Fix Bundler that re-exec $0 when a version is present in the config:

- ### Problem

  If you have a `version` in your config file (this feature was
  introduced in #6817), then running any `bundle` command will
  make Bundler re-exec and ultimately run the `bundle` binstub twice.

  ### Details

  When the `bundle` binstub gets executed, a `require "bundler"` is
  evaluated. RubyGems tries to require the `bundler.rb` file from
  the right `bundler` gem (in the event where you have multiple
  bundler versions in your system).
  RubyGems will prioritize a bundler version based on a few
  heurisitics.

  https://github.com/ruby/rubygems/blob/b50c40c92abb00bb172f1579356cc73c242b1849/lib/rubygems/bundler_version_finder.rb#L19-L21

  This prioritize logic doesn't take into account the bundler version
  a user has specific in this config. So what happens is:

  1. User execute the `bundle` binstub
  2. `require 'bundler'` is evaluated.
  3. RubyGems prioritize activating the bundler version specified
     in the Gemfile.lock
  4. The CLI starts, and [Auto switch kicks in](https://github.com/ruby/rubygems/blob/b50c40c92abb00bb172f1579356cc73c242b1849/bundler/lib/bundler/cli.rb#L81). Bundler detects that
     user specifed a version in its config and the current Bundler
     version doesn't match.
  5. Bundler exit and re-exec with the right bundler version.

  ### Solution

  This patch introduce two fixes. First, it reads the bundler config
  file and check for the local config first and then the global
  config. This is because the local has precedence over global.

  Second, the prioritization takes into account the version in config
  and let RubyGems activate the right version in order to prevent
  re-exec moments later.

  Finally, I also want to fix this problem because its a step toward
  fixing #8106. I'll open
  a follow up patch to explain.

Author: Edouard-chin

bundler/spec/runtime/self_management_spec.rb

@@ -171,6 +171,24 @@
       expect(out).to eq(previous_minor)
     end
 
+    it "requires the right bundler version from the config and run bundle CLI without re-exec" do
+      unless Bundler.rubygems.provides?(">= 4.1.0.dev")
+        skip "This spec can only run when Gem::BundlerVersionFinder.bundler_versions reads bundler configs"
+      end
+
+      lockfile_bundled_with(current_version)
+
+      bundle "config set --local version #{previous_minor}"
+      bundle "config set --local path.system true"
+      bundle "install"
+
+      script = bundled_app("script.rb")
+      create_file(script, "p 'executed once'")
+
+      bundle "-v", env: { "RUBYOPT" => "-r#{script}" }
+      expect(out).to eq(%("executed once"\n9.3.0))
+    end
+
     it "does not try to install when using bundle config version global" do
       lockfile_bundled_with(previous_minor)
 

lib/rubygems/bundler_version_finder.rb

@@ -10,6 +10,8 @@ def self.bundler_version
     v ||= bundle_update_bundler_version
     return if v == true
 
+    v ||= bundle_config_version
+
     v ||= lockfile_version
     return unless v
 
@@ -49,21 +51,7 @@ def self.lockfile_version
   private_class_method :lockfile_version
 
   def self.lockfile_contents
-    gemfile = ENV["BUNDLE_GEMFILE"]
-    gemfile = nil if gemfile&.empty?
-
-    unless gemfile
-      begin
-        Gem::Util.traverse_parents(Dir.pwd) do |directory|
-          next unless gemfile = Gem::GEM_DEP_FILES.find {|f| File.file?(f) }
-
-          gemfile = File.join directory, gemfile
-          break
-        end
-      rescue Errno::ENOENT
-        return
-      end
-    end
+    gemfile = gemfile_path
 
     return unless gemfile
 
@@ -82,19 +70,24 @@ def self.lockfile_contents
   private_class_method :lockfile_contents
 
   def self.bundle_config_version
-    config_file = bundler_config_file
-    return unless config_file && File.file?(config_file)
+    version = nil
 
-    contents = File.read(config_file)
-    contents =~ /^BUNDLE_VERSION:\s*["']?([^"'\s]+)["']?\s*$/
+    [bundler_local_config_file, bundler_global_config_file].each do |config_file|
+      next unless config_file && File.file?(config_file)
 
