jinja2/runtime.py

# -*- coding: utf-8 -*-
"""
    jinja2.runtime
    ~~~~~~~~~~~~~~

    Runtime helpers.

    :copyright: (c) 2017 by the Jinja Team.
    :license: BSD.
"""
import sys

from itertools import chain
from types import MethodType

from jinja2.nodes import EvalContext, _context_function_types
from jinja2.utils import Markup, soft_unicode, escape, missing, concat, \
     internalcode, object_type_repr, evalcontextfunction, Namespace
from jinja2.exceptions import UndefinedError, TemplateRuntimeError, \
     TemplateNotFound
from jinja2._compat import imap, text_type, iteritems, \
     implements_iterator, implements_to_string, string_types, PY2, \
     with_metaclass, abc


# these variables are exported to the template runtime
__all__ = ['LoopContext', 'TemplateReference', 'Macro', 'Markup',
           'TemplateRuntimeError', 'missing', 'concat', 'escape',
           'markup_join', 'unicode_join', 'to_string', 'identity',
           'TemplateNotFound', 'Namespace']

#: the name of the function that is used to convert something into
#: a string.  We can just use the text type here.
to_string = text_type

#: the identity function.  Useful for certain things in the environment
identity = lambda x: x

_first_iteration = object()
_last_iteration = object()


def markup_join(seq):
    """Concatenation that escapes if necessary and converts to unicode."""
    buf = []
    iterator = imap(soft_unicode, seq)
    for arg in iterator:
        buf.append(arg)
        if hasattr(arg, '__html__'):
            return Markup(u'').join(chain(buf, iterator))
    return concat(buf)


def unicode_join(seq):
    """Simple args to unicode conversion and concatenation."""
    return concat(imap(text_type, seq))


def new_context(environment, template_name, blocks, vars=None,
                shared=None, globals=None, locals=None):
    """Internal helper to for context creation."""
    if vars is None:
        vars = {}
    if shared:
        parent = vars
    else:
        parent = dict(globals or (), **vars)
    if locals:
        # if the parent is shared a copy should be created because
        # we don't want to modify the dict passed
        if shared:
            parent = dict(parent)
        for key, value in iteritems(locals):
            if value is not missing:
                parent[key] = value
    return environment.context_class(environment, parent, template_name,
                                     blocks)


class TemplateReference(object):
    """The `self` in templates."""

    def __init__(self, context):
        self.__context = context

    def __getitem__(self, name):
        blocks = self.__context.blocks[name]
        return BlockReference(name, self.__context, blocks, 0)

    def __repr__(self):
        return '<%s %r>' % (
            self.__class__.__name__,
            self.__context.name
        )


def _get_func(x):
    return getattr(x, '__func__', x)


class ContextMeta(type):

    def __new__(cls, name, bases, d):
        rv = type.__new__(cls, name, bases, d)
        if bases == ():
            return rv

        resolve = _get_func(rv.resolve)
        default_resolve = _get_func(Context.resolve)
        resolve_or_missing = _get_func(rv.resolve_or_missing)
        default_resolve_or_missing = _get_func(Context.resolve_or_missing)

        # If we have a changed resolve but no changed default or missing
        # resolve we invert the call logic.
        if resolve is not default_resolve and \
           resolve_or_missing is default_resolve_or_missing:
            rv._legacy_resolve_mode = True
        elif resolve is default_resolve and \
             resolve_or_missing is default_resolve_or_missing:
            rv._fast_resolve_mode = True

        return rv


def resolve_or_missing(context, key, missing=missing):
    if key in context.vars:
        return context.vars[key]
    if key in context.parent:
        return context.parent[key]
    return missing


class Context(with_metaclass(ContextMeta)):
    """The template context holds the variables of a template.  It stores the
    values passed to the template and also the names the template exports.
    Creating instances is neither supported nor useful as it's created
    automatically at various stages of the template evaluation and should not
    be created by hand.

