Fix crash when duplicating a dev dependency in Gemfile & gemspec

bundler/lib/bundler/dsl.rb

@@ -102,12 +102,13 @@ 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
+        deleted_dep = @dependencies.delete(current) if current.type == :development
+
         if current.requirement != dep.requirement
           current_requirement_open = current.requirements_list.include?(">= 0")
 
           if current.type == :development
-            @dependencies.delete(current)
-
             unless current_requirement_open || dep.type == :development
               Bundler.ui.warn "A gemspec development dependency (#{dep.name}, #{current.requirement}) is being overridden by a Gemfile dependency (#{dep.name}, #{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" \
@@ -129,12 +130,13 @@ def gem(name, *args)
                            "You specified: #{current.name} (#{current.requirement}) and #{dep.name} (#{dep.requirement})" \
                            "#{update_prompt}"
           end
+        elsif current.type == :development || dep.type == :development
+          return if deleted_dep.nil?
         elsif 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"
-        elsif current.type != :development && dep.type != :development
+        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" \

bundler/spec/commands/install_spec.rb

@@ -460,6 +460,41 @@
       expect(the_bundle).to include_gems("rubocop 1.37.1")
     end
 
+    it "does not warn if a gem is added once in Gemfile and also inside a gemspec as a development dependency, with same requirements, and different sources" do
+      build_lib "my-gem", :path => bundled_app do |s|
+        s.add_development_dependency "activesupport"
+      end
+
+      build_repo4 do
+        build_gem "activesupport"
+      end
+
+      build_git "activesupport", "1.0", :path => lib_path("activesupport")
+
+      install_gemfile <<~G
+        source "#{file_uri_for(gem_repo4)}"
+
+        gemspec
+
+        gem "activesupport", :git => "#{file_uri_for(lib_path("activesupport"))}"
+      G
+
+      expect(err).to be_empty
+      expect(the_bundle).to include_gems "activesupport 1.0", :source => "git@#{lib_path("activesupport")}"
+
+      # if the Gemfile dependency is specified first
+      install_gemfile <<~G
+        source "#{file_uri_for(gem_repo4)}"
+
+        gem "activesupport", :git => "#{file_uri_for(lib_path("activesupport"))}"
+
+        gemspec
+      G
+
+      expect(err).to be_empty
+      expect(the_bundle).to include_gems "activesupport 1.0", :source => "git@#{lib_path("activesupport")}"
+    end
+
     it "considers both dependencies for resolution if a gem is added once in Gemfile and also inside a local gemspec as a runtime dependency, with different requirements" do
       build_lib "my-gem", :path => bundled_app do |s|
         s.add_dependency "rubocop", "~> 1.36.0"