Added general de/activation mechanism for plugins (#2434)

Keep Markup, Line numbers, and Normalize whitespace now share the same per-element class-based de/activation logic.

components/prism-core.js

@@ -143,6 +143,41 @@ var _ = {
 				}
 				return null;
 			}
+		},
+
+		/**
+		 * Returns whether a given class is active for `element`.
+		 *
+		 * The class can be activated if `element` or one of its ancestors has the given class and it can be deactivated
+		 * if `element` or one of its ancestors has the negated version of the given class. The _negated version_ of the
+		 * given class is just the given class with a `no-` prefix.
+		 *
+		 * Whether the class is active is determined by the closest ancestor of `element` (where `element` itself is
+		 * closest ancestor) that has the given class or the negated version of it. If neither `element` nor any of its
+		 * ancestors have the given class or the negated version of it, then the default activation will be returned.
+		 *
+		 * In the paradoxical situation where the closest ancestor contains __both__ the given class and the negated
+		 * version of it, the class is considered active.
+		 *
+		 * @param {Element} element
+		 * @param {string} className
+		 * @param {boolean} [defaultActivation=false]
+		 * @returns {boolean}
+		 */
+		isActive: function (element, className, defaultActivation) {
+			var no = 'no-' + className;
+
+			while (element) {
+				var classList = element.classList;
+				if (classList.contains(className)) {
+					return true;
+				}
+				if (classList.contains(no)) {
+					return false;
+				}
+				element = element.parentElement;
+			}
+			return !!defaultActivation;
 		}
 	},
 

plugins/keep-markup/index.html

@@ -34,7 +34,10 @@
 <section>
 
 	<h1>How to use</h1>
-	<p>You have nothing to do. With this plugin loaded, all markup inside code will be kept.</p>
+
+	<p>You have nothing to do. The plugin is active by default. With this plugin loaded, all markup inside code will be kept.</p>
+
+	<p>However, you can deactivate the plugin for certain code element by adding the <code>no-keep-markup</code> class to it. You can also deactivate the plugin for the whole page by adding the <code>no-keep-markup</code> class to the body of the page and then selectively activate it again by adding the <code>keep-markup</code> class to code elements.</p>
 
 	<h1>Examples</h1>
 

plugins/keep-markup/prism-keep-markup.js

@@ -11,6 +11,10 @@
 			return;
 		}
 
+		if (!Prism.util.isActive(env.element, 'keep-markup', true)) {
+			return;
+		}
+
 		var pos = 0;
 		var data = [];
 		var f = function (elt, baseNode) {

plugins/line-numbers/prism-line-numbers.js

@@ -74,8 +74,8 @@
 			return;
 		}
 
-		var code = env.element;
-		var pre = code.parentNode;
+		var code = /** @type {Element} */ (env.element);
+		var pre = /** @type {Element} */ (code.parentNode);
 
 		// works only for <code> wrapped inside <pre> (not inline)
 		if (!pre || !/pre/i.test(pre.nodeName)) {
@@ -87,27 +87,15 @@
 			return;
 		}
 
-		var addLineNumbers = false;
-		var lineNumbersRegex = /(?:^|\s)line-numbers(?:\s|$)/;
-
-		for (var element = code; element; element = element.parentNode) {
-			if (lineNumbersRegex.test(element.className)) {
-				addLineNumbers = true;
-				break;
-			}
-		}
-
 		// only add line numbers if <code> or one of its ancestors has the `line-numbers` class
-		if (!addLineNumbers) {
+		if (!Prism.util.isActive(code, PLUGIN_NAME)) {
 			return;
 		}
 
 		// Remove the class 'line-numbers' from the <code>
-		code.className = code.className.replace(lineNumbersRegex, ' ');
+		code.classList.remove(PLUGIN_NAME);
 		// Add the class 'line-numbers' to the <pre>
-		if (!lineNumbersRegex.test(pre.className)) {
-			pre.className += ' line-numbers';
-		}
+		pre.classList.add(PLUGIN_NAME);
 
 		var match = env.code.match(NEW_LINE_EXP);
 		var linesNum = match ? match.length + 1 : 1;