//! This module implements the backing representation of runtime
//! values in the Nix language.
use std::cell::Ref;
use std::ops::Deref;
use std::rc::Rc;
use std::{fmt::Display, path::PathBuf};
#[cfg(feature = "arbitrary")]
mod arbitrary;
mod attrs;
mod builtin;
mod function;
mod list;
mod string;
mod thunk;
use crate::errors::ErrorKind;
use crate::opcode::StackIdx;
use crate::vm::VM;
pub use attrs::NixAttrs;
pub use builtin::Builtin;
pub use function::{Closure, Lambda};
pub use list::NixList;
pub use string::NixString;
pub use thunk::Thunk;
#[warn(variant_size_differences)]
#[derive(Clone, Debug, PartialEq)]
pub enum Value {
Null,
Bool(bool),
Integer(i64),
Float(f64),
String(NixString),
Path(PathBuf),
Attrs(Rc<NixAttrs>),
List(NixList),
Closure(Closure),
Builtin(Builtin),
// Internal values that, while they technically exist at runtime,
// are never returned to or created directly by users.
Thunk(Thunk),
AttrNotFound,
DynamicUpvalueMissing(NixString),
Blueprint(Rc<Lambda>),
DeferredUpvalue(StackIdx),
}
// Helper macros to generate the to_*/as_* macros while accounting for
// thunks.
/// Generate an `as_*` method returning a reference to the expected
/// type, or a type error. This only works for types that implement
/// `Copy`, as returning a reference to an inner thunk value is not
/// possible.
/// Generate an `as_*/to_*` accessor method that returns either the
/// expected type, or a type error.
macro_rules! gen_cast {
( $name:ident, $type:ty, $expected:expr, $variant:pat, $result:expr ) => {
pub fn $name(&self) -> Result<$type, ErrorKind> {
match self {
$variant => Ok($result),
Value::Thunk(thunk) => Self::$name(&thunk.value()),
other => Err(type_error($expected, &other)),
}
}
};
}
/// Generate an `is_*` type-checking method.
macro_rules! gen_is {
( $name:ident, $variant:pat ) => {
pub fn $name(&self) -> bool {
match self {
$variant => true,
Value::Thunk(thunk) => Self::$name(&thunk.value()),
_ => false,
}
}
};
}
/// Describes what input types are allowed when coercing a `Value` to a string
#[derive(Clone, Copy, Debug)]
pub enum CoercionKind {
/// Only coerce already "stringly" types like strings and paths, but also
/// coerce sets that have a `__toString` attribute. Equivalent to
/// `!coerceMore` in C++ Nix.
Weak,
/// Coerce all value types included by `Weak`, but also coerce `null`,
/// booleans, integers, floats and lists of coercible types. Equivalent to
/// `coerceMore` in C++ Nix.
Strong,
}
/// A reference to a [`Value`] returned by a call to [`Value::force`], whether the value was
/// originally a thunk or not.
///
/// Implements [`Deref`] to [`Value`], so can generally be used as a [`Value`]
pub(crate) enum ForceResult<'a> {
ForcedThunk(Ref<'a, Value>),
Immediate(&'a Value),
}
impl<'a> Deref for ForceResult<'a> {
type Target = Value;
fn deref(&self) -> &Self::Target {
match self {
ForceResult::ForcedThunk(r) => r,
ForceResult::Immediate(v) => v,
}
}
}
/// Constructors
impl Value {
/// Construct a [`Value::Attrs`] from a [`NixAttrs`].
pub fn attrs(attrs: NixAttrs) -> Self {
Self::Attrs(Rc::new(attrs))
}
}
impl Value {
/// Coerce a `Value` to a string. See `CoercionKind` for a rundown of what
/// input types are accepted under what circumstances.
pub fn coerce_to_string(
&self,
kind: CoercionKind,
vm: &mut VM,
) -> Result<NixString, ErrorKind> {
// TODO: eventually, this will need to handle string context and importing
// files into the Nix store depending on what context the coercion happens in
if let Value::Thunk(t) = self {
t.force(vm)?;
}
match (self, kind) {
// deal with thunks
(Value::Thunk(t), _) => t.value().coerce_to_string(kind, vm),
// coercions that are always done
(Value::String(s), _) => Ok(s.clone()),
// TODO(sterni): Think about proper encoding handling here. This needs
// general consideration anyways, since one current discrepancy between
// C++ Nix and Tvix is that the former's strings are arbitrary byte
// sequences without NUL bytes, whereas Tvix only allows valid
// Unicode. See also b/189.
(Value::Path(p), _) => Ok(p.to_string_lossy().into_owned().into()),
// Attribute sets can be converted to strings if they either have an
// `__toString` attribute which holds a function that receives the
// set itself or an `outPath` attribute which should be a string.
// `__toString` is preferred.
