Markdown pictures: an asset leaves the cache with its last holder

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>

src/primitives/held.rs

@@ -1,26 +1,59 @@
-use std::sync::Arc;
+use std::{
+    any::TypeId,
+    collections::HashMap,
+    hash::{DefaultHasher, Hash, Hasher},
+    sync::Arc,
+};
 
-use gpui::{App, Asset, ElementId, RenderImage, Window};
+use gpui::{App, Asset, ElementId, Global, RenderImage, Window};
 
-/// An element's asset; freed on change or when it leaves.
+/// Holders of each asset, keyed as gpui's cache keys it.
+#[derive(Default)]
+struct Holders(HashMap<(TypeId, u64), usize>);
+
+impl Global for Holders {}
+
+fn key<A: Asset>(source: &A::Source) -> (TypeId, u64) {
+    let mut hasher = DefaultHasher::new();
+    source.hash(&mut hasher);
+    (TypeId::of::<A>(), hasher.finish())
+}
+
+/// An element's asset; the last holder to leave frees it.
 pub(crate) struct Held<A: Asset> {
     source: Option<A::Source>,
     image: Option<Arc<RenderImage>>,
 }
 
 impl<A: Asset> Held<A> {
+    fn take(&mut self, source: &A::Source, cx: &mut App) {
+        let holders = &mut cx.default_global::<Holders>().0;
+        *holders.entry(key::<A>(source)).or_default() += 1;
+        self.source = Some(source.clone());
+    }
+
     fn free(&mut self, cx: &mut App) {
-        if let Some(source) = self.source.take() {
-            cx.remove_asset::<A>(&source);
+        let Some(source) = self.source.take() else {
+            return;
+        };
+        let image = self.image.take();
+        let holders = &mut cx.default_global::<Holders>().0;
+        let key = key::<A>(&source);
+        let count = holders.get_mut(&key).expect("a held asset is counted");
+        *count -= 1;
+        if *count > 0 {
+            return;
         }
-        if let Some(image) = self.image.take() {
+        holders.remove(&key);
+        cx.remove_asset::<A>(&source);
+        if let Some(image) = image {
             // The window may be drawing; free after it.
             cx.defer(move |cx| cx.drop_image(image, None));
         }
     }
 }
 
-/// `source` as `A` for element `id`; the previous one freed.
+/// `source` as `A` for element `id`; the previous one let go.
 pub(crate) fn hold<A: Asset>(
     id: impl Into<ElementId>,
     source: &A::Source,
@@ -43,7 +76,7 @@ where
     held.update(cx, |held, cx| {
         if held.source.as_ref() != Some(source) {
             held.free(cx);
-            held.source = Some(source.clone());
+            held.take(source, cx);
         }
         if let Some(loaded) = &loaded {
             held.image = image(loaded);