feat: Implement Copy-On-Write (CoW) behavior for Logger struct

Sources/Logging/Logging.swift

@@ -38,21 +38,61 @@ import WASILibc
 /// ```swift
 /// logger.info("Hello World!")
 /// ```
+
 public struct Logger {
+    /// Storage class to hold the label and log handler
+    @usableFromInline
+    internal final class Storage {
+        @usableFromInline
+        var label: String
+        @usableFromInline
+        var handler: LogHandler
+        @usableFromInline
+        init(label: String, handler: LogHandler) {
+            self.label = label
+            self.handler = handler
+        }
+    }
+
+    @usableFromInline
+    internal var _storage: Storage
     @usableFromInline
-    var handler: LogHandler
+    internal var label: String {
+        get {
+            return _storage.label
+        }
+        set {
+            if !isKnownUniquelyReferenced(&_storage) {
+                _storage = Storage(label: newValue, handler: _storage.handler)
+            } else {
+                _storage.label = newValue
+            }
+        }
+    }
 
-    /// An identifier of the creator of this `Logger`.
-    public let label: String
+    /// A computed property to access the `LogHandler`.
+    @inlinable
+    public var handler: LogHandler {
+        get {
+            return _storage.handler
+        }
+        set {
+            if !isKnownUniquelyReferenced(&_storage) {
+                _storage = Storage(label: label, handler: newValue)
+            } else {
+                _storage.handler = newValue
+            }
+        }
+    }
 
     /// The metadata provider this logger was created with.
+    @inlinable
     public var metadataProvider: Logger.MetadataProvider? {
-        return self.handler.metadataProvider
+        return handler.metadataProvider
     }
-
+    @usableFromInline
     internal init(label: String, _ handler: LogHandler) {
-        self.label = label
-        self.handler = handler
+        self._storage = Storage(label: label, handler: handler)
     }
 }
 
@@ -1330,6 +1370,7 @@ private final class WarnOnceBox {
 // MARK: - Sendable support helpers
 
 extension Logger.MetadataValue: Sendable {}
+extension Logger.Storage: @unchecked Sendable {}
 extension Logger: Sendable {}
 extension Logger.Level: Sendable {}
 extension Logger.Message: Sendable {}

Tests/LoggingTests/LoggingTest.swift

@@ -1039,6 +1039,11 @@ class LoggingTest: XCTestCase {
         LoggingSystem.bootstrap(StreamLogHandler.standardOutput, metadataProvider: .exampleMetadataProvider)
         LoggingSystem.bootstrap(StreamLogHandler.standardError, metadataProvider: .exampleMetadataProvider)
     }
+
+    func testLoggerIsJustHoldingASinglePointer() {
+        let expectedSize = MemoryLayout<UnsafeRawPointer>.size
+        XCTAssertEqual(MemoryLayout<Logger>.size, expectedSize)
+    }
 }
 
 extension Logger {