implement chain selector support

Author: btamas

lib/generate-descendant-pieces-from-selector.js

@@ -4,6 +4,21 @@
 // We could almost use `/\b\s(?![><+~][\s]+?)/` to split the selector but this doesn't work with attribute selectors
 var RE_SELECTOR_DESCENDANT_SPLIT = (/(.*?(?:(?:\([^\)]+\)|\[[^\]]+\]|(?![><+~\s]).)+)(?:(?:(?:\s(?!>>))|(?:\t(?!>>))|(?:\s?>>\s?))(?!\s+))(?![><+~][\s]+?))/);
 
+// Separate selector to classes and ids
+var RE_SELECTOR_SEPARATOR = /(([\.#]?)[^\.#]+)/g;
+
+// Helper function to get all combination of a text array
+var getCombinations = function(strings) {
+    var result = [];
+    var f = function(prefix, strings) {
+      for (var i = 0; i < strings.length; i++) {
+        result.push(prefix + strings[i]);
+        f(prefix + strings[i], strings.slice(i + 1));
+      }
+    }
+    f('', strings);
+    return result;
+}
 
 var generateDescendantPiecesFromSelector = function(selector) {
 	return selector.split(RE_SELECTOR_DESCENDANT_SPLIT)
@@ -17,7 +32,19 @@ var generateDescendantPiecesFromSelector = function(selector) {
 			// Trim whitespace which would be a normal descendant selector
 			// and trim off the CSS4 descendant `>>` into a normal descendant selector
 			return piece.trim().replace(/\s*?>>\s*?/g, '');
-		});
+		})
+		.reduce(function(result, piece) {
+			if (piece.indexOf(' ') !== -1) {
+				result.push(piece);
+				return result;
+			}
+			// a.b#c => [a, .b, #c]
+			var pieces = piece.match(RE_SELECTOR_SEPARATOR);
+			// [a, .b, #c] => [a, a.b, a.b#c, a#c, .b, .b#c, #c]
+            var combinations = getCombinations(pieces);
+			result = result.concat(combinations);
+            return result;
+        }, []);
 };
 
 module.exports = generateDescendantPiecesFromSelector;