Feature Proposal - Environment dependant directives

[TomasBarry]

Expected behavior

This feature proposal would address (at least) these issues:

• Need two assets compiled in rails test environment, but not compiled in rails production. #666 - Need two assets compiled in rails test environment, but not compiled in rails production.
• Failing to serve assets (Asset was not declared to be precompiled) #655 - Failing to serve assets (Asset was not declared to be precompiled)
• Rails Engine not compiling assets unless explicitly declared #542 - Rails Engine not compiling assets unless explicitly declared
• Images in engines: Asset was not declared to be precompiled in production. #426 - Images in engines: Asset was not declared to be precompiled in production.

I am proposing amending the process_directives method in lib/sprockets/directive_processor.rb which currently looks like:

def process_directives(directives)
  directives.each do |line_number, name, *args|
    begin
      send("process_#{name}_directive", *args)
    rescue Exception => e
      e.set_backtrace(["#{@filename}:#{line_number}"] + e.backtrace)
      raise e
    end
  end
end

My assumption is that within this method we can have access to Rails.env so that we can test for the environment that would be within args:

def process_directives(directives)
  directives.each do |line_number, name, *args|
    begin
      # If the target environment does not match the current environment
      # then skip the directive
      if args["target_environment"] && args["target_environment"] != Rails.env[args["target_environment"]]
        next
      end
      send("process_#{name}_directive", *args)
    rescue Exception => e
      e.set_backtrace(["#{@filename}:#{line_number}"] + e.backtrace)
      raise e
    end
  end
end

The API for the directive would be something along the lines of

//= DIRECTIVE PATH EXTENSION target_environment=[production|development|test|*]

Example:

//= link_directory ../stylesheets/some_specific_sheet .css target_environment=development

By default, the exclusion of target_environment would mean that the directive should apply to all environments. Perhaps multiple environments should be possible in one line too:

//= link_directory ../stylesheets/some_specific_sheet .css target_environment=[development,test]

Or perhaps event an exclude_environment argument should be present:

//= link_directory ../stylesheets/some_specific_sheet .css exclude_environment=production

//= link_directory ../stylesheets/some_specific_sheet .css exclude_environment=[production,test]

What drew me to this issue was GraphiQL from graphql-ruby which is only mounted in development and with the latest version of sprockets, the JS and CSS for GraphiQL would need to be added to the manifest.js file (//= link graphiql/rails/application.css) in all environments instead of just in development.

Actual behavior

Directives cannot be conditional depending on the Rails environment. Specifically for link_tree etc, assets are either pre-compiled in all environments or in none.

System configuration

• Sprockets version - 4.0.2
• Ruby version - 2.6.0

Example App (Reproduction) - THIS IS IMPORTANT YOUR ISSUE LIKELY WILL NOT BE RESOLVED WITHOUT THIS

Example of the manifest.js:

//= link_tree ../images
//= link_directory ../javascripts .js
//= link_directory ../stylesheets .css

//= link_directory ../stylesheets/some_specific_sheet_only_for_development .css target_environment=development

[schneems]

Sorry, i just can't. If you have a proposal please send a PR or maybe write it up in your own library that extends sprockets or sprockets-rails. It's extremely hard for me to pre-approve any discussion without also seeing the code involved to implement it.