fix(bun): handle malformed ANSI sequences in Bun.stringWidth

Fixed a bug where Bun.stringWidth() returned 0 for strings containing
malformed ANSI escape sequences (e.g., "\x1b[" without closing "m").

The issue was in two places:
1. visibleLatin1WidthExcludeANSIColors: When no closing 'm' was found after
   '\x1b[', the function returned early without counting remaining characters
2. visibleUTF16WidthFn: Similar issue with unclosed sequences

Now treats malformed ANSI sequences as literal text and counts their visible
width correctly.

Added comprehensive tests for edge cases including:
- Unclosed ANSI sequences
- Binary data with control characters
- Multiple malformed sequences

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

src/string/immutable/visible.zig

@@ -657,11 +657,19 @@ pub const visible = struct {
             length += visibleLatin1Width(input[0..i]);
             input = input[i..];
 
-            if (input.len < 3) return length;
+            if (input.len < 3) {
+                length += visibleLatin1Width(input);
+                return length;
+            }
 
             if (input[1] == '[') {
-                const end = indexFn(input[2..], 'm') orelse return length;
-                input = input[end + 3 ..];
+                if (indexFn(input[2..], 'm')) |end| {
+                    input = input[end + 3 ..];
+                } else {
+                    // No closing 'm' found, treat the rest as visible characters
+                    length += visibleLatin1Width(input);
+                    return length;
+                }
             } else {
                 input = input[1..];
             }
@@ -756,10 +764,19 @@ pub const visible = struct {
                     saw_1b = true;
                     continue;
                 }
-                len += stretch_len;
+                // If we're not in the middle of an ANSI sequence, add stretch_len and reset
+                // If we ARE in a sequence (saw_bracket is true), keep accumulating in stretch_len
+                if (!saw_bracket) {
+                    len += stretch_len;
+                    stretch_len = 0;
+                }
                 input = input[idx..];
             }
-            if (input.len == 0) break;
+            if (input.len == 0) {
+                // If we reach the end with an unclosed ANSI sequence, count the accumulated characters
+                len += stretch_len;
+                break;
+            }
             const replacement = utf16CodepointWithFFFD(input);
             defer input = input[replacement.len..];
             if (replacement.fail) continue;

test/js/bun/util/stringWidth.test.ts

@@ -149,3 +149,37 @@ for (let matcher of ["toMatchNPMStringWidth", "toMatchNPMStringWidthExcludeANSI"
     expect("👨‍❤️‍💋‍👨")[matcher]();
   });
 }
+
+// Test for strings with control characters and binary data (from gist)
+test("handles binary data with control characters", () => {
+  // This string caused freezing issues in earlier versions
+  const problematicString = `com.apple.lastuseddate#PS: S<>\u000bi\ncom.apple.macl: \x07@<40><>Y6<59>>J<><4A>'<27><>\x03<EFBFBD>FS\ncom.apple.metadata:kMDItemWhereFroms: bplist00<30>\x01\x02_\x11\x02\x04https://software.download.prss.microsoft.com/dbazure/Win11_25H2_English_Arm64.iso?t=984c522c-a10b-41d5-99ec-68cc848694c9&P1=1762014682&P2=601&P3=2&P4=G6eN0uFrG64Ft%2bDz061PD0rTvYV2UQjZUVtyS9Rn9Ytt0F%2bscgadBtf%2fUs5BKFyowVlDqPhEbTtqBsPEk21bgNAyRwBj%2fgnQcRhiIwEcqSJ9Wyf4ChE%2bYRuc0Eeha9IJakJwuBizc38a4qKsEIxihqroM01TM8iANCExlWWZKG3Gayc%2b18OcvGefTc1G%2bvtvd57AWmeK1kho00yTFtT1sqdS6OXV000YyaYoIVLjVypaoQj7MYJ46vCQb%2bVvn3QZgXaMVwbKjCMI15ezgpGptQPWBssWz9hYC9Fv1OuWcmBwvLGkvL1MczAWSuY3P0kqfezG%2fdkh2cX5NUo2G3zPtw%3d%3d_\x10\x1ahttps://www.microsoft.com/\ncom.apple.provenance: \x01\x02\n`;
+
+  // Should not freeze and should return a reasonable width
+  const width = Bun.stringWidth(problematicString);
+  expect(width).toBeGreaterThan(0);
+  expect(width).toBeLessThan(problematicString.length + 100);
+
+  // Also test with countAnsiEscapeCodes: false (the default)
+  const width2 = Bun.stringWidth(problematicString, { countAnsiEscapeCodes: false });
+  expect(width2).toBeGreaterThan(0);
+  expect(width2).toBeLessThan(problematicString.length + 100);
+});
+
+// Test edge cases with malformed ANSI sequences
+test("handles malformed ANSI sequences", () => {
+  // ESC without [
+  expect(Bun.stringWidth("\x1bHello")).toBeGreaterThan(0);
+
+  // ESC [ without closing m
+  expect(Bun.stringWidth("\x1b[31Hello")).toBeGreaterThan(0);
+
+  // ESC [ with other characters but no m
+  expect(Bun.stringWidth("\x1b[31;32;33Hello")).toBeGreaterThan(0);
+
+  // Multiple unclosed sequences
+  expect(Bun.stringWidth("\x1b[31\x1b[32\x1b[33Hello")).toBeGreaterThan(0);
+
+  // Control characters mixed with text
+  expect(Bun.stringWidth("\x01\x02\x03Hello\x07\x0b\x10\x1aWorld")).toBeGreaterThan(0);
+});