From 6348aa8382cb167a15955b995770f6a31489ceee Mon Sep 17 00:00:00 2001
From: Kyle Fuller <kyle@fuller.li>
Date: Mon, 22 Feb 2021 22:25:03 +0000
Subject: [PATCH] feat(oas3): support Schema Object const

---
 .../lib/parser/oas/parseSchemaObject.js       | 14 +++++++++
 .../unit/parser/oas/parseSchemaObject-test.js | 30 +++++++++++++++++++
 2 files changed, 44 insertions(+)

diff --git a/packages/openapi3-parser/lib/parser/oas/parseSchemaObject.js b/packages/openapi3-parser/lib/parser/oas/parseSchemaObject.js
index 5122d3f64..ccd07fcde 100644
--- a/packages/openapi3-parser/lib/parser/oas/parseSchemaObject.js
+++ b/packages/openapi3-parser/lib/parser/oas/parseSchemaObject.js
@@ -238,6 +238,12 @@ 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)],
@@ -251,6 +257,11 @@ 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)],
 
     // Return a warning for additional properties
@@ -265,11 +276,14 @@ 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) {
diff --git a/packages/openapi3-parser/test/unit/parser/oas/parseSchemaObject-test.js b/packages/openapi3-parser/test/unit/parser/oas/parseSchemaObject-test.js
index df68f1611..057814fbb 100644
--- a/packages/openapi3-parser/test/unit/parser/oas/parseSchemaObject-test.js
+++ b/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', () => {