diff options
Diffstat (limited to 'tvix/eval/src/vm')
| -rw-r--r-- | tvix/eval/src/vm/generators.rs | 783 | ||||
| -rw-r--r-- | tvix/eval/src/vm/macros.rs | 70 | ||||
| -rw-r--r-- | tvix/eval/src/vm/mod.rs | 1249 |
3 files changed, 2102 insertions, 0 deletions
diff --git a/tvix/eval/src/vm/generators.rs b/tvix/eval/src/vm/generators.rs new file mode 100644 index 000000000000..f9c5786d8f8f --- /dev/null +++ b/tvix/eval/src/vm/generators.rs @@ -0,0 +1,783 @@ +//! This module implements generator logic for the VM. Generators are functions +//! used during evaluation which can suspend their execution during their +//! control flow, and request that the VM do something. +//! +//! This is used to keep the VM's stack size constant even when evaluating +//! deeply nested recursive data structures. +//! +//! We implement generators using the [`genawaiter`] crate. + +use core::pin::Pin; +use genawaiter::rc::Co; +pub use genawaiter::rc::Gen; +use std::fmt::Display; +use std::future::Future; + +use crate::value::{PointerEquality, SharedThunkSet}; +use crate::warnings::{EvalWarning, WarningKind}; +use crate::FileType; +use crate::NixString; + +use super::*; + +// -- Implementation of generic generator logic. + +/// States that a generator can be in while being driven by the VM. +pub(crate) enum GeneratorState { + /// Normal execution of the generator. + Running, + + /// Generator is awaiting the result of a forced value. + AwaitingValue, +} + +/// Messages that can be sent from generators *to* the VM. In most +/// cases, the VM will suspend the generator when receiving a message +/// and enter some other frame to process the request. +/// +/// Responses are returned to generators via the [`GeneratorResponse`] type. +pub enum VMRequest { + /// Request that the VM forces this value. This message is first sent to the + /// VM with the unforced value, then returned to the generator with the + /// forced result. + ForceValue(Value), + + /// Request that the VM deep-forces the value. + DeepForceValue(Value, SharedThunkSet), + + /// Request the value at the given index from the VM's with-stack, in forced + /// state. + /// + /// The value is returned in the `ForceValue` message. + WithValue(usize), + + /// Request the value at the given index from the *captured* with-stack, in + /// forced state. + CapturedWithValue(usize), + + /// Request that the two values be compared for Nix equality. The result is + /// returned in the `ForceValue` message. + NixEquality(Box<(Value, Value)>, PointerEquality), + + /// Push the given value to the VM's stack. This is used to prepare the + /// stack for requesting a function call from the VM. + /// + /// The VM does not respond to this request, so the next message received is + /// `Empty`. + StackPush(Value), + + /// Pop a value from the stack and return it to the generator. + StackPop, + + /// Request that the VM coerces this value to a string. + StringCoerce(Value, CoercionKind), + + /// Request that the VM calls the given value, with arguments already + /// prepared on the stack. Value must already be forced. + Call(Value), + + /// Request a call frame entering the given lambda immediately. This can be + /// used to force thunks. + EnterLambda { + lambda: Rc<Lambda>, + upvalues: Rc<Upvalues>, + light_span: LightSpan, + }, + + /// Emit a runtime warning (already containing a span) through the VM. + EmitWarning(EvalWarning), + + /// Emit a runtime warning through the VM. The span of the current generator + /// is used for the final warning. + EmitWarningKind(WarningKind), + + /// Request a lookup in the VM's import cache, which tracks the + /// thunks yielded by previously imported files. + ImportCacheLookup(PathBuf), + + /// Provide the VM with an imported value for a given path, which + /// it can populate its input cache with. + ImportCachePut(PathBuf, Value), + + /// Request that the VM imports the given path through its I/O interface. + PathImport(PathBuf), + + /// Request that the VM reads the given path to a string. + ReadToString(PathBuf), + + /// Request that the VM checks whether the given path exists. + PathExists(PathBuf), + + /// Request that the VM reads the given path. + ReadDir(PathBuf), + + /// Request a reasonable span from the VM. + Span, + + /// Request evaluation of `builtins.tryEval` from the VM. See + /// [`VM::catch_result`] for an explanation of how this works. + TryForce(Value), + + /// Request serialisation of a value to JSON, according to the + /// slightly odd Nix evaluation rules. + ToJson(Value), +} + +/// Human-readable representation of a generator message, used by observers. +impl Display for VMRequest { + fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result { + match self { + VMRequest::ForceValue(v) => write!(f, "force_value({})", v.type_of()), + VMRequest::DeepForceValue(v, _) => { + write!(f, "deep_force_value({})", v.type_of()) + } + VMRequest::WithValue(_) => write!(f, "with_value"), + VMRequest::CapturedWithValue(_) => write!(f, "captured_with_value"), + VMRequest::NixEquality(values, ptr_eq) => { + write!( + f, + "nix_eq({}, {}, PointerEquality::{:?})", + values.0.type_of(), + values.1.type_of(), + ptr_eq + ) + } + VMRequest::StackPush(v) => write!(f, "stack_push({})", v.type_of()), + VMRequest::StackPop => write!(f, "stack_pop"), + VMRequest::StringCoerce(v, kind) => match kind { + CoercionKind::Weak => write!(f, "weak_string_coerce({})", v.type_of()), + CoercionKind::Strong => write!(f, "strong_string_coerce({})", v.type_of()), + }, + VMRequest::Call(v) => write!(f, "call({})", v), + VMRequest::EnterLambda { lambda, .. } => { + write!(f, "enter_lambda({:p})", *lambda) + } + VMRequest::EmitWarning(_) => write!(f, "emit_warning"), + VMRequest::EmitWarningKind(_) => write!(f, "emit_warning_kind"), + VMRequest::ImportCacheLookup(p) => { + write!(f, "import_cache_lookup({})", p.to_string_lossy()) + } + VMRequest::ImportCachePut(p, _) => { + write!(f, "import_cache_put({})", p.to_string_lossy()) + } + VMRequest::PathImport(p) => write!(f, "path_import({})", p.to_string_lossy()), + VMRequest::ReadToString(p) => { + write!(f, "read_to_string({})", p.to_string_lossy()) + } + VMRequest::PathExists(p) => write!(f, "path_exists({})", p.to_string_lossy()), + VMRequest::ReadDir(p) => write!(f, "read_dir({})", p.to_string_lossy()), + VMRequest::Span => write!(f, "span"), + VMRequest::TryForce(v) => write!(f, "try_force({})", v.type_of()), + VMRequest::ToJson(v) => write!(f, "to_json({})", v.type_of()), + } + } +} + +/// Responses returned to generators *from* the VM. +pub enum VMResponse { + /// Empty message. Passed to the generator as the first message, + /// or when return values were optional. + Empty, + + /// Value produced by the VM and returned to the generator. + Value(Value), + + /// Path produced by the VM in response to some IO operation. + Path(PathBuf), + + /// VM response with the contents of a directory. + Directory(Vec<(bytes::Bytes, FileType)>), + + /// VM response with a span to use at the current point. + Span(LightSpan), +} + +impl Display for VMResponse { + fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result { + match self { + VMResponse::Empty => write!(f, "empty"), + VMResponse::Value(v) => write!(f, "value({})", v), + VMResponse::Path(p) => write!(f, "path({})", p.to_string_lossy()), + VMResponse::Directory(d) => write!(f, "dir(len = {})", d.len()), + VMResponse::Span(_) => write!