Support discriminator with no parent/shared properties

demo/examples/tests/discriminator.yaml

@@ -233,6 +233,32 @@ paths:
               schema:
                 $ref: "#/components/schemas/BaseSharedMapping"
 
+  /discriminator-mapping-no-properties:
+    get:
+      tags:
+        - discriminator
+      summary: Discriminator with Mapping and No Shared Properties
+      description: |
+        Schema:
+        ```yaml
+        type: object
+        discriminator: 
+          propertyName: type
+          mapping:
+            typeA: "#/components/schemas/TypeA"
+            typeB: "#/components/schemas/TypeB"
+        oneOf:
+          - $ref: '#/components/schemas/TypeA'
+          - $ref: '#/components/schemas/TypeB'
+        ```
+      responses:
+        "200":
+          description: Successful response
+          content:
+            application/json:
+              schema:
+                $ref: "#/components/schemas/BaseSharedMappingNoProperties"
+
   /discriminator-allof-mapping:
     get:
       tags:
@@ -401,6 +427,17 @@ components:
         - $ref: "#/components/schemas/TypeA"
         - $ref: "#/components/schemas/TypeB"
 
+    BaseSharedMappingNoProperties:
+      type: object
+      discriminator:
+        propertyName: type
+        mapping:
+          typeA: "#/components/schemas/TypeA"
+          typeB: "#/components/schemas/TypeB"
+      oneOf:
+        - $ref: "#/components/schemas/TypeA"
+        - $ref: "#/components/schemas/TypeB"
+
     BaseAllOfMapping:
       type: object
       discriminator:
@@ -409,7 +446,8 @@ components:
           typeA: "#/components/schemas/TypeA"
           typeB: "#/components/schemas/TypeB"
       properties:
-        type: string
+        type:
+          type: string
       allOf:
         - oneOf:
             - $ref: "#/components/schemas/TypeA"

packages/docusaurus-theme-openapi-docs/src/theme/Schema/index.tsx

@@ -317,7 +317,10 @@ const DiscriminatorNode: React.FC<DiscriminatorNodeProps> = ({
   let discriminatedSchemas: any = {};
   let inferredMapping: any = {};
 
-  const discriminatorProperty = schema.properties![discriminator.propertyName];
+  // default to empty object if no parent-level properties exist
+  const discriminatorProperty = schema.properties
+    ? schema.properties![discriminator.propertyName]
+    : {};
 
   if (schema.allOf) {
     const mergedSchemas = mergeAllOf(schema) as SchemaObject;
@@ -350,21 +353,28 @@ const DiscriminatorNode: React.FC<DiscriminatorNodeProps> = ({
 
     const subProperties = subSchema.properties || mergedSubSchema.properties;
     if (subProperties[discriminator.propertyName]) {
-      schema.properties![discriminator.propertyName] = {
-        ...schema.properties![discriminator.propertyName],
-        ...subProperties[discriminator.propertyName],
-      };
-      if (subSchema.required && !schema.required) {
-        schema.required = subSchema.required;
+      if (schema.properties) {
+        schema.properties![discriminator.propertyName] = {
+          ...schema.properties![discriminator.propertyName],
+          ...subProperties[discriminator.propertyName],
+        };
+        if (subSchema.required && !schema.required) {
+          schema.required = subSchema.required;
+        }
+        // Avoid duplicating property
+        delete subProperties[discriminator.propertyName];
+      } else {
+        schema.properties = {};
+        schema.properties[discriminator.propertyName] =
+          subProperties[discriminator.propertyName];
+        // Avoid duplicating property
+        delete subProperties[discriminator.propertyName];
       }
-      // Avoid duplicating property
-      delete subProperties[discriminator.propertyName];
     }
   });
 
   const name = discriminator.propertyName;
   const schemaName = getSchemaName(discriminatorProperty);
-
   // Default case for discriminator without oneOf/anyOf/allOf
   return (
     <PropertyDiscriminator