    The context is immutable.  Modifications on :attr:`parent` **must not**
    happen and modifications on :attr:`vars` are allowed from generated
    template code only.  Template filters and global functions marked as
    :func:`contextfunction`\\s get the active context passed as first argument
    and are allowed to access the context read-only.

    The template context supports read only dict operations (`get`,
    `keys`, `values`, `items`, `iterkeys`, `itervalues`, `iteritems`,
    `__getitem__`, `__contains__`).  Additionally there is a :meth:`resolve`
    method that doesn't fail with a `KeyError` but returns an
    :class:`Undefined` object for missing variables.
    """
    # XXX: we want to eventually make this be a deprecation warning and
    # remove it.
    _legacy_resolve_mode = False
    _fast_resolve_mode = False

    def __init__(self, environment, parent, name, blocks):
        self.parent = parent
        self.vars = {}
        self.environment = environment
        self.eval_ctx = EvalContext(self.environment, name)
        self.exported_vars = set()
        self.name = name

        # create the initial mapping of blocks.  Whenever template inheritance
        # takes place the runtime will update this mapping with the new blocks
        # from the template.
        self.blocks = dict((k, [v]) for k, v in iteritems(blocks))

        # In case we detect the fast resolve mode we can set up an alias
        # here that bypasses the legacy code logic.
        if self._fast_resolve_mode:
            self.resolve_or_missing = MethodType(resolve_or_missing, self)

    def super(self, name, current):
        """Render a parent block."""
        try:
            blocks = self.blocks[name]
            index = blocks.index(current) + 1
            blocks[index]
        except LookupError:
            return self.environment.undefined('there is no parent block '
                                              'called %r.' % name,
                                              name='super')
        return BlockReference(name, self, blocks, index)

    def get(self, key, default=None):
        """Returns an item from the template context, if it doesn't exist
        `default` is returned.
        """
        try:
            return self[key]
        except KeyError:
            return default

    def resolve(self, key):
        """Looks up a variable like `__getitem__` or `get` but returns an
        :class:`Undefined` object with the name of the name looked up.
        """
        if self._legacy_resolve_mode:
            rv = resolve_or_missing(self, key)
        else:
            rv = self.resolve_or_missing(key)
        if rv is missing:
            return self.environment.undefined(name=key)
        return rv

    def resolve_or_missing(self, key):
        """Resolves a variable like :meth:`resolve` but returns the
        special `missing` value if it cannot be found.
        """
        if self._legacy_resolve_mode:
            rv = self.resolve(key)
            if isinstance(rv, Undefined):
                rv = missing
            return rv
        return resolve_or_missing(self, key)

    def get_exported(self):
        """Get a new dict with the exported variables."""
        return dict((k, self.vars[k]) for k in self.exported_vars)

    def get_all(self):
        """Return the complete context as dict including the exported
        variables.  For optimizations reasons this might not return an
        actual copy so be careful with using it.
        """
        if not self.vars:
            return self.parent
        if not self.parent:
            return self.vars
        return dict(self.parent, **self.vars)

    @internalcode
    def call(__self, __obj, *args, **kwargs):
        """Call the callable with the arguments and keyword arguments
        provided but inject the active context or environment as first
        argument if the callable is a :func:`contextfunction` or
        :func:`environmentfunction`.
        """
        if __debug__:
            __traceback_hide__ = True  # noqa

        # Allow callable classes to take a context
        if hasattr(__obj, '__call__'):
            fn = __obj.__call__
            for fn_type in ('contextfunction',
                            'evalcontextfunction',
                            'environmentfunction'):
                if hasattr(fn, fn_type):
                    __obj = fn
                    break

        if isinstance(__obj, _context_function_types):
            if getattr(__obj, 'contextfunction', 0):
                args = (__self,) + args
            elif getattr(__obj, 'evalcontextfunction', 0):
                args = (__self.eval_ctx,) + args
            elif getattr(__obj, 'environmentfunction', 0):
                args = (__self.environment,) + args
        try:
            return __obj(*args, **kwargs)
        except StopIteration:
            return __self.environment.undefined('value was undefined because '
                                                'a callable raised a '
                                                'StopIteration exception')

