After upgrading to Rails 5.0.0.beta4, I get an 'undefined method' error when trying to send an email using the Rails path helpers. I have an ActiveRecord class called
<%= project_path(@project.id) %>
Rails 4.2 allowed this feature as a carryover from Rails versions past; however, Rails 4.2 explicitly discouraged it via documentation in the Rails 4.2 Release Notes. This documented discouragement is called deprecation, and is used as advance notice that a feature will break code in a subsequent release.
The entire purpose of deprecation is to allow the feature to continue working in the current versions, so as not to disrupt productivity. Feature-wise, this is how the architecture, libraries, and even the language move forward in a controlled manner. Note that security issues do not follow the deprecation process, and are fixed in situ in order to eliminate vulnerabilities as quickly as possible.
Rails 5 was the version that actually removed the ActionMailer support for
_path helpers, which had previously been deprecated. The Rails 5.0.0.beta1 CHANGELOG shows that the break was made then. The pull request was merged in Rails 5 RC1 with this commit.