replace_bin_path

# File lib/bundler/rubygems_integration.rb, line 439
    def replace_bin_path(specs, 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

        spec_with_name = specs_by_name[gem_name]
        spec = if exec_name
          if spec_with_name && spec_with_name.executables.include?(exec_name)
            spec_with_name
          else
            specs.find {|s| s.executables.include?(exec_name) }
          end
        else
          spec_with_name
        end

        unless spec
          message = "can't find executable #{exec_name} for gem #{gem_name}"
          if !exec_name || spec_with_name.nil?
            message += ". #{gem_name} is not currently included in the bundle, "                         "perhaps you meant to add it to your #{Bundler.default_gemfile.basename}?"
          end
          raise Gem::Exception, message
        end

        raise Gem::Exception, "no default executable for #{spec.full_name}" unless exec_name ||= spec.default_executable

        unless spec.name == gem_name
          Bundler::SharedHelpers.major_deprecation 2,
            "Bundler is using a binstub that was created for a different gem (#{spec.name}).\n"              "You should run `bundle binstub #{gem_name}` "              "to work around a system/bundle conflict."
        end
        spec
      end

      redefine_method(gem_class, :activate_bin_path) do |name, *args|
        exec_name = args.first
        return ENV["BUNDLE_BIN_PATH"] if exec_name == "bundle"

        # Copy of Rubygems activate_bin_path impl
        requirement = args.last
        spec = find_spec_for_exe name, exec_name, [requirement]

        gem_bin = File.join(spec.full_gem_path, spec.bindir, exec_name)
        gem_from_path_bin = File.join(File.dirname(spec.loaded_from), spec.bindir, exec_name)
        File.exist?(gem_bin) ? gem_bin : gem_from_path_bin
      end

      redefine_method(gem_class, :bin_path) do |name, *args|
        exec_name = args.first
        return ENV["BUNDLE_BIN_PATH"] if exec_name == "bundle"

        spec = find_spec_for_exe(name, *args)
        exec_name ||= spec.default_executable

        gem_bin = File.join(spec.full_gem_path, spec.bindir, exec_name)
        gem_from_path_bin = File.join(File.dirname(spec.loaded_from), spec.bindir, exec_name)
        File.exist?(gem_bin) ? gem_bin : gem_from_path_bin
      end
    end