Add m-esr52 at 52.6.0

1 files changed, 777 insertions, 0 deletions

diff --git a/python/pytest/_pytest/vendored_packages/pluggy.py b/python/pytest/_pytest/vendored_packages/pluggy.py
new file mode 100644
index 000000000..2f848b23d
--- /dev/null
+++ b/python/pytest/_pytest/vendored_packages/pluggy.py
@@ -0,0 +1,777 @@
+"""
+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 specification
+  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__ = '0.3.1'
+__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 explicitly 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. """
+
+
+if hasattr(inspect, 'signature'):
+    def _formatdef(func):
+        return "%s%s" % (
+            func.__name__,
+            str(inspect.signature(func))
+        )
+else:
+    def _formatdef(func):
+        return "%s%s" % (
+            func.__name__,
+            inspect.formatargspec(*inspect.getargspec(func))
+        )