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feat(tvix/eval): track span of first force in a thunk blackhole

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This is step 1 towards being able to use all 4 spans that we know when
dealing with infinite recursion. It tracks the span at which the
force of a thunk was first requested when constructing a blackhole, so
that we can highlight the spans of the first and second forces.

These are actually the least relevant spans, but the easiest to put in
place, more coming soon.

Change-Id: I4c7e82f6211b98756439d4148a4191457cc46807
Reviewed-on: https://cl.tvl.fyi/c/depot/+/8269
Autosubmit: tazjin <tazjin@tvl.su>
Tested-by: BuildkiteCI
Reviewed-by: flokli <flokli@flokli.de>
This commit is contained in:
Vincent Ambo 2023-03-13 00:30:27 +03:00 committed by clbot
parent 5095e4f269
commit 3fa6b13c1e
5 changed files with 48 additions and 17 deletions
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25
tvix/eval/src/errors.rs
View file

@ -77,7 +77,9 @@ pub enum ErrorKind {
NotCallable(&'static str),
/// Infinite recursion encountered while forcing thunks.
InfiniteRecursion,
InfiniteRecursion {
first_force: Span,
},
ParseErrors(Vec<rnix::parser::ParseError>),
@ -354,7 +356,7 @@ to a missing value in the attribute set(s) included via `with`."#,
)
}
ErrorKind::InfiniteRecursion => write!(f, "infinite recursion encountered"),
ErrorKind::InfiniteRecursion { .. } => write!(f, "infinite recursion encountered"),
// Errors themselves ignored here & handled in Self::spans instead
ErrorKind::ParseErrors(_) => write!(f, "failed to parse Nix code:"),
@ -754,7 +756,7 @@ impl Error {
| ErrorKind::UnknownDynamicVariable(_)
| ErrorKind::VariableAlreadyDefined(_)
| ErrorKind::NotCallable(_)
| ErrorKind::InfiniteRecursion
| ErrorKind::InfiniteRecursion { .. }
| ErrorKind::ParseErrors(_)
| ErrorKind::NativeError { .. }
| ErrorKind::BytecodeError(_)
@ -797,7 +799,7 @@ impl Error {
ErrorKind::UnknownDynamicVariable(_) => "E011",
ErrorKind::VariableAlreadyDefined(_) => "E012",
ErrorKind::NotCallable(_) => "E013",
ErrorKind::InfiniteRecursion => "E014",
ErrorKind::InfiniteRecursion { .. } => "E014",
ErrorKind::ParseErrors(_) => "E015",
ErrorKind::DuplicateAttrsKey { .. } => "E016",
ErrorKind::NotCoercibleToString { .. } => "E018",
@ -869,6 +871,21 @@ impl Error {
]
}
ErrorKind::InfiniteRecursion { first_force } => {
vec![
SpanLabel {
label: Some("first requested here".into()),
span: *first_force,
style: SpanStyle::Secondary,
},
SpanLabel {
label: Some("requested again here".into()),
span: self.span,
style: SpanStyle::Primary,
},
]
}
// All other errors pretty much have the same shape.
_ => {
vec![SpanLabel {

5
tvix/eval/src/value/mod.rs
View file

@ -22,6 +22,7 @@ mod thunk;
use crate::errors::ErrorKind;
use crate::opcode::StackIdx;
use crate::spans::LightSpan;
use crate::vm::generators::{self, GenCo};
use crate::AddContext;
pub use attrs::NixAttrs;
@ -611,9 +612,9 @@ impl Value {
}
// TODO(amjoseph): de-asyncify this (when called directly by the VM)
pub async fn force(self, co: GenCo) -> Result<Value, ErrorKind> {
pub async fn force(self, co: GenCo, span: LightSpan) -> Result<Value, ErrorKind> {
if let Value::Thunk(thunk) = self {
return thunk.force(co).await;
return thunk.force(co, span).await;
}
Ok(self)

