From a2a1624c8656a7f633e455489e4ee22c73b278a5 Mon Sep 17 00:00:00 2001
From: chenxin <chenxin@me.com>
Date: Wed, 14 Oct 2026 16:23:22 +0800
Subject: [PATCH] fix: backspace once per character when replacing wide-char
 tokens
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Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

calculateReplacement used tokenLength, a display width, as the number of
backspaces to send. Shells delete one character per backspace, so a
token containing wide characters (CJK) over-deleted: typing `cd 中` and
accepting `中文目录/` sent two backspaces for one character and also
removed the space before it, producing `cd中文目录/`.

Convert the display width to a character count before sending
backspaces. Quotes and escape characters are single-width, so the
difference between the token text's display width and its character
count is exactly the extra width to subtract.

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>
---
 src/runtime/replacement.ts            | 12 +++++++++---
 src/tests/runtime/replacement.test.ts | 11 +++++++++--
 2 files changed, 18 insertions(+), 5 deletions(-)

diff --git a/src/runtime/replacement.ts b/src/runtime/replacement.ts
index 81a92eb0..d22e7288 100644
--- a/src/runtime/replacement.ts
+++ b/src/runtime/replacement.ts
@@ -3,6 +3,7 @@
 
 import { CommandToken } from "./parser.js";
 import { Suggestion } from "./model.js";
+import { wcswidth } from "../utils/unicode.js";
 
 export type ReplacementAction = {
   backspaceCount: number;
@@ -15,6 +16,11 @@ const commonPrefixLength = (a: string, b: string): number => {
   return i;
 };
 
+// Shells delete one character per backspace, but tokenLength is a display width in which wide
+// characters (e.g. CJK) count as 2. Quotes and escapes are single-width, so the difference between
+// the width and the character count of the token text is exactly the extra width to remove.
+const typedCharCount = (token: CommandToken): number => token.tokenLength - (wcswidth(token.token) - Array.from(token.token).length);
+
 export const calculateReplacement = (token: CommandToken | undefined, suggestion: Suggestion): ReplacementAction | undefined => {
   const suggestionText = suggestion.insertValue ?? suggestion.name + " ";
 
@@ -24,10 +30,10 @@ export const calculateReplacement = (token: CommandToken | undefined, suggestion
   }
 
   const typedText = token.token;
-  const tokenDisplayWidth = token.tokenLength;
+  const tokenCharCount = typedCharCount(token);
 
   if (suggestion.insertValue != null && suggestion.insertValue !== suggestion.name) {
-    return { backspaceCount: tokenDisplayWidth, insertText: suggestionText };
+    return { backspaceCount: tokenCharCount, insertText: suggestionText };
   }
 
   const target = suggestion.name + " ";
@@ -39,7 +45,7 @@ export const calculateReplacement = (token: CommandToken | undefined, suggestion
     return { backspaceCount: 0, insertText: remaining };
   }
 
-  return { backspaceCount: tokenDisplayWidth, insertText: target };
+  return { backspaceCount: tokenCharCount, insertText: target };
 };
 
 export const applyReplacement = (action: ReplacementAction): string => {
diff --git a/src/tests/runtime/replacement.test.ts b/src/tests/runtime/replacement.test.ts
index 43b330f5..53c996ec 100644
--- a/src/tests/runtime/replacement.test.ts
+++ b/src/tests/runtime/replacement.test.ts
@@ -64,12 +64,19 @@ describe("calculateReplacement", () => {
       insertText: "好 ",
     });
   });
-  test("wide-char divergent uses display width for backspace", () => {
+  test("wide-char divergent uses character count for backspace", () => {
+    // shells delete one character per backspace regardless of its display width
     expect(calculateReplacement(makeToken({ token: "你", tokenLength: 2 }), makeSuggestion({ name: "世界" }))).toEqual({
-      backspaceCount: 2,
+      backspaceCount: 1,
       insertText: "世界 ",
     });
   });
+  test("mixed-width divergent deletes one backspace per character", () => {
+    expect(calculateReplacement(makeToken({ token: "a你", tokenLength: 3 }), makeSuggestion({ name: "b" }))).toEqual({
+      backspaceCount: 2,
+      insertText: "b ",
+    });
+  });
   test("option prefix appends remaining", () => {
     expect(calculateReplacement(makeToken({ token: "--ver", isOption: true }), makeSuggestion({ name: "--version" }))).toEqual({
       backspaceCount: 0,