fix double-sync (#1)

if the preamble already exists, injecting the preamble would evaluate
the gemfile, and recursively load the plugin (and plugins.rb).
avoid the problems of that by only adding at_exit hooks in multilock.rb,
which will only be required once. the plugin hook needs to be more
carefully considered, because they'll be reset multiple times -
so avoid the re-entrant load in the first place

.rspec

@@ -0,0 +1 @@
+--require spec_helper

lib/bundler/multilock.rb

@@ -146,6 +146,7 @@ def after_install_all(install: true)
         require "tempfile"
         require_relative "multilock/lockfile_generator"
 
+        Bundler.ui.debug("Syncing to alternate lockfiles")
         Bundler.ui.info ""
 
         default_lockfile_contents = Bundler.default_lockfile.read.freeze
@@ -321,6 +322,8 @@ def loaded?
 
       # @!visibility private
       def inject_preamble
+        Bundler.ui.debug("Injecting multilock preamble")
+
         minor_version = Gem::Version.new(::Bundler::Multilock::VERSION).segments[0..1].join(".")
         bundle_preamble1_match = %(plugin "bundler-multilock")
         bundle_preamble1 = <<~RUBY
@@ -346,7 +349,16 @@ def inject_preamble
         end
 
         builder = Bundler::Plugin::DSL.new
-        builder.eval_gemfile(Bundler.default_gemfile)
+        # this method is called as part of the plugin loading, but @loaded_plugin_names
+        # hasn't been set yet, so avoid re-entrancy issues
+        plugins = Bundler::Plugin.instance_variable_get(:@loaded_plugin_names)
+        original_plugins = plugins.dup
+        plugins << "bundler-multilock"
+        begin
+          builder.eval_gemfile(Bundler.default_gemfile)
+        ensure
+          plugins.replace(original_plugins)
+        end
         gemfiles = builder.instance_variable_get(:@gemfiles).map(&:read)
 
         modified = inject_specific_preamble(gemfile, gemfiles, injection_point, bundle_preamble2, add_newline: true)
@@ -448,3 +460,26 @@ def write_lockfile(lockfile_definition, lockfile, install:, dependency_changes:
 end
 
 Bundler::Multilock.inject_preamble unless Bundler::Multilock.loaded?
+
+# this is terrible, but we can't prepend into these modules because we only load
+# _inside_ of the CLI commands already running
+if defined?(Bundler::CLI::Check)
+  require_relative "multilock/check"
+  at_exit do
+    next unless $!.nil?
+    next if $!.is_a?(SystemExit) && !$!.success?
+
+    next if Bundler::Multilock::Check.run
+
+    Bundler.ui.warn("You can attempt to fix by running `bundle install`")
+    exit 1
+  end
+end
+if defined?(Bundler::CLI::Lock)
+  at_exit do
+    next unless $!.nil?
+    next if $!.is_a?(SystemExit) && !$!.success?
+
+    Bundler::Multilock.after_install_all(install: false)
+  end
+end

plugins.rb

@@ -20,29 +20,6 @@
 
 require_relative "lib/bundler/multilock"
 
-# this is terrible, but we can't prepend into these modules because we only load
-# _inside_ of the CLI commands already running
-if defined?(Bundler::CLI::Check)
-  require_relative "lib/bundler/multilock/check"
-  at_exit do
-    next unless $!.nil?
-    next if $!.is_a?(SystemExit) && !$!.success?
-
-    next if Bundler::Multilock::Check.run
-
-    Bundler.ui.warn("You can attempt to fix by running `bundle install`")
-    exit 1
-  end
-end
-if defined?(Bundler::CLI::Lock)
-  at_exit do
-    next unless $!.nil?
-    next if $!.is_a?(SystemExit) && !$!.success?
-
-    Bundler::Multilock.after_install_all(install: false)
-  end
-end
-
 Bundler::Plugin.add_hook(Bundler::Plugin::Events::GEM_AFTER_INSTALL_ALL) do |_|
   Bundler::Multilock.after_install_all
 end

spec/bundler/multilock_spec.rb

@@ -192,7 +192,7 @@
 
       gem "concurrent-ruby", "1.2.2"
     RUBY
-      create_local_gem("test_local", "")
+      create_local_gem("test_local")
 
       invoke_bundler("install")
 
@@ -611,11 +611,32 @@
     end
   end
 
+  it "only syncs once per lockfile" do
+    with_gemfile(<<~RUBY) do
+      gemspec
+
+      lockfile("rails-7.0", default: true) do
+        gem "activesupport", "~> 7.0.0"
+      end
+    RUBY
+      create_local_gem("test", subdirectory: false)
+      invoke_bundler("install")
+      output = invoke_bundler("install", env: { "DEBUG" => "1" })
+
+      expect(output.split("\n").grep(/Syncing to alternate lockfiles/).length).to be 1
+    end
+  end
+
   private
 
-  def create_local_gem(name, content)
-    FileUtils.mkdir_p(name)
-    File.write("#{name}/#{name}.gemspec", <<~RUBY)
+  def create_local_gem(name, content = "", subdirectory: true)
+    if subdirectory
+      FileUtils.mkdir_p(name)
+      subdirectory = "#{name}/"
+    else
+      subdirectory = nil
+    end
+    File.write("#{subdirectory}#{name}.gemspec", <<~RUBY)
       Gem::Specification.new do |spec|
         spec.name          = #{name.inspect}
         spec.version       = "0.0.1"
@@ -626,6 +647,8 @@ def create_local_gem(name, content)
       end
     RUBY
 
+    return unless subdirectory
+
     File.write("#{name}/Gemfile", <<~RUBY)
       source "https://rubygems.org"
 

spec/spec_helper.rb

@@ -1,5 +1,7 @@
 # frozen_string_literal: true
 
+require "debug"
+
 RSpec.configure do |config|
   config.expect_with :rspec do |c|
     c.max_formatted_output_length = nil