feat(prompt): add support for wide characters in prompt preview

Cargo.lock

@@ -1664,6 +1664,7 @@ dependencies = [
  "textwrap",
  "thiserror",
  "tokio",
+ "unicode-width",
 ]
 
 [[package]]

Cargo.toml

@@ -31,6 +31,7 @@ lazy-regex = { version = "3.5.1", features = ["lite"] }
 thiserror = "2.0.18"
 tokio = { version = "1.49.0", features = ["macros", "rt-multi-thread"] }
 textwrap = "0.16.2"
+unicode-width = "0.2.2"
 
 [dev-dependencies]
 assert_cmd = "2.1.2"

src/prompts/prompter.rs

@@ -6,6 +6,7 @@
 //! in production while accepting mock implementations in tests.
 
 use inquire::{Confirm, Text};
+use unicode_width::UnicodeWidthStr;
 
 use crate::{
     commit::types::{BreakingChange, CommitType, Description, Scope},
@@ -40,14 +41,19 @@ pub trait Prompter: Send + Sync {
 }
 
 fn format_message_box(message: &str) -> String {
-    let preview_width = 72 + 2; // max width + space padding
+    let preview_width = message
+        .split('\n')
+        .map(|line| line.width())
+        .max()
+        .unwrap_or(0)
+        .max(72);
     let mut lines: Vec<String> = Vec::new();
-    lines.push(format!("┌{}┐", "─".repeat(preview_width)));
-    for line in message.split("\n") {
-        let padding = 72_usize.saturating_sub(line.chars().count());
+    lines.push(format!("┌{}┐", "─".repeat(preview_width + 2)));
+    for line in message.split('\n') {
+        let padding = preview_width.saturating_sub(line.width());
         lines.push(format!("│ {line}{:padding$} │", ""));
     }
-    lines.push(format!("└{}┘", "─".repeat(preview_width)));
+    lines.push(format!("└{}┘", "─".repeat(preview_width + 2)));
     lines.join("\n")
 }
 
@@ -270,4 +276,91 @@ mod tests {
         let expected = format!("│ {line_72} │");
         assert_eq!(lines[1], expected);
     }
+
+    /// A single CJK character (display width 2) is padded as if it occupies 2 columns,
+    /// not 1 — so the right-hand padding is 70 spaces, not 71
+    #[test]
+    fn format_message_box_single_cjk_char() {
+        let result = format_message_box("字");
+        let lines: Vec<&str> = result.split('\n').collect();
+        let expected = format!("│ 字{:70} │", "");
+        assert_eq!(lines[1], expected);
+    }
+
+    /// A single emoji (display width 2) is padded as if it occupies 2 columns
+    #[test]
+    fn format_message_box_single_emoji() {
+        let result = format_message_box("🦀");
+        let lines: Vec<&str> = result.split('\n').collect();
+        let expected = format!("│ 🦀{:70} │", "");
+        assert_eq!(lines[1], expected);
+    }
+
+    /// Mixed ASCII and CJK: padding accounts for the display width of the whole line
+    ///
+    /// "feat: " = 6 display cols, "漢字" = 4 display cols → total 10, padding = 62
+    #[test]
+    fn format_message_box_mixed_ascii_and_cjk() {
+        let result = format_message_box("feat: 漢字");
+        let lines: Vec<&str> = result.split('\n').collect();
+        let expected = format!("│ feat: 漢字{:62} │", "");
+        assert_eq!(lines[1], expected);
+    }
+
+    /// When a line exceeds 72 display columns the border expands to fit (width + 2 dashes)
+    #[test]
+    fn format_message_box_border_expands_beyond_72() {
+        let line_73 = "a".repeat(73);
+        let result = format_message_box(&line_73);
+        let lines: Vec<&str> = result.split('\n').collect();
+        let dashes = "─".repeat(75); // 73 + 2
+        assert_eq!(lines[0], format!("┌{dashes}┐"));
+        assert_eq!(lines[lines.len() - 1], format!("└{dashes}┘"));
+    }
+
+    /// A line that sets the box width gets zero right-hand padding
+    #[test]
+    fn format_message_box_widest_line_has_no_padding() {
+        let line_73 = "a".repeat(73);
+        let result = format_message_box(&line_73);
+        let lines: Vec<&str> = result.split('\n').collect();
+        assert_eq!(lines[1], format!("│ {line_73} │"));
+    }
+
+    /// In a multi-line message, shorter lines are padded out to match the widest line
+    #[test]
+    fn format_message_box_shorter_lines_padded_to_widest() {
+        let long_line = "a".repeat(80);
+        let result = format_message_box(&format!("{long_line}\nshort"));
+        let lines: Vec<&str> = result.split('\n').collect();
+        assert_eq!(lines[1], format!("│ {long_line} │"));
+        assert_eq!(lines[2], format!("│ short{:75} │", "")); // 80 - 5 = 75
+    }
+
+    /// All rows have equal char count when the box expands beyond 72
+    #[test]
+    fn format_message_box_all_rows_same_width_when_expanded() {
+        let long_line = "a".repeat(80);
+        let result = format_message_box(&format!("{long_line}\nshort"));
+        let widths: Vec<usize> = result.split('\n').map(|l| l.chars().count()).collect();
+        let expected = widths[0];
+        assert!(
+            widths.iter().all(|&w| w == expected),
+            "rows have differing widths: {:?}",
+            widths
+        );
+    }
+
+    /// Wide characters can also trigger box expansion beyond 72 columns
+    ///
+    /// 37 CJK characters × 2 display columns = 74 display columns → border uses 76 dashes
+    #[test]
+    fn format_message_box_wide_chars_expand_box() {
+        let wide_line = "字".repeat(37); // 74 display cols
+        let result = format_message_box(&wide_line);
+        let lines: Vec<&str> = result.split('\n').collect();
+        let dashes = "─".repeat(76); // 74 + 2
+        assert_eq!(lines[0], format!("┌{dashes}┐"));
+        assert_eq!(lines[1], format!("│ {wide_line} │")); // no padding
+    }
 }