gRPC-haskell/fetch-nixpkgs.nix
Parnell Springmeyer 2cfca15c31
Fix the output of the nixpkgs derivation and make the pin forwards compatible with Nix 2.0 (#52)
* Fix the output of the nixpkgs derivation

* Use the fixed-output sha256 hash for builtins.fetchTarball

This change makes the nixpkgs pin forwards compatible with Nix 1.12.x
and Nix 2.0.

* Correct the phrasing of the code comment
2018-03-12 11:06:21 -05:00

60 lines
1.9 KiB
Nix

{ rev # The Git revision of nixpkgs to fetch
, sha256 # The SHA256 of the downloaded data
, outputSha256 ? null # The SHA256 output hash
, system ? builtins.currentSystem # This is overridable if necessary
}:
with {
ifThenElse = { bool, thenValue, elseValue }: (
if bool then thenValue else elseValue);
};
ifThenElse {
bool = (0 <= builtins.compareVersions builtins.nixVersion "1.12");
# In Nix 1.12, we can just give a `sha256` to `builtins.fetchTarball`.
thenValue = (
builtins.fetchTarball {
url = "https://github.com/NixOS/nixpkgs/archive/${rev}.tar.gz";
# builtins.fetchTarball does not need the sha256 hash of the
# packed and compressed tarball but it _does_ need the
# fixed-output sha256 hash.
sha256 = outputSha256;
});
# This hack should at least work for Nix 1.11
elseValue = (
(rec {
tarball = import <nix/fetchurl.nix> {
url = "https://github.com/NixOS/nixpkgs/archive/${rev}.tar.gz";
inherit sha256;
};
builtin-paths = import <nix/config.nix>;
script = builtins.toFile "nixpkgs-unpacker" ''
"$coreutils/mkdir" "$out"
cd "$out"
"$gzip" --decompress < "$tarball" | "$tar" -x --strip-components=1
'';
nixpkgs = builtins.derivation ({
name = "nixpkgs-${builtins.substring 0 6 rev}";
builder = builtins.storePath builtin-paths.shell;
args = [ script ];
inherit tarball system;
tar = builtins.storePath builtin-paths.tar;
gzip = builtins.storePath builtin-paths.gzip;
coreutils = builtins.storePath builtin-paths.coreutils;
} // (if null == outputSha256 then { } else {
outputHashMode = "recursive";
outputHashAlgo = "sha256";
outputHash = outputSha256;
}));
}).nixpkgs);
}