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neovim-flake/lib/dag.nix
2024-03-23 20:31:33 -04:00

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Nix

# From home-manager: https://github.com/nix-community/home-manager/blob/master/modules/lib/dag.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 (builtins) isAttrs attrValues attrNames elem all;
inherit (lib.attrsets) filterAttrs mapAttrs;
inherit (lib.lists) toposort;
inherit (lib.nvim.dag) isEntry entryBetween;
in {
empty = {};
isEntry = e: e ? data && e ? after && e ? before;
isDag = dag:
isAttrs dag && all isEntry (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:
attrNames
(filterAttrs (_n: v: elem name v.before) dag);
normalizedDag =
mapAttrs (n: v: {
name = n;
data = v.data;
after = v.after ++ dagBefore dag n;
})
dag;
before = a: b: elem a.name b.after;
sorted = toposort before (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 = entryBetween [] [];
entryAfter = entryBetween [];
entryBefore = before: entryBetween before [];
}