dream2nix/flake-compat.nix

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# Compatibility function to allow flakes to be used by
# non-flake-enabled Nix versions. Given a source tree containing a
# 'flake.nix' and 'flake.lock' file, it fetches the flake inputs and
# calls the flake's 'outputs' function. It then returns an attrset
# containing 'defaultNix' (to be used in 'default.nix'), 'shellNix'
# (to be used in 'shell.nix').
{
src,
system ? builtins.currentSystem or "unknown-system",
}: let
lockFilePath = src + "/flake.lock";
lockFile = builtins.fromJSON (builtins.readFile lockFilePath);
fetchTree = info:
if info.type == "github"
then {
outPath =
fetchTarball
(
{url = "https://api.${info.host or "github.com"}/repos/${info.owner}/${info.repo}/tarball/${info.rev}";}
// (
if info ? narHash
then {sha256 = info.narHash;}
else {}
)
);
rev = info.rev;
shortRev = builtins.substring 0 7 info.rev;
lastModified = info.lastModified;
lastModifiedDate = formatSecondsSinceEpoch info.lastModified;
narHash = info.narHash;
}
else if info.type == "git"
then
{
outPath =
builtins.fetchGit
(
{url = info.url;}
// (
if info ? rev
then {inherit (info) rev;}
else {}
)
// (
if info ? ref
then {inherit (info) ref;}
else {}
)
// (
if info ? submodules
then {inherit (info) submodules;}
else {}
)
);
lastModified = info.lastModified;
lastModifiedDate = formatSecondsSinceEpoch info.lastModified;
narHash = info.narHash;
}
// (
if info ? rev
then {
rev = info.rev;
shortRev = builtins.substring 0 7 info.rev;
}
else {
}
)
else if info.type == "path"
then {
outPath = builtins.path {path = info.path;};
narHash = info.narHash;
}
else if info.type == "tarball"
then {
outPath =
fetchTarball
(
{inherit (info) url;}
// (
if info ? narHash
then {sha256 = info.narHash;}
else {}
)
);
}
else if info.type == "gitlab"
then {
inherit (info) rev narHash lastModified;
outPath =
fetchTarball
(
{url = "https://${info.host or "gitlab.com"}/api/v4/projects/${info.owner}%2F${info.repo}/repository/archive.tar.gz?sha=${info.rev}";}
// (
if info ? narHash
then {sha256 = info.narHash;}
else {}
)
);
shortRev = builtins.substring 0 7 info.rev;
}
else
# FIXME: add Mercurial, tarball inputs.
throw "flake input has unsupported input type '${info.type}'";
callFlake4 = flakeSrc: locks: let
flake = import (flakeSrc + "/flake.nix");
inputs = builtins.mapAttrs (n: v:
if v.flake or true
then callFlake4 (fetchTree (v.locked // v.info)) v.inputs
else fetchTree (v.locked // v.info))
locks;
outputs = flakeSrc // (flake.outputs (inputs // {self = outputs;}));
in
assert flake.edition == 201909; outputs;
callLocklessFlake = flakeSrc: let
flake = import (flakeSrc + "/flake.nix");
outputs = flakeSrc // (flake.outputs {self = outputs;});
in
outputs;
rootSrc = let
# Try to clean the source tree by using fetchGit, if this source
# tree is a valid git repository.
tryFetchGit = src:
if isGit && !isShallow
then let
res = builtins.fetchGit src;
in
if res.rev == "0000000000000000000000000000000000000000"
then removeAttrs res ["rev" "shortRev"]
else res
else {outPath = src;};
# NB git worktrees have a file for .git, so we don't check the type of .git
isGit = builtins.pathExists (src + "/.git");
isShallow = builtins.pathExists (src + "/.git/shallow");
in
{
lastModified = 0;
lastModifiedDate = formatSecondsSinceEpoch 0;
}
// (
if src ? outPath
then src
else tryFetchGit src
);
# Format number of seconds in the Unix epoch as %Y%m%d%H%M%S.
formatSecondsSinceEpoch = t: let
rem = x: y: x - x / y * y;
days = t / 86400;
secondsInDay = rem t 86400;
hours = secondsInDay / 3600;
minutes = (rem secondsInDay 3600) / 60;
seconds = rem t 60;
# Courtesy of https://stackoverflow.com/a/32158604.
z = days + 719468;
era =
(
if z >= 0
then z
else z - 146096
)
/ 146097;
doe = z - era * 146097;
yoe = (doe - doe / 1460 + doe / 36524 - doe / 146096) / 365;
y = yoe + era * 400;
doy = doe - (365 * yoe + yoe / 4 - yoe / 100);
mp = (5 * doy + 2) / 153;
d = doy - (153 * mp + 2) / 5 + 1;
m =
mp
+ (
if mp < 10
then 3
else -9
);
y' =
y
+ (
if m <= 2
then 1
else 0
);
pad = s:
if builtins.stringLength s < 2
then "0" + s
else s;
in "${toString y'}${pad (toString m)}${pad (toString d)}${pad (toString hours)}${pad (toString minutes)}${pad (toString seconds)}";
allNodes =
builtins.mapAttrs
(
key: node: let
sourceInfo =
if key == lockFile.root
then rootSrc
else fetchTree (node.info or {} // removeAttrs node.locked ["dir"]);
subdir =
if key == lockFile.root
then ""
else node.locked.dir or "";
flake = import (sourceInfo
+ (
if subdir != ""
then "/"
else ""
)
+ subdir
+ "/flake.nix");
inputs =
builtins.mapAttrs
(inputName: inputSpec: allNodes.${resolveInput inputSpec})
(node.inputs or {});
# Resolve a input spec into a node name. An input spec is
# either a node name, or a 'follows' path from the root
# node.
resolveInput = inputSpec:
if builtins.isList inputSpec
then getInputByPath lockFile.root inputSpec
else inputSpec;
# Follow an input path (e.g. ["dwarffs" "nixpkgs"]) from the
# root node, returning the final node.
getInputByPath = nodeName: path:
if path == []
then nodeName
else
getInputByPath
# Since this could be a 'follows' input, call resolveInput.
(resolveInput lockFile.nodes.${nodeName}.inputs.${builtins.head path})
(builtins.tail path);
outputs = flake.outputs (inputs // {self = result;});
result =
outputs
// sourceInfo
// {
inherit inputs;
inherit outputs;
inherit sourceInfo;
};
in
if node.flake or true
then assert builtins.isFunction flake.outputs; result
else sourceInfo
)
lockFile.nodes;
result =
if !(builtins.pathExists lockFilePath)
then callLocklessFlake rootSrc
else if lockFile.version == 4
then callFlake4 rootSrc (lockFile.inputs)
else if lockFile.version >= 5 && lockFile.version <= 7
then allNodes.${lockFile.root}
else throw "lock file '${lockFilePath}' has unsupported version ${toString lockFile.version}";
in rec {
# expose flake inputs
inherit (result) inputs;
defaultNix =
result
// (
if result ? defaultPackage.${system}
then {default = result.defaultPackage.${system};}
else {}
)
// (
if result ? packages.${system}.default
then {default = result.packages.${system}.default;}
else {}
);
shellNix =
defaultNix
// (
if result ? devShell.${system}
then {default = result.devShell.${system};}
else {}
)
// (
if result ? devShells.${system}.default
then {default = result.devShells.${system}.default;}
else {}
);
}