zulip/zerver/lib/markdown/fenced_code.py

"""
Fenced Code Extension for Python Markdown
=========================================

This extension adds Fenced Code Blocks to Python-Markdown.

    >>> import markdown
    >>> text = '''
    ... A paragraph before a fenced code block:
    ...
    ... ~~~
    ... Fenced code block
    ... ~~~
    ... '''
    >>> html = markdown.markdown(text, extensions=['fenced_code'])
    >>> print html
    <p>A paragraph before a fenced code block:</p>
    <pre><code>Fenced code block
    </code></pre>

Works with safe_mode also (we check this because we are using the HtmlStash):

    >>> print markdown.markdown(text, extensions=['fenced_code'], safe_mode='replace')
    <p>A paragraph before a fenced code block:</p>
    <pre><code>Fenced code block
    </code></pre>

Include tilde's in a code block and wrap with blank lines:

    >>> text = '''
    ... ~~~~~~~~
    ...
    ... ~~~~
    ... ~~~~~~~~'''
    >>> print markdown.markdown(text, extensions=['fenced_code'])
    <pre><code>
    ~~~~
    </code></pre>

Removes trailing whitespace from code blocks that cause horizontal scrolling
    >>> import markdown
    >>> text = '''
    ... A paragraph before a fenced code block:
    ...
    ... ~~~
    ... Fenced code block    \t\t\t\t\t\t\t
    ... ~~~
    ... '''
    >>> html = markdown.markdown(text, extensions=['fenced_code'])
    >>> print html
    <p>A paragraph before a fenced code block:</p>
    <pre><code>Fenced code block
    </code></pre>

Language tags:

    >>> text = '''
    ... ~~~~{.python}
    ... # Some python code
    ... ~~~~'''
    >>> print markdown.markdown(text, extensions=['fenced_code'])
    <pre><code class="python"># Some python code
    </code></pre>

Copyright 2007-2008 [Waylan Limberg](http://achinghead.com/).

Project website: <http://packages.python.org/Markdown/extensions/fenced_code_blocks.html>
Contact: markdown@freewisdom.org

License: BSD (see ../docs/LICENSE for details)

Dependencies:
* [Python 2.4+](http://python.org)
* [Markdown 2.0+](http://packages.python.org/Markdown/)
* [Pygments (optional)](http://pygments.org)

"""
import re
from typing import Any, Callable, Dict, Iterable, List, Mapping, MutableSequence, Optional, Sequence

import lxml.html
from django.utils.html import escape
from markdown import Markdown
from markdown.extensions import Extension, codehilite
from markdown.extensions.codehilite import CodeHiliteExtension, parse_hl_lines
from markdown.preprocessors import Preprocessor
from pygments.lexers import find_lexer_class_by_name
from pygments.util import ClassNotFound

from zerver.lib.exceptions import MarkdownRenderingError
from zerver.lib.markdown.priorities import PREPROCESSOR_PRIORITES
from zerver.lib.tex import render_tex

# Global vars
FENCE_RE = re.compile(
    r"""
    # ~~~ or ```
    (?P<fence>
        ^(?:~{3,}|`{3,})
    )

    [ ]* # spaces

    (?:
        # language, like ".py" or "{javascript}"
        \{?\.?
        (?P<lang>
            [a-zA-Z0-9_+-./#]+
        ) # "py" or "javascript"

        [ ]* # spaces

        # header for features that use fenced block header syntax (like spoilers)
        (?P<header>
            [^ ~`][^~`]*
        )?
        \}?
    )?
    $
    """,
    re.VERBOSE,
)


CODE_WRAP = "<pre><code{}>{}\n</code></pre>"
LANG_TAG = ' class="{}"'


def validate_curl_content(lines: List[str]) -> None:
    error_msg = """
Missing required -X argument in curl command:

{command}
""".strip()

    for line in lines:
        regex = r'curl [-](sS)?X "?(GET|DELETE|PATCH|POST)"?'
        if line.startswith("curl") and re.search(regex, line) is None:
            raise MarkdownRenderingError(error_msg.format(command=line.strip()))


