[rubygems/rubygems] Make sure empty gems are not reinstalled every time

Unfortunately this requires reverting a previous enhancement of
reinstalling gems if they incorrectly ship with an empty installation
dir.

However, there's no way to distinguish this kind of bad state from a gem
that's empty for real, for example, sorbet-static-and-runtime.

This reverts commit https://github.com/rubygems/rubygems/commit/9720a9b980d2, and adds a
spec to make sure empty gems are not reinstalled every time.

https://github.com/rubygems/rubygems/commit/7c102394af

lib/bundler/rubygems_ext.rb

@@ -259,7 +259,7 @@ module Gem
     end
 
     def installation_missing?
-      !default_gem? && (!Dir.exist?(full_gem_path) || Dir.empty?(full_gem_path))
+      !default_gem? && !File.directory?(full_gem_path)
     end
 
     unless VALIDATES_FOR_RESOLUTION

spec/bundler/commands/install_spec.rb

@@ -100,24 +100,30 @@ RSpec.describe "bundle install with gem sources" do
         gem 'myrack'
       G
 
-      gem_dir = default_bundle_path("gems/myrack-1.0.0")
-
-      FileUtils.rm_rf(gem_dir)
+      FileUtils.rm_rf(default_bundle_path("gems/myrack-1.0.0"))
 
       bundle "install --verbose"
 
       expect(out).to include("Installing myrack 1.0.0")
-      expect(gem_dir).to exist
+      expect(default_bundle_path("gems/myrack-1.0.0")).to exist
       expect(the_bundle).to include_gems("myrack 1.0.0")
+    end
 
-      FileUtils.rm_rf(gem_dir)
-      Dir.mkdir(gem_dir)
+    it "does not state that it's constantly reinstalling empty gems" do
+      build_repo4 do
+        build_gem "empty", "1.0.0", no_default: true, allowed_warning: "no files specified"
+      end
+
+      install_gemfile <<~G
+        source "https://gem.repo4"
+
+        gem "empty"
+      G
+      gem_dir = default_bundle_path("gems/empty-1.0.0")
+      expect(gem_dir).to be_empty
 
       bundle "install --verbose"
-
-      expect(out).to include("Installing myrack 1.0.0")
-      expect(gem_dir).to exist
-      expect(the_bundle).to include_gems("myrack 1.0.0")
+      expect(out).not_to include("Installing empty")
     end
 
     it "fetches gems when multiple versions are specified" do

spec/bundler/support/builders.rb

@@ -639,7 +639,7 @@ module Spec
         elsif opts[:skip_validation]
           @context.gem_command "build --force #{@spec.name}", dir: lib_path
         else
-          @context.gem_command "build #{@spec.name}", dir: lib_path
+          @context.gem_command "build #{@spec.name}", dir: lib_path, allowed_warning: opts[:allowed_warning]
         end
 
         gem_path = File.expand_path("#{@spec.full_name}.gem", lib_path)

spec/bundler/support/helpers.rb

@@ -194,9 +194,12 @@ module Spec
       # command is expired too. So give `gem install` commands a bit more time.
       options[:timeout] = 120
 
+      allowed_warning = options.delete(:allowed_warning)
+
       output = sys_exec("#{Path.gem_bin} #{command}", options)
       stderr = last_command.stderr
-      raise stderr if stderr.include?("WARNING") && !allowed_rubygems_warning?(stderr)
+
+      raise stderr if stderr.include?("WARNING") && !allowed_rubygems_warning?(stderr, allowed_warning)
       output
     end
 
@@ -548,8 +551,12 @@ module Spec
 
     private
 
-    def allowed_rubygems_warning?(text)
-      text.include?("open-ended") || text.include?("is a symlink") || text.include?("rake based") || text.include?("expected RubyGems version")
+    def allowed_rubygems_warning?(text, extra_allowed_warning)
+      allowed_warnings = ["open-ended", "is a symlink", "rake based", "expected RubyGems version"]
+      allowed_warnings << extra_allowed_warning if extra_allowed_warning
+      allowed_warnings.any? do |warning|
+        text.include?(warning)
+      end
     end
 
     def match_source(contents)