Sometimes fails to build on a fresh clone for seemingly no reason

[LoganDark]

What package within Headless UI are you using?

@headless/react

What version of that package are you using?

1.4.1 (latest commit)

Describe your issue

There seems to be an intermittent issue with Terser that prevents it from properly understanding the optional chaining operator (?.), causing it to emit useless error messages like these:

  241 |   }
  242 |
> 243 |   let isParentDisabled = parent?.getAttribute('disabled') === '' ?? false;
      |                                ^ Unexpected token: punc (.)
  244 |   if (isParentDisabled && isFirstLegend(legend)) return false;
  245 |   return isParentDisabled;
(terser plugin) SyntaxError: Unexpected token: punc (.)
SyntaxError: Unexpected token: punc (.)
    at ee (/home/logandark/headlessui/node_modules/terser/dist/bundle.min.js:1:19541)
    at c (/home/logandark/headlessui/node_modules/terser/dist/bundle.min.js:1:28244)
    at l (/home/logandark/headlessui/node_modules/terser/dist/bundle.min.js:1:28335)
    at f (/home/logandark/headlessui/node_modules/terser/dist/bundle.min.js:1:28388)
    at G (/home/logandark/headlessui/node_modules/terser/dist/bundle.min.js:1:42202)
    at ge (/home/logandark/headlessui/node_modules/terser/dist/bundle.min.js:1:48272)
    at /home/logandark/headlessui/node_modules/terser/dist/bundle.min.js:1:49152
    at be (/home/logandark/headlessui/node_modules/terser/dist/bundle.min.js:1:49167)
    at ze (/home/logandark/headlessui/node_modules/terser/dist/bundle.min.js:1:50421)
    at qe (/home/logandark/headlessui/node_modules/terser/dist/bundle.min.js:1:50653)

My first attempt at figuring out what was going on was to search keywords on GitHub. It appears that Terser versions before 5.2.0 do not support optional chaining. Taking a look at the node_modules/terser/package.json file to see which version was installed for headlessui, I see 5.5.1 was installed in the packages/@headlessui-react/node_modules folder, but 4.8.0 was installed in the root node_modules folder.

Manually copying Terser 5.5.1 into the root node_modules folder causes this error:

TypeError: Cannot read property 'length' of undefined
    at /home/logandark/headlessui/node_modules/rollup/dist/shared/node-entry.js:11277:55
    at processTicksAndRejections (node:internal/process/task_queues:96:5)
    at async Promise.all (index 0)

so clearly something depends on Terser 4, which doesn't support optional chaining, and breaks when Terser 5 is introduced in its place. But that can't be the issue, because headlessui is on NPM and you have working CI.

So, I searched the exact error message and found these:

GMOD/jbrowse-components#1377 - seems to say it appears randomly whenever it feels like
developit/microbundle#522 - headlessui doesn't use microbundle, but same error
https://www.npmjs.com/package/neoy-ui - not very useful, but some random chinese text that includes the error

The only real lead I have right now is that this is allegedly a weird, random issue that affects people for absolutely no reason and goes away on its own.

[LoganDark]

Tried doing npm i terser@5 rollup@2 rollup-plugin-terser@6, but then the latest tsdx brings in its own outdated version of terser which then goes and throws the error. Seems like Terser 4 cannot be escaped - but then, how come my build is the only one that is failing because of this? Maybe the TypeScript compilation is outputting optional chaining when it should not, or something like that?