Inspect a flake's outputs using flake schemas

From the Determinate Systems blog post about flake schemas:

While there are a number of “well-known” flake output types that are recognized by tools like the nix CLI—nix develop, for example, operates on the devShells output—nothing prevents you from defining your own flake output types.

Unfortunately, such “non-standard” flake output types have a big problem: tools like nix flake show and nix flake check don’t know anything about them, so they can’t display or check anything about those outputs.

Examples

Get a flake's output structure, without derivation and store path data. Excluding derivation and store path data means much less Nix evaluation, and a faster result:

nix eval --json \
    --override-input flake https://flakehub.com/f/DeterminateSystems/magic-nix-cache/0.1.341 \
    --no-write-lock-file 'https://flakehub.com/f/DeterminateSystems/inspect/*#contents.excludingOutputPaths' \
    | nix run nixpkgs#jq -- .

Get a flake's output structure, with derivation and store path data. Collecting derivation and store path data means a more extensive Nix evaluation:

nix eval --json \
    --override-input flake https://flakehub.com/f/DeterminateSystems/magic-nix-cache/0.1.341 \
    --no-write-lock-file 'https://flakehub.com/f/DeterminateSystems/inspect/*#contents.includingOutputPaths' \
    | nix run nixpkgs#jq -- .

Example Output

The data below is representative of the general structure. It incudes output paths and derivations, which would not be present in the output in the contents.excludingOutputPaths evaluation.

{
  "docs": {
    "devShells": "The `devShells` flake output contains derivations that provide a build environment for `nix develop`.\n",
    "packages": "The `packages` flake output contains packages that can be added to a shell using `nix shell`.\n"
  },
  "inventory": {
    "devShells": {
      "children": {
        "aarch64-darwin": {
          "children": {
            "default": {
              "derivation": "/nix/store/lzfbsl05jw3ixbppm11nmfd4xzj81qhs-nix-shell.drv",
              "forSystems": ["aarch64-darwin"],
              "outputs": {
                "out": "/nix/store/bq48b9naj2ihcwvc8vw6i98pj533qqbh-nix-shell"
              },
              "shortDescription": "",
              "what": "development environment"
            }
          }
        },
        "aarch64-linux": {
          "children": {
            "default": {
              "derivation": "/nix/store/d157gs8aqf2dizpk04wacbvwrzax23dq-nix-shell.drv",
              "forSystems": ["aarch64-linux"],
              "outputs": {
                "out": "/nix/store/s05laifrbik2xs4ri7351hzld857garz-nix-shell"
              },
              "shortDescription": "",
              "what": "development environment"
            }
          }
        }
      }
    },
    "packages": {
      "children": {
        "aarch64-darwin": {
          "children": {
            "default": {
              "derivation": "/nix/store/z593dppy4xjmbkkjasmy92blgzgvnapy-magic-nix-cache-0.2.0.drv",
              "forSystems": ["aarch64-darwin"],
              "outputs": {
                "out": "/nix/store/8lsqcz8vpx0s7mgcj33asrz0f99sr9ag-magic-nix-cache-0.2.0"
              },
              "shortDescription": "",
              "what": "package"
            },
            "magic-nix-cache": {
              "derivation": "/nix/store/z593dppy4xjmbkkjasmy92blgzgvnapy-magic-nix-cache-0.2.0.drv",
              "forSystems": ["aarch64-darwin"],
              "outputs": {
                "out": "/nix/store/8lsqcz8vpx0s7mgcj33asrz0f99sr9ag-magic-nix-cache-0.2.0"
              },
              "shortDescription": "",
              "what": "package"
            },
            "veryLongChain": {
              "derivation": "/nix/store/wdgjivv50ks5d48z54wwrw29kpz9hmqh-chain-200.drv",
              "forSystems": ["aarch64-darwin"],
              "outputs": {
                "out": "/nix/store/zjwhc6sj38cx2mms0nrl76cxaz70qd02-chain-200"
              },
              "shortDescription": "",
              "what": "package"
            }
          }
        },
        "aarch64-linux": {
          "children": {
            "default": {
              "derivation": "/nix/store/nl65gdz60cm3j774yqdfqr4hss5zl45b-magic-nix-cache-0.2.0.drv",
              "forSystems": ["aarch64-linux"],
              "outputs": {
                "out": "/nix/store/6nr5b7kqhxw738fplg22dl16fsalx3kq-magic-nix-cache-0.2.0"
              },
              "shortDescription": "",
              "what": "package"
            },
            "magic-nix-cache": {
              "derivation": "/nix/store/nl65gdz60cm3j774yqdfqr4hss5zl45b-magic-nix-cache-0.2.0.drv",
              "forSystems": ["aarch64-linux"],
              "outputs": {
                "out": "/nix/store/6nr5b7kqhxw738fplg22dl16fsalx3kq-magic-nix-cache-0.2.0"
              },
              "shortDescription": "",
              "what": "package"
            },
            "veryLongChain": {
              "derivation": "/nix/store/zk93kmbhk4b192w8176znd8p1g8wikv1-chain-200.drv",
              "forSystems": ["aarch64-linux"],
              "outputs": {
                "out": "/nix/store/k1nvfr1nq7as02ckh4dd6lwvjxcca5ph-chain-200"
              },
              "shortDescription": "",
              "what": "package"
            }
          }
        }
      }
    }
  },
  "version": 1
}