General: Introduce WP_DEVELOPMENT_MODE constant to signify context-specific development mode.

In recent releases, WordPress core added several instances of cache usage around specific files. While those caches are safe to use in a production context, in development certain nuances apply for whether or not those caches make sense to use. Initially, `WP_DEBUG` was used as a temporary workaround, but it was clear that a more granular method to signify a specific development mode was required: For example, caches around `theme.json` should be disabled when working on a theme as otherwise it would disrupt the theme developer's workflow, but when working on a plugin or WordPress core, this consideration does not apply.

This changeset introduces a `WP_DEVELOPMENT_MODE` constant which, for now, can be set to either "core", "plugin", "theme", or an empty string, the latter of which means no development mode, which is also the default. A new function `wp_get_development_mode()` is the recommended way to retrieve that configuration value.

With the new function available, this changeset replaces all existing instances of the aforementioned `WP_DEBUG` workaround to use `wp_get_development_mode()` with a more specific check.

Props azaozz, sergeybiryukov, peterwilsoncc, spacedmonkey.
Fixes #57487.


git-svn-id: https://develop.svn.wordpress.org/trunk@56042 602fd350-edb4-49c9-b593-d223f7449a82

.env

@@ -59,6 +59,7 @@ LOCAL_WP_DEBUG_LOG=true
 LOCAL_WP_DEBUG_DISPLAY=true
 LOCAL_SCRIPT_DEBUG=true
 LOCAL_WP_ENVIRONMENT_TYPE=local
+LOCAL_WP_DEVELOPMENT_MODE=core
 
 # The URL to use when running e2e tests.
 WP_BASE_URL=http://localhost:${LOCAL_PORT}

src/wp-includes/default-constants.php

@@ -77,9 +77,18 @@ function wp_initial_constants() {
 		define( 'WP_CONTENT_DIR', ABSPATH . 'wp-content' ); // No trailing slash, full paths only - WP_CONTENT_URL is defined further down.
 	}
 
+	/*
+	 * Add define( 'WP_DEVELOPMENT_MODE', 'core' ) or define( 'WP_DEVELOPMENT_MODE', 'plugin' ) or
+	 * define( 'WP_DEVELOPMENT_MODE', 'theme' ) to wp-config.php to signify development mode for WordPress core, a
+	 * plugin, or a theme respectively.
+	 */
+	if ( ! defined( 'WP_DEVELOPMENT_MODE' ) ) {
+		define( 'WP_DEVELOPMENT_MODE', '' );
+	}
+
 	// Add define( 'WP_DEBUG', true ); to wp-config.php to enable display of notices during development.
 	if ( ! defined( 'WP_DEBUG' ) ) {
-		if ( 'development' === wp_get_environment_type() ) {
+		if ( wp_get_development_mode() || 'development' === wp_get_environment_type() ) {
 			define( 'WP_DEBUG', true );
 		} else {
 			define( 'WP_DEBUG', false );

src/wp-includes/global-styles-and-settings.php

@@ -66,12 +66,10 @@ function wp_get_global_settings( $path = array(), $context = array() ) {
 	$cache_key   = 'wp_get_global_settings_' . $origin;
 
 	/*
-	 * Ignore cache when `WP_DEBUG` is enabled, so it doesn't interfere with the theme
+	 * Ignore cache when the development mode is set to 'theme', so it doesn't interfere with the theme
 	 * developer's workflow.
-	 *
-	 * @todo Replace `WP_DEBUG` once an "in development mode" check is available in Core.
 	 */
-	$can_use_cached = ! WP_DEBUG;
+	$can_use_cached = wp_get_development_mode() !== 'theme';
 
 	$settings = false;
 	if ( $can_use_cached ) {
@@ -151,12 +149,10 @@ function wp_get_global_styles( $path = array(), $context = array() ) {
  */
 function wp_get_global_stylesheet( $types = array() ) {
 	/*
-	 * Ignore cache when `WP_DEBUG` is enabled, so it doesn't interfere with the theme
+	 * Ignore cache when the development mode is set to 'theme', so it doesn't interfere with the theme
 	 * developer's workflow.
-	 *
-	 * @todo Replace `WP_DEBUG` once an "in development mode" check is available in Core.
 	 */
-	$can_use_cached = empty( $types ) && ! WP_DEBUG;
+	$can_use_cached = empty( $types ) && wp_get_development_mode() !== 'theme';
 
