Fix memory leak in BuildSystemManagerTests

The delegate of a `BuildSystem` is the `BuildSystemManager` itself, which causes a retain cycle if `BuildSystem` is a strong reference. All other build systems implement this as a weak var.

Author: ahoppen

Sources/SKCore/BuildSystem.swift

@@ -52,8 +52,10 @@ public protocol BuildSystem: AnyObject {
   /// Path remappings for remapping index data for local use.
   var indexPrefixMappings: [PathPrefixMapping] { get async }
 
-  /// Delegate to handle any build system events such as file build settings
-  /// initial reports as well as changes.
+  /// Delegate to handle any build system events such as file build settings initial reports as well as changes.
+  ///
+  /// The build system must not retain the delegate because the delegate can be the `BuildSystemManager`, which could
+  /// result in a retain cycle `BuildSystemManager` -> `BuildSystem` -> `BuildSystemManager`.
   var delegate: BuildSystemDelegate? { get async }
 
   /// Set the build system's delegate.

Sources/SKCore/BuildSystemDelegate.swift

@@ -12,7 +12,7 @@
 import BuildServerProtocol
 import LanguageServerProtocol
 
-/// Handles  build system events, such as file build settings changes.
+/// Handles build system events, such as file build settings changes.
 public protocol BuildSystemDelegate: AnyObject {
   /// Notify the delegate that the build targets have changed.
   ///

Tests/SKCoreTests/BuildSystemManagerTests.swift

@@ -429,7 +429,7 @@ class ManualBuildSystem: BuildSystem {
 
   var map: [DocumentURI: FileBuildSettings] = [:]
 
-  var delegate: BuildSystemDelegate? = nil
+  weak var delegate: BuildSystemDelegate? = nil
 
   func setDelegate(_ delegate: SKCore.BuildSystemDelegate?) async {
     self.delegate = delegate