Parsing and highlighting of fenced blocks

[pjeby]

• Can you reproduce the bug at https://try.gitea.io:
  • Yes (provide example URL)

Description

There are two problems visible in this page's rendering on try.gitea.io:

• First, gitea's markdown processor is not CommonMark compliant for parsing fenced code blocks. (Search for the line rendered as ```shell mdsh -- this syntax is CommonMark compliant and renders correctly on Github.)

• Second, even if the fence line is changed to something blackfriday can handle (i.e. wrapping it in { }), gitea appears to look up the entire shell mdsh line as a language name, instead of processing only the first word, the way github does. (Github's behavior in this respect is not part of the CommonMark spec, but is a reasonable default behavior.)

Probably the parsing issue needs to be reported upstream at blackfriday, but since it may impact their API, I assume that input from the gitea side would be relevant to that issue.

[pjeby]

FYI, the upstream parsing bug has been closed as fixed, so this can be revisited now. It appears that the vendored copy of blackfriday is two years old, so updating that to a newer version would be required.

Checking the upstream commits, it appears there have only been 8 PRs and one standalone commit since the dependency was vendored in late 2016. Of those, 3 PRs literally only touch the README, and 1 is the intended fix for this issue. The other five changes are dropping a dependency, adding CJK line joining, adding smart guillement formatting, fixing an infinite loop caused by self-referential footnotes, and dropping rel="footnote" from links to footnotes. All in all, updating the dependency shouldn't have a significant impact apart from the bug fixes.

[lunny]

will be closed by #3857

[lunny]

resolved by #3857