(f, "span"), + } + } +} + +pub(crate) type Generator = + Gen<VMRequest, VMResponse, Pin<Box<dyn Future<Output = Result<Value, ErrorKind>>>>>; + +/// Helper function to provide type annotations which are otherwise difficult to +/// infer. +pub fn pin_generator( + f: impl Future<Output = Result<Value, ErrorKind>> + 'static, +) -> Pin<Box<dyn Future<Output = Result<Value, ErrorKind>>>> { + Box::pin(f) +} + +impl<'o> VM<'o> { + /// Helper function to re-enqueue the current generator while it + /// is awaiting a value. + fn reenqueue_generator(&mut self, name: &'static str, span: LightSpan, generator: Generator) { + self.frames.push(Frame::Generator { + name, + generator, + span, + state: GeneratorState::AwaitingValue, + }); + } + + /// Helper function to enqueue a new generator. + pub(super) fn enqueue_generator<F, G>(&mut self, name: &'static str, span: LightSpan, gen: G) + where + F: Future<Output = Result<Value, ErrorKind>> + 'static, + G: FnOnce(GenCo) -> F, + { + self.frames.push(Frame::Generator { + name, + span, + state: GeneratorState::Running, + generator: Gen::new(|co| pin_generator(gen(co))), + }); + } + + /// Run a generator frame until it yields to the outer control loop, or runs + /// to completion. + /// + /// The return value indicates whether the generator has completed (true), + /// or was suspended (false). + pub(crate) fn run_generator( + &mut self, + name: &'static str, + span: LightSpan, + frame_id: usize, + state: GeneratorState, + mut generator: Generator, + initial_message: Option<VMResponse>, + ) -> EvalResult<bool> { + // Determine what to send to the generator based on its state. + let mut message = match (initial_message, state) { + (Some(msg), _) => msg, + (_, GeneratorState::Running) => VMResponse::Empty, + + // If control returned here, and the generator is + // awaiting a value, send it the top of the stack. + (_, GeneratorState::AwaitingValue) => VMResponse::Value(self.stack_pop()), + }; + + loop { + match generator.resume_with(message) { + // If the generator yields, it contains an instruction + // for what the VM should do. + genawaiter::GeneratorState::Yielded(request) => { + self.observer.observe_generator_request(name, &request); + + match request { + VMRequest::StackPush(value) => { + self.stack.push(value); + message = VMResponse::Empty; + } + + VMRequest::StackPop => { + message = VMResponse::Value(self.stack_pop()); + } + + // Generator has requested a force, which means that + // this function prepares the frame stack and yields + // back to the outer VM loop. + VMRequest::ForceValue(value) => { + self.reenqueue_generator(name, span.clone(), generator); + self.enqueue_generator("force", span.clone(), |co| { + value.force(co, span) + }); + return Ok(false); + } + + // Generator has requested a deep-force. + VMRequest::DeepForceValue(value, thunk_set) => { + self.reenqueue_generator(name, span.clone(), generator); + self.enqueue_generator("deep_force", span, |co| { + value.deep_force(co, thunk_set) + }); + return Ok(false); + } + + // Generator has requested a value from the with-stack. + // Logic is similar to `ForceValue`, except with the + // value being taken from that stack. + VMRequest::WithValue(idx) => { + self.reenqueue_generator(name, span.clone(), generator); + + let value = self.stack[self.with_stack[idx]].clone(); + self.enqueue_generator("force", span.clone(), |co| { + value.force(co, span) + }); + + return Ok(false); + } + + // Generator has requested a value from the *captured* + // with-stack. Logic is same as above, except for the + // value being from that stack. + VMRequest::CapturedWithValue(idx) => { + self.reenqueue_generator(name, span.clone(), generator); + + let call_frame = self.last_call_frame() + .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.clone(), |co| { + value.force(co, span) + }); + + return Ok(false); + } + + VMRequest::NixEquality(values, ptr_eq) => { + let values = *values; + self.reenqueue_generator(name, span.clone(), generator); + self.enqueue_generator("nix_eq", span, |co| { + values.0.nix_eq(values.1, co, ptr_eq) + }); + return Ok(false); + } + + VMRequest::StringCoerce(val, kind) => { + self.reenqueue_generator(name, span.clone(), generator); + self.enqueue_generator("coerce_to_string", span, |co| { + val.coerce_to_string(co, kind) + }); + return Ok(false); + } + + VMRequest::Call(callable) => { + self.reenqueue_generator(name, span.clone(), generator); + self.call_value(span, None, callable)?; + return Ok(false); + } + + VMRequest::EnterLambda { + lambda, + upvalues, + light_span, + } => { + self.reenqueue_generator(name, span, generator); + + self.frames.push(Frame::CallFrame { + span: light_span, + call_frame: CallFrame { + lambda, + upvalues, + ip: CodeIdx(0), + stack_offset: self.stack.len(), + }, + }); + + return Ok(false); + } + + VMRequest::EmitWarning(warning) => { + self.push_warning(warning); + message = VMResponse::Empty; + } + + VMRequest::EmitWarningKind(kind) => { + self.emit_warning(kind); + message = VMResponse::Empty; + } + + VMRequest::ImportCacheLookup(path) => { + if let Some(cached) = self.import_cache.get(path) { + message = VMResponse::Value(cached.clone()); + } else { + message = VMResponse::Empty; + } + } + + VMRequest::ImportCachePut(path, value) => { + self.import_cache.insert(path, value); + message = VMResponse::Empty; + } + + VMRequest::PathImport(path) => { + let imported = self + .io_handle + .import_path(&path) + .map_err(|e| ErrorKind::IO { + path: Some(path), + error: e.into(), + }) + .with_span(&span, self)?; + + message = VMResponse::Path(imported); + } + + VMRequest::ReadToString(path) => { + let content = self + .io_handle + .read_to_string(&path) + .map_err(|e| ErrorKind::IO { + path: Some(path), + error: e.into(), + }) + .with_span(&span, self)?; + + message = VMResponse::Value(Value::String(content.into())) + } + + VMRequest::PathExists(path) => { + let exists = self + .io_handle + .path_exists(&path) + .map_err(|e| ErrorKind::IO { + path: Some(path), + error: e.into(), + }) + .map(Value::Bool) + .with_span(&span, self)?; + + message = VMResponse::Value(exists); + } + + VMRequest::ReadDir(path) => { + let dir = self + .io_handle + .read_dir(&path) + .map_err(|e| ErrorKind::IO { + path: Some(path), + error: e.into(), + }) + .with_span(&span, self)?; + message = VMResponse::Directory(dir); + } + + VMRequest::Span => { + message = VMResponse::Span(self.reasonable_light_span()); + } + + VMRequest::TryForce(value) => { + self.try_eval_frames.push(frame_id); + self.reenqueue_generator(name, span.clone(), generator); + + debug_assert!( + self.frames.len() == frame_id + 1, + "generator should be reenqueued with the same frame ID" + ); + + self.enqueue_generator("force", span.clone(), |co| { + value.force(co, span) + }); + return Ok(false); + } + + VMRequest::ToJson(value) => { + self.reenqueue_generator(name, span.clone(), generator); + self.enqueue_generator("to_json", span, |co| { + value.to_json_generator(co) + }); + return Ok(false); + } + } + } + + // Generator has completed, and its result value should + // be left on the stack. + genawaiter::GeneratorState::Complete(result) => { + let value = result.with_span(&span, self)?; + self.stack.push(value); + return Ok(true); + } + } + } + } +} + +pub type GenCo = Co<VMRequest, VMResponse>; + +// -- Implementation of concrete generator use-cases. + +/// Request that the VM place the given value on its stack. +pub async fn request_stack_push(co: &GenCo, val: Value) { + match co.yield_(VMRequest::StackPush(val)).await { + VMResponse::Empty => {} + msg => panic!