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fix: backspace once per character when replacing wide-char tokens #487

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fix: backspace once per character when replacing wide-char tokens #487

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12 changes: 9 additions & 3 deletions src/runtime/replacement.ts
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Original file line number Diff line number Diff line change
Expand Up @@ -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;
Expand All @@ -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 + " ";

Expand All @@ -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 + " ";
Expand All @@ -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 => {
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11 changes: 9 additions & 2 deletions src/tests/runtime/replacement.test.ts
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Original file line number Diff line number Diff line change
Expand Up @@ -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,
Expand Down