'${name}' property in the 'fields' property at the ${j} inde

Error message

'${name}' property in the 'fields' property at the ${j} index of the 'forms' property in ${file} is malformed. The property must be an object or a call to form.define().

What it means

Inside the 'fields' object, each value must be either a plain object or a call to form.define(...) with a single object argument (checked via AST node types and callee names). A field whose value is neither (e.g. a variable reference, array, or multi-arg call) triggers this warning naming the offending field, and the whole entry is skipped.

Source

Thrown at packages/admin/admin-vite-plugin/src/custom-fields/generate-custom-field-forms.ts:391

        return
      }

      const name = field.key.name

      if (
        !isObjectExpression(field.value) &&
        !(
          isCallExpression(field.value) &&
          isMemberExpression(field.value.callee) &&
          isIdentifier(field.value.callee.object) &&
          isIdentifier(field.value.callee.property) &&
          field.value.callee.object.name === "form" &&
          field.value.callee.property.name === "define" &&
          field.value.arguments.length === 1 &&
          isObjectExpression(field.value.arguments[0])
        )
      ) {
        logger.warn(
          `'${name}' property in the 'fields' property at the ${j} index of the 'forms' property in ${file} is malformed. The property must be an object or a call to form.define().`,
          { file }
        )
        return
      }

      const fieldObject = isObjectExpression(field.value)
        ? field.value
        : (field.value.arguments[0] as ObjectExpression)

      const labelProperty = fieldObject.properties.find(
        (p) => isObjectProperty(p) && isIdentifier(p.key, { name: "label" })
      ) as ObjectProperty | undefined

      const descriptionProperty = fieldObject.properties.find(
        (p) =>
          isObjectProperty(p) && isIdentifier(p.key, { name: "description" })
      ) as ObjectProperty | undefined

View on GitHub (pinned to 5e06e544a2)

Solutions

Replace the value with an inline object literal: myField: { label: 'My Field', ... }
Or use a single-argument form.define({ ... }) call written inline
Do not reference imported constants or call custom helpers as field values

Example fix

// before
import { myDef } from './defs'
forms: [{ zone: 'general', fields: { myField: myDef } }]
// after
forms: [{ zone: 'general', fields: { myField: form.define({ label: 'My Field' }) } }]

Defensive patterns

Strategy: validation

Validate before calling

Object.entries(f.fields).forEach(([name, def]) => {
  const ok = (typeof def === 'object' && def !== null) ||
    (typeof def === 'function') // form.define call
  if (!ok) throw new Error(`field '${name}' must be an object or form.define() call`)
})

Type guard

const isFieldDef = (v: unknown) =>
  (typeof v === 'object' && v !== null) || typeof v === 'function'

Prevention

Write field definitions inline; do not import them from other modules
Always call form.define with exactly one object argument

When it happens

Trigger: fields: { myField: someImportedDef } where the value is an Identifier node, or form.define(cfg, extra) with two arguments.

Common situations: Importing field definitions from another file, wrapping definitions in helper functions, or passing form.define a spread/expression instead of a literal object.

Understand the failure class

Parsing and encoding errors: unexpected token, malformed input — why parsers reject input and how to find the real culprit.

Related errors

AI-assisted analysis of medusajs/medusa@5e06e544a2 (2026-08-27). Data as JSON: /api/errors/903765c18658ff1e. Report an issue: GitHub.