6c4b9bdce9
This function is reusable between thunks & closures. Change-Id: I44d5f9897b087a385c8e75027d2ff39c48a096f0 Reviewed-on: https://cl.tvl.fyi/c/depot/+/6349 Tested-by: BuildkiteCI Reviewed-by: sterni <sternenseemann@systemli.org>
596 lines
20 KiB
Rust
596 lines
20 KiB
Rust
//! This module implements the virtual (or abstract) machine that runs
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//! Tvix bytecode.
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use std::{cell::RefMut, rc::Rc};
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use crate::{
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chunk::Chunk,
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errors::{Error, ErrorKind, EvalResult},
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opcode::{ConstantIdx, Count, JumpOffset, OpCode, StackIdx, UpvalueIdx},
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upvalues::UpvalueCarrier,
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value::{Closure, Lambda, NixAttrs, NixList, Value},
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};
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#[cfg(feature = "disassembler")]
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use crate::disassembler::Tracer;
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struct CallFrame {
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lambda: Rc<Lambda>,
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upvalues: Vec<Value>,
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ip: usize,
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stack_offset: usize,
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}
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impl CallFrame {
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/// Retrieve an upvalue from this frame at the given index.
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fn upvalue(&self, idx: UpvalueIdx) -> &Value {
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&self.upvalues[idx.0]
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}
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}
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pub struct VM {
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frames: Vec<CallFrame>,
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stack: Vec<Value>,
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// Stack indices of attribute sets from which variables should be
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// dynamically resolved (`with`).
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with_stack: Vec<usize>,
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}
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macro_rules! arithmetic_op {
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( $self:ident, $op:tt ) => {{
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let b = $self.pop();
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let a = $self.pop();
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let result = arithmetic_op!(a, b, $op);
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$self.push(result);
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}};
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( $a:ident, $b:ident, $op:tt ) => {{
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match ($a, $b) {
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(Value::Integer(i1), Value::Integer(i2)) => Value::Integer(i1 $op i2),
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(Value::Float(f1), Value::Float(f2)) => Value::Float(f1 $op f2),
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(Value::Integer(i1), Value::Float(f2)) => Value::Float(i1 as f64 $op f2),
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(Value::Float(f1), Value::Integer(i2)) => Value::Float(f1 $op i2 as f64),
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(v1, v2) => return Err(ErrorKind::TypeError {
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expected: "number (either int or float)",
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actual: if v1.is_number() {
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v2.type_of()
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} else {
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v1.type_of()
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},
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}.into()),
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}
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}};
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}
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macro_rules! cmp_op {
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( $self:ident, $op:tt ) => {{
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let b = $self.pop();
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let a = $self.pop();
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// Comparable (in terms of ordering) values are numbers and
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// strings. Numbers need to be coerced similarly to arithmetic
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// ops if mixed types are encountered.
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let result = match (a, b) {
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(Value::Integer(i1), Value::Integer(i2)) => i1 $op i2,
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(Value::Float(f1), Value::Float(f2)) => f1 $op f2,
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(Value::Integer(i1), Value::Float(f2)) => (i1 as f64) $op f2,
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(Value::Float(f1), Value::Integer(i2)) => f1 $op (i2 as f64),
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(Value::String(s1), Value::String(s2)) => s1 $op s2,
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(lhs, rhs) => return Err(ErrorKind::Incomparable {
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lhs: lhs.type_of(),
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rhs: rhs.type_of(),
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}.into()),
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};
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$self.push(Value::Bool(result));
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}};
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}
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impl VM {
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fn frame(&self) -> &CallFrame {
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&self.frames[self.frames.len() - 1]
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}
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fn chunk(&self) -> &Chunk {
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&self.frame().lambda.chunk
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}
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fn frame_mut(&mut self) -> &mut CallFrame {
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let idx = self.frames.len() - 1;
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&mut self.frames[idx]
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}
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fn inc_ip(&mut self) -> OpCode {
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let op = self.chunk().code[self.frame().ip];
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self.frame_mut().ip += 1;
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op
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}
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fn peek_op(&self) -> OpCode {
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self.chunk().code[self.frame().ip]
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}
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fn pop(&mut self) -> Value {
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self.stack.pop().expect("runtime stack empty")
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}
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fn push(&mut self, value: Value) {
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self.stack.push(value)
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}
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fn peek(&self, offset: usize) -> &Value {
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&self.stack[self.stack.len() - 1 - offset]
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}
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pub fn call(&mut self, lambda: Rc<Lambda>, upvalues: Vec<Value>, arg_count: usize) {
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let frame = CallFrame {
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lambda,
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upvalues,
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ip: 0,
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stack_offset: self.stack.len() - arg_count,
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};
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self.frames.push(frame);
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}
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fn run(&mut self) -> EvalResult<Value> {
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#[cfg(feature = "disassembler")]
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let mut tracer = Tracer::new();
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loop {
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if self.frame().ip == self.chunk().code.len() {
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// If this is the end of the top-level function,
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// return, otherwise pop the call frame.
