Module expander for enabled field

Signed-off-by: Diogenes Fernandes <diofeher@gmail.com>

internal/configs/module_call.go

@@ -38,6 +38,7 @@ type ModuleCall struct {
 
 	Count   hcl.Expression
 	ForEach hcl.Expression
+	Enabled hcl.Expression
 
 	Providers []PassedProviderConfig
 

internal/instances/expander.go

@@ -59,6 +59,12 @@ func (e *Expander) SetModuleSingle(parentAddr addrs.ModuleInstance, callAddr add
 	e.setModuleExpansion(parentAddr, callAddr, expansionSingleVal)
 }
 
+// SetModuleEnabled records that the given module call inside the given parent
+// module uses the "enabled" lifecycle repetition argument, with the given value.
+func (e *Expander) SetModuleEnabled(parentAddr addrs.ModuleInstance, callAddr addrs.ModuleCall, enabled bool) {
+	e.setModuleExpansion(parentAddr, callAddr, expansionEnabled(enabled))
+}
+
 // SetModuleCount records that the given module call inside the given parent
 // module instance uses the "count" repetition argument, with the given value.
 func (e *Expander) SetModuleCount(parentAddr addrs.ModuleInstance, callAddr addrs.ModuleCall, count int) {

internal/instances/expander_test.go

@@ -22,6 +22,7 @@ func TestExpander(t *testing.T) {
 	count2ModuleAddr := addrs.ModuleCall{Name: "count2"}
 	count0ModuleAddr := addrs.ModuleCall{Name: "count0"}
 	forEachModuleAddr := addrs.ModuleCall{Name: "for_each"}
+	enabledModuleAddr := addrs.ModuleCall{Name: "enabled"}
 	singleResourceAddr := addrs.Resource{
 		Mode: addrs.ManagedResourceMode,
 		Type: "test",
@@ -42,6 +43,11 @@ func TestExpander(t *testing.T) {
 		Type: "test",
 		Name: "for_each",
 	}
+	enabledResourceAddr := addrs.Resource{
+		Mode: addrs.ManagedResourceMode,
+		Type: "test",
+		Name: "enabled",
+	}
 	eachMap := map[string]cty.Value{
 		"a": cty.NumberIntVal(1),
 		"b": cty.NumberIntVal(2),
@@ -88,6 +94,7 @@ func TestExpander(t *testing.T) {
 		ex.SetResourceCount(addrs.RootModuleInstance, count2ResourceAddr, 2)
 		ex.SetResourceCount(addrs.RootModuleInstance, count0ResourceAddr, 0)
 		ex.SetResourceForEach(addrs.RootModuleInstance, forEachResourceAddr, eachMap)
+		ex.SetResourceEnabled(addrs.RootModuleInstance, enabledResourceAddr, true)
 
 		ex.SetModuleSingle(addrs.RootModuleInstance, singleModuleAddr)
 		{
@@ -97,6 +104,12 @@ func TestExpander(t *testing.T) {
 			ex.SetResourceCount(moduleInstanceAddr, count2ResourceAddr, 2)
 		}
 
+		ex.SetModuleEnabled(addrs.RootModuleInstance, enabledModuleAddr, true)
+		{
+			moduleInstanceAddr := addrs.RootModuleInstance.Child("enabled", addrs.NoKey)
+			ex.SetResourceSingle(moduleInstanceAddr, singleResourceAddr)
+		}
+
 		ex.SetModuleCount(addrs.RootModuleInstance, count2ModuleAddr, 2)
 		for i1 := 0; i1 < 2; i1++ {
 			moduleInstanceAddr := addrs.RootModuleInstance.Child("count2", addrs.IntKey(i1))
@@ -146,6 +159,19 @@ func TestExpander(t *testing.T) {
 			t.Errorf("wrong result\n%s", diff)
 		}
 	})
+
+	t.Run("resource enabled", func(t *testing.T) {
+		got := ex.ExpandModuleResource(
+			addrs.RootModule,
+			enabledResourceAddr,
+		)
+		want := []addrs.AbsResourceInstance{
+			mustAbsResourceInstanceAddr(`test.enabled`),
+		}
+		if diff := cmp.Diff(want, got); diff != "" {
+			t.Errorf("wrong result\n%s", diff)
+		}
+	})
 	t.Run("resource count2", func(t *testing.T) {
 		got := ex.ExpandModuleResource(
 			addrs.RootModule,
@@ -169,6 +195,18 @@ func TestExpander(t *testing.T) {
 			t.Errorf("wrong result\n%s", diff)
 		}
 	})
+	t.Run("resource enabled", func(t *testing.T) {
+		got := ex.ExpandModuleResource(
+			addrs.RootModule,
+			enabledResourceAddr,
+		)
+		want := []addrs.AbsResourceInstance{
+			mustAbsResourceInstanceAddr(`test.enabled`),
+		}
+		if diff := cmp.Diff(want, got); diff != "" {
+			t.Errorf("wrong result\n%s", diff)
+		}
+	})
 	t.Run("resource for_each", func(t *testing.T) {
 		got := ex.ExpandModuleResource(
 			addrs.RootModule,
@@ -191,6 +229,16 @@ func TestExpander(t *testing.T) {
 			t.Errorf("wrong result\n%s", diff)
 		}
 	})
+
+	t.Run("module enabled", func(t *testing.T) {
+		got := ex.ExpandModule(addrs.RootModule.Child("enabled"))
+		want := []addrs.ModuleInstance{
+			mustModuleInstanceAddr(`module.enabled`),
+		}
+		if diff := cmp.Diff(want, got); diff != "" {
+			t.Errorf("wrong result\n%s", diff)
+		}
+	})
 	t.Run("module single resource single", func(t *testing.T) {
 		got := ex.ExpandModuleResource(
 			mustModuleAddr("single"),

