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home-manager/modules/lib/dag.nix
rcerc 4a724cb84c
lib: improve DAG library
Specifically,

- directly export `modules/lib/dag.nix` instead of renaming
  attributes,

- run through utilities to reuse code where possible,

- expose `lib.hm.dag.isEntry` and reuse it in
  `modules/lib/types-dag.nix`,

- reuse utilities through `lib` set instead of passing imports to
  functions, and

- eta reduction of `map`, `entryAnywhere`, `entryAfter` and
  `entryBefore`.
2022-07-18 15:32:48 +02:00

103 lines
3.2 KiB
Nix

# A generalization of Nixpkgs's `strings-with-deps.nix`.
#
# The main differences from the Nixpkgs version are
#
# - not specific to strings, i.e., any payload is OK,
#
# - the addition of the function `entryBefore` indicating a "wanted
# by" relationship.
{ lib }:
let inherit (lib) all filterAttrs hm mapAttrs toposort;
in {
empty = { };
isEntry = e: e ? data && e ? after && e ? before;
isDag = dag:
builtins.isAttrs dag && all hm.dag.isEntry (builtins.attrValues dag);
# Takes an attribute set containing entries built by entryAnywhere,
# entryAfter, and entryBefore to a topologically sorted list of
# entries.
#
# Internally this function uses the `toposort` function in
# `<nixpkgs/lib/lists.nix>` and its value is accordingly.
#
# Specifically, the result on success is
#
# { result = [ { name = ?; data = ?; } … ] }
#
# For example
#
# nix-repl> topoSort {
# a = entryAnywhere "1";
# b = entryAfter [ "a" "c" ] "2";
# c = entryBefore [ "d" ] "3";
# d = entryBefore [ "e" ] "4";
# e = entryAnywhere "5";
# } == {
# result = [
# { data = "1"; name = "a"; }
# { data = "3"; name = "c"; }
# { data = "2"; name = "b"; }
# { data = "4"; name = "d"; }
# { data = "5"; name = "e"; }
# ];
# }
# true
#
# And the result on error is
#
# {
# cycle = [ { after = ?; name = ?; data = ? } … ];
# loops = [ { after = ?; name = ?; data = ? } … ];
# }
#
# For example
#
# nix-repl> topoSort {
# a = entryAnywhere "1";
# b = entryAfter [ "a" "c" ] "2";
# c = entryAfter [ "d" ] "3";
# d = entryAfter [ "b" ] "4";
# e = entryAnywhere "5";
# } == {
# cycle = [
# { after = [ "a" "c" ]; data = "2"; name = "b"; }
# { after = [ "d" ]; data = "3"; name = "c"; }
# { after = [ "b" ]; data = "4"; name = "d"; }
# ];
# loops = [
# { after = [ "a" "c" ]; data = "2"; name = "b"; }
# ];
# }
# true
topoSort = dag:
let
dagBefore = dag: name:
builtins.attrNames
(filterAttrs (n: v: builtins.elem name v.before) dag);
normalizedDag = mapAttrs (n: v: {
name = n;
data = v.data;
after = v.after ++ dagBefore dag n;
}) dag;
before = a: b: builtins.elem a.name b.after;
sorted = toposort before (builtins.attrValues normalizedDag);
in if sorted ? result then {
result = map (v: { inherit (v) name data; }) sorted.result;
} else
sorted;
# Applies a function to each element of the given DAG.
map = f: mapAttrs (n: v: v // { data = f n v.data; });
entryBetween = before: after: data: { inherit data before after; };
# Create a DAG entry with no particular dependency information.
entryAnywhere = hm.dag.entryBetween [ ] [ ];
entryAfter = hm.dag.entryBetween [ ];
entryBefore = before: hm.dag.entryBetween before [ ];
}