//! This module implements the backing representation of runtime
//! values in the Nix language.
use std::cmp::Ordering;
use std::num::{NonZeroI32, NonZeroUsize};
use std::ops::Deref;
use std::path::PathBuf;
use std::rc::Rc;
use std::{cell::Ref, fmt::Display};
use lexical_core::format::CXX_LITERAL;
use serde::{Deserialize, Serialize};
#[cfg(feature = "arbitrary")]
mod arbitrary;
mod attrs;
mod builtin;
mod function;
mod list;
mod path;
mod string;
mod thunk;
use crate::errors::ErrorKind;
use crate::opcode::StackIdx;
use crate::vm::VM;
pub use attrs::NixAttrs;
pub use builtin::{Builtin, BuiltinArgument};
pub(crate) use function::Formals;
pub use function::{Closure, Lambda};
pub use list::NixList;
pub use path::canon_path;
pub use string::NixString;
pub use thunk::Thunk;
use self::thunk::ThunkSet;
use lazy_static::lazy_static;
#[warn(variant_size_differences)]
#[derive(Clone, Debug, Serialize, Deserialize)]
#[serde(untagged)]
pub enum Value {
Null,
Bool(bool),
Integer(i64),
Float(f64),
String(NixString),
#[serde(skip)]
Path(PathBuf),
Attrs(Box<NixAttrs>),
List(NixList),
#[serde(skip)]
Closure(Rc<Closure>), // must use Rc<Closure> here in order to get proper pointer equality
#[serde(skip)]
Builtin(Builtin),
// Internal values that, while they technically exist at runtime,
// are never returned to or created directly by users.
#[serde(skip_deserializing)]
Thunk(Thunk),
// See [`compiler::compile_select_or()`] for explanation
#[serde(skip)]
AttrNotFound,
// this can only occur in Chunk::Constants and nowhere else
#[serde(skip)]
Blueprint(Rc<Lambda>),
#[serde(skip)]
DeferredUpvalue(StackIdx),
#[serde(skip)]
UnresolvedPath(PathBuf),
}
lazy_static! {
static ref WRITE_FLOAT_OPTIONS: lexical_core::WriteFloatOptions =
lexical_core::WriteFloatOptionsBuilder::new()
.trim_floats(true)
.round_mode(lexical_core::write_float_options::RoundMode::Round)
.positive_exponent_break(Some(NonZeroI32::new(5).unwrap()))
.max_significant_digits(Some(NonZeroUsize::new(6).unwrap()))
.build()
.unwrap();
}
// 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 `as_*_mut/to_*_mut` accessor method that returns either the
/// expected type, or a type error.
macro_rules! gen_cast_mut {
( $name:ident, $type:ty, $expected:expr, $variant:ident) => {
pub fn $name(&mut self) -> Result<&mut $type, ErrorKind> {
match self {
Value::$variant(x) => Ok(x),
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, PartialEq, Debug)]
pub enum CoercionKind {
/// Force thunks, but perform no other coercions.
ThunksOnly,
/// 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 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,
}
}
}
impl<T> From<T> for Value
where
T: Into<NixString>,
{
fn from(t: T) -> Self {
Self::String(t.into())
}
}
/// Constructors
impl Value {
/// Construct a [`Value::Attrs`] from a [`NixAttrs`].
pub fn attrs(attrs: NixAttrs) -> Self {
Self::Attrs(Box::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), kind) if kind != CoercionKind::ThunksOnly => {
let imported = vm.io().import_path(p)?;
Ok(imported.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), kind) if kind != CoercionKind::ThunksOnly => {
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());
vm.call_value(value)?;
let result = vm.pop();
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::Path(_), _)
| (Value::Attrs(_), _)
| (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::Blueprint(_), _)
| (Value::DeferredUpvalue(_), _)
| (Value::UnresolvedPath(_), _) => {
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. Note: These are only elaborated here
// because it makes debugging easier. If a user ever sees
// any of these strings, it's a bug.
Value::Thunk(_) => "internal[thunk]",
Value::AttrNotFound => "internal[attr_not_found]",
Value::Blueprint(_) => "internal[blueprint]",
Value::DeferredUpvalue(_) => "internal[deferred_upvalue]",
Value::UnresolvedPath(_) => "internal[unresolved_path]",
}
}
gen_cast!(as_bool, bool, "bool", Value::Bool(b), *b);
gen_cast!(as_int, i64, "int", Value::Integer(x), *x);
gen_cast!(as_float, f64, "float", Value::Float(x), *x);
gen_cast!(to_str, NixString, "string", Value::String(s), s.clone());
gen_cast!(to_attrs, Box<NixAttrs>, "set", Value::Attrs(a), a.clone());
gen_cast!(to_list, NixList, "list", Value::List(l), l.clone());
gen_cast!(
as_closure,
Rc<Closure>,
"lambda",
Value::Closure(c),
c.clone()
);
gen_cast_mut!(as_list_mut, NixList, "list", List);
gen_is!(is_path, Value::Path(_));
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::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),
(Value::Attrs(_), Value::Attrs(_))
| (Value::List(_), Value::List(_))
| (Value::Thunk(_), _)
| (_, Value::Thunk(_)) => Ok(vm.nix_eq(self.clone(), other.clone(), false)?),
// Everything else is either incomparable (e.g. internal
// types) or false.
