In bug 1479127, we are adding a high level feature control, Feature Gates. They provide additional metadata for features and help enforce a particular pattern of preference access. Currently the library enabling feature gates is implemented in chrome JS, and is inaccessible from C++ where many features are enabled. This bug covers changing that, so that C++ code can access a FeatureGate just as well as JS code. One potential way of doing this would be to define an IDL that C++ and other callers can use to access the JS library.

We discussed this in triage and this doesn't sound like it needs actual build system work, it's just Firefox work that might involve using build system features like `GENERATED_FILES`.

Putting this in the build system was an accident, sorry. I agree that this is not a build system bug.

Is there a better bug component for this than Firefox::General? Most of Firefox doesn't even use C++, so at least this seems more like Toolkit. Or maybe another way of asking is, are there examples of C++ features that you're planning on supporting or that need this? I'll mark this P3 for now, please feel free to reassign a better priority