Add support for flattened value groups (#700)

Fixes #693.

Co-authored-by: Abhinav Gupta <abg@uber.com>

CHANGELOG.md

@@ -5,7 +5,10 @@ The format is based on [Keep a Changelog](http://keepachangelog.com/en/1.0.0/)
 and this project adheres to [Semantic Versioning](http://semver.org/spec/v2.0.0.html).
 
 ## [Unreleased]
-- Back to development.
+### Added
+- Value groups can use the `flatten` option to indicate values in a slice should
+  be provided individually rather than providing the slice itself. See package
+  documentation for details.
 
 ## [1.10.0] - 2019-11-20
 ### Added

annotated.go

@@ -64,6 +64,10 @@ type Annotated struct {
 	// by the constructor. For more information on value groups, see the package documentation.
 	//
 	// A group option may not be provided if a name option is provided.
+	//
+	// Similar to group tags, the group name may be followed by a `,flatten`
+	// option to indicate that each element in the slice returned by the
+	// constructor should be injected into the value group individually.
 	Group string
 
 	// Target is the constructor being annotated with fx.Annotated.

app_test.go

@@ -141,6 +141,26 @@ func TestNewApp(t *testing.T) {
 		require.NoError(t, app.Err())
 	})
 
+	t.Run("ProvidesWithAnnotateFlattened", func(t *testing.T) {
+		app := fxtest.New(t,
+			Provide(Annotated{
+				Target: func() []int { return []int{1} },
+				Group:  "foo,flatten",
+			}),
+			Invoke(
+				func(b struct {
+					In
+					Foos []int `group:"foo"`
+				}) {
+					assert.Len(t, b.Foos, 1)
+				},
+			),
+		)
+
+		defer app.RequireStart().RequireStop()
+		require.NoError(t, app.Err())
+	})
+
 	t.Run("ProvidesWithEmptyAnnotate", func(t *testing.T) {
 		type A struct{}
 
@@ -250,7 +270,7 @@ func TestInvokes(t *testing.T) {
 		)
 		err := app.Err()
 		require.Error(t, err)
-		assert.Contains(t, err.Error(), "fx_test.A is not in the container")
+		assert.Contains(t, err.Error(), "missing type: fx_test.A")
 	})
 
 	t.Run("ErrorHooksAreCalled", func(t *testing.T) {

go.mod

@@ -4,7 +4,7 @@ go 1.13
 
 require (
 	github.com/stretchr/testify v1.4.0
-	go.uber.org/dig v1.8.0
+	go.uber.org/dig v1.9.0
 	go.uber.org/goleak v0.10.0
 	go.uber.org/multierr v1.4.0
 	golang.org/x/lint v0.0.0-20190930215403-16217165b5de

go.sum

@@ -20,8 +20,8 @@ github.com/stretchr/testify v1.4.0 h1:2E4SXV/wtOkTonXsotYi4li6zVWxYlZuYNCXe9XRJy
 github.com/stretchr/testify v1.4.0/go.mod h1:j7eGeouHqKxXV5pUuKE4zz7dFj8WfuZ+81PSLYec5m4=
 go.uber.org/atomic v1.5.0 h1:OI5t8sDa1Or+q8AeE+yKeB/SDYioSHAgcVljj9JIETY=
 go.uber.org/atomic v1.5.0/go.mod h1:sABNBOSYdrvTF6hTgEIbc7YasKWGhgEQZyfxyTvoXHQ=
-go.uber.org/dig v1.8.0 h1:1rR6hnL/bu1EVcjnRDN5kx1vbIjEJDTGhSQ2B3ddpcI=
-go.uber.org/dig v1.8.0/go.mod h1:X34SnWGr8Fyla9zQNO2GSO2D+TIuqB14OS8JhYocIyw=
+go.uber.org/dig v1.9.0 h1:pJTDXKEhRqBI8W7rU7kwT5EgyRZuSMVSFcZolOvKK9U=
+go.uber.org/dig v1.9.0/go.mod h1:X34SnWGr8Fyla9zQNO2GSO2D+TIuqB14OS8JhYocIyw=
 go.uber.org/goleak v0.10.0 h1:G3eWbSNIskeRqtsN/1uI5B+eP73y3JUuBsv9AZjehb4=
 go.uber.org/goleak v0.10.0/go.mod h1:VCZuO8V8mFPlL0F5J5GK1rtHV3DrFcQ1R8ryq7FK0aI=
 go.uber.org/multierr v1.4.0 h1:f3WCSC2KzAcBXGATIxAB1E2XuCpNU255wNKZ505qi3E=

inout.go

@@ -251,4 +251,15 @@ type In struct{ dig.In }
 // value groups require parameter and result structs to use fields with
 // different types: if a group of constructors each returns type T, parameter
 // structs consuming the group must use a field of type []T.
+//
+// To provide multiple values for a group from a result struct, produce a
+// slice and use the `,flatten` option on the group tag. This indicates that
+// each element in the slice should be injected into the group individually.
+//
+//   type IntResult struct {
+//     fx.Out
+//
+//     Handler []int `group:"server"`         // Consume as [][]int
+//     Handler []int `group:"server,flatten"` // Consume as []int
+//   }
 type Out struct{ dig.Out }

populate_test.go

@@ -208,7 +208,7 @@ func TestPopulateErrors(t *testing.T) {
 		{
 			msg:     "container pointer without fx.In",
 			opt:     Populate(&containerNoIn{}),
-			wantErr: "is not in the container",
+			wantErr: "missing type: fx_test.containerNoIn",
 		},
 		{
 			msg:     "function",
@@ -218,7 +218,7 @@ func TestPopulateErrors(t *testing.T) {
 		{
 			msg:     "function pointer",
 			opt:     Populate(&fn),
-			wantErr: "is not in the container",
+			wantErr: "missing type: func()",
 		},
 		{
 			msg:     "invalid last argument",