command: Fix terraform show not outputting child_modules properly in certain circumstances (#27352)

* Add test for module nesting without resources.

* Add test

* Fix showing resources when a module has no resources, only submodules.

command/jsonstate/state.go

@@ -198,14 +198,30 @@ func marshalRootModule(s *states.State, schemas *terraform.Schemas) (module, err
 		return ret, err
 	}
 
-	// build a map of module -> [child module addresses]
-	moduleMap := make(map[string][]addrs.ModuleInstance)
+	// build a map of module -> set[child module addresses]
+	moduleChildSet := make(map[string]map[string]struct{})
 	for _, mod := range s.Modules {
 		if mod.Addr.IsRoot() {
 			continue
 		} else {
-			parent := mod.Addr.Parent().String()
-			moduleMap[parent] = append(moduleMap[parent], mod.Addr)
+			for childAddr := mod.Addr; !childAddr.IsRoot(); childAddr = childAddr.Parent() {
+				if _, ok := moduleChildSet[childAddr.Parent().String()]; !ok {
+					moduleChildSet[childAddr.Parent().String()] = map[string]struct{}{}
+				}
+				moduleChildSet[childAddr.Parent().String()][childAddr.String()] = struct{}{}
+			}
+		}
+	}
+
+	// transform the previous map into map of module -> [child module addresses]
+	moduleMap := make(map[string][]addrs.ModuleInstance)
+	for parent, children := range moduleChildSet {
+		for child := range children {
+			childModuleInstance, diags := addrs.ParseModuleInstanceStr(child)
+			if diags.HasErrors() {
+				return ret, diags.Err()
+			}
+			moduleMap[parent] = append(moduleMap[parent], childModuleInstance)
 		}
 	}
 
@@ -224,14 +240,19 @@ func marshalModules(
 ) ([]module, error) {
 	var ret []module
 	for _, child := range modules {
-		stateMod := s.Module(child)
 		// cm for child module, naming things is hard.
-		cm := module{Address: stateMod.Addr.String()}
-		rs, err := marshalResources(stateMod.Resources, stateMod.Addr, schemas)
-		if err != nil {
-			return nil, err
+		cm := module{Address: child.String()}
+
+		// the module may be resourceless and contain only submodules, it will then be nil here
+		stateMod := s.Module(child)
+		if stateMod != nil {
+			rs, err := marshalResources(stateMod.Resources, stateMod.Addr, schemas)
+			if err != nil {
+				return nil, err
+			}
+			cm.Resources = rs
 		}
-		cm.Resources = rs
+
 		if moduleMap[child.String()] != nil {
 			moreChildModules, err := marshalModules(s, schemas, moduleMap[child.String()], moduleMap)
 			if err != nil {

command/jsonstate/state_test.go

@@ -554,6 +554,59 @@ func TestMarshalModules_nested(t *testing.T) {
 	}
 }
 
+func TestMarshalModules_parent_no_resources(t *testing.T) {
+	subModule, _ := addrs.ParseModuleInstanceStr("module.child.module.submodule")
+	testState := states.BuildState(func(s *states.SyncState) {
+		s.SetResourceInstanceCurrent(
+			addrs.Resource{
+				Mode: addrs.ManagedResourceMode,
+				Type: "test_instance",
+				Name: "foo",
+			}.Instance(addrs.NoKey).Absolute(addrs.RootModuleInstance),
+			&states.ResourceInstanceObjectSrc{
+				AttrsJSON: []byte(`{"id":"bar","foo":"value","bar":"value"}`),
+				Status:    states.ObjectReady,
+			},
+			addrs.AbsProviderConfig{
+				Provider: addrs.NewDefaultProvider("test"),
+				Module:   addrs.RootModule,
+			},
+		)
+		s.SetResourceInstanceCurrent(
+			addrs.Resource{
+				Mode: addrs.ManagedResourceMode,
+				Type: "test_instance",
+				Name: "foo",
+			}.Instance(addrs.NoKey).Absolute(subModule),
+			&states.ResourceInstanceObjectSrc{
+				AttrsJSON: []byte(`{"id":"foo","foo":"value","bar":"value"}`),
+				Status:    states.ObjectReady,
+			},
+			addrs.AbsProviderConfig{
+				Provider: addrs.NewDefaultProvider("test"),
+				Module:   subModule.Module(),
+			},
+		)
+	})
+	got, err := marshalRootModule(testState, testSchemas())
+
+	if err != nil {
+		t.Fatalf("unexpected error: %s", err.Error())
+	}
+
+	if len(got.ChildModules) != 1 {
+		t.Fatalf("wrong result! got %d modules, expected 1", len(got.ChildModules))
+	}
+
+	if got.ChildModules[0].Address != "module.child" {
+		t.Fatalf("wrong result! got %#v\n", got)
+	}
+
+	if got.ChildModules[0].ChildModules[0].Address != "module.child.module.submodule" {
+		t.Fatalf("wrong result! got %#v\n", got)
+	}
+}
+
 func testSchemas() *terraform.Schemas {
 	return &terraform.Schemas{
 		Providers: map[addrs.Provider]*terraform.ProviderSchema{