[BUG] --out-link does not work

[hjkatz]

I think --out-link is being overridden by this logic here. Could you help confirm?

nix-fast-build/nix_fast_build/__init__.py

Lines 681 to 685 in cfff239

	else:
	args += [
	"--out-link",
	opts.out_link + "-" + attr,
	]

[hjkatz]

I expect that --out-link path/to/out should link to path/to/out not path/to/out-<attr> because when attr is unset (for --flake) then we see path/to/out- (notice the trailing -) which is different than what we specified in the option.

[Mic92]

We kind of depend on --out-link to have a gcroot. Than the package can be uploaded afterwards without things getting garbage collected right away.

[hjkatz]

@Mic92 Could you explain with an example? What do you mean by gcroot?

[Mic92]

A gcroot is a link that prevents nix from deleting files when using nix-collect-garbage. If you use nix-build '<nixpkgs>' -A hello, it will also put a symlink called result in the current directory. That symlink also serves as a gcroot.

[hjkatz]

I'm not understanding how --out-link=/my/custom/path.out would cause that gcroot to not be considered by nix. Must the out-link be named result- with no attribute?

[Mic92]

It probably would be but we would still need to append a custom suffix somehow since we build several builds instead of just one, and the name would clash here between those.