fix(oas3): validate server variable enum is not empty

Author: kylef

packages/openapi3-parser/lib/parser/oas/parseServerVariableObject.js

@@ -20,9 +20,15 @@ const parseEnumStrings = R.curry((context, element) => {
   const parseEnumString = R.unless(isString,
     createWarning(namespace, `'${name}' 'enum' array value is not a string`));
 
+  const validateArrayNotEmpty = R.when(
+    array => array.isEmpty,
+    createWarning(namespace, `'${name}' 'enum' array must contain 1 or more values`)
+  );
+
   const parseEnum = pipeParseResult(
     namespace,
     parseArray(context, `${name}' 'enum`, parseEnumString),
+    validateArrayNotEmpty,
     (array) => {
       const element = new context.namespace.elements.Enum();
       element.enumerations = array.map((value) => {

packages/openapi3-parser/test/unit/parser/oas/parseServerVariableObject-test.js

@@ -149,5 +149,20 @@ describe('#parseServerVariableObject', () => {
       expect(enumeration.toValue()).to.deep.equal('Tony');
       expect(enumeration.attributes.getValue('typeAttributes')).to.deep.equal(['fixed']);
     });
+
+    it('warns when enum is empty', () => {
+      const serverVariable = new namespace.elements.Object({
+        default: 'Mario',
+        enum: [],
+      });
+
+      const parseResult = parse(context)(serverVariable, 'name');
+
+      expect(parseResult).to.contain.warning("'Server Variable Object' 'enum' array must contain 1 or more values");
+
+      const member = parseResult.get(0);
+      expect(member).to.be.instanceof(namespace.elements.Member);
+      expect(member.value).to.be.instanceof(namespace.elements.String);
+    });
   });
 });