fix: allow Ctrl+C to interrupt build-scss command by peterkulko · Pull Request #4155 · openedx/paragon

peterkulko · 2026-03-04T11:05:48Z

Description

Issue: #3949

sass.compile() is a synchronous function. While it runs, Node.js is frozen - it can't do anything else, including responding to Ctrl+C. Instead of launching all compilations at once, we run them one at a time with a setTimeout(resolve, 0) pause between each.

For example:

Step	Operation	Description
1	sass.compile(core)	The first Sass compilation starts running
2	Ctrl+C pressed	A SIGINT signal is triggered and queued by the runtime
3	setTimeout(0)	The event loop processes the next task and detects the pending SIGINT
4	Process exits	The program terminates due to the interrupt signal
5	sass.compile(light)	This step is never executed because the process has already exited

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openedx-webhooks · 2026-03-04T11:05:54Z

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codecov · 2026-03-04T11:32:24Z

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 94.40%. Comparing base (dfc69e2) to head (4d9c5c2).
⚠️ Report is 37 commits behind head on release-23.x.

Additional details and impacted files

@@               Coverage Diff                @@
##           release-23.x    #4155      +/-   ##
================================================
+ Coverage         94.39%   94.40%   +0.01%     
================================================
  Files               242      242              
  Lines              4296     4306      +10     
  Branches           1020      981      -39     
================================================
+ Hits               4055     4065      +10     
  Misses              237      237              
  Partials              4        4

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brian-smith-tcril

Thanks for doing this! This definitely is an improvement over the current state. I left a few comments with small cleanup suggestions, and one with a bigger question.

brian-smith-tcril · 2026-04-13T13:43:37Z

+  process.on('SIGINT', () => {
+    // eslint-disable-next-line no-console
+    console.log(chalk.yellow('\nBuild interrupted. Partial output may exist in the output directory.'));
+    process.exit(130);
+  });


Nothing else in this file uses console.log, and directly calling process.exit from the lib file seems less than ideal. We already have error handling in

paragon/bin/paragon-scripts.js

Lines 275 to 287 in c4e95f0

try {

await executor.executor(commandArgs);

sendTrackInfo('openedx.paragon.cli-command.used', { command, status: 'success' });

} catch (error) {

// eslint-disable-next-line no-console

console.error(chalk.red.bold('An error occurred:', error));

if (error instanceof Error) {

// eslint-disable-next-line no-console

console.error(chalk.red(error.stack));

}

sendTrackInfo('openedx.paragon.cli-command.used', { command, status: 'error', errorMsg: error.message });

process.exit(1);

}

so it'd be nice to just surface the error from this function and hanve bin/paragon-scripts handle it.

Moved the SIGINT handler to bin/paragon-scripts.js. Unfortunately we can't surface SIGINT as a thrown error through the catch block because sass.compile() is synchronous, process.exit(130) in the signal handler is the only way to interrupt it immediately. So the handler lives in the entry point instead.

brian-smith-tcril · 2026-04-13T13:53:40Z

+  // eslint-disable-next-line no-console
+  console.log(chalk.grey('Press Ctrl+C to interrupt the build (takes effect between compilations).\n'));


Same thing about trying to keep console.log out of this file. I figure for this one we can just remove these lines.

I'd also like to look into what it would take to make it so we can actually interrupt the compilation. I was thinking we might be able to use sass.compileAsync but the sass docs mention

⚠️ Heads up!
When using the sass npm package, compile is almost twice as fast as compileAsync, due to the overhead of making the entire evaluation process asynchronous.

I also looked into using a worker thread to make the compilation truly interruptible. It would require a separate worker file with the sass importer logic duplicated, message passing for compilation results, and error handling across threads. It's more complexity than the current one-liner, and the benefit is just saving a few seconds on interruption...

Yeah, it's definitely worth landing an improvement instead of blocking this on a complicated rework.

Maybe just showing a "cancelling" or "exiting" message would be helpful? Just some form of immediate feedback so users know their Ctrl+C was picked up.

We're using the synchronous sass.compile, the event loop stays blocked during compilation, which means the SIGINT handler only gets a chance to run after the current theme finishes.

So even if we add an interrupt message, it wouldn't appear right away, it would show up once compilation of the current theme completes.

brian-smith-tcril · 2026-04-13T13:54:43Z

It'd be nice to add a test to this file checking the SIGINT functionality.

brian-smith-tcril

I'm happy with this PR. It's a solid improvement over the current state of things, and considering the tradeoffs required to make sass.compile async I think it's the best option we have.

