WP_Theme_JSON::merge() WordPress Method

	public function merge( $incoming ) {
		$incoming_data    = $incoming->get_raw_data();
		$this->theme_json = array_replace_recursive( $this->theme_json, $incoming_data );

		/*
		 * The array_replace_recursive algorithm merges at the leaf level,
		 * but we don't want leaf arrays to be merged, so we overwrite it.
		 *
		 * For leaf values that are sequential arrays it will use the numeric indexes for replacement.
		 * We rather replace the existing with the incoming value, if it exists.
		 * This is the case of spacing.units.
		 *
		 * For leaf values that are associative arrays it will merge them as expected.
		 * This is also not the behavior we want for the current associative arrays (presets).
		 * We rather replace the existing with the incoming value, if it exists.
		 * This happens, for example, when we merge data from theme.json upon existing
		 * theme supports or when we merge anything coming from the same source twice.
		 * This is the case of color.palette, color.gradients, color.duotone,
		 * typography.fontSizes, or typography.fontFamilies.
		 *
		 * Additionally, for some preset types, we also want to make sure the
		 * values they introduce don't conflict with default values. We do so
		 * by checking the incoming slugs for theme presets and compare them
		 * with the equivalent default presets: if a slug is present as a default
		 * we remove it from the theme presets.
		 */
		$nodes        = static::get_setting_nodes( $incoming_data );
		$slugs_global = static::get_default_slugs( $this->theme_json, array( 'settings' ) );
		foreach ( $nodes as $node ) {
			$slugs_node = static::get_default_slugs( $this->theme_json, $node['path'] );
			$slugs      = array_merge_recursive( $slugs_global, $slugs_node );

			// Replace the spacing.units.
			$path    = array_merge( $node['path'], array( 'spacing', 'units' ) );
			$content = _wp_array_get( $incoming_data, $path, null );
			if ( isset( $content ) ) {
				_wp_array_set( $this->theme_json, $path, $content );
			}

			// Replace the presets.
			foreach ( static::PRESETS_METADATA as $preset ) {
				$override_preset = ! static::get_metadata_boolean( $this->theme_json['settings'], $preset['prevent_override'], true );

				foreach ( static::VALID_ORIGINS as $origin ) {
					$base_path = array_merge( $node['path'], $preset['path'] );
					$path      = array_merge( $base_path, array( $origin ) );
					$content   = _wp_array_get( $incoming_data, $path, null );
					if ( ! isset( $content ) ) {
						continue;
					}

					if ( 'theme' === $origin && $preset['use_default_names'] ) {
						foreach ( $content as &$item ) {
							if ( ! array_key_exists( 'name', $item ) ) {
								$name = static::get_name_from_defaults( $item['slug'], $base_path );
								if ( null !== $name ) {
									$item['name'] = $name;
								}
							}
						}
					}

					if (
						( 'theme' !== $origin ) ||
						( 'theme' === $origin && $override_preset )
					) {
						_wp_array_set( $this->theme_json, $path, $content );
					} else {
						$slugs_for_preset = _wp_array_get( $slugs, $preset['path'], array() );
						$content          = static::filter_slugs( $content, $slugs_for_preset );
						_wp_array_set( $this->theme_json, $path, $content );
					}
				}
			}
		}
	}