support squashing embedded structs

mapstructure.go

diff --git a/mapstructure.go b/mapstructure.go
index 2941a51..70da05b 100644
--- a/mapstructure.go
+++ b/mapstructure.go
@@ -333,6 +333,29 @@
 		fieldType := valType.Field(i)
 		fieldName := fieldType.Name
 
+		if fieldType.Anonymous {
+			// We have an embedded field. We "squash" the fields down if
+			// specified in the tag.
+			squash := false
+			tagParts := strings.Split(fieldType.Tag.Get(d.config.TagName), ",")
+			for _, tag := range tagParts[1:] {
+				if tag == "squash" {
+					squash = true
+					break
+				}
+			}
+
+			if squash {
+				inner := val.FieldByName(fieldName)
+				err := d.decodeStruct(name, data, inner)
+				if err != nil {
+					errors = appendErrors(errors, err)
+				}
+
+				continue
+			}
+		}
+
 		tagValue := fieldType.Tag.Get(d.config.TagName)
 		if tagValue != "" {
 			fieldName = tagValue

mapstructure_examples_test.go

diff --git a/mapstructure_examples_test.go b/mapstructure_examples_test.go
index 5faae12..d7f3d00 100644
--- a/mapstructure_examples_test.go
+++ b/mapstructure_examples_test.go
@@ -71,16 +71,16 @@
 
 func ExampleDecode_metadata() {
 	type Person struct {
-		Name   string
-		Age    int
+		Name string
+		Age  int
 	}
 
 	// This input can come from anywhere, but typically comes from
 	// something like decoding JSON where we're not quite sure of the
 	// struct initially.
 	input := map[string]interface{}{
-		"name":   "Mitchell",
-		"age":    91,
+		"name":  "Mitchell",
+		"age":   91,
 		"email": "foo@bar.com",
 	}
 
@@ -91,7 +91,7 @@
 	var result Person
 	config := &DecoderConfig{
 		Metadata: &md,
-		Result: &result,
+		Result:   &result,
 	}
 
 	decoder, err := NewDecoder(config)

mapstructure_test.go

diff --git a/mapstructure_test.go b/mapstructure_test.go
index b3e1363..12e31c2 100644
--- a/mapstructure_test.go
+++ b/mapstructure_test.go
@@ -15,6 +15,16 @@
 	Vdata   interface{}
 }
 
+type Embedded struct {
+	Basic
+	Vunique string
+}
+
+type EmbeddedSquash struct {
+	Basic   `mapstructure:",squash"`
+	Vunique string
+}
+
 type Map struct {
 	Vfoo   string
 	Vother map[string]string
@@ -104,6 +114,55 @@
 	}
 }
 
+func TestDecode_Embedded(t *testing.T) {
+	t.Parallel()
+
+	input := map[string]interface{}{
+		"vstring": "foo",
+		"Basic": map[string]interface{}{
+			"vstring": "innerfoo",
+		},
+		"vunique": "bar",
+	}
+
+	var result Embedded
+	err := Decode(input, &result)
+	if err != nil {
+		t.Fatalf("got an err: %s", err.Error())
+	}
+
+	if result.Vstring != "innerfoo" {
+		t.Errorf("vstring value should be 'innerfoo': %#v", result.Vstring)
+	}
+
+	if result.Vunique != "bar" {
+		t.Errorf("vunique value should be 'bar': %#v", result.Vunique)
+	}
+}
+
+func TestDecode_EmbeddedSquash(t *testing.T) {
+	t.Parallel()
+
+	input := map[string]interface{}{
+		"vstring": "foo",
+		"vunique": "bar",
+	}
+
+	var result EmbeddedSquash
+	err := Decode(input, &result)
+	if err != nil {
+		t.Fatalf("got an err: %s", err.Error())
+	}
+
+	if result.Vstring != "foo" {
+		t.Errorf("vstring value should be 'foo': %#v", result.Vstring)
+	}
+
+	if result.Vunique != "bar" {
+		t.Errorf("vunique value should be 'bar': %#v", result.Vunique)
+	}
+}
+
 func TestDecode_NonStruct(t *testing.T) {
 	t.Parallel()
 
@@ -128,13 +187,13 @@
 
 	input := map[string]interface{}{
 		"vstring": "hello",
-		"foo": "bar",
+		"foo":     "bar",
 	}
 
 	var result Basic
 	config := &DecoderConfig{
 		ErrorUnused: true,
-		Result:   &result,
+		Result:      &result,
 	}
 
 	decoder, err := NewDecoder(config)