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[ESM] always load the ESM loader #279

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merged 3 commits into from
Mar 26, 2022
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kherock
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@kherock kherock commented Mar 26, 2022

I noticed that this library only monitors ESM when the program entrypoint is a module. Because of this, CJS programs making use of dynamic import() statements to load ESM code won't reload when the imported ESM changes.

To work around this, I updated the spawn logic to always enable --experimental-loader regardless of the entrypoint script's format. I took special care to avoid running into nodejs/node#33226 when TypeScript files are loaded.

Additionally, the approach for installing CJS hooks and intercepting vm and child_process calls by replacing the main program and subsequently masking it seemed unnecessarily complicated and was breaking tests with the ESM loader enabled. I replaced this logic with a simple --require option appended to the end of the execArgv.

const script = process.argv[1];
const { extensions, fork, vm } = getConfig(script);

if (process.env.NODE_DEV_PRELOAD) {
require(process.env.NODE_DEV_PRELOAD);
}
require('./suppress-experimental');
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I don't think we should be hiding warnings by default.

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Although I can see now that it gets quite annoying.

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I was also trying to hold off on implementing this but I figure that this way is probably for the best since it was affecting the test output a lot!

const require = createRequire(import.meta.url);

export async function load(url, context, defaultLoad) {
const getPackageType = require('get-package-type');
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It looks like this is only used in the unknown file extension case. Let's get it out of the critical path.

Comment on lines +12 to +19
try {
return await defaultLoad(url, context, defaultLoad);
} catch (err) {
if (err.code === 'ERR_UNKNOWN_FILE_EXTENSION') {
return { format: await getPackageType(filePath), source: null };
}
throw err;
}
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Suggested change
try {
return await defaultLoad(url, context, defaultLoad);
} catch (err) {
if (err.code === 'ERR_UNKNOWN_FILE_EXTENSION') {
return { format: await getPackageType(filePath), source: null };
}
throw err;
}
return defaultLoad(url, context, defaultLoad).catch(error => {
if (error.code !== 'ERR_UNKNOWN_FILE_EXTENSION') throw error;
return require('get-package-type')(filePath).then(format => ({ format, source: null });
});

@bjornstar
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I'll fix it up once I merge, thanks for the contribution!


export async function getFormat(url, context, defaultGetFormat) {
const getPackageType = require('get-package-type');
const filePath = fileURLToPath(url);
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@lehni lehni Mar 27, 2022

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@bjornstar @kherock this crashes on any import of built in modules now, of which the URL is in the format node:<identifier>, e.g. node:path:

TypeError [ERR_INVALID_URL_SCHEME]: The URL must be of scheme file

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I created an issue for this with a little test-case: #281

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3 participants