Warn on access/modify of $SAFE, and remove effects of modifying $SAFE

This removes the security features added by $SAFE = 1, and warns for access
or modification of $SAFE from Ruby-level, as well as warning when calling
all public C functions related to $SAFE.

This modifies some internal functions that took a safe level argument
to no longer take the argument.

rb_require_safe now warns, rb_require_string has been added as a
version that takes a VALUE and does not warn.

One public C function that still takes a safe level argument and that
this doesn't warn for is rb_eval_cmd.  We may want to consider
adding an alternative method that does not take a safe level argument,
and warn for rb_eval_cmd.

1 files changed, 2 insertions, 1 deletions

diff --git a/thread.c b/thread.c
index 15dea98b3c..52d89a01a9 100644
--- a/thread.c
+++ b/thread.c
@@ -3112,7 +3112,8 @@ rb_thread_stop_p(VALUE thread)
 static VALUE
 rb_thread_safe_level(VALUE thread)
 {
-    return UINT2NUM(rb_safe_level());
+    rb_warn("Thread#safe_level will be removed in Ruby 3.0");
+    return UINT2NUM(GET_VM()->safe_level_);
 }
 
 /*