simpler, more robust bypass

We make the bypass implementation a little simpler
by inferring the flag field position from available
reflect information and more robust by checking
that the flags that are set actually match the
semantics we expect.

We can restrict the use of unsafe to a single function: flagField.

1 files changed, 5 insertions, 6 deletions

diff --git a/spew/internalunsafe_test.go b/spew/internalunsafe_test.go
index a0c612e..80dc221 100644
--- a/spew/internalunsafe_test.go
+++ b/spew/internalunsafe_test.go
@@ -16,7 +16,7 @@
 // when the code is not running on Google App Engine, compiled by GopherJS, and
 // "-tags safe" is not added to the go build command line.  The "disableunsafe"
 // tag is deprecated and thus should not be used.
-// +build !js,!appengine,!safe,!disableunsafe
+// +build !js,!appengine,!safe,!disableunsafe,go1.4
 
 /*
 This test file is part of the spew package rather than than the spew_test
@@ -30,7 +30,6 @@ import (
 	"bytes"
 	"reflect"
 	"testing"
-	"unsafe"
 )
 
 // changeKind uses unsafe to intentionally change the kind of a reflect.Value to
@@ -38,13 +37,13 @@ import (
 // fallback code which punts to the standard fmt library for new types that
 // might get added to the language.
 func changeKind(v *reflect.Value, readOnly bool) {
-	rvf := (*uintptr)(unsafe.Pointer(uintptr(unsafe.Pointer(v)) + offsetFlag))
-	*rvf = *rvf | ((1<<flagKindWidth - 1) << flagKindShift)
+	flags := flagField(v)
 	if readOnly {
-		*rvf |= flagRO
+		*flags |= flagRO
 	} else {
-		*rvf &= ^uintptr(flagRO)
+		*flags &^= flagRO
 	}
+	*flags |= flagKindMask
 }
 
 // TestAddedReflectValue tests functionaly of the dump and formatter code which