 	/*
 	 * By using the 'theme_json' group, this data is marked to be non-persistent across requests.
@@ -252,12 +248,10 @@ function wp_get_global_styles_custom_css() {
 		return '';
 	}
 	/*
-	 * Ignore cache when `WP_DEBUG` is enabled, so it doesn't interfere with the theme
+	 * Ignore cache when the development mode is set to 'theme', so it doesn't interfere with the theme
 	 * developer's workflow.
-	 *
-	 * @todo Replace `WP_DEBUG` once an "in development mode" check is available in Core.
 	 */
-	$can_use_cached = ! WP_DEBUG;
+	$can_use_cached = wp_get_development_mode() !== 'theme';
 
 	/*
 	 * By using the 'theme_json' group, this data is marked to be non-persistent across requests.
@@ -303,12 +297,10 @@ function wp_get_global_styles_custom_css() {
  */
 function wp_get_global_styles_svg_filters() {
 	/*
-	 * Ignore cache when `WP_DEBUG` is enabled, so it doesn't interfere with the theme
+	 * Ignore cache when the development mode is set to 'theme', so it doesn't interfere with the theme
 	 * developer's workflow.
-	 *
-	 * @todo Replace `WP_DEBUG` once an "in development mode" check is available in Core.
 	 */
-	$can_use_cached = ! WP_DEBUG;
+	$can_use_cached = wp_get_development_mode() !== 'theme';
 	$cache_group    = 'theme_json';
 	$cache_key      = 'wp_get_global_styles_svg_filters';
 	if ( $can_use_cached ) {
@@ -402,12 +394,10 @@ function wp_theme_has_theme_json() {
 	if (
 		null !== $theme_has_support &&
 		/*
-		 * Ignore static cache when `WP_DEBUG` is enabled. Why? To avoid interfering with
+		 * Ignore static cache when the development mode is set to 'theme', to avoid interfering with
 		 * the theme developer's workflow.
-		 *
-		 * @todo Replace `WP_DEBUG` once an "in development mode" check is available in Core.
 		 */
-		! WP_DEBUG &&
+		wp_get_development_mode() !== 'theme' &&
 		/*
 		 * Ignore cache when automated test suites are running. Why? To ensure
 		 * the static cache is reset between each test.

src/wp-includes/load.php

@@ -261,6 +261,50 @@ function wp_get_environment_type() {
 	return $current_env;
 }
 
+/**
+ * Retrieves the current development mode.
+ *
+ * The development mode affects how certain parts of the WordPress application behave, which is relevant when
+ * developing for WordPress.
+ *
+ * Valid developer modes are 'core', 'plugin', 'theme', or an empty string to disable developer mode.
+ *
+ * Developer mode is considered separately from `WP_DEBUG` and {@see wp_get_environment_type()}. It does not affect
+ * debugging output, but rather functional nuances in WordPress.
+ *
+ * @since 6.3.0
+ *
+ * @return string The current development mode.
+ */
+function wp_get_development_mode() {
+	static $current_mode = null;
+
+	if ( ! defined( 'WP_RUN_CORE_TESTS' ) && null !== $current_mode ) {
+		return $current_mode;
+	}
+
+	$development_mode = WP_DEVELOPMENT_MODE;
+
+	// Exclusively for core tests, rely on a global `$_wp_tests_development_mode`.
+	if ( defined( 'WP_RUN_CORE_TESTS' ) && isset( $GLOBALS['_wp_tests_development_mode'] ) ) {
+		$development_mode = $GLOBALS['_wp_tests_development_mode'];
+	}
+
+	$valid_modes = array(
+		'core',
+		'plugin',
+		'theme',
+		'',
+	);
+	if ( ! in_array( $development_mode, $valid_modes, true ) ) {
+		$development_mode = '';
+	}
+
+	$current_mode = $development_mode;
+
+	return $current_mode;
+}
+
 /**
  * Don't load all of WordPress when handling a favicon.ico request.
  *

tests/phpunit/tests/load/wpGetDevelopmentMode.php

@@ -0,0 +1,46 @@
+<?php
+/**
+ * Unit tests for `wp_get_development_mode()`.
+ *
+ * @package WordPress
+ * @subpackage UnitTests
+ * @since 6.3.0
+ *
+ * @group load.php
+ * @covers ::wp_get_development_mode
+ */
+class Test_WP_Get_Development_Mode extends WP_UnitTestCase {
+
+	/**
+	 * Tests that `wp_get_development_mode()` returns the value of the `WP_DEVELOPMENT_MODE` constant.
+	 *
+	 * @ticket 57487
+	 */
+	public function test_wp_get_development_mode_constant() {
+		$this->assertSame( WP_DEVELOPMENT_MODE, wp_get_development_mode() );
+	}
+
+	/**
+	 * Tests that `wp_get_development_mode()` allows test overrides.
+	 *
+	 * @ticket 57487
+	 */
+	public function test_wp_get_development_mode_test_overrides() {
+		global $_wp_tests_development_mode;
+
+		$_wp_tests_development_mode = 'plugin';
+		$this->assertSame( 'plugin', wp_get_development_mode() );
+	}
+
+	/**
+	 * Tests that `wp_get_development_mode()` ignores invalid filter values.
+	 *
+	 * @ticket 57487
+	 */
+	public function test_wp_get_development_mode_filter_invalid_value() {
+		global $_wp_tests_development_mode;
+
+		$_wp_tests_development_mode = 'invalid';
+		$this->assertSame( '', wp_get_development_mode() );
+	}
+}

