Cleanup depsByKey when all dependant entries are disposed (#498)

src/dep.ts

@@ -17,6 +17,7 @@ export type OptimisticDependencyFunction<TKey> =
 
 export type Dep<TKey> = Set<AnyEntry> & {
   subscribe: OptimisticWrapOptions<[TKey]>["subscribe"];
+  cleanup: () => void,
 } & Unsubscribable;
 
 export function dep<TKey>(options?: {
@@ -28,9 +29,14 @@ export function dep<TKey>(options?: {
   function depend(key: TKey) {
     const parent = parentEntrySlot.getValue();
     if (parent) {
-      let dep = depsByKey.get(key);
+      let dep = depsByKey.get(key) as Dep<TKey>;
       if (!dep) {
         depsByKey.set(key, dep = new Set as Dep<TKey>);
+        dep.cleanup = () => {
+          if (dep.size === 0) {
+            depsByKey.delete(key);
+          }
+        };
       }
       parent.dependOn(dep);
       if (typeof subscribe === "function") {

src/entry.ts

@@ -111,6 +111,10 @@ export class Entry<TArgs extends any[], TValue> {
     // thereby preventing it from being fully garbage collected.
     forgetChildren(this);
 
+    // Remove this Entry from any sets to which it was added by the
+    // addToSet method (and do a cleanup).
+    this.forgetDeps(true);
+
     // Because this entry has been kicked out of the cache (in index.js),
     // we've lost the ability to find out if/when this entry becomes dirty,
     // whether that happens through a subscription, because of a direct call
@@ -145,9 +149,14 @@ export class Entry<TArgs extends any[], TValue> {
     this.deps.add(dep);
   }
 
-  public forgetDeps() {
+  public forgetDeps(cleanup?: boolean) {
     if (this.deps) {
-      toArray(this.deps).forEach(dep => dep.delete(this));
+      toArray(this.deps).forEach(dep => {
+        dep.delete(this);
+        if (cleanup) {
+          dep.cleanup();
+        }
+      });
       this.deps.clear();
       emptySetPool.push(this.deps);
       this.deps = null;
@@ -177,6 +186,10 @@ function rememberParent(child: AnyEntry) {
 function reallyRecompute(entry: AnyEntry, args: any[]) {
   forgetChildren(entry);
 
+  // Remove this Entry from any sets to which it was added by the
+  // addToSet method.
+  entry.forgetDeps();
+
   // Set entry as the parent entry while calling recomputeNewValue(entry).
   parentEntrySlot.withValue(entry, recomputeNewValue, [entry, args]);
 
@@ -313,10 +326,6 @@ function forgetChildren(parent: AnyEntry) {
     });
   }
 
-  // Remove this parent Entry from any sets to which it was added by the
-  // addToSet method.
-  parent.forgetDeps();
-
   // After we forget all our children, this.dirtyChildren must be empty
   // and therefore must have been reset to null.
   assert(parent.dirtyChildren === null);