* `submodules`: A Boolean denoting whether Git submodules should be fetched when this flake is used as an input. When set to `true`, Git submodules will be automatically fetched without requiring callers to specify `submodules=1` in the flake reference URL. Defaults to `false`.

* `lfs`: A Boolean denoting whether Git LFS (Large File Storage) files should be fetched when this flake is used as an input. When set to `true`, Git LFS files will be automatically fetched. Defaults to `false`.

These self-attributes eliminate the need for consumers of your flake to manually specify fetching options in their flake references.

Overrides and `follows` can be combined, e.g.

```nix
inputs.nixops.inputs.nixpkgs.follows = "dwarffs/nixpkgs";
```

sets the `nixpkgs` input of `nixops` to be the same as the `nixpkgs`
input of `dwarffs`. It is worth noting, however, that it is generally
not useful to eliminate transitive `nixpkgs` flake inputs in this
way. Most flakes provide their functionality through Nixpkgs overlays
or NixOS modules, which are composed into the top-level flake's
`nixpkgs` input; so their own `nixpkgs` input is usually irrelevant.

# Lock files

Inputs specified in `flake.nix` are typically "unlocked" in the sense
that they don't specify an exact revision. To ensure reproducibility,
Nix will automatically generate and use a *lock file* called
`flake.lock` in the flake's directory.
The lock file is a UTF-8 JSON file.
It contains a graph structure isomorphic to the graph of dependencies of the root
flake. Each node in the graph (except the root node) maps the
(usually) unlocked input specifications in `flake.nix` to locked input
specifications. Each node also contains some metadata, such as the
dependencies (outgoing edges) of the node.

For example, if `flake.nix` has the inputs in the example above, then
the resulting lock file might be:

```json
{
  "version": 7,
  "root": "n1",
  "nodes": {
    "n1": {
      "inputs": {
        "nixpkgs": "n2",
        "import-cargo": "n3",
        "grcov": "n4"
      }
    },
    "n2": {
      "inputs": {},
      "locked": {
        "owner": "edolstra",
        "repo": "nixpkgs",
        "rev": "7f8d4b088e2df7fdb6b513bc2d6941f1d422a013",
        "type": "github",
        "lastModified": 1580555482,
        "narHash": "sha256-OnpEWzNxF/AU4KlqBXM2s5PWvfI5/BS6xQrPvkF5tO8="
      },
      "original": {
        "id": "nixpkgs",
        "type": "indirect"
      }
    },
    "n3": {
      "inputs": {},
      "locked": {
        "owner": "edolstra",
        "repo": "import-cargo",
        "rev": "8abf7b3a8cbe1c8a885391f826357a74d382a422",
        "type": "github",
        "lastModified": 1567183309,
        "narHash": "sha256-wIXWOpX9rRjK5NDsL6WzuuBJl2R0kUCnlpZUrASykSc="
      },
      "original": {
        "owner": "edolstra",
        "repo": "import-cargo",
        "type": "github"
      }
    },
    "n4": {
      "inputs": {},
      "locked": {
        "owner": "mozilla",
        "repo": "grcov",
        "rev": "989a84bb29e95e392589c4e73c29189fd69a1d4e",
        "type": "github",
        "lastModified": 1580729070,
        "narHash": "sha256-235uMxYlHxJ5y92EXZWAYEsEb6mm+b069GAd+BOIOxI="
      },
      "original": {
        "owner": "mozilla",