    def derived(self, locals=None):
        """Internal helper function to create a derived context.  This is
        used in situations where the system needs a new context in the same
        template that is independent.
        """
        context = new_context(self.environment, self.name, {},
                              self.get_all(), True, None, locals)
        context.eval_ctx = self.eval_ctx
        context.blocks.update((k, list(v)) for k, v in iteritems(self.blocks))
        return context

    def _all(meth):
        proxy = lambda self: getattr(self.get_all(), meth)()
        proxy.__doc__ = getattr(dict, meth).__doc__
        proxy.__name__ = meth
        return proxy

    keys = _all('keys')
    values = _all('values')
    items = _all('items')

    # not available on python 3
    if PY2:
        iterkeys = _all('iterkeys')
        itervalues = _all('itervalues')
        iteritems = _all('iteritems')
    del _all

    def __contains__(self, name):
        return name in self.vars or name in self.parent

    def __getitem__(self, key):
        """Lookup a variable or raise `KeyError` if the variable is
        undefined.
        """
        item = self.resolve_or_missing(key)
        if item is missing:
            raise KeyError(key)
        return item

    def __repr__(self):
        return '<%s %s of %r>' % (
            self.__class__.__name__,
            repr(self.get_all()),
            self.name
        )


abc.Mapping.register(Context)


class BlockReference(object):
    """One block on a template reference."""

    def __init__(self, name, context, stack, depth):
        self.name = name
        self._context = context
        self._stack = stack
        self._depth = depth

    @property
    def super(self):
        """Super the block."""
        if self._depth + 1 >= len(self._stack):
            return self._context.environment. \
                undefined('there is no parent block called %r.' %
                          self.name, name='super')
        return BlockReference(self.name, self._context, self._stack,
                              self._depth + 1)

    @internalcode
    def __call__(self):
        rv = concat(self._stack[self._depth](self._context))
        if self._context.eval_ctx.autoescape:
            rv = Markup(rv)
        return rv


class LoopContextBase(object):
    """A loop context for dynamic iteration."""

    _before = _first_iteration
    _current = _first_iteration
    _after = _last_iteration
    _length = None

    def __init__(self, undefined, recurse=None, depth0=0):
        self._undefined = undefined
        self._recurse = recurse
        self.index0 = -1
        self.depth0 = depth0
        self._last_checked_value = missing

    def cycle(self, *args):
        """Cycles among the arguments with the current loop index."""
        if not args:
            raise TypeError('no items for cycling given')
        return args[self.index0 % len(args)]

    def changed(self, *value):
        """Checks whether the value has changed since the last call."""
        if self._last_checked_value != value:
            self._last_checked_value = value
            return True
        return False

    first = property(lambda x: x.index0 == 0)
    last = property(lambda x: x._after is _last_iteration)
    index = property(lambda x: x.index0 + 1)
    revindex = property(lambda x: x.length - x.index0)
    revindex0 = property(lambda x: x.length - x.index)
    depth = property(lambda x: x.depth0 + 1)

    @property
    def previtem(self):
        if self._before is _first_iteration:
            return self._undefined('there is no previous item')
        return self._before

    @property
    def nextitem(self):
        if self._after is _last_iteration:
            return self._undefined('there is no next item')
        return self._after

    def __len__(self):
        return self.length

    @internalcode
    def loop(self, iterable):
        if self._recurse is None:
            raise TypeError('Tried to call non recursive loop.  Maybe you '
                            "forgot the 'recursive' modifier.")
        return self._recurse(iterable, self._recurse, self.depth0 + 1)

    # a nifty trick to enhance the error message if someone tried to call
    # the the loop without or with too many arguments.
    __call__ = loop
    del loop

    def __repr__(self):
        return '<%s %r/%r>' % (
            self.__class__.__name__,
            self.index,
            self.length
        )


class LoopContext(LoopContextBase):

    def __init__(self, iterable, undefined, recurse=None, depth0=0):
        LoopContextBase.__init__(self, undefined, recurse, depth0)
        self._iterator = iter(iterable)

