Fix crash on multibyte string in commit diff

When a multibyte string was found during the scan for whitespace
characters, it could cause a crash due to an invalid index.

Author: MitMaro

CHANGELOG.md

@@ -3,6 +3,10 @@ All notable changes to this project will be documented in this file.
 
 The format is based on [Keep a Changelog](http://keepachangelog.com/).
 
+## [2.2.1] - 2022-10-13
+### Fixed
+- Crash on multibyte strings in commit diff view ([#755](https://github.com/MitMaro/git-interactive-rebase-tool/pull/755))
+
 ## [2.2.0] - 2022-04-21
 ### Added
 - Added mew keybindings for customizing the scrolling the view. ([#647](https://github.com/MitMaro/git-interactive-rebase-tool/pull/647))
@@ -161,7 +165,8 @@ The format is based on [Keep a Changelog](http://keepachangelog.com/).
 ### Added
 - Initial project release
 
-[Unreleased]: https://github.com/MitMaro/git-interactive-rebase-tool/compare/2.2.0...HEAD
+[Unreleased]: https://github.com/MitMaro/git-interactive-rebase-tool/compare/2.2.1...HEAD
+[2.2.1]: https://github.com/MitMaro/git-interactive-rebase-tool/compare/2.2.1...2.2.0
 [2.2.0]: https://github.com/MitMaro/git-interactive-rebase-tool/compare/2.2.0...2.1.0
 [2.1.0]: https://github.com/MitMaro/git-interactive-rebase-tool/compare/2.0.0...2.1.0
 [2.0.0]: https://github.com/MitMaro/git-interactive-rebase-tool/compare/1.2.1...2.0.0

src/core/src/modules/show_commit/util.rs

@@ -151,23 +151,52 @@ pub(super) fn get_files_changed_summary(diff: &CommitDiff, is_full_width: bool)
 
 pub(super) fn get_partition_index_on_whitespace_for_line(line: &str) -> (usize, usize) {
 	let graphemes = UnicodeSegmentation::graphemes(line, true);
-	let length = graphemes.clone().count();
+	let length = graphemes.clone().map(|c| c.len()).sum();
 	let mut start_partition_index = 0;
 	let mut end_partition_index = length;
 
-	for (index, c) in graphemes.clone().enumerate() {
+	let mut index = 0;
+	for c in graphemes.clone() {
 		if c != " " && c != "\t" && c != "\n" {
 			start_partition_index = index;
 			break;
 		}
+		index += c.len();
 	}
 
-	for (index, c) in graphemes.rev().enumerate() {
+	index = length;
+	for c in graphemes.rev() {
 		if c != " " && c != "\t" && c != "\n" {
-			end_partition_index = length - index;
+			end_partition_index = index;
 			break;
 		}
+		index -= c.len();
 	}
 
 	(start_partition_index, end_partition_index)
 }
+
+#[cfg(test)]
+mod tests {
+	use rstest::rstest;
+
+	use super::*;
+
+	#[rstest]
+	#[case::empty_string("", 0, 0)]
+	#[case::single_character("a", 0, 1)]
+	#[case::multiple_characters("abc", 0, 3)]
+	#[case::internal_spaces(" a b c ", 1, 6)]
+	#[case::leading_whitespace(" a", 1, 2)]
+	#[case::trailing_whitespace("a ", 0, 1)]
+	#[case::leading_trailing_whitespace(" a ", 1, 2)]
+	#[case::all_supported_whitespace_characters(" \ta \t\n", 2, 3)]
+	#[case::multi_byte_character("…", 0, 3)]
+	#[case::multi_byte_character_leading_whitespace(" …", 1, 4)]
+	#[case::multi_byte_character_trailing_whitespace("… ", 0, 3)]
+	#[case::multi_byte_character_leading_trailing_whitespace(" … ", 1, 4)]
+	#[case::multi_byte_character_in_middle(" a…b ", 1, 6)]
+	fn get_partition_index_on_whitespace_for_line_cases(#[case] s: &str, #[case] start: usize, #[case] end: usize) {
+		assert_eq!(get_partition_index_on_whitespace_for_line(s), (start, end));
+	}
+}