Add support for limited mode without unsafe pkg.

This commit adds support for compiling spew without the unsafe package.
When compiled without the unsafe package, some of the more advanced
features such as invoking stringers on pointers from non-pointer
variables and unexported struct fields are not available.

By default, spew will be compiled in the limited mode for Google App
Engine since the unsafe package is not available there.  Additionally,
spew can be compiled without the unsafe package manually by specifying
the "disableunsafe" build tag.

Finally, a new package-level constant named "UnsafeDisabled" has been
exposed which can be used to programmatically determine if spew was
compiled with access to the unsafe package.

1 files changed, 4 insertions, 1 deletions

diff --git a/spew/config.go b/spew/config.go
index 9e21b38..ee1ab07 100644
--- a/spew/config.go
+++ b/spew/config.go
@@ -61,7 +61,10 @@ type ConfigState struct {
 	// with a pointer receiver could technically mutate the value, however,
 	// in practice, types which choose to satisify an error or Stringer
 	// interface with a pointer receiver should not be mutating their state
-	// inside these interface methods.
+	// inside these interface methods.  As a result, this option relies on
+	// access to the unsafe package, so it will not have any effect when
+	// running in environments without access to the unsafe package such as
+	// Google App Engine or with the "disableunsafe" build tag specified.
 	DisablePointerMethods bool
 
 	// ContinueOnMethod specifies whether or not recursion should continue once