Support map value groups

This revision allows dig to specify value groups of map type.

For example:

```
type Params struct {
	dig.In

	Things      []int          `group:"foogroup"`
	MapOfThings map[string]int `group:"foogroup"`
}
type Result struct {
	dig.Out

	Int1 int `name:"foo1" group:"foogroup"`
	Int2 int `name:"foo2" group:"foogroup"`
	Int3 int `name:"foo3" group:"foogroup"`
}

c.Provide(func() Result {
		return Result{Int1: 1, Int2: 2, Int3: 3}
	})

c.Invoke(func(p Params) {
})
```

p.Things will be a value group slice as per usual, containing the
elements {1,2,3} in an arbitrary order.

p.MapOfThings will be a key-value pairing of
{"foo1":1, "foo2":2, "foo3":3}.

decorate.go

@@ -282,7 +282,9 @@ func findResultKeys(r resultList) ([]key, error) {
 		case resultSingle:
 			keys = append(keys, key{t: innerResult.Type, name: innerResult.Name})
 		case resultGrouped:
-			if innerResult.Type.Kind() != reflect.Slice {
+			isMap := innerResult.Type.Kind() == reflect.Map && innerResult.Type.Key().Kind() == reflect.String
+			isSlice := innerResult.Type.Kind() == reflect.Slice
+			if !isMap && !isSlice {
 				return nil, newErrInvalidInput("decorating a value group requires decorating the entire value group, not a single value", nil)
 			}
 			keys = append(keys, key{t: innerResult.Type.Elem(), group: innerResult.Group})

decorate_test.go

@@ -215,6 +215,64 @@ func TestDecorateSuccess(t *testing.T) {
 		}))
 	})
 
+	t.Run("map is treated as an ordinary dependency without group tag, named or unnamed, and passes through multiple scopes", func(t *testing.T) {
+		type params struct {
+			dig.In
+
+			Strings1 map[string]string
+			Strings2 map[string]string `name:"strings2"`
+		}
+
+		type childResult struct {
+			dig.Out
+
+			Strings1 map[string]string
+			Strings2 map[string]string `name:"strings2"`
+		}
+
+		type A map[string]string
+		type B map[string]string
+
+		parent := digtest.New(t)
+		parent.RequireProvide(func() map[string]string { return map[string]string{"key1": "val1", "key2": "val2"} })
+		parent.RequireProvide(func() map[string]string { return map[string]string{"key1": "val21", "key2": "val22"} }, dig.Name("strings2"))
+
+		parent.RequireProvide(func(p params) A { return A(p.Strings1) })
+		parent.RequireProvide(func(p params) B { return B(p.Strings2) })
+
+		child := parent.Scope("child")
+
+		parent.RequireDecorate(func(p params) childResult {
+			res := childResult{Strings1: make(map[string]string, len(p.Strings1))}
+			for k, s := range p.Strings1 {
+				res.Strings1[k] = strings.ToUpper(s)
+			}
+			res.Strings2 = p.Strings2
+			return res
+		})
+
+		child.RequireDecorate(func(p params) childResult {
+			res := childResult{Strings2: make(map[string]string, len(p.Strings2))}
+			for k, s := range p.Strings2 {
+				res.Strings2[k] = strings.ToUpper(s)
+			}
+			res.Strings1 = p.Strings1
+			res.Strings1["key3"] = "newval"
+			return res
+		})
+
+		require.NoError(t, child.Invoke(func(p params) {
+			require.Len(t, p.Strings1, 3)
+			assert.Equal(t, "VAL1", p.Strings1["key1"])
+			assert.Equal(t, "VAL2", p.Strings1["key2"])
+			assert.Equal(t, "newval", p.Strings1["key3"])
+			require.Len(t, p.Strings2, 2)
+			assert.Equal(t, "VAL21", p.Strings2["key1"])
+			assert.Equal(t, "VAL22", p.Strings2["key2"])
+
+		}))
+
+	})
 	t.Run("decorate values in soft group", func(t *testing.T) {
 		type params struct {
 			dig.In
@@ -393,6 +451,46 @@ func TestDecorateSuccess(t *testing.T) {
 		assert.Equal(t, `[]string[group = "animals"]`, info.Inputs[0].String())
 	})
 
