nixpkgs/pkgs/top-level/stage.nix
Nicolas B. Pierron f5dfe78a1e Add overlays mechanism to Nixpkgs.
This patch add a new argument to Nixpkgs default expression named "overlays".

By default, the value of the argument is either taken from the environment variable `NIXPKGS_OVERLAYS`,
or from the directory `~/.nixpkgs/overlays/`.  If the environment variable does not name a valid directory
then this mechanism would fallback on the home directory.  If the home directory does not exists it will
fallback on an empty list of overlays.

The overlays directory should contain the list of extra Nixpkgs stages which would be used to extend the
content of Nixpkgs, with additional set of packages.  The overlays, i-e directory, files, symbolic links
are used in alphabetical order.

The simplest overlay which extends Nixpkgs with nothing looks like:

```nix
self: super: {
}
```

More refined overlays can use `super` as the basis for building new packages, and `self` as a way to query
the final result of the fix-point.

An example of overlay which extends Nixpkgs with a small set of packages can be found at:
  https://github.com/nbp/nixpkgs-mozilla/blob/nixpkgs-overlay/moz-overlay.nix

To use this file, checkout the repository and add a symbolic link to
the `moz-overlay.nix` file in `~/.nixpkgs/overlays` directory.
2017-01-16 01:17:33 +01:00

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Nix

/* This file composes a single bootstrapping stage of the Nix Packages
collection. That is, it imports the functions that build the various
packages, and calls them with appropriate arguments. The result is a set of
all the packages in the Nix Packages collection for some particular platform
for some particular stage.
Default arguments are only provided for bootstrapping
arguments. Normal users should not import this directly but instead
import `pkgs/default.nix` or `default.nix`. */
{ # The system (e.g., `i686-linux') for which to build the packages.
system
, # The standard environment to use for building packages.
stdenv
, # This is used because stdenv replacement and the stdenvCross do benefit from
# the overridden configuration provided by the user, as opposed to the normal
# bootstrapping stdenvs.
allowCustomOverrides
, # Non-GNU/Linux OSes are currently "impure" platforms, with their libc
# outside of the store. Thus, GCC, GFortran, & co. must always look for
# files in standard system directories (/usr/include, etc.)
noSysDirs ? (system != "x86_64-freebsd" && system != "i686-freebsd"
&& system != "x86_64-solaris"
&& system != "x86_64-kfreebsd-gnu")
, # The configuration attribute set
config
, overlays # List of overlays to use in the fix-point.
, crossSystem
, platform
, lib
, nixpkgsFun
}:
let
stdenvAdapters = self: super:
let res = import ../stdenv/adapters.nix self; in res // {
stdenvAdapters = res;
};
trivialBuilders = self: super:
import ../build-support/trivial-builders.nix {
inherit lib; inherit (self) stdenv stdenvNoCC; inherit (self.xorg) lndir;
};
stdenvBootstappingAndPlatforms = self: super: {
stdenv = stdenv // { inherit platform; };
inherit
system platform crossSystem;
};
allPackages = self: super:
let res = import ./all-packages.nix
{ inherit lib nixpkgsFun noSysDirs config; }
res self;
in res;
aliases = self: super: import ./aliases.nix super;
# stdenvOverrides is used to avoid having multiple of versions
# of certain dependencies that were used in bootstrapping the
# standard environment.
stdenvOverrides = self: super:
(super.stdenv.overrides or (_: _: {})) self super;
# Allow packages to be overridden globally via the `packageOverrides'
# configuration option, which must be a function that takes `pkgs'
# as an argument and returns a set of new or overridden packages.
# The `packageOverrides' function is called with the *original*
# (un-overridden) set of packages, allowing packageOverrides
# attributes to refer to the original attributes (e.g. "foo =
# ... pkgs.foo ...").
configOverrides = self: super:
lib.optionalAttrs allowCustomOverrides
((config.packageOverrides or (super: {})) super);
# The complete chain of package set builders, applied from top to bottom
toFix = lib.foldl' (lib.flip lib.extends) (self: {}) ([
stdenvBootstappingAndPlatforms
stdenvAdapters
trivialBuilders
allPackages
aliases
stdenvOverrides
configOverrides
] ++ overlays);
in
# Return the complete set of packages.
lib.fix toFix