# Source code for pluggy

    """
    PluginManager, basic initialization and tracing.

    pluggy is the cristallized core of plugin management as used
    by some 150 plugins for pytest.

    Pluggy uses semantic versioning. Breaking changes are only foreseen for
    Major releases (incremented X in "X.Y.Z").  If you want to use pluggy in
    your project you should thus use a dependency restriction like
    "pluggy>=0.1.0,<1.0" to avoid surprises.

    pluggy is concerned with hook specification, hook implementations and hook
    calling.  For any given hook specification a hook call invokes up to N implementations.
    A hook implementation can influence its position and type of execution:
    if attributed "tryfirst" or "trylast" it will be tried to execute
    first or last.  However, if attributed "hookwrapper" an implementation
    can wrap all calls to non-hookwrapper implementations.  A hookwrapper
    can thus execute some code ahead and after the execution of other hooks.

    Hook specification is done by way of a regular python function where
    both the function name and the names of all its arguments are significant.
    Each hook implementation function is verified against the original specification
    function, including the names of all its arguments.  To allow for hook specifications
    to evolve over the livetime of a project, hook implementations can
    accept less arguments.  One can thus add new arguments and semantics to
    a hook specification by adding another argument typically without breaking
    existing hook implementations.

    The chosen approach is meant to let a hook designer think carefuly about
    which objects are needed by an extension writer.  By contrast, subclass-based
    extension mechanisms often expose a lot more state and behaviour than needed,
    thus restricting future developments.

    Pluggy currently consists of functionality for:

    - a way to register new hook specifications.  Without a hook
      specification no hook calling can be performed.

    - a registry of plugins which contain hook implementation functions.  It
      is possible to register plugins for which a hook specification is not yet
      known and validate all hooks when the system is in a more referentially
      consistent state.  Setting an "optionalhook" attribution to a hook
      implementation will avoid PluginValidationError's if a specifcation
      is missing.  This allows to have optional integration between plugins.

    - a "hook" relay object from which you can launch 1:N calls to
      registered hook implementation functions

    - a mechanism for ordering hook implementation functions

    - mechanisms for two different type of 1:N calls: "firstresult" for when
      the call should stop when the first implementation returns a non-None result.
      And the other (default) way of guaranteeing that all hook implementations
      will be called and their non-None result collected.

    - mechanisms for "historic" extension points such that all newly
      registered functions will receive all hook calls that happened
      before their registration.

    - a mechanism for discovering plugin objects which are based on
      setuptools based entry points.

    - a simple tracing mechanism, including tracing of plugin calls and
      their arguments.

    """
    import sys
    import inspect

    __version__ = '0.3.0'
    __all__ = ["PluginManager", "PluginValidationError",
               "HookspecMarker", "HookimplMarker"]

    _py3 = sys.version_info > (3, 0)

    class HookspecMarker:
        """ Decorator helper class for marking functions as hook specifications.

        You can instantiate it with a project_name to get a decorator.
        Calling PluginManager.add_hookspecs later will discover all marked functions
        if the PluginManager uses the same project_name.
        """

        def __init__(self, project_name):
            self.project_name = project_name

        def __call__(self, function=None, firstresult=False, historic=False):
            """ if passed a function, directly sets attributes on the function
            which will make it discoverable to add_hookspecs().  If passed no
            function, returns a decorator which can be applied to a function
            later using the attributes supplied.

            If firstresult is True the 1:N hook call (N being the number of registered
            hook implementation functions) will stop at I<=N when the I'th function
            returns a non-None result.

            If historic is True calls to a hook will be memorized and replayed
            on later registered plugins.

            """
            def setattr_hookspec_opts(func):
                if historic and firstresult:
                    raise ValueError("cannot have a historic firstresult hook")
                setattr(func, self.project_name + "_spec",
                       dict(firstresult=firstresult, historic=historic))
                return func

            if function is not None:
                return setattr_hookspec_opts(function)
            else:
                return setattr_hookspec_opts

    class HookimplMarker:
        """ Decorator helper class for marking functions as hook implementations.

        You can instantiate with a project_name to get a decorator.
        Calling PluginManager.register later will discover all marked functions
        if the PluginManager uses the same project_name.
        """
        def __init__(self, project_name):
            self.project_name = project_name

        def __call__(self, function=None, hookwrapper=False, optionalhook=False,
                     tryfirst=False, trylast=False):

            """ if passed a function, directly sets attributes on the function
            which will make it discoverable to register().  If passed no function,
            returns a decorator which can be applied to a function later using
            the attributes supplied.

