jinja2/ext.py

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

    Jinja extensions allow to add custom tags similar to the way django custom
    tags work.  By default two example extensions exist: an i18n and a cache
    extension.

    :copyright: (c) 2010 by the Jinja Team.
    :license: BSD.
"""
from collections import deque
from jinja2 import nodes
from jinja2.defaults import *
from jinja2.environment import get_spontaneous_environment
from jinja2.runtime import Undefined, concat
from jinja2.exceptions import TemplateAssertionError, TemplateSyntaxError
from jinja2.utils import contextfunction, import_string, Markup, next


# the only real useful gettext functions for a Jinja template.  Note
# that ugettext must be assigned to gettext as Jinja doesn't support
# non unicode strings.
GETTEXT_FUNCTIONS = ('_', 'gettext', 'ngettext')


class ExtensionRegistry(type):
    """Gives the extension an unique identifier."""

    def __new__(cls, name, bases, d):
        rv = type.__new__(cls, name, bases, d)
        rv.identifier = rv.__module__ + '.' + rv.__name__
        return rv


class Extension(object):
    """Extensions can be used to add extra functionality to the Jinja template
    system at the parser level.  Custom extensions are bound to an environment
    but may not store environment specific data on `self`.  The reason for
    this is that an extension can be bound to another environment (for
    overlays) by creating a copy and reassigning the `environment` attribute.

    As extensions are created by the environment they cannot accept any
    arguments for configuration.  One may want to work around that by using
    a factory function, but that is not possible as extensions are identified
    by their import name.  The correct way to configure the extension is
    storing the configuration values on the environment.  Because this way the
    environment ends up acting as central configuration storage the
    attributes may clash which is why extensions have to ensure that the names
    they choose for configuration are not too generic.  ``prefix`` for example
    is a terrible name, ``fragment_cache_prefix`` on the other hand is a good
    name as includes the name of the extension (fragment cache).
    """
    __metaclass__ = ExtensionRegistry

    #: if this extension parses this is the list of tags it's listening to.
    tags = set()

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

    def bind(self, environment):
        """Create a copy of this extension bound to another environment."""
        rv = object.__new__(self.__class__)
        rv.__dict__.update(self.__dict__)
        rv.environment = environment
        return rv

    def preprocess(self, source, name, filename=None):
        """This method is called before the actual lexing and can be used to
        preprocess the source.  The `filename` is optional.  The return value
        must be the preprocessed source.
        """
        return source

    def filter_stream(self, stream):
        """It's passed a :class:`~jinja2.lexer.TokenStream` that can be used
        to filter tokens returned.  This method has to return an iterable of
        :class:`~jinja2.lexer.Token`\s, but it doesn't have to return a
        :class:`~jinja2.lexer.TokenStream`.

        In the `ext` folder of the Jinja2 source distribution there is a file
        called `inlinegettext.py` which implements a filter that utilizes this
        method.
        """
        return stream

    def parse(self, parser):
        """If any of the :attr:`tags` matched this method is called with the
        parser as first argument.  The token the parser stream is pointing at
        is the name token that matched.  This method has to return one or a
        list of multiple nodes.
        """
        raise NotImplementedError()

    def attr(self, name, lineno=None):
        """Return an attribute node for the current extension.  This is useful
        to pass constants on extensions to generated template code::

            self.attr('_my_attribute', lineno=lineno)
        """
        return nodes.ExtensionAttribute(self.identifier, name, lineno=lineno)

    def call_method(self, name, args=None, kwargs=None, dyn_args=None,
                    dyn_kwargs=None, lineno=None):
        """Call a method of the extension.  This is a shortcut for
        :meth:`attr` + :class:`jinja2.nodes.Call`.
        """
        if args is None:
            args = []
        if kwargs is None:
            kwargs = []
        return nodes.Call(self.attr(name, lineno=lineno), args, kwargs,
                          dyn_args, dyn_kwargs, lineno=lineno)


@contextfunction
def _gettext_alias(context, string):
    return context.resolve('gettext')(string)


class InternationalizationExtension(Extension):
    """This extension adds gettext support to Jinja2."""
    tags = set(['trans'])

