Support array in package.json's sideEffects property

[ahocevar]

This pull request implements array support for the package.json's sideEffects property, like webpack does. Example:

"sideEffects": ["./a.js"]

Fixes #1566.

[fathyb]

Why was this changed?

[ahocevar]

Because findPackage() will add a pkgdir property to the package, which is needed later for globbing the sideEffects array entries.

[fathyb]

You can use path.normalize(sideEffects) instead of manually checking for windows and using replace
Oh, you're doing the opposite, nevermind

[ahocevar]

Thinking again, this is not necessary at all. "sideEffects": ["foo\\bar.js"] is not supported in package.json anyway.

[fathyb]

You can save some I/O and async overhead by setting pkgdir in cacheData preemptively in hoist.js like we do for sideEffects :

parcel/src/scope-hoisting/hoist.js

Lines 34 to 38 in 7423541

	asset.cacheData.imports = asset.cacheData.imports || Object.create(null);
	asset.cacheData.exports = asset.cacheData.exports || Object.create(null);
	asset.cacheData.wildcards = asset.cacheData.wildcards || [];
	asset.cacheData.sideEffects =
	asset._package && asset._package.sideEffects;

[fathyb]

nit: defaulting sideEffects using {sideEffects} = asset.cacheData could make the if conditions using it cleaner (await hasSideEffects(asset))

[ahocevar]

@fathyb Thanks for the review. I have addressed all your comments.

[devongovett]

this function could probably go in hoist.js. That way asset.cacheData.sideEffects could always be a boolean computed using this function. Might be slightly faster, especially since we can cache the results.

[devongovett]

I actually liked your original solution using the resolver. This one will result in two lookups.

[ahocevar]

Thanks @devongovett for your review. I have addressed your comments as well now.

[fathyb]

LGTM, thanks for working on this 👍