tests/phpunit/tests/theme/wpGetGlobalStylesSvgFilters.php

@@ -34,4 +34,29 @@ class Tests_Theme_wpGetGlobalStylesSvgFilters extends WP_UnitTestCase {
 		$this->assertStringContainsString( '<svg', $svg_for_default_theme, 'Block theme should contain SVG' );
 		$this->assertNotSame( $svg_for_default_theme, $svg_for_block_theme, 'Cache value should have changed' );
 	}
+
+	/**
+	 * Tests that the function relies on the development mode for whether to use caching.
+	 *
+	 * @ticket 57487
+	 *
+	 * @covers ::wp_get_global_styles_svg_filters
+	 */
+	public function test_caching_is_used_when_developing_theme() {
+		global $_wp_tests_development_mode;
+
+		switch_theme( 'block-theme' );
+
+		// Store SVG in cache.
+		$svg = '<svg></svg>';
+		wp_cache_set( 'wp_get_global_styles_svg_filters', $svg, 'theme_json' );
+
+		// By default, caching should be used, so the above value will be returned.
+		$_wp_tests_development_mode = '';
+		$this->assertSame( $svg, wp_get_global_styles_svg_filters(), 'Caching was not used despite development mode disabled' );
+
+		// When the development mode is set to 'theme', caching should not be used.
+		$_wp_tests_development_mode = 'theme';
+		$this->assertNotSame( $svg, wp_get_global_styles_svg_filters(), 'Caching was used despite theme development mode' );
+	}
 }

tests/phpunit/tests/theme/wpGetGlobalStylesheet.php

@@ -220,6 +220,29 @@ class Tests_Theme_WpGetGlobalStylesheet extends WP_Theme_UnitTestCase {
 		$this->assertStringContainsString( $expected, $stylesheet_for_block_theme, 'Custom font size (100px) should be present for block theme' );
 	}
 
+	/**
+	 * Tests that the function relies on the development mode for whether to use caching.
+	 *
+	 * @ticket 57487
+	 */
+	public function test_caching_is_used_when_developing_theme() {
+		global $_wp_tests_development_mode;
+
+		$this->maybe_switch_theme( 'block-theme' );
+
+		// Store CSS in cache.
+		$css = '.my-class { display: block; }';
+		wp_cache_set( 'wp_get_global_stylesheet', $css, 'theme_json' );
+
+		// By default, caching should be used, so the above value will be returned.
+		$_wp_tests_development_mode = '';
+		$this->assertSame( $css, wp_get_global_stylesheet(), 'Caching was not used despite development mode disabled' );
+
+		// When the development mode is set to 'theme', caching should not be used.
+		$_wp_tests_development_mode = 'theme';
+		$this->assertNotSame( $css, wp_get_global_stylesheet(), 'Caching was used despite theme development mode' );
+	}
+
 	/**
 	 * Adds the 'editor-font-sizes' theme support with custom font sizes.
 	 *

tools/local-env/scripts/install.js

@@ -16,6 +16,7 @@ wp_cli( `config set WP_DEBUG_LOG ${process.env.LOCAL_WP_DEBUG_LOG} --raw --type=
 wp_cli( `config set WP_DEBUG_DISPLAY ${process.env.LOCAL_WP_DEBUG_DISPLAY} --raw --type=constant` );
 wp_cli( `config set SCRIPT_DEBUG ${process.env.LOCAL_SCRIPT_DEBUG} --raw --type=constant` );
 wp_cli( `config set WP_ENVIRONMENT_TYPE ${process.env.LOCAL_WP_ENVIRONMENT_TYPE} --type=constant` );
+wp_cli( `config set WP_DEVELOPMENT_MODE ${process.env.LOCAL_WP_DEVELOPMENT_MODE} --type=constant` );
 
 // Move wp-config.php to the base directory, so it doesn't get mixed up in the src or build directories.
 renameSync( 'src/wp-config.php', 'wp-config.php' );