Change existing/cloned logger's LevelEnabler

[JeanMertz]

I'd like to take an existing logger, use WithOptions to clone/extend it, and also switch the LevelEnabler to zap.AtomicLevel (and keep a reference, to support log level switching on the newly created logger). That last part seems to be impossible right now.

I know I can set the LevelEnabler using zap.Config{}, but I'm dealing with an existing logger, and don't have access to the underlying config struct.

I also tried using zap.WrapCore() as an option, but that gives me back the Core interface, which hides access to the LevelEnabler field.

I did notice NewCore(enc Encoder, ws WriteSyncer, enab LevelEnabler), but then I'd still need access to the original logger's Encoder and WriteSyncer, which I don't have, as far as I can tell.

The documentation of the config struct states:

// Config offers a declarative way to construct a logger. It doesn't do
// anything that can't be done with New, Options, and the various
// zapcore.WriteSyncer and zapcore.Core wrappers, but it's a simpler way to
// toggle common options.

But so far, I've not been able to find any way to set the LevelEnabler other than via the config struct.

Any help would be much appreciated.

[ntnn]

Seconded, I've just hit this limitation as well.

[AlekSi]

Related to #581.