Refactor to improve internal severity coercion

Closes GH-287. Reviewed-by: Titus Wormer <tituswormer@gmail.com> Reviewed-by: Christian Murphy <christian.murphy.42@gmail.com>

Author: jablko

packages/unified-lint-rule/lib/index.js

@@ -19,8 +19,6 @@
 
 import {wrap} from 'trough'
 
-const primitives = new Set(['string', 'number', 'boolean'])
-
 /**
  * @param {string|RuleMeta} meta
  * @param {Rule} rule
@@ -80,54 +78,31 @@ export function lintRule(meta, rule) {
  * @returns {SeverityTuple}
  */
 function coerce(name, config) {
+ if (!Array.isArray(config)) return [1, config]
  /** @type {Array<unknown>} */
- let result
-
- if (config === null || config === undefined) {
- result = [1]
- } else if (
- Array.isArray(config) &&
- // `isArray(unknown)` is turned into `Array<any>`:
- // type-coverage:ignore-next-line
- primitives.has(typeof config[0])
- ) {
- // `isArray(unknown)` is turned into `Array<any>`:
- // type-coverage:ignore-next-line
- result = [...config]
- } else {
- result = [1, config]
- }
-
- let level = result[0]
-
- if (typeof level === 'boolean') {
- level = level ? 1 : 0
- } else if (typeof level === 'string') {
- if (level === 'off') {
- level = 0
- } else if (level === 'on' || level === 'warn') {
- level = 1
- } else if (level === 'error') {
- level = 2
- } else {
- level = 1
- result = [level, result]
- }
- }
-
- if (typeof level !== 'number' || level < 0 || level > 2) {
- throw new Error(
- 'Incorrect severity `' +
- level +
- '` for `' +
- name +
- '`, ' +
- 'expected 0, 1, or 2'
- )
+ const [severity, ...options] = config
+ switch (severity) {
+ case false:
+ case 'off':
+ case 0:
+ return [0, ...options]
+ case true:
+ case 'on':
+ case 'warn':
+ case 1:
+ return [1, ...options]
+ case 'error':
+ case 2:
+ return [2, ...options]
+ default:
+ if (typeof severity !== 'number') return [1, config]
+ throw new Error(
+ 'Incorrect severity `' +
+ severity +
+ '` for `' +
+ name +
+ '`, ' +
+ 'expected 0, 1, or 2'
+ )
  }
-
- result[0] = level
-
- // @ts-expect-error: it’s now a valid tuple.
- return result
 }