From 293ad7bada61561e59b7b0b845e8edcade69dfff Mon Sep 17 00:00:00 2001
From: Emilijus Stankus <e.stankus@nanoavionics.com>
Date: Mon, 18 Oct 2021 15:49:09 +0300
Subject: [PATCH] Fix deep file parsing not working when flag delimiter is set

---
 aconfig_test.go | 32 ++++++++++++++++++++++++++++++++
 reflection.go   |  5 ++++-
 2 files changed, 36 insertions(+), 1 deletion(-)

diff --git a/aconfig_test.go b/aconfig_test.go
index f91002d..506d44a 100644
--- a/aconfig_test.go
+++ b/aconfig_test.go
@@ -1450,3 +1450,35 @@ func TestBad(t *testing.T) {
 		t.Fatalf("want %v, got %v", want, got)
 	}
 }
+
+func TestFileConfigFlagDelim(t *testing.T) {
+	type TestConfig struct {
+		Options struct {
+			Foo float64
+			Bar float64
+		}
+	}
+	var cfg TestConfig
+
+	loader := LoaderFor(&cfg, Config{
+		SkipDefaults:  true,
+		SkipEnv:       true,
+		SkipFlags:     true,
+		FlagDelimiter: "_",
+
+		Files: []string{"testdata/toy.json"},
+	})
+
+	if err := loader.Load(); err != nil {
+		t.Fatal(err)
+	}
+
+	var want = TestConfig{Options: struct {
+		Foo float64
+		Bar float64
+	}{0.4, 0.25}}
+
+	if got := cfg; !reflect.DeepEqual(want, got) {
+		t.Fatalf("want %v, got %v", want, got)
+	}
+}
diff --git a/reflection.go b/reflection.go
index 07c6b97..f7fe2ce 100644
--- a/reflection.go
+++ b/reflection.go
@@ -73,7 +73,10 @@ func (l *Loader) tagsForField(field reflect.StructField) map[string]string {
 }
 
 func (l *Loader) fullTag(prefix string, f *fieldData, tag string) string {
-	sep := l.config.FlagDelimiter
+	sep := "."
+	if tag == flagNameTag {
+		sep = l.config.FlagDelimiter
+	}
 	if tag == envNameTag {
 		sep = l.config.envDelimiter
 	}