From e4b6972c051fbb69c4221b34c54ad4b02f979654 Mon Sep 17 00:00:00 2001
From: Eric Bailey <git@esb.lol>
Date: Mon, 6 Jan 2025 17:40:07 -0600
Subject: [PATCH] Add fastIsType util

---
 src/state/queries/notifications/util.ts | 18 +++++++++++-------
 src/state/queries/post-thread.ts        |  6 +++++-
 src/types/atproto/index.ts              | 23 +++++++++++++++++++++++
 3 files changed, 39 insertions(+), 8 deletions(-)

diff --git a/src/state/queries/notifications/util.ts b/src/state/queries/notifications/util.ts
index e5f957ec2b..0ffa7302dc 100644
--- a/src/state/queries/notifications/util.ts
+++ b/src/state/queries/notifications/util.ts
@@ -14,6 +14,7 @@ import {QueryClient} from '@tanstack/react-query'
 import chunk from 'lodash.chunk'
 
 import {labelIsHideableOffense} from '#/lib/moderation'
+import * as atp from '#/types/atproto'
 import {precacheProfile} from '../profile'
 import {FeedNotification, FeedPage, NotificationType} from './types'
 
@@ -255,14 +256,17 @@ function getSubjectUri(
     return notif.uri
   } else if (type === 'post-like' || type === 'repost') {
     if (
-      AppBskyFeedRepost.isRecord(notif.record) ||
-      AppBskyFeedLike.isRecord(notif.record)
+      atp.fastIsType<AppBskyFeedRepost.Record>(
+        notif.record,
+        AppBskyFeedRepost.isRecord,
+      ) ||
+      atp.fastIsType<AppBskyFeedLike.Record>(
+        notif.record,
+        AppBskyFeedLike.isRecord,
+      )
     ) {
-      const record = notif.record as
-        | AppBskyFeedRepost.Record
-        | AppBskyFeedLike.Record
-      return typeof record.subject?.uri === 'string'
-        ? record.subject?.uri
+      return typeof notif.record.subject?.uri === 'string'
+        ? notif.record.subject?.uri
         : undefined
     }
   } else if (type === 'feedgen-like') {
diff --git a/src/state/queries/post-thread.ts b/src/state/queries/post-thread.ts
index 5427268420..beb50752d0 100644
--- a/src/state/queries/post-thread.ts
+++ b/src/state/queries/post-thread.ts
@@ -18,6 +18,7 @@ import {
   findAllProfilesInQueryData as findAllProfilesInSearchQueryData,
 } from '#/state/queries/search-posts'
 import {useAgent} from '#/state/session'
+import * as atp from '#/types/atproto'
 import {
   findAllPostsInQueryData as findAllPostsInNotifsQueryData,
   findAllProfilesInQueryData as findAllProfilesInNotifsQueryData,
@@ -329,7 +330,10 @@ function responseToThreadNodes(
 ): ThreadNode {
   if (
     AppBskyFeedDefs.isThreadViewPost(node) &&
-    AppBskyFeedPost.isValidRecord(node.post.record)
+    atp.fastIsType<AppBskyFeedPost.Record>(
+      node.post.record,
+      AppBskyFeedPost.isRecord,
+    )
   ) {
     const post = node.post
     // These should normally be present. They're missing only for
diff --git a/src/types/atproto/index.ts b/src/types/atproto/index.ts
index 58e2a5eb23..0f17653cc7 100644
--- a/src/types/atproto/index.ts
+++ b/src/types/atproto/index.ts
@@ -1 +1,24 @@
 export * as profile from '#/types/atproto/profile'
+
+/**
+ * Use sparingly, and only when you know it's safe to do so.
+ *
+ * Our SDK's `is*` identity utils do not assert the type of the entire object,
+ * and although the `isValid*` utils do, they also fully validate the object
+ * shape, which has a performance cost. This util allows us to prescribe the
+ * type we expect, while only checking the `$type` value of the record.
+ *
+ * Usage:
+ * ```ts
+ * import * as atp from '#/types/atproto'
+ *
+ * if (atp.fastIsType<AppBskyFeedPost.Record>(node.post.record, AppBskyFeedPost.isRecord)) {
+ * }
+ * ```
+ */
+export function fastIsType<R>(
+  record: unknown,
+  identity: <V>(v: V) => boolean,
+): record is R {
+  return identity(record)
+}