ClassCastException when comparing schema changed from allOf to direct array type

[omarsy]

Description

When comparing two OpenAPI specifications where a property's schema changes from:

• an allOf composition referencing an array schema
• to a direct type: array definition

openapi-diff throws a ClassCastException instead of reporting the schema difference.

Affected versions:

• 2.1.7
• 2.1.0-beta.11 (also reproducible)

---

Error

Unexpected exception. Reason: class io.swagger.v3.oas.models.media.ComposedSchema 
cannot be cast to class io.swagger.v3.oas.models.media.ArraySchema

java.lang.ClassCastException: class io.swagger.v3.oas.models.media.ComposedSchema 
cannot be cast to class io.swagger.v3.oas.models.media.ArraySchema
	at org.openapitools.openapidiff.core.compare.schemadiffresult.ArraySchemaDiffResult.diff(ArraySchemaDiffResult.java:25)
	at org.openapitools.openapidiff.core.compare.SchemaDiff.computeDiffForReal(SchemaDiff.java:357)
	...

---

Minimal Reproduction

old.yml

openapi: 3.0.3
info:
  title: Test API
  version: 1.0.0

paths:
  /test:
    get:
      responses:
        '200':
          description: OK
          content:
            application/json:
              schema:
                $ref: '#/components/schemas/TestResponse'

components:
  schemas:
    TestResponse:
      type: object
      properties:
        valuations:
          allOf:
            - $ref: '#/components/schemas/Valuations'

    Valuations:
      type: array
      items:
        type: object
        properties:
          value:
            type: string

new.yml

openapi: 3.0.3
info:
  title: Test API
  version: 1.0.0

paths:
  /test:
    get:
      responses:
        '200':
          description: OK
          content:
            application/json:
              schema:
                $ref: '#/components/schemas/TestResponse'

components:
  schemas:
    TestResponse:
      type: object
      properties:
        valuations:
          type: array
          items:
            $ref: '#/components/schemas/Valuation'

    Valuation:
      type: object
      properties:
        value:
          type: string

---

Command Used

docker run --rm -v "$(pwd):/specs" openapitools/openapi-diff:2.1.7 \
  /specs/old.yml /specs/new.yml

---

Expected Behavior

• The tool should detect the schema change.
• It should classify the change as compatible or incompatible.
• It should not crash.

---

Actual Behavior

The tool throws a ClassCastException.

It appears the comparison logic assumes both schemas being compared are of the same concrete type. In this case:

• Old schema → ComposedSchema
• New schema → ArraySchema

The cast fails, resulting in a crash instead of a diff result.