Migrate @emotion/weak-memoize to TypeScript (#2429)

* [weak-memoize] Convert to TypeScript

* Add changeset

* tweak a bunch of stuff

Co-authored-by: Mateusz Burzyński <mateuszburzynski@gmail.com>

.changeset/loud-hairs-approve.md

@@ -0,0 +1,5 @@
+---
+'@emotion/weak-memoize': minor
+---
+
+Source code has been migrated to TypeScript. From now on type declarations will be emitted based on that, instead of being hand-written.

packages/memoize/package.json

@@ -18,8 +18,7 @@
   },
   "files": [
     "src",
-    "dist",
-    "types/*.d.ts"
+    "dist"
   ],
   "browser": {
     "./dist/emotion-memoize.cjs.js": "./dist/emotion-memoize.browser.cjs.js",

packages/weak-memoize/package.json

@@ -4,7 +4,7 @@
   "description": "A memoization function that uses a WeakMap",
   "main": "dist/emotion-weak-memoize.cjs.js",
   "module": "dist/emotion-weak-memoize.esm.js",
-  "types": "types/index.d.ts",
+  "types": "dist/declarations/src/index.d.ts",
   "license": "MIT",
   "repository": "https://github.com/emotion-js/emotion/tree/main/packages/weak-memoize",
   "scripts": {
@@ -18,8 +18,7 @@
   },
   "files": [
     "src",
-    "dist",
-    "types/*.d.ts"
+    "dist"
   ],
   "browser": {
     "./dist/emotion-weak-memoize.cjs.js": "./dist/emotion-weak-memoize.browser.cjs.js",

packages/weak-memoize/src/index.ts

@@ -0,0 +1,17 @@
+let weakMemoize = function <Arg extends object, Return>(
+  func: (arg: Arg) => Return
+): (arg: Arg) => Return {
+  let cache = new WeakMap<Arg, Return>()
+  return (arg: Arg) => {
+    if (cache.has(arg)) {
+      // Use non-null assertion because we just checked that the cache `has` it
+      // This allows us to remove `undefined` from the return value
+      return cache.get(arg)!
+    }
+    let ret = func(arg)
+    cache.set(arg, ret)
+    return ret
+  }
+}
+
+export default weakMemoize

packages/weak-memoize/types/index.d.ts

@@ -1,7 +1,3 @@
 // TypeScript Version: 2.2
 
-type UnaryFn<Arg, Return> = (arg: Arg) => Return
-
-export default function weakMemoize<Arg extends object, Return>(
-  func: UnaryFn<Arg, Return>
-): UnaryFn<Arg, Return>
+export { default } from '../src'

packages/weak-memoize/types/tests.ts

@@ -1,4 +1,4 @@
-import weakMemoize from '@emotion/weak-memoize'
+import weakMemoize from '../src'
 
 interface Foo {
   bar: 'xyz'

packages/weak-memoize/types/tslint.json

@@ -18,6 +18,7 @@
     ],
 
     "no-unnecessary-generics": false,
-    "strict-export-declare-modifiers": false
+    "strict-export-declare-modifiers": false,
+    "no-default-import": false
   }
 }