First Check

• I added a very descriptive title to this issue.
• I used the GitHub search to find a similar issue and didn't find it.
• I searched the FastAPI documentation, with the integrated search.
• I already searched in Google "How to X in FastAPI" and didn't find any information.
• I already read and followed all the tutorial in the docs and didn't find an answer.
• I already checked if it is not related to FastAPI but to Pydantic.
• I already checked if it is not related to FastAPI but to Swagger UI.
• I already checked if it is not related to FastAPI but to ReDoc.

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Example Code

# main.py

import uvicorn
from fastapi import FastAPI, Form

app = FastAPI()

@app.post("/")
def hello(arg: tuple[int, int] = Form(...)) -> str:
    pass

if __name__ == "__main__":
    uvicorn.run("main:app", port=8080)

Description

1. Run pip install uvicorn fastapi==0.68.0.
2. Run python ./main.py
3. Hit localhost:8080/docs, observe internal server error with below validation errors:

pydantic.error_wrappers.ValidationError: 2 validation errors for OpenAPI
components -> schemas -> Body_hello__post -> properties -> arg -> items
  value is not a valid dict (type=type_error.dict)
components -> schemas -> Body_hello__post -> $ref
  field required (type=value_error.missing)

4. Run pip install fastapi==0.67.0
5. Hit localhost:8080/docs, observe that endpoint documentation is successfully generated.

Operating System

Linux

Operating System Details

Ubuntu 20.04

FastAPI Version

0.68.0 has bug, 0.67.0 does not have bug.

Python Version

3.9

Additional Context

Any use of tuple in an input (Form, and BaseModel as JSON) or output (BaseModel as JSON) results in above error.