//! This module implements the backing representation of runtime
//! values in the Nix language.
use std::cmp::Ordering;
use std::fmt::Display;
use std::num::{NonZeroI32, NonZeroUsize};
use std::path::PathBuf;
use std::rc::Rc;
use bstr::{BString, ByteVec};
use codemap::Span;
use lexical_core::format::CXX_LITERAL;
use serde::Deserialize;
#[cfg(feature = "arbitrary")]
mod arbitrary;
mod attrs;
mod builtin;
mod function;
mod json;
mod list;
mod path;
mod string;
mod thunk;
use crate::errors::{CatchableErrorKind, ErrorKind};
use crate::opcode::StackIdx;
use crate::vm::generators::{self, GenCo};
use crate::AddContext;
pub use attrs::NixAttrs;
pub use builtin::{Builtin, BuiltinResult};
pub(crate) use function::Formals;
pub use function::{Closure, Lambda};
pub use list::NixList;
pub use path::canon_path;
pub use string::{NixContext, NixContextElement, NixString};
pub use thunk::Thunk;
pub use self::thunk::ThunkSet;
use lazy_static::lazy_static;
#[warn(variant_size_differences)]
#[derive(Clone, Debug, Deserialize)]
#[serde(untagged)]
pub enum Value {
Null,
Bool(bool),
Integer(i64),
Float(f64),
String(NixString),
#[serde(skip)]
Path(Box<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(Box<PathBuf>),
#[serde(skip)]
Json(Box<(serde_json::Value, NixContext)>),
#[serde(skip)]
FinaliseRequest(bool),
#[serde(skip)]
Catchable(Box<CatchableErrorKind>),
}
impl From<CatchableErrorKind> for Value {
#[inline]
fn from(c: CatchableErrorKind) -> Value {
Value::Catchable(Box::new(c))
}
}
impl<V> From<Result<V, CatchableErrorKind>> for Value
where
Value: From<V>,
{
#[inline]
fn from(v: Result<V, CatchableErrorKind>) -> Value {
match v {
Ok(v) => v.into(),
Err(e) => Value::Catchable(Box::new(e)),
}
}
}
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, Eq, Debug)]
pub struct CoercionKind {
/// If false only coerce already "stringly" types like strings and paths, but
/// also coerce sets that have a `__toString` attribute. In Tvix, this is
/// usually called a weak coercion. Equivalent to passing `false` as the
/// `coerceMore` argument of `EvalState::coerceToString` in C++ Nix.
///
/// If true coerce all value types included by a weak coercion, but also
/// coerce `null`, booleans, integers, floats and lists of coercible types.
/// Consequently, we call this a strong coercion. Equivalent to passing
/// `true` as `coerceMore` in C++ Nix.
pub strong: bool,
/// If `import_paths` is `true`, paths are imported into the store and their
/// store path is the result of the coercion (equivalent to the
/// `copyToStore` argument of `EvalState::coerceToString` in C++ Nix).
pub import_paths: bool,
}
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))
}
}
/// Controls what kind of by-pointer equality comparison is allowed.
///
/// See `//tvix/docs/value-pointer-equality.md` for details.
#[derive(Clone, Copy, Debug, PartialEq, Eq, PartialOrd, Ord)]
pub enum PointerEquality {
/// Pointer equality not allowed at all.
ForbidAll,
/// Pointer equality comparisons only allowed for nested values.
AllowNested,
/// Pointer equality comparisons are allowed in all contexts.
AllowAll,
}
impl Value {
/// Deeply forces a value, traversing e.g. lists and attribute sets and forcing
/// their contents, too.
///
/// This is a generator function.
pub(super) async fn deep_force(self, co: GenCo, span: Span) -> Result<Value, ErrorKind> {
if let Some(v) = Self::deep_force_(self.clone(), co, span).await? {
Ok(v)
} else {
Ok(self)
}
}
/// Returns Some(v) or None to indicate the returned value is myself
async fn deep_force_(myself: Value, co: GenCo, span: Span) -> Result<Option<Value>, ErrorKind> {
// This is a stack of values which still remain to be forced.
let mut vals = vec![myself];
let mut thunk_set: ThunkSet = Default::default();
loop {
let v = if let Some(v) = vals.pop() {
v
} else {
return Ok(None);
};
// Get rid of any top-level thunks, and bail out of self-recursive
// thunks.
let value = if let Value::Thunk(t) = &v {
if !thunk_set.insert(t) {
continue;
}
Thunk::force_(t.clone(), &co, span).await?
