More JSON schema improvements (#729)

* Add support for constant values

* Add contains check for arrays

* Add tests

* Simplify getValidValueOrDefault testing

ext/bg/js/json-schema.js

@@ -326,6 +326,11 @@ class JsonSchemaValidator {
             throw new JsonSchemaValidationError(`Value type ${type} does not match schema type ${schemaType}`, value, schema, info);
         }
 
+        const schemaConst = schema.const;
+        if (typeof schemaConst !== 'undefined' && !this.valuesAreEqual(value, schemaConst)) {
+            throw new JsonSchemaValidationError('Invalid constant value', value, schema, info);
+        }
+
         const schemaEnum = schema.enum;
         if (Array.isArray(schemaEnum) && !this.valuesAreEqualAny(value, schemaEnum)) {
             throw new JsonSchemaValidationError('Invalid enum value', value, schema, info);
@@ -414,6 +419,8 @@ class JsonSchemaValidator {
             throw new JsonSchemaValidationError('Array length too long', value, schema, info);
         }
 
+        this.validateArrayContains(value, schema, info);
+
         for (let i = 0, ii = value.length; i < ii; ++i) {
             const schemaPath = [];
             const propertySchema = this.getPropertySchema(schema, i, value, schemaPath);
@@ -431,6 +438,26 @@ class JsonSchemaValidator {
         }
     }
 
+    validateArrayContains(value, schema, info) {
+        const containsSchema = schema.contains;
+        if (!this.isObject(containsSchema)) { return; }
+
+        info.schemaPush('contains', containsSchema);
+        for (let i = 0, ii = value.length; i < ii; ++i) {
+            const propertyValue = value[i];
+            info.valuePush(i, propertyValue);
+            try {
+                this.validate(propertyValue, containsSchema, info);
+                info.schemaPop();
+                return;
+            } catch (e) {
+                // NOP
+            }
+            info.valuePop();
+        }
+        throw new JsonSchemaValidationError('contains schema didn\'t match', value, schema, info);
+    }
+
     validateObject(value, schema, info) {
         const properties = new Set(Object.getOwnPropertyNames(value));