Make mutating params#dig mutate underlying params

When #dig was called on a params object and return either a Hash or an
Array, and that value was subsquently mutated, it would not modify the
containing params object. That means that the behavior of
`params.dig(:a, :b)[:c] = 1` did not match either `params[:a][:b][:c] =
1` nor `hash.dig(:a, :b)[:c] = 1`. Similarly to
`ActionController::Parameters#[]`, use `#convert_hashes_to_parameters`
to pre-convert values and insert them in the receiving params object
prior to returning them.

1 files changed, 2 insertions, 1 deletions

diff --git a/actionpack/lib/action_controller/metal/strong_parameters.rb b/actionpack/lib/action_controller/metal/strong_parameters.rb
index 75ca282804..4789252550 100644
--- a/actionpack/lib/action_controller/metal/strong_parameters.rb
+++ b/actionpack/lib/action_controller/metal/strong_parameters.rb
@@ -590,7 +590,8 @@ module ActionController
     #   params2 = ActionController::Parameters.new(foo: [10, 11, 12])
     #   params2.dig(:foo, 1) # => 11
     def dig(*keys)
-      convert_value_to_parameters(@parameters.dig(*keys))
+      convert_hashes_to_parameters(keys.first, @parameters[keys.first])
+      @parameters.dig(*keys)
     end
 
     # Returns a new <tt>ActionController::Parameters</tt> instance that