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Diffstat (limited to 'home-manager/modules/lib/dag.nix')
-rw-r--r-- | home-manager/modules/lib/dag.nix | 124 |
1 files changed, 124 insertions, 0 deletions
diff --git a/home-manager/modules/lib/dag.nix b/home-manager/modules/lib/dag.nix new file mode 100644 index 00000000000..535dec35ad4 --- /dev/null +++ b/home-manager/modules/lib/dag.nix @@ -0,0 +1,124 @@ +# 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 `dagEntryBefore` indicating a +# "wanted by" relationship. + +{ lib }: + +with lib; + +rec { + + emptyDag = {}; + + isDag = dag: + let + isEntry = e: (e ? data) && (e ? after) && (e ? before); + in + builtins.isAttrs dag && all (x: x) (mapAttrsToList (n: isEntry) dag); + + # Takes an attribute set containing entries built by + # dagEntryAnywhere, dagEntryAfter, and dagEntryBefore 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> dagTopoSort { + # a = dagEntryAnywhere "1"; + # b = dagEntryAfter ["a" "c"] "2"; + # c = dagEntryBefore ["d"] "3"; + # d = dagEntryBefore ["e"] "4"; + # e = dagEntryAnywhere "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> dagTopoSort { + # a = dagEntryAnywhere "1"; + # b = dagEntryAfter ["a" "c"] "2"; + # c = dagEntryAfter ["d"] "3"; + # d = dagEntryAfter ["b"] "4"; + # e = dagEntryAnywhere "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 + dagTopoSort = dag: + let + dagBefore = dag: name: + mapAttrsToList (n: v: n) ( + filterAttrs (n: v: any (a: a == name) v.before) dag + ); + normalizedDag = + mapAttrs (n: v: { + name = n; + data = v.data; + after = v.after ++ dagBefore dag n; + }) dag; + before = a: b: any (c: a.name == c) b.after; + sorted = toposort before (mapAttrsToList (n: v: v) 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. + dagMap = f: dag: mapAttrs (n: v: v // { data = f n v.data; }) dag; + + # Create a DAG entry with no particular dependency information. + dagEntryAnywhere = data: { + inherit data; + before = []; + after = []; + }; + + dagEntryBetween = before: after: data: { + inherit data before after; + }; + + dagEntryAfter = after: data: { + inherit data after; + before = []; + }; + + dagEntryBefore = before: data: { + inherit data before; + after = []; + }; + +} |