Added the ability to override non-zero values

inject.go

@@ -254,11 +254,6 @@ StructLoop:
 			)
 		}
 
-		// Don't overwrite existing values.
-		if !isNilOrZero(field, fieldType) {
-			continue
-		}
-
 		// Named injects must have been explicitly provided.
 		if tag.Name != "" {
 			existing := g.named[tag.Name]
@@ -326,7 +321,19 @@ StructLoop:
 		}
 
 		// Interface injection is handled in a second pass.
+		if fieldType.Kind() == reflect.Interface && isNilOrZero(field, fieldType) {
+			continue
+		}
+
 		if fieldType.Kind() == reflect.Interface {
+			err := g.Provide(&Object{
+				Value:    field.Elem().Interface(),
+				private:  true,
+				embedded: o.reflectType.Elem().Field(i).Anonymous,
+			})
+			if err != nil {
+				return err
+			}
 			continue
 		}
 
@@ -383,6 +390,10 @@ StructLoop:
 			}
 		}
 
+		if !tag.Override && !isNilOrZero(field, fieldType) {
+			continue
+		}
+
 		newValue := reflect.New(fieldType.Elem())
 		newObject := &Object{
 			Value:   newValue.Interface(),
@@ -453,11 +464,6 @@ func (g *Graph) populateUnnamedInterface(o *Object) error {
 			)
 		}
 
-		// Don't overwrite existing values.
-		if !isNilOrZero(field, fieldType) {
-			continue
-		}
-
 		// Named injects must have already been handled in populateExplicit.
 		if tag.Name != "" {
 			panic(fmt.Sprintf("unhandled named instance with name %s", tag.Name))
@@ -482,6 +488,9 @@ func (g *Graph) populateUnnamedInterface(o *Object) error {
 						existing.reflectValue,
 					)
 				}
+				if !tag.Override && !isNilOrZero(field, fieldType) {
+					continue
+				}
 				found = existing
 				field.Set(reflect.ValueOf(existing.Value))
 				if g.Logger != nil {
@@ -497,13 +506,14 @@ func (g *Graph) populateUnnamedInterface(o *Object) error {
 		}
 
 		// If we didn't find an assignable value, we're missing something.
-		if found == nil {
+		if found == nil && isNilOrZero(field, fieldType) {
 			return fmt.Errorf(
 				"found no assignable value for field %s in type %s",
 				o.reflectType.Elem().Field(i).Name,
 				o.reflectType,
 			)
 		}
+
 	}
 	return nil
 }
@@ -531,15 +541,17 @@ func (g *Graph) Objects() []*Object {
 }
 
 var (
-	injectOnly    = &tag{}
-	injectPrivate = &tag{Private: true}
-	injectInline  = &tag{Inline: true}
+	injectOnly     = &tag{}
+	injectPrivate  = &tag{Private: true}
+	injectInline   = &tag{Inline: true}
+	injectOverride = &tag{Override: true}
 )
 
 type tag struct {
-	Name    string
-	Inline  bool
-	Private bool
+	Name     string
+	Inline   bool
+	Private  bool
+	Override bool
 }
 
 func parseTag(t string) (*tag, error) {
@@ -550,14 +562,15 @@ func parseTag(t string) (*tag, error) {
 	if !found {
 		return nil, nil
 	}
-	if value == "" {
+	switch value {
+	case "":
 		return injectOnly, nil
-	}
-	if value == "inline" {
+	case "inline":
 		return injectInline, nil
-	}
-	if value == "private" {
+	case "private":
 		return injectPrivate, nil
+	case "override":
+		return injectOverride, nil
 	}
 	return &tag{Name: value}, nil
 }

inject_test.go

@@ -3,6 +3,7 @@ package inject_test
 import (
 	"fmt"
 	"math/rand"
+	"reflect"
 	"strings"
 	"testing"
 	"time"
@@ -114,6 +115,44 @@ func TestInjectSimple(t *testing.T) {
 	}
 }
 
+func TestInjectOverride(t *testing.T) {
+	var v struct {
+		A *TypeAnswerStruct `inject:""`
+		B *TypeAnswerStruct `inject:"override"`
+	}
+	olda, oldb := &TypeAnswerStruct{}, &TypeAnswerStruct{}
+	v.A, v.B = olda, oldb
+	if err := inject.Populate(&v); err != nil {
+		t.Fatal(err)
+	}
+	if v.A != olda {
+		t.Fatal("original A was lost")
+	}
+	if v.B == oldb {
+		t.Fatal("original B was not overridden")
+	}
+}
+
+type TypeNestedInterfaceStruct struct {
+	A Answerable `inject:""`
+}
+
+func TestNonEmptyInterfaceTraversal(t *testing.T) {
+	olda := &TypeNestedStruct{}
+	v := TypeNestedInterfaceStruct{
+		A: olda,
+	}
+	if err := inject.Populate(&v); err != nil {
+		t.Fatal(err)
+	}
+	if v.A != olda {
+		t.Fatal("original A was lost")
+	}
+	if olda.A == nil {
+		t.Fatal("v.A.A is nil")
+	}
+}
+
 func TestDoesNotOverwrite(t *testing.T) {
 	a := &TypeAnswerStruct{}
 	var v struct {
@@ -238,7 +277,7 @@ func TestProvideTwoOfTheSame(t *testing.T) {
 		t.Fatal("expected error")
 	}
 
-	const msg = "provided two unnamed instances of type *github.com/facebookgo/inject_test.TypeAnswerStruct"
+	msg := fmt.Sprintf("provided two unnamed instances of type *%s.TypeAnswerStruct", reflect.TypeOf(a).PkgPath())
 	if err.Error() != msg {
 		t.Fatalf("expected:\n%s\nactual:\n%s", msg, err.Error())
 	}
@@ -251,7 +290,7 @@ func TestProvideTwoOfTheSameWithPopulate(t *testing.T) {
 		t.Fatal("expected error")
 	}
 
-	const msg = "provided two unnamed instances of type *github.com/facebookgo/inject_test.TypeAnswerStruct"
+	msg := fmt.Sprintf("provided two unnamed instances of type *%s.TypeAnswerStruct", reflect.TypeOf(a).PkgPath())
 	if err.Error() != msg {
 		t.Fatalf("expected:\n%s\nactual:\n%s", msg, err.Error())
 	}