//! This module implements a compiler for compiling the rnix AST
//! representation to Tvix bytecode.
//!
//! A note on `unwrap()`: This module contains a lot of calls to
//! `unwrap()` or `expect(...)` on data structures returned by `rnix`.
//! The reason for this is that rnix uses the same data structures to
//! represent broken and correct ASTs, so all typed AST variants have
//! the ability to represent an incorrect node.
//!
//! However, at the time that the AST is passed to the compiler we
//! have verified that `rnix` considers the code to be correct, so all
//! variants are fulfilled. In cases where the invariant is guaranteed
//! by the code in this module, `debug_assert!` has been used to catch
//! mistakes early during development.
mod bindings;
mod import;
mod optimiser;
mod scope;
use codemap::Span;
use rnix::ast::{self, AstToken};
use smol_str::SmolStr;
use std::collections::HashMap;
use std::path::{Path, PathBuf};
use std::rc::{Rc, Weak};
use std::sync::Arc;
use crate::chunk::Chunk;
use crate::errors::{Error, ErrorKind, EvalResult};
use crate::observer::CompilerObserver;
use crate::opcode::{CodeIdx, Count, JumpOffset, OpCode, UpvalueIdx};
use crate::spans::LightSpan;
use crate::spans::ToSpan;
use crate::value::{Closure, Formals, Lambda, NixAttrs, Thunk, Value};
use crate::warnings::{EvalWarning, WarningKind};
use crate::SourceCode;
use self::scope::{LocalIdx, LocalPosition, Scope, Upvalue, UpvalueKind};
/// Represents the result of compiling a piece of Nix code. If
/// compilation was successful, the resulting bytecode can be passed
/// to the VM.
pub struct CompilationOutput {
pub lambda: Rc<Lambda>,
pub warnings: Vec<EvalWarning>,
pub errors: Vec<Error>,
// This field must outlive the rc::Weak reference which breaks
// the builtins -> import -> builtins reference cycle.
//
// TODO: ensure through compiler
pub globals: Rc<GlobalsMap>,
}
/// Represents the lambda currently being compiled.
struct LambdaCtx {
lambda: Lambda,
scope: Scope,
captures_with_stack: bool,
}
impl LambdaCtx {
fn new() -> Self {
LambdaCtx {
lambda: Lambda::default(),
scope: Default::default(),
captures_with_stack: false,
}
}
fn inherit(&self) -> Self {
LambdaCtx {
lambda: Lambda::default(),
scope: self.scope.inherit(),
captures_with_stack: false,
}
}
}
/// The map of globally available functions and other values that
/// should implicitly be resolvable in the global scope.
pub(crate) type GlobalsMap = HashMap<&'static str, Value>;
/// Set of builtins that (if they exist) should be made available in
/// the global scope, meaning that they can be accessed not just
/// through `builtins.<name>`, but directly as `<name>`. This is not
/// configurable, it is based on what Nix 2.3 exposed.
const GLOBAL_BUILTINS: &'static [&'static str] = &[
"abort",
"baseNameOf",
"derivation",
"derivationStrict",
"dirOf",
"fetchGit",
"fetchMercurial",
"fetchTarball",
"fromTOML",
"import",
"isNull",
"map",
"placeholder",
"removeAttrs",
"scopedImport",
"throw",
"toString",
];
pub struct Compiler<'observer> {
contexts: Vec<LambdaCtx>,
warnings: Vec<EvalWarning>,
errors: Vec<Error>,
root_dir: PathBuf,
/// Carries all known global tokens; the full set of which is
/// created when the compiler is invoked.
///
/// Each global has an associated token, which when encountered as
/// an identifier is resolved against the scope poisoning logic,
/// and a function that should emit code for the token.
globals: Rc<GlobalsMap>,
/// File reference in the codemap contains all known source code
/// and is used to track the spans from which instructions where
/// derived.
file: Arc<codemap::File>,
/// Carry an observer for the compilation process, which is called
/// whenever a chunk is emitted.
observer: &'observer mut dyn CompilerObserver,
/// Carry a count of nested scopes which have requested the
/// compiler not to emit anything. This used for compiling dead
/// code branches to catch errors & warnings in them.
