1 files changed, 68 insertions, 0 deletions
diff --git a/lib/rubygems/core_ext/kernel_gem.rb b/lib/rubygems/core_ext/kernel_gem.rb
new file mode 100644
index 0000000000..4e09b95c44
--- /dev/null
+++ b/lib/rubygems/core_ext/kernel_gem.rb
@@ -0,0 +1,68 @@
+# frozen_string_literal: true
+
+module Kernel
+  ##
+  # Use Kernel#gem to activate a specific version of +gem_name+.
+  #
+  # +requirements+ is a list of version requirements that the
+  # specified gem must match, most commonly "= example.version.number".  See
+  # Gem::Requirement for how to specify a version requirement.
+  #
+  # If you will be activating the latest version of a gem, there is no need to
+  # call Kernel#gem, Kernel#require will do the right thing for you.
+  #
+  # Kernel#gem returns true if the gem was activated, otherwise false.  If the
+  # gem could not be found, didn't match the version requirements, or a
+  # different version was already activated, an exception will be raised.
+  #
+  # Kernel#gem should be called *before* any require statements (otherwise
+  # RubyGems may load a conflicting library version).
+  #
+  # Kernel#gem only loads prerelease versions when prerelease +requirements+
+  # are given:
+  #
+  #   gem 'rake', '>= 1.1.a', '< 2'
+  #
+  # In older RubyGems versions, the environment variable GEM_SKIP could be
+  # used to skip activation of specified gems, for example to test out changes
+  # that haven't been installed yet.  Now RubyGems defers to -I and the
+  # RUBYLIB environment variable to skip activation of a gem.
+  #
+  # Example:
+  #
+  #   GEM_SKIP=libA:libB ruby -I../libA -I../libB ./mycode.rb
+
+  def gem(gem_name, *requirements) # :doc:
+    skip_list = (ENV["GEM_SKIP"] || "").split(/:/)
+    raise Gem::LoadError, "skipping #{gem_name}" if skip_list.include? gem_name
+
+    if gem_name.is_a? Gem::Dependency
+      unless Gem::Deprecate.skip
+        warn "#{Gem.location_of_caller.join ":"}:Warning: Kernel.gem no longer "\
+          "accepts a Gem::Dependency object, please pass the name "\
+          "and requirements directly"
+      end
+
+      requirements = gem_name.requirement
+      gem_name = gem_name.name
+    end
+
+    dep = Gem::Dependency.new(gem_name, *requirements)
+
+    loaded = Gem.loaded_specs[gem_name]
+
+    return false if loaded && dep.matches_spec?(loaded)
+
+    spec = dep.to_spec
+
+    if spec
+      if Gem::LOADED_SPECS_MUTEX.owned?
+        spec.activate
+      else
+        Gem::LOADED_SPECS_MUTEX.synchronize { spec.activate }
+      end
+    end
+  end
+
+  private :gem
+end