-    $1
+      contents = File.read(config_file)
+      contents =~ /^BUNDLE_VERSION:\s*["']?([^"'\s]+)["']?\s*$/
+
+      version = $1
+      break if version
+    end
+
+    version
   end
   private_class_method :bundle_config_version
 
-  def self.bundler_config_file
-    # see Bundler::Settings#global_config_file and local_config_file
-    # global
+  def self.bundler_global_config_file
+    # see Bundler::Settings#global_config_file
     if ENV["BUNDLE_CONFIG"] && !ENV["BUNDLE_CONFIG"].empty?
       ENV["BUNDLE_CONFIG"]
     elsif ENV["BUNDLE_USER_CONFIG"] && !ENV["BUNDLE_USER_CONFIG"].empty?
@@ -103,10 +96,36 @@ def self.bundler_config_file
       ENV["BUNDLE_USER_HOME"] + "config"
     elsif Gem.user_home && !Gem.user_home.empty?
       Gem.user_home + ".bundle/config"
-    else
-      # local
-      "config"
     end
   end
-  private_class_method :bundler_config_file
+  private_class_method :bundler_global_config_file
+
+  def self.bundler_local_config_file
+    gemfile = gemfile_path
+    return unless gemfile
+
+    File.join(File.dirname(gemfile), ".bundle", "config")
+  end
+  private_class_method :bundler_local_config_file
+
+  def self.gemfile_path
+    gemfile = ENV["BUNDLE_GEMFILE"]
+    gemfile = nil if gemfile&.empty?
+
+    unless gemfile
+      begin
+        Gem::Util.traverse_parents(Dir.pwd) do |directory|
+          next unless gemfile = Gem::GEM_DEP_FILES.find {|f| File.file?(f) }
+
+          gemfile = File.join directory, gemfile
+          break
+        end
+      rescue Errno::ENOENT
+        return
+      end
+    end
+
+    gemfile
+  end
+  private_class_method :gemfile_path
 end

test/rubygems/test_gem_bundler_version_finder.rb

@@ -66,7 +66,7 @@ def test_bundler_version_with_bundle_config
       f.write(config_content)
       f.flush
 
-      bvf.stub(:bundler_config_file, f.path) do
+      bvf.stub(:bundler_global_config_file, f.path) do
         assert_nil bvf.bundler_version
       end
     end
@@ -81,7 +81,7 @@ def test_bundler_version_with_bundle_config_single_quoted
       f.write(config_with_single_quoted_version)
       f.flush
 
-      bvf.stub(:bundler_config_file, f.path) do
+      bvf.stub(:bundler_global_config_file, f.path) do
         assert_nil bvf.bundler_version
       end
     end
@@ -98,18 +98,33 @@ def test_bundler_version_with_bundle_config_version
       f.write(config_content)
       f.flush
 
-      bvf.stub(:bundler_config_file, f.path) do
+      bvf.stub(:bundler_global_config_file, f.path) do
         assert_equal v("1.1.1.1"), bvf.bundler_version
       end
     end
   end
 
   def test_bundler_version_with_bundle_config_non_existent_file
-    bvf.stub(:bundler_config_file, "/non/existent/path") do
+    bvf.stub(:bundler_global_config_file, "/non/existent/path") do
       assert_nil bvf.bundler_version
     end
   end
 
+  def test_bundler_version_set_on_local_config
+    config_content = <<~CONFIG
+      BUNDLE_VERSION: "1.2.3"
+    CONFIG
+
+    Tempfile.create("bundle_config") do |f|
+      f.write(config_content)
+      f.flush
+
+      bvf.stub(:bundler_local_config_file, f.path) do
+        assert_equal v("1.2.3"), bvf.bundler_version
+      end
+    end
+  end
+
   def test_bundler_version_with_bundle_config_without_version
     config_without_version = <<~CONFIG
       BUNDLE_JOBS: "8"
@@ -120,7 +135,7 @@ def test_bundler_version_with_bundle_config_without_version
       f.write(config_without_version)
       f.flush
 
-      bvf.stub(:bundler_config_file, f.path) do
+      bvf.stub(:bundler_global_config_file, f.path) do
         assert_nil bvf.bundler_version
       end
     end