Added support for identity functions.

src/components/fields/FunctionSpecField.jsx

@@ -6,12 +6,21 @@ import DataProperty from './_DataProperty'
 import ZoomProperty from './_ZoomProperty'
 import ExpressionProperty from './_ExpressionProperty'
 import {function as styleFunction} from '@mapbox/mapbox-gl-style-spec';
+import {findDefaultFromSpec} from '../util/spec-helper';
 
 
 function isLiteralExpression (value) {
   return (Array.isArray(value) && value.length === 2 && value[0] === "literal");
 }
 
+function isGetExpression (value) {
+  return (
+    Array.isArray(value) &&
+    value.length === 2 &&
+    value[0] === "get"
+  );
+}
+
 function isZoomField(value) {
   return (
     typeof(value) === 'object' &&
@@ -28,7 +37,15 @@ function isZoomField(value) {
   );
 }
 
-function isDataField(value) {
+function isIdentityProperty (value) {
+  return (
+    typeof(value) === 'object' &&
+    value.type === "identity" &&
+    value.hasOwnProperty("property")
+  );
+}
+
+function isDataStopProperty (value) {
   return (
     typeof(value) === 'object' &&
     value.stops &&
@@ -45,6 +62,13 @@ function isDataField(value) {
   );
 }
 
+function isDataField(value) {
+  return (
+    isIdentityProperty(value) ||
+    isDataStopProperty(value)
+  );
+}
+
 function isPrimative (value) {
   const valid = ["string", "boolean", "number"];
   return valid.includes(typeof(value));
@@ -78,24 +102,6 @@ function getDataType (value, fieldSpec={}) {
   }
 }
 
-/**
- * If we don't have a default value just make one up
- */
-function findDefaultFromSpec (spec) {
-  if (spec.hasOwnProperty('default')) {
-    return spec.default;
-  }
-
-  const defaults = {
-    'color': '#000000',
-    'string': '',
-    'boolean': false,
-    'number': 0,
-    'array': [],
-  }
-
-  return defaults[spec.type] || '';
-}
 
 /** Supports displaying spec field for zoom function objects
  * https://www.mapbox.com/mapbox-gl-style-spec/#types-function-zoom-property
@@ -206,7 +212,16 @@ export default class FunctionSpecProperty  extends React.Component {
   undoExpression = () => {
     const {value, fieldName} = this.props;
 
-    if (isLiteralExpression(value)) {
+    if (isGetExpression(value)) {
+      this.props.onChange(fieldName, {
+        "type": "identity",
+        "property": value[1]
+      });
+      this.setState({
+        dataType: "value",
+      });
+    }
+    else if (isLiteralExpression(value)) {
       this.props.onChange(fieldName, value[1]);
       this.setState({
         dataType: "value",
@@ -217,6 +232,7 @@ export default class FunctionSpecProperty  extends React.Component {
   canUndo = () => {
     const {value, fieldSpec} = this.props;
     return (
+      isGetExpression(value) ||
       isLiteralExpression(value) ||
       isPrimative(value) ||
       (Array.isArray(value) && fieldSpec.type === "array")
@@ -230,6 +246,9 @@ export default class FunctionSpecProperty  extends React.Component {
     if (typeof(value) === "object" && 'stops' in value) {
       expression = styleFunction.convertFunction(value, fieldSpec);
     }
+    else if (isIdentityProperty(value)) {
+      expression = ["get", value.property];
+    }
     else {
       expression = ["literal", value || this.props.fieldSpec.default];
     }

src/components/fields/_DataProperty.jsx

@@ -10,6 +10,7 @@ import DocLabel from './DocLabel'
 import InputBlock from '../inputs/InputBlock'
 import docUid from '../../libs/document-uid'
 import sortNumerically from '../../libs/sort-numerically'
+import {findDefaultFromSpec} from '../util/spec-helper';
 
 import labelFromFieldName from './_labelFromFieldName'
 import DeleteStopButton from './_DeleteStopButton'
@@ -89,10 +90,10 @@ export default class DataProperty extends React.Component {
 
   getDataFunctionTypes(fieldSpec) {
     if (fieldSpec.expression.interpolated) {
-      return ["categorical", "interval", "exponential"]
+      return ["categorical", "interval", "exponential", "identity"]
     }
     else {
-      return ["categorical", "interval"]
+      return ["categorical", "interval", "identity"]
     }
   }
 
@@ -122,6 +123,29 @@ export default class DataProperty extends React.Component {
     return mappedWithRef.map((item) => item.data);
   }
 
