#3493: key a layer reading a precomp on the LUT file its override names

A precomp instance whose Essential Property names another LUT file renders
with that file, but a layer reading the instance through a layer parameter
was keyed on the nested comp's own file, so editing the overriding file left
that layer cached.

crates/engine/src/tests/lut_files.rs

@@ -152,3 +152,37 @@ fn lumetri_follows_its_input_lut_file() {
     write(&lut, WHITE, 2_000);
     assert_all(colours(&s, comps), 1.0);
 }
+
+/// A precomp instance whose Essential Property names another LUT file follows that file, also
+/// for a layer that reads the instance through a layer parameter.
+#[test]
+fn an_overridden_lut_file_renders_again() {
+    let dir = tempfile::tempdir().unwrap();
+    let (base, overridden) = (dir.path().join("base.cube"), dir.path().join("override.cube"));
+    write(&base, WHITE, 1_000);
+    write(&overridden, BLACK, 1_000);
+    let mut s = session(None);
+    s.execute_checked("comp.new", json!({"name": "Grade", "width": 8, "height": 8, "frameRate": 24, "duration": 1})).unwrap();
+    let grade = s.active_comp_id().unwrap();
+    let plate = s.execute_checked("layer.newSolid", json!({"name": "Plate", "color": "#808080", "width": 8, "height": 8})).unwrap()["layer"].clone();
+    s.execute_checked("effect.apply", json!({"layer": plate, "effect": "Apply Color LUT"})).unwrap();
+    s.execute_checked("prop.set", json!({"layer": plate, "path": "effects/#1/lut", "value": base.to_string_lossy()})).unwrap();
+    let control = s.execute_checked("essential.addProperty", json!({"layer": plate, "path": "effects/#1/lut", "name": "LUT"})).unwrap()["controls"][0].clone();
+    s.execute_checked("comp.new", json!({"name": "Shot", "width": 8, "height": 8, "frameRate": 24, "duration": 1})).unwrap();
+    let shot = s.active_comp_id().unwrap();
+    let instance = s.execute_checked("layer.addItem", json!({"item": grade.0})).unwrap()["layer"].clone();
+    s.execute_checked("essential.set", json!({"layer": instance, "control": control, "value": overridden.to_string_lossy()})).unwrap();
+    let copy = s.execute_checked("layer.newSolid", json!({"name": "Copy", "color": "#00ff00", "width": 8, "height": 8})).unwrap()["layer"].clone();
+    s.execute_checked("effect.apply", json!({"layer": copy, "effect": "Set Channels"})).unwrap();
+    for i in 1..=3 {
+        s.execute_checked("prop.set", json!({"layer": copy, "path": format!("effects/#1/sourceLayer{i}"), "value": instance})).unwrap();
+    }
+    let centre = |s: &Session| {
+        let img = s.render(shot, Tick::ZERO, RenderOpts::default());
+        let p = img.get(i64::from(img.width / 2), i64::from(img.height / 2));
+        [p[0], p[1], p[0], p[1]]
+    };
+    assert_all(centre(&s), 0.0);
+    write(&overridden, WHITE, 2_000);
+    assert_all(centre(&s), 1.0);
+}

crates/render/src/cache/dependencies.rs

@@ -171,6 +171,17 @@ impl Dependencies<'_> {
                         ItemKind::Comp(comp) => {
                             let time = ctx.source_time(layer);
                             time.0.hash(self.h);
+                            // The nested layers are walked without this instance's Essential
+                            // Properties overrides, which the render applies: a LUT file one of
+                            // them names is read too (#3493).
+                            for o in crate::fx_host::essential_overrides(ctx, layer) {
+                                if let effectcraft_keyframe::Value::Str(src) = &o.value
+                                    && let Some(path) = effectcraft_effects::lut_file(src)
+                                {
+                                    crate::reads::ReadFile::new(path, crate::reads::FileStamp::native(path).unwrap_or(crate::reads::FileStamp::Missing))
+                                        .hash(self.h);
+                                }
+                            }
                             let nested = EvalCtx::new(ctx.project, item, comp, time);
                             for child in &comp.layers {
                                 self.layer(&nested, child)?;