nixpkgs/pkgs/top-level/impure.nix
Matthew Bauer 31eac6fd00 impure.nix: fix handling of localSystem
If we passed a localSystem in, we don’t want the current system to
override it. Now we check for localSystem first to avoid getting
"mixed" localSystem values from commands like this:

  nix-build --arg localSystem '{config="x86_64-unknown-linux-musl";}' -A hello

Which would eventually evaluate localSystem to this:

{
  config = "x86_64-unknown-linux-musl";
  system = "x86_64-darwin";
}

& Nix would not be able to run it correctly.

Fixes 

/cc @Ericson2314
2018-06-25 17:13:02 -04:00

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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
, crossSystem ? null
, # 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
isDir = path: pathExists (path + "/.");
pathOverlays = try (toString <nixpkgs-overlays>) "";
homeOverlaysFile = homeDir + "/.config/nixpkgs/overlays.nix";
homeOverlaysDir = homeDir + "/.config/nixpkgs/overlays";
overlays = path:
# check if the path is a directory or a file
if isDir path then
# it's a directory, so the set of overlays from the directory, ordered lexicographically
let content = readDir path; in
map (n: import (path + ("/" + n)))
(builtins.filter (n: builtins.match ".*\\.nix" n != null || pathExists (path + ("/" + n + "/default.nix")))
(attrNames content))
else
# it's a file, so the result is the contents of the file itself
import path;
in
if pathOverlays != "" && pathExists pathOverlays then overlays pathOverlays
else if pathExists homeOverlaysFile && pathExists homeOverlaysDir then
throw ''
Nixpkgs overlays can be specified with ${homeOverlaysFile} or ${homeOverlaysDir}, but not both.
Please remove one of them and try again.
''
else if pathExists homeOverlaysFile then
if isDir homeOverlaysFile then
throw (homeOverlaysFile + " should be a file")
else overlays homeOverlaysFile
else if pathExists homeOverlaysDir then
if !(isDir homeOverlaysDir) then
throw (homeOverlaysDir + " should be a directory")
else overlays homeOverlaysDir
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 crossSystem;
# Fallback: Assume we are building packages on the current (build, in GNU
# Autotools parlance) system.
localSystem = (if args ? localSystem then {}
else { system = builtins.currentSystem; }) // localSystem;
})