} else {
v
};
match value {
// Short-circuit on already evaluated values, or fail on internal values.
Value::Null
| Value::Bool(_)
| Value::Integer(_)
| Value::Float(_)
| Value::String(_)
| Value::Path(_)
| Value::Closure(_)
| Value::Builtin(_) => continue,
Value::List(list) => {
for val in list.into_iter().rev() {
vals.push(val);
}
continue;
}
Value::Attrs(attrs) => {
for (_, val) in attrs.into_iter().rev() {
vals.push(val);
}
continue;
}
Value::Thunk(_) => panic!("Tvix bug: force_value() returned a thunk"),
Value::Catchable(_) => return Ok(Some(value)),
Value::AttrNotFound
| Value::Blueprint(_)
| Value::DeferredUpvalue(_)
| Value::UnresolvedPath(_)
| Value::Json(..)
| Value::FinaliseRequest(_) => panic!(
"Tvix bug: internal value left on stack: {}",
value.type_of()
),
}
}
}
pub async fn coerce_to_string(
self,
co: GenCo,
kind: CoercionKind,
span: Span,
) -> Result<Value, ErrorKind> {
self.coerce_to_string_(&co, kind, span).await
}
/// Coerce a `Value` to a string. See `CoercionKind` for a rundown of what
/// input types are accepted under what circumstances.
pub async fn coerce_to_string_(
self,
co: &GenCo,
kind: CoercionKind,
span: Span,
) -> Result<Value, ErrorKind> {
let mut result = BString::default();
let mut vals = vec![self];
// Track if we are coercing the first value of a list to correctly emit
// separating white spaces.
let mut is_list_head = None;
// FIXME(raitobezarius): as per https://b.tvl.fyi/issues/364
// we might be interested into more powerful context-related coercion kinds.
let mut context: NixContext = NixContext::new();
loop {
let value = if let Some(v) = vals.pop() {
v.force(co, span).await?
} else {
return Ok(Value::String(NixString::new_context_from(context, result)));
};
let coerced: Result<BString, _> = match (value, kind) {
// coercions that are always done
(Value::String(mut s), _) => {
if let Some(ctx) = s.take_context() {
context.extend(ctx.into_iter());
}
Ok((*s).into())
}
// 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),
CoercionKind {
import_paths: true, ..
},
) => {
let imported = generators::request_path_import(co, *p).await;
// When we import a path from the evaluator, we must attach
// its original path as its context.
context = context.append(NixContextElement::Plain(
imported.to_string_lossy().to_string(),
));
Ok(imported.into_os_string().into_encoded_bytes().into())
}
(
Value::Path(p),
CoercionKind {
import_paths: false,
..
},
) => Ok(p.into_os_string().into_encoded_bytes().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 let Some(to_string) = attrs.select("__toString") {
let callable = to_string.clone().force(co, span).await?;
// Leave the attribute set on the stack as an argument
// to the function call.
generators::request_stack_push(co, Value::Attrs(attrs.clone())).await;
// Call the callable ...
let result = generators::request_call(co, callable).await;
// Recurse on the result, as attribute set coercion
// actually works recursively, e.g. you can even return
// /another/ set with a __toString attr.
vals.push(result);
continue;
} else if let Some(out_path) = attrs.select("outPath") {
vals.push(out_path.clone());
continue;
} else {
return Err(ErrorKind::NotCoercibleToString { from: "set", kind });
}
}
// strong coercions
(Value::Null, CoercionKind { strong: true, .. })
| (Value::Bool(false), CoercionKind { strong: true, .. }) => Ok("".into()),
(Value::Bool(true), CoercionKind { strong: true, .. }) => Ok("1".into()),
(Value::Integer(i), CoercionKind { strong: true, .. }) => Ok(format!("{i}").into()),
(Value::Float(f), CoercionKind { strong: true, .. }) => {
// 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(list), CoercionKind { strong: true, .. }) => {
for elem in list.into_iter().rev() {
vals.push(elem);
}
// In case we are coercing a list within a list we don't want
// to touch this. Since the algorithm is nonrecursive, the
// space would not have been created yet (due to continue).
