Extend the default doc xref regexp

[yuhan0]

This allows cider-doc buffers to recognize [[var]] syntax and fully qualified symbols as xref links.

Both are fairly common in docstrings in core and 3rd-party libraries that I've personally encountered, and it's otherwise somewhat annoying to navigate to a referenced var or function. (E.g. executing M-x cider-docin a *cider-doc* buffer doesn't pick up the symbol at point).

If this is acceptable I'll go ahead with adding tests and changelogs :)

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[bbatsov]

That's a nice improvement! I believe we did something similar a while ago in clojure-mode so that more xref formats are font-locked there properly.

[bbatsov]

Shouldn't the eval-and-compile be here?

[yuhan0]

Ah of course, changing it now-

[yuhan0]

I looked into writing tests for this, but realised there were none written for the entire cider-doc namespace- also it's not clear how to test functions which rely on a REPL connection.

[bbatsov]

The best approach is to simply stub the functions that require a REPL connection.

[yuhan0]

I added a test for the regexp matching in cider-util, which should cover the changes for this PR.

[bbatsov]

Great work! Thanks! 🙇

[bbatsov]

@yuhan0 Btw, it'd be a good idea to update the font-locking of fully-qualified vars appearing in docstrings in clojure-mode as well for consistency.