Hi,
I am not sure the category is correct but whatever…
Is there any place where I could find programming references when writing .Build.cs files?
Or any way to get auto-completion to work in them?
Because it’s a bit of an hindrance not to be able to find anything about it or not even be able to auto-complete names or member use.
Cheers,
Erio
Bump, anybody has an idea please? 
Just found this:
http://dmitry-yanovsky.com/2015/08/unreal-engine-4-build-file-demystified/
Though, I know that is not a complete list of things you can do in those files.
The class definition you are sub-classing is here:
UnrealEngine\Engine\Source\Programs\UnrealBuildTool\System\RulesCompiler.cs
Yep. I already knew of this one.
It sadly is not nearly enough to do interesting things with the Build Tool 
It’s giving a few hints at things that are present, but not really giving an exhaustive list of the functions we could find and use from it.
Thanks for the answer tho! 
The exhaustive list would be the source file, RulesCompiler.cs. It does have a reasonable level of comments?
that might be what I was looking for. I digged into it to a certain level, I think.
I’ve not been touching that in the last couple of weeks 
The most approachable doc is the Unreal Build System in the Programming Guide. It includes some information on building target files.
You can also look through the UnrealBuildTool code itself . You can use this to, for example, see the TargetRules abstract base class implementation.
I haven’t figured out how to get auto-completion working in my own build files.