progress: fix progress to not redraw every time there's new data

I think the idea of the code was try do 30 updates per second even if
events arrive at, say, every 20 milliseconds. If we had reset the
timer every time we printed, we would otherwise reset the timer every
40 milliseconds and end up with 25 updates per second. However, a bug
in the code caused it to print every update because it always set the
threshold to print the next update to `now`. I tried to keep what I
think was the intent of the original code while fixing the bug.

CHANGELOG.md

@@ -29,6 +29,9 @@ to [Semantic Versioning](https://semver.org/spec/v2.0.0.html).
 * Fixed incompatible rendering of empty hunks in git/unified diffs.
   [#5049](https://github.com/martinvonz/jj/issues/5049)
 
+* Fixed performance of progress bar rendering when fetching from Git remote.
+  [#5057](https://github.com/martinvonz/jj/issues/5057)
+
 ## [0.24.0] - 2024-12-04
 
 ### Release highlights

cli/src/progress.rs

@@ -53,6 +53,7 @@ impl Progress {
         if now < self.next_print {
             return Ok(());
         }
+        self.next_print = now + Duration::from_secs(1) / UPDATE_HZ;
         if self.guard.is_none() {
             let guard = output.output_guard(crossterm::cursor::Show.to_string());
             let guard = CleanupGuard::new(move || {
@@ -61,7 +62,6 @@ impl Progress {
             _ = write!(output, "{}", crossterm::cursor::Hide);
             self.guard = Some(guard);
         }
-        self.next_print = now.min(self.next_print + Duration::from_secs(1) / UPDATE_HZ);
 
         self.buffer.clear();
         write!(self.buffer, "\r").unwrap();
@@ -260,14 +260,14 @@ mod tests {
         // First output is after the initial delay
         assert_snapshot!(update(INITIAL_DELAY - Duration::from_millis(1), 0.1), @"");
         assert_snapshot!(update(Duration::from_millis(1), 0.10), @"[?25l\r 10% [█▊                ]");
-        // TODO: No updates for the next 30 milliseconds
-        assert_snapshot!(update(Duration::from_millis(10), 0.11), @" 11% [██                ][K");
-        assert_snapshot!(update(Duration::from_millis(10), 0.12), @" 12% [██▏               ][K");
-        assert_snapshot!(update(Duration::from_millis(10), 0.13), @" 13% [██▍               ][K");
+        // No updates for the next 30 milliseconds
+        assert_snapshot!(update(Duration::from_millis(10), 0.11), @"");
+        assert_snapshot!(update(Duration::from_millis(10), 0.12), @"");
+        assert_snapshot!(update(Duration::from_millis(10), 0.13), @"");
         // We get an update now that we go over the threshold
         assert_snapshot!(update(Duration::from_millis(100), 0.30), @" 30% [█████▍            ]");
-        // TODO: Even though we went over by quite a bit, the new threshold is relative
-        // to the previous output, so we don't get an update here
-        assert_snapshot!(update(Duration::from_millis(30), 0.40), @" 40% [███████▎          ][K");
+        // Even though we went over by quite a bit, the new threshold is relative to the
+        // previous output, so we don't get an update here
+        assert_snapshot!(update(Duration::from_millis(30), 0.40), @"");
     }
 }