From d5936f80350579ddececc766ecde52208070eb0e Mon Sep 17 00:00:00 2001
From: Tanmay Singh <tanmaysinghx@gmail.com>
Date: Fri, 30 Oct 2026 22:22:53 +0530
Subject: [PATCH] fix: stop a click beside an object from deadlocking the
 window

A click on the row of a formula, diagram or picture, beside the object
itself, lands on the row's own response. `show_block_zoomed` read that
response's `double_clicked()` inside `ui.data_mut`, and in egui 0.36
`double_clicked()` calls `ctx.input`, which takes the context lock that
`data_mut` already holds. The lock is not re-entrant, so the window froze;
a debug build panics after 10s with "Failed to acquire RwLock write after
10s. Deadlock?".

Read `double_clicked` before `data_mut`, as `clicked` already was. The new
UI test clicks beside a display formula; without the fix it fails with the
same epaint panic as the report.

Fixes AlienTechSoftware/notecraft#15

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
---
 crates/ui-egui/src/preview.rs |  5 ++++-
 crates/ui-egui/tests/ui.rs    | 26 ++++++++++++++++++++++++++
 2 files changed, 30 insertions(+), 1 deletion(-)

diff --git a/crates/ui-egui/src/preview.rs b/crates/ui-egui/src/preview.rs
index e29be20..a4d5c2b 100644
--- a/crates/ui-egui/src/preview.rs
+++ b/crates/ui-egui/src/preview.rs
@@ -661,7 +661,10 @@ pub(crate) fn show_block_zoomed(
     let rect = egui::Rect::from_min_max(start, egui::pos2(start.x + ui.available_width().max(1.0), end.y.max(start.y + 1.0)));
     let response = ui.interact(rect, id, egui::Sense::click());
     if let Some(kind) = object_kind(block) {
+        // Read every response flag before `data_mut`: `clicked` and
+        // `double_clicked` take the context lock that `data_mut` holds.
         let clicked = response.clicked();
+        let double_clicked = response.double_clicked();
         let pointer = response.interact_pointer_pos();
         ui.data_mut(|data| {
             let mut hits = data.get_temp::<Vec<(usize, egui::Rect, String)>>(object_hits_id()).unwrap_or_default();
@@ -670,7 +673,7 @@ pub(crate) fn show_block_zoomed(
             if clicked {
                 data.insert_temp(object_clicked_id(), (i, kind.to_string()));
             }
-            if response.double_clicked() {
+            if double_clicked {
                 data.insert_temp(object_double_clicked_id(), (i, kind.to_string()));
             }
         });
diff --git a/crates/ui-egui/tests/ui.rs b/crates/ui-egui/tests/ui.rs
index 2f61179..14b4bbe 100644
--- a/crates/ui-egui/tests/ui.rs
+++ b/crates/ui-egui/tests/ui.rs
@@ -3705,6 +3705,32 @@ fn double_clicking_an_attachment_card_opens_it() {
     assert!(h.query_all_by_label_contains("Open attachment").count() >= 1, "double click opened the attachment prompt: {}", look_at(&mut h));
 }
 
+/// Issue #15: a click beside a formula, diagram or picture lands on its row's own
+/// response. Reading that response's click state inside `data_mut` took the context lock twice
+/// and froze the window (a debug build panics after 10s).
+#[test]
+fn clicking_beside_a_formula_does_not_deadlock() {
+    let (_t, mut app, s) = sample_app("ui-object-row-click");
+    let md = s.md_page.to_string_lossy().to_string();
+    app.open_path(&md);
+    let mut h = harness(app, LIGHT);
+    settle(&mut h);
+    ask(&mut h, "engine.execute", json!({"command": "page.save", "params": {"path": md.clone(), "body": "Some words.\n\n$$\nx^2\n$$\n"}}))
+        .expect("write a page with a formula");
+    ask(&mut h, "engine.execute", json!({"command": "page.containers", "params": {"path": md.clone(), "boxes": "0,0,700,2"}}))
+        .expect("arrange the page in a wide box");
+    ask(&mut h, "ui.open", json!({"path": md})).expect("open the formula page");
+    settle(&mut h);
+    let origin = look_at(&mut h).pointer("/page/origin").and_then(Value::as_array).cloned().unwrap_or_default();
+    let ox = origin.first().and_then(Value::as_f64).unwrap_or(0.0);
+    let oy = origin.get(1).and_then(Value::as_f64).unwrap_or(0.0);
+    for count in [1, 2] {
+        ask(&mut h, "ui.click", json!({"x": ox + 680.0, "y": oy + 60.0, "count": count})).expect("click beside the formula");
+        settle(&mut h);
+    }
+    assert_eq!(look_at(&mut h).pointer("/page/blocks").and_then(Value::as_u64), Some(2), "the page still draws its formula");
+}
+
 #[test]
 fn delete_and_backspace_remove_a_selected_picture() {
     for key in ["Delete", "Backspace"] {