What causes "object schema nesting mode is invalid" in hashicorp/terraform?

Set Object.Nesting to a valid NestingMode constant (NestingSingle, NestingGroup, NestingList, NestingSet, NestingMap).

object schema nesting mode is invalid

Error message

object schema nesting mode is invalid

What it means

Raised by Object.InternalValidate when the Object's Nesting field equals nestingModeInvalid (the zero value). Every Object must declare a valid NestingMode so the decoder knows how to interpret the structure; the zero value means the field was never set. The check at internal_validate.go:207 short-circuits the whole validation.

Source

Thrown at internal/configs/configschema/internal_validate.go:208

			err = errors.Join(err, fmt.Errorf("%s%s: invalid nesting mode %s", prefix, name, a.NestedType.Nesting))
		}
		for name, attrS := range a.NestedType.Attributes {
			if attrS == nil {
				err = errors.Join(err, fmt.Errorf("%s%s: attribute schema is nil", prefix, name))
				continue
			}
			err = errors.Join(err, attrS.internalValidate(name, prefix))
		}
	}

	return err
}

func (o *Object) InternalValidate() error {
	var err error

	if o.Nesting == nestingModeInvalid {
		return fmt.Errorf("object schema nesting mode is invalid")
	}

	for name, attrS := range o.Attributes {
		if attrS == nil {
			err = errors.Join(err, fmt.Errorf("%s: attribute schema is nil", name))
			continue
		}
		err = errors.Join(err, attrS.internalValidate(name, ""))
	}

	return err
}

View on GitHub (pinned to c9def3e214)

Solutions

Set Object.Nesting to a valid NestingMode constant (NestingSingle, NestingGroup, NestingList, NestingSet, NestingMap).
If the Object is deserialized, validate the incoming nesting value before constructing it.
Add a unit test that calls InternalValidate on every Object the provider defines.

Example fix

// before
obj := &Object{Attributes: map[string]*Attribute{...}}

// after
obj := &Object{Nesting: NestingSingle, Attributes: map[string]*Attribute{...}}

Defensive patterns

Strategy: validation

Validate before calling

func assertObjectNestingValid(o *configschema.Object) error {
    if o.Nesting == configschema.nestingModeInvalid {
        return fmt.Errorf("object schema nesting mode is invalid")
    }
    return nil
}

Type guard

func hasValidNestingMode(o *configschema.Object) bool {
    return o.Nesting != configschema.nestingModeInvalid
}

Prevention

Always set Object.Nesting to a valid constant when constructing an Object.
Validate deserialized Objects before registering them in a schema.
Call Object.InternalValidate in unit tests covering every Object the provider defines.

When it happens

Trigger: Code constructs an Object literal without setting Nesting (leaving it as nestingModeInvalid == 0) and calls InternalValidate on it. The nil/zero check at line 207 returns immediately.

Common situations: Building an Object programmatically and forgetting the Nesting field; deserializing an Object from a format where the nesting key was absent; refactoring that constructs the Object in a helper not setting all required fields.

Related errors

AI-assisted analysis of hashicorp/terraform@c9def3e214 (2026-08-07). Data as JSON: /api/errors/11d4b1feb22ec6a8. Report an issue: GitHub.