Messages not always formatted

[bdurrer]

Problem description
Passing an exception to the logger does not log the exception in all cases and the message is not always formatted.

Example

Logger.Info("formatted exception {0}.", new Exception("exception message").Message);
Logger.Info("exception {0}.", new Exception("exception message"));
Logger.Info("param and exception {0}.", "some other param", new Exception("exception message"));

Output:

12|2019-10-16 11:41:01.475|INFO|1|Test|formatted exception exception message.
13|2019-10-16 11:41:01.475|INFO|1|Test|exception {0}.>>>System.Exception: exception message<<<
14|2019-10-16 11:41:01.475|INFO|1|Test|param and exception some other param.

1. works as expected
2. works but fails to format
3. fails to log the exception

Conclusion:
Only the methods with signature (string message, params object[] ps); apply formatting
Only the methods with signature (string message, Exception ex = null); log the stack trace

Expected behaviour:
NLog 4 moved the exception parameter in front of the message format string to avoid the confusion. Log4net has extra methods for logging formatted messages with an exception.

MetroLog Logger's interface has a signature close to log4j and slf4j and should behave like it:

• The Logger should not make assumptions on wheter an exception is an formatting parameter or whether it has to be logged as an exception.
• Both variants should check whether the last argument is an exception and pass it on as exception to the targets.