From b40d8152740918cc36e219431086a8c0d345149f Mon Sep 17 00:00:00 2001
From: Shadowfacts <me@shadowfacts.net>
Date: Fri, 10 Nov 2023 14:16:16 -0500
Subject: [PATCH] Ensure LazilyDecoding runs on the managed object context's
 thread

Maybe fix the crash in KeyPath machinery?
---
 Tusker/LazilyDecoding.swift | 69 ++++++++++++++++++++++---------------
 1 file changed, 42 insertions(+), 27 deletions(-)

diff --git a/Tusker/LazilyDecoding.swift b/Tusker/LazilyDecoding.swift
index 7d402eab..26fec37a 100644
--- a/Tusker/LazilyDecoding.swift
+++ b/Tusker/LazilyDecoding.swift
@@ -7,12 +7,13 @@
 //
 
 import Foundation
+import CoreData
 
 private let decoder = PropertyListDecoder()
 private let encoder = PropertyListEncoder()
 
 @propertyWrapper
-public struct LazilyDecoding<Enclosing: NSObject, Value: Codable> {
+public struct LazilyDecoding<Enclosing: NSManagedObject, Value: Codable> {
 
     private let keyPath: ReferenceWritableKeyPath<Enclosing, Data?>
     private let fallback: Value
@@ -32,37 +33,41 @@ public struct LazilyDecoding<Enclosing: NSObject, Value: Codable> {
     
     public static subscript(_enclosingInstance instance: Enclosing, wrapped wrappedKeyPath: ReferenceWritableKeyPath<Enclosing, Value>, storage storageKeyPath: ReferenceWritableKeyPath<Enclosing, Self>) -> Value {
         get {
-            var wrapper = instance[keyPath: storageKeyPath]
-            if let value = wrapper.value {
-                return value
-            } else {
-                guard let data = instance[keyPath: wrapper.keyPath] else { return wrapper.fallback }
-                do {
-                    let value = try decoder.decode(Box.self, from: data)
-                    wrapper.value = value.value
-                    wrapper.observation = instance.observe(wrapper.keyPath, changeHandler: { instance, _ in
-                        var wrapper = instance[keyPath: storageKeyPath]
-                        if wrapper.skipClearingOnNextUpdate {
-                            wrapper.skipClearingOnNextUpdate = false
-                        } else {
-                            wrapper.removeCachedValue()
-                        }
+            instance.performOnContext {
+                var wrapper = instance[keyPath: storageKeyPath]
+                if let value = wrapper.value {
+                    return value
+                } else {
+                    guard let data = instance[keyPath: wrapper.keyPath] else { return wrapper.fallback }
+                    do {
+                        let value = try decoder.decode(Box.self, from: data)
+                        wrapper.value = value.value
+                        wrapper.observation = instance.observe(wrapper.keyPath, changeHandler: { instance, _ in
+                            var wrapper = instance[keyPath: storageKeyPath]
+                            if wrapper.skipClearingOnNextUpdate {
+                                wrapper.skipClearingOnNextUpdate = false
+                            } else {
+                                wrapper.removeCachedValue()
+                            }
+                            instance[keyPath: storageKeyPath] = wrapper
+                        })
                         instance[keyPath: storageKeyPath] = wrapper
-                    })
-                    instance[keyPath: storageKeyPath] = wrapper
-                    return value.value
-                } catch {
-                    return wrapper.fallback
+                        return value.value
+                    } catch {
+                        return wrapper.fallback
+                    }
                 }
             }
         }
         set {
-            var wrapper = instance[keyPath: storageKeyPath]
-            wrapper.value = newValue
-            wrapper.skipClearingOnNextUpdate = true
-            instance[keyPath: storageKeyPath] = wrapper
-            let newData = try! encoder.encode(Box(value: newValue))
-            instance[keyPath: wrapper.keyPath] = newData
+            instance.performOnContext {
+                var wrapper = instance[keyPath: storageKeyPath]
+                wrapper.value = newValue
+                wrapper.skipClearingOnNextUpdate = true
+                instance[keyPath: storageKeyPath] = wrapper
+                let newData = try! encoder.encode(Box(value: newValue))
+                instance[keyPath: wrapper.keyPath] = newData
+            }
         }
     }
     
@@ -73,6 +78,16 @@ public struct LazilyDecoding<Enclosing: NSObject, Value: Codable> {
     
 }
 
+extension NSManagedObject {
+    fileprivate func performOnContext<V>(_ f: () -> V) -> V {
+        if let managedObjectContext {
+            managedObjectContext.performAndWait(f)
+        } else {
+            f()
+        }
+    }
+}
+
 extension LazilyDecoding {
     init<T>(arrayFrom keyPath: ReferenceWritableKeyPath<Enclosing, Data?>) where Value == [T] {
         self.init(from: keyPath, fallback: [])