Editor: Add CodeMirror-powered code editor with syntax highlighting, linting, and auto-completion.

* Code editor is integrated into the Theme/Plugin Editor, Additional CSS in Customizer, and Custom HTML widget. Code editor is not yet integrated into the post editor, and it may not be until accessibility concerns are addressed.
* The CodeMirror component in the Custom HTML widget is integrated in a similar way to TinyMCE being integrated into the Text widget, adopting the same approach for integrating dynamic JavaScript-initialized fields.
* Linting is performed for JS, CSS, HTML, and JSON via JSHint, CSSLint, HTMLHint, and JSONLint respectively. Linting is not yet supported for PHP.
* When user lacks `unfiltered_html` the capability, the Custom HTML widget will report any Kses-invalid elements and attributes as errors via a custom Kses rule for HTMLHint.
* When linting errors are detected, the user will be prevented from saving the code until the errors are fixed, reducing instances of broken websites.
* The placeholder value is removed from Custom CSS in favor of a fleshed-out section description which now auto-expands when the CSS field is empty. See #39892.
* The CodeMirror library is included as `wp.CodeMirror` to prevent conflicts with any existing `CodeMirror` global.
* An `wp.codeEditor.initialize()` API in JS is provided to convert a `textarea` into CodeMirror, with a `wp_enqueue_code_editor()` function in PHP to manage enqueueing the assets and settings needed to edit a given type of code.
* A user preference is added to manage whether or not "syntax highlighting" is enabled. The feature is opt-out, being enabled by default.
* Allowed file extensions in the theme and plugin editors have been updated to include formats which CodeMirror has modes for: `conf`, `css`, `diff`, `patch`, `html`, `htm`, `http`, `js`, `json`, `jsx`, `less`, `md`, `php`, `phtml`, `php3`, `php4`, `php5`, `php7`, `phps`, `scss`, `sass`, `sh`, `bash`, `sql`, `svg`, `xml`, `yml`, `yaml`, `txt`.

Props westonruter, georgestephanis, obenland, melchoyce, pixolin, mizejewski, michelleweber, afercia, grahamarmfield, samikeijonen, rianrietveld, iseulde.
See #38707.
Fixes #12423, #39892.


git-svn-id: https://develop.svn.wordpress.org/trunk@41376 602fd350-edb4-49c9-b593-d223f7449a82

src/wp-admin/js/theme-plugin-editor.js

@@ -0,0 +1,90 @@
+/* eslint no-magic-numbers: ["error", { "ignore": [-1, 0, 1] }] */
+
+if ( ! window.wp ) {
+	window.wp = {};
+}
+
+wp.themePluginEditor = (function( $ ) {
+	'use strict';
+
+	var component = {
+		l10n: {
+			lintError: {
+				singular: '',
+				plural: ''
+			}
+		},
+		instance: null
+	};
+
+	/**
+	 * Initialize component.
+	 *
+	 * @param {object} settings Settings.
+	 * @returns {void}
+	 */
+	component.init = function( settings ) {
+		var codeEditorSettings, noticeContainer, errorNotice = [], editor;
+
+		codeEditorSettings = $.extend( {}, settings );
+
+		/**
+		 * Handle tabbing to the field before the editor.
+		 *
+		 * @returns {void}
+		 */
+		codeEditorSettings.onTabPrevious = function() {
+			$( '#templateside' ).find( ':tabbable' ).last().focus();
+		};
+
+		/**
+		 * Handle tabbing to the field after the editor.
+		 *
+		 * @returns {void}
+		 */
+		codeEditorSettings.onTabNext = function() {
+			$( '#template' ).find( ':tabbable:not(.CodeMirror-code)' ).first().focus();
+		};
+
+		// Create the error notice container.
+		noticeContainer = $( '<div id="file-editor-linting-error"></div>' );
+		errorNotice = $( '<div class="inline notice notice-error"></div>' );
+		noticeContainer.append( errorNotice );
+		noticeContainer.hide();
+		$( 'p.submit' ).before( noticeContainer );
+
+		/**
+		 * Update error notice.
+		 *
+		 * @param {Array} errorAnnotations - Error annotations.
+		 * @returns {void}
+		 */
+		codeEditorSettings.onUpdateErrorNotice = function onUpdateErrorNotice( errorAnnotations ) {
+			var message;
+
+			$( '#submit' ).prop( 'disabled', 0 !== errorAnnotations.length );
+
+			if ( 0 !== errorAnnotations.length ) {
+				errorNotice.empty();
+				if ( 1 === errorAnnotations.length ) {
+					message = component.l10n.singular.replace( '%d', '1' );
+				} else {
+					message = component.l10n.plural.replace( '%d', String( errorAnnotations.length ) );
+				}
+				errorNotice.append( $( '<p></p>', {
+					text: message
+				} ) );
+				noticeContainer.slideDown( 'fast' );
+				wp.a11y.speak( message );
+			} else {
+				noticeContainer.slideUp( 'fast' );
+			}
+		};
+
+		editor = wp.codeEditor.initialize( $( '#newcontent' ), codeEditorSettings );
+
+		component.instance = editor;
+	};
+
+	return component;
+})( jQuery );