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Merge pull request #13349 from obsidiansystems/structured-attrs-json

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Introduce top-level `structuredAttrs` field in JSON derivation format
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John Ericson 2025-06-18 16:35:42 -04:00 • committed by GitHub
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20
doc/manual/source/language/advanced-attributes.md
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@ -53,23 +53,13 @@ Derivations can declare some infrequently used optional attributes.
- [`__structuredAttrs`]{#adv-attr-structuredAttrs}\
If the special attribute `__structuredAttrs` is set to `true`, the other derivation
attributes are serialised into a file in JSON format. The environment variable
`NIX_ATTRS_JSON_FILE` points to the exact location of that file both in a build
and a [`nix-shell`](../command-ref/nix-shell.md). This obviates the need for
[`passAsFile`](#adv-attr-passAsFile) since JSON files have no size restrictions,
unlike process environments.
attributes are serialised into a file in JSON format.
It also makes it possible to tweak derivation settings in a structured way; see
[`outputChecks`](#adv-attr-outputChecks) for example.
This obviates the need for [`passAsFile`](#adv-attr-passAsFile) since JSON files have no size restrictions, unlike process environments.
It also makes it possible to tweak derivation settings in a structured way;
see [`outputChecks`](#adv-attr-outputChecks) for example.
As a convenience to Bash builders,
Nix writes a script that initialises shell variables
corresponding to all attributes that are representable in Bash. The
environment variable `NIX_ATTRS_SH_FILE` points to the exact
location of the script, both in a build and a
[`nix-shell`](../command-ref/nix-shell.md). This includes non-nested
(associative) arrays. For example, the attribute `hardening.format = true`
ends up as the Bash associative array element `${hardening[format]}`.
See the [corresponding section in the derivation page](@docroot@/store/derivation/index.md#structured-attrs) for further details.
> **Warning**
>

4
doc/manual/source/protocols/json/derivation.md
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@ -91,3 +91,7 @@ is a JSON object with the following fields:
* `env`:
The environment passed to the `builder`.
* `structuredAttrs`:
[Strucutured Attributes](@docroot@/store/derivation/index.md#structured-attrs), only defined if the derivation contains them.
Structured attributes are JSON, and thus embedded as-is.

11
doc/manual/source/store/derivation/index.md
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@ -138,6 +138,17 @@ See [Wikipedia](https://en.wikipedia.org/wiki/Argv) for details.
Environment variables which will be passed to the [builder](#builder) executable.
#### Structured Attributes {#structured-attrs}
Nix also has special support for embedding JSON in the derivations.
The environment variable `NIX_ATTRS_JSON_FILE` points to the exact location of that file both in a build and a [`nix-shell`](@docroot@/command-ref/nix-shell.md).
As a convenience to Bash builders, Nix writes a script that initialises shell variables corresponding to all attributes that are representable in Bash.
The environment variable `NIX_ATTRS_SH_FILE` points to the exact location of the script, both in a build and a [`nix-shell`](@docroot@/command-ref/nix-shell.md).
This includes non-nested (associative) arrays.
For example, the attribute `hardening.format = true` ends up as the Bash associative array element `${hardening[format]}`.
### Placeholders
Placeholders are opaque values used within the [process creation fields] to [store objects] for which we don't yet know [store path]s.