(nextResolve) so we can get the resolved path. In the case the agent doesn't exist, still question this, you can see above, it means continue the loader chain. But we're essentially halting the loader chain. But we are going to suggest to be last in that chain. so technically we could just return without calling the parent resolve

My concern here was having a function that sometimes returns a promise and sometimes does not. I thought that might break API expectations, but if we tell our users, "put us last", then maybe this doesn't matter.

The API doesn't change. It's async we just do all the awaiting ourselves

bizob2828

Good work on the paring down from prototype to actual solution. Overall looks great. I tested it with a branch where I'm porting versioned tests and all is well.

bizob2828 · 2022-09-12T17:20:42Z

esm-loader.mjs

+ * @returns {Promise} Promise object representing the resolution of a given specifier
+ */
+export async function resolve(specifier, context, nextResolve) {
+  if (!newrelic.agent) {


I think the check for newrelic.shim was done because it follows the patterns of our external modules. I think checking for agent, shim or awsLambda is enough. but frankly everything we do in here I think is safe without checking anything agent properties but wasn't sure the intention when @michaelgoin wrote this into the prototype.

bizob2828 · 2022-09-12T17:25:22Z

esm-loader.mjs

+    }
+  }
+
+  return resolvedModule


we need to await the parent(nextResolve) so we can get the resolved path. In the case the agent doesn't exist, still question this, you can see above, it means continue the loader chain. But we're essentially halting the loader chain. But we are going to suggest to be last in that chain. so technically we could just return without calling the parent resolve

bizob2828 · 2022-09-12T17:26:15Z

package.json

@@ -232,6 +234,7 @@
    "THIRD_PARTY_NOTICES.md",
    "lib/",
    "bin/tracetractor",
-    "bin/test-naming-rules.js"
+    "bin/test-naming-rules.js",
+    "esm-loader.mjs"


nice catch. this would've been a downer to get through the work and forget to include this here.

bizob2828 · 2022-09-12T17:31:31Z

test/unit/esm-loader.test.mjs

+    await td.replaceEsm('../../lib/logger.js', {}, fakeLogger)
+
+    // eslint-disable-next-line node/no-unsupported-features/es-syntax
+    loader = await import('../../esm-loader.mjs')


It's worth noting this is ignored because of mysticatea/eslint-plugin-node#250. I also logged a ticket to update our plugin so we can remove these: https://issues.newrelic.com/browse/NEWRELIC-3321

esm-loader.mjs

jmartin4563 added 8 commits September 8, 2022 13:18

Add resolve hook for ES Modules

93a386c

Add unit tests using testdouble for dependency mocking

9507b44

Proxyquire doesn't work in an import setting, it only works with require

Update eslint config to support import() syntax

66b1dc5

Update unit tests to include explict end()

77e5e7c

Make unit test suite more DRY

06a70f9

Run eslint on our .mjs files

a0b1513

Add ESM unit test npm script and update CI to use it

7f19bc5

Update comments and logging to keep line length down

c125656

Update package.json files so loader file is shipped in package

022bf3e

jmartin4563 marked this pull request as ready for review September 9, 2022 15:41

michaelgoin reviewed Sep 9, 2022

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jmartin4563 added 3 commits September 9, 2022 13:54

Optimize return value to prevent GC thrashing and fix logic issue wit…

5951051

…h debug statements

Update to use logging module directly so we only instantiate once

ba96f68

bizob2828 self-assigned this Sep 12, 2022

jordigh reviewed Sep 12, 2022

View reviewed changes

Switch to use agent property to assert liveliness of instrumentation

3c260d5

bizob2828 previously approved these changes Sep 12, 2022

View reviewed changes

Added comment explaining call to nextResolve()

9335a6f

jmartin4563 dismissed bizob2828’s stale review via 9335a6f September 12, 2022 18:27

bizob2828 approved these changes Sep 12, 2022

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mrickard mentioned this pull request Sep 12, 2022

Newrelic 3123/esm test loader newrelic/node-test-utilities#141

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mrickard approved these changes Sep 12, 2022

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jmartin4563 merged commit c3a3b89 into newrelic:main Sep 12, 2022

jmartin4563 deleted the esm-loader branch September 12, 2022 21:04

github-actions bot mentioned this pull request Sep 22, 2022

Release v9.1.0 #1361

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bizob2828 mentioned this pull request Sep 22, 2022

Release v9.1.0 Redux #1362

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jmartin4563 mentioned this pull request Sep 28, 2022

Added plumbing for ESM instrumentation #1363

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Add ES Module loader initial implementation #1348

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Add ES Module loader initial implementation #1348

Add ES Module loader initial implementation #1348

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jmartin4563 commented Sep 9, 2022 • edited by bizob2828 Loading

Proposed Release Notes

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CLAassistant commented Sep 9, 2022 • edited Loading

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jmartin4563 commented Sep 9, 2022 •

edited by bizob2828

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