Merge pull request #7865 from hashicorp/b-filter-untargeted-variables

terraform: Filter untargeted variable nodes

terraform/context_plan_test.go

@@ -2114,6 +2114,43 @@ module.child:
 	}
 }
 
+func TestContext2Plan_targetedModuleUntargetedVariable(t *testing.T) {
+	m := testModule(t, "plan-targeted-module-untargeted-variable")
+	p := testProvider("aws")
+	p.DiffFn = testDiffFn
+	ctx := testContext2(t, &ContextOpts{
+		Module: m,
+		Providers: map[string]ResourceProviderFactory{
+			"aws": testProviderFuncFixed(p),
+		},
+		Targets: []string{"aws_instance.blue", "module.blue_mod"},
+	})
+
+	plan, err := ctx.Plan()
+	if err != nil {
+		t.Fatalf("err: %s", err)
+	}
+
+	actual := strings.TrimSpace(plan.String())
+	expected := strings.TrimSpace(`
+DIFF:
+
+CREATE: aws_instance.blue
+
+module.blue_mod:
+  CREATE: aws_instance.mod
+    type:  "" => "aws_instance"
+    value: "" => "<computed>"
+
+STATE:
+
+<no state>
+`)
+	if actual != expected {
+		t.Fatalf("expected:\n%s\n\ngot:\n%s", expected, actual)
+	}
+}
+
 // https://github.com/hashicorp/terraform/issues/4515
 func TestContext2Plan_targetedOverTen(t *testing.T) {
 	m := testModule(t, "plan-targeted-over-ten")

terraform/graph_config_node_variable.go

@@ -36,6 +36,14 @@ func (n *GraphNodeConfigVariable) DependableName() []string {
 	return []string{n.Name()}
 }
 
+// RemoveIfNotTargeted implements RemovableIfNotTargeted.
+// When targeting is active, variables that are not targeted should be removed
+// from the graph, because otherwise module variables trying to interpolate
+// their references can fail when they're missing the referent resource node.
+func (n *GraphNodeConfigVariable) RemoveIfNotTargeted() bool {
+	return true
+}
+
 func (n *GraphNodeConfigVariable) DependentOn() []string {
 	// If we don't have any value set, we don't depend on anything
 	if n.Value == nil {

terraform/test-fixtures/plan-targeted-module-untargeted-variable/child/main.tf

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

terraform/test-fixtures/plan-targeted-module-untargeted-variable/main.tf

@@ -0,0 +1,12 @@
+resource "aws_instance" "blue" { }
+resource "aws_instance" "green" { }
+
+module "blue_mod" {
+  source = "./child"
+  id = "${aws_instance.blue.id}"
+}
+
+module "green_mod" {
+  source = "./child"
+  id = "${aws_instance.green.id}"
+}

terraform/transform_targets.go

@@ -37,11 +37,16 @@ func (t *TargetsTransformer) Transform(g *Graph) error {
 		}
 
 		for _, v := range g.Vertices() {
+			removable := false
 			if _, ok := v.(GraphNodeAddressable); ok {
-				if !targetedNodes.Include(v) {
-					log.Printf("[DEBUG] Removing %q, filtered by targeting.", dag.VertexName(v))
-					g.Remove(v)
-				}
+				removable = true
+			}
+			if vr, ok := v.(RemovableIfNotTargeted); ok {
+				removable = vr.RemoveIfNotTargeted()
+			}
+			if removable && !targetedNodes.Include(v) {
+				log.Printf("[DEBUG] Removing %q, filtered by targeting.", dag.VertexName(v))
+				g.Remove(v)
 			}
 		}
 	}
@@ -110,3 +115,14 @@ func (t *TargetsTransformer) nodeIsTarget(
 	}
 	return false
 }
+
+// RemovableIfNotTargeted is a special interface for graph nodes that
+// aren't directly addressable, but need to be removed from the graph when they
+// are not targeted. (Nodes that are not directly targeted end up in the set of
+// targeted nodes because something that _is_ targeted depends on them.) The
+// initial use case for this interface is GraphNodeConfigVariable, which was
+// having trouble interpolating for module variables in targeted scenarios that
+// filtered out the resource node being referenced.
+type RemovableIfNotTargeted interface {
+	RemoveIfNotTargeted() bool
+}