markdown/extensions/codehilite.py

"""
CodeHilite Extension for Python-Markdown
========================================

Adds code/syntax highlighting to standard Python-Markdown code blocks.

See <https://Python-Markdown.github.io/extensions/code_hilite>
for documentation.

Original code Copyright 2006-2008 [Waylan Limberg](http://achinghead.com/).

All changes Copyright 2008-2014 The Python Markdown Project

License: [BSD](https://opensource.org/licenses/bsd-license.php)

"""

from . import Extension
from ..treeprocessors import Treeprocessor
from ..util import parseBoolValue

try:  # pragma: no cover
    from pygments import highlight
    from pygments.lexers import get_lexer_by_name, guess_lexer
    from pygments.formatters import get_formatter_by_name
    pygments = True
except ImportError:  # pragma: no cover
    pygments = False


def parse_hl_lines(expr):
    """Support our syntax for emphasizing certain lines of code.

    expr should be like '1 2' to emphasize lines 1 and 2 of a code block.
    Returns a list of ints, the line numbers to emphasize.
    """
    if not expr:
        return []

    try:
        return list(map(int, expr.split()))
    except ValueError:  # pragma: no cover
        return []


# ------------------ The Main CodeHilite Class ----------------------
class CodeHilite:
    """
    Determine language of source code, and pass it on to the Pygments highlighter.

    Usage:
        code = CodeHilite(src=some_code, lang='python')
        html = code.hilite()

    Arguments:
    * src: Source string or any object with a .readline attribute.

    * lang: String name of Pygments lexer to use for highlighting. Default: `None`.

    * guess_lang: Auto-detect which lexer to use. Ignored if `lang` is set to a valid
      value. Default: `True`.

    * use_pygments: Pass code to pygments for code highlighting. If `False`, the code is
      instead wrapped for highlighting by a JavaScript library. Default: `True`.

    * linenums: An alias to Pygments `linenos` formatter option. Default: `None`.

    * css_class: An alias to Pygments `cssclass` formatter option. Default: 'codehilite'.

    * lang_prefix: Prefix prepended to the language when `use_pygments` is `False`.
      Default: "language-".

    Other Options:
    Any other options are accepted and passed on to the lexer and formatter. Therefore,
    valid options include any options which are accepted by the `html` formatter or
    whichever lexer the code's language uses. Note that most lexers do not have any
    options. However, a few have very useful options, such as PHP's `startinline` option.
    Any invalid options are ignored without error.

    Formatter options: https://pygments.org/docs/formatters/#HtmlFormatter
    Lexer Options: https://pygments.org/docs/lexers/

    Advanced Usage:
        code = CodeHilite(
            src = some_code,
            lang = 'php',
            startinline = True,      # Lexer option. Snippet does not start with `<?php`.
            linenostart = 42,        # Formatter option. Snippet starts on line 42.
            hl_lines = [45, 49, 50], # Formatter option. Highlight lines 45, 49, and 50.
            linenos = 'inline'       # Formatter option. Avoid alignment problems.
        )
        html = code.hilite()

    """

    def __init__(self, src, **options):
        self.src = src
        self.lang = options.pop('lang', None)
        self.guess_lang = options.pop('guess_lang', True)
        self.use_pygments = options.pop('use_pygments', True)
        self.lang_prefix = options.pop('lang_prefix', 'language-')

        if 'linenos' not in options:
            options['linenos'] = options.pop('linenums', None)
        if 'cssclass' not in options:
            options['cssclass'] = options.pop('css_class', 'codehilite')
        if 'wrapcode' not in options:
            # Override pygments default
            options['wrapcode'] = True
        # Disallow use of `full` option
        options['full'] = False

        self.options = options

    def hilite(self):
        """
        Pass code to the [Pygments](http://pygments.pocoo.org/) highliter with
        optional line numbers. The output should then be styled with css to
        your liking. No styles are applied by default - only styling hooks
        (i.e.: <span class="k">).

        returns : A string of html.

        """

        self.src = self.src.strip('\n')

        if self.lang is None:
            self._parseHeader()

        if pygments and self.use_pygments:
            try:
                lexer = get_lexer_by_name(self.lang, **self.options)
            except ValueError:
                try:
                    if self.guess_lang:
                        lexer = guess_lexer(self.src, **self.options)
                    else:
                        lexer = get_lexer_by_name('text', **self.options)
                except ValueError:  # pragma: no cover
                    lexer = get_lexer_by_name('text', **self.options)
            formatter = get_formatter_by_name('html', **self.options)
            return highlight(self.src, lexer, formatter)
        else:
            # just escape and build markup usable by JS highlighting libs
            txt = self.src.replace('&', '&amp;')
            txt = txt.replace('<', '&lt;')
            txt = txt.replace('>', '&gt;')
            txt = txt.replace('"', '&quot;')
            classes = []
            if self.lang:
                classes.append('{}{}'.format(self.lang_prefix, self.lang))
            if self.options['linenos']:
                classes.append('linenums')
            class_str = ''
            if classes:
                class_str = ' class="{}"'.format(' '.join(classes))
            return '<pre class="{}"><code{}>{}\n</code></pre>\n'.format(
                self.options['cssclass'],
                class_str,
                txt
            )