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if self.frames.len() == 1 {
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return Ok(self.pop());
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}
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self.frames.pop();
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continue;
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}
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let op = self.inc_ip();
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match op {
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OpCode::OpConstant(idx) => {
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let c = self.chunk().constant(idx).clone();
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self.push(c);
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}
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OpCode::OpPop => {
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self.pop();
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}
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OpCode::OpAdd => {
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let b = self.pop();
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let a = self.pop();
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let result = if let (Value::String(s1), Value::String(s2)) = (&a, &b) {
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Value::String(s1.concat(s2))
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} else {
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arithmetic_op!(a, b, +)
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};
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self.push(result)
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}
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OpCode::OpSub => arithmetic_op!(self, -),
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OpCode::OpMul => arithmetic_op!(self, *),
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OpCode::OpDiv => arithmetic_op!(self, /),
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OpCode::OpInvert => {
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let v = self.pop().as_bool()?;
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self.push(Value::Bool(!v));
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}
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OpCode::OpNegate => match self.pop() {
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Value::Integer(i) => self.push(Value::Integer(-i)),
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Value::Float(f) => self.push(Value::Float(-f)),
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v => {
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return Err(ErrorKind::TypeError {
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expected: "number (either int or float)",
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actual: v.type_of(),
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}
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.into())
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}
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},
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OpCode::OpEqual => {
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let v2 = self.pop();
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let v1 = self.pop();
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self.push(Value::Bool(v1 == v2))
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}
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OpCode::OpLess => cmp_op!(self, <),
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OpCode::OpLessOrEq => cmp_op!(self, <=),
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OpCode::OpMore => cmp_op!(self, >),
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OpCode::OpMoreOrEq => cmp_op!(self, >=),
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OpCode::OpNull => self.push(Value::Null),
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OpCode::OpTrue => self.push(Value::Bool(true)),
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OpCode::OpFalse => self.push(Value::Bool(false)),
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OpCode::OpAttrs(Count(count)) => self.run_attrset(count)?,
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OpCode::OpAttrPath(Count(count)) => self.run_attr_path(count)?,
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OpCode::OpAttrsUpdate => {
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let rhs = unwrap_or_clone_rc(self.pop().to_attrs()?);
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let lhs = unwrap_or_clone_rc(self.pop().to_attrs()?);
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self.push(Value::Attrs(Rc::new(lhs.update(rhs))))
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}
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OpCode::OpAttrsSelect => {
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let key = self.pop().to_string()?;
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let attrs = self.pop().to_attrs()?;
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match attrs.select(key.as_str()) {
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Some(value) => self.push(value.clone()),
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None => {
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return Err(ErrorKind::AttributeNotFound {
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name: key.as_str().to_string(),
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}
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.into())
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}
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}
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}
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OpCode::OpAttrsTrySelect => {
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let key = self.pop().to_string()?;
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let value = match self.pop() {
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Value::Attrs(attrs) => match attrs.select(key.as_str()) {
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Some(value) => value.clone(),
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None => Value::AttrNotFound,
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},
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_ => Value::AttrNotFound,
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};
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self.push(value);
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}
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OpCode::OpAttrsIsSet => {
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let key = self.pop().to_string()?;
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let result = match self.pop() {
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Value::Attrs(attrs) => attrs.contains(key.as_str()),
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// Nix allows use of `?` on non-set types, but
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// always returns false in those cases.
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_ => false,
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};
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self.push(Value::Bool(result));
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}
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OpCode::OpList(Count(count)) => {
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let list =
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NixList::construct(count, self.stack.split_off(self.stack.len() - count));
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self.push(Value::List(list));
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}
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OpCode::OpConcat => {
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let rhs = self.pop().to_list()?;
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let lhs = self.pop().to_list()?;
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self.push(Value::List(lhs.concat(&rhs)))
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}
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OpCode::OpInterpolate(Count(count)) => self.run_interpolate(count)?,
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OpCode::OpJump(JumpOffset(offset)) => {
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self.frame_mut().ip += offset;
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}
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OpCode::OpJumpIfTrue(JumpOffset(offset)) => {
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if self.peek(0).as_bool()? {
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self.frame_mut().ip += offset;
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}
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}
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OpCode::OpJumpIfFalse(JumpOffset(offset)) => {
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if !self.peek(0).as_bool()? {
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self.frame_mut().ip += offset;
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}
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}
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OpCode::OpJumpIfNotFound(JumpOffset(offset)) => {
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if matches!(self.peek(0), Value::AttrNotFound) {
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self.pop();
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self.frame_mut().ip += offset;
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}
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}
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// These assertion operations error out if the stack
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// top is not of the expected type. This is necessary
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// to implement some specific behaviours of Nix
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// exactly.
