nixUnstable prints each log line twice when used against stable nix-daemon

[bjornfor]

Describe the bug

Using nixUnstable client from nixpkgs-20.09 (2.4pre20201102_550e11f) with nix-daemon v2.3.6 results in each log line from nix-build appearing twice.

Unlike this issue, I'm not using ssh-ng. (I'm not using remote building at all: nix-build --builders '' ....)

Expected behavior
Each build log line should appear only once.

** nix-env (Nix) 2.4pre20201102_550e11f **

Additional context
Updating the nix-daemon at the same version as the client fixed the issue.

[roberth]

This issue is the opposite of #4234 and seems to be caused by #3073 as well.

Nix 2.3 logs build logs both as "result" and general error logging internally. master could ignore results when the daemon version indicates Nix 2.3.

[stale]

I marked this as stale due to inactivity. → More info

[Congee]

not stale. still need a fix

[stale]

I marked this as stale due to inactivity. → More info