def find_plugins(self, plugin_env, full_env=None, installer=None, fallback=True):
        """Find all activatable distributions in `plugin_env`

        Example usage::

            distributions, errors = working_set.find_plugins(
                Environment(plugin_dirlist)
            )
            # add plugins+libs to sys.path
            map(working_set.add, distributions)
            # display errors
            print('Could not load', errors)

        The `plugin_env` should be an ``Environment`` instance that contains
        only distributions that are in the project's "plugin directory" or
        directories. The `full_env`, if supplied, should be an ``Environment``
        contains all currently-available distributions.  If `full_env` is not
        supplied, one is created automatically from the ``WorkingSet`` this
        method is called on, which will typically mean that every directory on
        ``sys.path`` will be scanned for distributions.

        `installer` is a standard installer callback as used by the
        ``resolve()`` method. The `fallback` flag indicates whether we should
        attempt to resolve older versions of a plugin if the newest version
        cannot be resolved.

        This method returns a 2-tuple: (`distributions`, `error_info`), where
        `distributions` is a list of the distributions found in `plugin_env`
        that were loadable, along with any other distributions that are needed
        to resolve their dependencies.  `error_info` is a dictionary mapping
        unloadable plugin distributions to an exception instance describing the
        error that occurred. Usually this will be a ``DistributionNotFound`` or
        ``VersionConflict`` instance.
        """

        plugin_projects = list(plugin_env)
        # scan project names in alphabetic order
        plugin_projects.sort()

        error_info = {}
        distributions = {}

        if full_env is None:
            env = Environment(self.entries)
            env += plugin_env
        else:
            env = full_env + plugin_env

        shadow_set = self.__class__([])
        # put all our entries in shadow_set
        list(map(shadow_set.add, self))

        for project_name in plugin_projects:
            for dist in plugin_env[project_name]:
                req = [dist.as_requirement()]

                try:
                    resolvees = shadow_set.resolve(req, env, installer)

                except ResolutionError as v:
                    # save error info
                    error_info[dist] = v
                    if fallback:
                        # try the next older version of project
                        continue
                    else:
                        # give up on this project, keep going
                        break

                else:
                    list(map(shadow_set.add, resolvees))
                    distributions.update(dict.fromkeys(resolvees))

                    # success, no need to try any more versions of this project
                    break

        distributions = list(distributions)
        distributions.sort()

        return distributions, error_info
Find all activatable distributions in `plugin_env`

        Example usage::

            distributions, errors = working_set.find_plugins(
                Environment(plugin_dirlist)
            )
            # add plugins+libs to sys.path
            map(working_set.add, distributions)
            # display errors
            print('Could not load', errors)

        The `plugin_env` should be an ``Environment`` instance that contains
        only distributions that are in the project's "plugin directory" or
        directories. The `full_env`, if supplied, should be an ``Environment``
        contains all currently-available distributions.  If `full_env` is not
        supplied, one is created automatically from the ``WorkingSet`` this
        method is called on, which will typically mean that every directory on
        ``sys.path`` will be scanned for distributions.

        `installer` is a standard installer callback as used by the
        ``resolve()`` method. The `fallback` flag indicates whether we should
        attempt to resolve older versions of a plugin if the newest version
        cannot be resolved.

        This method returns a 2-tuple: (`distributions`, `error_info`), where
        `distributions` is a list of the distributions found in `plugin_env`
        that were loadable, along with any other distributions that are needed
        to resolve their dependencies.  `error_info` is a dictionary mapping
        unloadable plugin distributions to an exception instance describing the
        error that occurred. Usually this will be a ``DistributionNotFound`` or
        ``VersionConflict`` instance.
        
product/gradle-plugin/src/main/python/pkg_resources/__init__.py