Settings: older settings files split layers above the original (#2545)

Create Split Layers Above Original Layer became on by default in #2083, but a settings
file saved before then still holds `false` (every later save keeps it), so Split Layer
kept stacking the new layer below. Settings version 4 moves a stored `false` to the new
default once, like version 3 did for the old disk cache size; a choice made since stays.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

crates/engine/src/settings/prefs.rs

@@ -36,7 +36,7 @@ pub use sections::{
 use sections::{Extra, default_labels, lenient_comp_presets};
 
 /// Current settings layout version.
-pub const PREFS_VERSION: u32 = 3;
+pub const PREFS_VERSION: u32 = 4;
 /// Settings file name in the config store.
 pub const PREFS_FILE: &str = "prefs.json";
 

crates/engine/src/settings/prefs/document.rs

@@ -9,6 +9,8 @@ use super::{Appearance, General, Map, PREFS_VERSION, Prefs, Startup, Value, json
 ///   `autoSaveMinutes`, `autoSaveVersions`, `labelNames` (array) and `theme` at the top level.
 /// - version 2 defaulted the disk cache to 100 GB, more than most laptops have free; the stored
 ///   old default becomes the new one (a size the user chose is kept).
+/// - version 3 and earlier could still hold `createSplitLayersAbove: false`, the default before
+///   #2083 (every save kept it); it becomes After Effects' default, above (#2545).
 pub fn migrate(mut v: Value) -> Value {
     let Some(obj) = v.as_object_mut() else { return json!({}) };
     let version = obj.get("version").and_then(Value::as_u64).unwrap_or(0);
@@ -42,6 +44,12 @@ pub fn migrate(mut v: Value) -> Value {
     {
         d.insert("diskCacheMaxGb".into(), json!(20));
     }
+    if version < 4
+        && let Some(g) = obj.get_mut("general").and_then(Value::as_object_mut)
+        && g.get("createSplitLayersAbove") == Some(&json!(false))
+    {
+        g.insert("createSplitLayersAbove".into(), json!(true));
+    }
     // Settings saved before appearance modes had one theme: keep showing it, as a fixed Dark or
     // Light mode, instead of switching established users to Auto.
     if let Some(a) = obj.get_mut("appearance").and_then(Value::as_object_mut)

crates/engine/src/tests/settings.rs

@@ -79,6 +79,15 @@ fn prefs_migrate_old_disk_cache_default() {
     assert_eq!(Prefs::from_json(r#"{"version": 3, "disk": {"diskCacheMaxGb": 100}}"#).disk.disk_cache_max_gb, 100);
 }
 
+#[test]
+fn prefs_migrate_old_split_layers_default() {
+    // Settings saved before #2083 kept "below"; they move to After Effects' "above" once (#2545).
+    let above = |doc: &str| Prefs::from_json(doc).general.create_split_layers_above;
+    assert!(above(r#"{"version": 3, "general": {"createSplitLayersAbove": false}}"#));
+    assert!(above(r#"{"version": 2, "general": {"createSplitLayersAbove": false}}"#));
+    assert!(!above(r#"{"version": 4, "general": {"createSplitLayersAbove": false}}"#), "a choice made since stays");
+}
+
 #[test]
 fn prefs_set_validates_keys_types_and_ranges() {
     let mut p = Prefs::default();