hasura/graphql-engine · error · TypecheckError

Error in array item: {inner_error:}

Error message

Error in array item: {inner_error:}

What it means

A wrapper variant of TypecheckError indicating that an element inside a JSON array literal failed its own typecheck. The inner error is boxed, so the message nests the underlying failure (frequently a ScalarTypeMismatch) and tells you the problem is with an individual item, not the array itself.

Source

Thrown at v3/crates/metadata-resolve/src/helpers/typecheck.rs:19

//! Functions for typechecking JSON literals against expected types
use std::collections::{BTreeMap, BTreeSet};

use crate::stages::object_types;
use crate::types::error::ShouldBeAnError;
use crate::{Qualified, QualifiedBaseType, QualifiedTypeName, QualifiedTypeReference};
use open_dds::flags::Flag;
use open_dds::types::{CustomTypeName, FieldName};
use thiserror::Error;

#[derive(Error, Debug, PartialEq)]
/// Errors that can occur when typechecking a value
pub enum TypecheckError {
    #[error("Expected a value of type {expected:} but got value {actual:}")]
    ScalarTypeMismatch {
        expected: open_dds::types::InbuiltType,
        actual: serde_json::Value,
    },
    #[error("Error in array item: {inner_error:}")]
    ArrayItemMismatch { inner_error: Box<TypecheckError> },
    #[error("Expected an array but instead got value {value:}")]
    NonArrayValue { value: serde_json::Value },
    #[error("Expected a non-null value but received null")]
    NullInNonNullableColumn,
}

#[derive(Error, Debug, PartialEq)]
/// Issues that can occur when typechecking a value against an object type
pub enum TypecheckIssue {
    #[error("Expected an object value of type {expected:} but got value {actual:}")]
    ObjectTypeMismatch {
        expected: Qualified<CustomTypeName>,
        actual: serde_json::Value,
    },

    #[error("Typecheck failed for field {field_name:} in object type {object_type:}: {error:}")]
    ObjectTypeField {

View on GitHub (pinned to 724551b9ae)

Solutions

1. Fix the specific array element reported by the nested {inner_error:}
2. Verify every element of the literal array against the declared element type
3. If heterogeneous values are intended, reconsider the element type definition

Example fix

// before
default: [1, "2", 3]   # element type Int

// after
default: [1, 2, 3]

fn all_items_match(element_check: impl Fn(&serde_json::Value) -> bool, v: &serde_json::Value) -> bool {
    v.as_array().map(|a| a.iter().all(&element_check)).unwrap_or(false)
}

// Unwrap ArrayItemMismatch and report the inner error's position when displaying:
if let TypecheckError::ArrayItemMismatch { inner_error } = err {
    report("array item failed: {inner_error}");
}

When it happens

Trigger: Declaring an array-typed argument or field with a default value where at least one element has the wrong JSON type for the element type, e.g. [1, "two"] for [Int!].

Common situations: Mixed-type arrays in metadata defaults, copy-paste errors in long literal arrays, or changing an element scalar type without updating existing defaults.

Related errors

• Expected an array but instead got value {value:}
• Expected a value of type {expected:} but got value {actual:}
• Expected an object value of type {expected:} but got value {
• parsing metadata as json: %w
• reading metadata file: %w

AI-assisted analysis of hasura/graphql-engine@724551b9ae (2026-08-28). Data as JSON: /api/errors/d807842ee53f07f4. Report an issue: GitHub.