( + "Tvix bug: VM responded with incorrect generator message: {}", + msg + ), + } +} + +/// Request that the VM pop a value from the stack and return it to the +/// generator. +pub async fn request_stack_pop(co: &GenCo) -> Value { + match co.yield_(VMRequest::StackPop).await { + VMResponse::Value(value) => value, + msg => panic!( + "Tvix bug: VM responded with incorrect generator message: {}", + msg + ), + } +} + +/// Force any value and return the evaluated result from the VM. +pub async fn request_force(co: &GenCo, val: Value) -> Value { + if let Value::Thunk(_) = val { + match co.yield_(VMRequest::ForceValue(val)).await { + VMResponse::Value(value) => value, + msg => panic!( + "Tvix bug: VM responded with incorrect generator message: {}", + msg + ), + } + } else { + val + } +} + +/// Force a value +pub(crate) async fn request_try_force(co: &GenCo, val: Value) -> Value { + if let Value::Thunk(_) = val { + match co.yield_(VMRequest::TryForce(val)).await { + VMResponse::Value(value) => value, + msg => panic!( + "Tvix bug: VM responded with incorrect generator message: {}", + msg + ), + } + } else { + val + } +} + +/// Call the given value as a callable. The argument(s) must already be prepared +/// on the stack. +pub async fn request_call(co: &GenCo, val: Value) -> Value { + let val = request_force(co, val).await; + match co.yield_(VMRequest::Call(val)).await { + VMResponse::Value(value) => value, + msg => panic!( + "Tvix bug: VM responded with incorrect generator message: {}", + msg + ), + } +} + +/// Helper function to call the given value with the provided list of arguments. +/// This uses the StackPush and Call messages under the hood. +pub async fn request_call_with<I>(co: &GenCo, mut callable: Value, args: I) -> Value +where + I: IntoIterator<Item = Value>, + I::IntoIter: DoubleEndedIterator, +{ + let mut num_args = 0_usize; + for arg in args.into_iter().rev() { + num_args += 1; + request_stack_push(co, arg).await; + } + + debug_assert!(num_args > 0, "call_with called with an empty list of args"); + + while num_args > 0 { + callable = request_call(co, callable).await; + num_args -= 1; + } + + callable +} + +pub async fn request_string_coerce( + co: &GenCo, + val: Value, + kind: CoercionKind, +) -> Result<NixString, CatchableErrorKind> { + match val { + Value::String(s) => Ok(s), + _ => match co.yield_(VMRequest::StringCoerce(val, kind)).await { + VMResponse::Value(Value::Catchable(c)) => Err(c), + VMResponse::Value(value) => Ok(value + .to_str() + .expect("coerce_to_string always returns a string")), + msg => panic!( + "Tvix bug: VM responded with incorrect generator message: {}", + msg + ), + }, + } +} + +/// Deep-force any value and return the evaluated result from the VM. +pub async fn request_deep_force(co: &GenCo, val: Value, thunk_set: SharedThunkSet) -> Value { + match co.yield_(VMRequest::DeepForceValue(val, thunk_set)).await { + VMResponse::Value(value) => value, + msg => panic!( + "Tvix bug: VM responded with incorrect generator message: {}", + msg + ), + } +} + +/// Ask the VM to compare two values for equality. +pub(crate) async fn check_equality( + co: &GenCo, + a: Value, + b: Value, + ptr_eq: PointerEquality, +) -> Result<bool, ErrorKind> { + match co + .yield_(VMRequest::NixEquality(Box::new((a, b)), ptr_eq)) + .await + { + VMResponse::Value(value) => value.as_bool(), + msg => panic!( + "Tvix bug: VM responded with incorrect generator message: {}", + msg + ), + } +} + +/// Emit a fully constructed runtime warning. +pub(crate) async fn emit_warning(co: &GenCo, warning: EvalWarning) { + match co.yield_(VMRequest::EmitWarning(warning)).await { + VMResponse::Empty => {} + msg => panic!( + "Tvix bug: VM responded with incorrect generator message: {}", + msg + ), + } +} + +/// Emit a runtime warning with the span of the current generator. +pub async fn emit_warning_kind(co: &GenCo, kind: WarningKind) { + match co.yield_(VMRequest::EmitWarningKind(kind)).await { + VMResponse::Empty => {} + msg => panic!( + "Tvix bug: VM responded with incorrect generator message: {}", + msg + ), + } +} + +/// Request that the VM enter the given lambda. +pub(crate) async fn request_enter_lambda( + co: &GenCo, + lambda: Rc<Lambda>, + upvalues: Rc<Upvalues>, + light_span: LightSpan, +) -> Value { + let msg = VMRequest::EnterLambda { + lambda, + upvalues, + light_span, + }; + + match co.yield_(msg).await { + VMResponse::Value(value) => value, + msg => panic!( + "Tvix bug: VM responded with incorrect generator message: {}", + msg + ), + } +} + +/// Request a lookup in the VM's import cache. +pub(crate) async fn request_import_cache_lookup(co: &GenCo, path: PathBuf) -> Option<Value> { + match co.yield_(VMRequest::ImportCacheLookup(path)).await { + VMResponse::Value(value) => Some(value), + VMResponse::Empty => None, + msg => panic!( + "Tvix bug: VM responded with incorrect generator message: {}", + msg + ), + } +} + +/// Request that the VM populate its input cache for the given path. +pub(crate) async fn request_import_cache_put(co: &GenCo, path: PathBuf, value: Value) { + match co.yield_(VMRequest::ImportCachePut(path, value)).await { + VMResponse::Empty => {} + msg => panic!( + "Tvix bug: VM responded with incorrect generator message: {}", + msg + ), + } +} + +/// Request that the VM import the given path. +pub(crate) async fn request_path_import(co: &GenCo, path: PathBuf) -> PathBuf { + match co.yield_(VMRequest::PathImport(path)).await { + VMResponse::Path(path) => path, + msg => panic!( + "Tvix bug: VM responded with incorrect generator message: {}", + msg + ), + } +} + +pub(crate) async fn request_read_to_string(co: &GenCo, path: PathBuf) -> Value { + match co.yield_(VMRequest::ReadToString(path)).await { + VMResponse::Value(value) => value, + msg => panic!( + "Tvix bug: VM responded with incorrect generator message: {}", + msg + ), + } +} + +pub(crate) async fn request_path_exists(co: &GenCo, path: PathBuf) -> Value { + match co.yield_(VMRequest::PathExists(path)).await { + VMResponse::Value(value) => value, + msg => panic!( + "Tvix bug: VM responded with incorrect generator message: {}", + msg + ), + } +} + +pub(crate) async fn request_read_dir(co: &GenCo, path: PathBuf) -> Vec<(bytes::Bytes, FileType)> { + match co.yield_(VMRequest::ReadDir(path)).await { + VMResponse::Directory(dir) => dir, + msg => panic!( + "Tvix bug: VM responded with incorrect generator message: {}", + msg + ), + } +} + +pub(crate) async fn request_span(co: &GenCo) -> LightSpan { + match co.yield_(VMRequest::Span).await { + VMResponse::Span(span) => span, + msg => panic!( + "Tvix bug: VM responded with incorrect generator message: {}", + msg + ), + } +} + +pub(crate) async fn request_to_json(co: &GenCo, value: Value) -> serde_json::Value { + match co.yield_(VMRequest::ToJson(value)).await { + VMResponse::Value(Value::Json(json)) => json, + msg => panic!