Error messages are sometimes not displayed

[esope]

Sometimes, error messages are not displayed at all when dune is run from a terminal.
If you redirect stderr to a file, however, then the error messages are correctly written to that file.
This bug seems to happen on the dev version of dune only.
I was not able to create a test that witnesses this behavior: tests seem to redirect stderr.

Expected Behavior

Whether stderr is redirected or not, the same error messages should be produced (with the exception of styles and colors, maybe).

Actual Behavior

It happens sometimes that dune command args produces no visible error messages, but dune command args 2> errors.txt writes some error messages to the file errors.txt.

Reproduction

dune describe bug displays no message at all.

dune describe bug 2> errors.txt writes the error message Error: Unknown constructor bug to errors.txt as expected.

Specifications

• Version of dune: dev version, with git hash 87bc1bfa16136a9f8833e236c23b8454a309e55e
• Version of ocaml: 4.14.0
• Operating system (distribution and version): Linuxmint 21

[emillon]

I've seen that too, I'll investigate

[emillon]

That has been introduced in #6068

[emillon]

@rgrinberg it's probably more efficient if you have a look at this one - looks like we're missing a flush on stderr at the end.

[rgrinberg]

Np. Should be simple enough to fix. I'll manually shut down the UI thread once the Term.t finishes executing.

[esope]

Fixed by #6119

[gridbugs]

Heads up that I'm still encountering this while building dune on an M1 Mac.

[gridbugs]

I see this on both macOS and dockerized ubuntu, and I see it when I build non-dune projects as long as I'm using a dune which I build from source. I don't see this error using 3.6.1 installed from opam.

[gridbugs]

Bisected and the problem was introduced in this commit 1f518fb

[gridbugs]

This seems to fix the problem:

diff --git a/src/dune_console/dune_console.ml b/src/dune_console/dune_console.ml
index f233e4637..22aab51fb 100644
--- a/src/dune_console/dune_console.ml
+++ b/src/dune_console/dune_console.ml
@@ -304,9 +304,9 @@ module Backend = struct
         Base.start ();
         while true do
           Mutex.lock mutex;
+          Base.render state;
           let finish_requested = state.finish_requested in
           if finish_requested then raise_notrace Exit;
-          Base.render state;
           Mutex.unlock mutex;
           let now = Unix.gettimeofday () in
           let elapsed = now -. !last in

[esope]

@rgrinberg @Alizter it seems that 1f518fb is your commit.
Do you want to have a look at this issue?

[Alizter]

@esope that commit has since been reverted.

[esope]

Oh, OK. My bad.
@gridbugs do you still observe the bug with a dune version close to tip?

[gridbugs]

I no longer observe the bug on tip (715825e)

[esope]

Great. I am closing the issue, then. Do not hesitate to reopen it if necessary.