From 0d8016d665dd7a8876dba754ad17b910c24cf033 Mon Sep 17 00:00:00 2001
From: Oleg Kovalov <oleg@hey.com>
Date: Mon, 6 Sep 2021 17:58:51 +0200
Subject: [PATCH] Fix omitempty in tags (#107)

---
 aconfig_test.go | 18 ++++++++++++++++++
 reflection.go   |  3 +++
 2 files changed, 21 insertions(+)

diff --git a/aconfig_test.go b/aconfig_test.go
index e22d413..f91002d 100644
--- a/aconfig_test.go
+++ b/aconfig_test.go
@@ -167,6 +167,24 @@ func TestJSON(t *testing.T) {
 	}
 }
 
+func TestJSONWithOmitempty(t *testing.T) {
+	type TestConfig struct {
+		APIKey string `json:"b,omitempty"`
+	}
+
+	var cfg TestConfig
+	loader := LoaderFor(&cfg, Config{
+		SkipDefaults:       true,
+		SkipEnv:            true,
+		SkipFlags:          true,
+		AllowUnknownFields: true,
+		Files:              []string{createTestFile(t)},
+	})
+	if err := loader.Load(); err != nil {
+		t.Fatal(err)
+	}
+}
+
 func TestCustomFile(t *testing.T) {
 	filepath := createTestFile(t, "custom.config")
 
diff --git a/reflection.go b/reflection.go
index 891a207..07c6b97 100644
--- a/reflection.go
+++ b/reflection.go
@@ -84,6 +84,9 @@ func (l *Loader) fullTag(prefix string, f *fieldData, tag string) string {
 	if before, _, ok := cut(res, ",exact"); ok {
 		return before
 	}
+	if before, _, ok := cut(res, ",omitempty"); ok {
+		return before
+	}
 	for p := f.parent; p != nil; p = p.parent {
 		if p.Tag(tag) != "-" {
 			res = p.Tag(tag) + sep + res