        # try to get the length of the iterable early.  This must be done
        # here because there are some broken iterators around where there
        # __len__ is the number of iterations left (i'm looking at your
        # listreverseiterator!).
        try:
            self._length = len(iterable)
        except (TypeError, AttributeError):
            self._length = None
        self._after = self._safe_next()

    @property
    def length(self):
        if self._length is None:
            # if was not possible to get the length of the iterator when
            # the loop context was created (ie: iterating over a generator)
            # we have to convert the iterable into a sequence and use the
            # length of that + the number of iterations so far.
            iterable = tuple(self._iterator)
            self._iterator = iter(iterable)
            iterations_done = self.index0 + 2
            self._length = len(iterable) + iterations_done
        return self._length

    def __iter__(self):
        return LoopContextIterator(self)

    def _safe_next(self):
        try:
            return next(self._iterator)
        except StopIteration:
            return _last_iteration


@implements_iterator
class LoopContextIterator(object):
    """The iterator for a loop context."""
    __slots__ = ('context',)

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

    def __iter__(self):
        return self

    def __next__(self):
        ctx = self.context
        ctx.index0 += 1
        if ctx._after is _last_iteration:
            raise StopIteration()
        ctx._before = ctx._current
        ctx._current = ctx._after
        ctx._after = ctx._safe_next()
        return ctx._current, ctx


class Macro(object):
    """Wraps a macro function."""

    def __init__(self, environment, func, name, arguments,
                 catch_kwargs, catch_varargs, caller,
                 default_autoescape=None):
        self._environment = environment
        self._func = func
        self._argument_count = len(arguments)
        self.name = name
        self.arguments = arguments
        self.catch_kwargs = catch_kwargs
        self.catch_varargs = catch_varargs
        self.caller = caller
        self.explicit_caller = 'caller' in arguments
        if default_autoescape is None:
            default_autoescape = environment.autoescape
        self._default_autoescape = default_autoescape

    @internalcode
    @evalcontextfunction
    def __call__(self, *args, **kwargs):
        # This requires a bit of explanation,  In the past we used to
        # decide largely based on compile-time information if a macro is
        # safe or unsafe.  While there was a volatile mode it was largely
        # unused for deciding on escaping.  This turns out to be
        # problemtic for macros because if a macro is safe or not not so
        # much depends on the escape mode when it was defined but when it
        # was used.
        #
        # Because however we export macros from the module system and
        # there are historic callers that do not pass an eval context (and
        # will continue to not pass one), we need to perform an instance
        # check here.
        #
        # This is considered safe because an eval context is not a valid
        # argument to callables otherwise anwyays.  Worst case here is
        # that if no eval context is passed we fall back to the compile
        # time autoescape flag.
        if args and isinstance(args[0], EvalContext):
            autoescape = args[0].autoescape
            args = args[1:]
        else:
            autoescape = self._default_autoescape

        # try to consume the positional arguments
        arguments = list(args[:self._argument_count])
        off = len(arguments)

        # For information why this is necessary refer to the handling
        # of caller in the `macro_body` handler in the compiler.
        found_caller = False

        # if the number of arguments consumed is not the number of
        # arguments expected we start filling in keyword arguments
        # and defaults.
        if off != self._argument_count:
            for idx, name in enumerate(self.arguments[len(arguments):]):
                try:
                    value = kwargs.pop(name)
                except KeyError:
                    value = missing
                if name == 'caller':
                    found_caller = True
                arguments.append(value)
        else:
            found_caller = self.explicit_caller

