Much better error reporting, did you mean

lib/carto/tree/call.js

@@ -1,4 +1,5 @@
 (function(tree) {
+var _ = require('underscore');
 
 tree.Call = function Call(name, args, index) {
     this.is = 'call';
@@ -52,8 +53,17 @@ tree.Call.prototype = {
         } else {
             var fn = tree.Reference.mapnikFunction(this.name);
             if (!fn) {
+                var functions = tree.Reference.mapnikFunctions();
+                // cheap closest, needs improvement.
+                var name_array = this.name.split('');
+                var mean = functions.map(function(f) {
+                    return [f[0], _.intersection(name_array, f[0].split('')).length, f[1]];
+                }).sort(function(a, b) {
+                    return b[1] - a[1];
+                });
                 env.error({
-                    message: 'unknown function ' + this.name,
+                    message: 'unknown function ' + this.name + '(), did you mean ' +
+                        mean[0][0] + '(' + mean[0][2] + ')',
                     index: this.index,
                     type: 'runtime',
                     filename: this.filename
@@ -65,7 +75,7 @@ tree.Call.prototype = {
             }
             if (fn[1] !== args.length) {
                 env.error({
-                    message: 'function ' + this.name + ' takes ' +
+                    message: 'function ' + this.name + '() takes ' +
                         fn[1] + ' arguments and was given ' + args.length,
                     index: this.index,
                     type: 'runtime',

lib/carto/tree/reference.js

@@ -76,7 +76,7 @@ tree.Reference.symbolizer = function(selector) {
  * For transform properties and image-filters,
  * mapnik has its own functions.
  */
-tree.Reference.mapnikFunction = function(name) {
+tree.Reference.mapnikFunctions = function() {
     var functions = [];
     for (var i in tree.Reference.data.symbolizers) {
         for (var j in tree.Reference.data.symbolizers[i]) {
@@ -85,7 +85,15 @@ tree.Reference.mapnikFunction = function(name) {
             }
         }
     }
-    return _.find(functions, function(f) {
+    return functions;
+};
+
+/*
+ * For transform properties and image-filters,
+ * mapnik has its own functions.
+ */
+tree.Reference.mapnikFunction = function(name) {
+    return _.find(this.mapnikFunctions(), function(f) {
         return f[0] === name;
     });
 };

test/errorhandling/function_args.mml

@@ -0,0 +1,15 @@
+{
+    "srs": "+proj=merc +a=6378137 +b=6378137 +lat_ts=0.0 +lon_0=0.0 +x_0=0.0 +y_0=0.0 +k=1.0 +units=m +nadgrids=@null +wktext +no_defs +over",
+    "Stylesheet": [
+        "function_args.mss"
+    ],
+    "Layer": [{
+        "id": "world",
+        "name": "world",
+        "srs": "+proj=merc +a=6378137 +b=6378137 +lat_ts=0.0 +lon_0=0.0 +x_0=0.0 +y_0=0.0 +k=1.0 +units=m +nadgrids=@null +wktext +no_defs +over",
+        "Datasource": {
+            "file": "http://tilemill-data.s3.amazonaws.com/test_data/shape_demo.zip",
+            "type": "shape"
+        }
+    }]
+}

test/errorhandling/function_args.mss

@@ -0,0 +1,4 @@
+#world {
+    point-transform: scale(2, 2);
+    image-filters: agg-stack-blu(2, 1);
+}

test/errorhandling/function_args.result

@@ -0,0 +1 @@
+function_args.mss:3:38 unknown function agg-stack-blu(), did you mean agg-stack-blur(2)