copy custom logger to namespace extension (fixes #646)

Author: Qix-

src/common.js

@@ -143,7 +143,9 @@ function setup(env) {
 	}
 
 	function extend(namespace, delimiter) {
-		return createDebug(this.namespace + (typeof delimiter === 'undefined' ? ':' : delimiter) + namespace);
+		const newDebug = createDebug(this.namespace + (typeof delimiter === 'undefined' ? ':' : delimiter) + namespace);
+		newDebug.log = this.log;
+		return newDebug;
 	}
 
 	/**

test.js

@@ -70,6 +70,14 @@ describe('debug', () => {
 			const logBar = log.extend('bar', '');
 			assert.deepStrictEqual(logBar.namespace, 'foobar');
 		});
+
+		it('should keep the log function between extensions', () => {
+			const log = debug('foo');
+			log.log = () => {};
+
+			const logBar = log.extend('bar');
+			assert.deepStrictEqual(log.log, logBar.log);
+		});
 	});
 
 	describe('rebuild namespaces string (disable)', () => {