run PrePlanBlock prior to other blocks to solve panic caused by calli…

…ng variable in for_each

dag.go

@@ -45,8 +45,20 @@ func (d *Dag) addEdge(from, to string) error {
 func (d *Dag) runDag(c Config, onReady func(Block) error) error {
 	var err error
 	pending := linkedlistqueue.New()
-	for _, n := range d.GetRoots() {
-		pending.Enqueue(n.(Block))
+	var prePlanBlocks, otherBlocks []Block
+	for _, v := range d.GetRoots() {
+		b := v.(Block)
+		if _, ok := b.(PrePlanBlock); ok {
+			prePlanBlocks = append(prePlanBlocks, b)
+			continue
+		}
+		otherBlocks = append(otherBlocks, b)
+	}
+	for _, b := range prePlanBlocks {
+		pending.Enqueue(b)
+	}
+	for _, b := range otherBlocks {
+		pending.Enqueue(b)
 	}
 	for !pending.Empty() {
 		next, _ := pending.Dequeue()

for_each_test.go

@@ -1,6 +1,7 @@
 package golden
 
 import (
+	"github.com/stretchr/testify/require"
 	"github.com/stretchr/testify/suite"
 	"testing"
 )
@@ -49,6 +50,28 @@ func (s *forEachTestSuite) TestForEachBlockWithAttributeThatHasDefaultValue() {
 	}
 }
 
+func (s *forEachTestSuite) TestForEachBlockInvolvingVariable() {
+	// The order of blocks is crucial here. The block with the variable must be defined first
+	config := `
+data "dummy" "sample" {
+	for_each = var.numbers
+}
+
+variable "numbers" {
+	type = set(number)
+}
+`
+	s.dummyFsWithFiles(map[string]string{
+		"test.hcl": config,
+	})
+	c, err := BuildDummyConfig("", "", []CliFlagAssignedVariables{
+		NewCliFlagAssignedVariable("numbers", "[1]"),
+	}, nil)
+	require.NoError(s.T(), err)
+	_, err = RunDummyPlan(c)
+	s.NoError(err)
+}
+
 func (s *forEachTestSuite) TestLocals_locals_as_for_each() {
 	code := `
 locals {