( + "Tvix bug: VM responded with incorrect generator message: {}", + msg + ), + } +} + +/// Call the given value as if it was an attribute set containing a functor. The +/// arguments must already be prepared on the stack when a generator frame from +/// this function is invoked. +/// +pub(crate) async fn call_functor(co: GenCo, value: Value) -> Result<Value, ErrorKind> { + let attrs = value.to_attrs()?; + + match attrs.select("__functor") { + None => Err(ErrorKind::NotCallable("set without `__functor_` attribute")), + Some(functor) => { + // The functor receives the set itself as its first argument and + // needs to be called with it. + let functor = request_force(&co, functor.clone()).await; + let primed = request_call_with(&co, functor, [value]).await; + Ok(request_call(&co, primed).await) + } + } +} diff --git a/tvix/eval/src/vm/macros.rs b/tvix/eval/src/vm/macros.rs new file mode 100644 index 000000000000..969b50807766 --- /dev/null +++ b/tvix/eval/src/vm/macros.rs @@ -0,0 +1,70 @@ +/// This module provides macros which are used in the implementation +/// of the VM for the implementation of repetitive operations. + +/// This macro simplifies the implementation of arithmetic operations, +/// correctly handling the behaviour on different pairings of number +/// types. +#[macro_export] +macro_rules! arithmetic_op { + ( $self:ident, $op:tt ) => {{ // TODO: remove + let b = $self.pop(); + let a = $self.pop(); + let result = fallible!($self, arithmetic_op!(&a, &b, $op)); + $self.push(result); + }}; + + ( $a:expr, $b:expr, $op:tt ) => {{ + match ($a, $b) { + (Value::Integer(i1), Value::Integer(i2)) => Ok(Value::Integer(i1 $op i2)), + (Value::Float(f1), Value::Float(f2)) => Ok(Value::Float(f1 $op f2)), + (Value::Integer(i1), Value::Float(f2)) => Ok(Value::Float(*i1 as f64 $op f2)), + (Value::Float(f1), Value::Integer(i2)) => Ok(Value::Float(f1 $op *i2 as f64)), + + (v1, v2) => Err(ErrorKind::TypeError { + expected: "number (either int or float)", + actual: if v1.is_number() { + v2.type_of() + } else { + v1.type_of() + }, + }), + } + }}; +} + +/// This macro simplifies the implementation of comparison operations. +#[macro_export] +macro_rules! cmp_op { + ( $vm:ident, $frame:ident, $span:ident, $op:tt ) => {{ + let b = $vm.stack_pop(); + let a = $vm.stack_pop(); + + async fn compare(a: Value, b: Value, co: GenCo) -> Result<Value, ErrorKind> { + let a = generators::request_force(&co, a).await; + let b = generators::request_force(&co, b).await; + let ordering = a.nix_cmp_ordering(b, co).await?; + Ok(Value::Bool(cmp_op!(@order $op ordering))) + } + + let gen_span = $frame.current_light_span(); + $vm.push_call_frame($span, $frame); + $vm.enqueue_generator("compare", gen_span, |co| compare(a, b, co)); + return Ok(false); + }}; + + (@order < $ordering:expr) => { + $ordering == Some(Ordering::Less) + }; + + (@order > $ordering:expr) => { + $ordering == Some(Ordering::Greater) + }; + + (@order <= $ordering:expr) => { + !matches!($ordering, None | Some(Ordering::Greater)) + }; + + (@order >= $ordering:expr) => { + !matches!($ordering, None | Some(Ordering::Less)) + }; +} diff --git a/tvix/eval/src/vm/mod.rs b/tvix/eval/src/vm/mod.rs new file mode 100644 index 000000000000..d8f38718c67a --- /dev/null +++ b/tvix/eval/src/vm/mod.rs @@ -0,0 +1,1249 @@ +//! This module implements the abstract/virtual machine that runs Tvix +//! bytecode. +//! +//! The operation of the VM is facilitated by the [`Frame`] type, +//! which controls the current execution state of the VM and is +//! processed within the VM's operating loop. +//! +//! A [`VM`] is used by instantiating it with an initial [`Frame`], +//! then triggering its execution and waiting for the VM to return or +//! yield an error. + +pub mod generators; +mod macros; + +use codemap::Span; +use serde_json::json; +use std::{cmp::Ordering, collections::HashMap, ops::DerefMut, path::PathBuf, rc::Rc}; + +use crate::{ + arithmetic_op, + chunk::Chunk, + cmp_op, + compiler::GlobalsMap, + errors::{CatchableErrorKind, Error, ErrorKind, EvalResult}, + io::EvalIO, + nix_search_path::NixSearchPath, + observer::RuntimeObserver, + opcode::{CodeIdx, Count, JumpOffset, OpCode, StackIdx, UpvalueIdx}, + spans::LightSpan, + upvalues::Upvalues, + value::{ + Builtin, BuiltinResult, Closure, CoercionKind, Lambda, NixAttrs, NixList, PointerEquality, + SharedThunkSet, Thunk, Value, + }, + vm::generators::GenCo, + warnings::{EvalWarning, WarningKind}, +}; + +use generators::{call_functor, Generator, GeneratorState}; + +use self::generators::{VMRequest, VMResponse}; + +/// Internal helper trait for taking a span from a variety of types, to make use +/// of `WithSpan` (defined below) more ergonomic at call sites. +trait GetSpan { + fn get_span(self) -> Span; +} + +impl<'o> GetSpan for &VM<'o> { + fn get_span(self) -> Span { + self.reasonable_span.span() + } +} + +impl GetSpan for &CallFrame { + fn get_span(self) -> Span { + self.current_span() + } +} + +impl GetSpan for &LightSpan { + fn get_span(self) -> Span { + self.span() + } +} + +impl GetSpan for Span { + fn get_span(self) -> Span { + self + } +} + +/// Internal helper trait for ergonomically converting from a `Result<T, +/// ErrorKind>` to a `Result<T, Error>` using the current span of a call frame, +/// and chaining the VM's frame stack around it for printing a cause chain. +trait WithSpan<T, S: GetSpan> { + fn with_span(self, top_span: S, vm: &VM) -> Result<T, Error>; +} + +impl<T, S: GetSpan> WithSpan<T, S> for Result<T, ErrorKind> { + fn with_span(self, top_span: S, vm: &VM) -> Result<T, Error> { + match self { + Ok(something) => Ok(something), + Err(kind) => { + let mut error = Error::new(kind, top_span.get_span()); + + // Wrap the top-level error in chaining errors for each element + // of the frame stack. + for frame in vm.frames.iter().rev() { + match frame { + Frame::CallFrame { span, .. } => { + error = + Error::new(ErrorKind::BytecodeError(Box::new(error)), span.span()); + } + Frame::Generator { name, span, .. } => { + error = Error::new( + ErrorKind::NativeError { + err: Box::new(error), + gen_type: name, + }, + span.span(), + ); + } + } + } + + Err(error) + } + } + } +} + +struct CallFrame { + /// The lambda currently being executed. + lambda: Rc<Lambda>, + + /// Optional captured upvalues of this frame (if a thunk or + /// closure if being evaluated). + upvalues: Rc<Upvalues>, + + /// Instruction pointer to the instruction currently being + /// executed. + ip: CodeIdx, + + /// Stack offset, i.e. the frames "view" into the VM's full stack. + stack_offset: usize, +} + +impl CallFrame { + /// Retrieve an upvalue from this frame at the given index. + fn upvalue(&self, idx: UpvalueIdx) -> &Value { + &self.upvalues[idx] + } + + /// Borrow the chunk of this frame's lambda. + fn chunk(&self) -> &Chunk { + &self.lambda.chunk + } + + /// Increment this frame's instruction pointer and return the operation that + /// the pointer moved past. + fn inc_ip(&mut self) -> OpCode { + let op = self.chunk()[self.ip]; + self.ip += 1; + op + } + + /// Construct an error result from the given ErrorKind and the source span + /// of the current instruction. + pub fn error<T>(&self, vm: &VM, kind: ErrorKind) -> Result<T, Error> { + Err(kind).with_span(self, vm) + } + + /// Returns the current span. This is potentially expensive and should only + /// be used when actually constructing an error or warning. + pub fn current_span(&self) -> Span { + self.chunk().get_span(self.ip - 1) + } + + /// Returns the information needed to calculate the current span, + /// but without performing that calculation. + // TODO: why pub? + pub(crate) fn current_light_span(&self) -> LightSpan { + LightSpan::new_delayed(self.lambda.clone(), self.ip - 1) + } +} + +/// A frame represents an execution state of the VM. The VM has a stack of +/// frames representing the nesting of execution inside of the VM, and operates +/// on the frame at the top. +/// +/// When a frame has been fully executed, it is removed from the VM's frame +/// stack and expected to leave a result [`Value`] on the top of the stack. +enum Frame { + /// CallFrame represents the