if is_list_head.is_none() {
is_list_head = Some(true);
}
continue;
}
(Value::Thunk(_), _) => panic!("Tvix bug: force returned unforced thunk"),
val @ (Value::Closure(_), _)
| val @ (Value::Builtin(_), _)
| val @ (Value::Null, _)
| val @ (Value::Bool(_), _)
| val @ (Value::Integer(_), _)
| val @ (Value::Float(_), _)
| val @ (Value::List(_), _) => Err(ErrorKind::NotCoercibleToString {
from: val.0.type_of(),
kind,
}),
(c @ Value::Catchable(_), _) => return Ok(c),
(Value::AttrNotFound, _)
| (Value::Blueprint(_), _)
| (Value::DeferredUpvalue(_), _)
| (Value::UnresolvedPath(_), _)
| (Value::Json(..), _)
| (Value::FinaliseRequest(_), _) => {
panic!("tvix bug: .coerce_to_string() called on internal value")
}
};
if let Some(head) = is_list_head {
if !head {
result.push(b' ');
} else {
is_list_head = Some(false);
}
}
result.push_str(&coerced?);
}
}
pub(crate) async fn nix_eq_owned_genco(
self,
other: Value,
co: GenCo,
ptr_eq: PointerEquality,
span: Span,
) -> Result<Value, ErrorKind> {
self.nix_eq(other, &co, ptr_eq, span).await
}
/// Compare two Nix values for equality, forcing nested parts of the structure
/// as needed.
///
/// This comparison needs to be invoked for nested values (e.g. in lists and
/// attribute sets) as well, which is done by suspending and asking the VM to
/// perform the nested comparison.
///
/// The `top_level` parameter controls whether this invocation is the top-level
/// comparison, or a nested value comparison. See
/// `//tvix/docs/value-pointer-equality.md`
pub(crate) async fn nix_eq(
self,
other: Value,
co: &GenCo,
ptr_eq: PointerEquality,
span: Span,
) -> Result<Value, ErrorKind> {
// this is a stack of ((v1,v2),peq) triples to be compared;
// after each triple is popped off of the stack, v1 is
// compared to v2 using peq-mode PointerEquality
let mut vals = vec![((self, other), ptr_eq)];
loop {
let ((a, b), ptr_eq) = if let Some(abp) = vals.pop() {
abp
} else {
// stack is empty, so comparison has succeeded
return Ok(Value::Bool(true));
};
let a = match a {
Value::Thunk(thunk) => {
// If both values are thunks, and thunk comparisons are allowed by
// pointer, do that and move on.
if ptr_eq == PointerEquality::AllowAll {
if let Value::Thunk(t1) = &b {
if t1.ptr_eq(&thunk) {
continue;
}
}
};
Thunk::force_(thunk, co, span).await?
}
_ => a,
};
let b = b.force(co, span).await?;
debug_assert!(!matches!(a, Value::Thunk(_)));
debug_assert!(!matches!(b, Value::Thunk(_)));
let result = match (a, b) {
// Trivial comparisons
(c @ Value::Catchable(_), _) => return Ok(c),
(_, c @ Value::Catchable(_)) => return Ok(c),
(Value::Null, Value::Null) => true,
(Value::Bool(b1), Value::Bool(b2)) => b1 == b2,
(Value::String(s1), Value::String(s2)) => s1 == s2,
(Value::Path(p1), Value::Path(p2)) => p1 == p2,
// Numerical comparisons (they work between float & int)
(Value::Integer(i1), Value::Integer(i2)) => i1 == i2,
(Value::Integer(i), Value::Float(f)) => i as f64 == f,
(Value::Float(f1), Value::Float(f2)) => f1 == f2,
(Value::Float(f), Value::Integer(i)) => i as f64 == f,
// List comparisons
(Value::List(l1), Value::List(l2)) => {
if ptr_eq >= PointerEquality::AllowNested && l1.ptr_eq(&l2) {
continue;
}
if l1.len() != l2.len() {
return Ok(Value::Bool(false));
}
vals.extend(l1.into_iter().rev().zip(l2.into_iter().rev()).zip(
std::iter::repeat(std::cmp::max(ptr_eq, PointerEquality::AllowNested)),
));
continue;
}
(_, Value::List(_)) | (Value::List(_), _) => return Ok(Value::Bool(false)),
// Attribute set comparisons
(Value::Attrs(a1), Value::Attrs(a2)) => {
if ptr_eq >= PointerEquality::AllowNested && a1.ptr_eq(&a2) {
continue;
}
// Special-case for derivation comparisons: If both attribute sets
// have `type = derivation`, compare them by `outPath`.
