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Diffstat (limited to 'tvix/eval/src/vm/generators.rs')
| -rw-r--r-- | tvix/eval/src/vm/generators.rs | 538 |
1 files changed, 538 insertions, 0 deletions
diff --git a/tvix/eval/src/vm/generators.rs b/tvix/eval/src/vm/generators.rs new file mode 100644 index 0000000000..3b822b0863 --- /dev/null +++ b/tvix/eval/src/vm/generators.rs @@ -0,0 +1,538 @@ +//! 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 smol_str::SmolStr; +use std::fmt::Display; +use std::future::Future; + +use crate::value::SharedThunkSet; +use crate::warnings::WarningKind; +use crate::FileType; +use crate::NixString; + +use super::*; + +/// Dummy type, before the actual implementation is in place. +#[derive(Debug)] +pub struct PointerEquality {} + +// -- 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 GeneratorRequest { + /// 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 + /// a `NoOp`. + 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 through the VM. Receives a NoOp-response. + EmitWarning(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), +} + +/// Human-readable representation of a generator message, used by observers. +impl Display for GeneratorRequest { + fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result { + match self { + GeneratorRequest::ForceValue(v) => write!(f, "force_value({})", v), + GeneratorRequest::DeepForceValue(v, _) => write!(f, "deep_force_value({})", v), + GeneratorRequest::WithValue(_) => write!(f, "with_value"), + GeneratorRequest::CapturedWithValue(_) => write!(f, "captured_with_value"), + GeneratorRequest::NixEquality(values, ptr_eq) => { + write!( + f, + "nix_eq({}, {}, PointerEquality::{:?})", + values.0, values.1, ptr_eq + ) + } + GeneratorRequest::StackPush(v) => write!(f, "stack_push({})", v), + GeneratorRequest::StackPop => write!(f, "stack_pop"), + GeneratorRequest::StringCoerce(v, kind) => match kind { + CoercionKind::Weak => write!(f, "weak_string_coerce({})", v), + CoercionKind::Strong => write!(f, "strong_string_coerce({})", v), + CoercionKind::ThunksOnly => todo!("remove this branch (not live)"), + }, + GeneratorRequest::Call(v) => write!(f, "call({})", v), + GeneratorRequest::EnterLambda { lambda, .. } => { + write!(f, "enter_lambda({:p})", *lambda) + } + GeneratorRequest::EmitWarning(_) => write!(f, "emit_warning"), + GeneratorRequest::ImportCacheLookup(p) => { + write!(f, "import_cache_lookup({})", p.to_string_lossy()) + } + GeneratorRequest::ImportCachePut(p, _) => { + write!(f, "import_cache_put({})", p.to_string_lossy()) + } + GeneratorRequest::PathImport(p) => write!(f, "path_import({})", p.to_string_lossy()), + GeneratorRequest::ReadToString(p) => { + write!(f, "read_to_string({})", p.to_string_lossy()) + } + GeneratorRequest::PathExists(p) => write!(f, "path_exists({})", p.to_string_lossy()), + GeneratorRequest::ReadDir(p) => write!(f, "read_dir({})", p.to_string_lossy()), + GeneratorRequest::Span => write!(f, "span"), + GeneratorRequest::TryForce(v) => write!(f, "try_force({})", v), + } + } +} + +/// Responses returned to generators from the VM. +pub enum GeneratorResponse { + /// 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<(SmolStr, FileType)>), + + /// VM response with a span to use at the current point. + Span(LightSpan), + + /// Message returned by the VM when a catchable error is encountered during + /// the evaluation of `builtins.tryEval`. + ForceError, +} + +impl Display for GeneratorResponse { + fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result { + match self { + GeneratorResponse::Empty => write!(f, "empty"), + GeneratorResponse::Value(v) => write!(f, "value({})", v), + GeneratorResponse::Path(p) => write!(f, "path({})", p.to_string_lossy()), + GeneratorResponse::Directory(d) => write!(f, "dir(len = {})", d.len()), + GeneratorResponse::Span(_) => write!(f, "span"), + GeneratorResponse::ForceError => write!(f, "force_error"), + } + } +} + +pub(crate) type Generator = Gen< + GeneratorRequest, + GeneratorResponse, + 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) +} + +pub type GenCo = Co<GeneratorRequest, GeneratorResponse>; + +// -- 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_(GeneratorRequest::StackPush(val)).await { + GeneratorResponse::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_(GeneratorRequest::StackPop).await { + GeneratorResponse::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_(GeneratorRequest::ForceValue(val)).await { + GeneratorResponse::Value(value) => value, + msg => panic!( + "Tvix bug: VM responded with incorrect generator message: {}", + msg + ), + } + } else { + val + } +} + +/// Force a value, but inform the caller (by returning `None`) if a catchable +/// error occured. +pub(crate) async fn request_try_force(co: &GenCo, val: Value) -> Option<Value> { + if let Value::Thunk(_) = val { + match co.yield_(GeneratorRequest::TryForce(val)).await { + GeneratorResponse::Value(value) => Some(value), + GeneratorResponse::ForceError => None, + msg => panic!( + "Tvix bug: VM responded with incorrect generator message: {}", + msg + ), + } + } else { + Some(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_(GeneratorRequest::Call(val)).await { + GeneratorResponse::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) -> NixString { + match val { + Value::String(s) => s, + _ => match co.yield_(GeneratorRequest::StringCoerce(val, kind)).await { + GeneratorResponse::Value(value) => 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_(GeneratorRequest::DeepForceValue(val, thunk_set)) + .await + { + GeneratorResponse::Value(value) => value, + msg => panic!( + "Tvix bug: VM responded with incorrect generator message: {}", + msg + ), + } +} + +/// 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_(GeneratorRequest::WithValue(idx)).await { + GeneratorResponse::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_(GeneratorRequest::CapturedWithValue(idx)).await { + GeneratorResponse::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_(GeneratorRequest::NixEquality(Box::new((a, b)), ptr_eq)) + .await + { + GeneratorResponse::Value(value) => value.as_bool(), + msg => panic!( + "Tvix bug: VM responded with incorrect generator message: {}", + msg + ), + } +} + +/// Emit a runtime warning. +pub(crate) async fn emit_warning(co: &GenCo, kind: WarningKind) { + match co.yield_(GeneratorRequest::EmitWarning(kind)).await { + GeneratorResponse::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 = GeneratorRequest::EnterLambda { + lambda, + upvalues, + light_span, + }; + + match co.yield_(msg).await { + GeneratorResponse::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_(GeneratorRequest::ImportCacheLookup(path)).await { + GeneratorResponse::Value(value) => Some(value), + GeneratorResponse::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_(GeneratorRequest::ImportCachePut(path, value)) + .await + { + GeneratorResponse::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_(GeneratorRequest::PathImport(path)).await { + GeneratorResponse::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_(GeneratorRequest::ReadToString(path)).await { + GeneratorResponse::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_(GeneratorRequest::PathExists(path)).await { + GeneratorResponse::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<(SmolStr, FileType)> { + match co.yield_(GeneratorRequest::ReadDir(path)).await { + GeneratorResponse::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_(GeneratorRequest::Span).await { + GeneratorResponse::Span(span) => span, + msg => panic!( + "Tvix bug: VM responded with incorrect generator message: {}", + msg + ), + } +} + +pub(crate) async fn neo_resolve_with( + co: GenCo, + ident: String, + vm_with_len: usize, + upvalue_with_len: usize, +) -> Result<Value, ErrorKind> { + 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)) +} + +/// 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) + } + } +} |