Forbidden reasons do not work with regular rules

Bug Report

When a rule has condition object, it’s custom message is ignored.

const { AbilityBuilder, ForbiddenError } = require("@casl/ability")

class Post {
  constructor(owner) {
    this.owner = owner;
  }
}

const ability = AbilityBuilder.define((can, cannot) => {
  can('read', 'Post', { owner: 'user_id_1' }).because('Only owner');
});

try {
  ForbiddenError.from(ability).throwUnlessCan('read', new Post('user_id_2'));
} catch (error) {
  console.log(error.message) // "Cannot execute "read" on "Post""
}

Expected behavior

error.message should be "Only owner" but it is "Cannot execute "read" on "Post""

Environment

• node version: 12.15.0
• @casl/ability version: 3.4.0
• os: Ubuntu 18.04

[stalniy]

The example above can be used to implement desired behavior starting from @casl/ability@4.1.0

[stalniy]

After some thinking, I realized there is no sense to enumerate all reasons which are not met, you can just say “none of the expected checks are satisfied”. But if you very need this, you can implement it by defining custom defaultErrorMessage:

import { ForbiddenError } from '@casl/ability';

ForbiddenError.setDefaultMessage((error) => {
  if (error.reason) {
    return error.reason
  }

  const reasons = error.ability.rulesFor(error.action, error.subject, error.field)
    .map(rule => `"${rule.reason}"`)
    .join(' nor ');
  return `Neither ${reasons}  are satisfied
});

error.ability is currently a private property, I will expose it in the next release to be a public one