    # TODO: the i18n extension is currently reevaluating values in a few
    # situations.  Take this example:
    #   {% trans count=something() %}{{ count }} foo{% pluralize
    #     %}{{ count }} fooss{% endtrans %}
    # something is called twice here.  One time for the gettext value and
    # the other time for the n-parameter of the ngettext function.

    def __init__(self, environment):
        Extension.__init__(self, environment)
        environment.globals['_'] = _gettext_alias
        environment.extend(
            install_gettext_translations=self._install,
            install_null_translations=self._install_null,
            uninstall_gettext_translations=self._uninstall,
            extract_translations=self._extract
        )

    def _install(self, translations):
        gettext = getattr(translations, 'ugettext', None)
        if gettext is None:
            gettext = translations.gettext
        ngettext = getattr(translations, 'ungettext', None)
        if ngettext is None:
            ngettext = translations.ngettext
        self.environment.globals.update(gettext=gettext, ngettext=ngettext)

    def _install_null(self):
        self.environment.globals.update(
            gettext=lambda x: x,
            ngettext=lambda s, p, n: (n != 1 and (p,) or (s,))[0]
        )

    def _uninstall(self, translations):
        for key in 'gettext', 'ngettext':
            self.environment.globals.pop(key, None)

    def _extract(self, source, gettext_functions=GETTEXT_FUNCTIONS):
        if isinstance(source, basestring):
            source = self.environment.parse(source)
        return extract_from_ast(source, gettext_functions)

    def parse(self, parser):
        """Parse a translatable tag."""
        lineno = next(parser.stream).lineno

        # find all the variables referenced.  Additionally a variable can be
        # defined in the body of the trans block too, but this is checked at
        # a later state.
        plural_expr = None
        variables = {}
        while parser.stream.current.type != 'block_end':
            if variables:
                parser.stream.expect('comma')

            # skip colon for python compatibility
            if parser.stream.skip_if('colon'):
                break

            name = parser.stream.expect('name')
            if name.value in variables:
                parser.fail('translatable variable %r defined twice.' %
                            name.value, name.lineno,
                            exc=TemplateAssertionError)

            # expressions
            if parser.stream.current.type == 'assign':
                next(parser.stream)
                variables[name.value] = var = parser.parse_expression()
            else:
                variables[name.value] = var = nodes.Name(name.value, 'load')
            if plural_expr is None:
                plural_expr = var

        parser.stream.expect('block_end')

        plural = plural_names = None
        have_plural = False
        referenced = set()

        # now parse until endtrans or pluralize
        singular_names, singular = self._parse_block(parser, True)
        if singular_names:
            referenced.update(singular_names)
            if plural_expr is None:
                plural_expr = nodes.Name(singular_names[0], 'load')

        # if we have a pluralize block, we parse that too
        if parser.stream.current.test('name:pluralize'):
            have_plural = True
            next(parser.stream)
            if parser.stream.current.type != 'block_end':
                name = parser.stream.expect('name')
                if name.value not in variables:
                    parser.fail('unknown variable %r for pluralization' %
                                name.value, name.lineno,
                                exc=TemplateAssertionError)
                plural_expr = variables[name.value]
            parser.stream.expect('block_end')
            plural_names, plural = self._parse_block(parser, False)
            next(parser.stream)
            referenced.update(plural_names)
        else:
            next(parser.stream)

        # register free names as simple name expressions
        for var in referenced:
            if var not in variables:
                variables[var] = nodes.Name(var, 'load')

        # no variables referenced?  no need to escape
        if not referenced:
            singular = singular.replace('%%', '%')
            if plural:
                plural = plural.replace('%%', '%')

        if not have_plural:
            plural_expr = None
        elif plural_expr is None:
            parser.fail('pluralize without variables', lineno)

        if variables:
            variables = nodes.Dict([nodes.Pair(nodes.Const(x, lineno=lineno), y)
                                    for x, y in variables.items()])
        else:
            variables = None

        node = self._make_node(singular, plural, variables, plural_expr)
        node.set_lineno(lineno)
        return node