execution of Tvix bytecode within a thunk, + /// function or closure. + CallFrame { + /// The call frame itself, separated out into another type to pass it + /// around easily. + call_frame: CallFrame, + + /// Span from which the call frame was launched. + span: LightSpan, + }, + + /// Generator represents a frame that can yield further + /// instructions to the VM while its execution is being driven. + /// + /// A generator is essentially an asynchronous function that can + /// be suspended while waiting for the VM to do something (e.g. + /// thunk forcing), and resume at the same point. + Generator { + /// human-readable description of the generator, + name: &'static str, + + /// Span from which the generator was launched. + span: LightSpan, + + state: GeneratorState, + + /// Generator itself, which can be resumed with `.resume()`. + generator: Generator, + }, +} + +impl Frame { + pub fn span(&self) -> LightSpan { + match self { + Frame::CallFrame { span, .. } | Frame::Generator { span, .. } => span.clone(), + } + } +} + +#[derive(Default)] +struct ImportCache(HashMap<PathBuf, Value>); + +/// The `ImportCache` holds the `Value` resulting from `import`ing a certain +/// file, so that the same file doesn't need to be re-evaluated multiple times. +/// Currently the real path of the imported file (determined using +/// [`std::fs::canonicalize()`], not to be confused with our +/// [`crate::value::canon_path()`]) is used to identify the file, +/// just like C++ Nix does. +/// +/// Errors while determining the real path are currently just ignored, since we +/// pass around some fake paths like `/__corepkgs__/fetchurl.nix`. +/// +/// In the future, we could use something more sophisticated, like file hashes. +/// However, a consideration is that the eval cache is observable via impurities +/// like pointer equality and `builtins.trace`. +impl ImportCache { + fn get(&self, path: PathBuf) -> Option<&Value> { + let path = match std::fs::canonicalize(path.as_path()).map_err(ErrorKind::from) { + Ok(path) => path, + Err(_) => path, + }; + self.0.get(&path) + } + + fn insert(&mut self, path: PathBuf, value: Value) -> Option<Value> { + self.0.insert( + match std::fs::canonicalize(path.as_path()).map_err(ErrorKind::from) { + Ok(path) => path, + Err(_) => path, + }, + value, + ) + } +} + +struct VM<'o> { + /// VM's frame stack, representing the execution contexts the VM is working + /// through. Elements are usually pushed when functions are called, or + /// thunks are being forced. + frames: Vec<Frame>, + + /// The VM's top-level value stack. Within this stack, each code-executing + /// frame holds a "view" of the stack representing the slice of the + /// top-level stack that is relevant to its operation. This is done to avoid + /// allocating a new `Vec` for each frame's stack. + pub(crate) stack: Vec<Value>, + + /// Stack indices (absolute indexes into `stack`) of attribute + /// sets from which variables should be dynamically resolved + /// (`with`). + with_stack: Vec<usize>, + + /// Runtime warnings collected during evaluation. + warnings: Vec<EvalWarning>, + + /// Import cache, mapping absolute file paths to the value that + /// they compile to. Note that this reuses thunks, too! + // TODO: should probably be based on a file hash + pub import_cache: ImportCache, + + /// Parsed Nix search path, which is used to resolve `<...>` + /// references. + nix_search_path: NixSearchPath, + + /// Implementation of I/O operations used for impure builtins and + /// features like `import`. + io_handle: Box<dyn EvalIO>, + + /// Runtime observer which can print traces of runtime operations. + observer: &'o mut dyn RuntimeObserver, + + /// Strong reference to the globals, guaranteeing that they are + /// kept alive for the duration of evaluation. + /// + /// This is important because recursive builtins (specifically + /// `import`) hold a weak reference to the builtins, while the + /// original strong reference is held by the compiler which does + /// not exist anymore at runtime. + #[allow(dead_code)] + globals: Rc<GlobalsMap>, + + /// A reasonably applicable span that can be used for errors in each + /// execution situation. + /// + /// The VM should update this whenever control flow changes take place (i.e. + /// entering or exiting a frame to yield control somewhere). + reasonable_span: LightSpan, + + /// This field is responsible for handling `builtins.tryEval`. When that + /// builtin is encountered, it sends a special message to the VM which + /// pushes the frame index that requested to be informed of catchable + /// errors in this field. + /// + /// The frame stack is then laid out like this: + /// + /// ```notrust + /// ┌──┬──────────────────────────┐ + /// │ 0│ `Result`-producing frame │ + /// ├──┼──────────────────────────┤ + /// │-1│ `builtins.tryEval` frame │ + /// ├──┼──────────────────────────┤ + /// │..│ ... other frames ... │ + /// └──┴──────────────────────────┘ + /// ``` + /// + /// Control is yielded to the outer VM loop, which evaluates the next frame + /// and returns the result itself to the `builtins.tryEval` frame. + try_eval_frames: Vec<usize>, +} + +impl<'o> VM<'o> { + pub fn new( + nix_search_path: NixSearchPath, + io_handle: Box<dyn EvalIO>, + observer: &'o mut dyn RuntimeObserver, + globals: Rc<GlobalsMap>, + reasonable_span: LightSpan, + ) -> Self { + Self { + nix_search_path, + io_handle, + observer, + globals, + reasonable_span, + frames: vec![], + stack: vec![], + with_stack: vec![], + warnings: vec![], + import_cache: Default::default(), + try_eval_frames: vec![], + } + } + + /// Push a call frame onto the frame stack. + fn push_call_frame(&mut self, span: LightSpan, call_frame: CallFrame) { + self.frames.push(Frame::CallFrame { span, call_frame }) + } + + /// Run the VM's primary (outer) execution loop, continuing execution based + /// on the current frame at the top of the frame stack. + fn execute(mut self) -> EvalResult<RuntimeResult> { + while let Some(frame) = self.frames.pop() { + self.reasonable_span = frame.span(); + let frame_id = self.frames.len(); + + match frame { + Frame::CallFrame { call_frame, span } => { + self.observer + .observe_enter_call_frame(0, &call_frame.lambda, frame_id); + + match self.execute_bytecode(span, call_frame) { + Ok(true) => self.observer.observe_exit_call_frame(frame_id, &self.stack), + Ok(false) => self + .observer + .observe_suspend_call_frame(frame_id, &self.stack), + + Err(err) => return Err(err), + }; + } + + // Handle generator frames, which can request thunk forcing + // during their execution. + Frame::Generator { + name, + span, + state, + generator, + } => { + self.observer + .observe_enter_generator(frame_id, name, &self.stack); + + match self.run_generator(name, span, frame_id, state, generator, None) { + Ok(true) => { + self.observer + .observe_exit_generator(frame_id, name, &self.stack) + } + Ok(false) => { + self.observer + .observe_suspend_generator(frame_id, name, &self.stack) + } + + Err(err) => return Err(err), + }; + } + } + } + + // Once no more frames are present, return the stack's top value as the + // result. + let value = self + .stack + .pop() + .expect("tvix bug: runtime stack empty after execution"); + Ok(RuntimeResult { + value: value, + warnings: self.warnings, + }) + } + + /// Run the VM's inner execution loop, processing Tvix bytecode from a + /// chunk. This function returns if: + /// + /// 1. The code has run to the end, and has left a value on the top of the + /// stack. In this case, the frame is not returned to the frame stack. + /// + /// 2. The code encounters a generator, in which case the frame in its + /// current state is pushed back on the stack, and the generator is left on + /// top of it for the outer loop to execute. + /// + /// 3. An error is encountered. + /// + /// This function *must* ensure that it leaves the frame stack in the + /// correct order, especially when re-enqueuing a frame to execute. + /// + /// The return value indicates whether the bytecode has been executed to + /// completion, or whether it has been suspended in favour of a generator. + fn execute_bytecode(&mut self, span: LightSpan, mut frame: CallFrame) -> EvalResult<bool> { + loop { + let op = frame.inc_ip(); + self.observer.observe_execute_op(frame.ip, &op, &self.stack); + + match op { + OpCode::OpThunkSuspended(idx) | OpCode::OpThunkClosure(idx) => { + let blueprint = match &frame.chunk()[idx] { + Value::Blueprint(lambda) => lambda.clone(), + _ => panic!