OpenApi extension fields causing recursion on big schemas

[ahmetveburak]

Describe the bug
Generator cannot process a big schema due to extension fields.
In my case, x-internalAPI is causing recursion if there are many components in the schema.

To Reproduce

Example schema:
The issue only happens with many components. I cannot share the exact one, but I tried to anonymize it.
https://gist.github.com/ahmetveburak/cd22bcd9666789b86e649e60595d9416

Used commandline:

$ datamodel-codegen --input anonymized-schema.json --input-file-type openapi --output model.py

Expected behavior
Produce schemas successfully.

Version:

• OS: MacOS 26.1
• Python version: 3.13.9
• datamodel-code-generator version: 0.48.1

[ilovelinux]

The input has so many nested references that the code hit Recursion Limit raising RecursionError
For reference, this is the (default) limit in my system:

>>> import sys
>>> sys.getrecursionlimit()
1000

I'm not sure it's related to x-internalAPI field

[ahmetveburak]

My file has 529 schemas, and the tool throws a recursion error if there are more than 31 schemas in it. The extension fields may also cause this behavior for other large schemas, too.

I resolved my issue by adding the key to __metadata_only_fields__ (main:datamodel-code-generator/src/datamodel_code_generator/parser/jsonschema.py:241 ). Then I created the PR with a different approach. I couldn't review the whole parsing flow. That's why I'm not confident with the solution.

I have the same recursion limit.

[koxudaxi]

This sample schema has $ref with only deprecated + x-internalAPI everywhere, so current logic treats every $ref as mergeable.
Then $ref is removed and inlined. There are circular refs (e.g. Model33 self-ref), so recursion does not terminate and finally hits recursion limit.

[github-actions]

🎉 Released in 0.51.0

The fix/feature from PR #2801 has been included in this release. See the release notes for details.

Thank you for your contribution!