libmain: don't print empty lines

this most notably affects `nix eval`: if there is no progress bar to be
shown and no activities going on we should not print anything at all. a
progress bar with no activities would print a bunch of terminal escapes
*and a space*, which is not helpful in simple cases like nix eval -E 1.
notably this does *not* affect nix eval called on non-terminal outputs,
but it is slightly confusing nevertheless (and not difficult to avoid).

fixes #424

Change-Id: Iee793c79ba5a485d6606e0d292ed2eae6dfb7216
This commit is contained in:
eldritch horrors 2024-06-26 14:08:20 +02:00
parent 9afb0fe41c
commit 3dd7d023f4

View file

@ -396,7 +396,7 @@ std::chrono::milliseconds ProgressBar::draw(State & state, const std::optional<s
if (printMultiline && moreActivities)
writeToStderr(fmt("And %d more...", moreActivities));
if (!printMultiline) {
if (!printMultiline && !line.empty()) {
line += " " + activity_line;
writeToStderr("\r" + filterANSIEscapes(line, false, width) + ANSI_NORMAL + "\e[K");
}