    def _parse_block(self, parser, allow_pluralize):
        """Parse until the next block tag with a given name."""
        referenced = []
        buf = []
        while 1:
            if parser.stream.current.type == 'data':
                buf.append(parser.stream.current.value.replace('%', '%%'))
                next(parser.stream)
            elif parser.stream.current.type == 'variable_begin':
                next(parser.stream)
                name = parser.stream.expect('name').value
                referenced.append(name)
                buf.append('%%(%s)s' % name)
                parser.stream.expect('variable_end')
            elif parser.stream.current.type == 'block_begin':
                next(parser.stream)
                if parser.stream.current.test('name:endtrans'):
                    break
                elif parser.stream.current.test('name:pluralize'):
                    if allow_pluralize:
                        break
                    parser.fail('a translatable section can have only one '
                                'pluralize section')
                parser.fail('control structures in translatable sections are '
                            'not allowed')
            elif parser.stream.eos:
                parser.fail('unclosed translation block')
            else:
                assert False, 'internal parser error'

        return referenced, concat(buf)

    def _make_node(self, singular, plural, variables, plural_expr):
        """Generates a useful node from the data provided."""
        # singular only:
        if plural_expr is None:
            gettext = nodes.Name('gettext', 'load')
            node = nodes.Call(gettext, [nodes.Const(singular)],
                              [], None, None)

        # singular and plural
        else:
            ngettext = nodes.Name('ngettext', 'load')
            node = nodes.Call(ngettext, [
                nodes.Const(singular),
                nodes.Const(plural),
                plural_expr
            ], [], None, None)

        # mark the return value as safe if we are in an
        # environment with autoescaping turned on
        if self.environment.autoescape:
            node = nodes.MarkSafe(node)

        if variables:
            node = nodes.Mod(node, variables)
        return nodes.Output([node])


class ExprStmtExtension(Extension):
    """Adds a `do` tag to Jinja2 that works like the print statement just
    that it doesn't print the return value.
    """
    tags = set(['do'])

    def parse(self, parser):
        node = nodes.ExprStmt(lineno=next(parser.stream).lineno)
        node.node = parser.parse_tuple()
        return node


class LoopControlExtension(Extension):
    """Adds break and continue to the template engine."""
    tags = set(['break', 'continue'])

    def parse(self, parser):
        token = next(parser.stream)
        if token.value == 'break':
            return nodes.Break(lineno=token.lineno)
        return nodes.Continue(lineno=token.lineno)


def extract_from_ast(node, gettext_functions=GETTEXT_FUNCTIONS,
                     babel_style=True):
    """Extract localizable strings from the given template node.  Per
    default this function returns matches in babel style that means non string
    parameters as well as keyword arguments are returned as `None`.  This
    allows Babel to figure out what you really meant if you are using
    gettext functions that allow keyword arguments for placeholder expansion.
    If you don't want that behavior set the `babel_style` parameter to `False`
    which causes only strings to be returned and parameters are always stored
    in tuples.  As a consequence invalid gettext calls (calls without a single
    string parameter or string parameters after non-string parameters) are
    skipped.

    This example explains the behavior:

    >>> from jinja2 import Environment
    >>> env = Environment()
    >>> node = env.parse('{{ (_("foo"), _(), ngettext("foo", "bar", 42)) }}')
    >>> list(extract_from_ast(node))
    [(1, '_', 'foo'), (1, '_', ()), (1, 'ngettext', ('foo', 'bar', None))]
    >>> list(extract_from_ast(node, babel_style=False))
    [(1, '_', ('foo',)), (1, 'ngettext', ('foo', 'bar'))]

    For every string found this function yields a ``(lineno, function,
    message)`` tuple, where:

    * ``lineno`` is the number of the line on which the string was found,
    * ``function`` is the name of the ``gettext`` function used (if the
      string was extracted from embedded Python code), and
    *  ``message`` is the string itself (a ``unicode`` object, or a tuple
       of ``unicode`` objects for functions with multiple string arguments).

