IntoParams optional parameter with #[serde(default)]

[kellpossible]

At the moment if a field is marked with #[serde(default)] it is still noted as a required field in the generated openapi schema.

[juhaku]

Yes serde(default) is not regarded in any way at the moment. Support for this could be added though. I have a plan to support flatten too so they could be implemented in tandem.

[tomharmon]

I am interested in working on this, I will update this issue with my progress. Don't let it stop anyone else though! This is my first contribution to this project so it will be slow.

[juhaku]

Alright its good to have more contributions :) Speeds up the overall development.

[qsantos]

I might have missed something, but I am unable to get a field to be documented as optional when using the IntoParams derive macro. To make sure this was not a regression, I have used the 2.3.0 release where #339 was published:

# Cargo.toml
[package]
name = "optional-utoipa-param"
version = "0.1.0"
edition = "2021"

[dependencies]
serde = "1.0.188"
utoipa = "=2.3.0"

I am currently using the code below.

// src/main.rs
use serde::Deserialize;
use utoipa::{IntoParams, OpenApi};

#[derive(Deserialize, IntoParams)]
pub struct Params {
    #[into_params(required = false)]
    pub a: String,
    pub b: Option<String>,
    #[serde(default)]
    pub c: String,
    #[serde(default)]
    pub d: Option<String>,
}

#[utoipa::path(get, path = "/test", params(Params))]
pub fn test() {
    unimplemented!();
}

#[derive(OpenApi)]
#[openapi(paths(test))]
struct ApiDoc;

fn main() {
    println!("{}", ApiDoc::openapi().to_json().unwrap());
}

However, with cargo build && ./target/debug/optional-utoipa-param | jq, we can see that all four fields are marked as required:

{
  "openapi": "3.0.3",
  "info": {
    "title": "optional-utoipa-param",
    "description": "",
    "contact": {
      "name": ""
    },
    "license": {
      "name": ""
    },
    "version": "0.1.0"
  },
  "paths": {
    "/test": {
      "get": {
        "tags": [
          "crate"
        ],
        "description": "",
        "operationId": "test",
        "parameters": [
          {
            "name": "a",
            "in": "path",
            "required": true,
            "schema": {
              "type": "string"
            }
          },
          {
            "name": "b",
            "in": "path",
            "required": true,
            "schema": {
              "type": "string"
            }
          },
          {
            "name": "c",
            "in": "path",
            "required": true,
            "schema": {
              "type": "string"
            }
          },
          {
            "name": "d",
            "in": "path",
            "required": true,
            "schema": {
              "type": "string"
            }
          }
        ],
        "responses": {},
        "deprecated": false
      }
    }
  }
}

Could you tell me if there is anything I missed?

[qsantos]

To anyone wondering, this is because the parameters_in default to path, where all fields are always required. This fixes the issue I had:

diff --git a/src/main.rs b/src/main.rs
index aa9ff69..b391236 100644
--- a/src/main.rs
+++ b/src/main.rs
@@ -2,6 +2,7 @@ use serde::Deserialize;
 use utoipa::{IntoParams, OpenApi, ToSchema};

 #[derive(Deserialize, IntoParams, ToSchema)]
+#[into_params(parameter_in = Query)]
 pub struct Params {
     #[into_params(required = false)]
     pub a: String,