Stop changes to a dupped `ActionController::Parameters` mutating the original #25735
This fixes the bug by defining a private
When `ActionController::Parameters` is duplicated with `#dup`, it doesn't create a duplicate of the instance variables (e.g. `@parameters`) but rather maintains the reference (see <http://ruby-doc.org/core-2.3.1/Object.html>). Given that the parameters object is often manipulated as if it were a hash (e.g. with `#delete` and similar methods), this leads to unexpected behaviour, like the following: ``` params = ActionController::Parameters.new(foo: "bar") duplicated_params = params.dup duplicated_params.delete(:foo) params == duplicated_params ``` This fixes the bug by defining a private `#initialize_copy` method, used internally by `#dup`, which makes a copy of `@parameters`.
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I imagine that may not have been true while this class inherited from Hash.
If you can confirm it works the same without it (and that we have test coverage to back that up), this seems like a good opportunity to clean up, before we make things look even more complicated, with a custom
…ize_copy` to manually duplicate the underlying parameters hash It looks like `ActionController::Parameters#dup` is leftover from when the class inherited from `Hash`. We can just trust `#dup`, which already copies the `@permitted` instance variable (confirmed by tests). We still define a `#initialize_copy` to make `@parameters` a copy that can be mutated without affecting the original instance.