defined local variable in ensure

ensure.txt

irb(main):010:0> def m
irb(main):011:1> puts defined?(a)
irb(main):012:1> a = 1
irb(main):013:1> puts defined?(a)
irb(main):014:1> raise "x"
irb(main):015:1> b = 3
irb(main):016:1> ensure
irb(main):017:1* puts defined?(a)
irb(main):018:1> puts defined?(b)
irb(main):019:1> end
=> nil
irb(main):020:0> m

local-variable
local-variable
local-variable
RuntimeError: x