(Value::Attrs(attrs), _) => {
match (attrs.select("__toString"), attrs.select("outPath")) {
(None, None) => Err(ErrorKind::NotCoercibleToString { from: "set", kind }),
(Some(f), _) => {
// use a closure here to deal with the thunk borrow we need to do below
let call_to_string = |value: &Value, vm: &mut VM| {
// Leave self on the stack as an argument to the function call.
vm.push(self.clone());
let result = vm.call_value(value)?;
match result {
Value::String(s) => Ok(s),
// Attribute set coercion actually works
// recursively, e.g. you can even return
// /another/ set with a __toString attr.
_ => result.coerce_to_string(kind, vm),
}
};
if let Value::Thunk(t) = f {
t.force(vm)?;
let guard = t.value();
call_to_string(&*guard, vm)
} else {
call_to_string(f, vm)
}
}
// Similarly to `__toString` we also coerce recursively for `outPath`
(None, Some(s)) => s.coerce_to_string(kind, vm),
}
}
// strong coercions
(Value::Null, CoercionKind::Strong) | (Value::Bool(false), CoercionKind::Strong) => {
Ok("".into())
}
(Value::Bool(true), CoercionKind::Strong) => Ok("1".into()),
(Value::Integer(i), CoercionKind::Strong) => Ok(format!("{i}").into()),
(Value::Float(f), CoercionKind::Strong) => {
// contrary to normal Display, coercing a float to a string will
// result in unconditional 6 decimal places
Ok(format!("{:.6}", f).into())
}
// Lists are coerced by coercing their elements and interspersing spaces
(Value::List(l), CoercionKind::Strong) => {
// TODO(sterni): use intersperse when it becomes available?
// https://github.com/rust-lang/rust/issues/79524
l.iter()
.map(|v| v.coerce_to_string(kind, vm))
.reduce(|acc, string| {
let a = acc?;
let s = &string?;
Ok(a.concat(&" ".into()).concat(s))
})
// None from reduce indicates empty iterator
.unwrap_or_else(|| Ok("".into()))
}
(Value::Closure(_), _)
| (Value::Builtin(_), _)
| (Value::Null, _)
| (Value::Bool(_), _)
| (Value::Integer(_), _)
| (Value::Float(_), _)
| (Value::List(_), _) => Err(ErrorKind::NotCoercibleToString {
from: self.type_of(),
kind,
}),
(Value::AttrNotFound, _)
| (Value::DynamicUpvalueMissing(_), _)
| (Value::Blueprint(_), _)
| (Value::DeferredUpvalue(_), _) => {
panic!("tvix bug: .coerce_to_string() called on internal value")
}
}
}
pub fn type_of(&self) -> &'static str {
match self {
Value::Null => "null",
Value::Bool(_) => "bool",
Value::Integer(_) => "int",
Value::Float(_) => "float",
Value::String(_) => "string",
Value::Path(_) => "path",
Value::Attrs(_) => "set",
Value::List(_) => "list",
Value::Closure(_) | Value::Builtin(_) => "lambda",
// Internal types
Value::Thunk(_)
| Value::AttrNotFound
| Value::DynamicUpvalueMissing(_)
| Value::Blueprint(_)
| Value::DeferredUpvalue(_) => "internal",
}
}
gen_cast!(as_bool, bool, "bool", Value::Bool(b), *b);
gen_cast!(as_int, i64, "int", Value::Integer(x), *x);
gen_cast!(to_str, NixString, "string", Value::String(s), s.clone());
gen_cast!(to_attrs, Rc<NixAttrs>, "set", Value::Attrs(a), a.clone());
gen_cast!(to_list, NixList, "list", Value::List(l), l.clone());
gen_cast!(to_closure, Closure, "lambda", Value::Closure(c), c.clone());
gen_is!(is_number, Value::Integer(_) | Value::Float(_));
gen_is!(is_bool, Value::Bool(_));
/// Compare `self` against `other` for equality using Nix equality semantics.
///
/// Takes a reference to the `VM` to allow forcing thunks during comparison
pub fn nix_eq(&self, other: &Self, vm: &mut VM) -> Result<bool, ErrorKind> {
match (self, other) {
// Trivial comparisons
(Value::Null, Value::Null) => Ok(true),
(Value::Bool(b1), Value::Bool(b2)) => Ok(b1 == b2),
(Value::List(l1), Value::List(l2)) => l1.nix_eq(l2, vm),
(Value::String(s1), Value::String(s2)) => Ok(s1 == s2),
(Value::Path(p1), Value::Path(p2)) => Ok(p1 == p2),
// Numerical comparisons (they work between float & int)
(Value::Integer(i1), Value::Integer(i2)) => Ok(i1 == i2),
(Value::Integer(i), Value::Float(f)) => Ok(*i as f64 == *f),
(Value::Float(f1), Value::Float(f2)) => Ok(f1 == f2),
(Value::Float(f), Value::Integer(i)) => Ok(*i as f64 == *f),
// Optimised attribute set comparison
(Value::Attrs(a1), Value::Attrs(a2)) => Ok(Rc::ptr_eq(a1, a2) || a1.nix_eq(a2, vm)?),
// If either value is a thunk, the thunk should be forced, and then the resulting value
// must be compared instead.
