[rubygems/rubygems] Allow ruby platform to be remove also when dependencies have changed

Since we will now add it back if the final resolution is compatible, we
can also get this kind of edge case (`bundle add`) working.

https://github.com/rubygems/rubygems/commit/cdc5ebec77

lib/bundler/definition.rb

@@ -1144,8 +1144,14 @@ module Bundler
 
       @originally_invalid_platforms = platforms.select do |platform|
         next if local_platform == platform ||
-                @new_platforms.include?(platform) ||
-                @dependency_changes
+                @new_platforms.include?(platform)
+
+        # We should probably avoid removing non-ruby platforms, since that means
+        # lockfile will no longer install on those platforms, so a error to give
+        # heads up to the user may be better. However, we have tests expecting
+        # non ruby platform autoremoval to work, so leaving that in place for
+        # now.
+        next if @dependency_changes && platform != Gem::Platform::RUBY
 
         spec_set_incomplete_for_platform?(@originally_locked_specs, platform)
       end

spec/bundler/install/gemfile/specific_platform_spec.rb

@@ -752,6 +752,80 @@ RSpec.describe "bundle install with specific platforms" do
     L
   end
 
+  it "automatically fixes the lockfile when adding a gem that introduces dependencies with no ruby platform variants transitively" do
+    simulate_platform "x86_64-linux" do
+      build_repo4 do
+        build_gem "nokogiri", "1.18.2"
+
+        build_gem "nokogiri", "1.18.2" do |s|
+          s.platform = "x86_64-linux"
+        end
+
+        build_gem("sorbet", "0.5.11835") do |s|
+          s.add_dependency "sorbet-static", "= 0.5.11835"
+        end
+
+        build_gem "sorbet-static", "0.5.11835" do |s|
+          s.platform = "x86_64-linux"
+        end
+      end
+
+      gemfile <<~G
+        source "https://gem.repo4"
+
+        gem "nokogiri"
+        gem "sorbet"
+      G
+
+      lockfile <<~L
+        GEM
+          remote: https://gem.repo4/
+          specs:
+            nokogiri (1.18.2)
+            nokogiri (1.18.2-x86_64-linux)
+
+        PLATFORMS
+          ruby
+          x86_64-linux
+
+        DEPENDENCIES
+          nokogiri
+
+        BUNDLED WITH
+           #{Bundler::VERSION}
+      L
+
+      bundle "lock"
+
+      checksums = checksums_section_when_enabled do |c|
+        c.checksum gem_repo4, "nokogiri", "1.18.2", "x86_64-linux"
+        c.checksum gem_repo4, "sorbet", "0.5.11835"
+        c.checksum gem_repo4, "sorbet-static", "0.5.11835", "x86_64-linux"
+      end
+
+      expect(lockfile).to eq <<~L
+        GEM
+          remote: https://gem.repo4/
+          specs:
+            nokogiri (1.18.2)
+            nokogiri (1.18.2-x86_64-linux)
+            sorbet (0.5.11835)
+              sorbet-static (= 0.5.11835)
+            sorbet-static (0.5.11835-x86_64-linux)
+
+        PLATFORMS
+          x86_64-linux
+
+        DEPENDENCIES
+          nokogiri
+          sorbet
+        #{checksums}
+        BUNDLED WITH
+           #{Bundler::VERSION}
+      L
+    end
+  end
+
   it "automatically fixes the lockfile if multiple platforms locked, but no valid versions of direct dependencies for all of them" do
     simulate_platform "x86_64-linux" do
       build_repo4 do