Add withMetadata() convenience function for adding multiple metadata …

…k/v pairs to a Logger

Sources/Logging/Logging.swift

@@ -166,6 +166,17 @@ extension Logger {
         }
     }
 
+    /// Convenience function for adding multiple metadata items to a logger.
+    ///
+    /// - note: Logging metadata behaves as a value that means a change to the logging metadata will only affect the
+    ///         very `Logger` it was changed on.
+    @inlinable
+    public mutating func withMetadata(metadata: Logger.Metadata) {
+        metadata.forEach { (key, value) in
+            self.handler[metadataKey: key] = value
+        }
+    }
+
     /// Get or set the log level configured for this `Logger`.
     ///
     /// - note: `Logger`s treat `logLevel` as a value. This means that a change in `logLevel` will only affect this

Tests/LoggingTests/LoggingTest.swift

@@ -357,6 +357,25 @@ class LoggingTest: XCTestCase {
                                                    "nested-list": ["l1str", ["l2str1", "l2str2"]]])
     }
 
+    func testWithMetadata() {
+        let testLogging = TestLogging()
+        LoggingSystem.bootstrapInternal { testLogging.make(label: $0) }
+
+        var logger = Logger(label: "\(#function)")
+        let metadata: Logger.Metadata = [
+            "foo": ["bar", "buz"],
+            "empty-list": [],
+            "nested-list": ["l1str", ["l2str1", "l2str2"]],
+        ]
+        logger.withMetadata(metadata: metadata)
+        logger.info("hello world!")
+        testLogging.history.assertExist(level: .info,
+                                        message: "hello world!",
+                                        metadata: ["foo": ["bar", "buz"],
+                                                   "empty-list": [],
+                                                   "nested-list": ["l1str", ["l2str1", "l2str2"]]])
+    }
+
     // Example of custom "box" which may be used to implement "render at most once" semantics
     // Not thread-safe, thus should not be shared across threads.
     internal final class LazyMetadataBox: CustomStringConvertible {