Decode: code cleanup for struct cache (#659)

unmarshaler_test.go

@@ -1037,6 +1037,19 @@ B = "data"`,
 				}
 			},
 		},
+		{
+			desc:  "unexported struct fields are ignored",
+			input: `foo = "bar"`,
+			gen: func() test {
+				type doc struct {
+					foo string
+				}
+				return test{
+					target:   &doc{},
+					expected: &doc{},
+				}
+			},
+		},
 		{
 			desc: "array table into nil ptr",
 			input: `[[foo]]