Logging exceptions with SLF4J

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SLF4J Logger interface provides several methods for logging errors.

public void error(String format, Object... arguments);
public void error(String msg, Throwable t);

It may look misleading as one can decide that you can either use a template string with arguments or log the exception.

In reality, SLF4J allows passing exception objects to the first method, assuming the exception is the last argument.

  try {
    if (true) throw new NullPointerException()
  } catch {
    case e: Exception =>
      log.error("MainModule param1={}, param2={}", 42, e)
  }

Notice that the second template parameter is not expanded

[error] [2023-03-09T12:22:07.473Z] [org.enso.languageserver.boot.MainModule] MainModule param1=42, param2={}
java.lang.NullPointerException: None
  at org.enso.languageserver.boot.MainModule.<init>(MainModule.scala:77)
  at org.enso.languageserver.boot.LanguageServerComponent.start(LanguageServerComponent.scala:49)
  at org.enso.runner.LanguageServerApp$.run(LanguageServerApp.scala:36)
  at org.enso.runner.Main$.runLanguageServer(Main.scala:861)
  at org.enso.runner.Main$.main(Main.scala:1096)
  at org.enso.runner.Main.main(Main.scala)

This is something I didn't know and just wanted to share. The behavior is described here https://www.slf4j.org/faq.html#paramException