[ruby-core:73556] [Ruby trunk - Bug #12030] [Open] Crash calling Hash#dig when hash contains ActiveRecord objects

Issue #12030 has been reported by Leon Miller-Out.

----------------------------------------
Bug #12030: Crash calling Hash#dig when hash contains ActiveRecord objects
https://bugs.ruby-lang.org/issues/12030

* Author: Leon Miller-Out
* Status: Open
* Priority: Normal
* Assignee: 
* ruby -v: ruby 2.3.0p0 (2015-12-25 revision 53290) [x86_64-darwin15]
* Backport: 2.0.0: UNKNOWN, 2.1: UNKNOWN, 2.2: UNKNOWN, 2.3: UNKNOWN
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This code results in a stack consistency error:

~~~
begin
  require 'bundler/inline'
rescue LoadError => e
  $stderr.puts 'Bundler version 1.10 or later is required. Please update your Bundler'
  raise e
end

gemfile(true) do
  ruby '2.3.0'
  source 'https://rubygems.org'
  gem 'activerecord', '4.2.5'
end

require 'active_record'

{ foo: ActiveRecord::Base }.dig(:foo, :bar)
~~~

## Output

~~~
crash.rb:5: [BUG] Stack consistency error (sp: 3, bp: 4)
ruby 2.3.0p0 (2015-12-25 revision 53290) [x86_64-darwin13]

[snip]

-- Control frame information -----------------------------------------------
c:0002 p:0050 s:0003 E:001a80 EVAL   crash.rb:5 [FINISH]
c:0001 p:0000 s:0002 E:000cd0 (none) [FINISH]

-- Ruby level backtrace information ----------------------------------------
crash.rb:5:in `<main>'

-- C level backtrace information -------------------------------------------
0   ruby                                0x000000010a3aa1e4 rb_vm_bugreport + 388
1   ruby                                0x000000010a248aa5 rb_bug + 485
2   ruby                                0x000000010a38abc3 vm_exec_core + 13315
3   ruby                                0x000000010a39b1f9 vm_exec + 121
4   ruby                                0x000000010a251ef4 ruby_exec_internal + 148
5   ruby                                0x000000010a251e1e ruby_run_node + 78
6   ruby                                0x000000010a20820f main + 79
~~~

## Expected output
~~~
crash.rb:5:in `dig': #<Class:ActiveRecord::Base> does not have #dig method (TypeError)
~~~

## Notes
In addition to crashing when trying to dig into ActiveRecord::Base, it will crash trying to dig into a child class of ActiveRecord::Base, or into an instance of a child class of ActiveRecord::Base. Putting AR objects into hashes is probably a common practice in Rails apps, and users will dig too far into those hashes by accident (as I did!)

More realistic production code could look more like:

~~~
class User < ActiveRecord::Base; end
{ foo: User.first }.dig(:foo, :bar)
~~~

This bug has also been reproduced on: ruby 2.3.0p0 (2015-12-25 revision 53290) [x86_64-linux-gnu]



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