Understanding 'nix flake metadata' Output

R""( # Examples * Show what `dwarffs` resolves to: ```console # nix flake metadata dwarffs Resolved URL: github:edolstra/dwarffs Locked URL: github:edolstra/dwarffs/f691e2c991e75edb22836f1dbe632c40324215c5 Description: A filesystem that fetches DWARF debug info from the Internet on demand Path: /nix/store/769s05vjydmc2lcf6b02az28wsa9ixh1-source Revision: f691e2c991e75edb22836f1dbe632c40324215c5 Last modified: 2021-01-21 15:41:26 Inputs: ├───nix: github:NixOS/nix/6254b1f5d298ff73127d7b0f0da48f142bdc753c │ ├───lowdown-src: github:kristapsdz/lowdown/1705b4a26fbf065d9574dce47a94e8c7c79e052f │ └───nixpkgs: github:NixOS/nixpkgs/ad0d20345219790533ebe06571f82ed6b034db31 └───nixpkgs follows input 'nix/nixpkgs' ``` * Show information about `dwarffs` in JSON format: ```console # nix flake metadata dwarffs --json | jq . { "description": "A filesystem that fetches DWARF debug info from the Internet on demand", "lastModified": 1597153508, "locked": { "lastModified": 1597153508, "narHash": "sha256-VHg3MYVgQ12LeRSU2PSoDeKlSPD8PYYEFxxwkVVDRd0=", "owner": "edolstra", "repo": "dwarffs", "rev": "d181d714fd36eb06f4992a1997cd5601e26db8f5", "type": "github" }, "locks": { ... }, "original": { "id": "dwarffs", "type": "indirect" }, "originalUrl": "flake:dwarffs", "path": "/nix/store/hang3792qwdmm2n0d9nsrs5n6bsws6kv-source", "resolved": { "owner": "edolstra", "repo": "dwarffs", "type": "github" }, "resolvedUrl": "github:edolstra/dwarffs", "revision": "d181d714fd36eb06f4992a1997cd5601e26db8f5", "url": "github:edolstra/dwarffs/d181d714fd36eb06f4992a1997cd5601e26db8f5" } ``` # Description This command shows information about the flake specified by the flake reference *flake-url*. It resolves the flake reference using the [flake registry](./nix3-registry.md), fetches it, and prints some meta data. This includes: * `Resolved URL`: If *flake-url* is a flake identifier, then this is the flake reference that specifies its actual location, looked up in the flake registry. * `Locked URL`: A flake reference that contains a commit or content hash and thus uniquely identifies a specific flake version. * `Description`: A one-line description of the flake, taken from the `description` field in `flake.nix`. * `Path`: The store path containing the source code of the flake. * `Revision`: The Git or Mercurial commit hash of the locked flake. * `Revisions`: The number of ancestors of the Git or Mercurial commit of the locked flake. Note that this is not available for `github` flakes. * `Last modified`: For Git or Mercurial flakes, this is the commit time of the commit of the locked flake; for tarball flakes, it's the most recent timestamp of any file inside the tarball. * `Inputs`: The flake inputs with their corresponding lock file entries. With `--json`, the output is a JSON object with the following fields: * `original` and `originalUrl`: The flake reference specified by the user (*flake-url*) in attribute set and URL representation. * `resolved` and `resolvedUrl`: The resolved flake reference (see above) in attribute set and URL representation. * `locked` and `lockedUrl`: The locked flake reference (see above) in attribute set and URL representation. * `description`: See `Description` above. * `path`: See `Path` above. * `revision`: See `Revision` above. * `revCount`: See `Revisions` above. * `lastModified`: See `Last modified` above. * `locks`: The contents of `flake.lock`. )""

The 'nix flake metadata' command displays information about a specified flake, resolving it through the flake registry and fetching its metadata. The output includes the resolved URL, locked URL, description, path, revision, last modified date, and inputs. When using the '--json' flag, the output is formatted as a JSON object containing the original, resolved, and locked flake references, along with metadata fields like description, path, revision, and the contents of 'flake.lock'.