dead_scope: usize,
}
impl Compiler<'_> {
pub(super) fn span_for<S: ToSpan>(&self, to_span: &S) -> Span {
to_span.span_for(&self.file)
}
}
/// Compiler construction
impl<'observer> Compiler<'observer> {
pub(crate) fn new(
location: Option<PathBuf>,
file: Arc<codemap::File>,
globals: Rc<GlobalsMap>,
observer: &'observer mut dyn CompilerObserver,
) -> EvalResult<Self> {
let mut root_dir = match location {
Some(dir) if cfg!(target_arch = "wasm32") || dir.is_absolute() => Ok(dir),
_ => {
let current_dir = std::env::current_dir().map_err(|e| {
Error::new(
ErrorKind::RelativePathResolution(format!(
"could not determine current directory: {}",
e
)),
file.span,
)
})?;
if let Some(dir) = location {
Ok(current_dir.join(dir))
} else {
Ok(current_dir)
}
}
}?;
// If the path passed from the caller points to a file, the
// filename itself needs to be truncated as this must point to a
// directory.
if root_dir.is_file() {
root_dir.pop();
}
#[cfg(not(target_arch = "wasm32"))]
debug_assert!(root_dir.is_absolute());
Ok(Self {
root_dir,
file,
observer,
globals,
contexts: vec![LambdaCtx::new()],
warnings: vec![],
errors: vec![],
dead_scope: 0,
})
}
}
// Helper functions for emitting code and metadata to the internal
// structures of the compiler.
impl Compiler<'_> {
fn context(&self) -> &LambdaCtx {
&self.contexts[self.contexts.len() - 1]
}
fn context_mut(&mut self) -> &mut LambdaCtx {
let idx = self.contexts.len() - 1;
&mut self.contexts[idx]
}
fn chunk(&mut self) -> &mut Chunk {
&mut self.context_mut().lambda.chunk
}
fn scope(&self) -> &Scope {
&self.context().scope
}
fn scope_mut(&mut self) -> &mut Scope {
&mut self.context_mut().scope
}
/// Push a single instruction to the current bytecode chunk and
/// track the source span from which it was compiled.
fn push_op<T: ToSpan>(&mut self, data: OpCode, node: &T) -> CodeIdx {
if self.dead_scope > 0 {
return CodeIdx(0);
}
let span = self.span_for(node);
self.chunk().push_op(data, span)
}
/// Emit a single constant to the current bytecode chunk and track
/// the source span from which it was compiled.
pub(super) fn emit_constant<T: ToSpan>(&mut self, value: Value, node: &T) {
if self.dead_scope > 0 {
return;
}
let idx = self.chunk().push_constant(value);
self.push_op(OpCode::OpConstant(idx), node);
}
}
// Actual code-emitting AST traversal methods.
impl Compiler<'_> {
fn compile(&mut self, slot: LocalIdx, expr: ast::Expr) {
let expr = optimiser::optimise_expr(self, slot, expr);
match &expr {
ast::Expr::Literal(literal) => self.compile_literal(literal),
ast::Expr::Path(path) => self.compile_path(slot, path),
ast::Expr::Str(s) => self.compile_str(slot, s),
ast::Expr::UnaryOp(op) => self.compile_unary_op(slot, op),
ast::Expr::BinOp(binop) => {
self.thunk(slot, binop, move |c, s| c.compile_binop(s, binop))
}
ast::Expr::HasAttr(has_attr) => self.compile_has_attr(slot, has_attr),
ast::Expr::List(list) => self.thunk(slot, list, move |c, s| c.compile_list(s, list)),
ast::Expr::AttrSet(attrs) => {
self.thunk(slot, attrs, move |c, s| c.compile_attr_set(s, attrs))
}
ast::Expr::Select(select) => {
self.thunk(slot, select, move |c, s| c.compile_select(s, select))
}
ast::Expr::Assert(assert) => {
self.thunk(slot, assert, move |c, s| c.compile_assert(s, assert))
}
ast::Expr::IfElse(if_else) => {
self.thunk(slot, if_else, move |c, s| c.compile_if_else(s, if_else))
}
ast::Expr::LetIn(let_in) => {
self.thunk(slot, let_in, move |c, s| c.compile_let_in(s, let_in))
}
ast::Expr::Ident(ident) => self.compile_ident(slot, ident),
ast::Expr::With(with) => self.thunk(slot, with, |c, s| c.compile_with(s, with)),
ast::Expr::Lambda(lambda) => {
self.compile_lambda_or_thunk(false, slot, lambda, |c, s| {
c.compile_lambda(s, lambda)
})
}
ast::Expr::Apply(apply) => {
self.thunk(slot, apply, move |c, s| c.compile_apply(s, apply))
}
// Parenthesized expressions are simply unwrapped, leaving
// their value on the stack.
