Add ModuleOutputs method to states

In order to efficiently build the module objects for evaluation, we need
to collect the outputs from a set of module instances. The ModuleOutputs
method will return a copy of the state outputs, while not requiring the
unnecessary copying of each entire module.

states/state.go

@@ -82,6 +82,35 @@ func (s *State) ModuleInstances(addr addrs.Module) []*Module {
 	return ms
 }
 
+// ModuleOutputs returns all outputs for the given module call under the
+// parentAddr instance.
+func (s *State) ModuleOutputs(parentAddr addrs.ModuleInstance, module addrs.ModuleCall) []*OutputValue {
+	var os []*OutputValue
+	for _, m := range s.Modules {
+		// can't get outputs from the root module
+		if m.Addr.IsRoot() {
+			continue
+		}
+
+		parent, call := m.Addr.Call()
+		// make sure this is a descendent in the correct path
+		if !parentAddr.Equal(parent) {
+			continue
+		}
+
+		// and check if this is the correct child
+		if call.Name != module.Name {
+			continue
+		}
+
+		for _, o := range m.OutputValues {
+			os = append(os, o)
+		}
+	}
+
+	return os
+}
+
 // RemoveModule removes the module with the given address from the state,
 // unless it is the root module. The root module cannot be deleted, and so
 // this method will panic if that is attempted.

states/state_test.go

@@ -43,6 +43,10 @@ func TestState(t *testing.T) {
 
 	childModule := state.EnsureModule(addrs.RootModuleInstance.Child("child", addrs.NoKey))
 	childModule.SetOutputValue("pizza", cty.StringVal("hawaiian"), false)
+	multiModA := state.EnsureModule(addrs.RootModuleInstance.Child("multi", addrs.StringKey("a")))
+	multiModA.SetOutputValue("pizza", cty.StringVal("cheese"), false)
+	multiModB := state.EnsureModule(addrs.RootModuleInstance.Child("multi", addrs.StringKey("b")))
+	multiModB.SetOutputValue("pizza", cty.StringVal("sausage"), false)
 
 	want := &State{
 		Modules: map[string]*Module{
@@ -114,6 +118,40 @@ func TestState(t *testing.T) {
 				},
 				Resources: map[string]*Resource{},
 			},
+			`module.multi["a"]`: {
+				Addr:        addrs.RootModuleInstance.Child("multi", addrs.StringKey("a")),
+				LocalValues: map[string]cty.Value{},
+				OutputValues: map[string]*OutputValue{
+					"pizza": {
+						Addr: addrs.AbsOutputValue{
+							Module: addrs.RootModuleInstance.Child("multi", addrs.StringKey("a")),
+							OutputValue: addrs.OutputValue{
+								Name: "pizza",
+							},
+						},
+						Value:     cty.StringVal("cheese"),
+						Sensitive: false,
+					},
+				},
+				Resources: map[string]*Resource{},
+			},
+			`module.multi["b"]`: {
+				Addr:        addrs.RootModuleInstance.Child("multi", addrs.StringKey("b")),
+				LocalValues: map[string]cty.Value{},
+				OutputValues: map[string]*OutputValue{
+					"pizza": {
+						Addr: addrs.AbsOutputValue{
+							Module: addrs.RootModuleInstance.Child("multi", addrs.StringKey("b")),
+							OutputValue: addrs.OutputValue{
+								Name: "pizza",
+							},
+						},
+						Value:     cty.StringVal("sausage"),
+						Sensitive: false,
+					},
+				},
+				Resources: map[string]*Resource{},
+			},
 		},
 	}
 
@@ -133,6 +171,25 @@ func TestState(t *testing.T) {
 	for _, problem := range deep.Equal(state, want) {
 		t.Error(problem)
 	}
+
+	expectedOutputs := map[string]string{
+		`module.multi["a"].output.pizza`: "cheese",
+		`module.multi["b"].output.pizza`: "sausage",
+	}
+
+	for _, o := range state.ModuleOutputs(addrs.RootModuleInstance, addrs.ModuleCall{Name: "multi"}) {
+		addr := o.Addr.String()
+		expected := expectedOutputs[addr]
+		delete(expectedOutputs, addr)
+
+		if expected != o.Value.AsString() {
+			t.Fatalf("expected %q:%q, got %q", addr, expected, o.Value.AsString())
+		}
+	}
+
+	for addr, o := range expectedOutputs {
+		t.Fatalf("missing output %q:%q", addr, o)
+	}
 }
 
 func TestStateDeepCopy(t *testing.T) {

states/sync.go

@@ -48,6 +48,18 @@ func (s *SyncState) Module(addr addrs.ModuleInstance) *Module {
 	return ret
 }
 
+// ModuleOutputs returns the set of OutputValues that matches the given path.
+func (s *SyncState) ModuleOutputs(parentAddr addrs.ModuleInstance, module addrs.ModuleCall) []*OutputValue {
+	s.lock.RLock()
+	defer s.lock.RUnlock()
+	var os []*OutputValue
+
+	for _, o := range s.state.ModuleOutputs(parentAddr, module) {
+		os = append(os, o.DeepCopy())
+	}
+	return os
+}
+
 // RemoveModule removes the entire state for the given module, taking with
 // it any resources associated with the module. This should generally be
 // called only for modules whose resources have all been destroyed, but