feat(tvix/eval): make NixList::clone() cheap

When we start unrecursivifying (sp?) things, Rust's borrow checker
is going to be a headache; its magic only works when you use the CPU
stack as your call stack.

Fixing the borrow checker issues usually involves adding lots of
`clone()`s.  Right now `NixList` is the only variant of `Value` that
isn't cheap to clone() -- all the others are either a wrapper around
Rc or else are of bounded size.

Note that this requires dropping the `DerefMut for NixList` instance
and using `Vec<Value>` instead in those situations.

Change-Id: I5a47df66855342aa2064f8f3cb7934ff422d26bd
Signed-off-by: Adam Joseph <adam@westernsemico.com>
Reviewed-on: https://cl.tvl.fyi/c/depot/+/7359
Reviewed-by: tazjin <tazjin@tvl.su>
Tested-by: BuildkiteCI
This commit is contained in:
Adam Joseph 2022-11-23 00:34:09 -08:00 committed by clbot
parent c537cc6fce
commit a740653c83
3 changed files with 36 additions and 38 deletions

View file

@ -360,7 +360,7 @@ mod pure_builtins {
let operator = attrs.select_required("operator")?;
let mut res = NixList::new();
let mut res: Vec<Value> = vec![];
let mut done_keys: Vec<Value> = vec![];
let mut insert_key = |k: Value, vm: &mut VM| -> Result<bool, ErrorKind> {
@ -387,7 +387,7 @@ mod pure_builtins {
work_set.extend(op_result.into_iter());
}
Ok(Value::List(res))
Ok(Value::List(NixList::from(res)))
}
#[builtin("genList")]
@ -415,15 +415,16 @@ mod pure_builtins {
#[builtin("groupBy")]
fn builtin_group_by(vm: &mut VM, f: Value, list: Value) -> Result<Value, ErrorKind> {
let mut res: BTreeMap<NixString, Value> = BTreeMap::new();
let mut res: BTreeMap<NixString, Vec<Value>> = BTreeMap::new();
for val in list.to_list()? {
let key = vm.call_with(&f, [val.clone()])?.force(vm)?.to_str()?;
res.entry(key)
.or_insert_with(|| Value::List(NixList::new()))
.as_list_mut()?
.push(val);
res.entry(key).or_insert_with(|| vec![]).push(val);
}
Ok(Value::attrs(NixAttrs::from_map(res)))
Ok(Value::attrs(NixAttrs::from_map(
res.into_iter()
.map(|(k, v)| (k, Value::List(NixList::from(v))))
.collect(),
)))
}
#[builtin("hasAttr")]
@ -745,7 +746,7 @@ mod pure_builtins {
let re: Regex = Regex::new(re.as_str()).unwrap();
let mut capture_locations = re.capture_locations();
let num_captures = capture_locations.len();
let mut ret = NixList::new();
let mut ret: Vec<Value> = vec![];
let mut pos = 0;
while let Some(thematch) = re.captures_read_at(&mut capture_locations, text, pos) {
@ -770,12 +771,12 @@ mod pure_builtins {
// push the unmatched characters following the last match
ret.push(Value::from(&text[pos..]));
Ok(Value::List(ret))
Ok(Value::List(NixList::from(ret)))
}
#[builtin("sort")]
fn builtin_sort(vm: &mut VM, comparator: Value, list: Value) -> Result<Value, ErrorKind> {
let mut list = list.to_list()?;
let mut list = list.to_list()?.into_vec();
// Used to let errors "escape" from the sorting closure. If anything
// ends up setting an error, it is returned from this function.
@ -806,7 +807,7 @@ mod pure_builtins {
});
match error {
None => Ok(Value::List(list)),
None => Ok(Value::List(NixList::from(list))),
Some(e) => Err(e),
}
}

View file

@ -1,5 +1,6 @@
//! This module implements Nix lists.
use std::ops::{Deref, DerefMut};
use std::ops::Deref;
use std::rc::Rc;
use crate::errors::ErrorKind;
use crate::vm::VM;
@ -10,13 +11,13 @@ use super::Value;
#[repr(transparent)]
#[derive(Clone, Debug)]
pub struct NixList(Vec<Value>);
pub struct NixList(Rc<Vec<Value>>);
impl TotalDisplay for NixList {
fn total_fmt(&self, f: &mut std::fmt::Formatter<'_>, set: &mut ThunkSet) -> std::fmt::Result {
f.write_str("[ ")?;
for v in &self.0 {
for v in self.0.as_ref() {
v.total_fmt(f, set)?;
f.write_str(" ")?;
}
@ -27,7 +28,7 @@ impl TotalDisplay for NixList {
impl From<Vec<Value>> for NixList {
fn from(vs: Vec<Value>) -> Self {
Self(vs)
Self(Rc::new(vs))
}
}
@ -45,24 +46,14 @@ mod arbitrary {
type Strategy = BoxedStrategy<Self>;
fn arbitrary_with(args: Self::Parameters) -> Self::Strategy {
any_with::<Vec<Value>>(args).prop_map(Self).boxed()
any_with::<Rc<Vec<Value>>>(args).prop_map(Self).boxed()
}
}
}
impl NixList {
pub fn new() -> Self {
Self(vec![])
}
pub fn push(&mut self, val: Value) {
self.0.push(val)
}
pub fn concat(&self, other: &Self) -> Self {
let mut ret = self.clone();
ret.0.extend_from_slice(&other.0);
ret
Self(Rc::new(vec![]))
}
pub fn len(&self) -> usize {
@ -81,15 +72,22 @@ impl NixList {
stack_slice.len(),
);
NixList(stack_slice)
NixList(Rc::new(stack_slice))
}
pub fn iter(&self) -> std::slice::Iter<Value> {
self.0.iter()
}
pub fn ptr_eq(&self, other: &Self) -> bool {
Rc::ptr_eq(&self.0, &other.0)
}
/// Compare `self` against `other` for equality using Nix equality semantics
pub fn nix_eq(&self, other: &Self, vm: &mut VM) -> Result<bool, ErrorKind> {
if self.ptr_eq(other) {
return Ok(true);
}
if self.len() != other.len() {
return Ok(false);
}
@ -107,6 +105,10 @@ impl NixList {
pub fn force_elements(&self, vm: &mut VM) -> Result<(), ErrorKind> {
self.iter().try_for_each(|v| v.force(vm).map(|_| ()))
}
pub fn into_vec(self) -> Vec<Value> {
crate::unwrap_or_clone_rc(self.0)
}
}
impl IntoIterator for NixList {
@ -114,7 +116,7 @@ impl IntoIterator for NixList {
type IntoIter = std::vec::IntoIter<Value>;
fn into_iter(self) -> std::vec::IntoIter<Value> {
self.0.into_iter()
self.into_vec().into_iter()
}
}
@ -135,9 +137,3 @@ impl Deref for NixList {
&self.0
}
}
impl DerefMut for NixList {
fn deref_mut(&mut self) -> &mut Self::Target {
&mut self.0
}
}

View file

@ -538,8 +538,9 @@ impl<'o> VM<'o> {
OpCode::OpConcat => {
let rhs = fallible!(self, self.pop().to_list());
let lhs = fallible!(self, self.pop().to_list());
self.push(Value::List(lhs.concat(&rhs)))
let mut lhs = fallible!(self, self.pop().to_list()).into_vec();
lhs.extend_from_slice(&rhs);
self.push(Value::List(NixList::from(lhs)))
}
OpCode::OpInterpolate(Count(count)) => self.run_interpolate(count)?,