Initial Recoil Sync implementation (facebookexperimental#1225)

Summary:
Pull Request resolved: facebookexperimental#1225

Initial implementation of `recoil-sync` with `useRecoilSync()` hook and `syncEffect()` atom effect.  This just includes the basic functionality of registering atoms and reading/writing from storage.  Lots more diffs to come to complete the full support.

Current RFC API (*in flux based on ongoing feedback*):
```
type AtomDiff = Map<ItemKey, ?Loadable<mixed>>; // null entry means reset

useRecoilSync({
  syncKey?: SyncKey,  // key to match with syncEffect()

  write?: ({diff: ItemDiff, items: ItemSnapshot}) => void,
  read?: ItemKey => ?Loadable<mixed>,
  listen?: (AtomDiff => void) => (() => void),
}) => void;
```
```
function syncEffect<T>(params: {
  syncKey?: SyncKey,  // key to match with useRecoilSync()
  key?: ItemKey,  // defaults to Atom key

  restore: mixed => ?Loadable<T>,

  // For advanced use-cases
  read?: ({read: ItemKey => ?Loadable<mixed>}) => Loadable<mixed>,
  write?: (Loadable<T>, {read: ItemKey => ?Loadable<mixed>}) => ItemDiff,
}): AtomEffect<T>
```

