Some carrier API specs have minor OpenAPI violations (e.g., pattern on number type, maximum on string type) that other tools like openapi-generator-cli handle gracefully by ignoring invalid constraints. ogen should offer a lenient mode for better real-world compatibility.

Specs Affected

• carriers/royal_mail/specs/openapi.yaml - maximum/minimum on string type
• carriers/hermes/specs/openapi.yaml - pattern on number type

Current Errors

openapi.yaml:6124:24 -> maximum: unexpected field for type "string"
	6124 |             "maximum": 1000000,
	6125 |             "minimum": 0.001,
	6127 |             "type": "string",

openapi.yaml:2403:24 -> pattern: unexpected field for type "number"
	2403 |             "pattern": "^\\d+(\\.\\d{1,6})?$",
	2404 |             "type": "number",

Context

These ARE spec errors (OpenAPI spec doesn't allow maximum on strings or pattern on numbers), BUT:

• Vendor-provided specs often have these issues
• The constraints are documentation, not enforceable in generated code anyway
• Other tools (openapi-generator-cli, Postman) silently ignore invalid constraints

Minimal Reproduction

openapi: 3.0.1
info:
  title: Invalid Constraints Test
  version: 1.0.0
paths:
  /product:
    post:
      operationId: createProduct
      requestBody:
        required: true
        content:
          application/json:
            schema:
              type: object
              properties:
                # Error: maximum/minimum on string type
                weight:
                  type: string
                  maximum: 1000
                  minimum: 0.001
                  description: Weight in KG
                # Error: pattern on number type
                quantity:
                  type: number
                  pattern: '^\d+(\.\d{1,2})?$'
                  description: Quantity
      responses:
        '201':
          description: Created

Test: ogen --target /tmp/test --clean test.yaml

Proposed Solution

Add --lenient flag or config option:

ogen --lenient --target ./client --clean spec.yaml

# ogen.yml
generator:
  validation_mode: lenient  # strict (default) | lenient | warn

Behavior:

• strict (default): Fail on schema validation errors (current behavior)
• lenient: Ignore invalid constraints, generate code anyway
• warn: Log warnings but continue generation

Expected

• Option to ignore/warn about schema validation errors
• Generate code anyway, treating constraints as documentation

Actual

Generation fails with validation error

Impact

• Cannot use ogen with real-world vendor-provided specs that have minor violations
• Forces manual spec editing before generation

Note

While these ARE spec errors, a lenient mode would improve ogen's compatibility with real-world APIs without compromising correctness of generated code (constraints wouldn't be enforced anyway).