Add warning when protocols are not consolidated

[devonestes]

This adds a warning when folks try to run benchmarks in environments
without protocol consolidation enabled.

I have no idea how to test this since you can't turn protocol
consolidation off at runtime, though. I did test this locally, and this
is the output I got:

~/sandbox/benchee   Issue-68±  mix run samples/run.exs
Not all of your protocols have been consolidated. In order to achieve the
best possible accuracy for benchmarks, please ensure protocol
consolidation is enabled in your benchmarking environment.

Operating System: macOS"
CPU Information: Intel(R) Core(TM) i5-4260U CPU @ 1.40GHz
Number of Available Cores: 4
Available memory: 8 GB
Elixir 1.6.4
Erlang 20.3

Benchmark suite executing with the following configuration:
warmup: 2 s
time: 10 s
memory time: 2 s
parallel: 1
inputs: none specified
Estimated total run time: 28 s


Benchmarking flat_map...
Benchmarking map.flatten...

Name                  ips        average  deviation         median         99th %
flat_map           1.31 K        0.76 ms    ±18.34%        0.73 ms        1.59 ms
map.flatten        0.68 K        1.47 ms    ±31.06%        1.27 ms        3.02 ms

Comparison:
flat_map           1.31 K
map.flatten        0.68 K - 1.92x slower

Memory usage statistics:

Name           Memory usage
flat_map          625.54 KB
map.flatten       781.85 KB - 1.25x memory usage

**All measurements for memory usage were the same**

Resolves #68

[PragTob]

Thanks a bunch! 👍

Like to have it in System :)

[PragTob]

I have no idea how this works :D

[devonestes]

It takes a list of paths to directories full of BEAM files and tells you which protocols have been defined in those directories. It nicely returns the list of atoms corresponding to the protocol name. Very helpful when combined with :code.lib_dir/2 to get the top level directory for the Elixir BEAM files. I used this as a proxy since if those aren't consolidated, then there's no way any of your other protocols are consolidated. In theory it's still possible for a protocol to have been defined and not consolidated, but that would emit a warning (like if you're defining a protocol in a test body or something).

[PragTob]

ah yeah that's what I wondered about - I thought this just caught it from elixir itself and not deps/libraries - but you're right, if I understand correctly it should usually be all or nothing in terms of consolidation if I understand it.

[PragTob]

I think I'd extract this into its own method, maybe just the puts maybe the whole thing. Takes up so much space that makes it seem like a more important piece then it actually is right now.

Maybe a method like warn_about_performance_degrading_settings or something? not sure

[devonestes]

works for me!