    This extraction function operates on the AST and is because of that unable
    to extract any comments.  For comment support you have to use the babel
    extraction interface or extract comments yourself.
    """
    for node in node.find_all(nodes.Call):
        if not isinstance(node.node, nodes.Name) or \
           node.node.name not in gettext_functions:
            continue

        strings = []
        for arg in node.args:
            if isinstance(arg, nodes.Const) and \
               isinstance(arg.value, basestring):
                strings.append(arg.value)
            else:
                strings.append(None)

        for arg in node.kwargs:
            strings.append(None)
        if node.dyn_args is not None:
            strings.append(None)
        if node.dyn_kwargs is not None:
            strings.append(None)

        if not babel_style:
            strings = tuple(x for x in strings if x is not None)
            if not strings:
                continue
        else:
            if len(strings) == 1:
                strings = strings[0]
            else:
                strings = tuple(strings)
        yield node.lineno, node.node.name, strings


class _CommentFinder(object):
    """Helper class to find comments in a token stream.  Can only
    find comments for gettext calls forwards.  Once the comment
    from line 4 is found, a comment for line 1 will not return a
    usable value.
    """

    def __init__(self, tokens, comment_tags):
        self.tokens = tokens
        self.comment_tags = comment_tags
        self.offset = 0
        self.last_lineno = 0

    def find_backwards(self, offset):
        try:
            for _, token_type, token_value in \
                    reversed(self.tokens[self.offset:offset]):
                if token_type in ('comment', 'linecomment'):
                    try:
                        prefix, comment = token_value.split(None, 1)
                    except ValueError:
                        continue
                    if prefix in self.comment_tags:
                        return [comment.rstrip()]
            return []
        finally:
            self.offset = offset

    def find_comments(self, lineno):
        if not self.comment_tags or self.last_lineno > lineno:
            return []
        for idx, (token_lineno, _, _) in enumerate(self.tokens[self.offset:]):
            if token_lineno > lineno:
                return self.find_backwards(self.offset + idx)
        return self.find_backwards(len(self.tokens))


def babel_extract(fileobj, keywords, comment_tags, options):
    """Babel extraction method for Jinja templates.

    .. versionchanged:: 2.3
       Basic support for translation comments was added.  If `comment_tags`
       is now set to a list of keywords for extraction, the extractor will
       try to find the best preceeding comment that begins with one of the
       keywords.  For best results, make sure to not have more than one
       gettext call in one line of code and the matching comment in the
       same line or the line before.

    :param fileobj: the file-like object the messages should be extracted from
    :param keywords: a list of keywords (i.e. function names) that should be
                     recognized as translation functions
    :param comment_tags: a list of translator tags to search for and include
                         in the results.
    :param options: a dictionary of additional options (optional)
    :return: an iterator over ``(lineno, funcname, message, comments)`` tuples.
             (comments will be empty currently)
    """
    extensions = set()
    for extension in options.get('extensions', '').split(','):
        extension = extension.strip()
        if not extension:
            continue
        extensions.add(import_string(extension))
    if InternationalizationExtension not in extensions:
        extensions.add(InternationalizationExtension)

    environment = get_spontaneous_environment(
        options.get('block_start_string', BLOCK_START_STRING),
        options.get('block_end_string', BLOCK_END_STRING),
        options.get('variable_start_string', VARIABLE_START_STRING),
        options.get('variable_end_string', VARIABLE_END_STRING),
        options.get('comment_start_string', COMMENT_START_STRING),
        options.get('comment_end_string', COMMENT_END_STRING),
        options.get('line_statement_prefix') or LINE_STATEMENT_PREFIX,
        options.get('line_comment_prefix') or LINE_COMMENT_PREFIX,
        str(options.get('trim_blocks', TRIM_BLOCKS)).lower() in \
            ('1', 'on', 'yes', 'true'),
        NEWLINE_SEQUENCE, frozenset(extensions),
        # fill with defaults so that environments are shared
        # with other spontaneus environments.  The rest of the
        # arguments are optimizer, undefined, finalize, autoescape,
        # loader, cache size, auto reloading setting and the
        # bytecode cache
        True, Undefined, None, False, None, 0, False, None
    )

    source = fileobj.read().decode(options.get('encoding', 'utf-8'))
    try:
        node = environment.parse(source)
        tokens = list(environment.lex(environment.preprocess(source)))
    except TemplateSyntaxError, e:
        # skip templates with syntax errors
        return

    finder = _CommentFinder(tokens, comment_tags)
    for lineno, func, message in extract_from_ast(node, keywords):
        yield lineno, func, message, finder.find_comments(lineno)


#: nicer import names
i18n = InternationalizationExtension
do = ExprStmtExtension
loopcontrols = LoopControlExtension