From ff65558a1b2c4c3af72585d5a2bde5e0598ea9d7 Mon Sep 17 00:00:00 2001
From: Benjamin Tan <benjamin@dev.ofcr.se>
Date: Sat, 16 Mar 2024 22:30:36 +0800
Subject: [PATCH] Align sideband progress message printing with Git's
 implementation

See https://github.com/git/git/blob/43072b4ca132437f21975ac6acc6b72dc22fd398/sideband.c#L178.
---
 cli/src/git_util.rs | 70 +++++++++++++++++++++++++++++++++++++++------
 1 file changed, 62 insertions(+), 8 deletions(-)

diff --git a/cli/src/git_util.rs b/cli/src/git_util.rs
index 41c703a173..5c4e712867 100644
--- a/cli/src/git_util.rs
+++ b/cli/src/git_util.rs
@@ -14,13 +14,14 @@
 
 //! Git utilities shared by various commands.
 
-use std::io::{Read, Write};
+use std::io::{IsTerminal, Read, Write};
 use std::path::{Path, PathBuf};
 use std::process::Stdio;
 use std::sync::Mutex;
 use std::time::Instant;
 use std::{error, iter};
 
+use gix::bstr::ByteSlice;
 use itertools::Itertools;
 use jj_lib::git::{self, FailedRefExport, FailedRefExportReason, GitImportStats, RefName};
 use jj_lib::git_backend::GitBackend;
@@ -155,16 +156,69 @@ pub fn with_remote_git_callbacks<T>(
     callbacks.progress = progress_callback
         .as_mut()
         .map(|x| x as &mut dyn FnMut(&git::Progress));
+    // Based on Git's implementation: https://github.com/git/git/blob/43072b4ca132437f21975ac6acc6b72dc22fd398/sideband.c#L178
     let mut sideband_progress_callback = None;
+    let mut scratch = Vec::new();
+    let display_prefix = "remote: ";
+    let suffix = if std::io::stdout().is_terminal() {
+        "\x1B[K"
+    } else {
+        "        "
+    };
     if print_sideband_messages {
-        sideband_progress_callback = Some(|progress: &[u8]| {
-            let message = String::from_utf8_lossy(progress);
-            if message.contains("\n") {
-                for line in message.lines() {
-                    _ = writeln!(ui.lock().unwrap().stderr(), "remote: {line}");
+        sideband_progress_callback = Some(|progress_message: &[u8]| {
+            let mut index = 0;
+            // Append a suffix to each nonempty line to clear the end of the screen line.
+            loop {
+                let Some(i) = progress_message[index..]
+                    .find_char('\n')
+                    .or_else(|| progress_message[index..].find_char('\r'))
+                    .map(|i| index + i)
+                else {
+                    break;
+                };
+                let line_length = i - index;
+
+                // For message across packet boundary, there would have a nonempty "scratch"
+                // buffer from last call of this function, and there may have a
+                // leading CR/LF in "buf". For this case we should add a clear-to-eol suffix to
+                // clean leftover letters we previously have written on the same line.
+                if !scratch.is_empty() && line_length == 0 {
+                    scratch.extend_from_slice(suffix.as_bytes());
+                }
+
+                if scratch.is_empty() {
+                    scratch.extend_from_slice(display_prefix.as_bytes());
+                }
+
+                // Do not add the clear-to-eol suffix to empty lines:
+                // For progress reporting we may receive a bunch of percentage updates followed
+                // by '\r' to remain on the same line, and at the end receive a
+                // single '\n' to move to the next line. We should preserve the final
+                // status report line by not appending clear-to-eol suffix to this single line
+                // break.
+                if line_length > 0 {
+                    scratch.extend_from_slice(&progress_message[index..i]);
+                    scratch.extend_from_slice(suffix.as_bytes());
+                }
+                scratch.extend_from_slice(&progress_message[i..i + 1]);
+
+                _ = write!(
+                    ui.lock().unwrap().stderr(),
+                    "{}",
+                    String::from_utf8_lossy(&scratch)
+                );
+                scratch.clear();
+
+                index = i + 1;
+            }
+
+            // Add leftover message to "scratch" buffer to be printed in next call.
+            if index < progress_message.len() && progress_message[index] != 0 {
+                if scratch.is_empty() {
+                    scratch.extend_from_slice(display_prefix.as_bytes());
                 }
-            } else {
-                _ = write!(ui.lock().unwrap().stderr(), "remote: {message}");
+                scratch.extend_from_slice(&progress_message[index..]);
             }
         });
     }