            If optionalhook is True a missing matching hook specification will not result
            in an error (by default it is an error if no matching spec is found).

            If tryfirst is True this hook implementation will run as early as possible
            in the chain of N hook implementations for a specfication.

            If trylast is True this hook implementation will run as late as possible
            in the chain of N hook implementations.

            If hookwrapper is True the hook implementations needs to execute exactly
            one "yield".  The code before the yield is run early before any non-hookwrapper
            function is run.  The code after the yield is run after all non-hookwrapper
            function have run.  The yield receives an ``_CallOutcome`` object representing
            the exception or result outcome of the inner calls (including other hookwrapper
            calls).

            """
            def setattr_hookimpl_opts(func):
                setattr(func, self.project_name + "_impl",
                       dict(hookwrapper=hookwrapper, optionalhook=optionalhook,
                            tryfirst=tryfirst, trylast=trylast))
                return func

            if function is None:
                return setattr_hookimpl_opts
            else:
                return setattr_hookimpl_opts(function)

    def normalize_hookimpl_opts(opts):
        opts.setdefault("tryfirst", False)
        opts.setdefault("trylast", False)
        opts.setdefault("hookwrapper", False)
        opts.setdefault("optionalhook", False)

    class _TagTracer:
        def __init__(self):
            self._tag2proc = {}
            self.writer = None
            self.indent = 0

        def get(self, name):
            return _TagTracerSub(self, (name,))

        def format_message(self, tags, args):
            if isinstance(args[-1], dict):
                extra = args[-1]
                args = args[:-1]
            else:
                extra = {}

            content = " ".join(map(str, args))
            indent = "  " * self.indent

            lines = [
                "%s%s [%s]\n" % (indent, content, ":".join(tags))
            ]

            for name, value in extra.items():
                lines.append("%s    %s: %s\n" % (indent, name, value))
            return lines

        def processmessage(self, tags, args):
            if self.writer is not None and args:
                lines = self.format_message(tags, args)
                self.writer(''.join(lines))
            try:
                self._tag2proc[tags](tags, args)
            except KeyError:
                pass

        def setwriter(self, writer):
            self.writer = writer

        def setprocessor(self, tags, processor):
            if isinstance(tags, str):
                tags = tuple(tags.split(":"))
            else:
                assert isinstance(tags, tuple)
            self._tag2proc[tags] = processor

    class _TagTracerSub:
        def __init__(self, root, tags):
            self.root = root
            self.tags = tags

        def __call__(self, *args):
            self.root.processmessage(self.tags, args)

        def setmyprocessor(self, processor):
            self.root.setprocessor(self.tags, processor)

        def get(self, name):
            return self.__class__(self.root, self.tags + (name,))

    def _raise_wrapfail(wrap_controller, msg):
        co = wrap_controller.gi_code
        raise RuntimeError("wrap_controller at %r %s:%d %s" %
                       (co.co_name, co.co_filename, co.co_firstlineno, msg))

    def _wrapped_call(wrap_controller, func):
        """ Wrap calling to a function with a generator which needs to yield
        exactly once.  The yield point will trigger calling the wrapped function
        and return its _CallOutcome to the yield point.  The generator then needs
        to finish (raise StopIteration) in order for the wrapped call to complete.
        """
        try:
            next(wrap_controller)   # first yield
        except StopIteration:
            _raise_wrapfail(wrap_controller, "did not yield")
        call_outcome = _CallOutcome(func)
        try:
            wrap_controller.send(call_outcome)
            _raise_wrapfail(wrap_controller, "has second yield")
        except StopIteration:
            pass
        return call_outcome.get_result()

    class _CallOutcome:
        """ Outcome of a function call, either an exception or a proper result.
        Calling the ``get_result`` method will return the result or reraise
        the exception raised when the function was called. """
        excinfo = None

        def __init__(self, func):
            try:
                self.result = func()
            except BaseException:
                self.excinfo = sys.exc_info()

        def force_result(self, result):
            self.result = result
            self.excinfo = None

        def get_result(self):
            if self.excinfo is None:
                return self.result
            else:
                ex = self.excinfo
                if _py3:
                    raise ex[1].with_traceback(ex[2])
                _reraise(*ex)  # noqa

