add CaseInsensitiveMap class

Note: class name is set to "Map" so that snapshots and inspect output
aren't affected.

lib/case-insensitive-map.js

@@ -0,0 +1,48 @@
+// package children are represented with a Map object, but many file systems
+// are case-insensitive and unicode-normalizing, so we need to treat
+// node.children.get('FOO') and node.children.get('foo') as the same thing.
+
+const _keys = Symbol('keys')
+const _normKey = Symbol('normKey')
+const normalize = s => s.normalize('NFKD').toLowerCase()
+const OGMap = Map
+module.exports = class Map extends OGMap {
+  constructor (items = []) {
+    super()
+    this[_keys] = new OGMap()
+    for (const [key, val] of items)
+      this.set(key, val)
+  }
+
+  [_normKey] (key) {
+    return typeof key === 'string' ? normalize(key) : key
+  }
+
+  get (key) {
+    const normKey = this[_normKey](key)
+    return this[_keys].has(normKey) ? super.get(this[_keys].get(normKey))
+      : undefined
+  }
+
+  set (key, val) {
+    const normKey = this[_normKey](key)
+    if (this[_keys].has(normKey))
+      super.delete(this[_keys].get(normKey))
+    this[_keys].set(normKey, key)
+    return super.set(key, val)
+  }
+
+  delete (key) {
+    const normKey = this[_normKey](key)
+    if (this[_keys].has(normKey)) {
+      const prevKey = this[_keys].get(normKey)
+      this[_keys].delete(normKey)
+      return super.delete(prevKey)
+    }
+  }
+
+  has (key) {
+    const normKey = this[_normKey](key)
+    return this[_keys].has(normKey) && super.has(this[_keys].get(normKey))
+  }
+}

test/case-insensitive-map.js

@@ -0,0 +1,47 @@
+const t = require('tap')
+const CMap = require('../lib/case-insensitive-map.js')
+
+t.test('set values in ctor', t => {
+  const cmap = new CMap([['a', 'a'], [null, 'null'], [{a: 1}, 'a:1'], ['A', 'A']])
+  t.strictSame([...cmap.entries()], [[null, 'null'], [{a: 1}, 'a:1'], ['A', 'A']])
+  t.equal(cmap.has('a'), true)
+  t.equal(cmap.has('A'), true)
+  t.equal(cmap.get('a'), 'A')
+  cmap.delete('a')
+  t.equal(cmap.has('a'), false)
+  t.equal(cmap.has('A'), false)
+  t.equal(cmap.get('A'), undefined)
+  t.end()
+})
+
+t.test('set values after ctor', t => {
+  const cmap = new CMap()
+  cmap.set('a', 'a')
+  t.equal(cmap.has('a'), true)
+  t.equal(cmap.has('A'), true)
+  cmap.set(null, 'null')
+  cmap.set({a: 1}, 'a:1')
+  cmap.set('A', 'A')
+  t.strictSame([...cmap.entries()], [[null, 'null'], [{a: 1}, 'a:1'], ['A', 'A']])
+  cmap.delete('a')
+  t.equal(cmap.has('a'), false)
+  t.equal(cmap.has('A'), false)
+  t.equal(cmap.get('A'), undefined)
+  t.end()
+})
+
+t.test('dont get confused with undefined or weird values', t => {
+  const cmap = new CMap()
+  cmap.set(undefined, 'this is not defined')
+  cmap.set(NaN, 'this is not a number')
+  cmap.set('NaN', 'this is a string')
+  cmap.set('nan', 'this is a quieter string')
+
+  cmap.delete('foo')
+  cmap.delete('NAN')
+  t.strictSame([...cmap.entries()], [
+    [undefined, 'this is not defined'],
+    [NaN, 'this is not a number'],
+  ])
+  t.end()
+})