("compiler bug: non-blueprint in blueprint slot"), + }; + + let upvalue_count = blueprint.upvalue_count; + let thunk = if matches!(op, OpCode::OpThunkClosure(_)) { + debug_assert!( + upvalue_count > 0, + "OpThunkClosure should not be called for plain lambdas" + ); + Thunk::new_closure(blueprint) + } else { + Thunk::new_suspended(blueprint, frame.current_light_span()) + }; + let upvalues = thunk.upvalues_mut(); + self.stack.push(Value::Thunk(thunk.clone())); + + // From this point on we internally mutate the + // upvalues. The closure (if `is_closure`) is + // already in its stack slot, which means that it + // can capture itself as an upvalue for + // self-recursion. + self.populate_upvalues(&mut frame, upvalue_count, upvalues)?; + } + + OpCode::OpForce => { + if let Some(Value::Thunk(_)) = self.stack.last() { + let thunk = match self.stack_pop() { + Value::Thunk(t) => t, + _ => unreachable!(), + }; + + let gen_span = frame.current_light_span(); + + self.push_call_frame(span, frame); + self.enqueue_generator("force", gen_span.clone(), |co| { + thunk.force(co, gen_span) + }); + + return Ok(false); + } + } + + OpCode::OpGetUpvalue(upv_idx) => { + let value = frame.upvalue(upv_idx).clone(); + self.stack.push(value); + } + + // Discard the current frame. + OpCode::OpReturn => { + return Ok(true); + } + + OpCode::OpConstant(idx) => { + let c = frame.chunk()[idx].clone(); + self.stack.push(c); + } + + OpCode::OpCall => { + let callable = self.stack_pop(); + self.call_value(frame.current_light_span(), Some((span, frame)), callable)?; + + // exit this loop and let the outer loop enter the new call + return Ok(true); + } + + // Remove the given number of elements from the stack, + // but retain the top value. + OpCode::OpCloseScope(Count(count)) => { + // Immediately move the top value into the right + // position. + let target_idx = self.stack.len() - 1 - count; + self.stack[target_idx] = self.stack_pop(); + + // Then drop the remaining values. + for _ in 0..(count - 1) { + self.stack.pop(); + } + } + + OpCode::OpClosure(idx) => { + let blueprint = match &frame.chunk()[idx] { + Value::Blueprint(lambda) => lambda.clone(), + _ => panic!("compiler bug: non-blueprint in blueprint slot"), + }; + + let upvalue_count = blueprint.upvalue_count; + debug_assert!( + upvalue_count > 0, + "OpClosure should not be called for plain lambdas" + ); + + let mut upvalues = Upvalues::with_capacity(blueprint.upvalue_count); + self.populate_upvalues(&mut frame, upvalue_count, &mut upvalues)?; + self.stack + .push(Value::Closure(Rc::new(Closure::new_with_upvalues( + Rc::new(upvalues), + blueprint, + )))); + } + + OpCode::OpAttrsSelect => { + let key = self.stack_pop().to_str().with_span(&frame, self)?; + let attrs = self.stack_pop().to_attrs().with_span(&frame, self)?; + + match attrs.select(key.as_str()) { + Some(value) => self.stack.push(value.clone()), + + None => { + return frame.error( + self, + ErrorKind::AttributeNotFound { + name: key.as_str().to_string(), + }, + ); + } + } + } + + OpCode::OpJumpIfFalse(JumpOffset(offset)) => { + debug_assert!(offset != 0); + if !self.stack_peek(0).as_bool().with_span(&frame, self)? { + frame.ip += offset; + } + } + + OpCode::OpJumpIfNoFinaliseRequest(JumpOffset(offset)) => { + debug_assert!(offset != 0); + match self.stack_peek(0) { + Value::FinaliseRequest(finalise) => { + if !finalise { + frame.ip += offset; + } + }, + val => panic!("Tvix bug: OpJumIfNoFinaliseRequest: expected FinaliseRequest, but got {}", val.type_of()), + } + } + + OpCode::OpPop => { + self.stack.pop(); + } + + OpCode::OpAttrsTrySelect => { + let key = self.stack_pop().to_str().with_span(&frame, self)?; + let value = match self.stack_pop() { + Value::Attrs(attrs) => match attrs.select(key.as_str()) { + Some(value) => value.clone(), + None => Value::AttrNotFound, + }, + + _ => Value::AttrNotFound, + }; + + self.stack.push(value); + } + + OpCode::OpGetLocal(StackIdx(local_idx)) => { + let idx = frame.stack_offset + local_idx; + self.stack.push(self.stack[idx].clone()); + } + + OpCode::OpJumpIfNotFound(JumpOffset(offset)) => { + debug_assert!(offset != 0); + if matches!(self.stack_peek(0), Value::AttrNotFound) { + self.stack_pop(); + frame.ip += offset; + } + } + + OpCode::OpJump(JumpOffset(offset)) => { + debug_assert!(offset != 0); + frame.ip += offset; + } + + OpCode::OpEqual => { + let b = self.stack_pop(); + let a = self.stack_pop(); + let gen_span = frame.current_light_span(); + self.push_call_frame(span, frame); + self.enqueue_generator("nix_eq", gen_span, |co| { + a.nix_eq(b, co, PointerEquality::ForbidAll) + }); + return Ok(false); + } + + // These assertion operations error out if the stack + // top is not of the expected type. This is necessary + // to implement some specific behaviours of Nix + // exactly. + OpCode::OpAssertBool => { + let val = self.stack_peek(0); + if !val.is_bool() { + return frame.error( + self, + ErrorKind::TypeError { + expected: "bool", + actual: val.type_of(), + }, + ); + } + } + + OpCode::OpAssertAttrs => { + let val = self.stack_peek(0); + if !val.is_attrs() { + return frame.error( + self, + ErrorKind::TypeError { + expected: "set", + actual: val.type_of(), + }, + ); + } + } + + OpCode::OpAttrs(Count(count)) => self.run_attrset(&frame, count)?, + + OpCode::OpAttrsUpdate => { + let rhs = self.stack_pop().to_attrs().with_span(&frame, self)?; + let lhs = self.stack_pop().to_attrs().with_span(&frame, self)?; + + self.stack.push(Value::attrs(lhs.update(*rhs))) + } + + OpCode::OpInvert => { + let v = self.stack_pop().as_bool().with_span(&frame, self)?; + self.stack.push(Value::Bool(!v)); + } + + OpCode::OpList(Count(count)) => { + let list = + NixList::construct(count, self.stack.split_off(self.stack.len() - count)); + + self.stack.push(Value::List(list)); + } + + OpCode::OpJumpIfTrue(JumpOffset(offset)) => { + debug_assert!(offset != 0); + if self.stack_peek(0).as_bool().with_span(&frame, self)? { + frame.ip += offset; + } + } + + OpCode::OpHasAttr => { + let key = self.stack_pop().to_str().with_span(&frame, self)?; + let result = match self.stack_pop() { + Value::Attrs(attrs) => attrs.contains(key.as_str()), + + // Nix allows use of `?