    if not _py3:
        exec("""
    def _reraise(cls, val, tb):
        raise cls, val, tb
    """)

    class _TracedHookExecution:
        def __init__(self, pluginmanager, before, after):
            self.pluginmanager = pluginmanager
            self.before = before
            self.after = after
            self.oldcall = pluginmanager._inner_hookexec
            assert not isinstance(self.oldcall, _TracedHookExecution)
            self.pluginmanager._inner_hookexec = self

        def __call__(self, hook, hook_impls, kwargs):
            self.before(hook.name, hook_impls, kwargs)
            outcome = _CallOutcome(lambda: self.oldcall(hook, hook_impls, kwargs))
            self.after(outcome, hook.name, hook_impls, kwargs)
            return outcome.get_result()

        def undo(self):
            self.pluginmanager._inner_hookexec = self.oldcall

    class PluginManager(object):
        """ Core Pluginmanager class which manages registration
        of plugin objects and 1:N hook calling.

        You can register new hooks by calling ``addhooks(module_or_class)``.
        You can register plugin objects (which contain hooks) by calling
        ``register(plugin)``.  The Pluginmanager is initialized with a
        prefix that is searched for in the names of the dict of registered
        plugin objects.  An optional excludefunc allows to blacklist names which
        are not considered as hooks despite a matching prefix.

        For debugging purposes you can call ``enable_tracing()``
        which will subsequently send debug information to the trace helper.
        """

        def __init__(self, project_name, implprefix=None):
            """ if implprefix is given implementation functions
            will be recognized if their name matches the implprefix. """
            self.project_name = project_name
            self._name2plugin = {}
            self._plugin2hookcallers = {}
            self._plugin_distinfo = []
            self.trace = _TagTracer().get("pluginmanage")
            self.hook = _HookRelay(self.trace.root.get("hook"))
            self._implprefix = implprefix
            self._inner_hookexec = lambda hook, methods, kwargs: \
                _MultiCall(methods, kwargs, hook.spec_opts).execute()

        def _hookexec(self, hook, methods, kwargs):
            # called from all hookcaller instances.
            # enable_tracing will set its own wrapping function at self._inner_hookexec
            return self._inner_hookexec(hook, methods, kwargs)

        def register(self, plugin, name=None):
            """ Register a plugin and return its canonical name or None if the name
            is blocked from registering.  Raise a ValueError if the plugin is already
            registered. """
            plugin_name = name or self.get_canonical_name(plugin)

            if plugin_name in self._name2plugin or plugin in self._plugin2hookcallers:
                if self._name2plugin.get(plugin_name, -1) is None:
                    return  # blocked plugin, return None to indicate no registration
                raise ValueError("Plugin already registered: %s=%s\n%s" %
                                (plugin_name, plugin, self._name2plugin))

            # XXX if an error happens we should make sure no state has been
            # changed at point of return
            self._name2plugin[plugin_name] = plugin

            # register matching hook implementations of the plugin
            self._plugin2hookcallers[plugin] = hookcallers = []
            for name in dir(plugin):
                hookimpl_opts = self.parse_hookimpl_opts(plugin, name)
                if hookimpl_opts is not None:
                    normalize_hookimpl_opts(hookimpl_opts)
                    method = getattr(plugin, name)
                    hookimpl = HookImpl(plugin, plugin_name, method, hookimpl_opts)
                    hook = getattr(self.hook, name, None)
                    if hook is None:
                        hook = _HookCaller(name, self._hookexec)
                        setattr(self.hook, name, hook)
                    elif hook.has_spec():
                        self._verify_hook(hook, hookimpl)
                        hook._maybe_apply_history(hookimpl)
                    hook._add_hookimpl(hookimpl)
                    hookcallers.append(hook)
            return plugin_name

        def parse_hookimpl_opts(self, plugin, name):
            method = getattr(plugin, name)
            res = getattr(method, self.project_name + "_impl", None)
            if res is not None and not isinstance(res, dict):
                # false positive
                res = None
            elif res is None and self._implprefix and name.startswith(self._implprefix):
                res = {}
            return res

        def unregister(self, plugin=None, name=None):
            """ unregister a plugin object and all its contained hook implementations
            from internal data structures. """
            if name is None:
                assert plugin is not None, "one of name or plugin needs to be specified"
                name = self.get_name(plugin)

            if plugin is None:
                plugin = self.get_plugin(name)

