hasura/graphql-engine · warning · ScalarTypesIssue

Scalar type {type_name} conflicts with existing inbuilt type

Error message

Scalar type {type_name} conflicts with existing inbuilt type

What it means

An issue (not hard error) where a custom scalar type's name collides with a built-in scalar type name.

Source

Thrown at v3/crates/metadata-resolve/src/stages/scalar_types/types.rs:24

use open_dds::types::CustomTypeName;

#[derive(Serialize, Deserialize, Clone, Debug, PartialEq, Eq)]
pub struct ScalarTypeRepresentation {
    pub graphql_type_name: Option<ast::TypeName>,
    #[serde(default = "serde_ext::ser_default")]
    #[serde(skip_serializing_if = "serde_ext::is_ser_default")]
    pub description: Option<String>,
}

pub struct ScalarTypesOutput {
    pub scalar_types: BTreeMap<Qualified<CustomTypeName>, ScalarTypeRepresentation>,
    pub issues: Vec<ScalarTypesIssue>,
}

#[derive(Debug, thiserror::Error)]
pub enum ScalarTypesIssue {
    #[error("Scalar type {type_name} conflicts with existing inbuilt type")]
    NameConflictsWithBuiltInType { type_name: CustomTypeName },
}

impl ShouldBeAnError for ScalarTypesIssue {
    fn should_be_an_error(&self, flags: &open_dds::flags::OpenDdFlags) -> bool {
        match self {
            ScalarTypesIssue::NameConflictsWithBuiltInType { .. } => flags.contains(
                open_dds::flags::Flag::DisallowScalarTypeNamesConflictingWithInbuiltTypes,
            ),
        }
    }
}

View on GitHub (pinned to 724551b9ae)

Solutions

1. Rename the custom scalar type to something not used by builtin scalars
2. Check the list of builtin scalar names for the version in use

Example fix

// before
kind: ScalarType
name: String
// after
kind: ScalarType
name: MyString

const BUILTIN: [&str; 6] = ["String", "Int", "Float", "Boolean", "ID", "uuid"];
if BUILTIN.contains(&scalar_type.name.as_str()) {
    return Err("custom scalar shadows builtin type");
}

When it happens

Trigger: Defining a ScalarType with a name that matches an inbuilt scalar (e.g. String, Int, Float, Boolean, ID, uuid, date, etc.).

Common situations: Custom scalars named after builtin types, which shadows or conflicts with the inbuilt representations.

Related errors

• duplicate field name {field_name} generated while building o
• the operand type '{operand_type}' must be a scalar type
• the boolean expression '{type_name}' has a GraphQL field nam
• the aggregate expression '{aggregate_expression}' is used wi
• scalar type representation required for type {scalar_type:}

AI-assisted analysis of hasura/graphql-engine@724551b9ae (2026-08-28). Data as JSON: /api/errors/eae382b7bdad01f8. Report an issue: GitHub.