#[allow(clippy::single_match)] // might need more match arms later
match (a1.select("type"), a2.select("type")) {
(Some(v1), Some(v2)) => {
let s1 = v1.clone().force(co, span).await?;
if s1.is_catchable() {
return Ok(s1);
}
let s2 = v2.clone().force(co, span).await?;
if s2.is_catchable() {
return Ok(s2);
}
let s1 = s1.to_str();
let s2 = s2.to_str();
if let (Ok(s1), Ok(s2)) = (s1, s2) {
if s1 == "derivation" && s2 == "derivation" {
// TODO(tazjin): are the outPaths really required,
// or should it fall through?
let out1 = a1
.select_required("outPath")
.context("comparing derivations")?
.clone();
let out2 = a2
.select_required("outPath")
.context("comparing derivations")?
.clone();
let out1 = out1.clone().force(co, span).await?;
let out2 = out2.clone().force(co, span).await?;
if out1.is_catchable() {
return Ok(out1);
}
if out2.is_catchable() {
return Ok(out2);
}
let result =
out1.to_contextful_str()? == out2.to_contextful_str()?;
if !result {
return Ok(Value::Bool(false));
} else {
continue;
}
}
}
}
_ => {}
};
if a1.len() != a2.len() {
return Ok(Value::Bool(false));
}
// note that it is important to be careful here with the
// order we push the keys and values in order to properly
// compare attrsets containing `throw` elements.
let iter1 = a1.into_iter_sorted().rev();
let iter2 = a2.into_iter_sorted().rev();
for ((k1, v1), (k2, v2)) in iter1.zip(iter2) {
vals.push((
(v1, v2),
std::cmp::max(ptr_eq, PointerEquality::AllowNested),
));
vals.push((
(k1.into(), k2.into()),
std::cmp::max(ptr_eq, PointerEquality::AllowNested),
));
}
continue;
}
(Value::Attrs(_), _) | (_, Value::Attrs(_)) => return Ok(Value::Bool(false)),
(Value::Closure(c1), Value::Closure(c2))
if ptr_eq >= PointerEquality::AllowNested =>
{
if Rc::ptr_eq(&c1, &c2) {
continue;
} else {
return Ok(Value::Bool(false));
}
}
// Everything else is either incomparable (e.g. internal types) or
// false.
_ => return Ok(Value::Bool(false)),
};
if !result {
return Ok(Value::Bool(false));
}
}
}
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]",
Value::Json(..) => "internal[json]",
Value::FinaliseRequest(_) => "internal[finaliser_sentinel]",
Value::Catchable(_) => "internal[catchable]",
}
}
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);
/// Cast the current value into a **context-less** string.
/// If you wanted to cast it into a potentially contextful string,
/// you have to explicitly use `to_contextful_str`.
/// Contextful strings are special, they should not be obtained
/// everytime you want a string.
pub fn to_str(&self) -> Result<NixString, ErrorKind> {
match self {
Value::String(s) if !s.has_context() => Ok((*s).clone()),
Value::Thunk(thunk) => Self::to_str(&thunk.value()),
other => Err(type_error("contextless strings", other)),
}
}
gen_cast!(
to_contextful_str,
NixString,
"contextful string",
Value::String(s),
(*s).clone()
);
gen_cast!(to_path, Box<PathBuf>, "path", Value::Path(p), p.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(_));
gen_is!(is_attrs, Value::Attrs(_));
gen_is!(is_catchable, Value::Catchable(_));
/// Returns `true` if the value is a [`Thunk`].
///
/// [`Thunk`]: Value::Thunk
pub fn is_thunk(&self) -> bool {
matches!(self, Self::Thunk(..))
}
/// Compare `self` against other using (fallible) Nix ordering semantics.
