prefer-static-collator.ts

import type {Rule} from 'eslint';
import type {
  CallExpression,
  ArrowFunctionExpression,
  FunctionExpression,
  Node
} from 'estree';

const COMPARATOR_METHODS = new Set(['sort', 'toSorted']);

type FunctionExpr = (ArrowFunctionExpression | FunctionExpression) &
  Rule.NodeParentExtension;

function findEnclosingCallback(node: Rule.Node): FunctionExpr | null {
  let cur: Rule.Node | null | undefined = node.parent;
  while (cur) {
    if (
      cur.type === 'ArrowFunctionExpression' ||
      cur.type === 'FunctionExpression'
    ) {
      return cur;
    }
    if (cur.type === 'FunctionDeclaration') {
      return null;
    }
    cur = cur.parent;
  }
  return null;
}

function isComparatorCallback(fn: FunctionExpr): boolean {
  const parent = fn.parent;
  if (!parent || parent.type !== 'CallExpression') return false;
  const callee = parent.callee;
  if (callee.type !== 'MemberExpression' || callee.computed) return false;
  if (callee.property.type !== 'Identifier') return false;
  if (!COMPARATOR_METHODS.has(callee.property.name)) return false;
  return (parent.arguments as Node[]).includes(fn);
}

export const preferStaticCollator: Rule.RuleModule = {
  meta: {
    type: 'suggestion',
    docs: {
      description:
        'Prefer hoisting an `Intl.Collator` instance over calling localeCompare in a sort callback',
      recommended: false
    },
    schema: [],
    messages: {
      preferStaticCollator:
        '`localeCompare` constructs an `Intl.Collator` on every call. Hoist `const collator = new Intl.Collator(...)` outside the callback and use `collator.compare(a, b)`.'
    }
  },
  create(context) {
    return {
      CallExpression(node: CallExpression & Rule.NodeParentExtension) {
        if (node.callee.type !== 'MemberExpression') return;
        if (node.callee.computed) return;
        if (
          node.callee.property.type !== 'Identifier' ||
          node.callee.property.name !== 'localeCompare'
        )
          return;
        const fn = findEnclosingCallback(node);
        if (!fn) return;
        if (!isComparatorCallback(fn)) return;
        context.report({node, messageId: 'preferStaticCollator'});
      }
    };
  }
};