` on non-set types, but + // always returns false in those cases. + _ => false, + }; + + self.stack.push(Value::Bool(result)); + } + + OpCode::OpConcat => { + let rhs = self + .stack_pop() + .to_list() + .with_span(&frame, self)? + .into_inner(); + let lhs = self + .stack_pop() + .to_list() + .with_span(&frame, self)? + .into_inner(); + self.stack.push(Value::List(NixList::from(lhs + rhs))) + } + + OpCode::OpResolveWith => { + let ident = self.stack_pop().to_str().with_span(&frame, self)?; + + // Re-enqueue this frame. + let op_span = frame.current_light_span(); + self.push_call_frame(span, frame); + + // Construct a generator frame doing the lookup in constant + // stack space. + let with_stack_len = self.with_stack.len(); + let closed_with_stack_len = self + .last_call_frame() + .map(|frame| frame.upvalues.with_stack_len()) + .unwrap_or(0); + + self.enqueue_generator("resolve_with", op_span, |co| { + resolve_with( + co, + ident.as_str().to_owned(), + with_stack_len, + closed_with_stack_len, + ) + }); + + return Ok(false); + } + + OpCode::OpFinalise(StackIdx(idx)) => match &self.stack[frame.stack_offset + idx] { + Value::Closure(_) => panic!("attempted to finalise a closure"), + Value::Thunk(thunk) => thunk.finalise(&self.stack[frame.stack_offset..]), + _ => panic!("attempted to finalise a non-thunk"), + }, + + OpCode::OpCoerceToString => { + let value = self.stack_pop(); + let gen_span = frame.current_light_span(); + self.push_call_frame(span, frame); + + self.enqueue_generator("coerce_to_string", gen_span, |co| { + value.coerce_to_string(co, CoercionKind::Weak) + }); + + return Ok(false); + } + + OpCode::OpInterpolate(Count(count)) => self.run_interpolate(&frame, count)?, + + OpCode::OpValidateClosedFormals => { + let formals = frame.lambda.formals.as_ref().expect( + "OpValidateClosedFormals called within the frame of a lambda without formals", + ); + + let args = self.stack_peek(0).to_attrs().with_span(&frame, self)?; + for arg in args.keys() { + if !formals.contains(arg) { + return frame.error( + self, + ErrorKind::UnexpectedArgument { + arg: arg.clone(), + formals_span: formals.span, + }, + ); + } + } + } + + OpCode::OpAdd => { + let b = self.stack_pop(); + let a = self.stack_pop(); + + let gen_span = frame.current_light_span(); + self.push_call_frame(span, frame); + + // OpAdd can add not just numbers, but also string-like + // things, which requires more VM logic. This operation is + // evaluated in a generator frame. + self.enqueue_generator("add_values", gen_span, |co| add_values(co, a, b)); + return Ok(false); + } + + OpCode::OpSub => { + let b = self.stack_pop(); + let a = self.stack_pop(); + let result = arithmetic_op!(&a, &b, -).with_span(&frame, self)?; + self.stack.push(result); + } + + OpCode::OpMul => { + let b = self.stack_pop(); + let a = self.stack_pop(); + let result = arithmetic_op!(&a, &b, *).with_span(&frame, self)?; + self.stack.push(result); + } + + OpCode::OpDiv => { + let b = self.stack_pop(); + + match b { + Value::Integer(0) => return frame.error(self, ErrorKind::DivisionByZero), + Value::Float(b) if b == 0.0_f64 => { + return frame.error(self, ErrorKind::DivisionByZero) + } + _ => {} + }; + + let a = self.stack_pop(); + let result = arithmetic_op!(&a, &b, /).with_span(&frame, self)?; + self.stack.push(result); + } + + OpCode::OpNegate => match self.stack_pop() { + Value::Integer(i) => self.stack.push(Value::Integer(-i)), + Value::Float(f) => self.stack.push(Value::Float(-f)), + v => { + return frame.error( + self, + ErrorKind::TypeError { + expected: "number (either int or float)", + actual: v.type_of(), + }, + ); + } + }, + + OpCode::OpLess => cmp_op!(self, frame, span, <), + OpCode::OpLessOrEq => cmp_op!(self, frame, span, <=), + OpCode::OpMore => cmp_op!(self, frame, span, >), + OpCode::OpMoreOrEq => cmp_op!(self, frame, span, >=), + + OpCode::OpFindFile => match self.stack_pop() { + Value::UnresolvedPath(path) => { + let resolved = self + .nix_search_path + .resolve(&mut *self.io_handle, *path) + .with_span(&frame, self)?; + self.stack.push(resolved.into()); + } + + _ => panic!("tvix compiler bug: OpFindFile called on non-UnresolvedPath"), + }, + + OpCode::OpResolveHomePath => match self.stack_pop() { + Value::UnresolvedPath(path) => { + match dirs::home_dir() { + None => { + return frame.error( + self, + ErrorKind::RelativePathResolution( + "failed to determine home directory".into(), + ), + ); + } + Some(mut buf) => { + buf.push(*path); + self.stack.push(buf.into()); + } + }; + } + + _ => { + panic!("tvix compiler bug: OpResolveHomePath called on non-UnresolvedPath") + } + }, + + OpCode::OpPushWith(StackIdx(idx)) => self.with_stack.push(frame.stack_offset + idx), + + OpCode::OpPopWith => { + self.with_stack.pop(); + } + + OpCode::OpAssertFail => { + self.stack + .push(Value::Catchable(CatchableErrorKind::AssertionFailed)); + } + + // Data-carrying operands should never be executed, + // that is a critical error in the VM/compiler. + OpCode::DataStackIdx(_) + | OpCode::DataDeferredLocal(_) + | OpCode::DataUpvalueIdx(_) + | OpCode::DataCaptureWith => { + panic!("Tvix bug: attempted to execute data-carrying operand") + } + } + } + } +} + +/// Implementation of helper functions for the runtime logic above. +impl<'o> VM<'o> { + pub(crate) fn stack_pop(&mut self) -> Value { + self.stack.pop().expect("runtime stack empty") + } + + fn stack_peek(&self, offset: usize) -> &Value { + &self.stack[self.stack.len() - 1 - offset] + } + + fn run_attrset(&mut self, frame: &CallFrame, count: usize) -> EvalResult<()> { + let attrs = NixAttrs::construct(count, self.stack.split_off(self.stack.len() - count * 2)) + .with_span(frame, self)?; + + self.stack.push(Value::attrs(attrs)); + Ok(()) + } + + /// Access the last call frame present in the frame stack. + fn last_call_frame(&self) -> Option<&CallFrame> { + for frame in self.frames.iter().rev() { + if let Frame::CallFrame { call_frame, .. } = frame { + return Some(call_frame); + } + } + + None + } + + /// Push an already constructed warning. + pub fn push_warning(&mut self, warning: EvalWarning) { + self.warnings.push(warning); + } + + /// Emit a warning with the given WarningKind and the source span + /// of the current instruction. + pub fn emit_warning(&mut self, _kind: WarningKind) { + // TODO: put LightSpan in warning, calculate only *after* eval + // TODO: what to do with the spans? + // self.push_warning(EvalWarning { + // kind, + // span: self.current_span(), + // }); + } + + /// Interpolate string fragments by popping the specified number of + /// fragments of the stack, evaluating them to strings, and pushing + /// the concatenated result string back on the stack. + fn run_interpolate(&mut self, frame: &CallFrame, count: usize) -> EvalResult<()> { + let mut out = String::new(); + + for _ in 0..count { + out.push_str(self.stack_pop().to_str().with_span(frame, self)?.as_str()); + } + + self.stack.push(Value::String(out.into())); + Ok(()) + } + + /// Returns a reasonable light span for the current situation that the VM is + /// in. + pub fn reasonable_light_span(&self) -> LightSpan { + self.reasonable_span.clone() + } + + /// Apply an argument from the stack to a builtin, and attempt to call it. + /// + /// All calls are tail-calls in Tvix, as every function application is a + /// separate thunk and OpCall is thus the last result in the thunk. + /// + /// Due to this, once control flow exits this function, the generator will + /// automatically be run by the VM. + fn call_builtin(&mut self, span: LightSpan, mut builtin: Builtin) -> EvalResult<()> { + let builtin_name = builtin.name(); + self.observer.observe_enter_builtin(builtin_name); + + builtin.apply_arg(self.stack_pop()); + + match builtin.call() { + // Partially applied builtin is just pushed back on the