[rubygems/rubygems] Fix development gem unintentionally removed on an edge case

When a development dependency was duplicated inside the gemspec and
Gemfile with the same requirements, we went from printing a warning to
removing the gem altogether.

This change makes it not print a warning, but don't remove the gem
either.

https://github.com/rubygems/rubygems/commit/8bb2488131

lib/bundler/dsl.rb

@@ -102,38 +102,39 @@ module Bundler
       # if there's already a dependency with this name we try to prefer one
       if current = @dependencies.find {|d| d.name == dep.name }
         deleted_dep = @dependencies.delete(current) if current.type == :development
-        return if deleted_dep
 
-        if current.requirement != dep.requirement
-          return if dep.type == :development
+        unless deleted_dep
+          if current.requirement != dep.requirement
+            return if dep.type == :development
 
-          update_prompt = ""
+            update_prompt = ""
 
-          if File.basename(@gemfile) == Injector::INJECTED_GEMS
-            if dep.requirements_list.include?(">= 0") && !current.requirements_list.include?(">= 0")
-              update_prompt = ". Gem already added"
-            else
-              update_prompt = ". If you want to update the gem version, run `bundle update #{current.name}`"
+            if File.basename(@gemfile) == Injector::INJECTED_GEMS
+              if dep.requirements_list.include?(">= 0") && !current.requirements_list.include?(">= 0")
+                update_prompt = ". Gem already added"
+              else
+                update_prompt = ". If you want to update the gem version, run `bundle update #{current.name}`"
 
-              update_prompt += ". You may also need to change the version requirement specified in the Gemfile if it's too restrictive." unless current.requirements_list.include?(">= 0")
+                update_prompt += ". You may also need to change the version requirement specified in the Gemfile if it's too restrictive." unless current.requirements_list.include?(">= 0")
+              end
             end
+
+            raise GemfileError, "You cannot specify the same gem twice with different version requirements.\n" \
+                            "You specified: #{current.name} (#{current.requirement}) and #{dep.name} (#{dep.requirement})" \
+                             "#{update_prompt}"
+          else
+            Bundler.ui.warn "Your Gemfile lists the gem #{current.name} (#{current.requirement}) more than once.\n" \
+                            "You should probably keep only one of them.\n" \
+                            "Remove any duplicate entries and specify the gem only once.\n" \
+                            "While it's not a problem now, it could cause errors if you change the version of one of them later."
           end
 
-          raise GemfileError, "You cannot specify the same gem twice with different version requirements.\n" \
-                          "You specified: #{current.name} (#{current.requirement}) and #{dep.name} (#{dep.requirement})" \
-                           "#{update_prompt}"
-        else
-          Bundler.ui.warn "Your Gemfile lists the gem #{current.name} (#{current.requirement}) more than once.\n" \
-                          "You should probably keep only one of them.\n" \
-                          "Remove any duplicate entries and specify the gem only once.\n" \
-                          "While it's not a problem now, it could cause errors if you change the version of one of them later."
-        end
-
-        if current.source != dep.source
-          return if dep.type == :development
-          raise GemfileError, "You cannot specify the same gem twice coming from different sources.\n" \
-                          "You specified that #{dep.name} (#{dep.requirement}) should come from " \
-                          "#{current.source || "an unspecified source"} and #{dep.source}\n"
+          if current.source != dep.source
+            return if dep.type == :development
+            raise GemfileError, "You cannot specify the same gem twice coming from different sources.\n" \
+                            "You specified that #{dep.name} (#{dep.requirement}) should come from " \
+                            "#{current.source || "an unspecified source"} and #{dep.source}\n"
+          end
         end
       end
 

spec/bundler/commands/install_spec.rb

@@ -388,6 +388,7 @@ RSpec.describe "bundle install with gem sources" do
       bundle :install
 
       expect(err).to be_empty
+      expect(the_bundle).to include_gems("my-private-gem 1.0")
     end
 
     it "throws an error if a gem is added twice in Gemfile when version of one dependency is not specified" do