different behavior of stdlib ostruct vs. ostruct-gem

lib/ostruct.rb の304行目で報告されている []= の呼び出しから始め、issue の例を使って ostruct 0.5.0 で Ruby 3.0 の動作を再現します。繰り返しの代入と dup を stdlib OpenStruct と比較します。更新された代入で期待されるシンボルキーが保持され、dup が示されている NoMethodError を発生させなくなれば完了です。

I am on Ruby 3.0

With stdlib ostruct I get:

irb(main):002:0> x = OpenStruct.new
=> #<OpenStruct>
irb(main):002:0> x.varname1 = 'varval 1'
=> "varval 1"
irb(main):003:0> x.to_h
=> {:varname1=>"varval 1"}
irb(main):004:0> x.varname1 = 'varval 2'
=> "varval 2"
irb(main):005:0> x.to_h
=> {:varname1=>"varval 2"}
irb(main):006:0> x.varname2 = 'varval 3'
=> "varval 3"
irb(main):007:0> x.to_h
=> {:varname1=>"varval 2", :varname2=>"varval 3"}
irb(main):008:0> x.varname2 = 'varval 4'
=> "varval 4"
irb(main):009:0> x.to_h
=> {:varname1=>"varval 2", :varname2=>"varval 4"}

Starting with version 0.5.0 of the ostruct-gem: I get:

irb(main):001:0> x = OpenStruct.new
=> #<OpenStruct>
irb(main):002:0> x.varname1 = 'varval 1'
=> "varval 1"
irb(main):003:0> x.to_h
=> {:varname1=>"varval 1"}
irb(main):004:0> x.varname1 = 'varval 2'
=> "varval 2"
irb(main):005:0> x.to_h
=> {:varname1=>"varval 1", false=>"varval 2"}
irb(main):006:0> x.varname2 = 'varval 3'
=> "varval 3"
irb(main):007:0> x.to_h
=> {:varname1=>"varval 1", false=>"varval 2", :varname2=>"varval 3"}
irb(main):008:0> x.varname2 = 'varval 4'
=> "varval 4"
irb(main):009:0> x.to_h
=> {:varname1=>"varval 1", false=>"varval 4", :varname2=>"varval 3"}

one of many side effects is:

irb(main):009:0> y = x.dup
/var/lib/gems/3.0.0/gems/ostruct-0.5.0/lib/ostruct.rb:304:in `[]=': undefined method `to_sym' for false:FalseClass (NoMethodError)
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