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fix(tvix/eval): getContext merges underlying values

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Previously, we were assembling very naively an attribute set composed of context we saw.

But it was forgetting that `"${drv}${drv.drvPath}"` would contain 2 contexts with the same key, but
with different values, one with `outputs = [ "out" ];` and `allOutputs = true;`.

Following this reasoning and comparing with what Nix does, we ought to merge underlying values systematically.

Hence, I bring `itertools` to perform a group by on the key and merge everything on the fly, it's not
beautiful but it's the best I could find, notice that I don't use
`group_by` but I talk about group by, that is, because `group_by` is a
`group_by_consecutive`, see
https://github.com/rust-itertools/itertools/issues/374.

Initially, I tried to do it without a `into_grouping_map_by`, it was akin to assemble the final `NixAttrs` directly,
it was less readable and harder to pull out because we don't have a lot of in-place mutable functions on
our data structures.

Change-Id: I9933c9bd88ffe04de50dda14f21879b60d8b8cd4
Reviewed-on: https://cl.tvl.fyi/c/depot/+/10620
Tested-by: BuildkiteCI
Reviewed-by: tazjin <tazjin@tvl.su>
This commit is contained in:
Ryan Lahfa 2024-01-14 02:40:07 +01:00 • committed by raitobezarius
parent 5e67b94704
commit 75cc52ddb1
5 changed files with 1695 additions and 2055 deletions
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82
tvix/eval/src/builtins/mod.rs
View file

@ -76,6 +76,9 @@ pub async fn coerce_value_to_path(
#[builtins]
mod pure_builtins {
use imbl::Vector;
use itertools::Itertools;
use crate::{value::PointerEquality, NixContext, NixContextElement};
use super::*;
@ -705,25 +708,70 @@ mod pure_builtins {
.await?;
let s = v.to_contextful_str()?;
let elements = s
let groups = s
.iter_context()
.flat_map(|context| context.iter())
.map(|ctx_element| match ctx_element {
NixContextElement::Plain(spath) => (
spath.clone(),
Value::attrs(NixAttrs::from_iter([("path", true)])),
),
NixContextElement::Single { name, derivation } => (
derivation.clone(),
Value::attrs(NixAttrs::from_iter([(
"outputs",
Value::List(NixList::construct(1, vec![name.clone().into()])),
)])),
),
NixContextElement::Derivation(drv_path) => (
drv_path.clone(),
Value::attrs(NixAttrs::from_iter([("allOutputs", true)])),
),
// Do not think `group_by` works here.
// `group_by` works on consecutive elements of the iterator.
// Due to how `HashSet` works (ordering is not guaranteed),
// this can become a source of non-determinism if you `group_by` naively.
// I know I did.
.into_grouping_map_by(|ctx_element| match ctx_element {
NixContextElement::Plain(spath) => spath,
NixContextElement::Single { derivation, .. } => derivation,
NixContextElement::Derivation(drv_path) => drv_path,
})
.collect::<Vec<_>>();
let elements = groups
.into_iter()
.map(|(key, group)| {
let mut outputs: Vector<NixString> = Vector::new();
let mut is_path = false;
let mut all_outputs = false;
for ctx_element in group {
match ctx_element {
NixContextElement::Plain(spath) => {
debug_assert!(spath == key, "Unexpected group containing mixed keys, expected: {:?}, encountered {:?}", key, spath);
is_path = true;
}
NixContextElement::Single { name, derivation } => {
debug_assert!(derivation == key, "Unexpected group containing mixed keys, expected: {:?}, encountered {:?}", key, derivation);
outputs.push_back(name.clone().into());
}
NixContextElement::Derivation(drv_path) => {
debug_assert!(drv_path == key, "Unexpected group containing mixed keys, expected: {:?}, encountered {:?}", key, drv_path);
all_outputs = true;
}
}
}
// FIXME(raitobezarius): is there a better way to construct an attribute set
// conditionally?
let mut vec_attrs: Vec<(&str, Value)> = Vec::new();
if is_path {
vec_attrs.push(("path", true.into()));
}
if all_outputs {
vec_attrs.push(("allOutputs", true.into()));
}
if !outputs.is_empty() {
outputs.sort();
vec_attrs.push(("outputs", Value::List(outputs
.into_iter()
.map(|s| s.into())
.collect::<Vector<Value>>()
.into()
)));
}
(key.clone(), Value::attrs(NixAttrs::from_iter(vec_attrs.into_iter())))
});
Ok(Value::attrs(NixAttrs::from_iter(elements)))