refactor: move lib out of modules

lib/dag.nix

@@ -0,0 +1,107 @@
+# 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 (lib) all filterAttrs nvim mapAttrs toposort;
+in {
+  empty = {};
+
+  isEntry = e: e ? data && e ? after && e ? before;
+  isDag = dag:
+    builtins.isAttrs dag && all nvim.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 = nvim.dag.entryBetween [] [];
+
+  entryAfter = nvim.dag.entryBetween [];
+  entryBefore = before: nvim.dag.entryBetween before [];
+}