Add before and after options to refresh middleware

[cichli]

I'm still refining the elisp bits for this, but am posting the middleware changes for review. The options are passed in as namespace-qualified function names, which must have zero arity. before is invoked before refreshing, and refreshing does not proceed if it throws an exception. after is invoked after refreshing.

refresh-tracker is now an agent, and the logic for refreshing dispatched using send-off - this means that only one refresh request will be being processed at any given time, so you don't have to worry about your before and after functions running concurrently or being retried. This is also means they won't lock up an nREPL thread if they block for a long time.

*out* and *err* are both captured and streamed back to the client while invoking both before and after, and if an exception is thrown either during their execution or while reloading, it is printed to *out* as it would be at the REPL (using clojure.main/repl-caught) and sent back to the client in stacktrace format for rendering in the error buffer.

Here's the client UI so far (a log buffer that prints the output of before and after, the list of namespaces being refreshed, and whether or not it was successful):

[bbatsov]

The changes look good to me. Btw, this log buffer reminds me that it might be nice to add some generic "server-side" logging to cider-nrepl.

[cichli]

Pushed a slight tweak to send a message both prior and subsequent to calling before/after - otherwise, if they don't emit any output, the client has no indication of them being called.

Btw, this log buffer reminds me that it might be nice to add some generic "server-side" logging to cider-nrepl.

Do you mean something that user programs hook into, or some logging performed by cider-nrepl itself (enabled in the client by some debug mode flag, presumably)?

[bbatsov]

Do you mean something that user programs hook into, or some logging performed by cider-nrepl itself (enabled in the client by some debug mode flag, presumably)?

The latter. This would be valuable info when trying to pin point where a problem originates (or so I think).

[Malabarba]

Nice, I didn't know about this syntax.