Cleanup unnecessary gems when removing lockfile platforms

bundler/lib/bundler/definition.rb

@@ -79,6 +79,7 @@ def initialize(lockfile, dependencies, sources, unlock, ruby_version = nil, opti
       @locked_bundler_version = nil
       @locked_ruby_version    = nil
       @new_platform = nil
+      @removed_platform = nil
 
       if lockfile && File.exist?(lockfile)
         @lockfile_contents = Bundler.read_file(lockfile)
@@ -267,7 +268,7 @@ def resolve
           SpecSet.new(filter_specs(@locked_specs, @dependencies - deleted_deps))
         else
           Bundler.ui.debug "Found no changes, using resolution from the lockfile"
-          if @locked_gems.may_include_redundant_platform_specific_gems?
+          if @removed_platform || @locked_gems.may_include_redundant_platform_specific_gems?
             SpecSet.new(filter_specs(@locked_specs, @dependencies))
           else
             @locked_specs
@@ -446,7 +447,9 @@ def add_platform(platform)
     end
 
     def remove_platform(platform)
-      return if @platforms.delete(Gem::Platform.new(platform))
+      removed_platform = @platforms.delete(Gem::Platform.new(platform))
+      @removed_platform ||= removed_platform
+      return if removed_platform
       raise InvalidOption, "Unable to remove the platform `#{platform}` since the only platforms are #{@platforms.join ", "}"
     end
 

bundler/spec/commands/lock_spec.rb

@@ -319,6 +319,61 @@ def read_lockfile(file = "Gemfile.lock")
     expect(lockfile.platforms).to match_array([x86_mingw32, specific_local_platform].uniq)
   end
 
+  it "also cleans up redundant platform gems when removing platforms" do
+    build_repo4 do
+      build_gem "nokogiri", "1.12.0"
+      build_gem "nokogiri", "1.12.0" do |s|
+        s.platform = "x86_64-darwin"
+      end
+    end
+
+    simulate_platform "x86_64-darwin-22" do
+      install_gemfile <<~G
+        source "#{file_uri_for(gem_repo4)}"
+
+        gem "nokogiri"
+      G
+    end
+
+    lockfile <<~L
+      GEM
+        remote: #{file_uri_for(gem_repo4)}/
+        specs:
+          nokogiri (1.12.0)
+          nokogiri (1.12.0-x86_64-darwin)
+
+      PLATFORMS
+        ruby
+        x86_64-darwin
+
+      DEPENDENCIES
+        nokogiri
+
+      BUNDLED WITH
+         #{Bundler::VERSION}
+    L
+
+    simulate_platform "x86_64-darwin-22" do
+      bundle "lock --remove-platform ruby"
+    end
+
+    expect(lockfile).to eq <<~L
+      GEM
+        remote: #{file_uri_for(gem_repo4)}/
+        specs:
+          nokogiri (1.12.0-x86_64-darwin)
+
+      PLATFORMS
+        x86_64-darwin
+
+      DEPENDENCIES
+        nokogiri
+
+      BUNDLED WITH
+         #{Bundler::VERSION}
+    L
+  end
+
   it "errors when removing all platforms" do
     bundle "lock --remove-platform #{specific_local_platform}", :raise_on_error => false
     expect(err).to include("Removing all platforms from the bundle is not allowed")