Reapply "[rubygems/rubygems] Fix activation conflicts when circularly requiring a gem"

This reverts commit 04cf66765a8a9d48baea6d9aee266dc9aa21df27.

lib/rubygems.rb

@@ -1216,6 +1216,13 @@ An Array (#{env.inspect}) was passed in from #{caller[3]}
     ##
     # Find a Gem::Specification of default gem from +path+
 
+    def find_default_spec(path)
+      @path_to_default_spec_map[path]
+    end
+
+    ##
+    # Find an unresolved Gem::Specification of default gem from +path+
+
     def find_unresolved_default_spec(path)
       default_spec = @path_to_default_spec_map[path]
       default_spec if default_spec && loaded_specs[default_spec.name] != default_spec

lib/rubygems/core_ext/kernel_require.rb

@@ -42,7 +42,11 @@ module Kernel
       # If +path+ belongs to a default gem, we activate it and then go straight
       # to normal require
 
-      if spec = Gem.find_unresolved_default_spec(path)
+      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
@@ -60,7 +64,7 @@ module Kernel
           rp
         end
 
-        Kernel.send(:gem, spec.name, Gem::Requirement.default_prerelease) unless
+        Kernel.send(:gem, name, Gem::Requirement.default_prerelease) unless
           resolved_path
 
         next

test/rubygems/test_require.rb

@@ -560,6 +560,45 @@ class TestGemRequire < Gem::TestCase
     assert_require "net/http"
   end
 
+  def test_default_gem_required_circulary_with_unresolved_gems_depending_on_it
+    net_http_old = util_spec "net-http", "0.1.1", nil, "lib/net/http.rb"
+    install_gem net_http_old
+
+    net_http_default = new_default_spec "net-http", "0.3.0", nil, "net/http.rb"
+    net_http_default_path = File.join(@tempdir, "default_gems", "lib", "net/http.rb")
+    install_default_gems net_http_default
+    File.write(net_http_default_path, 'require "net/http"')
+
+    faraday_1 = util_spec "faraday", "1", { "net-http" => ">= 0" }
+    install_gem faraday_1
+
+    faraday_2 = util_spec "faraday", "2", { "net-http" => ">= 0" }
+    install_gem faraday_2
+
+    chef = util_spec "chef", "1", { "faraday" => [">= 1", "< 3"] }, "lib/chef.rb"
+    install_gem chef
+
+    assert_require "chef"
+
+    out, err = capture_output do
+      assert_require "net/http"
+    end
+
+    assert_empty out
+
+    circular_require_warning = false
+
+    err_lines = err.split("\n").reject do |line|
+      if line.include?("circular require")
+        circular_require_warning = true
+      elsif circular_require_warning # ignore backtrace lines for circular require warning
+        circular_require_warning = line.start_with?(/[\s]/)
+      end
+    end
+
+    assert_empty err_lines
+  end
+
   def loaded_spec_names
     Gem.loaded_specs.values.map(&:full_name).sort
   end