hashicorp/terraform · critical

invalid element type: %T

Error message

invalid element type: %T

What it means

Panics in serializeCollectionMemberForHash (serialize.go:126). When hashing a list/set member, it requires the Elem to be *Schema or *Resource; any other concrete type (nil, a ValueType, a plain struct) panics with 'invalid element type: %T'.

Source

Thrown at internal/legacy/helper/schema/serialize.go:126

		}

		buf.WriteString(k)
		buf.WriteRune(':')
		innerVal := m[k]
		SerializeValueForHash(buf, innerVal, innerSchema)
	}
}

func serializeCollectionMemberForHash(buf *bytes.Buffer, val interface{}, elem interface{}) {
	switch tElem := elem.(type) {
	case *Schema:
		SerializeValueForHash(buf, val, tElem)
	case *Resource:
		buf.WriteRune('<')
		SerializeResourceForHash(buf, val, tElem)
		buf.WriteString(">;")
	default:
		panic(fmt.Sprintf("invalid element type: %T", tElem))
	}
}

View on GitHub (pinned to c9def3e214)

Solutions

1. Set Elem to &schema.Schema{...} or &schema.Resource{...} on every list/set.
2. Lint schemas for collections whose Elem is not *Schema/*Resource.

Example fix

// before
"rules": { Type: schema.TypeSet, Elem: schema.TypeString },
// after
"rules": { Type: schema.TypeSet, Elem: &schema.Schema{Type: schema.TypeString} },

func collectionElemOk(s *schema.Schema) bool {
    if s.Type != schema.TypeList && s.Type != schema.TypeSet { return true }
    switch s.Elem.(type) {
    case *schema.Schema, *schema.Resource: return true
    }
    return false
}

func isSchemaOrResource(v interface{}) bool {
    switch v.(type) {
    case *schema.Schema, *schema.Resource: return true
    }
    return false
}

When it happens

Trigger: A TypeList/TypeSet whose Elem is nil or a non-Schema/non-Resource value, used as a member of a parent TypeSet that is being hashed.

Common situations: Provider schema bugs: Elem set to a bare ValueType (schema.TypeString) or a plain struct instead of &schema.Schema/&schema.Resource.

Related errors

• unknown value type in TypeMap %T
• unknown schema type to serialize
• missing field in set: %s.%s
• set item just set doesn't exist
• invalid set element type

AI-assisted analysis of hashicorp/terraform@c9def3e214 (2026-08-07). Data as JSON: /api/errors/dbb32cb87e6b1450. Report an issue: GitHub.