Automatically remove "ruby" from lockfile if incomplete

bundler/lib/bundler/definition.rb

@@ -484,6 +484,7 @@ def unlocking?
 
     def reresolve
       last_resolve = converge_locked_specs
+      remove_ruby_from_platforms_if_necessary!(dependencies)
       expanded_dependencies = expand_dependencies(dependencies + metadata_dependencies, true)
       Resolver.resolve(expanded_dependencies, source_requirements, last_resolve, gem_version_promoter, additional_base_requirements_for_resolve, platforms)
     end
@@ -865,6 +866,17 @@ def additional_base_requirements_for_resolve
       end
     end
 
+    def remove_ruby_from_platforms_if_necessary!(dependencies)
+      return if Bundler.frozen_bundle? ||
+        Bundler.local_platform == Gem::Platform::RUBY ||
+        !platforms.include?(Gem::Platform::RUBY) ||
+        (@new_platform && platforms.last == Gem::Platform::RUBY) ||
+        !@originally_locked_specs.incomplete_ruby_specs?(dependencies)
+
+      remove_platform(Gem::Platform::RUBY)
+      add_current_platform
+    end
+
     def source_map
       @source_map ||= SourceMap.new(sources, dependencies, @locked_specs)
     end

bundler/lib/bundler/spec_set.rb

@@ -91,6 +91,10 @@ def materialized_for_resolution
       SpecSet.new(materialized)
     end
 
+    def incomplete_ruby_specs?(deps)
+      self.class.new(self.for(deps, true, [Gem::Platform::RUBY])).incomplete_specs.any?
+    end
+
     def missing_specs
       @specs.select {|s| s.is_a?(LazySpecification) }
     end

bundler/spec/install/gemfile/specific_platform_spec.rb

@@ -374,6 +374,77 @@
     ERROR
   end
 
+  it "automatically fixes the lockfile if 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
+        #{lockfile_platforms_for([specific_local_platform, "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 "can fallback to a source gem when platform gems are incompatible with current ruby version" do
     setup_multiplatform_gem_with_source_gem