stack. + BuiltinResult::Partial(partial) => self.stack.push(Value::Builtin(partial)), + + // Builtin is fully applied and the generator needs to be run by the VM. + BuiltinResult::Called(name, generator) => self.frames.push(Frame::Generator { + generator, + span, + name, + state: GeneratorState::Running, + }), + } + + Ok(()) + } + + fn call_value( + &mut self, + span: LightSpan, + parent: Option<(LightSpan, CallFrame)>, + callable: Value, + ) -> EvalResult<()> { + match callable { + Value::Builtin(builtin) => self.call_builtin(span, builtin), + Value::Thunk(thunk) => self.call_value(span, parent, thunk.value().clone()), + + Value::Closure(closure) => { + let lambda = closure.lambda(); + self.observer.observe_tail_call(self.frames.len(), &lambda); + + // The stack offset is always `stack.len() - arg_count`, and + // since this branch handles native Nix functions (which always + // take only a single argument and are curried), the offset is + // `stack_len - 1`. + let stack_offset = self.stack.len() - 1; + + // Reenqueue the parent frame, which should only have + // `OpReturn` left. Not throwing it away leads to more + // useful error traces. + if let Some((parent_span, parent_frame)) = parent { + self.push_call_frame(parent_span, parent_frame); + } + + self.push_call_frame( + span, + CallFrame { + lambda, + upvalues: closure.upvalues(), + ip: CodeIdx(0), + stack_offset, + }, + ); + + Ok(()) + } + + // Attribute sets with a __functor attribute are callable. + val @ Value::Attrs(_) => { + if let Some((parent_span, parent_frame)) = parent { + self.push_call_frame(parent_span, parent_frame); + } + + self.enqueue_generator("__functor call", span, |co| call_functor(co, val)); + Ok(()) + } + v => Err(ErrorKind::NotCallable(v.type_of())).with_span(&span, self), + } + } + + /// Populate the upvalue fields of a thunk or closure under construction. + fn populate_upvalues( + &mut self, + frame: &mut CallFrame, + count: usize, + mut upvalues: impl DerefMut<Target = Upvalues>, + ) -> EvalResult<()> { + for _ in 0..count { + match frame.inc_ip() { + OpCode::DataStackIdx(StackIdx(stack_idx)) => { + let idx = frame.stack_offset + stack_idx; + + let val = match self.stack.get(idx) { + Some(val) => val.clone(), + None => { + return frame.error( + self, + ErrorKind::TvixBug { + msg: "upvalue to be captured was missing on stack", + metadata: Some(Rc::new(json!({ + "ip": format!("{:#x}", frame.ip.0 - 1), + "stack_idx(relative)": stack_idx, + "stack_idx(absolute)": idx, + }))), + }, + ); + } + }; + + upvalues.deref_mut().push(val); + } + + OpCode::DataUpvalueIdx(upv_idx) => { + upvalues.deref_mut().push(frame.upvalue(upv_idx).clone()); + } + + OpCode::DataDeferredLocal(idx) => { + upvalues.deref_mut().push(Value::DeferredUpvalue(idx)); + } + + OpCode::DataCaptureWith => { + // Start the captured with_stack off of the + // current call frame's captured with_stack, ... + let mut captured_with_stack = frame + .upvalues + .with_stack() + .map(Clone::clone) + // ... or make an empty one if there isn't one already. + .unwrap_or_else(|| Vec::with_capacity(self.with_stack.len())); + + for idx in &self.with_stack { + captured_with_stack.push(self.stack[*idx].clone()); + } + + upvalues.deref_mut().set_with_stack(captured_with_stack); + } + + _ => panic!("compiler error: missing closure operand"), + } + } + + Ok(()) + } +} + +// TODO(amjoseph): de-asyncify this +/// Resolve a dynamically bound identifier (through `with`) by looking +/// for matching values in the with-stacks carried at runtime. +async fn resolve_with( + co: GenCo, + ident: String, + vm_with_len: usize, + upvalue_with_len: usize, +) -> Result<Value, ErrorKind> { + /// Fetch and force a value on the with-stack from the VM. + async fn fetch_forced_with(co: &GenCo, idx: usize) -> Value { + match co.yield_(VMRequest::WithValue(idx)).await { + VMResponse::Value(value) => value, + msg => panic!( + "Tvix bug: VM responded with incorrect generator message: {}", + msg + ), + } + } + + /// Fetch and force a value on the *captured* with-stack from the VM. + async fn fetch_captured_with(co: &GenCo, idx: usize) -> Value { + match co.yield_(VMRequest::CapturedWithValue(idx)).await { + VMResponse::Value(value) => value, + msg => panic!( + "Tvix bug: VM responded with incorrect generator message: {}", + msg + ), + } + } + + for with_stack_idx in (0..vm_with_len).rev() { + // TODO(tazjin): is this branch still live with the current with-thunking? + let with = fetch_forced_with(&co, with_stack_idx).await; + + match with.to_attrs()?.select(&ident) { + None => continue, + Some(val) => return Ok(val.clone()), + } + } + + for upvalue_with_idx in (0..upvalue_with_len).rev() { + let with = fetch_captured_with(&co, upvalue_with_idx).await; + + match with.to_attrs()?.select(&ident) { + None => continue, + Some(val) => return Ok(val.clone()), + } + } + + Err(ErrorKind::UnknownDynamicVariable(ident)) +} + +// TODO(amjoseph): de-asyncify this +async fn add_values(co: GenCo, a: Value, b: Value) -> Result<Value, ErrorKind> { + let result = match (a, b) { + (Value::Path(p), v) => { + let mut path = p.to_string_lossy().into_owned(); + match generators::request_string_coerce(&co, v, CoercionKind::Weak).await { + Ok(vs) => { + path.push_str(vs.as_str()); + crate::value::canon_path(PathBuf::from(path)).into() + } + Err(c) => Value::Catchable(c), + } + } + (Value::String(s1), Value::String(s2)) => Value::String(s1.concat(&s2)), + (Value::String(s1), v) => Value::String( + match generators::request_string_coerce(&co, v, CoercionKind::Weak).await { + Ok(s2) => s1.concat(&s2), + Err(c) => return Ok(Value::Catchable(c)), + }, + ), + (v, Value::String(s2)) => Value::String( + match generators::request_string_coerce(&co, v, CoercionKind::Weak).await { + Ok(s1) => s1.concat(&s2), + Err(c) => return Ok(Value::Catchable(c)), + }, + ), + (a, b) => arithmetic_op!(&a, &b, +)?, + }; + + Ok(result) +} + +/// The result of a VM's runtime evaluation. +pub struct RuntimeResult { + pub value: Value, + pub warnings: Vec<EvalWarning>, +} + +// TODO(amjoseph): de-asyncify this +/// Generator that retrieves the final value from the stack, and deep-forces it +/// before returning. +async fn final_deep_force(co: GenCo) -> Result<Value, ErrorKind> { + let value = generators::request_stack_pop(&co).await; + Ok(generators::request_deep_force(&co, value, SharedThunkSet::default()).await) +} + +pub fn run_lambda( + nix_search_path: NixSearchPath, + io_handle: Box<dyn EvalIO>, + observer: &mut dyn RuntimeObserver, + globals: Rc<GlobalsMap>, + lambda: Rc<Lambda>, + strict: bool, +) -> EvalResult<RuntimeResult> { + // Retain the top-level span of the expression in this lambda, as + // synthetic "calls" in deep_force will otherwise not have a span + // to fall back to. + // + // We exploit the fact that the compiler emits a final instruction + // with the span of the entire file for top-level expressions. + let root_span = lambda.chunk.get_span(CodeIdx(lambda.chunk.code.len() - 1)); + + let mut vm = VM::new( + nix_search_path, + io_handle, + observer, + globals, + root_span.into(), + ); + + // When evaluating strictly, synthesise a frame that will instruct + // the VM to deep-force the final value before returning it. + if strict { + vm.enqueue_generator("final_deep_force", root_span.into(), final_deep_force); + } + + vm.frames.push(Frame::CallFrame { + span: root_span.into(), + call_frame: CallFrame { + lambda, + upvalues: Rc::new(Upvalues::with_capacity(0)), + ip: CodeIdx(0), + stack_offset: 0, + }, + }); + + vm.execute() +} |