        # it's important that the order of these arguments does not change
        # if not also changed in the compiler's `function_scoping` method.
        # the order is caller, keyword arguments, positional arguments!
        if self.caller and not found_caller:
            caller = kwargs.pop('caller', None)
            if caller is None:
                caller = self._environment.undefined('No caller defined',
                                                     name='caller')
            arguments.append(caller)

        if self.catch_kwargs:
            arguments.append(kwargs)
        elif kwargs:
            if 'caller' in kwargs:
                raise TypeError('macro %r was invoked with two values for '
                                'the special caller argument.  This is '
                                'most likely a bug.' % self.name)
            raise TypeError('macro %r takes no keyword argument %r' %
                            (self.name, next(iter(kwargs))))
        if self.catch_varargs:
            arguments.append(args[self._argument_count:])
        elif len(args) > self._argument_count:
            raise TypeError('macro %r takes not more than %d argument(s)' %
                            (self.name, len(self.arguments)))

        return self._invoke(arguments, autoescape)

    def _invoke(self, arguments, autoescape):
        """This method is being swapped out by the async implementation."""
        rv = self._func(*arguments)
        if autoescape:
            rv = Markup(rv)
        return rv

    def __repr__(self):
        return '<%s %s>' % (
            self.__class__.__name__,
            self.name is None and 'anonymous' or repr(self.name)
        )


@implements_to_string
class Undefined(object):
    """The default undefined type.  This undefined type can be printed and
    iterated over, but every other access will raise an :exc:`UndefinedError`:

    >>> foo = Undefined(name='foo')
    >>> str(foo)
    ''
    >>> not foo
    True
    >>> foo + 42
    Traceback (most recent call last):
      ...
    jinja2.exceptions.UndefinedError: 'foo' is undefined
    """
    __slots__ = ('_undefined_hint', '_undefined_obj', '_undefined_name',
                 '_undefined_exception')

    def __init__(self, hint=None, obj=missing, name=None, exc=UndefinedError):
        self._undefined_hint = hint
        self._undefined_obj = obj
        self._undefined_name = name
        self._undefined_exception = exc

    @internalcode
    def _fail_with_undefined_error(self, *args, **kwargs):
        """Regular callback function for undefined objects that raises an
        `UndefinedError` on call.
        """
        if self._undefined_hint is None:
            if self._undefined_obj is missing:
                hint = '%r is undefined' % self._undefined_name
            elif not isinstance(self._undefined_name, string_types):
                hint = '%s has no element %r' % (
                    object_type_repr(self._undefined_obj),
                    self._undefined_name
                )
            else:
                hint = '%r has no attribute %r' % (
                    object_type_repr(self._undefined_obj),
                    self._undefined_name
                )
        else:
            hint = self._undefined_hint
        raise self._undefined_exception(hint)

    @internalcode
    def __getattr__(self, name):
        if name[:2] == '__':
            raise AttributeError(name)
        return self._fail_with_undefined_error()

    __add__ = __radd__ = __mul__ = __rmul__ = __div__ = __rdiv__ = \
        __truediv__ = __rtruediv__ = __floordiv__ = __rfloordiv__ = \
        __mod__ = __rmod__ = __pos__ = __neg__ = __call__ = \
        __getitem__ = __lt__ = __le__ = __gt__ = __ge__ = __int__ = \
        __float__ = __complex__ = __pow__ = __rpow__ = __sub__ = \
        __rsub__ = _fail_with_undefined_error

    def __eq__(self, other):
        return type(self) is type(other)

    def __ne__(self, other):
        return not self.__eq__(other)

    def __hash__(self):
        return id(type(self))

    def __str__(self):
        return u''

    def __len__(self):
        return 0

    def __iter__(self):
        if 0:
            yield None

    def __nonzero__(self):
        return False
    __bool__ = __nonzero__

    def __repr__(self):
        return 'Undefined'


def make_logging_undefined(logger=None, base=None):
    """Given a logger object this returns a new undefined class that will
    log certain failures.  It will log iterations and printing.  If no
    logger is given a default logger is created.