Differential Revision: D30467990

fbshipit-source-id: 594c6cbe8067f1d7917e99e2eca74a250caf51be

src/contrib/recoil-sync/__tests__/recoil-sync-test.js

@@ -0,0 +1,256 @@
+/**
+ * Copyright (c) Facebook, Inc. and its affiliates. Confidential and proprietary.
+ *
+ * @emails oncall+recoil
+ * @flow strict-local
+ * @format
+ */
+'use strict';
+
+// TODO UPDATE IMPORTS TO USE PUBLIC INTERFACE
+// TODO PUBLIC LOADABLE INTERFACE
+
+const {act} = require('ReactTestUtils');
+
+const {
+  loadableWithError,
+  loadableWithPromise,
+  loadableWithValue,
+} = require('../../../adt/Recoil_Loadable');
+const atom = require('../../../recoil_values/Recoil_atom');
+const selectorFamily = require('../../../recoil_values/Recoil_selectorFamily');
+const {
+  ReadsAtom,
+  componentThatReadsAndWritesAtom,
+  flushPromisesAndTimers,
+  renderElements,
+} = require('../../../testing/Recoil_TestingUtils');
+const {syncEffect, useRecoilSync} = require('../recoil-sync');
+const React = require('react');
+
+test('Write to storage', async () => {
+  const atomA = atom({
+    key: 'recoil-sync write A',
+    default: 'DEFAULT',
+    effects_UNSTABLE: [syncEffect({validate: x => loadableWithValue(x)})],
+  });
+  const atomB = atom({
+    key: 'recoil-sync write B',
+    default: 'DEFAULT',
+    effects_UNSTABLE: [syncEffect({validate: x => loadableWithValue(x)})],
+  });
+  const ignoreAtom = atom({
+    key: 'recol-sync write ignore',
+    default: 'DEFAULT',
+  });
+
+  const storage = new Map();
+
+  function write({diff}) {
+    for (const [key, loadable] of diff.entries()) {
+      loadable != null ? storage.set(key, loadable) : storage.delete(key);
+    }
+  }
+  function RecoilSync() {
+    useRecoilSync({write});
+    return null;
+  }
+
+  const [AtomA, setA, resetA] = componentThatReadsAndWritesAtom(atomA);
+  const [AtomB, setB] = componentThatReadsAndWritesAtom(atomB);
+  const [IgnoreAtom, setIgnore] = componentThatReadsAndWritesAtom(ignoreAtom);
+  const container = renderElements(
+    <>
+      <RecoilSync />
+      <AtomA />
+      <AtomB />
+      <IgnoreAtom />
+    </>,
+  );
+
+  expect(storage.size).toBe(0);
+  expect(container.textContent).toBe('"DEFAULT""DEFAULT""DEFAULT"');
+
+  act(() => setA('A'));
+  act(() => setB('B'));
+  act(() => setIgnore('IGNORE'));
+  expect(container.textContent).toBe('"A""B""IGNORE"');
+  expect(storage.size).toBe(2);
+  expect(storage.get('recoil-sync write A')?.getValue()).toBe('A');
+  expect(storage.get('recoil-sync write B')?.getValue()).toBe('B');
+
+  act(() => resetA());
+  act(() => setB('BB'));
+  expect(container.textContent).toBe('"DEFAULT""BB""IGNORE"');
+  expect(storage.size).toBe(1);
+  expect(storage.has('recoil-sync write A')).toBe(false);
+  expect(storage.get('recoil-sync write B')?.getValue()).toBe('BB');
+});
+
+test('Write to multiple storages', async () => {
+  const atomA = atom({
+    key: 'recoil-sync multiple storage A',
+    default: 'DEFAULT',
+    effects_UNSTABLE: [
+      syncEffect({syncKey: 'A', validate: x => loadableWithValue(x)}),
+    ],
+  });
+  const atomB = atom({
+    key: 'recoil-sync multiple storage B',
+    default: 'DEFAULT',
+    effects_UNSTABLE: [
+      syncEffect({syncKey: 'B', validate: x => loadableWithValue(x)}),
+    ],
+  });
+
+  const storageA = new Map();
+  const storageB = new Map();
+
+  const write = storage => ({diff}) => {
+    for (const [key, loadable] of diff.entries()) {
+      loadable != null ? storage.set(key, loadable) : storage.delete(key);
+    }
+  };
+  function RecoilSync({syncKey, storage}) {
+    useRecoilSync({syncKey, write: write(storage)});
+    return null;
+  }
+
+  const [AtomA, setA] = componentThatReadsAndWritesAtom(atomA);
+  const [AtomB, setB] = componentThatReadsAndWritesAtom(atomB);
+  renderElements(
+    <>
+      <RecoilSync syncKey="A" storage={storageA} />
+      <RecoilSync syncKey="B" storage={storageB} />
+      <AtomA />
+      <AtomB />
+    </>,
+  );
+
+  expect(storageA.size).toBe(0);
+  expect(storageB.size).toBe(0);
+
+  act(() => setA('A'));
+  act(() => setB('B'));
+  expect(storageA.size).toBe(1);
+  expect(storageB.size).toBe(1);
+  expect(storageA.get('recoil-sync multiple storage A')?.getValue()).toBe('A');
+  expect(storageB.get('recoil-sync multiple storage B')?.getValue()).toBe('B');
+});
+
+test('Read from storage', async () => {
+  const atomA = atom({
+    key: 'recoil-sync read A',
+    default: 'DEFAULT',
+    effects_UNSTABLE: [syncEffect({validate: x => loadableWithValue(x)})],
+  });
+  const atomB = atom({
+    key: 'recoil-sync read B',
+    default: 'DEFAULT',
+    effects_UNSTABLE: [syncEffect({validate: x => loadableWithValue(x)})],
+  });
+  const atomC = atom({
+    key: 'recoil-sync read C',
+    default: 'DEFAULT',
+    effects_UNSTABLE: [syncEffect({validate: x => loadableWithValue(x)})],
+  });
+
+  const storage = {
+    'recoil-sync read A': loadableWithValue('A'),
+    'recoil-sync read B': loadableWithValue('B'),
+  };
+
+  function RecoilSync() {
+    useRecoilSync({read: itemKey => storage[itemKey]});
+    return null;
+  }
+
+  const container = renderElements(
+    <>
+      <RecoilSync />
+      <ReadsAtom atom={atomA} />
+      <ReadsAtom atom={atomB} />
+      <ReadsAtom atom={atomC} />
+    </>,
+  );
+
+  expect(container.textContent).toBe('"A""B""DEFAULT"');
+});
+
+test('Read from storage async', async () => {
+  const atomA = atom({
+    key: 'recoil-sync read async',
+    default: 'DEFAULT',
+    effects_UNSTABLE: [syncEffect({validate: x => loadableWithValue(x)})],
+  });
+
+  const storage = {
+    'recoil-sync read async': loadableWithPromise(
+      Promise.resolve({__value: 'A'}),
+    ),
+  };
+
+  function RecoilSync() {
+    useRecoilSync({read: itemKey => storage[itemKey]});
+    return null;
+  }
+
+  const container = renderElements(
+    <>
+      <RecoilSync />
+      <ReadsAtom atom={atomA} />
+    </>,
+  );
+
+  expect(container.textContent).toBe('loading');
+  await flushPromisesAndTimers();
+  expect(container.textContent).toBe('"A"');
+});
+
+test('Read from storage error', async () => {
+  const atomA = atom({
+    key: 'recoil-sync read error A',
+    default: 'DEFAULT',
+    effects_UNSTABLE: [syncEffect({validate: x => loadableWithValue(x)})],
+  });
+  const atomB = atom({
+    key: 'recoil-sync read error B',
+    default: 'DEFAULT',
+    effects_UNSTABLE: [syncEffect({validate: x => loadableWithValue(x)})],
+  });
+  const mySelector = selectorFamily({
+    key: 'recoil-sync read error selector',
+    get: ({myAtom}) => ({get}) => {
+      try {
+        return get(myAtom);
+      } catch (e) {
+        return e.message;
+      }
+    },
+  });
+
+  const storage = {
+    'recoil-sync read error A': loadableWithError(new Error('ERROR A')),
+  };
+  function RecoilSync() {
+    useRecoilSync({
+      read: itemKey => {
+        if (storage[itemKey] != null) {
+          return storage[itemKey];
+        }
+        throw new Error('ERROR MISSING');
+      },
+    });
+    return null;
+  }
+
+  const container = renderElements(
+    <>
+      <RecoilSync />
+      <ReadsAtom atom={mySelector({myAtom: atomA})} />
+      <ReadsAtom atom={mySelector({myAtom: atomB})} />
+    </>,
+  );
+
+  expect(container.textContent).toBe('"ERROR A""ERROR MISSING"');
+});