From cd5d3e4aab20f86867daa507a1b57d1ab416f389 Mon Sep 17 00:00:00 2001
From: urso <steffen@xata.io>
Date: Wed, 22 Dec 2021 15:22:57 +0100
Subject: [PATCH] Allow structs without public fields to implement Setter

If a struct does not provide a public field that might be set by
cleanenv, then the struct was ignored. This did make it impossible to
implement a custom struct with SetValue.

The change checks if a field implements SetValue. If SetValue is
implemented we stop recursing into the type to looks for other fields
that might be populated via cleanenv.
---
 cleanenv.go     | 28 ++++++++++++++++++++--------
 example_test.go | 31 +++++++++++++++++++++++++++++++
 2 files changed, 51 insertions(+), 8 deletions(-)

diff --git a/cleanenv.go b/cleanenv.go
index 3b03d74..1491e08 100644
--- a/cleanenv.go
+++ b/cleanenv.go
@@ -238,15 +238,27 @@ func readStructMetadata(cfgRoot interface{}) ([]structMeta, error) {
 
 			// process nested structure (except of time.Time)
 			if fld := s.Field(idx); fld.Kind() == reflect.Struct {
-				// add structure to parsing stack
-				if fld.Type() != reflect.TypeOf(time.Time{}) {
-					prefix, _ := fType.Tag.Lookup(TagEnvPrefix)
-					cfgStack = append(cfgStack, cfgNode{fld.Addr().Interface(), sPrefix + prefix})
-					continue
+				// check if type implements a custom setter
+				canSet := false
+				if fld.CanInterface() {
+					if _, ok := fld.Interface().(Setter); ok {
+						canSet = true
+					} else if _, ok := fld.Addr().Interface().(Setter); ok {
+						canSet = true
+					}
 				}
-				// process time.Time
-				if l, ok := fType.Tag.Lookup(TagEnvLayout); ok {
-					layout = &l
+
+				if !canSet {
+					// add structure to parsing stack
+					if fld.Type() != reflect.TypeOf(time.Time{}) {
+						prefix, _ := fType.Tag.Lookup(TagEnvPrefix)
+						cfgStack = append(cfgStack, cfgNode{fld.Addr().Interface(), sPrefix + prefix})
+						continue
+					}
+					// process time.Time
+					if l, ok := fType.Tag.Lookup(TagEnvLayout); ok {
+						layout = &l
+					}
 				}
 			}
 
diff --git a/example_test.go b/example_test.go
index bc5473e..3b91886 100644
--- a/example_test.go
+++ b/example_test.go
@@ -1,6 +1,7 @@
 package cleanenv_test
 
 import (
+	"errors"
 	"flag"
 	"fmt"
 	"os"
@@ -195,6 +196,36 @@ func Example_setter() {
 	//Output: {Default:test1 Custom:my field is: test2}
 }
 
+// MyCustomStruct is an example type with a custom setter on a struct with
+// private fields only.
+type MyCustomStruct struct {
+	priv string
+}
+
+func (cs *MyCustomStruct) SetValue(s string) error {
+	if s == "" {
+		return errors.New("empty value")
+	}
+	cs.priv = s
+	return nil
+}
+
+func (cs *MyCustomStruct) String() string {
+	return cs.priv
+}
+
+func Example_structsetter() {
+	type config struct {
+		Custom MyCustomStruct `env:"CUSTOM"`
+	}
+
+	var cfg config
+	os.Setenv("CUSTOM", "test")
+	cleanenv.ReadEnv(&cfg)
+	fmt.Println(cfg.Custom.String())
+	//Output: test
+}
+
 // ConfigUpdate is a type with a custom updater
 type ConfigUpdate struct {
 	Default string `env:"DEFAULT"`