_ => Ok(false),
}
}
/// Compare `self` against other using (fallible) Nix ordering semantics.
pub fn nix_cmp(&self, other: &Self, vm: &mut VM) -> Result<Option<Ordering>, ErrorKind> {
match (self, other) {
// same types
(Value::Integer(i1), Value::Integer(i2)) => Ok(i1.partial_cmp(i2)),
(Value::Float(f1), Value::Float(f2)) => Ok(f1.partial_cmp(f2)),
(Value::String(s1), Value::String(s2)) => Ok(s1.partial_cmp(s2)),
(Value::List(l1), Value::List(l2)) => {
for i in 0.. {
if i == l2.len() {
return Ok(Some(Ordering::Greater));
} else if i == l1.len() {
return Ok(Some(Ordering::Less));
} else if !vm.nix_eq(l1[i].clone(), l2[i].clone(), true)? {
return l1[i].force(vm)?.nix_cmp(&*l2[i].force(vm)?, vm);
}
}
unreachable!()
}
// different types
(Value::Integer(i1), Value::Float(f2)) => Ok((*i1 as f64).partial_cmp(f2)),
(Value::Float(f1), Value::Integer(i2)) => Ok(f1.partial_cmp(&(*i2 as f64))),
// unsupported types
(lhs, rhs) => Err(ErrorKind::Incomparable {
lhs: lhs.type_of(),
rhs: rhs.type_of(),
}),
}
}
/// Ensure `self` is forced if it is a thunk, and return a reference to the resulting value.
pub 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)),
}
}
/// Ensure `self` is *deeply* forced, including all recursive sub-values
pub(crate) fn deep_force(
&self,
vm: &mut VM,
thunk_set: &mut ThunkSet,
) -> Result<(), ErrorKind> {
match self {
Value::Null
| Value::Bool(_)
| Value::Integer(_)
| Value::Float(_)
| Value::String(_)
| Value::Path(_)
| Value::Closure(_)
| Value::Builtin(_)
| Value::AttrNotFound
| Value::Blueprint(_)
| Value::DeferredUpvalue(_)
| Value::UnresolvedPath(_) => Ok(()),
Value::Attrs(a) => {
for (_, v) in a.iter() {
v.deep_force(vm, thunk_set)?;
}
Ok(())
}
Value::List(l) => {
for val in l {
val.deep_force(vm, thunk_set)?;
}
Ok(())
}
Value::Thunk(thunk) => {
if !thunk_set.insert(thunk) {
return Ok(());
}
thunk.force(vm)?;
let value = thunk.value().clone();
value.deep_force(vm, thunk_set)
}
}
}
/// Explain a value in a human-readable way, e.g. by presenting
/// the docstrings of functions if present.
pub fn explain(&self) -> String {
match self {
Value::Null => "the 'null' value".into(),
Value::Bool(b) => format!("the boolean value '{}'", b),
Value::Integer(i) => format!("the integer '{}'", i),
Value::Float(f) => format!("the float '{}'", f),
Value::String(s) => format!("the string '{}'", s),
Value::Path(p) => format!("the path '{}'", p.to_string_lossy()),
Value::Attrs(attrs) => format!("a {}-item attribute set", attrs.len()),
Value::List(list) => format!("a {}-item list", list.len()),
Value::Closure(f) => {
if let Some(name) = &f.lambda.name {
format!("the user-defined Nix function '{}'", name)
} else {
"a user-defined Nix function".to_string()
}
}
Value::Builtin(b) => {
let mut out = format!("the builtin function '{}'", b.name());
if let Some(docs) = b.documentation() {
out.push_str("\n\n");
out.push_str(docs);
}
out
}
// TODO: handle suspended thunks with a different explanation instead of panicking
Value::Thunk(t) => t.value().explain(),
Value::AttrNotFound
| Value::Blueprint(_)
| Value::DeferredUpvalue(_)
| Value::UnresolvedPath(_) => "an internal Tvix evaluator value".into(),
}
}
}
trait TotalDisplay {
fn total_fmt(&self, f: &mut std::fmt::Formatter<'_>, set: &mut ThunkSet) -> std::fmt::Result;
}
impl Display for Value {
fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
self.total_fmt(f, &mut Default::default())
}
}
/// Emulates the C++-Nix style formatting of floats, which diverges
/// significantly from Rust's native float formatting.
