Fix development dependency not being added if introduced by two gemspecs

bundler/lib/bundler/dsl.rb

@@ -102,9 +102,6 @@ def gem(name, *args)
 
       # if there's already a dependency with this name we try to prefer one
       if current = @dependencies.find {|d| d.name == dep.name }
-        # Always prefer the dependency from the Gemfile
-        @dependencies.delete(current) if current.gemspec_dev_dep?
-
         if current.requirement != dep.requirement
           current_requirement_open = current.requirements_list.include?(">= 0")
 
@@ -116,8 +113,6 @@ def gem(name, *args)
               Bundler.ui.warn "A gemspec development dependency (#{gemspec_dep.name}, #{gemspec_dep.requirement}) is being overridden by a Gemfile dependency (#{gemfile_dep.name}, #{gemfile_dep.requirement}).\n" \
                               "This behaviour may change in the future. Please remove either of them, or make sure they both have the same requirement\n"
             end
-
-            return if dep.gemspec_dev_dep?
           else
             update_prompt = ""
 
@@ -135,8 +130,13 @@ def gem(name, *args)
                            "You specified: #{current.name} (#{current.requirement}) and #{dep.name} (#{dep.requirement})" \
                            "#{update_prompt}"
           end
-        elsif current.gemspec_dev_dep? || dep.gemspec_dev_dep?
-          return if dep.gemspec_dev_dep?
+        end
+
+        # Always prefer the dependency from the Gemfile
+        if current.gemspec_dev_dep?
+          @dependencies.delete(current)
+        elsif dep.gemspec_dev_dep?
+          return
         elsif current.source != dep.source
           raise GemfileError, "You cannot specify the same gem twice coming from different sources.\n" \
                           "You specified that #{dep.name} (#{dep.requirement}) should come from " \

bundler/spec/commands/install_spec.rb

@@ -460,6 +460,35 @@
       expect(the_bundle).to include_gems("rubocop 1.37.1")
     end
 
+    it "includes the gem without warning if two gemspecs add it with the same requirement" do
+      gem1 = tmp.join("my-gem-1")
+      gem2 = tmp.join("my-gem-2")
+
+      build_lib "my-gem", path: gem1 do |s|
+        s.add_development_dependency "rubocop", "~> 1.36.0"
+      end
+
+      build_lib "my-gem-2", path: gem2 do |s|
+        s.add_development_dependency "rubocop", "~> 1.36.0"
+      end
+
+      build_repo4 do
+        build_gem "rubocop", "1.36.0"
+      end
+
+      gemfile <<~G
+        source "#{file_uri_for(gem_repo4)}"
+
+        gemspec path: "#{gem1}"
+        gemspec path: "#{gem2}"
+      G
+
+      bundle :install
+
+      expect(err).to be_empty
+      expect(the_bundle).to include_gems("rubocop 1.36.0")
+    end
+
     it "warns when a Gemfile dependency is overriding a gemspec development dependency, with different requirements" do
       build_lib "my-gem", path: bundled_app do |s|
         s.add_development_dependency "rails", ">= 5"