fix(asyncgit): use from_utf8_lossy when staging lines from non-UTF-8 files

asyncgit/src/sync/staging/mod.rs

@@ -13,10 +13,20 @@ use std::{collections::HashSet, fs::File, io::Read};
 
 const NEWLINE: char = '\n';
 
-#[derive(Default)]
 struct NewFromOldContent {
 	lines: Vec<String>,
 	old_index: usize,
+	trailing_newline: bool,
+}
+
+impl Default for NewFromOldContent {
+	fn default() -> Self {
+		Self {
+			lines: Vec::new(),
+			old_index: 0,
+			trailing_newline: true,
+		}
+	}
 }
 
 impl NewFromOldContent {
@@ -57,14 +67,11 @@ impl NewFromOldContent {
 		for line in old_lines.iter().skip(self.old_index) {
 			self.lines.push((*line).to_string());
 		}
-		let lines = self.lines.join("\n");
-		if lines.ends_with(NEWLINE) {
-			lines
-		} else {
-			let mut lines = lines;
+		let mut lines = self.lines.join("\n");
+		if self.trailing_newline && !lines.ends_with(NEWLINE) {
 			lines.push(NEWLINE);
-			lines
 		}
+		lines
 	}
 }
 
@@ -133,6 +140,18 @@ pub fn apply_selection(
 					|| hunk_line.origin_value()
 						== DiffLineType::AddEOFNL
 				{
+					let applying = (is_staged && !selected_line)
+						|| (!is_staged && selected_line);
+					new_content.trailing_newline =
+						if hunk_line.origin_value()
+							== DiffLineType::DeleteEOFNL
+						{
+							// old had newline, new doesn't; applying removal → no newline
+							!applying
+						} else {
+							// AddEOFNL: old had no newline, new does; applying addition → newline
+							applying
+						};
 					break;
 				}
 

asyncgit/src/sync/staging/stage_tracked.rs

@@ -142,6 +142,48 @@ c = 4";
 		assert_eq!(&*diff.hunks[0].lines[0].content, "@@ -1,2 +1 @@");
 	}
 
+	#[test]
+	fn test_stage_preserves_no_trailing_newline() {
+		// Both files have no trailing newline
+		static FILE_1: &str = "line1\nline2";
+		static FILE_2: &str = "line1_changed\nline2";
+
+		let (path, repo) = repo_init().unwrap();
+		let path: &RepoPath = &path.path().to_str().unwrap().into();
+
+		write_commit_file(&repo, "test.txt", FILE_1, "c1");
+		repo_write_file(&repo, "test.txt", FILE_2).unwrap();
+
+		// Stage only the changed first line
+		stage_lines(
+			path,
+			"test.txt",
+			false,
+			&[DiffLinePosition {
+				old_lineno: Some(1),
+				new_lineno: Some(1),
+			}],
+		)
+		.unwrap();
+
+		// Read the staged blob and verify it has no trailing newline
+		let git_repo = repo(path).unwrap();
+		let mut index = git_repo.index().unwrap();
+		index.read(true).unwrap();
+		let entry = index
+			.get_path(Path::new("test.txt"), 0)
+			.expect("entry not found");
+		let blob = git_repo.find_blob(entry.id).unwrap();
+		let staged = std::str::from_utf8(blob.content()).unwrap();
+
+		assert!(
+			!staged.ends_with('\n'),
+			"staged content must not gain a trailing newline; got: {:?}",
+			staged
+		);
+		assert_eq!(staged, "line1_changed\nline2");
+	}
+
 	#[test]
 	fn test_unstage() {
 		static FILE_1: &str = r"0