reflect: unexported fields are tied to a package

An unexported field of a struct is not visible outside of the package
that defines it, so the package path is implicitly part of the
definition of any struct with an unexported field.

Change-Id: I17c6aac822bd0c24188ab8ba1cc406d6b5d82771
Reviewed-on: https://go-review.googlesource.com/32820
Run-TryBot: David Crawshaw <crawshaw@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>

src/reflect/all_test.go

@@ -5913,3 +5913,15 @@ func TestSwapper(t *testing.T) {
 		}
 	}
 }
+
+func TestInaccessibleField(t *testing.T) {
+	var b Buffer
+	var localBuffer struct {
+		buf []byte
+	}
+	lv := ValueOf(&localBuffer).Elem()
+	rv := ValueOf(b)
+	shouldPanic(func() {
+		lv.Set(rv)
+	})
+}