+	t.Run("decorate with map value groups", func(t *testing.T) {
+		type Params struct {
+			dig.In
+
+			Animals map[string]string `group:"animals"`
+		}
+
+		type Result struct {
+			dig.Out
+
+			Animals map[string]string `group:"animals"`
+		}
+
+		c := digtest.New(t)
+		c.RequireProvide(func() string { return "dog" }, dig.Name("animal1"), dig.Group("animals"))
+		c.RequireProvide(func() string { return "cat" }, dig.Name("animal2"), dig.Group("animals"))
+		c.RequireProvide(func() string { return "gopher" }, dig.Name("animal3"), dig.Group("animals"))
+
+		var info dig.DecorateInfo
+		c.RequireDecorate(func(p Params) Result {
+			animals := p.Animals
+			for k, v := range animals {
+				animals[k] = "good " + v
+			}
+			return Result{
+				Animals: animals,
+			}
+		}, dig.FillDecorateInfo(&info))
+
+		c.RequireInvoke(func(p Params) {
+			assert.Len(t, p.Animals, 3)
+			assert.Equal(t, "good dog", p.Animals["animal1"])
+			assert.Equal(t, "good cat", p.Animals["animal2"])
+			assert.Equal(t, "good gopher", p.Animals["animal3"])
+		})
+
+		require.Equal(t, 1, len(info.Inputs))
+		assert.Equal(t, `map[string]string[group = "animals"]`, info.Inputs[0].String())
+	})
+
 	t.Run("decorate with optional parameter", func(t *testing.T) {
 		c := digtest.New(t)
 
@@ -918,6 +1016,7 @@ func TestMultipleDecorates(t *testing.T) {
 			assert.ElementsMatch(t, []int{2, 3, 4}, a.Values)
 		})
 	})
+
 }
 
 func TestFillDecorateInfoString(t *testing.T) {

dig_test.go

@@ -1241,6 +1241,27 @@ func TestGroups(t *testing.T) {
 		})
 	})
 
+	t.Run("provide multiple with the same name and group but different type", func(t *testing.T) {
+		c := digtest.New(t)
+		type A struct{}
+		type B struct{}
+		type ret1 struct {
+			dig.Out
+			*A `name:"foo" group:"foos"`
+		}
+		type ret2 struct {
+			dig.Out
+			*B `name:"foo" group:"foos"`
+		}
+		c.RequireProvide(func() ret1 {
+			return ret1{A: &A{}}
+		})
+
+		c.RequireProvide(func() ret2 {
+			return ret2{B: &B{}}
+		})
+	})
+
 	t.Run("different types may be grouped", func(t *testing.T) {
 		c := digtest.New(t, dig.SetRand(rand.New(rand.NewSource(0))))
 
