tagging.rb giving me an undefined method 'merge' for nil::NilClass

[arjitj2]

Current behaviour
This line: https://github.com/DataDog/dd-trace-rb/blob/master/lib/datadog/tracing/metadata/tagging.rb#L114

This error:

/app/vendor/bundle/ruby/3.0.0/gems/ddtrace-1.12.1/lib/datadog/tracing/metadata/tagging.rb:114:in `tags': undefined method `merge' for nil:NilClass (NoMethodError)

Expected behaviour
Maybe it should be

def tags
  meta.merge(metrics)
end

because meta and metrics are defined in the protected right below this function, which set @meta & @metrics if not already set.

Also, I might be going crazy, but I don't see tags being called anywhere in a way that seems intentional. set_tags at L62 takes a tags argument and uses it, but that seems like pretty much it.

TraceOperation includes the module but I don't see it using tags anywhere that isn't a passed argument to each respective function.

Steps to reproduce
not sure how to provide this because this is just the output of a pretty specific rails console command i'm runing

[GustavoCaso]

@arjitj2 Thank you so much for reporting the issue.

I think your code suggestion is reasonable to me.

By looking at the code, it looks like you might have hit an edge case in which you ask for the tags for a TraceOpertaion or SpanOpertaion before calling any of these methods:

set_tags(tags)
clear_tag(key)
get_metric(key)
set_metric(key, value)

Those methods call meta or metrics, which set up @meta and @metrcis

I don't currently work on the APM product, so I will default @TonyCTHsu or @marcotc make the final call.

[arjitj2]

@arjitj2 Thank you so much for reporting the issue.

I think your code suggestion is reasonable to me.

By looking at the code, it looks like you might have hit an edge case in which you ask for the tags for a TraceOpertaion or SpanOpertaion before calling any of these methods:

set_tags(tags)
clear_tag(key)
get_metric(key)
set_metric(key, value)

Those methods call meta or metrics, which set up @meta and @metrcis

I don't currently work on the APM product, so I will default @TonyCTHsu or @marcotc make the final call.

@GustavoCaso yup that checks out-- I was trying to access span.tags to tag a metric before the span closed. I think that's what caused this issue.

I worked around it by just using my own tags hash instead of span.tags, though I still think this undefined method error was rough to figure out.

Thanks!

[GustavoCaso]

I worked around it by just using my own tags hash instead of span.tags, though I still think this undefined method error was rough to figure out.

Agree. We most probably should fix on our end to avoid that unwanted behaviour