15 files changed, 55 insertions, 24 deletions
diff --git a/lib/bundler/cli.rb b/lib/bundler/cli.rb
index c0c7d9f899..198c9e2846 100644
--- a/lib/bundler/cli.rb
+++ b/lib/bundler/cli.rb
@@ -512,7 +512,7 @@ module Bundler
       end
     end
 
-    unless Bundler.feature_flag.bundler_3_mode?
+    unless Bundler.feature_flag.bundler_4_mode?
       desc "viz [OPTIONS]", "Generates a visual dependency graph", hide: true
       long_desc <<-D
         Viz generates a PNG file of the current Gemfile as a dependency graph.
diff --git a/lib/bundler/cli/config.rb b/lib/bundler/cli/config.rb
index 77b502fe60..d963679085 100644
--- a/lib/bundler/cli/config.rb
+++ b/lib/bundler/cli/config.rb
@@ -26,8 +26,8 @@ module Bundler
         end
 
       message = "Using the `config` command without a subcommand [list, get, set, unset] is deprecated and will be removed in the future. Use `bundle #{new_args.join(" ")}` instead."
-      removed_message = "Using the `config` command without a subcommand [list, get, set, unset] is has been removed. Use `bundle #{new_args.join(" ")}` instead."
-      SharedHelpers.major_deprecation 3, message, removed_message: removed_message
+      removed_message = "Using the `config` command without a subcommand [list, get, set, unset] has been removed. Use `bundle #{new_args.join(" ")}` instead."
+      SharedHelpers.major_deprecation 4, message, removed_message: removed_message
 
       Base.new(options, name, value, self).run
     end
diff --git a/lib/bundler/cli/update.rb b/lib/bundler/cli/update.rb
index ab31d00879..ba3f1ec056 100644
--- a/lib/bundler/cli/update.rb
+++ b/lib/bundler/cli/update.rb
@@ -26,7 +26,7 @@ module Bundler
         if Bundler.feature_flag.update_requires_all_flag?
           raise InvalidOption, "To update everything, pass the `--all` flag."
         end
-        SharedHelpers.major_deprecation 3, "Pass --all to `bundle update` to update everything"
+        SharedHelpers.major_deprecation 4, "Pass --all to `bundle update` to update everything"
       elsif !full_update && options[:all]
         raise InvalidOption, "Cannot specify --all along with specific options."
       end
diff --git a/lib/bundler/dsl.rb b/lib/bundler/dsl.rb
index 8ebc3d0020..4f9fbc55b1 100644
--- a/lib/bundler/dsl.rb
+++ b/lib/bundler/dsl.rb
@@ -521,7 +521,7 @@ module Bundler
     end
 
     def multiple_global_source_warning
-      if Bundler.feature_flag.bundler_3_mode?
+      if Bundler.feature_flag.bundler_4_mode?
         msg = "This Gemfile contains multiple global sources. " \
           "Each source after the first must include a block to indicate which gems " \
           "should come from that source"
diff --git a/lib/bundler/environment_preserver.rb b/lib/bundler/environment_preserver.rb
index 444ab6fd37..ffffceb487 100644
--- a/lib/bundler/environment_preserver.rb
+++ b/lib/bundler/environment_preserver.rb
@@ -6,6 +6,7 @@ module Bundler
     BUNDLER_KEYS = %w[
       BUNDLE_BIN_PATH
       BUNDLE_GEMFILE
+      BUNDLER_4_MODE
       BUNDLER_VERSION
       BUNDLER_SETUP
       GEM_HOME
diff --git a/lib/bundler/feature_flag.rb b/lib/bundler/feature_flag.rb
index b19cf42cc3..38498b245f 100644
--- a/lib/bundler/feature_flag.rb
+++ b/lib/bundler/feature_flag.rb
@@ -27,20 +27,20 @@ module Bundler
 
