Add slugify and duplicateslugs operators

Fixes #3379

core/modules/filters/duplicateslugs.js

@@ -0,0 +1,36 @@
+/*\
+title: $:/core/modules/filters/duplicateslugs.js
+type: application/javascript
+module-type: filteroperator
+
+Filter function for [duplicateslugs[]]
+
+\*/
+(function(){
+
+/*jslint node: true, browser: true */
+/*global $tw: false */
+"use strict";
+
+/*
+Export our filter function
+*/
+exports.duplicateslugs = function(source,operator,options) {
+	var slugs = Object.create(null), // Hashmap by slug of title, replaced with "true" if the duplicate title has already been output
+		results = [];
+	source(function(tiddler,title) {
+		var slug = options.wiki.slugify(title);
+		if(slug in slugs) {
+			if(slugs[slug] !== true) {
+				results.push(slugs[slug]);
+				slugs[slug] = true;
+			}
+			results.push(title);
+		} else {
+			slugs[slug] = title;
+		}
+	});
+	return results;
+};
+
+})();

core/modules/filters/slugify.js

@@ -0,0 +1,23 @@
+/*\
+title: $:/plugins/tiddlywiki/static/filters/slugify.js
+type: application/javascript
+module-type: filteroperator
+
+Filter operator for slugifying a tiddler title
+
+\*/
+(function(){
+
+/*jslint node: true, browser: true */
+/*global $tw: false */
+"use strict";
+
+exports.slugify = function(source,operator,options) {
+	var results = [];
+	source(function(tiddler,title) {
+		results.push(options.wiki.slugify(title));
+	});
+	return results;
+};
+
+})();

core/modules/wiki.js

@@ -1503,5 +1503,30 @@ exports.doesPluginInfoRequireReload = function(pluginInfo) {
 	}
 };
 
+exports.slugify = function(title,options) {
+	var tiddler = this.getTiddler(title),
+		slug;
+	if(tiddler && tiddler.fields.slug) {
+		slug = tiddler.fields.slug;
+	} else {
+		slug = $tw.utils.transliterate(title.toString().toLowerCase()) // Replace diacritics with basic lowercase ASCII
+			.replace(/\s+/g,"-")                                       // Replace spaces with -
+			.replace(/[^\w\-\.]+/g,"")                                 // Remove all non-word chars except dash and dot
+			.replace(/\-\-+/g,"-")                                     // Replace multiple - with single -
+			.replace(/^-+/,"")                                         // Trim - from start of text
+			.replace(/-+$/,"");                                        // Trim - from end of text
+	}
+	// If the resulting slug is blank (eg because the title is just punctuation characters)
+	if(!slug) {
+		// ...then just use the character codes of the title
+		var result = [];
+		$tw.utils.each(title.split(""),function(char) {
+			result.push(char.charCodeAt(0).toString());
+		});
+		slug = result.join("-");
+	}
+	return slug;
+};
+
 })();