    Example::

        logger = logging.getLogger(__name__)
        LoggingUndefined = make_logging_undefined(
            logger=logger,
            base=Undefined
        )

    .. versionadded:: 2.8

    :param logger: the logger to use.  If not provided, a default logger
                   is created.
    :param base: the base class to add logging functionality to.  This
                 defaults to :class:`Undefined`.
    """
    if logger is None:
        import logging
        logger = logging.getLogger(__name__)
        logger.addHandler(logging.StreamHandler(sys.stderr))
    if base is None:
        base = Undefined

    def _log_message(undef):
        if undef._undefined_hint is None:
            if undef._undefined_obj is missing:
                hint = '%s is undefined' % undef._undefined_name
            elif not isinstance(undef._undefined_name, string_types):
                hint = '%s has no element %s' % (
                    object_type_repr(undef._undefined_obj),
                    undef._undefined_name)
            else:
                hint = '%s has no attribute %s' % (
                    object_type_repr(undef._undefined_obj),
                    undef._undefined_name)
        else:
            hint = undef._undefined_hint
        logger.warning('Template variable warning: %s', hint)

    class LoggingUndefined(base):

        def _fail_with_undefined_error(self, *args, **kwargs):
            try:
                return base._fail_with_undefined_error(self, *args, **kwargs)
            except self._undefined_exception as e:
                logger.error('Template variable error: %s', str(e))
                raise e

        def __str__(self):
            rv = base.__str__(self)
            _log_message(self)
            return rv

        def __iter__(self):
            rv = base.__iter__(self)
            _log_message(self)
            return rv

        if PY2:
            def __nonzero__(self):
                rv = base.__nonzero__(self)
                _log_message(self)
                return rv

            def __unicode__(self):
                rv = base.__unicode__(self)
                _log_message(self)
                return rv
        else:
            def __bool__(self):
                rv = base.__bool__(self)
                _log_message(self)
                return rv

    return LoggingUndefined


# No @implements_to_string decorator here because __str__
# is not overwritten from Undefined in this class.
# This would cause a recursion error in Python 2.
class ChainableUndefined(Undefined):
    """An undefined that is chainable, where both
    __getattr__ and __getitem__ return itself rather than
    raising an :exc:`UndefinedError`:

    >>> foo = ChainableUndefined(name='foo')
    >>> str(foo.bar['baz'])
    ''
    >>> foo.bar['baz'] + 42
    Traceback (most recent call last):
      ...
    jinja2.exceptions.UndefinedError: 'foo' is undefined

    .. versionadded:: 2.11
    """
    __slots__ = ()

    def __getattr__(self, _):
        return self

    __getitem__ = __getattr__


@implements_to_string
class DebugUndefined(Undefined):
    """An undefined that returns the debug info when printed.

    >>> foo = DebugUndefined(name='foo')
    >>> str(foo)
    '{{ foo }}'
    >>> not foo
    True
    >>> foo + 42
    Traceback (most recent call last):
      ...
    jinja2.exceptions.UndefinedError: 'foo' is undefined
    """
    __slots__ = ()

    def __str__(self):
        if self._undefined_hint is None:
            if self._undefined_obj is missing:
                return u'{{ %s }}' % self._undefined_name
            return '{{ no such element: %s[%r] }}' % (
                object_type_repr(self._undefined_obj),
                self._undefined_name
            )
        return u'{{ undefined value printed: %s }}' % self._undefined_hint


@implements_to_string
class StrictUndefined(Undefined):
    """An undefined that barks on print and iteration as well as boolean
    tests and all kinds of comparisons.  In other words: you can do nothing
    with it except checking if it's defined using the `defined` test.

    >>> foo = StrictUndefined(name='foo')
    >>> str(foo)
    Traceback (most recent call last):
      ...
    jinja2.exceptions.UndefinedError: 'foo' is undefined
    >>> not foo
    Traceback (most recent call last):
      ...
    jinja2.exceptions.UndefinedError: 'foo' is undefined
    >>> foo + 42
    Traceback (most recent call last):
      ...
    jinja2.exceptions.UndefinedError: 'foo' is undefined
    """
    __slots__ = ()
    __iter__ = __str__ = __len__ = __nonzero__ = __eq__ = \
        __ne__ = __bool__ = __hash__ = \
        Undefined._fail_with_undefined_error


# remove remaining slots attributes, after the metaclass did the magic they
# are unneeded and irritating as they contain wrong data for the subclasses.
del Undefined.__slots__, ChainableUndefined.__slots__, \
    DebugUndefined.__slots__, StrictUndefined.__slots__