Disable more editing features

Since we're managing the content, title, and slug elsewhere, we should
disable editing these fields in the dashboard.

wp-content/mu-plugins/markdown-sync.php

@@ -1,10 +1,12 @@
 <?php
 
 require_once __DIR__ . '/markdown-sync/plugin.php';
+require_once __DIR__ . '/markdown-sync/class-cpdocs-editor.php';
 require_once __DIR__ . '/markdown-sync/class-cpdocs-importer.php';
 
 $cpnet_docs_importer = new CPDocs_Importer();
-$cpnet_docs_editor = new WordPressdotorg\Markdown\Editor( $cpnet_docs_importer );
+$cpnet_docs_editor = new CPDocs_Editor( $cpnet_docs_importer );
+add_action( 'init', [ $cpnet_docs_editor, 'init' ] );
 
 if ( class_exists( 'WP_CLI' ) ) {
 	WP_CLI::add_command(

wp-content/mu-plugins/markdown-sync/class-cpdocs-editor.php

@@ -0,0 +1,137 @@
+<?php
+
+use WordPressdotorg\Markdown\Editor;
+
+class CPDocs_Editor extends Editor {
+	/**
+	 * Override for main initialization function - we will modify some of the
+	 * parent class' behavior.
+	 */
+	public function init() {
+		parent::init();
+		// Disable some features of the post editor.
+		add_filter( 'replace_editor', [ $this, 'maybe_disable_edits' ], 10, 2 );
+	}
+
+	/**
+	 * New function to determine whether this particular post is handled by the
+	 * markdown sync system.
+	 */
+	public function is_markdown_post( WP_Post $post ) {
+		if ( $post->post_type !== $this->importer->get_post_type() ) {
+			return false;
+		}
+
+		$source = $this->importer->get_markdown_source( $post->ID );
+		if ( is_wp_error( $source ) || empty( $source ) ) {
+			return false;
+		}
+
+		return true;
+	}
+
+	/**
+	 * Override for rendering an editor warning: we shouldn't do this for all
+	 * pages, only the ones where we actually have Markdown content.
+	 *
+	 * We also modify the text of this warning slightly.
+	 *
+	 * @param WP_Post $post Post being edited.
+	 */
+	public function render_editor_warning( WP_Post $post ) {
+		if ( ! $this->is_markdown_post( $post ) ) {
+			return;
+		}
+
+		printf(
+			'<div class="notice notice-warning"><p>%s</p><p><a href="%s">%s</a></p></div>',
+			'This page is maintained on GitHub, please make any changes to the content, title, and slug there instead.',
+			$this->get_markdown_edit_link( $post->ID ),
+			'Edit on GitHub'
+		);
+	}
+
+	/**
+	 * New function to disable editing content, title, and slug for posts that
+	 * are edited on GitHub.
+	 */
+	public function maybe_disable_edits( $replace, $post ) {
+		if ( $this->is_markdown_post( $post ) ) {
+			// Don't return true because that will replace the entire editor
+			// interface.  Instead use this hack to disable the content box
+			// just in time.
+			remove_post_type_support( $post->post_type, 'editor' );
+			// Disable editing the title and the slug.  This just disables the
+			// UI controls (doesn't actually disable the related POST request)
+			// but that is good enough for our use-case.
+			add_action(
+				'edit_form_top',
+				[ $this, 'disable_edits_step1' ]
+			);
+		}
+
+		return $replace;
+	}
+
+	/**
+	 * New function to disable editing the title and the permalink (slug).
+	 *
+	 * Step 1: Setup - enable these hacks just in time.
+	 */
+	public function disable_edits_step1( $post ) {
+		ob_start(); // Catch the HTML for the title edit box.
+		add_filter(
+			'page_link',
+			[ $this, 'disable_edits_step2' ],
+			10,
+			3
+		);
+		add_action(
+			'edit_form_after_title',
+			[ $this, 'disable_edits_step3' ]
+		);
+	}
+
+	/**
+	 * New function to disable editing the title and the permalink (slug).
+	 *
+	 * Step 2: Disable editing the slug by changing the sample permalink HTML.
+	 *
+	 * See: https://github.com/ClassicPress/ClassicPress/blob/1.1.2+dev/src/wp-admin/includes/post.php#L1355-L1385
+	 */
+	public function disable_edits_step2( $link, $post_id, $sample ) {
+		if ( ! $sample ) {
+			return $link;
+		}
+
+		return str_replace(
+			'%pagename%',
+			get_post( $post_id )->post_name,
+			$link
+		);
+	}
+
+	/**
+	 * New function to disable editing the title and the permalink (slug).
+	 *
+	 * Step 3: Make the title edit box read-only, and unhook temporary filters.
+	 *
+	 * See: https://github.com/ClassicPress/ClassicPress/blob/1.1.2+dev/src/wp-admin/edit-form-advanced.php#L574
+	 */
+	public function disable_edits_step3() {
+		// Get the currently buffered HTML including the title edit box.
+		$html = ob_get_clean();
+		// Add a readonly attribute. input[readonly] has background #eee but
+		// this is overridden by the CSS rules for the title edit box.
+		echo preg_replace(
+			'#<input type="text" name="post_title"#',
+			'<input type="text" name="post_title" readonly style="background:#eee"',
+			$html
+		);
+		// Remove the temporary filter we used to disable editing the slug.
+		remove_filter(
+			'page_link',
+			[ $this, 'disable_edits_step2' ]
+		);
+	}
+}