allow uninstalling gems with bundler

Fixes #2450

lib/logstash/bundler_patch.rb

@@ -1,6 +1,25 @@
 require 'bundler'
 
 module Bundler
+  class SpecSet
+    # Usually Bundler's SpecSet is a read only/created once database
+    # I am modifying this behavior to allow `Gem` to uninstall gems.
+    def delete(key)
+      value = @specs.delete(key)
+      reset_state!
+      value
+    end
+
+    def delete_if(&block)
+      @specs.delete_if(&block)
+      reset_state!
+    end
+
+    def reset_state!
+      @lookup = nil
+      @sorted = nil
+    end
+  end
   class RubygemsIntegration
     # When you call Bundler#setup it will bootstrap
     # a new rubygems environment and wipe all the existing

lib/logstash/pluginmanager/main.rb

@@ -1,11 +1,12 @@
 require "logstash/namespace"
 require "logstash/errors"
-require 'clamp'
-require 'logstash/pluginmanager/install'
-require 'logstash/pluginmanager/uninstall'
-require 'logstash/pluginmanager/list'
-require 'logstash/pluginmanager/update'
-require 'logstash/pluginmanager/util'
+require "logstash/pluginmanager/install"
+require "logstash/pluginmanager/uninstall"
+require "logstash/pluginmanager/list"
+require "logstash/pluginmanager/update"
+require "logstash/pluginmanager/util"
+require "clamp"
+
 
 class LogStash::PluginManager::Main < Clamp::Command
 

lib/logstash/pluginmanager/uninstall.rb

@@ -1,10 +1,11 @@
 require "logstash/namespace"
 require "logstash/logging"
 require "logstash/errors"
-require 'clamp'
-require 'logstash/pluginmanager'
-require 'logstash/pluginmanager/util'
-require 'rubygems/uninstaller'
+require "logstash/environment"
+require "logstash/pluginmanager"
+require "logstash/pluginmanager/util"
+require "rubygems/uninstaller"
+require "clamp"
 
 class LogStash::PluginManager::Uninstall < Clamp::Command
 
@@ -12,11 +13,15 @@ class LogStash::PluginManager::Uninstall < Clamp::Command
 
   public
   def execute
-
     ::Gem.configuration.verbose = false
 
     puts ("Validating removal of #{plugin}.")
     
+    #
+    # TODO: This is a special case, Bundler doesnt allow you to uninstall 1 gem.
+    # Bundler will only uninstall the gems if they dont exist in his Gemfile.lock
+    # (source of truth)
+    #
     unless gem_data = LogStash::PluginManager::Util.logstash_plugin?(plugin)
       $stderr.puts ("Trying to remove a non logstash plugin. Aborting")
       return 99