ast::Expr::Paren(paren) => self.compile(slot, paren.expr().unwrap()),
ast::Expr::LegacyLet(legacy_let) => self.compile_legacy_let(slot, legacy_let),
ast::Expr::Root(_) => unreachable!("there cannot be more than one root"),
ast::Expr::Error(_) => unreachable!("compile is only called on validated trees"),
}
}
/// Compiles an expression, but does not emit any code for it as
/// it is considered dead. This will still catch errors and
/// warnings in that expression.
fn compile_dead_code(&mut self, slot: LocalIdx, node: ast::Expr) {
self.dead_scope += 1;
self.emit_warning(&node, WarningKind::DeadCode);
self.compile(slot, node);
self.dead_scope -= 1;
}
fn compile_literal(&mut self, node: &ast::Literal) {
let value = match node.kind() {
ast::LiteralKind::Float(f) => Value::Float(f.value().unwrap()),
ast::LiteralKind::Integer(i) => match i.value() {
Ok(v) => Value::Integer(v),
Err(err) => return self.emit_error(node, err.into()),
},
ast::LiteralKind::Uri(u) => {
self.emit_warning(node, WarningKind::DeprecatedLiteralURL);
Value::String(u.syntax().text().into())
}
};
self.emit_constant(value, node);
}
fn compile_path(&mut self, slot: LocalIdx, node: &ast::Path) {
// TODO(tazjin): placeholder implementation while waiting for
// https://github.com/nix-community/rnix-parser/pull/96
let raw_path = node.to_string();
let path = if raw_path.starts_with('/') {
Path::new(&raw_path).to_owned()
} else if raw_path.starts_with('~') {
return self.thunk(slot, node, move |c, _| {
// We assume that paths that home paths start with ~/ or fail to parse
// TODO: this should be checked using a parse-fail test.
debug_assert!(raw_path.len() > 2 && raw_path.starts_with("~/"));
let home_relative_path = &raw_path[2..(raw_path.len())];
c.emit_constant(Value::UnresolvedPath(home_relative_path.into()), node);
c.push_op(OpCode::OpResolveHomePath, node);
});
} else if raw_path.starts_with('.') {
let mut buf = self.root_dir.clone();
buf.push(&raw_path);
buf
} else if raw_path.starts_with('<') {
// TODO: decide what to do with findFile
if raw_path.len() == 2 {
return self.emit_error(
node,
ErrorKind::NixPathResolution("Empty <> path not allowed".into()),
);
}
let path = &raw_path[1..(raw_path.len() - 1)];
// Make a thunk to resolve the path (without using `findFile`, at least for now?)
return self.thunk(slot, node, move |c, _| {
c.emit_constant(Value::UnresolvedPath(path.into()), node);
c.push_op(OpCode::OpFindFile, node);
});
} else {
self.emit_error(
node,
ErrorKind::NotImplemented("other path types not yet implemented"),
);
return;
};
// TODO: Use https://github.com/rust-lang/rfcs/issues/2208
// once it is available
let value = Value::Path(crate::value::canon_path(path));
self.emit_constant(value, node);
}
/// Helper that compiles the given string parts strictly. The caller
/// (`compile_str`) needs to figure out if the result of compiling this
/// needs to be thunked or not.
fn compile_str_parts(
&mut self,
slot: LocalIdx,
parent_node: &ast::Str,
parts: Vec<ast::InterpolPart<String>>,
) {
// The string parts are produced in literal order, however
// they need to be reversed on the stack in order to
// efficiently create the real string in case of
// interpolation.
for part in parts.iter().rev() {
match part {
// Interpolated expressions are compiled as normal and
// dealt with by the VM before being assembled into
// the final string. We need to coerce them here,
// so OpInterpolate definitely has a string to consume.
ast::InterpolPart::Interpolation(ipol) => {
self.compile(slot, ipol.expr().unwrap());
// implicitly forces as well
self.push_op(OpCode::OpCoerceToString, ipol);
}
ast::InterpolPart::Literal(lit) => {
self.emit_constant(Value::String(lit.as_str().into()), parent_node);
}
}
}
if parts.len() != 1 {
self.push_op(OpCode::OpInterpolate(Count(parts.len())), parent_node);
}
}
fn compile_str(&mut self, slot: LocalIdx, node: &ast::Str) {
let parts = node.normalized_parts();
// We need to thunk string expressions if they are the result of
// interpolation. A string that only consists of a single part (`"${foo}"`)
// can't desugar to the enclosed expression (`foo`) because we need to
// coerce the result to a string value. This would require forcing the
// value of the inner expression, so we need to wrap it in another thunk.
