Support debug mode

[majori]

Currently we already have a global flag --debug, but it does not do anything. Enabling debug mode should cause more verbose logging

[vesse]

What kind of stuff you had in mind here? Most(?) of the current output seems to be Cobra cmd prints but using that deeper in the engine would require passing it forward which would not be cool, and some output comes from fmt directly.

There's golang log package and then naturally multiple loggers offering all kinds of features that could make sense for having configurable log level and other options. Some examples:

• https://github.com/sirupsen/logrus
• https://github.com/rs/zerolog
• https://github.com/op/go-logging
• https://github.com/inconshreveable/log15
• https://github.com/golang/glog
• https://github.com/go-kit/log
• https://github.com/uber-go/zap

And then one can implement some kind of DIY logger of course.

[majori]

I haven't actually thought about the logging library that much, but I think we can start with the Go's log package. My idea was that on root CLI function we hook the logger to the cmd output with log.SetOutput(cmd.OutOrStdout()) and set log.SetPrefix("[DEBUG]: "). Then just start using the log.Printf(...).

[majori]

My initial though was just conditionally run the log.Print like if opts.Debug { log.Print(...) } but I realized that is dumb. So we need to set the log.SetOutput(cmd.OutOrStdout()) conditionally, and otherwise set the logger output to "/dev/null". This might require setting the Common options to root level and passing them to subcommands.

[vesse]

Yeah using if would be dumb 😄 Using conditionally set output seems fine if you you don't see a need more fine-grained logging. With a proper logger the code would just log stuff with different level and flags would configure log output based on the levels, but this might be an overkill for the need.