Added rule to detect multiple usage of the same background-image

src/rules/duplicate-background-url.js

@@ -0,0 +1,37 @@
+/*
+ * Rule: Disallow duplicate background-images (using url).
+ */
+/*global CSSLint*/
+CSSLint.addRule({
+
+    //rule information
+    id: "duplicate-background-url",
+    name: "Disallow duplicate background-url",
+    desc: "Every background-image should be unique. Use a common class for e.g. sprites.",
+    browsers: "All",
+
+    //initialization
+    init: function(parser, reporter){
+        var rule = this,
+            stack = {};
+
+        parser.addListener("property", function(event){
+            var name = event.property.text,
+                value = event.value,
+                i;
+
+            if (name.match(/background/i)) {
+                for (i in value.parts) {
+                    if (value.parts[i].type == 'uri') {
+                        if (typeof stack[value.parts[i].uri] === 'undefined') {
+                            stack[value.parts[i].uri] = event;
+                        }
+                        else {
+                            reporter.report("Background-Image (" + value.parts[i].uri + ") was used multiple times, first declared at line " + stack[value.parts[i].uri].line + ", col " + + stack[value.parts[i].uri].col + ".", event.line, event.col, rule);
+                        }
+                    }
+                }
+            }
+        });
+    }
+});

tests/rules/duplicate-background-url.js

@@ -0,0 +1,25 @@
+(function(){
+
+    /*global YUITest, CSSLint*/
+    var Assert = YUITest.Assert;
+
+    YUITest.TestRunner.add(new YUITest.TestCase({
+
+        name: "Duplicate Background-URL Rule Errors",
+
+        "duplicate background-image should result in a warning": function(){
+            var result = CSSLint.verify(".foo { background-image: url('mega-sprite.png'); } .foofoo { background-image: url('fancy-sprite.png'); } .bar { background-image: url(\"mega-sprite.png\"); } .foobar { background: white url(mega-sprite.png); }", {"duplicate-background-url": 1 });
+            Assert.areEqual(2, result.messages.length);
+            Assert.areEqual("warning", result.messages[0].type);
+            Assert.areEqual("Background-Image (mega-sprite.png) was used multiple times, first declared at line 1, col 8.", result.messages[0].message);
+        },
+
+        "duplicate background with url should result in a warning": function(){
+            var result = CSSLint.verify(".foo { background: url(mega-sprite.png) repeat-x; } .foofoo { background-image: url('fancy-sprite.png'); } .bar { background: white url(\"mega-sprite.png\") no-repeat left top; } .foobar { background: white url('mega-sprite.png'); }", {"duplicate-background-url": 1 });
+            Assert.areEqual(2, result.messages.length);
+            Assert.areEqual("warning", result.messages[0].type);
+            Assert.areEqual("Background-Image (mega-sprite.png) was used multiple times, first declared at line 1, col 8.", result.messages[0].message);
+        }
+    }));
+
+})();