///
/// The function is intended to be used from within other generator
/// functions or `gen!` blocks.
pub async fn nix_cmp_ordering(
self,
other: Self,
co: GenCo,
span: Span,
) -> Result<Result<Ordering, CatchableErrorKind>, ErrorKind> {
Self::nix_cmp_ordering_(self, other, co, span).await
}
async fn nix_cmp_ordering_(
myself: Self,
other: Self,
co: GenCo,
span: Span,
) -> Result<Result<Ordering, CatchableErrorKind>, ErrorKind> {
// this is a stack of ((v1,v2),peq) triples to be compared;
// after each triple is popped off of the stack, v1 is
// compared to v2 using peq-mode PointerEquality
let mut vals = vec![((myself, other), PointerEquality::ForbidAll)];
loop {
let ((mut a, mut b), ptr_eq) = if let Some(abp) = vals.pop() {
abp
} else {
// stack is empty, so they are equal
return Ok(Ok(Ordering::Equal));
};
if ptr_eq == PointerEquality::AllowAll {
if a.clone()
.nix_eq(b.clone(), &co, PointerEquality::AllowAll, span)
.await?
.as_bool()?
{
continue;
}
a = a.force(&co, span).await?;
b = b.force(&co, span).await?;
}
let result = match (a, b) {
(Value::Catchable(c), _) => return Ok(Err(*c)),
(_, Value::Catchable(c)) => return Ok(Err(*c)),
// same types
(Value::Integer(i1), Value::Integer(i2)) => i1.cmp(&i2),
(Value::Float(f1), Value::Float(f2)) => f1.total_cmp(&f2),
(Value::String(s1), Value::String(s2)) => s1.cmp(&s2),
(Value::List(l1), Value::List(l2)) => {
let max = l1.len().max(l2.len());
for j in 0..max {
let i = max - 1 - j;
if i >= l2.len() {
vals.push(((1.into(), 0.into()), PointerEquality::ForbidAll));
} else if i >= l1.len() {
vals.push(((0.into(), 1.into()), PointerEquality::ForbidAll));
} else {
vals.push(((l1[i].clone(), l2[i].clone()), PointerEquality::AllowAll));
}
}
continue;
}
// different types
(Value::Integer(i1), Value::Float(f2)) => (i1 as f64).total_cmp(&f2),
(Value::Float(f1), Value::Integer(i2)) => f1.total_cmp(&(i2 as f64)),
// unsupported types
(lhs, rhs) => {
return Err(ErrorKind::Incomparable {
lhs: lhs.type_of(),
rhs: rhs.type_of(),
})
}
};
if result != Ordering::Equal {
return Ok(Ok(result));
}
}
}
// TODO(amjoseph): de-asyncify this (when called directly by the VM)
pub async fn force(self, co: &GenCo, span: Span) -> Result<Value, ErrorKind> {
if let Value::Thunk(thunk) = self {
// TODO(amjoseph): use #[tailcall::mutual]
return Thunk::force_(thunk, co, span).await;
}
Ok(self)
}
// need two flavors, because async
pub async fn force_owned_genco(self, co: GenCo, span: Span) -> Result<Value, ErrorKind> {
if let Value::Thunk(thunk) = self {
// TODO(amjoseph): use #[tailcall::mutual]
return Thunk::force_(thunk, &co, span).await;
}
Ok(self)
}
/// 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) if s.has_context() => format!("the contextful string '{}'", s),
Value::String(s) => format!("the contextless 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::Catchable(_) => "a catchable failure".into(),
Value::AttrNotFound
| Value::Blueprint(_)
| Value::DeferredUpvalue(_)
| Value::UnresolvedPath(_)
| Value::Json(..)
| Value::FinaliseRequest(_) => "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,
&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.is_empty() {
s = &mut new_s
}
} else if s.contains(&b'.') {
// 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.
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, "{}", 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),
// TODO: fancy REPL display with position
Value::Closure(_) => f.write_str("<LAMBDA>"),
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]"),
Value::Json(..) => f.write_str("internal[json]"),
Value::FinaliseRequest(_) => f.write_str("internal[finaliser_sentinel]"),
// 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),
Value::Catchable(_) => panic!("total_fmt() called on a CatchableErrorKind"),
}
}
}
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(Box::new(path))
}
}
fn type_error(expected: &'static str, actual: &Value) -> ErrorKind {
ErrorKind::TypeError {
expected,
actual: actual.type_of(),
}
}
#[cfg(test)]
mod tests {
use super::*;
use std::mem::size_of;
#[test]
fn size() {
assert_eq!(size_of::<Value>(), 16);
}
mod floats {
use crate::value::total_fmt_float;
#[test]
fn format_float() {
let ff = [
(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_227, "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
);
}
}
}
}