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OpCode::OpAssertBool => {
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let val = self.peek(0);
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if !val.is_bool() {
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return Err(ErrorKind::TypeError {
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expected: "bool",
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actual: val.type_of(),
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}
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.into());
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}
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}
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// Remove the given number of elements from the stack,
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// but retain the top value.
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OpCode::OpCloseScope(Count(count)) => {
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// Immediately move the top value into the right
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// position.
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let target_idx = self.stack.len() - 1 - count;
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self.stack[target_idx] = self.pop();
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// Then drop the remaining values.
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for _ in 0..(count - 1) {
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self.pop();
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}
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}
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OpCode::OpGetLocal(StackIdx(local_idx)) => {
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let idx = self.frame().stack_offset + local_idx;
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self.push(self.stack[idx].clone());
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}
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OpCode::OpPushWith(StackIdx(idx)) => {
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self.with_stack.push(self.frame().stack_offset + idx)
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}
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OpCode::OpPopWith => {
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self.with_stack.pop();
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}
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OpCode::OpResolveWith => {
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let ident = self.pop().to_string()?;
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let value = self.resolve_with(ident.as_str())?;
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self.push(value)
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}
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OpCode::OpResolveWithOrUpvalue(idx) => {
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let ident = self.pop().to_string()?;
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match self.resolve_with(ident.as_str()) {
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// Variable found in local `with`-stack.
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Ok(value) => self.push(value),
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// Variable not found => check upvalues.
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Err(Error {
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kind: ErrorKind::UnknownDynamicVariable(_),
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..
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}) => {
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let value = self.frame().upvalue(idx).clone();
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self.push(value);
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}
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Err(err) => return Err(err),
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}
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}
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OpCode::OpAssert => {
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if !self.pop().as_bool()? {
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return Err(ErrorKind::AssertionFailed.into());
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}
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}
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OpCode::OpCall => {
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let callable = self.pop();
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match callable {
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Value::Closure(closure) => {
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self.call(closure.lambda(), closure.upvalues().to_vec(), 1)
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}
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Value::Builtin(builtin) => {
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let arg = self.pop();
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let result = builtin.apply(arg)?;
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self.push(result);
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}
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_ => return Err(ErrorKind::NotCallable.into()),
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};
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}
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OpCode::OpGetUpvalue(upv_idx) => {
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let value = self.frame().upvalue(upv_idx).clone();
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if let Value::DynamicUpvalueMissing(name) = value {
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return Err(
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ErrorKind::UnknownDynamicVariable(name.as_str().to_string()).into()
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);
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}
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self.push(value);
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}
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OpCode::OpClosure(idx) => {
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let blueprint = match self.chunk().constant(idx) {
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Value::Blueprint(lambda) => lambda.clone(),
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_ => panic!("compiler bug: non-blueprint in blueprint slot"),
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};
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let upvalue_count = blueprint.upvalue_count;
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debug_assert!(
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upvalue_count > 0,
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"OpClosure should not be called for plain lambdas"
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);
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let closure = Closure::new(blueprint);
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let upvalues = closure.upvalues_mut();
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self.push(Value::Closure(closure.clone()));
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// From this point on we internally mutate the
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// closure object's upvalues. The closure is
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// already in its stack slot, which means that it
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// can capture itself as an upvalue for
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// self-recursion.
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self.populate_upvalues(upvalue_count, upvalues)?;
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}
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OpCode::OpThunk(_idx) => todo!("runtime thunk construction"),
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OpCode::OpFinalise(StackIdx(idx)) => {
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match &self.stack[self.frame().stack_offset + idx] {
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Value::Closure(closure) => closure
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.resolve_deferred_upvalues(&self.stack[self.frame().stack_offset..]),
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v => {
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#[cfg(feature = "disassembler")]
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drop(tracer);
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panic!("compiler error: invalid finaliser value: {}", v);
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}
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}
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}
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// Data-carrying operands should never be executed,
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// that is a critical error in the VM.
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OpCode::DataLocalIdx(_)
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| OpCode::DataDeferredLocal(_)
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| OpCode::DataUpvalueIdx(_)
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| OpCode::DataDynamicIdx(_)
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| OpCode::DataDynamicAncestor(_) => {
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panic!("VM bug: attempted to execute data-carrying operand")
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}
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}
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#[cfg(feature = "disassembler")]
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{
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tracer.trace(&op, self.frame().ip, &self.stack);
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}
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}
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}
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// Construct runtime representation of an attr path (essentially
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// just a list of strings).
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//
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// The difference to the list construction operation is that this
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// forces all elements into strings, as attribute set keys are
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// required to be strict in Nix.
