Improve Old prefixes offenders readability

lib/metadata/policies.js

@@ -752,36 +752,53 @@ var policies = {
     "cssOldPropertyPrefixes": {
         "tool": "phantomas",
         "label": "Old prefixes",
-        "message": "<p>Many property prefixes such as -moz- or -webkit- are not needed anymore, or by very few people. You can remove them or replace them with the non-prefixed version. This will help reducing your stylesheets weight.</p>",
+        "message": "<p>Many property prefixes such as -moz- or -webkit- are not needed anymore, or by very few people. Sometimes, they have never even existed. You can remove them or replace them with the non-prefixed version. This will help reducing your stylesheets weight.</p><p>The prefixes database comes from <a href=\"http://caniuse.com/\" target=\"_blank\">Can I Use</a>.</p>",
         "isOkThreshold": 0,
         "isBadThreshold": 75,
         "isAbnormalThreshold": 300,
         "hasOffenders": true,
         "offendersTransformFn": function(offenders) {
+            var properties = {};
+            offenders.forEach(function(offender) {
+                var splittedOffender = offendersHelpers.cssOffenderPattern(offender);
+
+                var parts = /^([^{]*)(?: ?{ ?([^ ]+): (.*) ?}) \/\/ (.*)$/.exec(splittedOffender.css);
+
+                if (!parts) {
+                    debug('cssOldPropertyPrefixes offenders transform function error with "%s"', offender);
+                    return {
+                        parseError: offender
+                    };
+                }
+
+                var propertyName = parts[2];
+
+                if (!properties[propertyName]) {
+                    properties[propertyName] = {
+                        property: propertyName,
+                        message: parts[4],
+                        rules: []
+                    };
+                }
+
+                properties[propertyName].rules.push({
+                    rule: parts[1],
+                    value: parts[3],
+                    file: splittedOffender.file,
+                    line: splittedOffender.line,
+                    column: splittedOffender.column
+                });
+            });
+
+            // Object to array
+            var list = [];
+            for (var propertyName in properties) {
+                list.push(properties[propertyName]);
+            }
+
             return {
                 count: offenders.length,
-                list: offenders.map(function(offender) {
-                    var splittedOffender = offendersHelpers.cssOffenderPattern(offender);
-
-                    var parts = /^([^{]*)(?: ?{ ?([^ ]+): (.*) ?}) \/\/ (.*)$/.exec(splittedOffender.css);
-
-                    if (!parts) {
-                        debug('cssOldPropertyPrefixes offenders transform function error with "%s"', offender);
-                        return {
-                            parseError: offender
-                        };
-                    }
-
-                    return {
-                        rule: parts[1],
-                        property: parts[2],
-                        value: parts[3],
-                        message: parts[4],
-                        file: splittedOffender.file,
-                        line: splittedOffender.line,
-                        column: splittedOffender.column
-                    };
-                })
+                list: list
             };
         }
     },