allow expressions in filters, fixes mapbox#377

CHANGELOG.md

@@ -13,6 +13,8 @@ There is a new command line / API switch (`-q / --quiet` / `quiet`) to suppress
 (`-o / --output` / `outputFormat`) to choose the output format. Possible values are `mapnik` (default)
 for Mapnik XML and `json` for the JSON variant (part of [#413](https://github.com/mapbox/carto/issues/413)).
 For Mapnik XML all character data as tag content is now prefixed with CDATA.
+* Expressions are allowed in filters e.g. `[height] % 50 = 0` or `[height] + 10 = 0`, fields have to be properly written within brackets
+([#377](https://github.com/mapbox/carto/issues/377))
 
 ### Breaking changes
 

docs/styling_concepts.rst

@@ -134,3 +134,8 @@ String comparisons::
 
     /* a regular expression over name */
     #world[name =~ "A.*"]
+
+More complex expressions::
+
+    #world[[population] % 50 = 0]
+    #world[[population] * 2 < 1000]

lib/carto/parser.js

@@ -547,6 +547,7 @@ carto.Parser = function Parser(env) {
                 /*eslint-disable no-cond-assign */
                 if (key = $(/^[a-zA-Z0-9\-_]+/) ||
                     $(this.entities.quoted) ||
+                    $(this.expression) ||
                     $(this.entities.variable) ||
                     $(this.entities.keyword) ||
                     $(this.entities.field)) {

test/rendering-mss/issue_377.mss

@@ -0,0 +1,3 @@
+[[height] % 50 = 0] {
+    marker-fill: red;
+}

test/rendering-mss/issue_377.xml

@@ -0,0 +1,6 @@
+<Style filter-mode="first" name="style">
+  <Rule>
+    <Filter><![CDATA[([height]%50 = 0)]]></Filter>
+    <MarkersSymbolizer fill="#ff0000" />
+  </Rule>
+</Style>