Using a Ruby Pathname as the output file results in error

[originalpete]

In Ruby its common to use the helpful Pathname class to represent a path to a file. However, if you use this with stackprof you get an exception with no helpful stacktrace (because the IO flush happens in the compiled library).

2.4.0 :063 >  StackProf.run(mode: :cpu, out: Rails.root.join("tmp/stackprof-cpu.dump")) do
2.4.0 :064 >     10.times {2**10}
2.4.0 :065?>   end
NoMethodError: undefined method `flush' for nil:NilClass
	from (irb):63:in `run'

[rest of stacktrace removed because it's not helpful, and only shows the Ruby call stack down to the console]

However, if you call .to_son the end of the pathname object then it works:

StackProf.run(mode: :cpu, out: Rails.root.join("tmp/stackprof-cpu.dump").to_s) do
2.4.0 :055 >     10.times {2**10}
2.4.0 :056?>   end
 => #<File:/[...]/tmp/stackprof-cpu.dump>

Presumably this is due to the fact that (upon reading the code) it seems that the out parameter can take eithert an IO object or a file path. In which case, this should be documented, and / or checked internally and converted to a string if necessary.

This caused much head-scratching and gnashing of teeth!

[tmm1]

Can you open a PR which adds a to_s in the right spot, and maybe a test.