I think this is probably not a good direction for fetchFromGitHub: it is not so complicated from the code level, but I think conceptually makes the behavior much more complicated. Instead, maybe a fetchGitHubRelease function?

What benefits does this abstraction provide over using fetchurl?

src = fetchurl {
  url = "https://github.com/hannesm/duration/releases/download/${version}/duration-${version}.tbz";
  sha256 = "0m9r0ayhpl98g9vdxrbjdcllns274jilic5v8xj1x7dphw21p95h";
};

We don't need things like fetchzip for releases assets since they are not suppose to change.

@grahamc I see your point, probably would make (more) sense.

@Mic92 I guess mostly convenience, since these URLs are kind of annoying too manually insert and construct every time. Also I guess you could argue the same thing for fetchFromGitHub in the first place, as you can also use fetchzip directly. Additionally I think this is a functionality packagers expect from fetchFromGitHub because intuitively it makes little sense why you can't download files using fetchFromGitHub listed directly next to files that you can.

I implemented it now according to @grahamc's suggestion. I'm not sure, if it's worth merging it in this state though, I'd be interested in your opinions.

One idea to improve this would be to add support for fetching release assets of private repositories. This is not possible at all currently, because GitHub always returns a 404 on private release assets, even if you are authenticated. It'd be required to send two API requests in order to get an download URL for the download. I am unsure, if that might be beyond the scope of nixpkgs fetchers?

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It sounds like we prefer to just keep it simple and use fetchurl for now. I'm going to close this stale PR to cleanup the backlog, but if you'd like to re-raise for discussion feel free to re-open.