nvf/docs/manual/configuring/dags.md

Using DAGs

We conform to the NixOS options types for the most part, however, a noteworthy addition for certain options is the DAG (Directed acyclic graph) type which is borrowed from home-manager's extended library. This type is most used for topologically sorting strings. The DAG type allows the attribute set entries to express dependency relations among themselves. This can, for example, be used to control the order of configuration sections in your configRC or luaConfigRC.

The below section, mostly taken from the home-manager manual explains in more detail the overall usage logic of the DAG type.

entryAnywhere

lib.dag.entryAnywhere (value: T) : DagEntry<T>

Indicates that value can be placed anywhere within the DAG. This is also the default for plain attribute set entries, that is

foo.bar = {
  a = lib.dag.entryAnywhere 0;
}

and

foo.bar = {
  a = 0;
}

are equivalent.

entryAfter

lib.dag.entryAfter (afters: list string) (value: T) : DagEntry<T>

Indicates that value must be placed after each of the attribute names in the given list. For example

foo.bar = {
  a = 0;
  b = lib.dag.entryAfter [ "a" ] 1;
}

would place b after a in the graph.

entryBefore

lib.dag.entryBefore (befores: list string) (value: T) : DagEntry<T>

Indicates that value must be placed before each of the attribute names in the given list. For example

foo.bar = {
  b = lib.dag.entryBefore [ "a" ] 1;
  a = 0;
}

would place b before a in the graph.

entryBetween

lib.dag.entryBetween (befores: list string) (afters: list string) (value: T) : DagEntry<T>

Indicates that value must be placed before the attribute names in the first list and after the attribute names in the second list. For example

foo.bar = {
  a = 0;
  c = lib.dag.entryBetween [ "b" ] [ "a" ] 2;
  b = 1;
}

would place c before b and after a in the graph.

There are also a set of functions that generate a DAG from a list. These are convenient when you just want to have a linear list of DAG entries, without having to manually enter the relationship between each entry. Each of these functions take a tag as argument and the DAG entries will be named ${tag}-${index}.

entriesAnywhere

lib.dag.entriesAnywhere (tag: string) (values: [T]) : Dag<T>

Creates a DAG with the given values with each entry labeled using the given tag. For example

foo.bar = lib.dag.entriesAnywhere "a" [ 0 1 ];

is equivalent to

foo.bar = {
  a-0 = 0;
  a-1 = lib.dag.entryAfter [ "a-0" ] 1;
}

entriesAfter

lib.dag.entriesAfter (tag: string) (afters: list string) (values: [T]) : Dag<T>

Creates a DAG with the given values with each entry labeled using the given tag. The list of values are placed are placed after each of the attribute names in afters. For example

foo.bar =
  { b = 0; } // lib.dag.entriesAfter "a" [ "b" ] [ 1 2 ];

is equivalent to

foo.bar = {
  b = 0;
  a-0 = lib.dag.entryAfter [ "b" ] 1;
  a-1 = lib.dag.entryAfter [ "a-0" ] 2;
}

entriesBefore

lib.dag.entriesBefore (tag: string) (befores: list string) (values: [T]) : Dag<T>

Creates a DAG with the given values with each entry labeled using the given tag. The list of values are placed before each of the attribute names in befores. For example

  foo.bar =
    { b = 0; } // lib.dag.entriesBefore "a" [ "b" ] [ 1 2 ];

is equivalent to

foo.bar = {
  b = 0;
  a-0 = 1;
  a-1 = lib.dag.entryBetween [ "b" ] [ "a-0" ] 2;
}

entriesBetween

lib.dag.entriesBetween (tag: string) (befores: list string) (afters: list string) (values: [T]) : Dag<T>

Creates a DAG with the given values with each entry labeled using the given tag. The list of values are placed before each of the attribute names in befores and after each of the attribute names in afters. For example

foo.bar =
  { b = 0; c = 3; } // lib.dag.entriesBetween "a" [ "b" ] [ "c" ] [ 1 2 ];

is equivalent to

foo.bar = {
  b = 0;
  c = 3;
  a-0 = lib.dag.entryAfter [ "c" ] 1;
  a-1 = lib.dag.entryBetween [ "b" ] [ "a-0" ] 2;
}