+  onChange = (fieldName, value) => {
+    if (value.type === "identity") {
+      value = {
+        type: value.type,
+        property: value.property,
+      };
+    }
+    else {
+      const stopValue = value.type === 'categorical' ? '' : 0;
+      value = {
+        property: "",
+        type: value.type,
+        // Default props if they don't already exist.
+        stops: [
+          [{zoom: 6, value: stopValue}, findDefaultFromSpec(this.props.fieldSpec)],
+          [{zoom: 10, value: stopValue}, findDefaultFromSpec(this.props.fieldSpec)]
+        ],
+        ...value,
+      }
+    }
+    this.props.onChange(fieldName, value);
+  }
+
   changeStop(changeIdx, stopData, value) {
     const stops = this.props.value.stops.slice(0)
     const changedStop = stopData.zoom === undefined ? stopData.value : stopData
@@ -133,7 +157,7 @@ export default class DataProperty extends React.Component {
       ...this.props.value,
       stops: orderedStops,
     }
-    this.props.onChange(this.props.fieldName, changedValue)
+    this.onChange(this.props.fieldName, changedValue)
   }
 
   changeDataProperty(propName, propVal) {
@@ -143,7 +167,7 @@ export default class DataProperty extends React.Component {
     else {
       delete this.props.value[propName]
     }
-    this.props.onChange(this.props.fieldName, this.props.value)
+    this.onChange(this.props.fieldName, this.props.value)
   }
 
   render() {
@@ -153,7 +177,9 @@ export default class DataProperty extends React.Component {
       this.props.value.type = this.getFieldFunctionType(this.props.fieldSpec)
     }
 
-    const dataFields = this.props.value.stops.map((stop, idx) => {
+    let dataFields;
+    if (this.props.value.stops) {
+      dataFields = this.props.value.stops.map((stop, idx) => {
         const zoomLevel = typeof stop[0] === 'object' ? stop[0].zoom : undefined;
         const key  = this.state.refs[idx];
         const dataLevel = typeof stop[0] === 'object' ? stop[0].value : stop[0];
@@ -216,6 +242,7 @@ export default class DataProperty extends React.Component {
           </div>
         </InputBlock>
       })
+    }
 
     return <div className="maputnik-data-spec-block">
       <div className="maputnik-data-spec-property">
@@ -223,18 +250,6 @@ export default class DataProperty extends React.Component {
           fieldSpec={this.props.fieldSpec}
           label={labelFromFieldName(this.props.fieldName)}
         >
-          <div className="maputnik-data-spec-property-group">
-            <DocLabel
-              label="Property"
-            />
-            <div className="maputnik-data-spec-property-input">
-              <StringInput
-                value={this.props.value.property}
-                title={"Input a data property to base styles off of."}
-                onChange={propVal => this.changeDataProperty("property", propVal)}
-              />
-            </div>
-          </div>
           <div className="maputnik-data-spec-property-group">
             <DocLabel
               label="Type"
@@ -248,6 +263,19 @@ export default class DataProperty extends React.Component {
               />
             </div>
           </div>
+          <div className="maputnik-data-spec-property-group">
+            <DocLabel
+              label="Property"
+            />
+            <div className="maputnik-data-spec-property-input">
+              <StringInput
+                value={this.props.value.property}
+                title={"Input a data property to base styles off of."}
+                onChange={propVal => this.changeDataProperty("property", propVal)}
+              />
+            </div>
+          </div>
+          {dataFields &&
             <div className="maputnik-data-spec-property-group">
               <DocLabel
                 label="Default"
@@ -261,8 +289,11 @@ export default class DataProperty extends React.Component {
                 />
               </div>
             </div>
+          }
         </InputBlock>
       </div>
+      {dataFields &&
+        <>
           {dataFields}
           <Button
             className="maputnik-add-stop"
@@ -270,6 +301,8 @@ export default class DataProperty extends React.Component {
           >
             Add stop
           </Button>
+        </>
+      }
       <Button
         className="maputnik-add-stop"
         onClick={this.props.onExpressionClick.bind(this)}

src/components/util/spec-helper.js

@@ -0,0 +1,18 @@
+/**
+ * If we don't have a default value just make one up
+ */
+export function findDefaultFromSpec (spec) {
+  if (spec.hasOwnProperty('default')) {
+    return spec.default;
+  }
+
+  const defaults = {
+    'color': '#000000',
+    'string': '',
+    'boolean': false,
+    'number': 0,
+    'array': [],
+  }
+
+  return defaults[spec.type] || '';
+}