Unnecessary initialization of struct pointers fix

envconfig.go

@@ -224,7 +224,42 @@ func Process(prefix string, spec interface{}) error {
 		}
 	}
 
-	return err
+	return removeEmptyStructs(spec)
+}
+
+func removeEmptyStructs(spec interface{}) error {
+	s := reflect.ValueOf(spec)
+
+	if s.Kind() != reflect.Ptr {
+		return ErrInvalidSpecification
+	}
+	s = s.Elem()
+	if s.Kind() != reflect.Struct {
+		return ErrInvalidSpecification
+	}
+
+	for i := 0; i < s.NumField(); i++ {
+		f := s.Field(i)
+
+		switch f.Kind() {
+		case reflect.Struct:
+			if err := removeEmptyStructs(f.Addr().Interface()); err != nil {
+				return err
+			}
+		case reflect.Ptr:
+			if f.Elem().Kind() == reflect.Struct && !f.IsNil() {
+				if err := removeEmptyStructs(f.Elem().Addr().Interface()); err != nil {
+					return err
+				}
+
+				if f.Elem().IsZero() {
+					f.Set(reflect.Zero(f.Type()))
+				}
+			}
+		}
+	}
+
+	return nil
 }
 
 // MustProcess is the same as Process but panics if an error occurs

envconfig_test.go

@@ -12,6 +12,9 @@ import (
 	"strings"
 	"testing"
 	"time"
+
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
 )
 
 type HonorDecodeInStruct struct {
@@ -794,7 +797,7 @@ func TestCheckDisallowedIgnored(t *testing.T) {
 
 func TestErrorMessageForRequiredAltVar(t *testing.T) {
 	var s struct {
-		Foo    string `envconfig:"BAR" required:"true"`
+		Foo string `envconfig:"BAR" required:"true"`
 	}
 
 	os.Clearenv()
@@ -862,3 +865,43 @@ func BenchmarkGatherInfo(b *testing.B) {
 		gatherInfo("env_config", &s)
 	}
 }
+
+func Test_removeEmptyStructs(t *testing.T) {
+	type t3 struct {
+		Field3 string
+	}
+	type t2 struct {
+		Field2 *t3
+	}
+	type t1 struct {
+		Field1 *t2
+	}
+
+	type t4 struct {
+		Field4 t1
+	}
+
+	t.Run("remove_empty_struct_all_pointers", func(t *testing.T) {
+		v := t1{Field1: &t2{Field2: &t3{}}}
+
+		err := removeEmptyStructs(&v)
+		require.NoError(t, err)
+		assert.Equal(t, t1{}, v)
+	})
+
+	t.Run("remove_empty_struct_non_pointer_level", func(t *testing.T) {
+		v := t4{Field4: t1{Field1: &t2{Field2: &t3{}}}}
+
+		err := removeEmptyStructs(&v)
+		require.NoError(t, err)
+		assert.Equal(t, t4{}, v)
+	})
+
+	t.Run("dont_remove_nonempty_struct", func(t *testing.T) {
+		v := t1{Field1: &t2{Field2: &t3{Field3: "hello"}}}
+
+		err := removeEmptyStructs(&v)
+		require.NoError(t, err)
+		assert.Equal(t, t1{Field1: &t2{Field2: &t3{Field3: "hello"}}}, v)
+	})
+}

go.mod

@@ -1 +1,9 @@
 module github.com/kelseyhightower/envconfig
+
+go 1.16
+
+require (
+	github.com/davecgh/go-spew v1.1.1 // indirect
+	github.com/stretchr/testify v1.7.0
+	gopkg.in/yaml.v3 v3.0.0-20200605160147-a5ece683394c // indirect
+)

go.sum

@@ -0,0 +1,13 @@
+github.com/davecgh/go-spew v1.1.0/go.mod h1:J7Y8YcW2NihsgmVo/mv3lAwl/skON4iLHjSsI+c5H38=
+github.com/davecgh/go-spew v1.1.1 h1:vj9j/u1bqnvCEfJOwUhtlOARqs3+rkHYY13jYWTU97c=
+github.com/davecgh/go-spew v1.1.1/go.mod h1:J7Y8YcW2NihsgmVo/mv3lAwl/skON4iLHjSsI+c5H38=
+github.com/pmezard/go-difflib v1.0.0 h1:4DBwDE0NGyQoBHbLQYPwSUPoCMWR5BEzIk/f1lZbAQM=
+github.com/pmezard/go-difflib v1.0.0/go.mod h1:iKH77koFhYxTK1pcRnkKkqfTogsbg7gZNVY4sRDYZ/4=
+github.com/stretchr/objx v0.1.0/go.mod h1:HFkY916IF+rwdDfMAkV7OtwuqBVzrE8GR6GFx+wExME=
+github.com/stretchr/testify v1.7.0 h1:nwc3DEeHmmLAfoZucVR881uASk0Mfjw8xYJ99tb5CcY=
+github.com/stretchr/testify v1.7.0/go.mod h1:6Fq8oRcR53rry900zMqJjRRixrwX3KX962/h/Wwjteg=
+gopkg.in/check.v1 v0.0.0-20161208181325-20d25e280405 h1:yhCVgyC4o1eVCa2tZl7eS0r+SDo693bJlVdllGtEeKM=
+gopkg.in/check.v1 v0.0.0-20161208181325-20d25e280405/go.mod h1:Co6ibVJAznAaIkqp8huTwlJQCZ016jof/cbN4VW5Yz0=
+gopkg.in/yaml.v3 v3.0.0-20200313102051-9f266ea9e77c/go.mod h1:K4uyk7z7BCEPqu6E+C64Yfv1cQ7kz7rIZviUmN+EgEM=
+gopkg.in/yaml.v3 v3.0.0-20200605160147-a5ece683394c h1:grhR+C34yXImVGp7EzNk+DTIk+323eIUWOmEevy6bDo=
+gopkg.in/yaml.v3 v3.0.0-20200605160147-a5ece683394c/go.mod h1:K4uyk7z7BCEPqu6E+C64Yfv1cQ7kz7rIZviUmN+EgEM=