            # if self._name2plugin[name] == None registration was blocked: ignore
            if self._name2plugin.get(name):
                del self._name2plugin[name]

            for hookcaller in self._plugin2hookcallers.pop(plugin, []):
                hookcaller._remove_plugin(plugin)

            return plugin

        def set_blocked(self, name):
            """ block registrations of the given name, unregister if already registered. """
            self.unregister(name=name)
            self._name2plugin[name] = None

        def is_blocked(self, name):
            """ return True if the name blogs registering plugins of that name. """
            return name in self._name2plugin and self._name2plugin[name] is None

        def add_hookspecs(self, module_or_class):
            """ add new hook specifications defined in the given module_or_class.
            Functions are recognized if they have been decorated accordingly. """
            names = []
            for name in dir(module_or_class):
                spec_opts = self.parse_hookspec_opts(module_or_class, name)
                if spec_opts is not None:
                    hc = getattr(self.hook, name, None)
                    if hc is None:
                        hc = _HookCaller(name, self._hookexec, module_or_class, spec_opts)
                        setattr(self.hook, name, hc)
                    else:
                        # plugins registered this hook without knowing the spec
                        hc.set_specification(module_or_class, spec_opts)
                        for hookfunction in (hc._wrappers + hc._nonwrappers):
                            self._verify_hook(hc, hookfunction)
                    names.append(name)

            if not names:
                raise ValueError("did not find any %r hooks in %r" %
                                 (self.project_name, module_or_class))

        def parse_hookspec_opts(self, module_or_class, name):
            method = getattr(module_or_class, name)
            return getattr(method, self.project_name + "_spec", None)

        def get_plugins(self):
            """ return the set of registered plugins. """
            return set(self._plugin2hookcallers)

        def is_registered(self, plugin):
            """ Return True if the plugin is already registered. """
            return plugin in self._plugin2hookcallers

        def get_canonical_name(self, plugin):
            """ Return canonical name for a plugin object. Note that a plugin
            may be registered under a different name which was specified
            by the caller of register(plugin, name). To obtain the name
            of an registered plugin use ``get_name(plugin)`` instead."""
            return getattr(plugin, "__name__", None) or str(id(plugin))

        def get_plugin(self, name):
            """ Return a plugin or None for the given name. """
            return self._name2plugin.get(name)

        def get_name(self, plugin):
            """ Return name for registered plugin or None if not registered. """
            for name, val in self._name2plugin.items():
                if plugin == val:
                    return name

        def _verify_hook(self, hook, hookimpl):
            if hook.is_historic() and hookimpl.hookwrapper:
                raise PluginValidationError(
                    "Plugin %r\nhook %r\nhistoric incompatible to hookwrapper" %
                    (hookimpl.plugin_name, hook.name))

            for arg in hookimpl.argnames:
                if arg not in hook.argnames:
                    raise PluginValidationError(
                        "Plugin %r\nhook %r\nargument %r not available\n"
                        "plugin definition: %s\n"
                        "available hookargs: %s" %
                        (hookimpl.plugin_name, hook.name, arg,
                        _formatdef(hookimpl.function), ", ".join(hook.argnames)))

        def check_pending(self):
            """ Verify that all hooks which have not been verified against
            a hook specification are optional, otherwise raise PluginValidationError"""
            for name in self.hook.__dict__:
                if name[0] != "_":
                    hook = getattr(self.hook, name)
                    if not hook.has_spec():
                        for hookimpl in (hook._wrappers + hook._nonwrappers):
                            if not hookimpl.optionalhook:
                                raise PluginValidationError(
                                    "unknown hook %r in plugin %r" %
                                    (name, hookimpl.plugin))

        def load_setuptools_entrypoints(self, entrypoint_name):
            """ Load modules from querying the specified setuptools entrypoint name.
            Return the number of loaded plugins. """
            from pkg_resources import iter_entry_points, DistributionNotFound
            for ep in iter_entry_points(entrypoint_name):
                # is the plugin registered or blocked?
                if self.get_plugin(ep.name) or self.is_blocked(ep.name):
                    continue
                try:
                    plugin = ep.load()
                except DistributionNotFound:
                    continue
                self.register(plugin, name=ep.name)
                self._plugin_distinfo.append((plugin, ep.dist))
            return len(self._plugin_distinfo)

