From 7fa225115ef6b6b33e0ecadb99fcf92adb80eedb Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Elena=20Torr=C3=B3?= <elenatorro@gmail.com>
Date: Fri, 6 Nov 2026 11:33:37 +0100
Subject: [PATCH] :zap: Reuse uuid instances when decoding transit on the
 frontend (#12792)

---
 common/src/app/common/transit.cljc        | 33 ++++++++++++++++++++++-
 frontend/src/app/main/data/workspace.cljs |  2 ++
 frontend/src/app/worker/index.cljs        |  2 ++
 3 files changed, 36 insertions(+), 1 deletion(-)

diff --git a/common/src/app/common/transit.cljc b/common/src/app/common/transit.cljc
index 41b503316f..5e205144ba 100644
--- a/common/src/app/common/transit.cljc
+++ b/common/src/app/common/transit.cljc
@@ -110,6 +110,37 @@
                (.set cache value kw)
                kw))))))
 
+#?(:cljs
+   (def ^:private uuid-cache-size
+     "Twice the ids of a very large page (~60k shapes), so decoding one
+     page does not rotate the cache."
+     131072))
+
+#?(:cljs (def ^:private recent-uuids (js/Map.)))
+#?(:cljs (def ^:private previous-uuids (js/Map.)))
+
+#?(:cljs
+   (defn clear-uuid-cache
+     "Forget the cached uuids, so the ids of a closed file can be freed."
+     []
+     (set! recent-uuids (js/Map.))
+     (set! previous-uuids (js/Map.))))
+
+#?(:cljs
+   (defn- read-uuid
+     "Give the same uuid instance for each value. Entries live in two
+     generations: when the recent one is full it becomes the previous one
+     and the older one is dropped, so the cache stays bounded."
+     [value]
+     (or (.get recent-uuids value)
+         (let [id (or (.get previous-uuids value)
+                      (parse-uuid value))]
+           (when (>= (.-size recent-uuids) uuid-cache-size)
+             (set! previous-uuids recent-uuids)
+             (set! recent-uuids (js/Map.)))
+           (.set recent-uuids value id)
+           id))))
+
 (add-handlers!
  #?@(:clj
      [{:id "file"
@@ -128,7 +159,7 @@
 
  #?(:cljs
     {:id "u"
-     :rfn parse-uuid})
+     :rfn read-uuid})
 
  #?(:cljs
     {:id ":"
diff --git a/frontend/src/app/main/data/workspace.cljs b/frontend/src/app/main/data/workspace.cljs
index f9bae33c38..7581866dc6 100644
--- a/frontend/src/app/main/data/workspace.cljs
+++ b/frontend/src/app/main/data/workspace.cljs
@@ -21,6 +21,7 @@
    [app.common.math :as mth]
    [app.common.path-names :as cpn]
    [app.common.render-wasm.wasm :as wasm-state]
+   [app.common.transit :as t]
    [app.common.types.component :as ctc]
    [app.common.types.components-list :as ctkl]
    [app.common.types.shape :as cts]
@@ -631,6 +632,7 @@
 
     ptk/WatchEvent
     (watch [_ state _]
+      (t/clear-uuid-cache)
       (let [project-id (:current-project-id state)]
         (rx/of (dwn/finalize file-id)
                (dpj/finalize-project project-id)
diff --git a/frontend/src/app/worker/index.cljs b/frontend/src/app/worker/index.cljs
index 102b0b38d9..910fa74fae 100644
--- a/frontend/src/app/worker/index.cljs
+++ b/frontend/src/app/worker/index.cljs
@@ -12,6 +12,7 @@
    [app.common.geom.rect :as grc]
    [app.common.logging :as log]
    [app.common.time :as ct]
+   [app.common.transit :as t]
    [app.worker.impl :as impl]
    [app.worker.selection :as selection]
    [app.worker.snap :as snap]
@@ -78,6 +79,7 @@
                     (update :pages-index dissoc page-id)
                     (update ::selection dissoc page-id)
                     (update ::snap dissoc page-id)))
+  (t/clear-uuid-cache)
   (log/dbg :hint "page index dropped" :id page-id ::log/sync? true)
   nil)