Also specified specific revisions of the file to download to not have
a breaking package whenever the author decides to update the package.
This happened on 2018-01-01 when the author updated the copyright of
the package to match the new year.
Somewhat amusingly given its name, "clang.patch" applies to both 5 and 6
but is the cause of ncurses6 breakage on 6 but is required on 5...
gcc is happy in all four configurations:
5 5p 6 6p
gcc ✓ ✓ ✓ ✓
clang ✗ ✓ ✓ ✗
Which is why this commit enables the patch for 5 but not 6;
this matches behavior in Gentoo, for example.
For further simplification, we also use gcc-5 patch regardless.
This pushes check-meta evaluation to derivation evaluation step, leaving all other
attributes accessible.
Before this commit:
> $ HOME=/homeless-shelter NIX_PATH=nixpkgs=$(pwd) nix-instantiate --eval --strict ./default.nix -A xen --argstr system aarch64-linux
> Package ‘xen-4.5.5’ in pkgs/applications/virtualization/xen/generic.nix:226 is not supported on ‘aarch64-linux’, refusing to evaluate.
as expected
> $ HOME=/homeless-shelter NIX_PATH=nixpkgs=$(pwd) nix-instantiate --eval --strict ./default.nix -A xen.name --argstr system aarch64-linux
> Package ‘xen-4.5.5’ in pkgs/applications/virtualization/xen/generic.nix:226 is not supported on ‘aarch64-linux’, refusing to evaluate.
> $ HOME=/homeless-shelter NIX_PATH=nixpkgs=$(pwd) nix-instantiate --eval --strict ./default.nix -A xen.meta.description --argstr system aarch64-linux
> Package ‘xen-4.5.5’ in pkgs/applications/virtualization/xen/generic.nix:226 is not supported on ‘aarch64-linux’, refusing to evaluate.
which is unfortunate since its impossible to use packages in autogenerated
documentation on all platforms.
After this commit:
> $ HOME=/homeless-shelter NIX_PATH=nixpkgs=$(pwd) nix-instantiate --eval --strict ./default.nix -A xen --argstr system aarch64-linux
still fails
> $ HOME=/homeless-shelter NIX_PATH=nixpkgs=$(pwd) nix-instantiate --eval --strict ./default.nix -A xen.name --argstr system aarch64-linux
> "xen-4.5.5"
> $ HOME=/homeless-shelter NIX_PATH=nixpkgs=$(pwd) nix-instantiate --eval --strict ./default.nix -A xen.meta.description --argstr system aarch64-linux
> "Xen hypervisor and related components (vanilla)"
