Currently on master branch the following code example fails on startup:

from typing import Annotated

from fastapi import FastAPI, Query
from pydantic import Field

MaxSizedSet = Annotated[set[str], Field(max_length=3)]

app = FastAPI()


@app.get("/")
def read_root(foo: Annotated[MaxSizedSet | None, Query()] = None):
    return {"foo": foo}

  File "/home/yurii/code/fastapi/fastapi/dependencies/utils.py", line 521, in analyze_param
    is_scalar_field(field)
AssertionError: Query parameter 'foo' must be one of the supported types

(the error traceback is a bit misleading - the issue is actually not in is_scalar_field, but in field_annotation_is_scalar_sequence which is a part of the same assert)

This is because field_annotation_is_scalar_sequence doesn't unwrap Annotated.

We also need to unwrap Annotated in field_annotation_is_sequence to make _get_multidict_value correctly recognize this parameter as sequence and extract the value using get_list.

See: #14852