@@ -1745,6 +1766,118 @@ func TestGroups(t *testing.T) {
 			assert.ElementsMatch(t, []string{"a"}, param.Value)
 		})
 	})
+	/* map tests */
+	t.Run("empty map received without provides", func(t *testing.T) {
+		c := digtest.New(t)
+
+		type in struct {
+			dig.In
+
+			Values map[string]int `group:"foo"`
+		}
+
+		c.RequireInvoke(func(i in) {
+			require.Empty(t, i.Values)
+		})
+	})
+
+	t.Run("map value group using dig.Name and dig.Group", func(t *testing.T) {
+		c := digtest.New(t, dig.SetRand(rand.New(rand.NewSource(0))))
+
+		c.RequireProvide(func() int {
+			return 1
+		}, dig.Name("value1"), dig.Group("val"))
+		c.RequireProvide(func() int {
+			return 2
+		}, dig.Name("value2"), dig.Group("val"))
+		c.RequireProvide(func() int {
+			return 3
+		}, dig.Name("value3"), dig.Group("val"))
+
+		type in struct {
+			dig.In
+
+			Value1   int            `name:"value1"`
+			Value2   int            `name:"value2"`
+			Value3   int            `name:"value3"`
+			Values   []int          `group:"val"`
+			ValueMap map[string]int `group:"val"`
+		}
+
+		c.RequireInvoke(func(i in) {
+			assert.Equal(t, []int{2, 3, 1}, i.Values)
+			assert.Equal(t, i.ValueMap["value1"], 1)
+			assert.Equal(t, i.ValueMap["value2"], 2)
+			assert.Equal(t, i.ValueMap["value3"], 3)
+			assert.Equal(t, i.Value1, 1)
+			assert.Equal(t, i.Value2, 2)
+			assert.Equal(t, i.Value3, 3)
+		})
+	})
+	t.Run("values are provided, map and name and slice", func(t *testing.T) {
+		c := digtest.New(t, dig.SetRand(rand.New(rand.NewSource(0))))
+		type out struct {
+			dig.Out
+
+			Value1 int `name:"value1" group:"val"`
+			Value2 int `name:"value2" group:"val"`
+			Value3 int `name:"value3" group:"val"`
+		}
+
+		c.RequireProvide(func() out {
+			return out{Value1: 1, Value2: 2, Value3: 3}
+		})
+
+		type in struct {
+			dig.In
+
+			Value1   int            `name:"value1"`
+			Value2   int            `name:"value2"`
+			Value3   int            `name:"value3"`
+			Values   []int          `group:"val"`
+			ValueMap map[string]int `group:"val"`
+		}
+
+		c.RequireInvoke(func(i in) {
+			assert.Equal(t, []int{2, 3, 1}, i.Values)
+			assert.Equal(t, i.ValueMap["value1"], 1)
+			assert.Equal(t, i.ValueMap["value2"], 2)
+			assert.Equal(t, i.ValueMap["value3"], 3)
+			assert.Equal(t, i.Value1, 1)
+			assert.Equal(t, i.Value2, 2)
+			assert.Equal(t, i.Value3, 3)
+		})
+	})
+
+	t.Run("Every item used in a map must have a named key", func(t *testing.T) {
+		c := digtest.New(t, dig.SetRand(rand.New(rand.NewSource(0))))
+
+		type out struct {
+			dig.Out
+
+			Value1 int `name:"value1" group:"val"`
+			Value2 int `name:"value2" group:"val"`
+			Value3 int `group:"val"`
+		}
+
+		c.RequireProvide(func() out {
+			return out{Value1: 1, Value2: 2, Value3: 3}
+		})
+
+		type in struct {
+			dig.In
+
+			ValueMap map[string]int `group:"val"`
+		}
+		var called = false
+		err := c.Invoke(func(i in) { called = true })
+		dig.AssertErrorMatches(t, err,
+			`could not build arguments for function "go.uber.org/dig_test".TestGroups\S+`,
+			`dig_test.go:\d+`, // file:line
+			`every entry in a map value groups must have a name, group "val" is missing a name`)
+		assert.False(t, called, "shouldn't call invoked function when deps aren't available")
+	})
+
 }
 
 // --- END OF END TO END TESTS
@@ -2753,7 +2886,27 @@ func testProvideFailures(t *testing.T, dryRun bool) {
 		)
 	})
 
-	t.Run("provide multiple instances with the same name but different group", func(t *testing.T) {
+	t.Run("provide multiple instances with the same name and same group using options", func(t *testing.T) {
+		c := digtest.New(t, dig.DryRun(dryRun))
+		type A struct{}
+
+		c.RequireProvide(func() *A {
+			return &A{}
+		}, dig.Group("foos"), dig.Name("foo"))
+
+		err := c.Provide(func() *A {
+			return &A{}
+		}, dig.Group("foos"), dig.Name("foo"))
+		require.Error(t, err, "expected error on the second provide")
+		dig.AssertErrorMatches(t, err,
+			`cannot provide function "go.uber.org/dig_test".testProvideFailures\S+`,
+			`dig_test.go:\d+`, // file:line
+			`cannot provide \*dig_test.A\[name="foo"\] from \[1\]:`,
+			`already provided by "go.uber.org/dig_test".testProvideFailures\S+`,
+		)
+	})
+
+	t.Run("provide multiple instances with the same name and type but different group", func(t *testing.T) {
 		c := digtest.New(t, dig.DryRun(dryRun))
 		type A struct{}
 		type ret1 struct {

graph.go

@@ -28,7 +28,7 @@ type graphNode struct {
 }
 
 // graphHolder is the dependency graph of the container.
-// It saves constructorNodes and paramGroupedSlice (value groups)
+// It saves constructorNodes and paramGroupedCollection (value groups)
 // as nodes in the graph.
 // It implements the graph interface defined by internal/graph.
 // It has 1-1 correspondence with the Scope whose graph it represents.
@@ -68,7 +68,7 @@ func (gh *graphHolder) EdgesFrom(u int) []int {
 		for _, param := range w.paramList.Params {
 			orders = append(orders, getParamOrder(gh, param)...)
 		}
-	case *paramGroupedSlice:
+	case *paramGroupedCollection:
 		providers := gh.s.getAllGroupProviders(w.Group, w.Type.Elem())
 		for _, provider := range providers {
 			orders = append(orders, provider.Order(gh.s))