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package terraform
import (
// EvalNode is the interface that must be implemented by graph nodes to
// evaluate/execute.
type EvalNode interface {
// Eval evaluates this node with the given context. The second parameter
// are the argument values. These will match in order and 1-1 with the
// results of the Args() return value.
Eval(EvalContext) (interface{}, error)
// GraphNodeEvalable is the interface that graph nodes must implement
// to enable valuation.
type GraphNodeEvalable interface {
EvalTree() EvalNode
// EvalEarlyExitError is a special error return value that can be returned
// by eval nodes that does an early exit.
type EvalEarlyExitError struct{}
func (EvalEarlyExitError) Error() string { return "early exit" }
// Eval evaluates the given EvalNode with the given context, properly
// evaluating all args in the correct order.
func Eval(n EvalNode, ctx EvalContext) (interface{}, error) {
// Call the lower level eval which doesn't understand early exit,
// and if we early exit, it isn't an error.
result, err := EvalRaw(n, ctx)
if err != nil {
if _, ok := err.(EvalEarlyExitError); ok {
return nil, nil
return result, err
// EvalRaw is like Eval except that it returns all errors, even if they
// signal something normal such as EvalEarlyExitError.
func EvalRaw(n EvalNode, ctx EvalContext) (interface{}, error) {
path := "unknown"
if ctx != nil {
path = ctx.Path().String()
if path == "" {
path = "<root>"
log.Printf("[TRACE] %s: eval: %T", path, n)
output, err := n.Eval(ctx)
if err != nil {
switch err.(type) {
case EvalEarlyExitError:
log.Printf("[TRACE] %s: eval: %T, early exit err: %s", path, n, err)
case tfdiags.NonFatalError:
log.Printf("[WARN] %s: eval: %T, non-fatal err: %s", path, n, err)
log.Printf("[ERROR] %s: eval: %T, err: %s", path, n, err)
return output, err
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