Add DisableGC option to document (#644)

Recently we have implemented multi-user undo/redo feature and added
inverse operation for Text.edit. While implementing, we noticed that
the inverse operation accessed the removed node by GC. To address this
issue, we've added the disableGC option to skip GC temporarily.

src/document/document.ts

@@ -66,6 +66,18 @@ import {
   PresenceChangeType,
 } from '@yorkie-js-sdk/src/document/presence/presence';
 
+/**
+ * `DocumentOptions` are the options to create a new document.
+ *
+ * @public
+ */
+export interface DocumentOptions {
+  /**
+   * `disableGC` disables garbage collection if true.
+   */
+  disableGC?: boolean;
+}
+
 /**
  * `DocumentStatus` represents the status of the document.
  * @public
@@ -388,6 +400,7 @@ type PathOf<TDocument, Depth extends number = 10> = PathOfInternal<
 export class Document<T, P extends Indexable = Indexable> {
   private key: DocumentKey;
   private status: DocumentStatus;
+  private opts: DocumentOptions;
 
   private changeID: ChangeID;
   private checkpoint: Checkpoint;
@@ -412,7 +425,9 @@ export class Document<T, P extends Indexable = Indexable> {
    */
   private presences: Map<ActorID, P>;
 
-  constructor(key: string) {
+  constructor(key: string, opts?: DocumentOptions) {
+    this.opts = opts || {};
+
     this.key = key;
     this.status = DocumentStatus.Detached;
     this.root = CRDTRoot.create();
@@ -888,6 +903,10 @@ export class Document<T, P extends Indexable = Indexable> {
    * @internal
    */
   public garbageCollect(ticket: TimeTicket): number {
+    if (this.opts.disableGC) {
+      return 0;
+    }
+
     if (this.clone) {
       this.clone.root.garbageCollect(ticket);
     }

test/integration/gc_test.ts

@@ -50,6 +50,29 @@ describe('Garbage Collection', function () {
     assert.equal(0, doc.getGarbageLen());
   });
 
+  it('disable GC test', function () {
+    const doc = new yorkie.Document<{
+      1: number;
+      2?: Array<number>;
+      3: number;
+    }>('test-doc', { disableGC: true });
+
+    doc.update((root) => {
+      root['1'] = 1;
+      root['2'] = [1, 2, 3];
+      root['3'] = 3;
+    }, 'set 1, 2, 3');
+    assert.equal('{"1":1,"2":[1,2,3],"3":3}', doc.toSortedJSON());
+
+    doc.update((root) => {
+      delete root['2'];
+    }, 'deletes 2');
+    assert.equal('{"1":1,"3":3}', doc.toSortedJSON());
+    assert.equal(4, doc.getGarbageLen());
+    assert.equal(0, doc.garbageCollect(MaxTimeTicket));
+    assert.equal(4, doc.getGarbageLen());
+  });
+
   it('garbage collection test2', function () {
     const size = 10000;
     const doc = new yorkie.Document<{ 1?: Array<unknown> }>('test-doc');