ui/node_modules/svelte/src/compiler/utils/get_code_frame.js

const regex_tabs = /^\t+/;

/**
 * @param {string} str
 */
function tabs_to_spaces(str) {
	return str.replace(regex_tabs, (match) => match.split('\t').join('  '));
}

/**
 * @param {string} source
 * @param {number} line
 * @param {number} column
 */
export default function get_code_frame(source, line, column) {
	const lines = source.split('\n');
	const frame_start = Math.max(0, line - 2);
	const frame_end = Math.min(line + 3, lines.length);
	const digits = String(frame_end + 1).length;
	return lines
		.slice(frame_start, frame_end)
		.map((str, i) => {
			const is_error_line = frame_start + i === line;
			const line_num = String(i + frame_start + 1).padStart(digits, ' ');
			if (is_error_line) {
				const indicator =
					' '.repeat(digits + 2 + tabs_to_spaces(str.slice(0, column)).length) + '^';
				return `${line_num}: ${tabs_to_spaces(str)}\n${indicator}`;
			}
			return `${line_num}: ${tabs_to_spaces(str)}`;
		})
		.join('\n');
}