if parts.len() != 1 || matches!(&parts[0], ast::InterpolPart::Interpolation(_)) {
self.thunk(slot, node, move |c, s| {
c.compile_str_parts(s, node, parts);
});
} else {
self.compile_str_parts(slot, node, parts);
}
}
fn compile_unary_op(&mut self, slot: LocalIdx, op: &ast::UnaryOp) {
self.compile(slot, op.expr().unwrap());
self.emit_force(op);
let opcode = match op.operator().unwrap() {
ast::UnaryOpKind::Invert => OpCode::OpInvert,
ast::UnaryOpKind::Negate => OpCode::OpNegate,
};
self.push_op(opcode, op);
}
fn compile_binop(&mut self, slot: LocalIdx, op: &ast::BinOp) {
use ast::BinOpKind;
// Short-circuiting and other strange operators, which are
// under the same node type as NODE_BIN_OP, but need to be
// handled separately (i.e. before compiling the expressions
// used for standard binary operators).
match op.operator().unwrap() {
BinOpKind::And => return self.compile_and(slot, op),
BinOpKind::Or => return self.compile_or(slot, op),
BinOpKind::Implication => return self.compile_implication(slot, op),
_ => {}
};
// For all other operators, the two values need to be left on
// the stack in the correct order before pushing the
// instruction for the operation itself.
self.compile(slot, op.lhs().unwrap());
self.emit_force(&op.lhs().unwrap());
self.compile(slot, op.rhs().unwrap());
self.emit_force(&op.rhs().unwrap());
match op.operator().unwrap() {
BinOpKind::Add => self.push_op(OpCode::OpAdd, op),
BinOpKind::Sub => self.push_op(OpCode::OpSub, op),
BinOpKind::Mul => self.push_op(OpCode::OpMul, op),
BinOpKind::Div => self.push_op(OpCode::OpDiv, op),
BinOpKind::Update => self.push_op(OpCode::OpAttrsUpdate, op),
BinOpKind::Equal => self.push_op(OpCode::OpEqual, op),
BinOpKind::Less => self.push_op(OpCode::OpLess, op),
BinOpKind::LessOrEq => self.push_op(OpCode::OpLessOrEq, op),
BinOpKind::More => self.push_op(OpCode::OpMore, op),
BinOpKind::MoreOrEq => self.push_op(OpCode::OpMoreOrEq, op),
BinOpKind::Concat => self.push_op(OpCode::OpConcat, op),
BinOpKind::NotEqual => {
self.push_op(OpCode::OpEqual, op);
self.push_op(OpCode::OpInvert, op)
}
// Handled by separate branch above.
BinOpKind::And | BinOpKind::Implication | BinOpKind::Or => {
unreachable!()
}
};
}
fn compile_and(&mut self, slot: LocalIdx, node: &ast::BinOp) {
debug_assert!(
matches!(node.operator(), Some(ast::BinOpKind::And)),
"compile_and called with wrong operator kind: {:?}",
node.operator(),
);
// Leave left-hand side value on the stack.
self.compile(slot, node.lhs().unwrap());
self.emit_force(&node.lhs().unwrap());
// If this value is false, jump over the right-hand side - the
// whole expression is false.
let end_idx = self.push_op(OpCode::OpJumpIfFalse(JumpOffset(0)), node);
// Otherwise, remove the previous value and leave the
// right-hand side on the stack. Its result is now the value
// of the whole expression.
self.push_op(OpCode::OpPop, node);
self.compile(slot, node.rhs().unwrap());
self.emit_force(&node.rhs().unwrap());
self.patch_jump(end_idx);
self.push_op(OpCode::OpAssertBool, node);
}
fn compile_or(&mut self, slot: LocalIdx, node: &ast::BinOp) {
debug_assert!(
matches!(node.operator(), Some(ast::BinOpKind::Or)),
"compile_or called with wrong operator kind: {:?}",
node.operator(),
);
// Leave left-hand side value on the stack
self.compile(slot, node.lhs().unwrap());
self.emit_force(&node.lhs().unwrap());
// Opposite of above: If this value is **true**, we can
// short-circuit the right-hand side.
