Fix extra bracket in template literal syntax highlighting (#17327)

[robobun]

Summary

Fixes an issue where the JavaScript syntax highlighter was incorrectly adding an extra closing bracket (}) when highlighting template literal interpolations containing JSON.stringify() calls in colored terminal output.

Problem

When running code like this with colors enabled:

const result = {success:false};
const err = new Error(`error: ${JSON.stringify(result)}`);
throw err;

The error output would show an extra } character after JSON.stringify(, causing malformed syntax highlighting in the error display.

Root Cause

The bug was in the template literal parsing code in src/fmt.zig where it would always write a closing brace after processing template literal interpolation, even when a closing brace was already found and consumed from the input.

Before (buggy):

if (i < text.len and text[i] == '}') {
    i += 1;  // consume the brace
}
try writer.writeAll("}");  // always write a brace (BUG\!)

After (fixed):

if (i < text.len and text[i] == '}') {
    try writer.writeAll("}");  // only write if found
    i += 1;  // then consume it
}

Solution

• Only write the closing } character when it's actually found in the input
• This ensures the syntax highlighter doesn't add extra brackets to the output
• The fix is minimal and surgical, affecting only the specific case where the bug occurred

Test plan

• Manual reproduction confirmed the issue existed before the fix
• Manual verification confirmed the extra bracket no longer appears after the fix
• Created comprehensive regression test in test/regression/issue/17327.test.ts
• Tested edge cases with nested JSON objects and arrays
• Verified fix works with both FORCE_COLOR=1 and NO_COLOR=1 modes
• All tests pass locally

🤖 Generated with Claude Code

[robobun]

^{Updated 5:58 PM PT - Jul 18th, 2025}

@autofix-ci[bot], your commit 487e4a6 is building: #20962

[markovejnovic]

Would potentially suggest making these tests shorter since, as it turns out, the issue is in the highlighting of interpolated strings specifically.

I've gotten minimum reproducibility with:

import { highlightJavaScript as highlighter } from "bun:internal-for-testing";
import { expect, test } from "bun:test";
import stripAnsiColors from "strip-ansi";

test("highlighter-with-multiline-interpolated-string", () => {
  const testStr = '`foo: \${bar';
  const highlighted = highlighter(testStr);
  expect(stripAnsiColors(highlighted)).toBe(testStr);
});

test("highlighter-with-interpolated-string", () => {
  const testStr = '`foo: \${bar}';
  const highlighted = highlighter(testStr);
  expect(stripAnsiColors(highlighted)).toBe(testStr);
});