Add validation for 'zoom' expression usage

src/style-spec/function/parse.js

@@ -38,7 +38,8 @@ module.exports = parseExpression;
 function parseExpression(
     definitions: {[string]: Definition},
     expr: mixed,
-    path: Array<number> = []
+    path: Array<number> = [],
+    parentExpressionName?: string
 ) /*: TypedExpression | ParseError */ {
     const key = path.join('.');
     if (expr === null || typeof expr === 'undefined') return {
@@ -92,14 +93,24 @@ function parseExpression(
         };
     }
 
+    // special case validation for `zoom`
+    if (op === 'zoom') {
+        if (parentExpressionName !== 'curve' || path.length > 1) {
+            return {
+                key,
+                error: 'The "zoom" expression may only be used as the input to a top-level "curve" expression.'
+            };
+        }
+    }
+
     // special case parsing for `match`
     if (op === 'match') {
         if (expr.length < 3) return {
             key,
             error: `Expected at least 2 arguments, but found only ${expr.length - 1}.`
         };
 
-        const inputExpression = parseExpression(definitions, expr[1], path.concat(1));
+        const inputExpression = parseExpression(definitions, expr[1], path.concat(1), op);
         if (inputExpression.error) return inputExpression;
 
         // parse input/output pairs.
@@ -116,7 +127,7 @@ function parseExpression(
 
             const parsedInputGroup = [];
             for (let j = 0; j < inputGroup.length; j++) {
-                const parsedValue = parseExpression(definitions, inputGroup[j], path.concat(i, j));
+                const parsedValue = parseExpression(definitions, inputGroup[j], path.concat(i, j), op);
                 if (parsedValue.error) return parsedValue;
                 if (!parsedValue.literal) return {
                     key: `${key}.${i}.${j}`,
@@ -126,12 +137,12 @@ function parseExpression(
             }
             matchInputs.push(parsedInputGroup);
 
-            const output = parseExpression(definitions, expr[i + 1], path.concat(i));
+            const output = parseExpression(definitions, expr[i + 1], path.concat(i), op);
             if (output.error) return output;
             outputExpressions.push(output);
         }
 
-        const otherwise = parseExpression(definitions, expr[expr.length - 1], path.concat(expr.length - 1));
+        const otherwise = parseExpression(definitions, expr[expr.length - 1], path.concat(expr.length - 1), op);
         if (otherwise.error) return otherwise;
         outputExpressions.push(otherwise);
 
@@ -147,7 +158,7 @@ function parseExpression(
 
     const args = [];
     for (const arg of expr.slice(1)) {
-        const parsedArg = parseExpression(definitions, arg, path.concat(1 + args.length));
+        const parsedArg = parseExpression(definitions, arg, path.concat(1 + args.length), op);
         if (parsedArg.error) return parsedArg;
         args.push(parsedArg);
     }

test/integration/expression-tests/zoom/basic/test.json

@@ -1,6 +1,16 @@
 {
   "expression": [
-    "zoom"
+    "curve",
+    [
+      "linear"
+    ],
+    [
+      "zoom"
+    ],
+    0,
+    0,
+    30,
+    30
   ],
   "evaluate": [
     [

test/integration/expression-tests/zoom/too-deep/test.json

@@ -0,0 +1,34 @@
+{
+  "expression": [
+    "curve",
+    [
+      "step"
+    ],
+    1,
+    0,
+    [
+      "curve",
+      [
+        "linear"
+      ],
+      [
+        "zoom"
+      ],
+      0,
+      0,
+      22,
+      22
+    ]
+  ],
+  "expected": {
+    "compileResult": {
+      "result": "error",
+      "errors": [
+        {
+          "key": "4.2",
+          "error": "The \"zoom\" expression may only be used as the input to a top-level \"curve\" expression."
+        }
+      ]
+    }
+  }
+}