     (1..10).each {|v| define_method("bundler_#{v}_mode?") { @major_version >= v } }
 
-    settings_flag(:allow_offline_install) { bundler_3_mode? }
-    settings_flag(:auto_clean_without_path) { bundler_3_mode? }
-    settings_flag(:cache_all) { bundler_3_mode? }
-    settings_flag(:default_install_uses_path) { bundler_3_mode? }
-    settings_flag(:forget_cli_options) { bundler_3_mode? }
-    settings_flag(:global_gem_cache) { bundler_3_mode? }
-    settings_flag(:lockfile_checksums) { bundler_3_mode? }
-    settings_flag(:path_relative_to_cwd) { bundler_3_mode? }
+    settings_flag(:allow_offline_install) { bundler_4_mode? }
+    settings_flag(:auto_clean_without_path) { bundler_4_mode? }
+    settings_flag(:cache_all) { bundler_4_mode? }
+    settings_flag(:default_install_uses_path) { bundler_4_mode? }
+    settings_flag(:forget_cli_options) { bundler_4_mode? }
+    settings_flag(:global_gem_cache) { bundler_4_mode? }
+    settings_flag(:lockfile_checksums) { bundler_4_mode? }
+    settings_flag(:path_relative_to_cwd) { bundler_4_mode? }
     settings_flag(:plugins) { @bundler_version >= Gem::Version.new("1.14") }
-    settings_flag(:print_only_version_number) { bundler_3_mode? }
-    settings_flag(:setup_makes_kernel_gem_public) { !bundler_3_mode? }
-    settings_flag(:update_requires_all_flag) { bundler_4_mode? }
+    settings_flag(:print_only_version_number) { bundler_4_mode? }
+    settings_flag(:setup_makes_kernel_gem_public) { !bundler_4_mode? }
+    settings_flag(:update_requires_all_flag) { bundler_5_mode? }
 
-    settings_option(:default_cli_command) { bundler_3_mode? ? :cli_help : :install }
+    settings_option(:default_cli_command) { bundler_4_mode? ? :cli_help : :install }
 
     def initialize(bundler_version)
       @bundler_version = Gem::Version.create(bundler_version)
diff --git a/lib/bundler/rubygems_ext.rb b/lib/bundler/rubygems_ext.rb
index 6777c78194..8cf3b56b83 100644
--- a/lib/bundler/rubygems_ext.rb
+++ b/lib/bundler/rubygems_ext.rb
@@ -283,6 +283,18 @@ module Gem
       end
     end
 
+    if Gem.rubygems_version < Gem::Version.new("3.5.22")
+      module FixPathSourceMissingExtensions
+        def missing_extensions?
+          return false if %w[Bundler::Source::Path Bundler::Source::Gemspec].include?(source.class.name)
+
+          super
+        end
+      end
+
+      prepend FixPathSourceMissingExtensions
+    end
+
     private
 
     def dependencies_to_gemfile(dependencies, group = nil)
diff --git a/lib/bundler/rubygems_integration.rb b/lib/bundler/rubygems_integration.rb
index eddf36278c..5342c3dbf9 100644
--- a/lib/bundler/rubygems_integration.rb
+++ b/lib/bundler/rubygems_integration.rb
@@ -222,8 +222,6 @@ module Bundler
 
     # Used to give better error messages when activating specs outside of the current bundle
     def replace_bin_path(specs_by_name)
-      gem_class = (class << Gem; self; end)
-
       redefine_method(gem_class, :find_spec_for_exe) do |gem_name, *args|
         exec_name = args.first
         raise ArgumentError, "you must supply exec_name" unless exec_name
@@ -345,9 +343,13 @@ module Bundler
         Gem::Specification.all = specs
       end
 
-      redefine_method((class << Gem; self; end), :finish_resolve) do |*|
+      redefine_method(gem_class, :finish_resolve) do |*|
         []
       end
+
+      redefine_method(gem_class, :load_plugins) do |*|
+        load_plugin_files specs.flat_map(&:plugins)
+      end
     end
 
     def plain_specs
@@ -447,6 +449,12 @@ module Bundler
     def default_stubs
       Gem::Specification.default_stubs("*.gemspec")
     end
+
+    private
+
+    def gem_class
+      class << Gem; self; end
+    end
   end
 
   def self.rubygems
diff --git a/lib/bundler/self_manager.rb b/lib/bundler/self_manager.rb
index 72bcb264ab..ab16061dc7 100644
--- a/lib/bundler/self_manager.rb
+++ b/lib/bundler/self_manager.rb
@@ -105,6 +105,7 @@ module Bundler
 
