Make child themes inherit parent's style variations.

[jffng]

What?

Makes parent theme style variations inherited by the child theme.

cc @WordPress/block-themers

Why?

Closes #45965

How?

Changes the get_style_variations method of the theme json resolver. Checks if it's a child theme and returns the parent theme variations in addition to the child's. If the file basename of the child variation is the same as its parent, it will only include the child's ("overwriting" the parent variation).

Testing Instructions

1. Activate a child of a theme that has style variations. You can use this TT3 child for testing: TT3: add a test child theme that overwrites the Canary variation theme-experiments#311
2. Verify the child theme's variations appear in addition to the parent themes:

Before	After

Testing Instructions for Keyboard

Screenshots or screencast

[jffng]

I saw there is an effort to reorganize the theme json code instead of inheriting per WP version: #46579 (comment)

I may wait on that PR to land this one, to simplify backporting later, but any general feedback is welcome.

[scruffian]

This is looking good. It might be good to add a unit test, so that we don't introduce regressions in the future.

[ockham]

Thanks a lot for for working on this, @jffng!

I agree with @scruffian that this is the kind of code we'd want covered by some unit test(s) to avoid regressions.
I think we have some prior art in the repo that we can use as inspiration: In the phpunit/data/themedir1/ directory, we have a few test themes that we might be able to use here.

You could e.g. add some variations to block-theme's theme.json and write a test that sets block-theme-child as the active theme and verifies that its parent's style variations are returned by the relevant function.

I think that this existing test looks like we could copy and modify it to cover the behavior for child themes:

gutenberg/phpunit/class-gutenberg-rest-global-styles-controller-test.php

Lines 83 to 117 in 8a71fd8

	public function test_get_theme_items() {
	wp_set_current_user( self::$admin_id );
	$request = new WP_REST_Request( 'GET', '/wp/v2/global-styles/themes/emptytheme/variations' );
	$response = rest_get_server()->dispatch( $request );
	$data = $response->get_data();
	$expected = array(
	array(
	'version' => 2,
	'settings' => array(
	'color' => array(
	'palette' => array(
	'theme' => array(
	array(
	'slug' => 'foreground',
	'color' => '#3F67C6',
	'name' => 'Foreground',
	),
	),
	),
	),
	),
	'styles' => array(
	'blocks' => array(
	'core/post-title' => array(
	'typography' => array(
	'fontWeight' => '700',
	),
	),
	),
	),
	'title' => 'variation',
	),
	);
	$this->assertSameSetsWithIndex( $data, $expected );
	}

[jffng]

I rebased this since the resolver class was bundled into a single file.

Will work on updating the tests next.

[github-actions]

Flaky tests detected in fcfbc12.
Some tests passed with failed attempts. The failures may not be related to this commit but are still reported for visibility. See the documentation for more information.

🔍 Workflow run URL: https://github.com/WordPress/gutenberg/actions/runs/3936732768
📝 Reported issues:

• [Flaky Test] should move the blocks up #39782 in specs/editor/various/block-editor-keyboard-shortcuts.test.js

[madhusudhand]

It fails to show style variations from parent when child theme doesn't have a styles directory. I guess, it should still have them displayed.

[jffng]

Nice catch, thanks for testing.

I addressed this in 1fdb35d

[jffng]

I updated the version number here, which seems like it was incorrect to begin with since it was already using the customTemplates and templateParts properties which were added in v2.

[jffng]

I added a unit test in 1a892f3, let me know what you think @ockham @scruffian when you have a moment 🙏

[ockham]

I added a unit test in 1a892f3, let me know what you think @ockham @scruffian when you have a moment 🙏

Thank you for that! The PR is looking pretty good! One final suggestion, would you mind adding another style variation to also cover the "overwriting" behavior in the test:

If the file basename of the child variation is the same as its parent, it will only include the child's ("overwriting" the parent variation).

---

Aside, some unrelated tests are currently failing for me when running them locally. I'll rebase this PR to make sure it's inconsequential.

[jffng]

@ockham thanks for the review!

would you mind adding another style variation to also cover the "overwriting" behavior in the test:

Done in fcfbc12. I added an additional variation to the parent, so the test covers both the following behaviors of the get_style_variations function:

• a child theme's variation overwrites a parent theme's variation of the same name (variation-a)
• the parent theme's variation is inherited (variation-b)

[ockham]

Thank you, that's exactly the kind of coverage I had in mind 👍

[ockham]

Tested manually with the child theme from WordPress/theme-experiments#311. Code looks good, and unit tests cover the expected behavior nicely 😊