CODE_VALIDATORS: Dict[Optional[str], Callable[[List[str]], None]] = {
    "curl": validate_curl_content,
}


class FencedCodeExtension(Extension):
    def __init__(self, config: Mapping[str, Any] = {}) -> None:
        self.config = {
            "run_content_validators": [
                config.get("run_content_validators", False),
                "Boolean specifying whether to run content validation code in CodeHandler",
            ],
        }

        for key, value in config.items():
            self.setConfig(key, value)

    def extendMarkdown(self, md: Markdown) -> None:
        """Add FencedBlockPreprocessor to the Markdown instance."""
        md.registerExtension(self)
        processor = FencedBlockPreprocessor(
            md, run_content_validators=self.config["run_content_validators"][0]
        )
        md.preprocessors.register(
            processor, "fenced_code_block", PREPROCESSOR_PRIORITES["fenced_code_block"]
        )


class ZulipBaseHandler:
    def __init__(
        self,
        processor: "FencedBlockPreprocessor",
        output: MutableSequence[str],
        fence: Optional[str] = None,
        process_contents: bool = False,
    ) -> None:
        self.processor = processor
        self.output = output
        self.fence = fence
        self.process_contents = process_contents
        self.lines: List[str] = []

    def handle_line(self, line: str) -> None:
        if line.rstrip() == self.fence:
            self.done()
        else:
            self.lines.append(line.rstrip())

    def done(self) -> None:
        if self.lines:
            text = "\n".join(self.lines)
            text = self.format_text(text)

            # For code blocks, the contents should not receive further
            # processing.  Whereas with quote and spoiler blocks, we
            # explicitly want Markdown formatting of the content
            # inside. This behavior is controlled by the
            # process_contents configuration flag.
            if not self.process_contents:
                text = self.processor.placeholder(text)

            processed_lines = text.split("\n")
            self.output.append("")
            self.output.extend(processed_lines)
            self.output.append("")
        self.processor.pop()

    def format_text(self, text: str) -> str:
        """Returns a formatted text.
        Subclasses should override this method.
        """
        raise NotImplementedError()


def generic_handler(
    processor: "FencedBlockPreprocessor",
    output: MutableSequence[str],
    fence: str,
    lang: Optional[str],
    header: Optional[str],
    run_content_validators: bool = False,
    default_language: Optional[str] = None,
) -> ZulipBaseHandler:
    if lang is not None:
        lang = lang.lower()
    if lang in ("quote", "quoted"):
        return QuoteHandler(processor, output, fence, default_language)
    elif lang == "math":
        return TexHandler(processor, output, fence)
    elif lang == "spoiler":
        return SpoilerHandler(processor, output, fence, header)
    else:
        return CodeHandler(processor, output, fence, lang, run_content_validators)


def check_for_new_fence(
    processor: "FencedBlockPreprocessor",
    output: MutableSequence[str],
    line: str,
    run_content_validators: bool = False,
    default_language: Optional[str] = None,
) -> None:
    m = FENCE_RE.match(line)
    if m:
        fence = m.group("fence")
        lang: Optional[str] = m.group("lang")
        header: Optional[str] = m.group("header")
        if not lang and default_language:
            lang = default_language
        handler = generic_handler(
            processor, output, fence, lang, header, run_content_validators, default_language
        )
        processor.push(handler)
    else:
        output.append(line)


class OuterHandler(ZulipBaseHandler):
    def __init__(
        self,
        processor: "FencedBlockPreprocessor",
        output: MutableSequence[str],
        run_content_validators: bool = False,
        default_language: Optional[str] = None,
    ) -> None:
        self.run_content_validators = run_content_validators
        self.default_language = default_language
        super().__init__(processor, output)

    def handle_line(self, line: str) -> None:
        check_for_new_fence(
            self.processor, self.output, line, self.run_content_validators, self.default_language
        )


