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nix/doc/manual/source/protocols/json/schema/derivation-v3.yaml
John Ericson c2609df08c Better JSON schema for derivation outputs
It now uses a `oneOf` and properly models each type of output
(corresponding to each type of derivation) separately.
2025-10-30 17:05:00 -04:00

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"$schema": "http://json-schema.org/draft-04/schema"
"$id": "https://nix.dev/manual/nix/latest/protocols/json/schema/derivation-v3.json"
title: Derivation
description: |
Experimental JSON representation of a Nix derivation (version 3).
This schema describes the JSON representation of Nix's `Derivation` type.
> **Warning**
>
> This JSON format is currently
> [**experimental**](@docroot@/development/experimental-features.md#xp-feature-nix-command)
> and subject to change.
type: object
required:
- name
- version
- outputs
- inputSrcs
- inputDrvs
- system
- builder
- args
- env
properties:
name:
type: string
title: Derivation name
description: |
The name of the derivation.
Used when calculating store paths for the derivations outputs.
version:
const: 3
title: Format version (must be 3)
description: |
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
- Version 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:
type: object
title: Output specifications
description: |
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 as described.
> **Example**
>
> ```json
> "outputs": {
> "out": {
> "method": "nar",
> "hashAlgo": "sha256",
> "hash": "6fc80dcc62179dbc12fc0b5881275898f93444833d21b89dfe5f7fbcbb1d0d62"
> }
> }
> ```
additionalProperties:
"$ref": "#/$defs/output/overall"
inputSrcs:
type: array
title: Input source paths
description: |
List of store paths on which this derivation depends.
> **Example**
>
> ```json
> "inputSrcs": [
> "47y241wqdhac3jm5l7nv0x4975mb1975-separate-debug-info.sh",
> "56d0w71pjj9bdr363ym3wj1zkwyqq97j-fix-pop-var-context-error.patch"
> ]
> ```
items:
$ref: "store-path-v1.yaml"
inputDrvs:
type: object
title: Input derivations
description: |
Mapping of derivation paths to lists of output names they provide.
> **Example**
>
> ```json
> "inputDrvs": {
> "6lkh5yi7nlb7l6dr8fljlli5zfd9hq58-curl-7.73.0.drv": ["dev"],
> "fn3kgnfzl5dzym26j8g907gq3kbm8bfh-unzip-6.0.drv": ["out"]
> }
> ```
>
> specifies that this derivation depends on the `dev` output of `curl`, and the `out` output of `unzip`.
patternProperties:
"^[0123456789abcdfghijklmnpqrsvwxyz]{32}-.+\\.drv$":
title: Store Path
description: |
A store path to a derivation, mapped to the outputs of that derivation.
oneOf:
- "$ref": "#/$defs/outputNames"
- "$ref": "#/$defs/dynamicOutputs"
additionalProperties: false
system:
type: string
title: Build system type
description: |
The system type on which this derivation is to be built
(e.g. `x86_64-linux`).
builder:
type: string
title: Build program path
description: |
Absolute path of the program used to perform the build.
Typically this is the `bash` shell
(e.g. `/nix/store/r3j288vpmczbl500w6zz89gyfa4nr0b1-bash-4.4-p23/bin/bash`).
args:
type: array
title: Builder arguments
description: |
Command-line arguments passed to the `builder`.
items:
type: string
env:
type: object
title: Environment variables
description: |
Environment variables passed to the `builder`.
additionalProperties:
type: string
structuredAttrs:
title: Structured attributes
description: |
[Structured Attributes](@docroot@/store/derivation/index.md#structured-attrs), only defined if the derivation contains them.
Structured attributes are JSON, and thus embedded as-is.
type: object
additionalProperties: true
"$defs":
output:
overall:
title: Derivation Output
description: |
A single output of a derivation, with different variants for different output types.
oneOf:
- "$ref": "#/$defs/output/inputAddressed"
- "$ref": "#/$defs/output/caFixed"
- "$ref": "#/$defs/output/caFloating"
- "$ref": "#/$defs/output/deferred"
- "$ref": "#/$defs/output/impure"
inputAddressed:
title: Input-Addressed Output
description: |
The traditional non-fixed-output derivation type.
The output path is determined from the derivation itself.
See [Input-addressing derivation outputs](@docroot@/store/derivation/outputs/input-address.md) for more details.
type: object
required:
- path
properties:
path:
$ref: "store-path-v1.yaml"
title: Output path
description: |
The output path determined from the derivation itself.
additionalProperties: false
caFixed:
title: Fixed Content-Addressed Output
description: |
The output is content-addressed, and the content-address is fixed in advance.
See [Fixed-output content-addressing](@docroot@/store/derivation/outputs/content-address.md#fixed) for more details.
type: object
required:
- method
- hashAlgo
- hash
properties:
method:
"$ref": "./content-address-v1.yaml#/$defs/method"
description: |
Method of content addressing used for this output.
hashAlgo:
title: Hash algorithm
"$ref": "./hash-v1.yaml#/$defs/algorithm"
hash:
type: string
title: Expected hash value
description: |
The expected content hash in base-16.
additionalProperties: false
caFloating:
title: Floating Content-Addressed Output
description: |
Floating-output derivations, whose outputs are content
addressed, but not fixed, and so the output paths are dynamically calculated from
whatever the output ends up being.
See [Floating Content-Addressing](@docroot@/store/derivation/outputs/content-address.md#floating) for more details.
type: object
required:
- method
- hashAlgo
properties:
method:
"$ref": "./content-address-v1.yaml#/$defs/method"
description: |
Method of content addressing used for this output.
hashAlgo:
title: Hash algorithm
"$ref": "./hash-v1.yaml#/$defs/algorithm"
description: |
What hash algorithm to use for the given method of content-addressing.
additionalProperties: false
deferred:
title: Deferred Output
description: |
Input-addressed output which depends on a (CA) derivation whose outputs (and thus their content-address
are not yet known.
type: object
properties: {}
additionalProperties: false
impure:
title: Impure Output
description: |
Impure output which is just like a floating content-addressed output, but this derivation runs without sandboxing.
As such, we don't record it in the build trace, under the assumption that if we need it again, we should rebuild it, as it might produce something different.
required:
- impure
- method
- hashAlgo
properties:
impure:
const: true
method:
"$ref": "./content-address-v1.yaml#/$defs/method"
description: |
How the file system objects will be serialized for hashing.
hashAlgo:
title: Hash algorithm
"$ref": "./hash-v1.yaml#/$defs/algorithm"
description: |
How the serialization will be hashed.
additionalProperties: false
outputName:
type: string
title: Output name
description: Name of the derivation output to depend on
outputNames:
type: array
title: Output Names
description: Set of names of derivation outputs to depend on
items:
"$ref": "#/$defs/outputName"
dynamicOutputs:
type: object
title: Dynamic Outputs
description: |
**Experimental feature**: [`dynamic-derivations`](@docroot@/development/experimental-features.md#xp-feature-dynamic-derivations)
This recursive data type allows for depending on outputs of outputs.
properties:
outputs:
"$ref": "#/$defs/outputNames"
dynamicOutputs:
"$ref": "#/$defs/dynamicOutputs"