extlinks.py

"""Extension to save typing and prevent hard-coding of base URLs in reST files.

This adds a new config value called ``extlinks`` that is created like this::

   extlinks = {'exmpl': ('https://example.invalid/%s.html', caption), ...}

Now you can use e.g. :exmpl:`foo` in your documents.  This will create a
link to ``https://example.invalid/foo.html``.  The link caption depends on
the *caption* value given:

- If it is ``None``, the caption will be the full URL.
- If it is a string, it must contain ``%s`` exactly once.  In this case the
  caption will be *caption* with the role content substituted for ``%s``.

You can also give an explicit caption, e.g. :exmpl:`Foo <foo>`.

Both, the url string and the caption string must escape ``%`` as ``%%``.
"""

import re
import sys
from typing import Any, Dict, List, Tuple

from docutils import nodes, utils
from docutils.nodes import Node, system_message
from docutils.parsers.rst.states import Inliner

import sphinx
from sphinx.application import Sphinx
from sphinx.locale import __
from sphinx.transforms.post_transforms import SphinxPostTransform
from sphinx.util import logging, rst
from sphinx.util.nodes import split_explicit_title
from sphinx.util.typing import RoleFunction

logger = logging.getLogger(__name__)


class ExternalLinksChecker(SphinxPostTransform):
    """
    For each external link, check if it can be replaced by an extlink.

    We treat each ``reference`` node without ``internal`` attribute as an external link.
    """

    default_priority = 500

    def run(self, **kwargs: Any) -> None:
        if not self.config.extlinks_detect_hardcoded_links:
            return

        for refnode in self.document.findall(nodes.reference):
            self.check_uri(refnode)

    def check_uri(self, refnode: nodes.reference) -> None:
        """
        If the URI in ``refnode`` has a replacement in ``extlinks``,
        emit a warning with a replacement suggestion.
        """
        if 'internal' in refnode or 'refuri' not in refnode:
            return

        uri = refnode['refuri']
        title = refnode.astext()

        for alias, (base_uri, _caption) in self.app.config.extlinks.items():
            if sys.version_info < (3, 7):
                # Replace a leading backslash because re.escape() inserts a backslash before %
                # on python 3.6
                uri_pattern = re.compile(re.escape(base_uri).replace('\\%s', '(?P<value>.+)'))
            else:
                uri_pattern = re.compile(re.escape(base_uri).replace('%s', '(?P<value>.+)'))

            match = uri_pattern.match(uri)
            if match and match.groupdict().get('value'):
                # build a replacement suggestion
                msg = __('hardcoded link %r could be replaced by an extlink '
                         '(try using %r instead)')
                value = match.groupdict().get('value')
                if uri != title:
                    replacement = f":{alias}:`{rst.escape(title)} <{value}>`"
                else:
                    replacement = f":{alias}:`{value}`"
                logger.warning(msg, uri, replacement, location=refnode)


def make_link_role(name: str, base_url: str, caption: str) -> RoleFunction:
    # Check whether we have base_url and caption strings have an '%s' for
    # expansion.  If not, fall back the the old behaviour and use the string as
    # a prefix.
    # Remark: It is an implementation detail that we use Pythons %-formatting.
    # So far we only expose ``%s`` and require quoting of ``%`` using ``%%``.
    try:
        base_url % 'dummy'
    except (TypeError, ValueError):
        logger.warn(__('extlinks: Sphinx-6.0 will require base URL to '
                       'contain exactly one \'%s\' and all other \'%\' need '
                       'to be escaped as \'%%\'.'))  # RemovedInSphinx60Warning
        base_url = base_url.replace('%', '%%') + '%s'
    if caption is not None:
        try:
            caption % 'dummy'
        except (TypeError, ValueError):
            logger.warning(__('extlinks: Sphinx-6.0 will require a caption string to '
                              'contain exactly one \'%s\' and all other \'%\' need '
                              'to be escaped as \'%%\'.'))  # RemovedInSphinx60Warning
            caption = caption.replace('%', '%%') + '%s'

    def role(typ: str, rawtext: str, text: str, lineno: int,
             inliner: Inliner, options: Dict = {}, content: List[str] = []
             ) -> Tuple[List[Node], List[system_message]]:
        text = utils.unescape(text)
        has_explicit_title, title, part = split_explicit_title(text)
        full_url = base_url % part
        if not has_explicit_title:
            if caption is None:
                title = full_url
            else:
                title = caption % part
        pnode = nodes.reference(title, title, internal=False, refuri=full_url)
        return [pnode], []
    return role


def setup_link_roles(app: Sphinx) -> None:
    for name, (base_url, caption) in app.config.extlinks.items():
        app.add_role(name, make_link_role(name, base_url, caption))


def setup(app: Sphinx) -> Dict[str, Any]:
    app.add_config_value('extlinks', {}, 'env')
    app.add_config_value('extlinks_detect_hardcoded_links', False, 'env')

    app.connect('builder-inited', setup_link_roles)
    app.add_post_transform(ExternalLinksChecker)
    return {'version': sphinx.__display_version__, 'parallel_read_safe': True}