feat(oas3): support Schema Object const

Author: kylef

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

@@ -258,6 +258,12 @@ function parseSchema(context) {
       return element;
     });
 
+  const parseConst = (value) => {
+    const element = value.clone();
+    element.attributes.set('typeAttributes', ['fixed']);
+    return element;
+  };
+
   const parseMember = R.cond([
     [hasKey('type'), R.compose(parseType(context), getValue)],
     [hasKey('enum'), R.compose(parseEnum(context, name), getValue)],
@@ -271,6 +277,11 @@ function parseSchema(context) {
     [hasKey('example'), e => e.clone()],
     [hasKey('oneOf'), R.compose(parseOneOf, getValue)],
 
+    [
+      R.both(hasKey('const'), R.always(context.isOpenAPIVersionMoreThanOrEqual(3, 1))),
+      R.compose(parseConst, getValue),
+    ],
+
     [isUnsupportedKey, createUnsupportedMemberWarning(namespace, name)],
     [
       R.both(
@@ -292,11 +303,14 @@ function parseSchema(context) {
       let element;
 
       const oneOf = schema.get('oneOf');
+      const constValue = schema.get('const');
       const enumerations = schema.get('enum');
       const type = schema.getValue('type') || [];
 
       if (oneOf) {
         element = oneOf;
+      } else if (constValue) {
+        element = constValue;
       } else if (enumerations) {
         element = enumerations;
       } else if (type.length > 1) {

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

@@ -310,6 +310,36 @@ describe('Schema Object', () => {
     });
   });
 
+  describe('#const', () => {
+    it('warns when used on OpenAPI 3.0', () => {
+      const schema = new namespace.elements.Object({
+        const: { message: 'Hello' },
+      });
+      const parseResult = parse(context, schema);
+
+      expect(parseResult).to.contain.warning(
+        "'Schema Object' contains invalid key 'const'"
+      );
+    });
+
+    it('returns a fixed element', () => {
+      context.openapiVersion = { major: 3, minor: 1 };
+      const schema = new namespace.elements.Object({
+        const: { message: 'Hello' },
+      });
+      const parseResult = parse(context, schema);
+
+      expect(parseResult.length).to.equal(1);
+      expect(parseResult.get(0)).to.be.instanceof(namespace.elements.DataStructure);
+      expect(parseResult).to.not.contain.annotations;
+
+      const element = parseResult.get(0).content;
+      expect(element).to.be.instanceof(namespace.elements.Object);
+      expect(element.toValue()).to.deep.equal({ message: 'Hello' });
+      expect(element.attributes.getValue('typeAttributes')).to.deep.equal(['fixed']);
+    });
+  });
+
   describe('object type', () => {
     describe('#required', () => {
       it('warns when required is not an array', () => {