Add FrozenError#receiver

Similar to NameError#receiver, this returns the object on which
the modification was attempted.  This is useful as it can pinpoint
exactly what is frozen.  In many cases when a FrozenError is
raised, you cannot determine from the context which object is
frozen that you attempted to modify.

Users of the current rb_error_frozen C function will have to switch
to using rb_error_frozen_object or the new rb_frozen_error_raise
in order to set the receiver of the FrozenError.

To allow the receiver to be set from Ruby, support an optional
second argument to FrozenError#initialize.

Implements [Feature #15751]

1 files changed, 9 insertions, 0 deletions

diff --git a/NEWS b/NEWS
index 7e9450b9dd..89ed64ce4b 100644
--- a/NEWS
+++ b/NEWS
@@ -66,6 +66,15 @@ Enumerator::
       can be directly passed to another method as a block
       argument.  [Feature #15618]
 
+FrozenError::
+
+  New method::
+
+    * Added FrozenError#receiver to return the frozen object that
+      modification was attempted on.  To set this object when raising
+      FrozenError in Ruby code, pass it as the second argument to
+      FrozenError.new.
+
 Integer::
 
   Modified method::