Fix `nrepl-switch-to-repl-buffer' to work with all connections

[vedang]

Commit 12558e8 breaks nrepl-switch-to-repl-buffer functionality by
assuming that all nrepl connections will be made using
nrepl-jack-in.

Using nrepl-jack-in sets the variable nrepl-project-dir to the
correct value, but this information cannot be retrieved when we
connect to an existing nRepl server using nrepl-connect. Since
nrepl-project-dir is unbound, the function file-truename throws a
null value exception.

This commit checks if nrepl-project-dir is set before calling
file-truename. Further, the message "nREPL connection not found"
does not make sense and thus should not be displayed.

[vedang]

Hi @bbatsov,

While my commit fixes the obvious breakage of not being able to switch to nrepl buffer, it exposes a more subtle bug that was introduced in 12558e8:

Suppose I have used nrepl-jack-in to connect to my project. Now I want to work on the production env (for the same project), so I connect to the production repl using M-x nrepl. Now, I go back to work in my clojure file, knowing that my production repl is my active repl. I punch C-c C-z. nrepl-switch-to-repl-buffer will detect that I have a local repl belonging to this project, it will mark that connection as active and will switch to my local repl.

This is absolutely the wrong thing to do, IMHO. People who are connected to multiple repls know that they are connected to multiple repls, and don't need nrepl to switch to the correct repl for them. Please consider rolling back this entire functionality and going back to the way nrepl-switch-to-repl-buffer worked in 0.1.8

[jonpither]

One option is to keep the functionality as a separate function.

The functionality is there for convenience sake.

[vedang]

Yes, +1. Keep this as a separate function that can be bound to a separate key and used as per requirement.

[vedang]

I have changed the nrepl-switch-to-repl-buffer function back to the one found in 0.1.8 - 12558e8~1 to be precise. In addition, I've added the new functionality in the function nrepl-switch-to-relevant-buffer as proposed in the original pull request #350.

If this change is acceptable, we can add a new key binding for nrepl-switch-to-relevant-buffer in the nrepl-interaction-mode-map. (I propose C-c C-v)

[jonpither]

Other options are having a flag to turn on/off the behaviour in the single function, or to think harder about how the 'magic' should be applied, i.e. if there is a connection present not based off a project and there is some level of ambiguity then don't do it.

[vedang]

I'm against 'magic' code in general. Since this is a convenience function, keeping it separate is the right thing to do.

[jonpither]

Yes I agree, just throwing up the other options.

[bbatsov]

Fair enough. Separate function it is. I'd suggest C-c C-Z as the binding for it. Add the new function to the menus as well. Since I generally keep a REPL per project I didn't properly assess the situation originally.

[vedang]

I've added the documentation changes and tests for nrepl-switch-to-relevant-buffer. If this is okay to merge, then I'll squash everything into a single commit.

[bbatsov]

I think we should name this nrepl-switch-to-relevant-repl(-buffer).

[vedang]

okay.

[bbatsov]

I've added my comments. As soon as you've addressed them we'll be good to merge this.

[vedang]

Alright, I'll make the changes and push the commit.

[vedang]

Done. Rebased on top of master and good to merge.