From b0b842f83496d477ed176ce704096ba40c67e91e Mon Sep 17 00:00:00 2001
From: rustbasic <127506429+rustbasic@users.noreply.github.com>
Date: Wed, 24 Jan 2024 18:53:27 +0900
Subject: [PATCH 1/3] Fix: panic when pressing Shift + TAB in a TextEdit

panic when pressing Shift + TAB in a TextEdit #3846
rev() is panic with UTF8

Not byte_index
It's char_index ( for UTF8 )
---
 crates/egui/src/widgets/text_edit/text_buffer.rs | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/crates/egui/src/widgets/text_edit/text_buffer.rs b/crates/egui/src/widgets/text_edit/text_buffer.rs
index f28878a1dd3..e70ce695af9 100644
--- a/crates/egui/src/widgets/text_edit/text_buffer.rs
+++ b/crates/egui/src/widgets/text_edit/text_buffer.rs
@@ -89,10 +89,12 @@ pub trait TextBuffer {
     fn decrease_indentation(&mut self, ccursor: &mut CCursor) {
         let line_start = find_line_start(self.as_str(), *ccursor);
 
-        let remove_len = if self.as_str()[line_start.index..].starts_with('\t') {
+        let remove_len = if self.as_str().chars().nth(line_start.index) == Some('\t') {
             Some(1)
-        } else if self.as_str()[line_start.index..]
+        } else if self
+            .as_str()
             .chars()
+            .skip(line_start.index)
             .take(TAB_SIZE)
             .all(|c| c == ' ')
         {

From 3b8fe476163469de446cb27aac940e180295b5ad Mon Sep 17 00:00:00 2001
From: rustbasic <127506429+rustbasic@users.noreply.github.com>
Date: Wed, 24 Jan 2024 19:12:21 +0900
Subject: [PATCH 2/3] Update text_cursor_state.rs

---
 .../src/text_selection/text_cursor_state.rs   | 42 +++++++++++++++----
 1 file changed, 33 insertions(+), 9 deletions(-)

diff --git a/crates/egui/src/text_selection/text_cursor_state.rs b/crates/egui/src/text_selection/text_cursor_state.rs
index d8adfb83376..a3d59274d17 100644
--- a/crates/egui/src/text_selection/text_cursor_state.rs
+++ b/crates/egui/src/text_selection/text_cursor_state.rs
@@ -300,18 +300,42 @@ pub fn find_line_start(text: &str, current_index: CCursor) -> CCursor {
     // number of multi byte chars.
     // We need to know the char index to be able to correctly set the cursor
     // later.
-    let chars_count = text.chars().count();
+    let mut char_line_indexes: Vec<usize> = create_char_line_indexes(text);
+    let line_start_index = get_line_start_index(&mut char_line_indexes, current_index.index);
 
-    let position = text
-        .chars()
-        .rev()
-        .skip(chars_count - current_index.index)
-        .position(|x| x == '\n');
+    CCursor::new(line_start_index)
+}
+
+pub fn create_char_line_indexes(text: &str) -> Vec<usize> {
+    let mut line_indexes = vec![0];
 
-    match position {
-        Some(pos) => CCursor::new(current_index.index - pos),
-        None => CCursor::new(0),
+    let mut count = 0;
+    for (_i, c) in text.chars().enumerate() {
+        count += 1;
+        if c == '\n' {
+            line_indexes.push(count);
+        }
     }
+    line_indexes.push(count);
+
+    line_indexes
+}
+
+pub fn get_line_start_index(line_indexes: &mut [usize], index: usize) -> usize {
+    let (_current_line, line_start) = get_line_and_start_index(line_indexes, index);
+    line_start
+}
+
+pub fn get_line_and_start_index(line_indexes: &mut [usize], index: usize) -> (usize, usize) {
+    let mut current_line = 1;
+    for (i, line_start) in line_indexes.iter().enumerate() {
+        current_line = i;
+        if *line_start > index {
+            break;
+        }
+    }
+
+    (current_line, line_indexes[current_line - 1])
 }
 
 pub fn byte_index_from_char_index(s: &str, char_index: usize) -> usize {

From a493bf40b0026cc9c47e372577a49eebda8d264f Mon Sep 17 00:00:00 2001
From: rustbasic <127506429+rustbasic@users.noreply.github.com>
Date: Fri, 26 Jan 2024 10:40:27 +0900
Subject: [PATCH 3/3] Update text_cursor_state.rs

---
 crates/egui/src/text_selection/text_cursor_state.rs | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/crates/egui/src/text_selection/text_cursor_state.rs b/crates/egui/src/text_selection/text_cursor_state.rs
index c4423a4aef6..ed51fde3153 100644
--- a/crates/egui/src/text_selection/text_cursor_state.rs
+++ b/crates/egui/src/text_selection/text_cursor_state.rs
@@ -312,7 +312,7 @@ pub fn create_char_line_indexes(text: &str) -> Vec<usize> {
     let mut line_indexes = vec![0];
 
     let mut count = 0;
-    for (_i, c) in text.chars().enumerate() {
+    for c in text.chars() {
         count += 1;
         if c == '\n' {
             line_indexes.push(count);