More verbose and informative error messages, especially when dealing

with keyword values. Fixes #109

lib/carto/tree/rule.js

@@ -58,13 +58,20 @@ tree.Rule.prototype.toXML = function(env, content, sep, format) {
                 filename: this.filename
             });
         } else {
+            var typename;
+            if (tree.Reference.selector(this.name).validate) {
+                typename = tree.Reference.selector(this.name).validate;
+            } else if (typeof tree.Reference.selector(this.name).type === 'object') {
+                typename = 'keyword (options: ' + tree.Reference.selector(this.name).type.join(', ') + ')';
+            } else {
+                typename = tree.Reference.selector(this.name).type;
+            }
             return env.error({
                 message: 'Invalid value for ' +
                     this.name +
-                    ', a valid ' +
-                    (tree.Reference.selector(this.name).validate ||
-                        tree.Reference.selector(this.name).type) +
+                    ', the type ' + typename +
                     ' is expected. ' + this.value +
+                    ' (of type ' + this.value.value[0].is + ') ' +
                     ' was given.',
                 index: this.index,
                 type: 'syntax',

test/errorhandling/invalid_value.mss

@@ -1,3 +1,5 @@
 #world[zoom=5] {
-  polygon-opacity: #f00;
+  text-face-name: 2;
+  line-rasterizer: 'full';
+  text-name: 'foo';
 }

test/errorhandling/invalid_value.result

@@ -1 +1,2 @@
-invalid_value.mss:2:2 Invalid value for polygon-opacity, a valid float is expected. #ff0000 was given.
+invalid_value.mss:2:2 Invalid value for text-face-name, the type font is expected. 2 (of type float)  was given.
+invalid_value.mss:3:2 Invalid value for line-rasterizer, the type keyword (options: full, fast) is expected. full (of type string)  was given.