Allow layers to be rendered without datasources.

lib/carto/tree/layer.js

@@ -20,9 +20,11 @@ tree.LayerXML = function(obj, styles) {
         styles.reverse().map(function(s) {
             return '<StyleName>' + s + '</StyleName>';
         }).join('\n    ') +
+        (dsoptions.length ?
         '\n    <Datasource>\n       ' +
         dsoptions.join('\n       ') +
-        '\n    </Datasource>\n' +
+        '\n    </Datasource>\n'
+        : '') +
         '  </Layer>\n';
 };
 

test/rendering/layer_nodatasource.mml

@@ -0,0 +1,10 @@
+{
+    "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": [
+        "layer_nodatasource.mss"
+    ],
+    "Layer": [{
+        "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"
+    }]
+}

test/rendering/layer_nodatasource.mss

@@ -0,0 +1,4 @@
+#world {
+  polygon-fill: green;
+  line-color: hsl(30, 40%, 90%);
+}

test/rendering/layer_nodatasource.result

@@ -0,0 +1,17 @@
+<?xml version="1.0" encoding="utf-8"?>
+<!DOCTYPE Map[]>
+<Map 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"  maximum-extent="-20037508.34,-20037508.34,20037508.34,20037508.34">
+
+
+<Style name="world" filter-mode="first">
+  <Rule>
+    <PolygonSymbolizer fill="#008000" />
+    <LineSymbolizer stroke="#f0e6db" />
+  </Rule>
+</Style>
+<Layer 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">
+    <StyleName>world</StyleName>
+  </Layer>
+
+</Map>

test/support/helper.js

@@ -195,6 +195,7 @@ helper.removeAbsoluteImages = function(xml) {
 helper.removeAbsoluteDatasources = function(xml) {
     xml.Map.forEach(function(map) {
         if (map.Layer) map.Layer.forEach(function(layer) {
+            if (!layer.Datasource) return;
             layer.Datasource.forEach(function(datasource) {
                 datasource.Parameter.forEach(function(param) {
                     if (param.name === 'file') {