[rubygems/rubygems] Fix bundle lock --minor --update <dep> edge case

When the latest allowed minor of `dep` adds a new dependency, that new
dependency would be incorrectly resolved to the latest minor of the
first major version.

https://github.com/rubygems/rubygems/commit/fd50c9d4f3

lib/bundler/gem_version_promoter.rb

@@ -101,7 +101,7 @@ module Bundler
           next  1 if b_pre && !a_pre
         end
 
-        if major?
+        if major? || locked_version.nil?
           a <=> b
         elsif either_version_older_than_locked?(a, b, locked_version)
           a <=> b
@@ -117,7 +117,7 @@ module Bundler
     end
 
     def either_version_older_than_locked?(a, b, locked_version)
-      locked_version && (a.version < locked_version || b.version < locked_version)
+      a.version < locked_version || b.version < locked_version
     end
 
     def segments_do_not_match?(a, b, level)

spec/bundler/commands/lock_spec.rb

@@ -289,6 +289,47 @@ RSpec.describe "bundle lock" do
     end
   end
 
+  context "conservative updates when minor update adds a new dependency" do
+    before do
+      build_repo4 do
+        build_gem "sequel", "5.71.0"
+        build_gem "sequel", "5.72.0" do |s|
+          s.add_dependency "bigdecimal", ">= 0"
+        end
+        build_gem "bigdecimal", %w[1.4.4 3.1.4]
+      end
+
+      gemfile <<~G
+        source "#{file_uri_for(gem_repo4)}"
+        gem 'sequel'
+      G
+
+      lockfile <<~L
+        GEM
+          remote: #{file_uri_for(gem_repo4)}/
+          specs:
+            sequel (5.71.0)
+
+        PLATFORMS
+          ruby
+
+        DEPENDENCIES
+          sequel
+
+        BUNDLED WITH
+           #{Bundler::VERSION}
+      L
+
+      allow(Bundler::SharedHelpers).to receive(:find_gemfile).and_return(bundled_app_gemfile)
+    end
+
+    it "adds the latest version of the new dependency" do
+      bundle "lock --minor --update sequel"
+
+      expect(the_bundle.locked_gems.specs.map(&:full_name)).to eq(%w[sequel-5.72.0 bigdecimal-3.1.4].sort)
+    end
+  end
+
   it "updates the bundler version in the lockfile to the latest bundler version" do
     build_repo4 do
       build_gem "bundler", "55"