ikiwiki/doc/bugs/discount_stopped_rendering_markdown_links.mdwn

# What I did

Upgraded from 3.20180105 to 3.20180228 (from pkgsrc).
No change to installed Text::Markdown::Discount (0.11nb4 from pkgsrc, using upstream's bundled Discount library).

# What I expected to happen

Markdown-style links to continue being rendered as before.

# What actually happened

Markdown-style links stopped being links.
Instead, they render the part in square brackets as ordinary text.

# Proximate cause

In [f46e429](http://source.ikiwiki.branchable.com/?p=source.git;a=commitdiff;h=f46e429d96ead32943cb2670d7686df8c77de361), if I comment out the `MKD_GITHUBTAGS` if block, the problem goes away.

# Further causes and possible solutions

Some guesses:

- Sufficiently old versions of the Discount library may break when passed unrecognized flags, in which case ikiwiki might want to version-check before passing flags
- The version of the Discount library bundled with upstream Text::Markdown::Discount may be extremely old, in which case pkgsrc might want to make it depend instead on an external Discount package

> This appears to be because `MKD_GITHUBTAGS` and `MKD_LATEX` both have numeric values that
> were previously used for the internal flag `IS_LABEL`, which strips HTML (its value has
> changed a couple of times).
>
> Having thought about this a bit, I realise I can probe for the values of these flags by
> processing HTML that should have different results with the flag set or unset, which
> would be safer than just blindly using them.
>
> Orthogonally, pkgsrc should probably use an up-to-date version of Discount, and
> [we already know that Text::Markdown::Discount needs updating](https://rt.cpan.org/Public/Bug/Display.html?id=124188).
> --[[smcv]]

>> This should be [[fixed|done]] in current git. The mdwn module now
>> detects what your version of Discount supports by trying several
>> short HTML fragments that render differently under the different
>> flags. --[[smcv]]