debug tracing patch for gem error "`check_version_conflict': can't activate foo-2.0, already activated foo-1.0 (Gem::LoadError)"

gem_trace.rb

def ___trace_push mark
  Thread.current[:__prefix] ||= ''
  Thread.current[:__prefix] << "#{mark}  "
end

def ___trace_pop
  Thread.current[:__prefix].slice!(-3, 3)
end

def ___trace_puts mark, *msgs
  $stderr.print Thread.current[:__prefix]
  $stderr.print "#{mark} #{msgs.map {|m| m.is_a?(Array) ? '[' + m.join(', ') + ']' : m.to_s }.join(' ')}\n"
end

module ObjectTrace_
  def require path
    ___trace_puts 'R', path
    ___trace_push '|'

    super.tap do |result|
      ___trace_pop
      ___trace_puts (result ? '+' : '`'), path
    end

  rescue Exception
    ___trace_pop
    ___trace_puts 'X', path, 'failed'
    raise
  end

  def gem gem_name, *requirements
    Thread.current[:require] ||= []
    ___trace_puts 'G', gem_name, requirements
    super
  end
end
Object.prepend(ObjectTrace_)

module GemSpecTrace_
  module ClassMethods
    def find_active_stub_by_path path
      super.tap {|spec| ___trace_puts 'S', spec.full_name if spec }
    end

    def find_in_unresolved path
      super.tap {|specs| ___trace_puts 'U', specs.map(&:full_name) unless specs.empty? }
    end

    def find_in_unresolved_tree path
      ___trace_puts 'T', unresolved_deps.values.map { |dep| dep.to_specs }.flatten.map(&:full_name)
      ___trace_push ':'
      super.tap do |specs|
        ___trace_pop
        ___trace_puts '`', specs.map(&:full_name)
      end
    rescue Exception
      ___trace_pop
      ___trace_puts 'X', "failed (#{$!})"
      raise
    end
  end

  def traverse trail = [], visited = {}, &block
    ___trace_puts 't', full_name, dependencies.select(&:runtime?).each_with_object({}) {|d,h| h[d.to_s] = d.to_specs.map(&:full_name) }
    ___trace_push ':'
    super
  ensure
    ___trace_pop
  end

  def activate
    ___trace_puts 'A', full_name
    ___trace_push ':'
    super.tap do
      ___trace_pop
      ___trace_puts '+', full_name
    end
  rescue Exception
    ___trace_pop
    ___trace_puts 'X', full_name, "failed (#{$!})"
    raise
  end
end
class Gem::Specification
  prepend(GemSpecTrace_)
  class << self
    prepend(GemSpecTrace_::ClassMethods)
  end
end