Don't log nothing.

[maleadt]

The logging macros support a very useful block-like syntax where the body builds and returns the message to log, making it easy to conditionalize complex or expensive message building code:

julia> @info begin
           msg = "expensive log message"
           msg
       end
[ Info: expensive log message

Meanwhile, some C APIs have additional log buffer or log level arguments, and as such need some log-conditional set-up that does not immediately produce a message. One solution would be for the logging macros to ignore nothing messages, enabling the following paradigm (taken from CUDAdrv.jl):

@debug begin
    options[INFO_LOG_BUFFER] = Vector{UInt8}(undef, 1024*1024)
    options[LOG_VERBOSE] = true
    nothing
end
optionKeys, optionVals = encode(options)

@apicall(:cuModuleLoadDataEx,
         (Ptr{CuModule_t}, Ptr{Cchar}, Cuint, Ptr{CUjit_option}, Ptr{Ptr{Cvoid}}),
         handle_ref, data, length(optionKeys), optionKeys, optionVals)

@debug begin
    options = decode(optionKeys, optionVals)
    if isempty(options[INFO_LOG_BUFFER])
        """JIT info log is empty"""
    else
        """JIT info log:
           $(options[INFO_LOG_BUFFER])"""
    end
end

An alternative solution would be to query the log level of the active logger, but that could be complex (which logger, env flag overrides, ...). This seemed like a DRY solution. Thoughts?

[StefanKarpinski]

An alternative would be having a @debug_setup macro or similar for this.

[maleadt]

Yeah sure, I wanted to keep the API simple and nothing seemed like a good fit, but if deemed too creative I'm fine with _setup versions. I'll add some tests etc later today.

[yurivish]

#27352 is possibly related, discussing the printing of nothing and missing when interpolated into strings.

[c42f]

Sorry I haven't been responsive on this — I generally don't have time to keep up with all the activity in JuliaLang/julia so I often miss things. You can ping me though ;-)

Does something like the alternative over at #29672 make sense? I think we could probably factor apart the early log checks so that they're usable independently of the log sinking part of the interface.

[maleadt]

Does something like the alternative over at #29672 make sense? I think we could probably factor apart the early log checks so that they're usable independently of the log sinking part of the interface.

Yeah sure, the @debug nothing approach here seemed like a clean solution, but a proper @logif is fine for me as well. As long as I can get rid of these useless log messages 🙂

[vtjnash]

This is stale, but still seems reasonable to me, if you want to revive it (or perhaps "missing" would be the more canonical?)

My opinion would be to require !(msg === nothing || isempty(kwargs)) to skip generating a log entry