class CodeHandler(ZulipBaseHandler):
    def __init__(
        self,
        processor: "FencedBlockPreprocessor",
        output: MutableSequence[str],
        fence: str,
        lang: Optional[str],
        run_content_validators: bool = False,
    ) -> None:
        self.lang = lang
        self.run_content_validators = run_content_validators
        super().__init__(processor, output, fence)

    def done(self) -> None:
        # run content validators (if any)
        if self.run_content_validators:
            validator = CODE_VALIDATORS.get(self.lang, lambda text: None)
            validator(self.lines)
        super().done()

    def format_text(self, text: str) -> str:
        return self.processor.format_code(self.lang, text)


class QuoteHandler(ZulipBaseHandler):
    def __init__(
        self,
        processor: "FencedBlockPreprocessor",
        output: MutableSequence[str],
        fence: str,
        default_language: Optional[str] = None,
    ) -> None:
        self.default_language = default_language
        super().__init__(processor, output, fence, process_contents=True)

    def handle_line(self, line: str) -> None:
        if line.rstrip() == self.fence:
            self.done()
        else:
            check_for_new_fence(
                self.processor, self.lines, line, default_language=self.default_language
            )

    def format_text(self, text: str) -> str:
        return self.processor.format_quote(text)


class SpoilerHandler(ZulipBaseHandler):
    def __init__(
        self,
        processor: "FencedBlockPreprocessor",
        output: MutableSequence[str],
        fence: str,
        spoiler_header: Optional[str],
    ) -> None:
        self.spoiler_header = spoiler_header
        super().__init__(processor, output, fence, process_contents=True)

    def handle_line(self, line: str) -> None:
        if line.rstrip() == self.fence:
            self.done()
        else:
            check_for_new_fence(self.processor, self.lines, line)

    def format_text(self, text: str) -> str:
        return self.processor.format_spoiler(self.spoiler_header, text)


class TexHandler(ZulipBaseHandler):
    def format_text(self, text: str) -> str:
        return self.processor.format_tex(text)


class CodeHilite(codehilite.CodeHilite):
    def _parseHeader(self) -> None:
        # Python-Markdown has a feature to parse-and-hide shebang
        # lines present in code blocks:
        #
        # https://python-markdown.github.io/extensions/code_hilite/#shebang-no-path
        #
        # While using shebang lines for language detection is
        # reasonable, we don't want this feature because it can be
        # really confusing when doing anything else in a one-line code
        # block that starts with `!` (which would then render as an
        # empty code block!).  So we disable the feature, by
        # overriding this function, which implements it in CodeHilite
        # upstream.

        # split text into lines
        lines = self.src.split("\n")
        # Python-Markdown pops out the first line which we are avoiding here.
        # Examine first line
        fl = lines[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:  # nocoverage
                self.lang = None

            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"))

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


class FencedBlockPreprocessor(Preprocessor):
    def __init__(self, md: Markdown, run_content_validators: bool = False) -> None:
        super().__init__(md)

        self.checked_for_codehilite = False
        self.run_content_validators = run_content_validators
        self.codehilite_conf: Mapping[str, Sequence[Any]] = {}

    def push(self, handler: ZulipBaseHandler) -> None:
        self.handlers.append(handler)

    def pop(self) -> None:
        self.handlers.pop()

    def run(self, lines: Iterable[str]) -> List[str]:
        """Match and store Fenced Code Blocks in the HtmlStash."""

        from zerver.lib.markdown import ZulipMarkdown

        output: List[str] = []

        processor = self
        self.handlers: List[ZulipBaseHandler] = []

        default_language = None
        if isinstance(self.md, ZulipMarkdown) and self.md.zulip_realm is not None:
            default_language = self.md.zulip_realm.default_code_block_language
        handler = OuterHandler(processor, output, self.run_content_validators, default_language)
        self.push(handler)

        for line in lines:
            self.handlers[-1].handle_line(line)

        while self.handlers:
            self.handlers[-1].done()

