Attribute Macro graphql_scalar 

#[graphql_scalar]

#[graphql_scalar] macro.is interchangeable with the #[derive(GraphQLScalar)] macro, and is used for deriving a GraphQL scalar implementation.

/// Doc comments are used for the GraphQL type description.
#[graphql_scalar]
#[graphql(
    // Custom GraphQL name.
    name = "MyUserId",
    // Description can also specified in the attribute.
    // This will the doc comment, if one exists.
    description = "...",
    // Optional specification URL.
    specified_by_url = "https://tools.ietf.org/html/rfc4122",
    // Explicit generic scalar.
    scalar = S: juniper::ScalarValue,
    transparent,
)]
struct UserId(String);

Foreign types

Additionally, #[graphql_scalar] can be used directly on foreign types via type alias, without using the newtype pattern.

NOTE: To satisfy orphan rules you should provide local ScalarValue implementation.

use juniper::{graphql_scalar, ScalarValue};

#[graphql_scalar]
#[graphql(
    with = date_scalar,
    to_output_with = ScalarValue::from_displayable, // use `Display` representation
    parse_token(String),
    scalar = CustomScalarValue,
)]
//           ^^^^^^^^^^^^^^^^^ local `ScalarValue` implementation
type Date = date::Date;
//          ^^^^^^^^^^ type from another crate

mod date_scalar {
    use super::Date;

    pub(super) fn from_input(s: &str) -> Result<Date, Box<str>> {
        s.parse().map_err(|e| format!("Failed to parse `Date`: {e}").into())
    }
}