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nix-expr: Improve docs

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... and fix an error message

(cherry picked from commit ec3b5cfb911545ecf756336e792b59c5dd1be9b5)
This commit is contained in:
Robert Hensing 2025-09-30 15:50:42 +02:00
parent e68ec02d05
commit 65c9d937cd
3 changed files with 514 additions and 51 deletions
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31
rust/nix-expr/src/value.rs
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@ -8,28 +8,41 @@ use std::ptr::{null_mut, NonNull};
pub type Int = i64;
/// The type of a value (or thunk)
/// The type discriminator of a [`Value`] that has successfully evaluated to at least [weak head normal form](https://nix.dev/manual/nix/latest/language/evaluation.html?highlight=WHNF#values).
///
/// Typically acquired with [`EvalState::value_type`][`crate::eval_state::EvalState::value_type`]
#[derive(Eq, PartialEq, Debug)]
pub enum ValueType {
/// A Nix [attribute set](https://nix.dev/manual/nix/stable/language/types.html#type-attrs)
AttrSet,
/// A Nix [boolean](https://nix.dev/manual/nix/stable/language/types.html#type-bool)
Bool,
/// A Nix external value (mostly-opaque value for plugins, linked applications)
External,
/// A Nix [float](https://nix.dev/manual/nix/stable/language/types.html#type-float)
Float,
/// A Nix [function](https://nix.dev/manual/nix/stable/language/types.html#type-function)
Function,
/// A Nix [integer](https://nix.dev/manual/nix/stable/language/types.html#type-int)
Int,
/// A Nix [list](https://nix.dev/manual/nix/stable/language/types.html#type-list)
List,
/// A Nix [`null`](https://nix.dev/manual/nix/stable/language/types.html#type-null)
Null,
/// A Nix [path value](https://nix.dev/manual/nix/stable/language/types.html#type-path)
Path,
/// A Nix [string](https://nix.dev/manual/nix/stable/language/types.html#type-string)
String,
/// An unknown value, presumably from a new, partially unsupported version of Nix
Unknown,
}
impl ValueType {
/// Convert a raw value type to a `ValueType`.
/// Convert a raw value type to a [`ValueType`].
///
/// Return `None` if the Value is still a thunk (i.e. not yet evaluated).
/// Return [`None`] if the Value is still a thunk (i.e. not yet evaluated).
///
/// Return `Some(ValueType::Unknown)` if the value type is not recognized.
/// Return `Some(`[`ValueType::Unknown`]`)` if the value type is not recognized.
pub(crate) fn from_raw(raw: raw::ValueType) -> Option<ValueType> {
match raw {
raw::ValueType_NIX_TYPE_ATTRS => Some(ValueType::AttrSet),
@ -51,14 +64,14 @@ impl ValueType {
}
}
/* A pointer to a value or thunk, to be used with EvalState methods. */
/// A pointer to a [value](https://nix.dev/manual/nix/latest/language/types.html) or [thunk](https://nix.dev/manual/nix/2.31/language/evaluation.html?highlight=thunk#laziness), to be used with [`EvalState`][`crate::eval_state::EvalState`] methods.
pub struct Value {
inner: NonNull<raw::Value>,
}
impl Value {
/// Take ownership of a new Value.
/// Take ownership of a new [`Value`].
///
/// This does not call `nix_gc_incref`, but does call `nix_gc_decref` when dropped.
/// This does not call [`nix_c_raw::gc_incref`], but does call [`nix_c_raw::nix_gc_decref`] when [dropped][`Drop`].
///
/// # Safety
///
@ -69,9 +82,9 @@ impl Value {
}
}
/// Borrow a reference to a Value.
/// Borrow a reference to a [`Value`].
///
/// This calls `nix_gc_incref`, and the returned Value will call `nix_gc_decref` when dropped.
/// This calls [`nix_c_raw::value_incref`], and the returned Value will call [`nix_c_raw::value_decref`] when dropped.
///
/// # Safety
///