let end_idx = self.push_op(OpCode::OpJumpIfTrue(JumpOffset(0)), node);
self.push_op(OpCode::OpPop, node);
self.compile(slot, node.rhs().unwrap());
self.emit_force(&node.rhs().unwrap());
self.patch_jump(end_idx);
self.push_op(OpCode::OpAssertBool, node);
}
fn compile_implication(&mut self, slot: LocalIdx, node: &ast::BinOp) {
debug_assert!(
matches!(node.operator(), Some(ast::BinOpKind::Implication)),
"compile_implication called with wrong operator kind: {:?}",
node.operator(),
);
// Leave left-hand side value on the stack and invert it.
self.compile(slot, node.lhs().unwrap());
self.emit_force(&node.lhs().unwrap());
self.push_op(OpCode::OpInvert, node);
// Exactly as `||` (because `a -> b` = `!a || b`).
let end_idx = self.push_op(OpCode::OpJumpIfTrue(JumpOffset(0)), node);
self.push_op(OpCode::OpPop, node);
self.compile(slot, node.rhs().unwrap());
self.emit_force(&node.rhs().unwrap());
self.patch_jump(end_idx);
self.push_op(OpCode::OpAssertBool, node);
}
/// Compile list literals into equivalent bytecode. List
/// construction is fairly simple, consisting of pushing code for
/// each literal element and an instruction with the element
/// count.
///
/// The VM, after evaluating the code for each element, simply
/// constructs the list from the given number of elements.
fn compile_list(&mut self, slot: LocalIdx, node: &ast::List) {
let mut count = 0;
// Open a temporary scope to correctly account for stack items
// that exist during the construction.
self.scope_mut().begin_scope();
for item in node.items() {
// Start tracing new stack slots from the second list
// element onwards. The first list element is located in
// the stack slot of the list itself.
let item_slot = match count {
0 => slot,
_ => {
let item_span = self.span_for(&item);
self.scope_mut().declare_phantom(item_span, false)
}
};
count += 1;
self.compile(item_slot, item);
self.scope_mut().mark_initialised(item_slot);
}
self.push_op(OpCode::OpList(Count(count)), node);
self.scope_mut().end_scope();
}
fn compile_attr(&mut self, slot: LocalIdx, node: &ast::Attr) {
match node {
ast::Attr::Dynamic(dynamic) => {
self.compile(slot, dynamic.expr().unwrap());
self.emit_force(&dynamic.expr().unwrap());
}
ast::Attr::Str(s) => {
self.compile_str(slot, s);
self.emit_force(s);
}
ast::Attr::Ident(ident) => self.emit_literal_ident(ident),
}
}
fn compile_has_attr(&mut self, slot: LocalIdx, node: &ast::HasAttr) {
// Put the attribute set on the stack.
self.compile(slot, node.expr().unwrap());
self.emit_force(node);
// Push all path fragments with an operation for fetching the
// next nested element, for all fragments except the last one.
for (count, fragment) in node.attrpath().unwrap().attrs().enumerate() {
if count > 0 {
self.push_op(OpCode::OpAttrsTrySelect, &fragment);
self.emit_force(&fragment);
}
self.compile_attr(slot, &fragment);
}
// After the last fragment, emit the actual instruction that
// leaves a boolean on the stack.
self.push_op(OpCode::OpHasAttr, node);
}
fn compile_select(&mut self, slot: LocalIdx, node: &ast::Select) {
let set = node.expr().unwrap();
let path = node.attrpath().unwrap();
if node.or_token().is_some() {
self.compile_select_or(slot, set, path, node.default_expr().unwrap());
return;
}
// Push the set onto the stack
self.compile(slot, set);
// Compile each key fragment and emit access instructions.
//
// TODO: multi-select instruction to avoid re-pushing attrs on
// nested selects.
for fragment in path.attrs() {
// Force the current set value.
self.emit_force(&fragment);
self.compile_attr(slot, &fragment);
self.push_op(OpCode::OpAttrsSelect, &fragment);
}
}
/// Compile an `or` expression into a chunk of conditional jumps.
///
/// If at any point during attribute set traversal a key is
/// missing, the `OpAttrOrNotFound` instruction will leave a
/// special sentinel value on the stack.
///
/// After each access, a conditional jump evaluates the top of the
/// stack and short-circuits to the default value if it sees the
/// sentinel.
