Allowing judges to link to files in syntax highlighted code

[niknetniko]

Some judges (I know of the Python judge, which is a special case, and TESTed) link to files when the filename appears in the input for a testcase:

In the example above, the "europe.txt" is clickable and opens the file.

Dodona supports syntax highlighting for pieces of code, such as the $ migration '[europe.txt] in the example above.
However, there is no support for linking files.
TESTed currently works around this by not generating code, but generating HTML as the input: by using pygments, the outputted HTML is luckily compatible with Rouge, which is what Dodona uses to create syntax highlighting.

I propose moving this functionality to Dodona itself: a judge would generate input (with type code), and also provide an accompanying map of parts to be replaced with a link. This way, Dodona has full control on how this linking should be done (e.g. something like the popups of the Python judge would also be possible).

A concrete proposal of the format (in the partial one) would be to add an attribute to the start-testcase command, which contains an object: the keys of which will be replaced by a link to the file given by the value of the object. The replacement would be simple: all occurrences of the keys would be replaced by the links. It is up to the exercise designer to then ensure that things that shouldn't be links have a different name.

{
 "command": "start-testcase",
 "description": {
  "description": "$ migrate 'europe.txt'",
  "format": "console",
  "files": {
   "europe.txt": "media/workdir/europe.txt"
  }
 }
}

We could also make it simpler by just accepting an array of file names, and always automatically link $FILE to media/workdir/$FILE.

In TESTed, we handle the replacement with big 'ol regex, but in Dodona, I would suggest looking into subclassing a lexer from Rouge to handle this more cleanly.