github.com/hashicorp/terraform-plugin-sdk@v1.17.2/internal/addrs/module.go

package addrs

import (
	"strings"
)

// Module is an address for a module call within configuration. This is
// the static counterpart of ModuleInstance, representing a traversal through
// the static module call tree in configuration and does not take into account
// the potentially-multiple instances of a module that might be created by
// "count" and "for_each" arguments within those calls.
//
// This type should be used only in very specialized cases when working with
// the static module call tree. Type ModuleInstance is appropriate in more cases.
//
// Although Module is a slice, it should be treated as immutable after creation.
type Module []string

// IsRoot returns true if the receiver is the address of the root module,
// or false otherwise.
func (m Module) IsRoot() bool {
	return len(m) == 0
}

func (m Module) String() string {
	if len(m) == 0 {
		return ""
	}
	return strings.Join([]string(m), ".")
}

// Call returns the module call address that corresponds to the given module
// instance, along with the address of the module that contains it.
//
// There is no call for the root module, so this method will panic if called
// on the root module address.
//
// In practice, this just turns the last element of the receiver into a
// ModuleCall and then returns a slice of the receiever that excludes that
// last part. This is just a convenience for situations where a call address
// is required, such as when dealing with *Reference and Referencable values.
func (m Module) Call() (Module, ModuleCall) {
	if len(m) == 0 {
		panic("cannot produce ModuleCall for root module")
	}

	caller, callName := m[:len(m)-1], m[len(m)-1]
	return caller, ModuleCall{
		Name: callName,
	}
}