(Value::Thunk(lhs), Value::Thunk(rhs)) => {
lhs.force(vm)?;
rhs.force(vm)?;
Ok(*lhs.value() == *rhs.value())
}
(Value::Thunk(lhs), rhs) => {
lhs.force(vm)?;
Ok(&*lhs.value() == rhs)
}
(lhs, Value::Thunk(rhs)) => {
rhs.force(vm)?;
Ok(lhs == &*rhs.value())
}
// Everything else is either incomparable (e.g. internal
// types) or false.
// TODO(tazjin): mirror Lambda equality behaviour
_ => Ok(false),
}
}
/// Ensure `self` is forced if it is a thunk, and return a reference to the resulting value.
pub(crate) fn force(&self, vm: &mut VM) -> Result<ForceResult, ErrorKind> {
match self {
Self::Thunk(thunk) => {
thunk.force(vm)?;
Ok(ForceResult::ForcedThunk(thunk.value()))
}
_ => Ok(ForceResult::Immediate(self)),
}
}
}
impl Display for Value {
fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
match self {
Value::Null => f.write_str("null"),
Value::Bool(true) => f.write_str("true"),
Value::Bool(false) => f.write_str("false"),
Value::Integer(num) => write!(f, "{}", num),
Value::String(s) => s.fmt(f),
Value::Path(p) => p.display().fmt(f),
Value::Attrs(attrs) => attrs.fmt(f),
Value::List(list) => list.fmt(f),
Value::Closure(_) => f.write_str("lambda"), // TODO: print position
Value::Builtin(builtin) => builtin.fmt(f),
// Nix prints floats with a maximum precision of 5 digits
// only.
Value::Float(num) => {
write!(f, "{}", format!("{:.5}", num).trim_end_matches(['.', '0']))
}
// Delegate thunk display to the type, as it must handle
// the case of already evaluated thunks.
Value::Thunk(t) => t.fmt(f),
// internal types
Value::AttrNotFound => f.write_str("internal[not found]"),
Value::Blueprint(_) => f.write_str("internal[blueprint]"),
Value::DeferredUpvalue(_) => f.write_str("internal[deferred_upvalue]"),
Value::DynamicUpvalueMissing(name) => {
write!(f, "internal[no_dyn_upvalue({name})]")
}
}
}
}
impl From<bool> for Value {
fn from(b: bool) -> Self {
Value::Bool(b)
}
}
impl From<i64> for Value {
fn from(i: i64) -> Self {
Self::Integer(i)
}
}
impl From<&str> for Value {
fn from(val: &str) -> Self {
Self::String(val.into())
}
}
fn type_error(expected: &'static str, actual: &Value) -> ErrorKind {
ErrorKind::TypeError {
expected,
actual: actual.type_of(),
}
}
#[cfg(test)]
mod tests {
use super::*;
mod nix_eq {
use crate::observer::NoOpObserver;
use super::*;
use proptest::prelude::ProptestConfig;
use test_strategy::proptest;
#[proptest(ProptestConfig { cases: 5, ..Default::default() })]
fn reflexive(x: Value) {
let mut observer = NoOpObserver {};
let mut vm = VM::new(&mut observer);
assert!(x.nix_eq(&x, &mut vm).unwrap())
}
#[proptest(ProptestConfig { cases: 5, ..Default::default() })]
fn symmetric(x: Value, y: Value) {
let mut observer = NoOpObserver {};
let mut vm = VM::new(&mut observer);
assert_eq!(
x.nix_eq(&y, &mut vm).unwrap(),
y.nix_eq(&x, &mut vm).unwrap()
)
}
#[proptest(ProptestConfig { cases: 5, ..Default::default() })]
fn transitive(x: Value, y: Value, z: Value) {
let mut observer = NoOpObserver {};
let mut vm = VM::new(&mut observer);
if x.nix_eq(&y, &mut vm).unwrap() && y.nix_eq(&z, &mut vm).unwrap() {
assert!(x.nix_eq(&z, &mut vm).unwrap())
}
}
#[test]
fn list_int_float_fungibility() {
let mut observer = NoOpObserver {};
let mut vm = VM::new(&mut observer);
let v1 = Value::List(NixList::from(vec![Value::Integer(1)]));
let v2 = Value::List(NixList::from(vec![Value::Float(1.0)]));
assert!(v1.nix_eq(&v2, &mut vm).unwrap())
}
}
}