        # This fiddly handling of new lines at the end of our output was done to make
        # existing tests pass. Markdown is just kind of funny when it comes to new lines,
        # but we could probably remove this hack.
        if len(output) > 2 and output[-2] != "":
            output.append("")
        return output

    def format_code(self, lang: Optional[str], text: str) -> str:
        if lang:
            langclass = LANG_TAG.format(lang)
        else:
            langclass = ""

        # Check for code hilite extension
        if not self.checked_for_codehilite:
            for ext in self.md.registeredExtensions:
                if isinstance(ext, CodeHiliteExtension):
                    self.codehilite_conf = ext.config
                    break

            self.checked_for_codehilite = True

        # If config is not empty, then the codehighlite extension
        # is enabled, so we call it to highlight the code
        if self.codehilite_conf:
            highliter = CodeHilite(
                text,
                linenums=self.codehilite_conf["linenums"][0],
                guess_lang=self.codehilite_conf["guess_lang"][0],
                css_class=self.codehilite_conf["css_class"][0],
                style=self.codehilite_conf["pygments_style"][0],
                use_pygments=self.codehilite_conf["use_pygments"][0],
                lang=(lang or None),
                noclasses=self.codehilite_conf["noclasses"][0],
            )

            code = highliter.hilite().rstrip("\n")
        else:
            code = CODE_WRAP.format(langclass, self._escape(text))

        # To support our "view in playground" feature, the frontend
        # needs to know what Pygments language was used for
        # highlighting this code block.  We record this in a data
        # attribute attached to the outer `pre` element.
        # Unfortunately, the pygments API doesn't offer a way to add
        # this, so we need to do it in a post-processing step.
        if lang:
            div_tag = lxml.html.fromstring(code)

            # For the value of our data element, we get the lexer
            # subclass name instead of directly using the language,
            # since that canonicalizes aliases (Eg: `js` and
            # `javascript` will be mapped to `JavaScript`).
            try:
                code_language = find_lexer_class_by_name(lang).name
            except ClassNotFound:
                # If there isn't a Pygments lexer by this name, we
                # still tag it with the user's data-code-language
                # value, since this allows hooking up a "playground"
                # for custom "languages" that aren't known to Pygments.
                code_language = lang

            div_tag.attrib["data-code-language"] = code_language
            code = lxml.html.tostring(div_tag, encoding="unicode")
        return code

    def format_quote(self, text: str) -> str:
        paragraphs = text.split("\n")
        quoted_paragraphs = []
        for paragraph in paragraphs:
            lines = paragraph.split("\n")
            quoted_paragraphs.append("\n".join("> " + line for line in lines))
        return "\n".join(quoted_paragraphs)

    def format_spoiler(self, header: Optional[str], text: str) -> str:
        output = []
        header_div_open_html = '<div class="spoiler-block"><div class="spoiler-header">'
        end_header_start_content_html = '</div><div class="spoiler-content" aria-hidden="true">'
        footer_html = "</div></div>"

        output.append(self.placeholder(header_div_open_html))
        if header is not None:
            output.append(header)
        output.append(self.placeholder(end_header_start_content_html))
        output.append(text)
        output.append(self.placeholder(footer_html))
        return "\n\n".join(output)

    def format_tex(self, text: str) -> str:
        paragraphs = text.split("\n\n")
        tex_paragraphs = []
        for paragraph in paragraphs:
            html = render_tex(paragraph, is_inline=False)
            if html is not None:
                tex_paragraphs.append(html)
            else:
                tex_paragraphs.append('<span class="tex-error">' + escape(paragraph) + "</span>")
        return "\n\n".join(tex_paragraphs)

    def placeholder(self, code: str) -> str:
        return self.md.htmlStash.store(code)

    def _escape(self, txt: str) -> str:
        """basic html escaping"""
        txt = txt.replace("&", "&amp;")
        txt = txt.replace("<", "&lt;")
        txt = txt.replace(">", "&gt;")
        txt = txt.replace('"', "&quot;")
        return txt


def makeExtension(*args: Any, **kwargs: None) -> FencedCodeExtension:
    return FencedCodeExtension(kwargs)


if __name__ == "__main__":
    import doctest

    doctest.testmod()