nix/doc/manual/source/protocols/json/derivation.md

Derivation JSON Format

Warning

This JSON format is currently experimental and subject to change.

The JSON serialization of a derivations is a JSON object with the following fields:

• name: The name of the derivation. This is used when calculating the store paths of the derivation's outputs.

• version: Must be 3. This is a guard that allows us to continue evolving this format. The choice of 3 is fairly arbitrary, but corresponds to this informal version:

  • Version 0: A-Term format

  • Version 1: Original JSON format, with ugly "r:sha256" inherited from A-Term format.

  • Version 2: Separate method and hashAlgo fields in output specs

  • Verison 3: Drop store dir from store paths, just include base name.

  Note that while this format is experimental, the maintenance of versions is best-effort, and not promised to identify every change.

• outputs: Information about the output paths of the derivation. This is a JSON object with one member per output, where the key is the output name and the value is a JSON object with these fields:

  • path: The output path, if it is known in advanced. Otherwise, null.

  • method: For an output which will be [content addressed], a string representing the method of content addressing that is chosen. Valid method strings are:

    • flat
    • nar
    • text
    • git

    Otherwise, null.

  • hashAlgo: For an output which will be [content addressed], the name of the hash algorithm used. Valid algorithm strings are:

    • blake3
    • md5
    • sha1
    • sha256
    • sha512

  • hash: For fixed-output derivations, the expected content hash in base-16.

  Example

  "outputs": {
    "out": {
      "method": "nar",
      "hashAlgo": "sha256",
      "hash": "6fc80dcc62179dbc12fc0b5881275898f93444833d21b89dfe5f7fbcbb1d0d62"
    }
  }
  

• inputSrcs: A list of store paths on which this derivation depends.

  Example

  "inputSrcs": [
    "47y241wqdhac3jm5l7nv0x4975mb1975-separate-debug-info.sh",
    "56d0w71pjj9bdr363ym3wj1zkwyqq97j-fix-pop-var-context-error.patch"
  ]
  

• inputDrvs: A JSON object specifying the derivations on which this derivation depends, and what outputs of those derivations.

  Example

  "inputDrvs": {
    "6lkh5yi7nlb7l6dr8fljlli5zfd9hq58-curl-7.73.0.drv": ["dev"],
    "fn3kgnfzl5dzym26j8g907gq3kbm8bfh-unzip-6.0.drv": ["out"]
  }
  

  specifies that this derivation depends on the dev output of curl, and the out output of unzip.

• system: The system type on which this derivation is to be built (e.g. x86_64-linux).

• builder: The absolute path of the program to be executed to run the build. Typically this is the bash shell (e.g. /nix/store/r3j288vpmczbl500w6zz89gyfa4nr0b1-bash-4.4-p23/bin/bash).

• args: The command-line arguments passed to the builder.

• env: The environment passed to the builder.

• structuredAttrs: Strucutured Attributes, only defined if the derivation contains them. Structured attributes are JSON, and thus embedded as-is.