Remove empty scripts after webpack compilation

[delawski]

Summary

Fixes #6778

So far, a custom IgnoreExtraneousStyleAssets webpack plugin has been used to prevent generation of empty JS files (e.g. when CSS has been an entry point). After updating webpack from version 4 to 5, the custom plugin stopped working due to webpack internal API changes.

It turns out there is a third-party plugin, webpack-remove-empty-scripts that does exactly what we need. It should be run before DependencyExtractionWebpackPlugin so that empty JS files are removed before .asset.php files are created.

Checklist

• My code is tested and passes existing tests.
• My code follows the Engineering Guidelines (updates are often made to the guidelines, check it out periodically).

[github-actions]

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[westonruter]

Here's a comparison before/after:

The empty files are all getting deleted as expected, except there's one interesting thing: amp-post-meta-box.js was empty before but now it is not empty. Was this broken before? It seems so! I just checked with the Classic Editor plugin active and there is an error:

Clicking the “Edit” link for enabling AMP does nothing. Why was this file empty before?

Checking the same page with the changes in this PR shows shows no errors and the toggle is working:

This file was not empty in 2.1.4, so something broke in develop between then and now which you are fixing here.

[westonruter]

Changes to *.js files between 2.1.4 and this PR:

All that looks right.

---

Changes to *.asset.php files:

This looks similarly right, except for the wp-components.asset.php file. This file seems to still be generated incorrectly.

Or maybe not? Is it being generated for wp-components.css and we should actually be updating register_shimmed_styles to use the version in the assets file instead of the hard-coded 13.0.3 (which is probably wrong):

amp-wp/src/Admin/Polyfills.php

Lines 164 to 177 in 5ab4412

	/**
	* Registers shimmed assets not guaranteed to be available in core.
	*
	* @param WP_Styles $wp_styles The WP_Styles instance for the current page.
	*/
	public function register_shimmed_styles( $wp_styles ) {
	$this->override_style(
	$wp_styles,
	'wp-components',
	amp_get_asset_url( 'css/wp-components.css' ),
	[],
	'13.0.3'
	);
	}

But if that is the case, then why is the wp-components.asset.php file in the assets/js directory and not the assets/css directory?

These are the changes to the *.css files between 2.1.4 and this PR:

[delawski]

This looks similarly right, except for the wp-components.asset.php file. This file seems to still be generated incorrectly.

I think it is the case. This file should not be generated since wp-components.js is bundled with the script files it is used on. The accompanying CSS file is, however, not manually imported to any of the JS entry points meaning we need to rely on Core exposing wp-components.css or polyfill it for older WP versions.

So far, wp-components has been added as one of the entry points in the settingsPage task. This resulted in a superfluous wp-components.asset.php file generation. With 544b66d we add wp-components stylesheet to the styles task, where it better fits. Also, thanks to that, no .asset.php file is created.

Or maybe not? Is it being generated for wp-components.css and we should actually be updating register_shimmed_styles to use the version in the assets file instead of the hard-coded 13.0.3 (which is probably wrong):

I guess we can use the hard-coded value and update it anytime the @wordpress/components package is bumped (alternatively use the plugin version instead).

[westonruter]

I guess we can use the hard-coded value and update it anytime the @wordpress/components package is bumped (alternatively use the plugin version instead).

Good idea. I've done that in 99a3a89.

[westonruter]

So far, wp-components has been added as one of the entry points in the settingsPage task. This resulted in a superfluous wp-components.asset.php file generation. With 544b66d we add wp-components stylesheet to the styles task, where it better fits. Also, thanks to that, no .asset.php file is created.

Perfect!