Add debug logs to generateItems

It's always worth having logs for when state holders are created or destroyed (these are often the most interesting things happening in the application), so I thought it would be nice to have generateItems always log for you when it's doing that.

src/utils/observable.test.ts

@@ -47,6 +47,7 @@ test("generateItems", () => {
     expectObservable(
       hot<string>(inputMarbles).pipe(
         generateItems(
+          "test items",
           function* (input) {
             for (let i = 1; i <= +input; i++) {
               yield { keys: [i], data: undefined };

src/utils/observable.ts

@@ -24,6 +24,7 @@ import {
   type OperatorFunction,
   distinctUntilChanged,
 } from "rxjs";
+import { logger } from "matrix-js-sdk/lib/logger";
 
 import { type Behavior } from "../state/Behavior";
 import { Epoch, ObservableScope } from "../state/ObservableScope";
@@ -122,8 +123,9 @@ export function pauseWhen<T>(pause$: Behavior<boolean>) {
     );
 }
 
-interface ItemHandle<Data, Item> {
+interface ItemHandle<Keys extends unknown[], Data, Item> {
   scope: ObservableScope;
+  keys: readonly [...Keys];
   data$: BehaviorSubject<Data>;
   item: Item;
 }
@@ -135,6 +137,7 @@ interface ItemHandle<Data, Item> {
  * requested at a later time, and destroyed (have their scope ended) when the
  * key is no longer requested.
  *
+ * @param name A name for this collection to use in debug logs.
  * @param generator A generator function yielding a tuple of keys and the
  *   currently associated data for each item that it wants to exist.
  * @param factory A function constructing an individual item, given the item's key,
@@ -146,16 +149,17 @@ export function generateItems<
   Data,
   Item,
 >(
+  name: string,
   generator: (
     input: Input,
-  ) => Generator<{ keys: readonly [...Keys]; data: Data }, void, void>,
+  ) => Iterable<{ keys: readonly [...Keys]; data: Data }, void, void>,
   factory: (
     scope: ObservableScope,
     data$: Behavior<Data>,
     ...keys: Keys
   ) => Item,
 ): OperatorFunction<Input, Item[]> {
-  return generateItemsInternal(generator, factory, (items) => items);
+  return generateItemsInternal(name, generator, factory, (items) => items);
 }
 
 /**
@@ -167,9 +171,10 @@ export function generateItemsWithEpoch<
   Data,
   Item,
 >(
+  name: string,
   generator: (
     input: Input,
-  ) => Generator<{ keys: readonly [...Keys]; data: Data }, void, void>,
+  ) => Iterable<{ keys: readonly [...Keys]; data: Data }, void, void>,
   factory: (
     scope: ObservableScope,
     data$: Behavior<Data>,
@@ -177,6 +182,7 @@ export function generateItemsWithEpoch<
   ) => Item,
 ): OperatorFunction<Epoch<Input>, Epoch<Item[]>> {
   return generateItemsInternal(
+    name,
     function* (input) {
       yield* generator(input.value);
     },
@@ -214,9 +220,10 @@ function generateItemsInternal<
   Item,
   Output,
 >(
+  name: string,
   generator: (
     input: Input,
-  ) => Generator<{ keys: readonly [...Keys]; data: Data }, void, void>,
+  ) => Iterable<{ keys: readonly [...Keys]; data: Data }, void, void>,
   factory: (
     scope: ObservableScope,
     data$: Behavior<Data>,
@@ -232,26 +239,34 @@ function generateItemsInternal<
         Input,
         {
           map: Map<any, any>;
-          items: Set<ItemHandle<Data, Item>>;
+          items: Set<ItemHandle<Keys, Data, Item>>;
           input: Input;
         },
-        { map: Map<any, any>; items: Set<ItemHandle<Data, Item>> }
+        { map: Map<any, any>; items: Set<ItemHandle<Keys, Data, Item>> }
       >(
         ({ map: prevMap, items: prevItems }, input) => {
           const nextMap = new Map();
-          const nextItems = new Set<ItemHandle<Data, Item>>();
+          const nextItems = new Set<ItemHandle<Keys, Data, Item>>();
 
           for (const { keys, data } of generator(input)) {
             // Disable type checks for a second to grab the item out of a nested map
             let i: any = prevMap;
             for (const key of keys) i = i?.get(key);
-            let item = i as ItemHandle<Data, Item> | undefined;
+            let item = i as ItemHandle<Keys, Data, Item> | undefined;
 
             if (item === undefined) {
               // First time requesting the key; create the item
               const scope = new ObservableScope();
               const data$ = new BehaviorSubject(data);
-              item = { scope, data$, item: factory(scope, data$, ...keys) };
+              logger.debug(
+                `[${name}] Creating item with keys ${keys.join(", ")}`,
+              );
+              item = {
+                scope,
+                keys,
+                data$,
+                item: factory(scope, data$, ...keys),
+              };
             } else {
               item.data$.next(data);
             }
@@ -269,7 +284,7 @@ function generateItemsInternal<
             const finalKey = keys[keys.length - 1];
             if (m.has(finalKey))
               throw new Error(
-                `Keys must be unique (tried to generate multiple items for key ${keys})`,
+                `Keys must be unique (tried to generate multiple items for key ${keys.join(", ")})`,
               );
             m.set(keys[keys.length - 1], item);
             nextItems.add(item);
@@ -277,7 +292,12 @@ function generateItemsInternal<
 
           // Destroy all items that are no longer being requested
           for (const item of prevItems)
-            if (!nextItems.has(item)) item.scope.end();
+            if (!nextItems.has(item)) {
+              logger.debug(
+                `[${name}] Destroying item with keys ${item.keys.join(", ")}`,
+              );
+              item.scope.end();
+            }
 
           return { map: nextMap, items: nextItems, input };
         },
@@ -285,7 +305,15 @@ function generateItemsInternal<
       ),
       finalizeValue(({ items }) => {
         // Destroy all remaining items when no longer subscribed
-        for (const { scope } of items) scope.end();
+        logger.debug(
+          `[${name}] End of scope, destroying all ${items.size} items…`,
+        );
+        for (const item of items) {
+          logger.debug(
+            `[${name}] Destroying item with keys ${item.keys.join(", ")}`,
+          );
+          item.scope.end();
+        }
       }),
       map(({ items, input }) =>
         project(