Allow non-block themes to add theme support for `appearance-tools`

[ironprogrammer]

Allow themes without theme.json to opt-in to ​appearance tools via:

add_theme_support( 'appearance-tools' );

Originally planned for 6.1, this backport missed the original cutoff. Backports changes from ​https://github.com/WordPress/gutenberg/pull/43337.

Related: #56467

Adds unit test to #3337. See ​original PR for additional details.

Backport of ​https://github.com/WordPress/gutenberg/pull/43337.

Props ockham, hellofromtonya, dream-encode, carolinan.

Trac ticket: https://core.trac.wordpress.org/ticket/57460

[ironprogrammer]

Testing Instructions

Setup

• Disable the Gutenberg plugin, if active.
• Install and activate a theme that does not use theme.json (e.g. a "classic" theme").

Steps to Test

1. In the theme's functions.php file, add the following ​theme support (often located in an after_setup_theme hook):

   add_theme_support( 'appearance-tools' );
   

2. Create a new post with a Group block. Inside the group, add a Paragraph with a link, and add a Buttons block with a few buttons.
3. Make sure the Settings sidebar is visible (gear icon, upper right of editor).
4. Select the Group, Buttons, and Paragraph blocks to verify the new appearance tools style options available in the sidebar.

Expected Results

• ✅ Color > Link allows the selection of hyperlink color in the Group and Paragraph blocks (not in Buttons).
• ✅ Dimensions > Block Spacing allows spacing between elements to be changed. The Buttons block is an easy way to verify this.
• ✅ The Border section is displayed for the Group block, and allows changing the border color, style, width, and radius.

Test Report Icons:
✅ <= Behavior is expected.
❌ <= Behavior is NOT expected.

[ironprogrammer]

Test Report

Patch tested: ​https://github.com/WordPress/wordpress-develop/pull/3846

Environment

• Hardware: MacBook Pro Apple M1 Pro
• OS: macOS 12.6.2
• Browser: Safari 16.2
• Server: nginx/1.23.3
• PHP: 7.4.33
• WordPress: 6.2-alpha-54642-src
• Theme: blank-canvas v1.2.9
• Gutenberg DISABLED 🔴

Actual Results

• ✅ New styles options are available in the editor's Settings sidebar.
• ✅ When applied, the styles are visible in the editor and frontend post.

Supplemental Artifacts

Example "After" post has border, button spacing, and link color adjustments applied.

Post in Blank Canvas Theme	Post After Adding appearance-tools Support

[audrasjb]

Before patch: group block

[audrasjb]

Before patch: paragraph block

[audrasjb]

Before patch: button block

[audrasjb]

After patch: group block ✅

[audrasjb]

After patch: paragraph block ✅

[audrasjb]

After patch: button block ✅

[audrasjb]

Patch works fine!

Self assigning for commit.

[audrasjb]

In 55067:

Themes: Add opt-in Appearance Tools support for Classic Themes.

This changeset merges the following changes from Gutenberg repository:

• Allow themes without theme.json to opt-in to appearance tools via add_theme_support( 'appearance-tools' );
• Update wpThemeJsonResolver unit tests accordingly

See the following pull request for more info: ​https://github.com/WordPress/gutenberg/pull/43337

Props ironprogrammer, audrasjb.
Fixes #57460.

Committed in https://core.trac.wordpress.org/changeset/55067

[audrasjb]

Oops, missed some props.
Adding bernhard-reiter, hellofromtonya, davidbaumwald, and poena manually.

[poena]

I've found a bug with the block gap (in the Dimensions panel this is called block spacing),
and opened ​issue 47386 in the Gutenberg GitHub repository.

I think we can give it a few days to try to find a CSS solution, if not, we can perhaps revert this and add support for all appearance tools except block gap?

[audrasjb]

Thanks @poena, yes sounds like a good plan 👌

[hellofromTonya]

Adding experimental keyword for tracking backports/syncs from Gutenberg into Core.

[andrewserong]

I think we can give it a few days to try to find a CSS solution, if not, we can perhaps revert this and add support for all appearance tools except block gap?

Thanks for following up here @poena — for Classic themes, I think it'd be safer for the appearance tools opt-in to not include block gap, as it was written with block themes in mind, and it sounds like it could add a fair bit of complexity to attempt to get the layout block gap rules playing nicely with Classic themes.

[poena]

I suggest the following:

Re add the link color theme support, which was the feature that was removed without replacement in 5.9.

Add a new border theme support.

So these two would be separate.

[azaozz]

Replying to poena:

I've found a bug with...

As this is an enhancement that was already added to core trunk, and "feature freeze" is tomorrow, could you open a new trac ticket for this bug, and mention the Gutenberg PR in it. Then the bugfix (when ready) can be committed from that ticket.

This should be closed as fixed imho.

[poena]

I have asked the release leads for guidance since the bug fix is the revert.

[poena]

New ticket: https://core.trac.wordpress.org/ticket/57649

[costdev]

As the ticket has been created for the bug, I'll close this ticket as fixed per comment:16

[audrasjb]

Removing needs-dev-note keyword as this was reverted in [55273].