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top-level: Introduce targetPackages and a "double link fold"

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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 :)
This commit is contained in:
John Ericson
2017-02-06 18:13:02 -05:00
parent d59e4fbb75
commit 863d79b364
4 changed files with 52 additions and 6 deletions
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41
pkgs/stdenv/booter.nix
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@@ -41,6 +41,35 @@
# 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.
@@ -55,19 +84,21 @@ stageFuns: let
# Adds the stdenv to the arguments, and sticks in it the previous stage for
# debugging purposes.
folder = stageFun: finalSoFar: let
args = stageFun finalSoFar;
folder = nextStage: stageFun: prevStage: let
args = stageFun prevStage;
args' = args // {
stdenv = args.stdenv // {
# For debugging
__bootPackages = finalSoFar;
__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 finalSoFar;
buildPackages = if args.selfBuild or true then null else prevStage;
__targetPackages = if args.selfBuild or true then null else nextStage;
});
in lib.lists.fold folder {} withAllowCustomOverrides
in dfold folder {} {} withAllowCustomOverrides