Copy implementation from ember-cached-decorator-polyfill and add types

NullVoxPopuli · buschtoens · NullVoxPopuli · commit 23b17f900ac6 · 2022-02-24T16:57:57.000-05:00
Co-Authored-By: Jan Buschtöns &lt;jan@buschtoens.me&gt;
diff --git a/packages/@glimmer/tracking/index.ts b/packages/@glimmer/tracking/index.ts
@@ -1 +1,2 @@
+export { cached } from './src/cached';
 export { tracked } from './src/tracked';
diff --git a/packages/@glimmer/tracking/src/cached.ts b/packages/@glimmer/tracking/src/cached.ts
@@ -0,0 +1,50 @@
+import { DEBUG } from '@glimmer/env';
+import { createCache, getValue } from '@glimmer/validator';
+
+// eslint-disable-next-line @typescript-eslint/no-explicit-any
+export const cached: PropertyDecorator = (...args: any[]) => {
+  const [target, key, descriptor] = args;
+
+  // Error on `@cached()`, `@cached(...args)`, and `@cached propName = value;`
+  if (DEBUG && target === undefined) throwCachedExtraneousParens();
+  if (
+    DEBUG &&
+    (typeof target !== 'object' ||
+      typeof key !== 'string' ||
+      typeof descriptor !== 'object' ||
+      args.length !== 3)
+  ) {
+    throwCachedInvalidArgsError(args);
+  }
+  if (DEBUG && 'get' in descriptor && typeof descriptor.get !== 'function')
+    throwCachedGetterOnlyError(key);
+
+  const caches = new WeakMap();
+  const getter = descriptor.get;
+  descriptor.get = function (): unknown {
+    if (!caches.has(this)) caches.set(this, createCache(getter.bind(this)));
+    return getValue(caches.get(this));
+  };
+};
+
+function throwCachedExtraneousParens(): never {
+  throw new Error(
+    'You attempted to use @cached(), which is not necessary nor supported. Remove the parentheses and you will be good to go!'
+  );
+}
+
+function throwCachedGetterOnlyError(key: string): never {
+  throw new Error(`The @cached decorator must be applied to getters. '${key}' is not a getter.`);
+}
+
+function throwCachedInvalidArgsError(args: unknown[]): never {
+  throw new Error(
+    `You attempted to use @cached on with ${
+      args.length > 1 ? 'arguments' : 'an argument'
+    } ( @cached(${args
+      .map((d) => `'${d}'`)
+      .join(
+        ', '
+      )}), which is not supported. Dependencies are automatically tracked, so you can just use ${'`@cached`'}`
+  );
+}
diff --git a/test/types/tracking-test.ts b/test/types/tracking-test.ts
@@ -3,7 +3,10 @@ import { hasExactKeys } from './utils';
 
 hasExactKeys<{
   tracked: unknown;
+  cached: unknown;
 }>()(tracking);
 
 // $ExpectType PropertyDecorator
 tracking.tracked;
+// $ExpectType PropertyDecorator
+tracking.cached;

Original file line number	Diff line number	Diff line change
`@@ -1 +1,2 @@`
	`1`	`+export { cached } from './src/cached';`
`1`	`2`	`export { tracked } from './src/tracked';`