pyrox.dev
lol
1# This file defines a single function for booting a package set from a list of
2# stages. The exact mechanics of that function are defined below; here I
3# (@Ericson2314) wish to describe the purpose of the abstraction.
4#
5# The first goal is consistency across stdenvs. Regardless of what this function
6# does, by making every stdenv use it for bootstrapping we ensure that they all
7# work in a similar way. [Before this abstraction, each stdenv was its own
8# special snowflake due to different authors writing in different times.]
9#
10# The second goal is consistency across each stdenv's stage functions. By
11# writing each stage it terms of the previous stage, commonalities between them
12# are more easily observable. [Before, there usually was a big attribute set
13# with each stage, and stages would access the previous stage by name.]
14#
15# The third goal is composition. Because each stage is written in terms of the
16# previous, the list can be reordered or, more practically, extended with new
17# stages. The latter is used for cross compiling and custom
18# stdenvs. Additionally, certain options should by default apply only to the
19# last stage, whatever it may be. By delaying the creation of stage package sets
20# until the final fold, we prevent these options from inhibiting composition.
21#
22# The fourth and final goal is debugging. Normal packages should only source
23# their dependencies from the current stage. But for the sake of debugging, it
24# is nice that all packages still remain accessible. We make sure previous
25# stages are kept around with a `stdenv.__bootPackges` attribute referring the
26# previous stage. It is idiomatic that attributes prefixed with `__` come with
27# special restrictions and should not be used under normal circumstances.
28{ lib, allPackages }:
29
30# Type:
31# [ pkgset -> (args to stage/default.nix) or ({ __raw = true; } // pkgs) ]
32# -> pkgset
33#
34# In english: This takes a list of function from the previous stage pkgset and
35# returns the final pkgset. Each of those functions returns, if `__raw` is
36# undefined or false, args for this stage's pkgset (the most complex and
37# important arg is the stdenv), or, if `__raw = true`, simply this stage's
38# pkgset itself.
39#
40# The list takes stages in order, so the final stage is last in the list. In
41# other words, this does a foldr not foldl.
42stageFuns: let
43
44 /* "dfold" a ternary function `op' between successive elements of `list' as if
45 it was a doubly-linked list with `lnul' and `rnul` base cases at either
46 end. In precise terms, `fold op lnul rnul [x_0 x_1 x_2 ... x_n-1]` is the
47 same as
48
49 let
50 f_-1 = lnul f_0;
51 f_0 = op f_-1 x_0 f_1;
52 f_1 = op f_0 x_1 f_2;
53 f_2 = op f_1 x_2 f_3;
54 ...
55 f_n = op f_n-1 x_n f_n+1;
56 f_n+1 = rnul f_n;
57 in
58 f_0
59 */
60 dfold = op: lnul: rnul: list:
61 let
62 len = builtins.length list;
63 go = pred: n:
64 if n == len
65 then rnul pred
66 else let
67 # Note the cycle -- call-by-need ensures finite fold.
68 cur = op pred (builtins.elemAt list n) succ;
69 succ = go cur (n + 1);
70 in cur;
71 lapp = lnul cur;
72 cur = go lapp 0;
73 in cur;
74
75 # Take the list and disallow custom overrides in all but the final stage,
76 # and allow it in the final flag. Only defaults this boolean field if it
77 # isn't already set.
78 withAllowCustomOverrides = lib.lists.imap1
79 (index: stageFun: prevStage:
80 # So true by default for only the first element because one
81 # 1-indexing. Since we reverse the list, this means this is true
82 # for the final stage.
83 { allowCustomOverrides = index == 1; }
84 // (stageFun prevStage))
85 (lib.lists.reverseList stageFuns);
86
87 # Adds the stdenv to the arguments, and sticks in it the previous stage for
88 # debugging purposes.
89 folder = nextStage: stageFun: prevStage: let
90 args = stageFun prevStage;
91 args' = args // {
92 stdenv = args.stdenv // {
93 # For debugging
94 __bootPackages = prevStage;
95 __hatPackages = nextStage;
96 };
97 };
98 in
99 if args.__raw or false
100 then args'
101 else allPackages ((builtins.removeAttrs args' ["selfBuild"]) // {
102 buildPackages = if args.selfBuild or true then null else prevStage;
103 targetPackages = if args.selfBuild or true then null else nextStage;
104 });
105
106 # This is a hack for resolving cross-compiled compilers' run-time
107 # deps. (That is, compilers that are themselves cross-compiled, as
108 # opposed to used to cross-compile packages.)
109 postStage = buildPackages: {
110 __raw = true;
111 stdenv.cc =
112 if buildPackages.stdenv.cc.isClang or false
113 then buildPackages.clang
114 else buildPackages.gcc;
115 };
116
117in dfold folder postStage (_: {}) withAllowCustomOverrides