Navigation: Fix performance regression

[scruffian]

What?

This is another attempt at #58506.

In #55605 we changed the navigation rendering logic so that inner_blocks were rendered multiple times. This updates that logic so that inner_blocks are only rendered once.

Why?

To improve performance.

How?

Instead of calling render every time we want to check that a navigation has a submenu, we now save that as a member variable on the class. This means we only need to call render once for each inner block.

There should be a more performant way to determine if a navigation contains submenus.

Testing Instructions

Check that a navigation block with submenus displays as on trunk.

[draganescu]

I did a bit of an analysis.

We have a "function bag" class WP_Navigation_Block_Renderer, and its entry point is WP_Navigation_Block_Renderer::render.

Here is the flow that appears in the code:

• WP_Navigation_Block_Renderer::render
  • static::get_inner_blocks
  • static::handle_view_script_module_loading
    • static::is_interactive (1)
      • static::has_submenus (1)
  • static::get_nav_wrapper_attributes
    • static::is_interactive (2)
      • static::has_submenus (2)
  • static::get_wrapper_markup
    • static::get_inner_blocks_html
      • static::has_submenus (3)
      • static::is_interactive (3)
        • static::has_submenus (4)
    • static::is_responsive ? static::get_responsive_container_markup
      • static::is_interactive (4)
        • static::has_submenus (5)

We can see above that has_submenus which renders every inner_blocks is called 5 times, but 4 out of five is because of the check for is_interactive.

Either we fix is_interactive so know the previous has_submenus result or we come up with a more efficient way to check for submenus. get_inner_blocks results in a nice WP_Block_List which holds this answer and is already computed (once).

[oandregal]

Nice! Thanks for looking into this, it fixes the issue: the navigation block is back to rendering the inner blocks once.

	Trunk	This PR
Total (ms)	631	532
gutenberg_render_block_core_navigation (ms)	103	16
# calls to WP_Block->render	439	434
# calls to gutenberg_render_block_core_page_list	6	1

I don't want to share % of performance, because this analysis is using a profiler (xdebug). This is good for understanding whether it fixes the issue, but not for gauging the impact in production. I'll share this later.

[oandregal]

I'm sharing my before/after cachegrind files: cachegrind-files.zip. Anyone can open them with a tool such as qcachegrind. This 6 minutes video by XDebug's main developer explains the gist of how to navigate and understand them. They look like this:

Before (trunk)	After (branch)

This is the step-by-step process I used to get them, so anyone can replicate.

1. Set up a production environment:

# Create a `.wp-env.override.json` with the following contents.
{
  "config": {
    "WP_DEBUG": false,
    "SCRIPT_DEBUG": false
  }
}

2. Build & start the env with XDEBUG profile enabled:

npm install && npm run build
npm run wp-env start -- --xdebug=profile

3. Use the theme test data. Download the theme test data, and manually upload it to Settings > Import > WordPress importer. This step is not strictly necessary, though it helps stress-testing the navigation block. We need to incorporate it to our automated performance tests, otherwise, changes like this would go unnoticed again.
4. Activate TwentyTwentyThree. This is the same theme in use by Gutenberg & Core tests.
5. Log out and visit the front-end of your site at localhost:8888.
6. Take the cachegrind files generated by xdebug:

# List the files. They should be something like cachegrind.out.PID.gz.
docker exec -it `docker ps -f name=e-wordpress -q` ls -lat --time-style=+%H:%M:%S /tmp/

# Take the latest one, which corresponds with the front-page load.
docker cp `docker ps -f name=e-wordpress -q`:'/tmp/cachegrind.out.PID.gz' ~/Desktop/
gzip -d ~/Desktop/cachegrind.out.PID.gz

7. Open with any tool to inspect. For example, qcachegrind.

[oandregal]

1. [webkit] › editor/blocks/navigation-frontend-interactivity.spec.js:462:3 › Navigation block - Frontend interactivity › Page list block (firefox, webkit) › page-list submenu user interactions

There are some e2e errors related to navigation.

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Props: scruffian, andraganescu, oandregal.

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Co-authored-by: scruffian <scruffian@git.wordpress.org>
Co-authored-by: draganescu <andraganescu@git.wordpress.org>
Co-authored-by: oandregal <oandregal@git.wordpress.org>

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