svelte/src/compiler/compile/render-dom/wrappers/shared/create_debugging_comment.ts

import Component from '../../../Component';
import { INode } from '../../../nodes/interfaces';

export default function create_debugging_comment(
	node: INode,
	component: Component
) {
	const { locate, source } = component;

	let c = node.start;
	if (node.type === 'ElseBlock') {
		while (source[c - 1] !== '{') c -= 1;
		while (source[c - 1] === '{') c -= 1;
	}

	let d;

	if (node.type === 'InlineComponent' || node.type === 'Element') {
		d = node.children.length ? node.children[0].start : node.start;
		while (source[d - 1] !== '>') d -= 1;
	} else {
		// @ts-ignore
		d = node.expression ? node.expression.node.end : c;
		while (source[d] !== '}') d += 1;
		while (source[d] === '}') d += 1;
	}

	const start = locate(c);
	const loc = `(${start.line + 1}:${start.column})`;

	return `${loc} ${source.slice(c, d)}`.replace(/\s/g, ' ');
}