Accept {expression: [...]} in style spec validation

src/style-spec/function/index.js

@@ -76,6 +76,7 @@ function createFunction(parameters, propertySpec) {
 
 module.exports = createFunction;
 module.exports.isFunctionDefinition = isFunctionDefinition;
+module.exports.getExpectedType = getExpectedType;
 
 function isFunctionDefinition(value) {
     return typeof value === 'object' &&

src/style-spec/reference/v8.json

@@ -1666,6 +1666,10 @@
     "doc": "The geometry type for the filter to select."
   },
   "function": {
+    "expression": {
+      "type": "expression",
+      "doc": "An expression."
+    },
     "stops": {
       "type": "array",
       "doc": "An array of stops.",
@@ -1734,6 +1738,12 @@
     "length": 2,
     "doc": "Zoom level and value pair."
   },
+  "expression": {
+    "type": "array",
+    "value": "*",
+    "minimum": 1,
+    "doc": "An expression defines a function that can be used for data-driven style properties or feature filters."
+  },
   "light": {
     "anchor": {
       "type": "enum",

src/style-spec/validate/validate_expression.js

@@ -0,0 +1,23 @@
+
+const ValidationError = require('../error/validation_error');
+const {getExpectedType} = require('../function');
+const compile = require('../function/compile');
+const unbundle = require('../util/unbundle_jsonlint');
+
+module.exports = function validateExpression(options) {
+    const expression = deepUnbundle(options.value.expression);
+    const compiled = compile(expression, getExpectedType(options.valueSpec));
+    if (compiled.result === 'success') return [];
+
+    const key = `${options.key}.expression`;
+    return compiled.errors.map((error) => {
+        return new ValidationError(`${key}${error.key}`, options.value, error.error);
+    });
+};
+
+function deepUnbundle (value) {
+    if (Array.isArray(value)) {
+        return value.map(deepUnbundle);
+    }
+    return unbundle(value);
+}

src/style-spec/validate/validate_function.js

@@ -5,6 +5,7 @@ const validate = require('./validate');
 const validateObject = require('./validate_object');
 const validateArray = require('./validate_array');
 const validateNumber = require('./validate_number');
+const validateExpression = require('./validate_expression');
 const unbundle = require('../util/unbundle_jsonlint');
 
 module.exports = function validateFunction(options) {
@@ -22,6 +23,10 @@ module.exports = function validateFunction(options) {
         getType(options.value.stops[0]) === 'array' &&
         getType(options.value.stops[0][0]) === 'object';
 
+    if (options.value.expression) {
+        return validateExpression(options);
+    }
+
     const errors = validateObject({
         key: options.key,
         value: options.value,

test/unit/style-spec/fixture/functions.input.json

@@ -839,6 +839,39 @@
           "default": "invalid"
         }
       }
+    },
+    {
+      "id": "valid expression",
+      "type": "fill",
+      "source": "source",
+      "source-layer": "layer",
+      "paint": {
+        "fill-color": {
+          "expression": ["rgba", 10, ["number", ["get", "x"]], 30, 1]
+        }
+      }
+    },
+    {
+      "id": "invalid expression type - color",
+      "type": "fill",
+      "source": "source",
+      "source-layer": "layer",
+      "paint": {
+        "fill-color": {
+          "expression": ["pi"]
+        }
+      }
+    },
+    {
+      "id": "invalid expression - fails type checking",
+      "type": "fill",
+      "source": "source",
+      "source-layer": "layer",
+      "paint": {
+        "fill-color": {
+          "expression": ["rgba", 1, "should be a number", 0, 1]
+        }
+      }
     }
   ]
 }

test/unit/style-spec/fixture/functions.output.json

@@ -83,13 +83,13 @@
     "message": "layers[22].paint.fill-color: missing required property \"property\"",
     "line": 401
   },
-  {
-    "message": "layers[32].paint.fill-color.stops[0][0]: stop domain value must be a number, string, or boolean"
-  },
   {
     "message": "layers[23].paint.fill-color.stops: identity function may not have a \"stops\" property",
     "line": 415
   },
+  {
+    "message": "layers[32].paint.fill-color.stops[0][0]: stop domain value must be a number, string, or boolean"
+  },
   {
     "message": "layers[24].paint.fill-color.stops[1][0]: number stop domain type must match previous stop domain type string",
     "line": 434
@@ -157,5 +157,13 @@
   {
     "message": "layers[43].paint.fill-color.default: color expected, \"invalid\" found",
     "line": 839
+  },
+  {
+    "message": "layers[45].paint.fill-color.expression: Expected Color but found Number instead.",
+    "line": 860
+  },
+  {
+    "message": "layers[46].paint.fill-color.expression[2]: Expected Number but found String instead.",
+    "line": 871
   }
 ]