From fa12c02e81bdff1e9c11ee8a70b938b8c02da6b6 Mon Sep 17 00:00:00 2001
From: Alex Flint <alex.flint@gmail.com>
Date: Mon, 24 May 2021 21:45:11 -0700
Subject: [PATCH] recurse into unexported embedded structs

---
 parse.go      | 13 ++++++++++---
 parse_test.go | 23 +++++++++++++++++++++++
 2 files changed, 33 insertions(+), 3 deletions(-)

diff --git a/parse.go b/parse.go
index 13e8195..d76ef0f 100644
--- a/parse.go
+++ b/parse.go
@@ -257,17 +257,24 @@ func cmdFromStruct(name string, dest path, t reflect.Type) (*command, error) {
 
 	var errs []string
 	walkFields(t, func(field reflect.StructField, t reflect.Type) bool {
-		// Check for the ignore switch in the tag
+		// check for the ignore switch in the tag
 		tag := field.Tag.Get("arg")
-		if tag == "-" || !isExported(field.Name) {
+		if tag == "-" {
 			return false
 		}
 
-		// If this is an embedded struct then recurse into its fields
+		// if this is an embedded struct then recurse into its fields, even if
+		// it is unexported, because exported fields on unexported embedded
+		// structs are still writable
 		if field.Anonymous && field.Type.Kind() == reflect.Struct {
 			return true
 		}
 
+		// ignore any other unexported field
+		if !isExported(field.Name) {
+			return false
+		}
+
 		// duplicate the entire path to avoid slice overwrites
 		subdest := dest.Child(field)
 		spec := spec{
diff --git a/parse_test.go b/parse_test.go
index 695b1d8..e78b4d4 100644
--- a/parse_test.go
+++ b/parse_test.go
@@ -1095,6 +1095,29 @@ func TestEmbeddedWithDuplicateField2(t *testing.T) {
 	assert.Equal(t, "", args.U.A)
 }
 
+func TestUnexportedEmbedded(t *testing.T) {
+	type embeddedArgs struct {
+		Foo string
+	}
+	var args struct {
+		embeddedArgs
+	}
+	err := parse("--foo bar", &args)
+	require.NoError(t, err)
+	assert.Equal(t, "bar", args.Foo)
+}
+
+func TestIgnoredEmbedded(t *testing.T) {
+	type embeddedArgs struct {
+		Foo string
+	}
+	var args struct {
+		embeddedArgs `arg:"-"`
+	}
+	err := parse("--foo bar", &args)
+	require.Error(t, err)
+}
+
 func TestEmptyArgs(t *testing.T) {
 	origArgs := os.Args