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nixpkgs/pkgs/top-level/impure.nix
Tom Hunger 4a524cf662 Allow directories with a default.nix to be imported as an overlay. Closes #23016.
Note that ${} substitution doesn't work because of the "cannot refer
to other paths" constraint. The paranthesis are needed to enforce
right-first evaluation.
2017-02-25 02:32:04 +01:00

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/* Impure default args for `pkgs/top-level/default.nix`. See that file
for the meaning of each argument. */
with builtins;
let
homeDir = builtins.getEnv "HOME";
# Return x if it evaluates, or def if it throws an exception.
try = x: def: let res = tryEval x; in if res.success then res.value else def;
in
{ # We combine legacy `system` and `platform` into `localSystem`, if
# `localSystem` was not passed. Strictly speaking, this is pure desugar, but
# it is most convient to do so before the impure `localSystem.system` default,
# so we do it now.
localSystem ? builtins.intersectAttrs { system = null; platform = null; } args
, # These are needed only because nix's `--arg` command-line logic doesn't work
# with unnamed parameters allowed by ...
system ? localSystem.system
, platform ? localSystem.platform
, # Fallback: The contents of the configuration file found at $NIXPKGS_CONFIG or
# $HOME/.config/nixpkgs/config.nix.
config ? let
configFile = getEnv "NIXPKGS_CONFIG";
configFile2 = homeDir + "/.config/nixpkgs/config.nix";
configFile3 = homeDir + "/.nixpkgs/config.nix"; # obsolete
in
if configFile != "" && pathExists configFile then import configFile
else if homeDir != "" && pathExists configFile2 then import configFile2
else if homeDir != "" && pathExists configFile3 then import configFile3
else {}
, # Overlays are used to extend Nixpkgs collection with additional
# collections of packages. These collection of packages are part of the
# fix-point made by Nixpkgs.
overlays ? let
dirPath = try (if pathExists <nixpkgs-overlays> then <nixpkgs-overlays> else "") "";
dirHome = homeDir + "/.config/nixpkgs/overlays";
dirCheck = dir: dir != "" && pathExists (dir + "/.");
overlays = dir:
let content = readDir dir; in
map (n: import (dir + ("/" + n)))
(builtins.filter (n: builtins.match ".*\.nix" n != null || pathExists (dir + ("/" + n + "/default.nix")))
(attrNames content));
in
if dirPath != "" then
overlays dirPath
else if dirCheck dirHome then overlays dirHome
else []
, ...
} @ args:
# If `localSystem` was explicitly passed, legacy `system` and `platform` should
# not be passed.
assert args ? localSystem -> !(args ? system || args ? platform);
import ./. (builtins.removeAttrs args [ "system" "platform" ] // {
inherit config overlays;
# Fallback: Assume we are building packages on the current (build, in GNU
# Autotools parlance) system.
localSystem = { system = builtins.currentSystem; } // localSystem;
})