1 files changed, 152 insertions, 0 deletions
diff --git a/lib/rubygems/core_ext/kernel_require.rb b/lib/rubygems/core_ext/kernel_require.rb
new file mode 100644
index 0000000000..3a9bdbdc9d
--- /dev/null
+++ b/lib/rubygems/core_ext/kernel_require.rb
@@ -0,0 +1,152 @@
+# frozen_string_literal: true
+
+#--
+# Copyright 2006 by Chad Fowler, Rich Kilmer, Jim Weirich and others.
+# All rights reserved.
+# See LICENSE.txt for permissions.
+#++
+
+require "monitor"
+
+module Kernel
+  RUBYGEMS_ACTIVATION_MONITOR = Monitor.new # :nodoc:
+
+  # Make sure we have a reference to Ruby's original Kernel#require
+  unless defined?(gem_original_require)
+    # :stopdoc:
+    alias_method :gem_original_require, :require
+    private :gem_original_require
+    # :startdoc:
+  end
+
+  ##
+  # When RubyGems is required, Kernel#require is replaced with our own which
+  # is capable of loading gems on demand.
+  #
+  # When you call <tt>require 'x'</tt>, this is what happens:
+  # * If the file can be loaded from the existing Ruby loadpath, it
+  #   is.
+  # * Otherwise, installed gems are searched for a file that matches.
+  #   If it's found in gem 'y', that gem is activated (added to the
+  #   loadpath).
+  #
+  # The normal <tt>require</tt> functionality of returning false if
+  # that file has already been loaded is preserved.
+
+  def require(path) # :doc:
+    return gem_original_require(path) unless Gem.discover_gems_on_require
+
+    RUBYGEMS_ACTIVATION_MONITOR.synchronize do
+      path = File.path(path)
+
+      # If +path+ belongs to a default gem, we activate it and then go straight
+      # to normal require
+
+      if spec = Gem.find_default_spec(path)
+        name = spec.name
+
+        next if Gem.loaded_specs[name]
+
+        # Ensure -I beats a default gem
+        resolved_path = begin
+          rp = nil
+          load_path_check_index = Gem.load_path_insert_index - Gem.activated_gem_paths
+          Gem.suffixes.find do |s|
+            $LOAD_PATH[0...load_path_check_index].find do |lp|
+              if File.symlink? lp # for backward compatibility
+                next
+              end
+
+              full_path = File.expand_path(File.join(lp, "#{path}#{s}"))
+              rp = full_path if File.file?(full_path)
+            end
+          end
+          rp
+        end
+
+        next if resolved_path
+
+        Kernel.send(:gem, name, Gem::Requirement.default_prerelease)
+
+        Gem.load_bundler_extensions(Gem.loaded_specs[name].version) if name == "bundler"
+
+        next
+      end
+
+      # If there are no unresolved deps, then we can use just try
+      # normal require handle loading a gem from the rescue below.
+
+      if Gem::Specification.unresolved_deps.empty?
+        next
+      end
+
+      # If +path+ is for a gem that has already been loaded, don't
+      # bother trying to find it in an unresolved gem, just go straight
+      # to normal require.
+      #--
+      # TODO request access to the C implementation of this to speed up RubyGems
+
+      if Gem::Specification.find_active_stub_by_path(path)
+        next
+      end
+
+      # Attempt to find +path+ in any unresolved gems...
+
+      found_specs = Gem::Specification.find_in_unresolved path
+
+      # If there are no directly unresolved gems, then try and find +path+
+      # in any gems that are available via the currently unresolved gems.
+      # For example, given:
+      #
+      #   a => b => c => d
+      #
+      # If a and b are currently active with c being unresolved and d.rb is
+      # requested, then find_in_unresolved_tree will find d.rb in d because
+      # it's a dependency of c.
+      #
+      if found_specs.empty?
+        found_specs = Gem::Specification.find_in_unresolved_tree path
+
+        found_specs.each(&:activate)
+
+      # We found +path+ directly in an unresolved gem. Now we figure out, of
+      # the possible found specs, which one we should activate.
+      else
+
+        # Check that all the found specs are just different
+        # versions of the same gem
+        names = found_specs.map(&:name).uniq
+
+        if names.size > 1
+          raise Gem::LoadError, "#{path} found in multiple gems: #{names.join ", "}"
+        end
+
+        # Ok, now find a gem that has no conflicts, starting
+        # at the highest version.
+        valid = found_specs.find {|s| !s.has_conflicts? }
+
+        unless valid
+          le = Gem::LoadError.new "unable to find a version of '#{names.first}' to activate"
+          le.name = names.first
+          raise le
+        end
+
+        valid.activate
+      end
+    end
+
+    begin
+      gem_original_require(path)
+    rescue LoadError => load_error
+      if load_error.path == path &&
+         RUBYGEMS_ACTIVATION_MONITOR.synchronize { Gem.try_activate(path) }
+
+        return gem_original_require(path)
+      end
+
+      raise load_error
+    end
+  end
+
+  private :require
+end