    def _parseHeader(self):
        """
        Determines language of a code block from shebang line and whether the
        said line should be removed or left in place. If the sheband line
        contains a path (even a single /) then it is assumed to be a real
        shebang line and left alone. However, if no path is given
        (e.i.: #!python or :::python) then it is assumed to be a mock shebang
        for language identification of a code fragment and removed from the
        code block prior to processing for code highlighting. When a mock
        shebang (e.i: #!python) is found, line numbering is turned on. When
        colons are found in place of a shebang (e.i.: :::python), line
        numbering is left in the current state - off by default.

        Also parses optional list of highlight lines, like:

            :::python hl_lines="1 3"
        """

        import re

        # split text into lines
        lines = self.src.split("\n")
        # pull first line to examine
        fl = lines.pop(0)

        c = re.compile(r'''
            (?:(?:^::+)|(?P<shebang>^[#]!)) # Shebang or 2 or more colons
            (?P<path>(?:/\w+)*[/ ])?        # Zero or 1 path
            (?P<lang>[\w#.+-]*)             # The language
            \s*                             # Arbitrary whitespace
            # Optional highlight lines, single- or double-quote-delimited
            (hl_lines=(?P<quot>"|')(?P<hl_lines>.*?)(?P=quot))?
            ''',  re.VERBOSE)
        # search first line for shebang
        m = c.search(fl)
        if m:
            # we have a match
            try:
                self.lang = m.group('lang').lower()
            except IndexError:  # pragma: no cover
                self.lang = None
            if m.group('path'):
                # path exists - restore first line
                lines.insert(0, fl)
            if self.options['linenos'] is None and m.group('shebang'):
                # Overridable and Shebang exists - use line numbers
                self.options['linenos'] = True

            self.options['hl_lines'] = parse_hl_lines(m.group('hl_lines'))
        else:
            # No match
            lines.insert(0, fl)

        self.src = "\n".join(lines).strip("\n")


# ------------------ The Markdown Extension -------------------------------


class HiliteTreeprocessor(Treeprocessor):
    """ Hilight source code in code blocks. """

    def code_unescape(self, text):
        """Unescape code."""
        text = text.replace("&lt;", "<")
        text = text.replace("&gt;", ">")
        # Escaped '&' should be replaced at the end to avoid
        # conflicting with < and >.
        text = text.replace("&amp;", "&")
        return text

    def run(self, root):
        """ Find code blocks and store in htmlStash. """
        blocks = root.iter('pre')
        for block in blocks:
            if len(block) == 1 and block[0].tag == 'code':
                code = CodeHilite(
                    self.code_unescape(block[0].text),
                    tab_length=self.md.tab_length,
                    style=self.config.pop('pygments_style', 'default'),
                    **self.config
                )
                placeholder = self.md.htmlStash.store(code.hilite())
                # Clear codeblock in etree instance
                block.clear()
                # Change to p element which will later
                # be removed when inserting raw html
                block.tag = 'p'
                block.text = placeholder


class CodeHiliteExtension(Extension):
    """ Add source code hilighting to markdown codeblocks. """

    def __init__(self, **kwargs):
        # define default configs
        self.config = {
            'linenums': [None,
                         "Use lines numbers. True|table|inline=yes, False=no, None=auto"],
            'guess_lang': [True,
                           "Automatic language detection - Default: True"],
            'css_class': ["codehilite",
                          "Set class name for wrapper <div> - "
                          "Default: codehilite"],
            'pygments_style': ['default',
                               'Pygments HTML Formatter Style '
                               '(Colorscheme) - Default: default'],
            'noclasses': [False,
                          'Use inline styles instead of CSS classes - '
                          'Default false'],
            'use_pygments': [True,
                             'Use Pygments to Highlight code blocks. '
                             'Disable if using a JavaScript library. '
                             'Default: True'],
            'lang_prefix': [
                'language-',
                'Prefix prepended to the language when use_pygments is false. Default: "language-"'
            ]
            }

        for key, value in kwargs.items():
            if key in self.config:
                self.setConfig(key, value)
            else:
                # manually set unknown keywords.
                if isinstance(value, str):
                    try:
                        # Attempt to parse str as a bool value
                        value = parseBoolValue(value, preserve_none=True)
                    except ValueError:
                        pass  # Assume it's not a bool value. Use as-is.
                self.config[key] = [value, '']

    def extendMarkdown(self, md):
        """ Add HilitePostprocessor to Markdown instance. """
        hiliter = HiliteTreeprocessor(md)
        hiliter.config = self.getConfigs()
        md.treeprocessors.register(hiliter, 'hilite', 30)

        md.registerExtension(self)


def makeExtension(**kwargs):  # pragma: no cover
    return CodeHiliteExtension(**kwargs)