allow single quotes in preamble

lib/bundler/multilock.rb

@@ -329,7 +329,7 @@ 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_match = /plugin ["']bundler-multilock["']/
         bundle_preamble1 = <<~RUBY
           plugin "bundler-multilock", "~> #{minor_version}"
         RUBY
@@ -384,8 +384,10 @@ def reset!
 
       private
 
-      def inject_specific_preamble(gemfile, gemfiles, injection_point, preamble, add_newline:, match: preamble)
-        return false if gemfiles.any? { |g| g.include?(match) }
+      def inject_specific_preamble(gemfile, gemfiles, injection_point, preamble, add_newline:, match: nil)
+        # allow either type of quotes
+        match ||= Regexp.new(Regexp.escape(preamble).gsub('"', %(["'])))
+        return false if gemfiles.any? { |g| match.match?(g) }
 
         add_newline = false unless gemfile[injection_point - 1] == "\n"
 

spec/bundler/multilock_spec.rb

@@ -46,6 +46,30 @@
     end
   end
 
+  it "does not inject duplicate plugin load commands when you prefer single quotes" do
+    gemfile = <<~RUBY
+      # frozen_string_literal: true
+
+      source 'https://rubygems.org'
+
+      plugin 'bundler-multilock', '~> 1.0'
+      return unless Plugin.installed?('bundler-multilock')
+
+      Plugin.send(:load_plugin, 'bundler-multilock')
+
+      gem 'concurrent-ruby', '1.2.2'
+    RUBY
+
+    with_gemfile("") do
+      File.write("Gemfile", gemfile)
+
+      local_git = Shellwords.escape(File.expand_path("../..", __dir__))
+      invoke_bundler("plugin install bundler-multilock --local_git=#{local_git}")
+
+      expect(File.read("Gemfile")).to eq gemfile
+    end
+  end
+
   it "does not inject when a secondary Gemfile has the necessary commands" do
     with_gemfile("") do
       File.write("Gemfile", <<~RUBY)