fix(decode): let the later field win an equal-depth name clash

Assisted-by: GLM 5.3

CHANGELOG.md

@@ -58,6 +58,8 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
   is not valid UTF-8, the way scalar keys already did, instead of silently
   emitting corrupt TOML (a header that lost its key, an inline table with a
   missing key).
+- Struct fields that resolve to one key at equal depth decode through the
+  field declared later, matching the documented rule; the first one won before.
 - A float with an exponent marker but no digits (`1e`, `0.0E`) is rejected;
   the exponent requires at least one digit.
 - A date-time offset outside 00:00 through 23:59 is rejected; such offsets

decode.go

@@ -289,7 +289,7 @@ func newStructSchema(t reflect.Type) structSchema {
 				name = f.Name
 			}
 			key := strings.ToLower(name)
-			if existing, ok := s.byName[key]; !ok || depth < existing.depth {
+			if existing, ok := s.byName[key]; !ok || depth <= existing.depth {
 				s.byName[key] = structFieldLoc{index: path, depth: depth}
 			}
 		}

decode_test.go

@@ -586,6 +586,22 @@ func TestUnmarshalEmbeddedNameClashShallowerWins(t *testing.T) {
 	}
 }
 
+func TestUnmarshalNameClashEqualDepthLaterWins(t *testing.T) {
+	// At equal depth the field declared later resolves the name, matching the
+	// documented rule.
+	type C struct {
+		First  string `toml:"v"`
+		Second int    `toml:"v"`
+	}
+	var c C
+	if err := Unmarshal([]byte("v = 1\n"), &c); err != nil {
+		t.Fatalf("unmarshal: %v", err)
+	}
+	if c.Second != 1 {
+		t.Fatalf("decoded: %+v, want the later field to take the value", c)
+	}
+}
+
 func TestUnmarshalUnknownKeyWithoutEmbeddedMap(t *testing.T) {
 	var cfg RoundTripDerived
 	if err := Unmarshal([]byte("rogue = 1\n"), &cfg); err != nil {