RegExp literal oblivious to unescaped whitespace

regexpx.mts

const cacheRegExpx = new WeakMap<readonly string[], string[]>();
export function RegExpx<T extends { [key: string]: string | undefined }>(
	{ raw }: TemplateStringsArray,
	...substitutions: unknown[]
) {
	let strs = cacheRegExpx.get(raw);

	if (!strs) {
		cacheRegExpx.set(raw, (strs = raw.slice()));
		for (let i = 0; i < strs.length; i++) {
			// We strip all spaces, except for ones preceeded by an unbalanced number of backslashes
			// where we retain the space and drop the escape backsclash.
			strs[i] = strs[i]!.replace(/(\\*)\s+/g, (m, { length: s }) => m.substring(s & 1, s + (s & 1)));
		}
	}

	// Apply the substitutions, this can't be cached
	let acc = strs[0]!;
	for (let i = 1; i < strs.length; i++) {
		acc += String(substitutions[i - 1]) + strs[i]!;
	}

	return new RegExp(acc) as Omit<RegExp, "exec"> & {
		exec(string: string): RegExpExecArrayWithGroups<T> | null;
	};
}

export interface RegExpExecArrayWithGroups<T extends { [key: string]: string | undefined }>
	extends Omit<RegExpExecArray, "groups"> {
	groups: T;
}