        def list_plugin_distinfo(self):
            """ return list of distinfo/plugin tuples for all setuptools registered
            plugins. """
            return list(self._plugin_distinfo)

        def list_name_plugin(self):
            """ return list of name/plugin pairs. """
            return list(self._name2plugin.items())

        def get_hookcallers(self, plugin):
            """ get all hook callers for the specified plugin. """
            return self._plugin2hookcallers.get(plugin)

        def add_hookcall_monitoring(self, before, after):
            """ add before/after tracing functions for all hooks
            and return an undo function which, when called,
            will remove the added tracers.

            ``before(hook_name, hook_impls, kwargs)`` will be called ahead
            of all hook calls and receive a hookcaller instance, a list
            of HookImpl instances and the keyword arguments for the hook call.

            ``after(outcome, hook_name, hook_impls, kwargs)`` receives the
            same arguments as ``before`` but also a :py:class:`_CallOutcome`` object
            which represents the result of the overall hook call.
            """
            return _TracedHookExecution(self, before, after).undo

        def enable_tracing(self):
            """ enable tracing of hook calls and return an undo function. """
            hooktrace = self.hook._trace

            def before(hook_name, methods, kwargs):
                hooktrace.root.indent += 1
                hooktrace(hook_name, kwargs)

            def after(outcome, hook_name, methods, kwargs):
                if outcome.excinfo is None:
                    hooktrace("finish", hook_name, "-->", outcome.result)
                hooktrace.root.indent -= 1

            return self.add_hookcall_monitoring(before, after)

        def subset_hook_caller(self, name, remove_plugins):
            """ Return a new _HookCaller instance for the named method
            which manages calls to all registered plugins except the
            ones from remove_plugins. """
            orig = getattr(self.hook, name)
            plugins_to_remove = [plug for plug in remove_plugins if hasattr(plug, name)]
            if plugins_to_remove:
                hc = _HookCaller(orig.name, orig._hookexec, orig._specmodule_or_class,
                                 orig.spec_opts)
                for hookimpl in (orig._wrappers + orig._nonwrappers):
                    plugin = hookimpl.plugin
                    if plugin not in plugins_to_remove:
                        hc._add_hookimpl(hookimpl)
                        # we also keep track of this hook caller so it
                        # gets properly removed on plugin unregistration
                        self._plugin2hookcallers.setdefault(plugin, []).append(hc)
                return hc
            return orig

    class _MultiCall:
        """ execute a call into multiple python functions/methods. """

        # XXX note that the __multicall__ argument is supported only
        # for pytest compatibility reasons.  It was never officially
        # supported there and is explicitely deprecated since 2.8
        # so we can remove it soon, allowing to avoid the below recursion
        # in execute() and simplify/speed up the execute loop.

        def __init__(self, hook_impls, kwargs, specopts={}):
            self.hook_impls = hook_impls
            self.kwargs = kwargs
            self.kwargs["__multicall__"] = self
            self.specopts = specopts

        def execute(self):
            all_kwargs = self.kwargs
            self.results = results = []
            firstresult = self.specopts.get("firstresult")

            while self.hook_impls:
                hook_impl = self.hook_impls.pop()
                args = [all_kwargs[argname] for argname in hook_impl.argnames]
                if hook_impl.hookwrapper:
                    return _wrapped_call(hook_impl.function(*args), self.execute)
                res = hook_impl.function(*args)
                if res is not None:
                    if firstresult:
                        return res
                    results.append(res)

            if not firstresult:
                return results

        def __repr__(self):
            status = "%d meths" % (len(self.hook_impls),)
            if hasattr(self, "results"):
                status = ("%d results, " % len(self.results)) + status
            return "<_MultiCall %s, kwargs=%r>" % (status, self.kwargs)

    def varnames(func, startindex=None):
        """ return argument name tuple for a function, method, class or callable.