14
tvix/eval/src/value/thunk.rs
View file

@ -65,7 +65,7 @@ enum ThunkRepr {
/// Thunk currently under-evaluation; encountering a blackhole
/// value means that infinite recursion has occured.
Blackhole,
Blackhole { forced_at: LightSpan },
/// Fully evaluated thunk.
Evaluated(Value),
@ -75,7 +75,7 @@ impl ThunkRepr {
fn debug_repr(&self) -> String {
match self {
ThunkRepr::Evaluated(v) => format!("thunk(val|{})", v),
ThunkRepr::Blackhole => "thunk(blackhole)".to_string(),
ThunkRepr::Blackhole { .. } => "thunk(blackhole)".to_string(),
ThunkRepr::Native(_) => "thunk(native)".to_string(),
ThunkRepr::Suspended { lambda, .. } => format!("thunk({:p})", *lambda),
}
@ -114,7 +114,7 @@ impl Thunk {
}
// TODO(amjoseph): de-asyncify this
pub async fn force(self, co: GenCo) -> Result<Value, ErrorKind> {
pub async fn force(self, co: GenCo, span: LightSpan) -> Result<Value, ErrorKind> {
// If the current thunk is already fully evaluated, return its evaluated
// value. The VM will continue running the code that landed us here.
if self.is_forced() {
@ -124,12 +124,14 @@ impl Thunk {
// Begin evaluation of this thunk by marking it as a blackhole, meaning
// that any other forcing frame encountering this thunk before its
// evaluation is completed detected an evaluation cycle.
let inner = self.0.replace(ThunkRepr::Blackhole);
let inner = self.0.replace(ThunkRepr::Blackhole { forced_at: span });
match inner {
// If there was already a blackhole in the thunk, this is an
// evaluation cycle.
ThunkRepr::Blackhole => Err(ErrorKind::InfiniteRecursion),
ThunkRepr::Blackhole { forced_at } => Err(ErrorKind::InfiniteRecursion {
first_force: forced_at.span(),
}),
// If there is a native function stored in the thunk, evaluate it
// and replace this thunk's representation with the result.
@ -206,7 +208,7 @@ impl Thunk {
pub fn value(&self) -> Ref<Value> {
Ref::map(self.0.borrow(), |thunk| match thunk {
ThunkRepr::Evaluated(value) => value,
ThunkRepr::Blackhole => panic!("Thunk::value called on a black-holed thunk"),
ThunkRepr::Blackhole { .. } => panic!("Thunk::value called on a black-holed thunk"),
ThunkRepr::Suspended { .. } | ThunkRepr::Native(_) => {
panic!("Thunk::value called on a suspended thunk")
}

16
tvix/eval/src/vm/generators.rs
View file

@ -293,7 +293,9 @@ impl<'o> VM<'o> {
// back to the outer VM loop.
VMRequest::ForceValue(value) => {
self.reenqueue_generator(name, span.clone(), generator);
self.enqueue_generator("force", span, |co| value.force(co));
self.enqueue_generator("force", span.clone(), |co| {
value.force(co, span)
});
return Ok(false);
}
@ -313,7 +315,9 @@ impl<'o> VM<'o> {
self.reenqueue_generator(name, span.clone(), generator);
let value = self.stack[self.with_stack[idx]].clone();
self.enqueue_generator("force", span, |co| value.force(co));
self.enqueue_generator("force", span.clone(), |co| {
value.force(co, span)
});
return Ok(false);
}
@ -328,7 +332,9 @@ impl<'o> VM<'o> {
.expect("Tvix bug: generator requested captured with-value, but there is no call frame");
let value = call_frame.upvalues.with_stack().unwrap()[idx].clone();
self.enqueue_generator("force", span, |co| value.force(co));
self.enqueue_generator("force", span.clone(), |co| {
value.force(co, span)
});
return Ok(false);
}
@ -441,7 +447,9 @@ impl<'o> VM<'o> {
"generator should be reenqueued with the same frame ID"
);
self.enqueue_generator("force", span, |co| value.force(co));
self.enqueue_generator("force", span.clone(), |co| {
value.force(co, span)
});
return Ok(false);
}

5
tvix/eval/src/vm/mod.rs
View file

@ -483,7 +483,10 @@ impl<'o> VM<'o> {
let gen_span = frame.current_light_span();
self.push_call_frame(span, frame);
self.enqueue_generator("force", gen_span, |co| thunk.force(co));
self.enqueue_generator("force", gen_span.clone(), |co| {
thunk.force(co, gen_span)
});
return Ok(false);
}
}