How to tame clippy field is never read?

[azzamsa]

Hi, 👋🏽

I am using cynic to test my API. The structure looks like this.
Let's say I wanted to test my meta endpoint. I have

• meta/tests.rs
• meta/schema.rs
• meta/graphql.rs

The graphql.rs contains cynic definition.

mod schema {
    cynic::use_schema!("tests/schema.graphql");
}

#[cynic::schema_for_derives(file = "tests/schema.graphql", module = "schema")]
pub mod queries {
    use super::schema;

    #[derive(cynic::QueryFragment, Debug)]
    #[cynic(graphql_type = "Query")]
    pub struct MetaQuery {
        pub meta: Meta,
    }

    #[derive(cynic::QueryFragment, Debug)]
    pub struct Meta {
        pub build: String,
        pub version: String,
    }
}

It is used in my code, but clippy doesn't say so.

warning: field `meta` is never read
  --> tests/meta/graphql.rs:12:13
   |
11 |     pub struct MetaQuery {
   |                --------- field in this struct
12 |         pub meta: Meta,
   |             ^^^^
   |
   = note: `MetaQuery` has a derived impl for the trait `Debug`, but this is intentionally ignored during dead code analysis
   = note: `#[warn(dead_code)]` on by default

warning: field `build` is never read
  --> tests/meta/graphql.rs:17:13
   |
16 |     pub struct Meta {
   |                ---- field in this struct
17 |         pub build: String,
   |             ^^^^^
   |
   = note: `Meta` has a derived impl for the trait `Debug`, but this is intentionally ignored during dead code analysis

Do you have any suggestion to tame clippy? I don't think using #[warn(dead_code)] is wise enough.

Thanks for Cynic 🍩

[obmarg]

Hi, so this is quite a tricky question to answer generally. I wouldn't be that against just adding an #[expect(dead_code)] on the individual structs personally - that is what I've done when I've encountered this in cynic example code.

However, depending on your use case there might be something better you can do: it seems like you're using cynic in your tests - could you assert on the values that you're getting back from your tests somehow? Either a manual assert on the fields that clippy thinks are unused, or maybe something more sophisticated like a snapshot test with insta? That might be enough for clippy to see that the fields of the struct are actually used.

[azzamsa]

I decided to convert the value to json::Value first, so I can get the inner value and make every field usable. Now all the link warnings are gone. azzamsa/tin@12beffd.

Here, I don't need HealtResponse struct anymore.

     let body = response.into_body().collect().await?.to_bytes();
-    let health_response: HealthResponse = json::from_slice(&body)?;
-    assert_eq!(health_response.data.health.status, "running");
+   let response: json::Value = json::from_slice(&body)?;
+   let response: HealthQuery = json::from_value(response["data"].clone())?;
+   assert_eq!(response.health.status, "running");

Another example, I don't need CreateUserResponse struct helper.

    let body = response.into_body().collect().await?.to_bytes();
-   let user_response: CreateUserResponse = json::from_slice(&body)?;
-   assert_eq!(user_response.data.create_user.name, "khawa");
-   assert_eq!(user_response.data.create_user.full_name, None);
+  let response: json::Value = json::from_slice(&body)?;
+  let response: queries::User = json::from_value(response["data"]["createUser"].clone())?;
+  assert_eq!(response.name, "aragorn");
+  assert_eq!(response.full_name, None);

If cynic is able to give me response.<data>.<createUser> or "the inner response", it would be better :)
By the way, what is your approach to getting the inner response?