Editor, Themes: Evaluate count() once per loop instead of once per iteration

[mukeshpanchal27]

Summary

A for loop condition is evaluated once per iteration, plus once more to terminate. When that condition is $i < count( $array ), PHP calls count() n + 1 times to walk an n-element array whose length never changes inside the body.

This moves the count into the loop initialiser at the four core sites that still re-evaluate it:

for ( $i = 0, $c = count( $array ); $i < $c; $i++ ) {

That form is already the dominant idiom in core — formatting.php:769/:780, class-wp-comment-query.php:1113, class-wpdb.php:3151, functions.php:2106, class-wp-filesystem-base.php:448, image-edit.php:673 and deprecated.php:1741 all use it. These were the remaining outliers.

Benchmark

100,000 loop runs per row, PHP 8.x:

Array size	count() in condition	count() hoisted	Saved
3 elements	7.48 ms	6.53 ms	13%
10 elements	16.65 ms	12.71 ms	24%
50 elements	62.29 ms	50.95 ms	18%

To be clear about what this is and isn't: count() on a PHP array is O(1) — it reads a cached length — so this is not an algorithmic fix. What it removes is per-iteration function-call overhead (opcode dispatch, frame push, return) repeated n times. Modest per loop, but free, and it makes the fixed bound explicit.

Sites changed

File	Line	Note
src/wp-includes/blocks.php	620	register_block_type_from_metadata(), script handles. Runs for every registered block on every request — core alone registers ~100 blocks — and the enclosing foreach covers three script fields (editorScript, script, viewScript).
src/wp-includes/blocks.php	654	Same function, script module IDs.
src/wp-includes/blocks.php	690	Same function, style handles — three style fields (editorStyle, style, viewStyle).
src/wp-includes/class-wp-theme-json.php	5382	set_spacing_sizes(), relabelling spacing presets.

Safety

Hoisting is only valid if the body cannot change the array's length. Each site was checked:

• blocks.php (all three) — $scripts, $modules and $styles are local copies of a $metadata field. The body calls register_block_script_handle() / register_block_script_module_id() / register_block_style_handle() and appends to a separate accumulator ($processed_scripts etc.). The iterated array is never written to, and the registration helpers receive $metadata by value, so they cannot resize it either.
• class-wp-theme-json.php — the body assigns $spacing_sizes[ $i ]['name'], overwriting a key on an existing element. It never adds or removes elements, so the count is invariant.

No behaviour change: for a fixed-length array, $i < count( $a ) and $i < $c where $c = count( $a ) are the same condition.

Deliberately not changed

• formatting.php:3406 — wp_targeted_link_rel() has the same pattern with an invariant array, but was deprecated in 6.7.0 and calls _deprecated_function() on entry. Not worth the review surface.
• for ( $i = count( $x ) - 1; $i >= 0; $i-- ) loops — class-wp-http.php:746, html-api/class-wp-html-open-elements.php:645, html-api/class-wp-html-active-formatting-elements.php:200, html-api/class-wp-html-processor.php:944, nav-menu.php:1561, file.php:1630. These call count() in the initialiser, which already runs exactly once. Nothing to hoist.
• Bundled third-party code — class-pclzip.php and rss.php (MagpieRSS) have many sizeof()-in-condition loops, but are vendored libraries core does not maintain.

Testing instructions

php -l src/wp-includes/blocks.php
php -l src/wp-includes/class-wp-theme-json.php
vendor/bin/phpcs src/wp-includes/blocks.php src/wp-includes/class-wp-theme-json.php
npm run test:php -- --filter '(Blocks_Register|ThemeJson)'

Results on this branch:

• php -l — no syntax errors in either file.
• phpcs — clean, 0 errors / 0 warnings.
• PHPUnit — OK (377 tests, 881 assertions).

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This Pull Request is for code review only. Please keep all other discussion in the Trac ticket. Do not merge this Pull Request. See Contributing to WordPress for more information.