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fn run_attr_path(&mut self, count: usize) -> EvalResult<()> {
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debug_assert!(count > 1, "AttrPath needs at least two fragments");
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let mut path = Vec::with_capacity(count);
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for _ in 0..count {
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path.push(self.pop().to_string()?);
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}
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self.push(Value::AttrPath(path));
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Ok(())
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}
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fn run_attrset(&mut self, count: usize) -> EvalResult<()> {
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let attrs = NixAttrs::construct(count, self.stack.split_off(self.stack.len() - count * 2))?;
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self.push(Value::Attrs(Rc::new(attrs)));
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Ok(())
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}
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// Interpolate string fragments by popping the specified number of
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// fragments of the stack, evaluating them to strings, and pushing
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// the concatenated result string back on the stack.
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fn run_interpolate(&mut self, count: usize) -> EvalResult<()> {
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let mut out = String::new();
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for _ in 0..count {
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out.push_str(self.pop().to_string()?.as_str());
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}
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self.push(Value::String(out.into()));
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Ok(())
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}
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fn resolve_dynamic_upvalue(&mut self, ident_idx: ConstantIdx) -> EvalResult<Value> {
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let chunk = self.chunk();
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let ident = chunk.constant(ident_idx).as_str()?.to_string();
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drop(chunk); // some lifetime trickery due to cell::Ref
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// Peek at the current instruction (note: IP has already
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// advanced!) to see if it is actually data indicating a
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// "fallback upvalue" in case the dynamic could not be
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// resolved at this level.
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let up = match self.peek_op() {
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OpCode::DataDynamicAncestor(idx) => {
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// advance ip past this data
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self.inc_ip();
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Some(idx)
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}
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_ => None,
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};
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match self.resolve_with(&ident) {
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Ok(v) => Ok(v),
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Err(Error {
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kind: ErrorKind::UnknownDynamicVariable(_),
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..
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}) => match up {
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Some(idx) => Ok(self.frame().upvalue(idx).clone()),
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None => Ok(Value::DynamicUpvalueMissing(ident.into())),
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},
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Err(err) => Err(err),
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}
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}
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/// Resolve a dynamic identifier through the with-stack at runtime.
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fn resolve_with(&self, ident: &str) -> EvalResult<Value> {
|
|
for idx in self.with_stack.iter().rev() {
|
|
let with = self.stack[*idx].as_attrs()?;
|
|
match with.select(ident) {
|
|
None => continue,
|
|
Some(val) => return Ok(val.clone()),
|
|
}
|
|
}
|
|
|
|
Err(ErrorKind::UnknownDynamicVariable(ident.to_string()).into())
|
|
}
|
|
|
|
/// Populate the upvalue fields of a thunk or closure under construction.
|
|
fn populate_upvalues(
|
|
&mut self,
|
|
count: usize,
|
|
mut upvalues: RefMut<'_, Vec<Value>>,
|
|
) -> EvalResult<()> {
|
|
for _ in 0..count {
|
|
match self.inc_ip() {
|
|
OpCode::DataLocalIdx(StackIdx(local_idx)) => {
|
|
let idx = self.frame().stack_offset + local_idx;
|
|
upvalues.push(self.stack[idx].clone());
|
|
}
|
|
|
|
OpCode::DataUpvalueIdx(upv_idx) => {
|
|
upvalues.push(self.frame().upvalue(upv_idx).clone());
|
|
}
|
|
|
|
OpCode::DataDynamicIdx(ident_idx) => {
|
|
let value = self.resolve_dynamic_upvalue(ident_idx)?;
|
|
upvalues.push(value);
|
|
}
|
|
|
|
OpCode::DataDeferredLocal(idx) => {
|
|
upvalues.push(Value::DeferredUpvalue(idx));
|
|
}
|
|
|
|
_ => panic!("compiler error: missing closure operand"),
|
|
}
|
|
}
|
|
|
|
Ok(())
|
|
}
|
|
}
|
|
|
|
// TODO: use Rc::unwrap_or_clone once it is stabilised.
|
|
// https://doc.rust-lang.org/std/rc/struct.Rc.html#method.unwrap_or_clone
|
|
fn unwrap_or_clone_rc<T: Clone>(rc: Rc<T>) -> T {
|
|
Rc::try_unwrap(rc).unwrap_or_else(|rc| (*rc).clone())
|
|
}
|
|
|
|
pub fn run_lambda(lambda: Lambda) -> EvalResult<Value> {
|
|
let mut vm = VM {
|
|
frames: vec![],
|
|
stack: vec![],
|
|
with_stack: vec![],
|
|
};
|
|
|
|
vm.call(Rc::new(lambda), vec![], 0);
|
|
vm.run()
|
|
}
|