        In case of a class, its "__init__" method is considered.
        For methods the "self" parameter is not included unless you are passing
        an unbound method with Python3 (which has no supports for unbound methods)
        """
        cache = getattr(func, "__dict__", {})
        try:
            return cache["_varnames"]
        except KeyError:
            pass
        if inspect.isclass(func):
            try:
                func = func.__init__
            except AttributeError:
                return ()
            startindex = 1
        else:
            if not inspect.isfunction(func) and not inspect.ismethod(func):
                func = getattr(func, '__call__', func)
            if startindex is None:
                startindex = int(inspect.ismethod(func))

        try:
            rawcode = func.__code__
        except AttributeError:
            return ()
        try:
            x = rawcode.co_varnames[startindex:rawcode.co_argcount]
        except AttributeError:
            x = ()
        else:
            defaults = func.__defaults__
            if defaults:
                x = x[:-len(defaults)]
        try:
            cache["_varnames"] = x
        except TypeError:
            pass
        return x

    class _HookRelay:
        """ hook holder object for performing 1:N hook calls where N is the number
        of registered plugins.

        """

        def __init__(self, trace):
            self._trace = trace

    class _HookCaller(object):
        def __init__(self, name, hook_execute, specmodule_or_class=None, spec_opts=None):
            self.name = name
            self._wrappers = []
            self._nonwrappers = []
            self._hookexec = hook_execute
            if specmodule_or_class is not None:
                assert spec_opts is not None
                self.set_specification(specmodule_or_class, spec_opts)

        def has_spec(self):
            return hasattr(self, "_specmodule_or_class")

        def set_specification(self, specmodule_or_class, spec_opts):
            assert not self.has_spec()
            self._specmodule_or_class = specmodule_or_class
            specfunc = getattr(specmodule_or_class, self.name)
            argnames = varnames(specfunc, startindex=inspect.isclass(specmodule_or_class))
            assert "self" not in argnames  # sanity check
            self.argnames = ["__multicall__"] + list(argnames)
            self.spec_opts = spec_opts
            if spec_opts.get("historic"):
                self._call_history = []

        def is_historic(self):
            return hasattr(self, "_call_history")

        def _remove_plugin(self, plugin):
            def remove(wrappers):
                for i, method in enumerate(wrappers):
                    if method.plugin == plugin:
                        del wrappers[i]
                        return True
            if remove(self._wrappers) is None:
                if remove(self._nonwrappers) is None:
                    raise ValueError("plugin %r not found" % (plugin,))

        def _add_hookimpl(self, hookimpl):
            if hookimpl.hookwrapper:
                methods = self._wrappers
            else:
                methods = self._nonwrappers

            if hookimpl.trylast:
                methods.insert(0, hookimpl)
            elif hookimpl.tryfirst:
                methods.append(hookimpl)
            else:
                # find last non-tryfirst method
                i = len(methods) - 1
                while i >= 0 and methods[i].tryfirst:
                    i -= 1
                methods.insert(i + 1, hookimpl)

        def __repr__(self):
            return "<_HookCaller %r>" % (self.name,)

        def __call__(self, **kwargs):
            assert not self.is_historic()
            return self._hookexec(self, self._nonwrappers + self._wrappers, kwargs)

        def call_historic(self, proc=None, kwargs=None):
            self._call_history.append((kwargs or {}, proc))
            # historizing hooks don't return results
            self._hookexec(self, self._nonwrappers + self._wrappers, kwargs)

        def call_extra(self, methods, kwargs):
            """ Call the hook with some additional temporarily participating
            methods using the specified kwargs as call parameters. """
            old = list(self._nonwrappers), list(self._wrappers)
            for method in methods:
                opts = dict(hookwrapper=False, trylast=False, tryfirst=False)
                hookimpl = HookImpl(None, "<temp>", method, opts)
                self._add_hookimpl(hookimpl)
            try:
                return self(**kwargs)
            finally:
                self._nonwrappers, self._wrappers = old

        def _maybe_apply_history(self, method):
            if self.is_historic():
                for kwargs, proc in self._call_history:
                    res = self._hookexec(self, [method], kwargs)
                    if res and proc is not None:
                        proc(res[0])

    class HookImpl:
        def __init__(self, plugin, plugin_name, function, hook_impl_opts):
            self.function = function
            self.argnames = varnames(self.function)
            self.plugin = plugin
            self.opts = hook_impl_opts
            self.plugin_name = plugin_name
            self.__dict__.update(hook_impl_opts)

    class PluginValidationError(Exception):
        """ plugin failed validation. """

    def _formatdef(func):
        return "%s%s" % (
            func.__name__,
            inspect.formatargspec(*inspect.getargspec(func))
        )