Add YAML support

[mavam]

To be rebased onto master after #1017 is merged. Ignore everything up to and including 6b4e564.

[dominiklohmann]

Second pass.

[lava]

That's pretty harsh, why not just throw YAML::Exception and fail to parse the file?

[mavam]

The idea is that this is more like a developer issue. We enumerated all switch statements above, so we should never reach this code. If so, it's a logic error. In order to make the compiler happy (and not spit out a warning), I plugged in a [[noreturn]] function for which we conveniently have die.

[lava]

I'm fine with leaving it as-is here, but in general we should be careful with jumping from "programmer error" to "kill the database", especially when there's a perfectly reasonable recovery path.

Related rant: https://lkml.org/lkml/2016/10/4/1

[mavam]

If yaml-cpp indeed uses exceptions on the print path, the to_yaml() function below needs a try-catch block as well

@lava I could not find a single throw in the emitter code in yaml-cpp, that's why I didn't wrap it into a try-catch block.

[mavam]

I've added a changelog as well. Before the next release, we may consolidate it with a single entry about the new config file format.

[dominiklohmann]

Please install libyaml-cpp-dev in the bundled Dockerfile as well.

[mavam]

Please install libyaml-cpp-dev in the bundled Dockerfile as well.

Why didn't CI complain about this missing dependency, @dominiklohmann?

[dominiklohmann]

Just cosmetic requests now. Approving already.

Please fix these and wait for CI before merging, especially because of the Docker CI.

[mavam]

@dominiklohmann I pushed a minor fixup and now the Docker build failed with this error:

Warning: apt-key output should not be parsed (stdout is not a terminal)
Executing: /tmp/apt-key-gpghome.rS81EKvBWf/gpg.1.sh --keyserver hkp://pool.sks-keyservers.net:80 --recv-keys 5C808C2B65558117
gpg: keyserver receive failed: Cannot assign requested address

Any objections if I merge nonetheless?

[mavam]

I got your approval in person, @dominiklohmann. 🙂