fn total_fmt_float<F: std::fmt::Write>(num: f64, mut f: F) -> std::fmt::Result {
let mut buf = [b'0'; lexical_core::BUFFER_SIZE];
let mut s = lexical_core::write_with_options::<f64, { CXX_LITERAL }>(
num.clone(),
&mut buf,
&WRITE_FLOAT_OPTIONS,
);
// apply some postprocessing on the buffer. If scientific
// notation is used (we see an `e`), and the next character is
// a digit, add the missing `+` sign.)
let mut new_s = Vec::with_capacity(s.len());
if s.contains(&b'e') {
for (i, c) in s.iter().enumerate() {
// encountered `e`
if c == &b'e' {
// next character is a digit (so no negative exponent)
if s.len() > i && s[i + 1].is_ascii_digit() {
// copy everything from the start up to (including) the e
new_s.extend_from_slice(&s[0..=i]);
// add the missing '+'
new_s.push(b'+');
// check for the remaining characters.
// If it's only one, we need to prepend a trailing zero
if s.len() == i + 2 {
new_s.push(b'0');
}
new_s.extend_from_slice(&s[i + 1..]);
break;
}
}
}
// if we modified the scientific notation, flip the reference
if new_s.len() != 0 {
s = &mut new_s
}
}
// else, if this is not scientific notation, and there's a
// decimal point, make sure we really drop trailing zeroes.
// In some cases, lexical_core doesn't.
else if s.contains(&b'.') {
for (i, c) in s.iter().enumerate() {
// at `.``
if c == &b'.' {
// trim zeroes from the right side.
let frac = String::from_utf8_lossy(&s[i + 1..]);
let frac_no_trailing_zeroes = frac.trim_end_matches("0");
if frac.len() != frac_no_trailing_zeroes.len() {
// we managed to strip something, construct new_s
if frac_no_trailing_zeroes.is_empty() {
// if frac_no_trailing_zeroes is empty, the fractional part was all zeroes, so we can drop the decimal point as well
new_s.extend_from_slice(&s[0..=i - 1]);
} else {
// else, assemble the rest of the string
new_s.extend_from_slice(&s[0..=i]);
new_s.extend_from_slice(frac_no_trailing_zeroes.as_bytes());
}
// flip the reference
s = &mut new_s;
break;
}
}
}
}
write!(f, "{}", format!("{}", String::from_utf8_lossy(&s)))
}
impl TotalDisplay for Value {
fn total_fmt(&self, f: &mut std::fmt::Formatter<'_>, set: &mut ThunkSet) -> 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.total_fmt(f, set),
Value::List(list) => list.total_fmt(f, set),
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. Except when it decides to use scientific notation
// (with a + after the `e`, and zero-padded to 0 digits)
Value::Float(num) => total_fmt_float(*num, 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::UnresolvedPath(_) => f.write_str("internal[unresolved_path]"),
// Delegate thunk display to the type, as it must handle
// the case of already evaluated or cyclic thunks.
Value::Thunk(t) => t.total_fmt(f, set),
}
}
}
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<f64> for Value {
fn from(i: f64) -> Self {
Self::Float(i)
}
}
impl From<PathBuf> for Value {
fn from(path: PathBuf) -> Self {
Self::Path(path)
}
}
fn type_error(expected: &'static str, actual: &Value) -> ErrorKind {
ErrorKind::TypeError {
expected,
actual: actual.type_of(),
}
}
#[cfg(test)]
mod tests {
use super::*;
use imbl::vector;
mod floats {
use crate::value::total_fmt_float;
#[test]
fn format_float() {
let ff = vec![
(0f64, "0"),
(1.0f64, "1"),
(-0.01, "-0.01"),
(5e+22, "5e+22"),
(1e6, "1e+06"),
(-2E-2, "-0.02"),
(6.626e-34, "6.626e-34"),
(9_224_617.445_991_228_313, "9.22462e+06"),
];
for (n, expected) in ff.iter() {
let mut buf = String::new();
let res = total_fmt_float(*n, &mut buf);
assert!(res.is_ok());
assert_eq!(
expected, &buf,
"{} should be formatted as {}, but got {}",
n, expected, &buf
);
}
}
}
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(
Default::default(),
Box::new(crate::DummyIO),
&mut observer,
Default::default(),
);
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(
Default::default(),
Box::new(crate::DummyIO),
&mut observer,
Default::default(),
);
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(
Default::default(),
Box::new(crate::DummyIO),
&mut observer,
Default::default(),
);
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(
Default::default(),
Box::new(crate::DummyIO),
&mut observer,
Default::default(),
);
let v1 = Value::List(NixList::from(vector![Value::Integer(1)]));
let v2 = Value::List(NixList::from(vector![Value::Float(1.0)]));
assert!(v1.nix_eq(&v2, &mut vm).unwrap())
}
}
}
