Repository: tiangolo/fastapi

Issue:
The generated OpenAPI schema duplicates parameter IDs when used with dependencies
### Describe the bug

The generated OpenAPI schema duplicates parameter IDs when used with dependencies.

### To Reproduce

Steps to reproduce the behavior with a minimum self-contained file.

* Create a file with:

```Python
from fastapi import Depends, FastAPI
from starlette.testclient import TestClient

app = FastAPI()


async def user_exists(user_id: int):
    return True


@app.post("/users/{user_id}", dependencies=[Depends(user_exists)])
async def bug(user_id: int):
    pass


client = TestClient(app)

openapi_schema = {
    "openapi": "3.0.2",
    "info": {"title": "FastAPI", "version": "0.1.0"},
    "paths": {
        "/users/{user_id}": {
            "post": {
                "summary": "Bug",
                "operationId": "bug_users__user_id__post",
                "parameters": [
                    {
                        "required": True,
                        "schema": {"title": "User Id", "type": "integer"},
                        "name": "user_id",
                        "in": "path",
                    },
                    # This duplicated user_id shouldn't be here
                    # {
                    #     "required": True,
                    #     "schema": {"title": "User Id", "type": "integer"},
                    #     "name": "user_id",
                    #     "in": "path",
                    # },
                ],
                "responses": {
                    "200": {
                        "description": "Successful Response",
                        "content": {"application/json": {"schema": {}}},
                    },
                    "422": {
                        "description": "Validation Error",
                        "content": {
                            "application/json": {
                                "schema": {
                                    "$ref": "#/components/schemas/HTTPValidationError"
                                }
                            }
                        },
                    },
                },
            }
        }
    },
    "components": {
        "schemas": {
            "HTTPValidationError": {
                "title": "HTTPValidationError",
                "type": "object",
                "properties": {
                    "detail": {
                        "title": "Detail",
                        "type": "array",
                        "items": {"$ref": "#/components/schemas/ValidationError"},
                    }
                },
            },
            "ValidationError": {
                "title": "ValidationError",
                "required": ["loc", "msg", "type"],
                "type": "object",
                "properties": {
                    "loc": {
                        "title": "Location",
                        "type": "array",
                        "items": {"type": "string"},
                    },
                    "msg": {"title": "Message", "type": "string"},
                    "type": {"title": "Error Type", "type": "string"},
                },
            },
        }
    },
}


def test_reused_param():
    response = client.get("/openapi.json")
    data = response.json()
    assert data == openapi_schema
```

* Run it with `pytest`.

Alternatively, you can run it with Uvicorn go to `/openapi.json`, copy that and validate it at: https://editor.swagger.io/ . It should be valid.

### Expected behavior

The `user_id` used by the path operation and the dependency shouldn't be duplicated in the OpenAPI schema.

### Environment

- OS: all
- FastAPI Version [e.g. 0.3.0], get it with: 0.48.0

```bash
python -c "import fastapi; print(fastapi.__version__)"
```

- Python version, get it with: 3.7

```bash
python --version
```

### Additional context

Supersedes #395



Discussion:

Resolving patch:
diff --git a/fastapi/openapi/utils.py b/fastapi/openapi/utils.py
--- a/fastapi/openapi/utils.py
+++ b/fastapi/openapi/utils.py
@@ -180,7 +180,9 @@ def get_openapi_path(
             operation_parameters = get_openapi_operation_parameters(all_route_params)
             parameters.extend(operation_parameters)
             if parameters:
-                operation["parameters"] = parameters
+                operation["parameters"] = list(
+                    {param["name"]: param for param in parameters}.values()
+                )
             if method in METHODS_WITH_BODY:
                 request_body_oai = get_openapi_operation_request_body(
                     body_field=route.body_field, model_name_map=model_name_map


Test patch:
diff --git a/tests/test_param_in_path_and_dependency.py b/tests/test_param_in_path_and_dependency.py
new file mode 100644
--- /dev/null
+++ b/tests/test_param_in_path_and_dependency.py
@@ -0,0 +1,93 @@
+from fastapi import Depends, FastAPI
+from starlette.testclient import TestClient
+
+app = FastAPI()
+
+
+async def user_exists(user_id: int):
+    return True
+
+
+@app.get("/users/{user_id}", dependencies=[Depends(user_exists)])
+async def read_users(user_id: int):
+    pass
+
+
+client = TestClient(app)
+
+openapi_schema = {
+    "openapi": "3.0.2",
+    "info": {"title": "FastAPI", "version": "0.1.0"},
+    "paths": {
+        "/users/{user_id}": {
+            "get": {
+                "summary": "Read Users",
+                "operationId": "read_users_users__user_id__get",
+                "parameters": [
+                    {
+                        "required": True,
+                        "schema": {"title": "User Id", "type": "integer"},
+                        "name": "user_id",
+                        "in": "path",
+                    },
+                ],
+                "responses": {
+                    "200": {
+                        "description": "Successful Response",
+                        "content": {"application/json": {"schema": {}}},
+                    },
+                    "422": {
+                        "description": "Validation Error",
+                        "content": {
+                            "application/json": {
+                                "schema": {
+                                    "$ref": "#/components/schemas/HTTPValidationError"
+                                }
+                            }
+                        },
+                    },
+                },
+            }
+        }
+    },
+    "components": {
+        "schemas": {
+            "HTTPValidationError": {
+                "title": "HTTPValidationError",
+                "type": "object",
+                "properties": {
+                    "detail": {
+                        "title": "Detail",
+                        "type": "array",
+                        "items": {"$ref": "#/components/schemas/ValidationError"},
+                    }
+                },
+            },
+            "ValidationError": {
+                "title": "ValidationError",
+                "required": ["loc", "msg", "type"],
+                "type": "object",
+                "properties": {
+                    "loc": {
+                        "title": "Location",
+                        "type": "array",
+                        "items": {"type": "string"},
+                    },
+                    "msg": {"title": "Message", "type": "string"},
+                    "type": {"title": "Error Type", "type": "string"},
+                },
+            },
+        }
+    },
+}
+
+
+def test_reused_param():
+    response = client.get("/openapi.json")
+    data = response.json()
+    assert data == openapi_schema
+
+
+def test_read_users():
+    response = client.get("/users/42")
+    assert response.status_code == 200