mirror of
https://github.com/NixOS/nixpkgs.git
synced 2024-11-24 14:41:17 +00:00
863d79b364
Each bootstrapping stage ought to just depend on the previous stage, but poorly-written compilers break this elegence. This provides an easy-enough way to depend on the next stage: targetPackages. PLEASE DO NOT USE IT UNLESS YOU MUST! I'm hoping someday in a pleasant future I can revert this commit :)
105 lines
4.3 KiB
Nix
105 lines
4.3 KiB
Nix
# This file defines a single function for booting a package set from a list of
|
|
# stages. The exact mechanics of that function are defined below; here I
|
|
# (@Ericson2314) wish to describe the purpose of the abstraction.
|
|
#
|
|
# The first goal is consistency across stdenvs. Regardless of what this function
|
|
# does, by making every stdenv use it for bootstrapping we ensure that they all
|
|
# work in a similar way. [Before this abstraction, each stdenv was its own
|
|
# special snowflake due to different authors writing in different times.]
|
|
#
|
|
# The second goal is consistency across each stdenv's stage functions. By
|
|
# writing each stage it terms of the previous stage, commonalities between them
|
|
# are more easily observable. [Before, there usually was a big attribute set
|
|
# with each stage, and stages would access the previous stage by name.]
|
|
#
|
|
# The third goal is composition. Because each stage is written in terms of the
|
|
# previous, the list can be reordered or, more practically, extended with new
|
|
# stages. The latter is used for cross compiling and custom
|
|
# stdenvs. Additionally, certain options should by default apply only to the
|
|
# last stage, whatever it may be. By delaying the creation of stage package sets
|
|
# until the final fold, we prevent these options from inhibiting composition.
|
|
#
|
|
# The fourth and final goal is debugging. Normal packages should only source
|
|
# their dependencies from the current stage. But for the sake of debugging, it
|
|
# is nice that all packages still remain accessible. We make sure previous
|
|
# stages are kept around with a `stdenv.__bootPackges` attribute referring the
|
|
# previous stage. It is idiomatic that attributes prefixed with `__` come with
|
|
# special restrictions and should not be used under normal circumstances.
|
|
{ lib, allPackages }:
|
|
|
|
# Type:
|
|
# [ pkgset -> (args to stage/default.nix) or ({ __raw = true; } // pkgs) ]
|
|
# -> pkgset
|
|
#
|
|
# In english: This takes a list of function from the previous stage pkgset and
|
|
# returns the final pkgset. Each of those functions returns, if `__raw` is
|
|
# undefined or false, args for this stage's pkgset (the most complex and
|
|
# important arg is the stdenv), or, if `__raw = true`, simply this stage's
|
|
# pkgset itself.
|
|
#
|
|
# The list takes stages in order, so the final stage is last in the list. In
|
|
# other words, this does a foldr not foldl.
|
|
stageFuns: let
|
|
|
|
/* "dfold" a ternary function `op' between successive elements of `list' as if
|
|
it was a doubly-linked list with `lnul' and `rnul` base cases at either
|
|
end. In precise terms, `fold op lnul rnul [x_0 x_1 x_2 ... x_n-1]` is the
|
|
same as
|
|
|
|
let
|
|
f_-1 = lnul;
|
|
f_0 = op f_-1 x_0 f_1;
|
|
f_1 = op f_0 x_1 f_2;
|
|
f_2 = op f_1 x_2 f_3;
|
|
...
|
|
f_n = op f_n-1 x_n f_n+1;
|
|
f_n+1 = rnul;
|
|
in
|
|
f_0
|
|
*/
|
|
dfold = op: lnul: rnul: list:
|
|
let
|
|
len = builtins.length list;
|
|
go = pred: n:
|
|
if n == len
|
|
then rnul
|
|
else let
|
|
# Note the cycle -- call-by-need ensures finite fold.
|
|
cur = op pred (builtins.elemAt list n) succ;
|
|
succ = go cur (n + 1);
|
|
in cur;
|
|
in go lnul 0;
|
|
|
|
# Take the list and disallow custom overrides in all but the final stage,
|
|
# and allow it in the final flag. Only defaults this boolean field if it
|
|
# isn't already set.
|
|
withAllowCustomOverrides = lib.lists.imap
|
|
(index: stageFun: prevStage:
|
|
# So true by default for only the first element because one
|
|
# 1-indexing. Since we reverse the list, this means this is true
|
|
# for the final stage.
|
|
{ allowCustomOverrides = index == 1; }
|
|
// (stageFun prevStage))
|
|
(lib.lists.reverseList stageFuns);
|
|
|
|
# Adds the stdenv to the arguments, and sticks in it the previous stage for
|
|
# debugging purposes.
|
|
folder = nextStage: stageFun: prevStage: let
|
|
args = stageFun prevStage;
|
|
args' = args // {
|
|
stdenv = args.stdenv // {
|
|
# For debugging
|
|
__bootPackages = prevStage;
|
|
__hatPackages = nextStage;
|
|
};
|
|
};
|
|
in
|
|
if args.__raw or false
|
|
then args'
|
|
else allPackages ((builtins.removeAttrs args' ["selfBuild"]) // {
|
|
buildPackages = if args.selfBuild or true then null else prevStage;
|
|
__targetPackages = if args.selfBuild or true then null else nextStage;
|
|
});
|
|
|
|
in dfold folder {} {} withAllowCustomOverrides
|