does using “:platforms =>” in your gemfile work?

问题

I have a Rails app that I'm developing on Windows and deploying to Linux. I suspect I'll just switch entirely over to Linux in the future. Anyway, on Linux I need 'execjs' and 'therubyracer' but I don't need those in Win7. So I put these lines in my gemfile:

gem 'therubyracer', :platforms => :ruby
gem 'execjs', :platforms => :ruby

Ran a bundle install on the Linux VM and the app started up fine. But on Windows I get:

Uncaught exception: Could not find execjs-1.2.11 in any of the sources

Now, from what I read (here under PLATFORMS) it tells me that "If a gem should only be used in a particular platform or set of platforms, you can specify them" and the sample is this:

gem "weakling",   :platforms => :jruby 

And it says "ruby C Ruby (MRI) or Rubinius, but NOT Windows". So to me that says that bundler should be ignoring the execjs line on Windows. However on Windows when I ran bundle install I saw this:

Installing execjs (1.2.11)

So that says to me I'm missing something about the docs or bundler is ignoring the platforms command. Am I doing something wrong?

PS>bundle -v
Bundler version 1.0.21

回答1:

:platforms => :ruby does indeed exclude gems from being installed on Windows.

However, it does not work in a cygwin environment. In cygwin, it considers the platform to be :mri.

You'll also notice that ruby -e 'puts RUBY_PLATFORM' outputs i386-cygwin, not i386-mingw32 or i386-mswin like it would on Windows ruby.

Were you working in a cygwin environment?

回答2:

Add code to the Gemfile like this that excludes/includes gems depending on the OS platform

if RUBY_PLATFORM=~ /win32/ 
   gem "windows-only-gem"
else
   gem "os-agnostic-gem"
end

回答3:

Bundler concept of platform differs from normal understanding of RUBY_PLATFORM matching or RubyGems behaviors.

You can find the entire documentation about how to use platforms for Bundler here:

http://bundler.io/v1.14/man/gemfile.5.html

You might not need therubyraceron Windows (it actually doesn't work), but you might need execjs so CoffeeScript or other details of Asset Pipeline work properly

In your case, I will do:

gem "execjs"
gem "therubyracer", :platforms => :ruby

UPDATE: execjs gem might be installed because another dependency (not limited by platforms) is depending on it to be installed.

回答4:

Rails 5:

if Gem.win_platform?
  # Install gem for Windows
else
  # Install another gem
end

回答5:

I'm not sure about the :platform switch as I've never used it. However, an alternative that I think will work for your scenario would be to wrap your declarations for those two gems in a 'group' block in your Gemfile. Such as...

group :production do
  gem 'therubyracer'
  gem 'execjs'
end

This way, those gems will only be used in your production environment, not in development.

Note that I believe bundler will still install them in development (something to do with dependency checking), but they won't actually get loaded and therefore shouldn't cause problems.

回答6:

gem 'win32-security', '~> 0.3.1' if (RbConfig::CONFIG['host_os'] =~ /mswin|mingw|cygwin/)

That works pretty well for me.

回答7:

A variation of @ffoeg's answer worked for me, and handles all windows environments, whereas just using RUBY_PLATFORM=~ /win32/ didn't work:

if RUBY_PLATFORM =~ /mswin|mingw|cygwin/i

  gem 'windows-only'

else

  gem 'non-windows'    

end

I agree that it's not ideal to have different gemfiles, however since I'm using unicorn to serve my Jekyll blog on Heroku, so I need gem unicorn - and this relies on kgio which several sources have confirmed is virtually impossible to install on windows...

来源：https://stackoverflow.com/questions/8421321/does-using-platforms-in-your-gemfile-work