Add ID attribute to style element from wp_add_inline_style()

[westonruter]

In order to support partial preview refreshes (#27355), it is important for all partials being updated to have an element with a distinct CSS selector for targeting. In the case of Twenty Fifteen, styles output via wp_add_inline_style() may be dynamically refreshed by JS and so the style elements output by this function should have distinct IDs. Once this is in place, then the Twenty Fifteen theme can make use of it in #29988.

[westonruter]

​https://github.com/xwpco/wordpress-develop/pull/34

[westonruter]

In 30032.diff​, add id="wp-inline-style-$handle" to style elements added via wp_add_inline_style()

[SergeyBiryukov]

In 29956:

Add ID attribute to style element from wp_add_inline_style().

props westonruter.
fixes #30032.

[obenland]

What if there is more than one inline style added to one handle?

[westonruter]

Replying to obenland:

What if there is more than one inline style added to one handle?

The after data for the style dependency is actually an array and print_inline_style() concatenates the array into a single string: https://core.trac.wordpress.org/browser/trunk/src/wp-includes/class.wp-styles.php#L144

So adding multiple inline styles won't be a problem.

[SergeyBiryukov]

In 29958:

wp_add_inline_style():

• Change the wp-inline-style-$handle class added in [29956] to $handle-inline-css for consistency with existing patterns.
• Add the ID attribute when concatenation is enabled as well.

props georgestephanis.
see #30032.

[boonebgorges]

[29958] broke a couple unit tests - phpunit --filter _inline_styles. The expected strings need to be updated.

[georgestephanis]

on it.

[georgestephanis]

fixes broken unit tests.

[SergeyBiryukov]

In 29967:

Update expected results in wp_add_inline_style() unit tests after [29958].

props georgestephanis.
see #30032.