Add Drone CI

[Flamefire]

Supersedes and closes #27

I simply C&P the config file from Boost.CI, so not sure if everything passes.

Notes on Drone (if not already done, can you do that please @cmazakas ?):

• To activate Drone, visit https://drone.cpp.al/. Authorize Drone: Click the "Authorize cppalliance-drone" button. Sync repositories: Click the "sync" button. A list of repositories will appear. For the relevant repo, click and then choose "Activate Repository". In the settings page, change Configuration from .drone.yml to .drone.star. "Save".

More pointers about Drone:

• "asan" jobs require elevated privileges. Contact an administrator or open an issue at drone-ci to set your drone repository to "Trusted".
• If not using asan, simply remove the jobs.

CC @tobias-loew. Just want to make sure your work doesn't get forgotten.

[codecov[bot]]

Codecov Report

Merging #124 (6446e0e) into develop (23f1594) will not change coverage. The diff coverage is 84.61%.

@@           Coverage Diff            @@
##           develop     #124   +/-   ##
========================================
  Coverage    97.30%   97.30%           
========================================
  Files           73       73           
  Lines         9790     9790           
========================================
  Hits          9526     9526           
  Misses         264      264           

Impacted Files	Coverage Δ
test/objects/test.hpp	94.76% <80.00%> (ø)
test/objects/exception.hpp	96.96% <100.00%> (ø)

---

Continue to review full report at Codecov.

Legend - Click here to learn more Δ = absolute <relative> (impact), ø = not affected, ? = missing data Powered by Codecov. Last update 23f1594...6446e0e. Read the comment docs.

[Flamefire]

@cmazakas For Codecov on Drone you need to copy the "Repository Upload Token" from the settings page of the repo on Codecov and use it to create a new secret named codecov_token on the settings page of the repo on Drone.

Besides that it passes: https://drone.cpp.al/Flamefire/unordered/3 (now: https://drone.cpp.al/Flamefire/unordered/4)

And it seems the codecov bot is now running. It detects that there is some dead code in test/objects/test.hpp: The int-functor part of the hash class is only called on a default constructed hash-object.

[pdimov]

What's the purpose of this? The benefit of Drone is that we can use it to cover configurations GHA lacks (GCC 4.4, 4.6, 4.7, ARM, s390x, etc), but this PR doesn't do this, it just duplicates the same configs already covered.

[pdimov]

Here's my Drone variation: https://github.com/boostorg/system/blob/develop/.drone.jsonnet (self-contained as usual)

I prefer jsonnet, see if you like it better. We didn't have s390x yet when I wrote it, but it's an important configuration because it's big endian.

[Flamefire]

Redundancy, as that was also a reason to add Drone. I just used the config as it is on boost-ci. If there are more supported and useful then those should be added to boost-ci, which is the blueprint / testbed for the other repos to copy from. I don't think it is feasible to go looking in random boost repos for a good config. So if yours is better, can you add/replace it on boost-ci with instructions how to use it?

[pdimov]

drone.cpp.al has limited capacity and I don't think we should be carpet bombing it with jobs we don't actually need because they are already covered elsewhere. This will ruin it for everyone.

[Flamefire]

Sure. Closing this then.