Fix #508: Add custom variable eglot-flymake-immediate-report.

[JimDBh]

Setting it to nil would make eglot respect flymake-no-changes-timeout.

[joaotavora]

Hmmm, I think I understand what you mean. But it's not flymake-no-change-timeout that's being ignored. The LSP server is sending multiple updates for the same request by flymake (which does respect f-n-c-t). You probably want to customize eglot-send-changes-idle-time.

[joaotavora]

Hi @JimDBh, I've been thinking about this, and I think this proposal has merit. Let's continue discussion here.

[JimDBh]

Yep. Although I think maybe this PR is not correct now, as I suspect if we do it this way then the flymake report would not be up to date and is always one step behind?

[joaotavora]

I haven't tested. The idea seems solid, but it has to be well tested. So I hope you could test this with the two values for the flag in a small number of LSP servers. Better yet, you could add automated tests to eglot-tests.el.

Another matter: this enhancement is small enough to not need a FSF copyright assignment, but any larger contribution (like one with tests) would need it.

[JimDBh]

Thanks for the reply! Yeah I'll try to test this and change it if needed. Not quite familiar with eglot-tests, but will also try to do that too.
I'll also check the copyright forms too. Will update here with anything new.

[joaotavora]

I suspect if we do it this way then the flymake report would not be up to date and is always one step behind?

Yes, exactly. I've just tested it minimally and it has that glaring problem. The problem only happens when Flymake "takes the initiative", and when flymake-no-changes-timeout is less than (eglot-send-changes-idle-time + time-it-takes-for-lsp-server-to-issue-diagnostics).

This suggests that if flymake-no-changes-timeout is large enough (or nil == infinite) then your strategy works. The problem is that time-it-takes-for-lsp-server-to-issue-diagnostics is a hard unknown and depends on many factors (project complexity, LSP server's whims, etc)

So then only way I can see this working is if flymake-no-changes-timeout is nil. In other words, this patch:

diff --git a/eglot.el b/eglot.el
index e8f060c..46b9e13 100644
--- a/eglot.el
+++ b/eglot.el
@@ -1996,7 +1996,11 @@ COMMAND is a symbol naming the command."
                                              collect it)))
                           `((face . ,faces))))))
            into diags
-           finally (cond (eglot--current-flymake-report-fn
+           finally (cond ((and
+                           ;; if f-n-c-t is nil, i.e. "infinite",
+                           ;; don't add to current report.
+                           (not (null flymake-no-changes-timeout))
+                           eglot--current-flymake-report-fn)
                           (eglot--report-to-flymake diags))
                          (t
                           (setq eglot--diagnostics diags)))))

Then you can M-x flymake-start (or use some keybinding) to get the up-to-date diagnostics that Eglot has been holding on to.