Unable to use serde_with::serde_as in conjunction with schemars(schema_with)

[indietyp]

I am trying to properly encode Base64 encoded data using schemars, but I am failing while the schemars_0_8 feature is enabled. Base64 does not implement JsonSchemaAs, so I went ahead and tried to implement it myself using the schema_with annotation.

#[serde_with::serde_as]
#[derive(Debug, Clone, PartialEq, serde::Serialize, serde::Deserialize)]
#[cfg_attr(feature = "schemars", derive(schemars::JsonSchema))]
#[serde(rename_all = "camelCase")]
pub struct Image {
    #[serde_as(as = "serde_with::base64::Base64")]
    #[cfg_attr(feature = "schemars", schemars(schema_with = "base_64_schema"))]
    pub buffer: Vec<u8>,
}

#[cfg(feature = "schemars")]
fn base_64_schema(_: &mut schemars::gen::SchemaGenerator) -> schemars::schema::Schema {
    // These properties are valid JSON-schema properties, but they are not supported by schemars
    let mut extensions = std::collections::BTreeMap::new();
    extensions.insert(
        "contentEncoding".to_owned(),
        serde_json::Value::from("base64"),
    );
    extensions.insert(
        "contentMediaType".to_owned(),
        serde_json::Value::from("image/*"),
    );

    schemars::schema::SchemaObject {
        instance_type: Some(schemars::schema::InstanceType::String.into()),
        extensions,
        ..schemars::schema::SchemaObject::default()
    }
    .into()
}

This fails with the error: schemars attribute cannot contain both with and schema_with

any help would be immensely appreciated. Thank you so much for the great library and overall integration of schemars into it!

[indietyp]

I just found out that schemars = false works on a container level, but something similar would be great on a per field level.

[jonasbb]

The macro should handle such conflicts. There is a test, but it might only work for schemars(with = ...) and not schemars(schema_with = ...).

serde_with/serde_with/tests/schemars_0_8.rs

Lines 96 to 118 in f30519a

	fn schemars_custom_with() {
	#[serde_as]
	#[derive(JsonSchema, Serialize)]
	struct Test {
	#[serde_as(as = "DisplayFromStr")]
	#[schemars(with = "i32")]
	custom: i32,
	#[serde_as(as = "DisplayFromStr")]
	#[cfg_attr(any(), schemars(with = "i32"))]
	with_disabled: i32,
	#[serde_as(as = "DisplayFromStr")]
	#[cfg_attr(all(), schemars(with = "i32"))]
	always_enabled: i32,
	}
	check_matches_schema::<Test>(&json!({
	"custom": 3,
	"with_disabled": "5",
	"always_enabled": 7,
	}));
	}

You should be able to work around this for now, by using a type and with instead of schema_with.

The schema_with seems to have an identical functionality to with, but with different syntax. That in that case, the macro should detect both. I will check how to update the serde_as macro here.

[jonasbb]

A fix for this is released in v3.7.0