I left one last comment about changing the tests back to sync from async now that buildScssCommand is staying sync, once that's cleaned up I'll be happy to merge this!

brian-smith-tcril · 2026-04-21T14:57:26Z

  });

-  it('should compile core and theme stylesheets', () => {
+  it('should compile core and theme stylesheets', async () => {


Now that buildScssCommand is back to not being async we can probably go back to a sync test to make the diff smaller

Corrected, thanks

openedx-semantic-release-bot · 2026-04-22T15:15:56Z

🎉 This PR is included in version 23.21.2 🎉

The release is available on:

Your semantic-release bot 📦🚀

Changed color.primary.base/light (light theme) and the full primary ramp + brand/text/body/header colors (dark theme) in the design token JSON sources, plus 6 hardcoded brand-tinted hex values found by hunt in themes/dark/_extras.scss, _discussion.scss and _learning.scss. Replaced logo/favicon assets with vivai's. NOTE on build method: 'npm run build' / 'make build' hangs indefinitely on this environment during the postCSS stage of the Light theme compilation (paragon build-scss), reproduced identically even with completely unmodified stock colors, so it is NOT caused by this change's content. Upgraded @openedx/paragon 23.14.9 -> 23.22.2 first (fixes a known forEach-without-await hang, openedx/paragon#4155) which did not resolve it either -- points to a deeper environment-specific issue with the postcss-combine-duplicated-selectors step on this machine, not yet root-caused. Workaround applied instead: restored edly-io's own pre-built dist/ CSS (already committed on this branch, produced by their CI) via 'git checkout HEAD -- dist/', then patched the compiled light/dark .css and .min.css directly with the same hex substitutions (see list below), rather than rebuilding via the broken local pipeline. Source maps (.css.map) were left untouched/stale as a result -- fine for production use, only affects devtools CSS source attribution. Substitutions applied: 15376D->808C48, F2F7F8->FAF3E0, AEC7F6->B5C48A, 8e9fbf->9AAB6E, 747e92->6B7A45, 5a6278->4F5A32, 292A2C->22201A, 777792->8A9463, CE80AA->D4903D, 112F6B->2B3318, 0D0D0E->1A1C12, 211E82->4F5A32, 6B7A94->6B7A5A, 717D8A->6B7A5A. If this needs a real source rebuild later (e.g. to add a new component override), retry 'make build' first -- the paragon version bump may combine with a future postcss-combine-duplicated-selectors fix to resolve it; if it still hangs, the same dist/-patching approach here can be reapplied.

peterkulko self-assigned this Mar 4, 2026

openedx-webhooks added the open-source-contribution PR author is not from Axim or 2U label Mar 4, 2026

openedx-webhooks added this to Contributions Mar 4, 2026

github-project-automation Bot moved this to Needs Triage in Contributions Mar 4, 2026

peterkulko requested a review from brian-smith-tcril March 4, 2026 12:32

fix: allow Ctrl+C to interrupt build-scss command

ff6a39f

mphilbrick211 moved this from Needs Triage to Ready for Review in Contributions Mar 5, 2026

brian-smith-tcril reviewed Apr 13, 2026

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refactor: after review

47c78fc

peterkulko requested a review from brian-smith-tcril April 17, 2026 08:28

brian-smith-tcril reviewed Apr 21, 2026

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test: revert build-scss test to synchronous invocation

4d9c5c2

peterkulko requested a review from brian-smith-tcril April 22, 2026 08:10

brian-smith-tcril approved these changes Apr 22, 2026

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brian-smith-tcril merged commit 5651001 into openedx:release-23.x Apr 22, 2026
10 checks passed

github-project-automation Bot moved this from Ready for Review to Done in Contributions Apr 22, 2026

openedx-semantic-release-bot added the released label Apr 22, 2026

	try {
	await executor.executor(commandArgs);
	sendTrackInfo('openedx.paragon.cli-command.used', { command, status: 'success' });
	} catch (error) {
	// eslint-disable-next-line no-console
	console.error(chalk.red.bold('An error occurred:', error));
	if (error instanceof Error) {
	// eslint-disable-next-line no-console
	console.error(chalk.red(error.stack));
	}
	sendTrackInfo('openedx.paragon.cli-command.used', { command, status: 'error', errorMsg: error.message });
	process.exit(1);
	}

		// eslint-disable-next-line no-console
		console.log(chalk.grey('Press Ctrl+C to interrupt the build (takes effect between compilations).\n'));

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