fix: validate nullable oas3 example correctly

.changeset/rich-falcons-act.md

@@ -0,0 +1,5 @@
+---
+"@redocly/openapi-core": patch
+---
+
+Fixed the `no-invalid-schema-examples` rule that incorrectly validated nullable OpenAPI 3.0 schemas.

packages/core/src/rules/common/__tests__/no-invalid-schema-examples.test.ts

@@ -48,4 +48,39 @@ describe('no-invalid-schema-examples', () => {
       ]
     `);
   });
+
+  it('should not report on nullable example for OAS3', async () => {
+    const document = parseYamlToDocument(
+      outdent`
+        openapi: 3.0.3
+        info: {}
+        paths:
+          /subscriptions:
+            get:
+              responses:
+                "200":
+                  content:
+                    application/json:
+                      schema:
+                        nullable: true
+                        type: object
+                        example: null
+                        allOf:
+                          - $ref: "#/components/schemas/RiskMetadata"
+        components:
+          schemas:
+            RiskMetadata:
+              type: object
+      `,
+      'foobar.yaml'
+    );
+
+    const results = await lintDocument({
+      externalRefResolver: new BaseResolver(),
+      document,
+      config: await makeConfig({ rules: { 'no-invalid-schema-examples': 'error' } }),
+    });
+
+    expect(replaceSourceWithRef(results)).toMatchInlineSnapshot(`[]`);
+  });
 });

packages/core/src/rules/common/no-invalid-schema-examples.ts

@@ -1,25 +1,37 @@
 import { getAdditionalPropertiesOption, validateExample } from '../utils';
 
 import type { UserContext } from '../../walk';
-import type { Oas3_1Schema } from '../../typings/openapi';
+import type { Oas3_1Schema, Oas3Schema } from '../../typings/openapi';
+import type { Oas2Rule, Oas3Rule } from '../../visitors';
 
-export const NoInvalidSchemaExamples: any = (opts: any) => {
+export const NoInvalidSchemaExamples: Oas3Rule | Oas2Rule = (opts: any) => {
   const allowAdditionalProperties = getAdditionalPropertiesOption(opts) ?? false;
   return {
     Schema: {
-      leave(schema: Oas3_1Schema, ctx: UserContext) {
-        if (schema.examples) {
-          for (const example of schema.examples) {
+      leave(schema: Oas3_1Schema | Oas3Schema, ctx: UserContext) {
+        const examples = (schema as Oas3_1Schema).examples;
+        if (examples) {
+          for (const example of examples) {
             validateExample(
               example,
               schema,
-              ctx.location.child(['examples', schema.examples.indexOf(example)]),
+              ctx.location.child(['examples', examples.indexOf(example)]),
               ctx,
               allowAdditionalProperties
             );
           }
         }
+
         if (schema.example !== undefined) {
+          // Handle nullable example for OAS3
+          if (
+            (schema as Oas3Schema).nullable === true &&
+            schema.example === null &&
+            schema.type !== undefined
+          ) {
+            return;
+          }
+
           validateExample(schema.example, schema, ctx.location.child('example'), ctx, true);
         }
       },

packages/core/src/rules/oas2/index.ts

@@ -52,7 +52,7 @@ export const rules: Oas2RuleSet<'built-in'> = {
   //@ts-ignore TODO: This is depricated property `spec` and should be removed in the future
   spec: Struct as Oas2Rule,
   struct: Struct as Oas2Rule,
-  'no-invalid-schema-examples': NoInvalidSchemaExamples,
+  'no-invalid-schema-examples': NoInvalidSchemaExamples as Oas2Rule,
   'no-invalid-parameter-examples': NoInvalidParameterExamples,
   'info-contact': InfoContact as Oas2Rule,
   'info-license': InfoLicense as Oas2Rule,

packages/core/src/rules/oas3/index.ts

@@ -109,7 +109,7 @@ export const rules: Oas3RuleSet<'built-in'> = {
   'request-mime-type': RequestMimeType,
   'response-mime-type': ResponseMimeType,
   'path-segment-plural': PathSegmentPlural as Oas3Rule,
-  'no-invalid-schema-examples': NoInvalidSchemaExamples,
+  'no-invalid-schema-examples': NoInvalidSchemaExamples as Oas3Rule,
   'no-invalid-parameter-examples': NoInvalidParameterExamples,
   'response-contains-header': ResponseContainsHeader as Oas3Rule,
   'response-contains-property': ResponseContainsProperty,