     def autoswitching_applies?
       ENV["BUNDLER_VERSION"].nil? &&
+        ENV["BUNDLER_4_MODE"].nil? &&
         ruby_can_restart_with_same_arguments? &&
         lockfile_version
     end
diff --git a/lib/bundler/source/git/git_proxy.rb b/lib/bundler/source/git/git_proxy.rb
index 1a7a0959c9..f613377cb2 100644
--- a/lib/bundler/source/git/git_proxy.rb
+++ b/lib/bundler/source/git/git_proxy.rb
@@ -408,7 +408,7 @@ module Bundler
         def capture3_args_for(cmd, dir)
           return ["git", *cmd] unless dir
 
-          if Bundler.feature_flag.bundler_3_mode? || supports_minus_c?
+          if Bundler.feature_flag.bundler_4_mode? || supports_minus_c?
             ["git", "-C", dir.to_s, *cmd]
           else
             ["git", *cmd, { chdir: dir.to_s }]
diff --git a/lib/bundler/source/path.rb b/lib/bundler/source/path.rb
index 885dd96d85..ac76ae1fa0 100644
--- a/lib/bundler/source/path.rb
+++ b/lib/bundler/source/path.rb
@@ -167,6 +167,13 @@ module Bundler
             next unless spec = load_gemspec(file)
             spec.source = self
 
+            # The ignore attribute is for ignoring installed gems that don't
+            # have extensions correctly compiled for activation. In the case of
+            # path sources, there's a single version of each gem in the path
+            # source available to Bundler, so we always certainly want to
+            # consider that for activation and never makes sense to ignore it.
+            spec.ignored = false
+
             # Validation causes extension_dir to be calculated, which depends
             # on #source, so we validate here instead of load_gemspec
             validate_spec(spec)
diff --git a/lib/bundler/source_map.rb b/lib/bundler/source_map.rb
index ca73e01f9d..a8e12d08c3 100644
--- a/lib/bundler/source_map.rb
+++ b/lib/bundler/source_map.rb
@@ -23,7 +23,7 @@ module Bundler
           if previous_source.nil?
             requirements[indirect_dependency_name] = source
           else
-            no_ambiguous_sources = Bundler.feature_flag.bundler_3_mode?
+            no_ambiguous_sources = Bundler.feature_flag.bundler_4_mode?
 
             msg = ["The gem '#{indirect_dependency_name}' was found in multiple relevant sources."]
             msg.concat [previous_source, source].map {|s| "  * #{s}" }.sort
diff --git a/lib/bundler/templates/newgem/github/workflows/main.yml.tt b/lib/bundler/templates/newgem/github/workflows/main.yml.tt
index d1b5ae0534..9224ee0ca2 100644
--- a/lib/bundler/templates/newgem/github/workflows/main.yml.tt
+++ b/lib/bundler/templates/newgem/github/workflows/main.yml.tt
@@ -18,6 +18,8 @@ jobs:
 
     steps:
       - uses: actions/checkout@v4
+        with:
+          persist-credentials: false
 <%- if config[:ext] == 'rust' -%>
       - name: Set up Ruby & Rust
         uses: oxidize-rb/actions/setup-ruby-and-rust@v1
diff --git a/lib/bundler/version.rb b/lib/bundler/version.rb
index fa24b4966e..a995f4f281 100644
--- a/lib/bundler/version.rb
+++ b/lib/bundler/version.rb
@@ -1,7 +1,7 @@
 # frozen_string_literal: false
 
 module Bundler
-  VERSION = "2.7.0.dev".freeze
+  VERSION = (ENV["BUNDLER_4_MODE"] == "true" ? "4.0.0" : "2.7.0.dev").freeze
 
   def self.bundler_major_version
     @bundler_major_version ||= VERSION.split(".").first.to_i
diff --git a/lib/weakref.rb b/lib/weakref.rb
index f0a7e7b318..0a09f7f993 100644
--- a/lib/weakref.rb
+++ b/lib/weakref.rb
@@ -17,7 +17,7 @@ require "delegate"
 #
 
 class WeakRef < Delegator
-  VERSION = "0.1.3"
+  VERSION = "0.1.4"
 
   ##
   # RefError is raised when a referenced object has been recycled by the