Merge pull request #10060 from hashicorp/b-computed-count

terraform: detect compute counts and show a nicer error

terraform/context_plan_test.go

@@ -1309,6 +1309,26 @@ func TestContext2Plan_countComputed(t *testing.T) {
 	}
 }
 
+func TestContext2Plan_countComputedModule(t *testing.T) {
+	m := testModule(t, "plan-count-computed-module")
+	p := testProvider("aws")
+	p.DiffFn = testDiffFn
+	ctx := testContext2(t, &ContextOpts{
+		Module: m,
+		Providers: map[string]ResourceProviderFactory{
+			"aws": testProviderFuncFixed(p),
+		},
+	})
+
+	_, err := ctx.Plan()
+
+	expectedErr := "aws_instance.bar: value of 'count'"
+	if !strings.Contains(fmt.Sprintf("%s", err), expectedErr) {
+		t.Fatalf("expected err would contain %q\nerr: %s\n",
+			expectedErr, err)
+	}
+}
+
 func TestContext2Plan_countIndex(t *testing.T) {
 	m := testModule(t, "plan-count-index")
 	p := testProvider("aws")

terraform/eval_count_computed.go

@@ -0,0 +1,25 @@
+package terraform
+
+import (
+	"fmt"
+
+	"github.com/hashicorp/terraform/config"
+)
+
+// EvalCountCheckComputed is an EvalNode that checks if a resource count
+// is computed and errors if so. This can possibly happen across a
+// module boundary and we don't yet support this.
+type EvalCountCheckComputed struct {
+	Resource *config.Resource
+}
+
+// TODO: test
+func (n *EvalCountCheckComputed) Eval(ctx EvalContext) (interface{}, error) {
+	if n.Resource.RawCount.Value() == unknownValue() {
+		return nil, fmt.Errorf(
+			"%s: value of 'count' cannot be computed",
+			n.Resource.Id())
+	}
+
+	return nil, nil
+}

terraform/graph_config_node_resource.go

@@ -215,6 +215,7 @@ func (n *GraphNodeConfigResource) EvalTree() EvalNode {
 	return &EvalSequence{
 		Nodes: []EvalNode{
 			&EvalInterpolate{Config: n.Resource.RawCount},
+			&EvalCountCheckComputed{Resource: n.Resource},
 			&EvalOpFilter{
 				Ops:  []walkOperation{walkValidate},
 				Node: &EvalValidateCount{Resource: n.Resource},

terraform/node_resource_plan.go

@@ -31,6 +31,7 @@ func (n *NodePlannableResource) EvalTree() EvalNode {
 			// into the proper number of instances.
 			&EvalInterpolate{Config: n.Config.RawCount},
 
+			&EvalCountCheckComputed{Resource: n.Config},
 			&EvalCountFixZeroOneBoundary{Resource: n.Config},
 		},
 	}

terraform/test-fixtures/plan-count-computed-module/child/main.tf

@@ -0,0 +1,5 @@
+variable "value" {}
+
+resource "aws_instance" "bar" {
+    count = "${var.value}"
+}

terraform/test-fixtures/plan-count-computed-module/main.tf

@@ -0,0 +1,8 @@
+resource "aws_instance" "foo" {
+    compute = "foo"
+}
+
+module "child" {
+    source = "./child"
+    value = "${aws_instance.foo.foo}"
+}