ActionController::RespondToMismatchError in wiki controller

https://sentry.gitlab.net/gitlab/gitlabcom/issues/1726282/?referrer=gitlab_plugin

ActionController::RespondToMismatchError: respond_to was called multiple times and matched with conflicting formats in this action. Please note that you may only call respond_to and match on a single format per action.
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...
  active_support/callbacks.rb:428:in `block in make_lambda'
    target.send(method, *arguments, &block)
  projects/application_controller.rb:61:in `method_missing'
    authorize_action!($1.to_sym)
  projects/application_controller.rb:45:in `authorize_action!'
    access_denied!
  application_controller.rb:215:in `access_denied!'
    respond_to do |format|
  action_controller/metal/mime_responds.rb:209:in `respond_to'
    raise ActionController::RespondToMismatchError

ActionController::RespondToMismatchError: respond_to was called multiple times and matched with conflicting formats in this action. Please note that you may only call respond_to and match on a single format per action.

Issue was refined in #237798 (closed).

Permissions and Security

None.

Documentation

None.

Availability & Testing

Controller tests.

Recommended MR Breakdown

1 MR.

Proposed solution

See the upstream issue where two workarounds were proposed: https://github.com/rails/rails/issues/40023#issuecomment-673675138

1. Swap the order in access_denied! so format.html comes first.
   • This means we'd return a HTML response for a client sending Accept: */*.
2. Explicitly check for request.formats.include?(Mime::ALL) in access_denied!.
   • This means we'd return a header-only response for a client sending Accept: */*.