terraform/terraform/eval_count.go

package terraform

import (
	"github.com/hashicorp/terraform/config"
)

// EvalCountFixZeroOneBoundary is an EvalNode that fixes up the state
// when there is a resource count with zero/one boundary, i.e. fixing
// a resource named "aws_instance.foo" to "aws_instance.foo.0" and vice-versa.
type EvalCountFixZeroOneBoundary struct {
	Resource *config.Resource
}

// TODO: test
func (n *EvalCountFixZeroOneBoundary) Eval(ctx EvalContext) (interface{}, error) {
	// Get the count, important for knowing whether we're supposed to
	// be adding the zero, or trimming it.
	count, err := n.Resource.Count()
	if err != nil {
		return nil, err
	}

	// Figure what to look for and what to replace it with
	hunt := n.Resource.Id()
	replace := hunt + ".0"
	if count < 2 {
		hunt, replace = replace, hunt
	}

	state, lock := ctx.State()

	// Get a lock so we can access this instance and potentially make
	// changes to it.
	lock.Lock()
	defer lock.Unlock()

	// Look for the module state. If we don't have one, then it doesn't matter.
	mod := state.ModuleByPath(ctx.Path())
	if mod == nil {
		return nil, nil
	}

	// Look for the resource state. If we don't have one, then it is okay.
	rs, ok := mod.Resources[hunt]
	if !ok {
		return nil, nil
	}

	// If the replacement key exists, we just keep both
	if _, ok := mod.Resources[replace]; ok {
		return nil, nil
	}

	mod.Resources[replace] = rs
	delete(mod.Resources, hunt)

	return nil, nil
}