field_reassign_with_default triggers in custom derives

[jan-auer]

Lint name: field_reassign_with_default

I tried this code:

use schemars::JsonSchema;

#[derive(Default, JsonSchema)]
#[serde(default)]
pub struct MyStruct {
    pub field: i32,
}

Click to show cargo expand output

#![feature(prelude_import)]
#[prelude_import]
use std::prelude::v1::*;
#[macro_use]
extern crate std;
use schemars::JsonSchema;
#[serde(default)]
pub struct MyStruct {
    pub field: i32,
}
#[automatically_derived]
#[allow(unused_qualifications)]
impl ::core::default::Default for MyStruct {
    #[inline]
    fn default() -> MyStruct {
        MyStruct {
            field: ::core::default::Default::default(),
        }
    }
}
#[automatically_derived]
#[allow(unused_braces)]
impl schemars::JsonSchema for MyStruct {
    fn schema_name() -> std::string::String {
        "MyStruct".to_owned()
    }
    fn json_schema(gen: &mut schemars::gen::SchemaGenerator) -> schemars::schema::Schema {
        {
            let schema = {
                let container_default = Self::default();
                let mut schema_object = schemars::schema::SchemaObject {
                    instance_type: Some(schemars::schema::InstanceType::Object.into()),
                    ..Default::default()
                };
                <i32 as schemars::JsonSchema>::add_schema_as_property(
                    gen,
                    &mut schema_object,
                    "field".to_owned(),
                    Some({
                        let mut metadata = schemars::schema::Metadata::default();
                        metadata.default = Some(container_default.field)
                            .and_then(|d| schemars::_serde_json::value::to_value(d).ok());
                        metadata
                    }),
                    false,
                );
                schemars::schema::Schema::Object(schema_object)
            };
            gen.apply_metadata(schema, None)
        }
    }
}

I expected to see this happen:
No lint violations in generated code annotated with #[automatically_derived].

Instead, this happened:

 $ cargo clippy -- -D clippy::all
error: field assignment outside of initializer for an instance created with Default::default()
 --> src/lib.rs:3:19
  |
3 | #[derive(Default, JsonSchema)]
  |                   ^^^^^^^^^^

Meta

• cargo clippy -V: clippy 0.0.212 (e1884a8e 2020-12-29)
• rustc -Vv:

  rustc 1.49.0 (e1884a8e3 2020-12-29)
  binary: rustc
  commit-hash: e1884a8e3c3e813aada8254edfa120e85bf5ffca
  commit-date: 2020-12-29
  host: x86_64-apple-darwin
  release: 1.49.0