internal/tofu/evaluate.go

@@ -565,16 +565,23 @@ func (d *evaluationStateData) GetModule(_ context.Context, addr addrs.ModuleCall
 		}
 
 	default:
-		val, ok := moduleInstances[addrs.NoKey]
+		vals, ok := moduleInstances[addrs.NoKey]
 		if !ok {
-			// create the object if there wasn't one known
-			val = map[string]cty.Value{}
-			for k := range outputConfigs {
-				val[k] = cty.DynamicVal
+			if callConfig.Enabled == nil {
+				// create the object if there wasn't one known
+				vals = map[string]cty.Value{}
+				for k := range outputConfigs {
+					vals[k] = cty.DynamicVal
+				}
+				ret = cty.ObjectVal(vals)
+			} else {
+				// when we're using enabled it's okay to have no
+				// instance, and the entire object is null.
+				ret = cty.NullVal(cty.DynamicPseudoType)
 			}
+		} else {
+			ret = cty.ObjectVal(vals)
 		}
-
-		ret = cty.ObjectVal(val)
 	}
 
 	// The module won't be expanded during validation, so we need to return an

internal/tofu/node_module_expand.go

@@ -77,6 +77,10 @@ func (n *nodeExpandModule) References() []*addrs.Reference {
 		forEachRefs, _ := lang.ReferencesInExpr(addrs.ParseRef, n.ModuleCall.ForEach)
 		refs = append(refs, forEachRefs...)
 	}
+	if n.ModuleCall.Enabled != nil {
+		enabledRefs, _ := lang.ReferencesInExpr(addrs.ParseRef, n.ModuleCall.Enabled)
+		refs = append(refs, enabledRefs...)
+	}
 
 	for _, passed := range n.ModuleCall.Providers {
 		if passed.InParent.KeyExpression != nil {
@@ -142,6 +146,23 @@ func (n *nodeExpandModule) Execute(ctx context.Context, evalCtx EvalContext, op
 			}
 			expander.SetModuleForEach(module, call, forEach)
 
+		case n.ModuleCall.Enabled != nil:
+			// For enabled expressions, we need to evaluate in the parent module context
+			// since the expression may reference variables defined in the parent module. e.g.
+			// variable "on" { type = bool }
+			// module "mod1" {
+			// 	 source = "./mod1"
+			// 	 lifecycle {
+			// 	   enabled = var.on
+			// 	 }
+			// }
+			parentEvalCtx := evalCtx.WithPath(module.Parent())
+			enabled, enDiags := evaluateEnabledExpression(ctx, n.ModuleCall.Enabled, parentEvalCtx)
+			diags = diags.Append(enDiags)
+			if diags.HasErrors() {
+				return diags
+			}
+			expander.SetModuleEnabled(module, call, enabled)
 		default:
 			expander.SetModuleSingle(module, call)
 		}

internal/tofu/testdata/apply-enabled-module/apply-enabled-module.tf

@@ -0,0 +1,19 @@
+variable "on" {
+  type = bool
+}
+
+module "mod1" {
+  source = "./mod1"
+
+  lifecycle {
+    enabled = var.on
+  }
+}
+
+output "result" {
+  // This is in a 1-tuple just because OpenTofu treats a fully-null
+  // root module output value as if it wasn't declared at all,
+  // but we want to make sure we're actually testing the result
+  // of this resource directly.
+  value = [try(module.mod1.result, "")]
+}