[rubygems/rubygems] Fix another regression for sorbet

Recently a changed was introduced to update the resolver platforms after
it has been created, in order to remove the "ruby" platform from it if
it's to be removed from the lockfile. However, it did not update the
`@resolving_only_for_ruby` instance variable in that case, so the
resolver was not properly doing the right thing anymore.

To fix this, I tweaked the code to restore not changing resolver
platforms after the resolver has been instantiated.

https://github.com/rubygems/rubygems/commit/8fbc30a1d0

lib/bundler/definition.rb

@@ -484,15 +484,13 @@ module Bundler
     def resolver
       @resolver ||= begin
         last_resolve = converge_locked_specs
+        remove_ruby_from_platforms_if_necessary!(dependencies)
         Resolver.new(source_requirements, last_resolve, gem_version_promoter, additional_base_requirements_for_resolve, platforms)
       end
     end
 
     def expanded_dependencies
-      @expanded_dependencies ||= begin
-        remove_ruby_from_platforms_if_necessary!(dependencies)
-        expand_dependencies(dependencies + metadata_dependencies, true)
-      end
+      @expanded_dependencies ||= expand_dependencies(dependencies + metadata_dependencies, true)
     end
 
     def filter_specs(specs, deps)
@@ -896,7 +894,6 @@ module Bundler
 
       remove_platform(Gem::Platform::RUBY)
       add_current_platform
-      resolver.platforms = @platforms
     end
 
     def source_map

lib/bundler/resolver.rb

@@ -7,8 +7,6 @@ module Bundler
 
     include GemHelpers
 
-    attr_writer :platforms
-
     # Figures out the best possible configuration of gems that satisfies
     # the list of passed dependencies and any child dependencies without
     # causing any gem activation errors.

spec/bundler/install/gemfile/specific_platform_spec.rb

@@ -445,6 +445,77 @@ RSpec.describe "bundle install with specific platforms" do
     L
   end
 
+  it "automatically fixes the lockfile if only RUBY platform is locked and some gem has no RUBY variant available" do
+    build_repo4 do
+      build_gem("sorbet-static-and-runtime", "0.5.10160") do |s|
+        s.add_runtime_dependency "sorbet", "= 0.5.10160"
+        s.add_runtime_dependency "sorbet-runtime", "= 0.5.10160"
+      end
+
+      build_gem("sorbet", "0.5.10160") do |s|
+        s.add_runtime_dependency "sorbet-static", "= 0.5.10160"
+      end
+
+      build_gem("sorbet-runtime", "0.5.10160")
+
+      build_gem("sorbet-static", "0.5.10160") do |s|
+        s.platform = Gem::Platform.local
+      end
+    end
+
+    gemfile <<~G
+      source "#{file_uri_for(gem_repo4)}"
+
+      gem "sorbet-static-and-runtime"
+    G
+
+    lockfile <<~L
+      GEM
+        remote: #{file_uri_for(gem_repo4)}/
+        specs:
+          sorbet (0.5.10160)
+            sorbet-static (= 0.5.10160)
+          sorbet-runtime (0.5.10160)
+          sorbet-static (0.5.10160-#{Gem::Platform.local})
+          sorbet-static-and-runtime (0.5.10160)
+            sorbet (= 0.5.10160)
+            sorbet-runtime (= 0.5.10160)
+
+      PLATFORMS
+        ruby
+
+      DEPENDENCIES
+        sorbet-static-and-runtime
+
+      BUNDLED WITH
+         #{Bundler::VERSION}
+    L
+
+    bundle "update"
+
+    expect(lockfile).to eq <<~L
+      GEM
+        remote: #{file_uri_for(gem_repo4)}/
+        specs:
+          sorbet (0.5.10160)
+            sorbet-static (= 0.5.10160)
+          sorbet-runtime (0.5.10160)
+          sorbet-static (0.5.10160-#{Gem::Platform.local})
+          sorbet-static-and-runtime (0.5.10160)
+            sorbet (= 0.5.10160)
+            sorbet-runtime (= 0.5.10160)
+
+      PLATFORMS
+        #{lockfile_platforms}
+
+      DEPENDENCIES
+        sorbet-static-and-runtime
+
+      BUNDLED WITH
+         #{Bundler::VERSION}
+    L
+  end
+
   it "does not remove ruby if gems for other platforms, and not present in the lockfile, exist in the Gemfile" do
     build_repo4 do
       build_gem "nokogiri", "1.13.8"