[PATCH v2 3/4] progress: clear previous progress update dynamically

From: SZEDER Gábor <szeder.dev@gmail.com>
Date: Apr 1, 2019, 11:52 UTC
Message-ID: <20190401115217.3423-4-szeder.dev@gmail.com>
In-Reply-To: <20190401115217.3423-1-szeder.dev@gmail.com>

When the progress bar includes throughput, its length can shorten as the unit of display changes from KiB to MiB. To cover up remnants of the previous progress bar when such a change of units happens we always print three spaces at the end of the progress bar.

Alas, covering only three characters is not quite enough: when both the total and the throughput happen to change units from KiB to MiB in the same update, then the progress bar's length is shortened by four characters (or maybe even more!):

  Receiving objects:  25% (2901/11603), 772.01 KiB | 733.00 KiB/s
  Receiving objects:  27% (3133/11603), 1.43 MiB | 1.16 MiB/s   s

and a stray 's' is left behind.

So instead of hard-coding the three characters to cover, let's compare the length of the current progress bar with the previous one, and cover up as many characters as needed.

Sure, it would be much simpler to just print more spaces at the end of the progress bar, but this approach is more future-proof, and it won't print extra spaces when none are needed, notably when the progress bar doesn't show throughput and thus never shrinks.

Signed-off-by: SZEDER Gábor <szeder.dev@gmail.com>
---
 progress.c | 10 ++++++----
 1 file changed, 6 insertions(+), 4 deletions(-)

diff --git a/progress.c b/progress.c
index 842db14b72..3149ecd460 100644
--- a/progress.c
+++ b/progress.c
@@ -84,6 +84,7 @@ static void display(struct progress *progress, uint64_t n, const char *done)
 	const char *tp;
 	struct strbuf *counters_sb = &progress->counters_sb;
 	int show_update = 0;
+	int last_count_len = counters_sb->len;
 
 	if (progress->delay && (!progress_update || --progress->delay))
 		return;
@@ -110,10 +111,11 @@ static void display(struct progress *progress, uint64_t n, const char *done)
 
 	if (show_update) {
 		if (is_foreground_fd(fileno(stderr)) || done) {
-			const char *eol = done ? done : "   \r";
-
-			fprintf(stderr, "%s: %s%s", progress->title,
-				counters_sb->buf, eol);
+			const char *eol = done ? done : "\r";
+			int clear_len = counters_sb->len < last_count_len ?
+					last_count_len - counters_sb->len : 0;
+			fprintf(stderr, "%s: %s%-*s", progress->title,
+				counters_sb->buf, clear_len, eol);
 			fflush(stderr);
 		}
 		progress_update = 0;

-- 
2.21.0.539.g07239c3a71.dirty