Terminal: measure grapheme display width

src/terminal/ansi.ts

@@ -4,11 +4,29 @@ const OSC8_PATTERN = "\\x1b\\]8;;.*?\\x1b\\\\|\\x1b\\]8;;\\x1b\\\\";
 
 const ANSI_REGEX = new RegExp(ANSI_SGR_PATTERN, "g");
 const OSC8_REGEX = new RegExp(OSC8_PATTERN, "g");
+const graphemeSegmenter =
+  typeof Intl !== "undefined" && "Segmenter" in Intl
+    ? new Intl.Segmenter(undefined, { granularity: "grapheme" })
+    : null;
 
 export function stripAnsi(input: string): string {
   return input.replace(OSC8_REGEX, "").replace(ANSI_REGEX, "");
 }
 
+export function splitGraphemes(input: string): string[] {
+  if (!input) {
+    return [];
+  }
+  if (!graphemeSegmenter) {
+    return Array.from(input);
+  }
+  try {
+    return Array.from(graphemeSegmenter.segment(input), (segment) => segment.segment);
+  } catch {
+    return Array.from(input);
+  }
+}
+
 /**
  * Sanitize a value for safe interpolation into log messages.
  * Strips ANSI escape sequences, C0 control characters (U+0000–U+001F),
@@ -22,6 +40,75 @@ export function sanitizeForLog(v: string): string {
   return out.replaceAll(String.fromCharCode(0x7f), "");
 }
 
-export function visibleWidth(input: string): number {
+function isZeroWidthCodePoint(codePoint: number): boolean {
-  return Array.from(stripAnsi(input)).length;
+  return (
+    (codePoint >= 0x0300 && codePoint <= 0x036f) ||
+    (codePoint >= 0x1ab0 && codePoint <= 0x1aff) ||
+    (codePoint >= 0x1dc0 && codePoint <= 0x1dff) ||
+    (codePoint >= 0x20d0 && codePoint <= 0x20ff) ||
+    (codePoint >= 0xfe20 && codePoint <= 0xfe2f) ||
+    (codePoint >= 0xfe00 && codePoint <= 0xfe0f) ||
+    codePoint === 0x200d
+  );
+}
+
+function isFullWidthCodePoint(codePoint: number): boolean {
+  if (codePoint < 0x1100) {
+    return false;
+  }
+  return (
+    codePoint <= 0x115f ||
+    codePoint === 0x2329 ||
+    codePoint === 0x232a ||
+    (codePoint >= 0x2e80 && codePoint <= 0x3247 && codePoint !== 0x303f) ||
+    (codePoint >= 0x3250 && codePoint <= 0x4dbf) ||
+    (codePoint >= 0x4e00 && codePoint <= 0xa4c6) ||
+    (codePoint >= 0xa960 && codePoint <= 0xa97c) ||
+    (codePoint >= 0xac00 && codePoint <= 0xd7a3) ||
+    (codePoint >= 0xf900 && codePoint <= 0xfaff) ||
+    (codePoint >= 0xfe10 && codePoint <= 0xfe19) ||
+    (codePoint >= 0xfe30 && codePoint <= 0xfe6b) ||
+    (codePoint >= 0xff01 && codePoint <= 0xff60) ||
+    (codePoint >= 0xffe0 && codePoint <= 0xffe6) ||
+    (codePoint >= 0x1aff0 && codePoint <= 0x1aff3) ||
+    (codePoint >= 0x1aff5 && codePoint <= 0x1affb) ||
+    (codePoint >= 0x1affd && codePoint <= 0x1affe) ||
+    (codePoint >= 0x1b000 && codePoint <= 0x1b2ff) ||
+    (codePoint >= 0x1f200 && codePoint <= 0x1f251) ||
+    (codePoint >= 0x20000 && codePoint <= 0x3fffd)
+  );
+}
+
+const emojiLikePattern = /[\p{Extended_Pictographic}\p{Regional_Indicator}\u20e3]/u;
+
+function graphemeWidth(grapheme: string): number {
+  if (!grapheme) {
+    return 0;
+  }
+  if (emojiLikePattern.test(grapheme)) {
+    return 2;
+  }
+
+  let sawPrintable = false;
+  for (const char of grapheme) {
+    const codePoint = char.codePointAt(0);
+    if (codePoint == null) {
+      continue;
+    }
+    if (isZeroWidthCodePoint(codePoint)) {
+      continue;
+    }
+    if (isFullWidthCodePoint(codePoint)) {
+      return 2;
+    }
+    sawPrintable = true;
+  }
+  return sawPrintable ? 1 : 0;
+}
+
+export function visibleWidth(input: string): number {
+  return splitGraphemes(stripAnsi(input)).reduce(
+    (sum, grapheme) => sum + graphemeWidth(grapheme),
+    0,
+  );
 }