///
/// Code like `{ a.b = 1; }.a.c or 42` yields this bytecode and
/// runtime stack:
///
/// ```notrust
/// Bytecode Runtime stack
/// โโโโโโโโโโโโโโโโโโโโโโโโโโโโโโ โโโโโโโโโโโโโโโโโโโโโโโโโโโ
/// โ ... โ โ ... โ
/// โ 5 OP_ATTRS(1) โ โ โ 5 [ { a.b = 1; } ] โ
/// โ 6 OP_CONSTANT("a") โ โ โ 6 [ { a.b = 1; } "a" ] โ
/// โ 7 OP_ATTR_OR_NOT_FOUND โ โ โ 7 [ { b = 1; } ] โ
/// โ 8 JUMP_IF_NOT_FOUND(13) โ โ โ 8 [ { b = 1; } ] โ
/// โ 9 OP_CONSTANT("C") โ โ โ 9 [ { b = 1; } "c" ] โ
/// โ 10 OP_ATTR_OR_NOT_FOUND โ โ โ 10 [ NOT_FOUND ] โ
/// โ 11 JUMP_IF_NOT_FOUND(13) โ โ โ 11 [ ] โ
/// โ 12 JUMP(14) โ โ .. jumped over โ
/// โ 13 CONSTANT(42) โ โ โ 12 [ 42 ] โ
/// โ 14 ... โ โ .. .... โ
/// โโโโโโโโโโโโโโโโโโโโโโโโโโโโโโ โโโโโโโโโโโโโโโโโโโโโโโโโโโ
/// ```
fn compile_select_or(
&mut self,
slot: LocalIdx,
set: ast::Expr,
path: ast::Attrpath,
default: ast::Expr,
) {
self.compile(slot, set);
let mut jumps = vec![];
for fragment in path.attrs() {
self.emit_force(&fragment);
self.compile_attr(slot, &fragment.clone());
self.push_op(OpCode::OpAttrsTrySelect, &fragment);
jumps.push(self.push_op(OpCode::OpJumpIfNotFound(JumpOffset(0)), &fragment));
}
let final_jump = self.push_op(OpCode::OpJump(JumpOffset(0)), &path);
for jump in jumps {
self.patch_jump(jump);
}
// Compile the default value expression and patch the final
// jump to point *beyond* it.
self.compile(slot, default);
self.patch_jump(final_jump);
}
/// Compile `assert` expressions using jumping instructions in the VM.
///
/// ```notrust
/// โโโโโโโโโโโโโโโโโโโโโโโ
/// โ 0 [ conditional ] โ
/// โ 1 JUMP_IF_FALSE โโผโโ
/// โ 2 [ main body ] โ โ Jump to else body if
/// โโผโ3โโ JUMP โ โ condition is false.
/// Jump over else body โโ 4 OP_ASSERT_FAIL โโผโโ
/// if condition is true.โโผโ5โโ ... โ
/// โโโโโโโโโโโโโโโโโโโโโโโ
/// ```
fn compile_assert(&mut self, slot: LocalIdx, node: &ast::Assert) {
// Compile the assertion condition to leave its value on the stack.
self.compile(slot, node.condition().unwrap());
self.emit_force(&node.condition().unwrap());
let then_idx = self.push_op(OpCode::OpJumpIfFalse(JumpOffset(0)), node);
self.push_op(OpCode::OpPop, node);
self.compile(slot, node.body().unwrap());
let else_idx = self.push_op(OpCode::OpJump(JumpOffset(0)), node);
self.patch_jump(then_idx);
self.push_op(OpCode::OpPop, node);
self.push_op(OpCode::OpAssertFail, &node.condition().unwrap());
self.patch_jump(else_idx);
}
/// Compile conditional expressions using jumping instructions in the VM.
///
/// ```notrust
/// โโโโโโโโโโโโโโโโโโโโโโ
/// โ 0 [ conditional ] โ
/// โ 1 JUMP_IF_FALSE โโผโโ
/// โ 2 [ main body ] โ โ Jump to else body if
/// โโผโ3โโ JUMP โ โ condition is false.
/// Jump over else body โโ 4 [ else body ]โโผโโ
/// if condition is true.โโผโ5โโ ... โ
/// โโโโโโโโโโโโโโโโโโโโโโ
/// ```
fn compile_if_else(&mut self, slot: LocalIdx, node: &ast::IfElse) {
self.compile(slot, node.condition().unwrap());
self.emit_force(&node.condition().unwrap());
let then_idx = self.push_op(
OpCode::OpJumpIfFalse(JumpOffset(0)),
&node.condition().unwrap(),
);
self.push_op(OpCode::OpPop, node); // discard condition value
self.compile(slot, node.body().unwrap());
let else_idx = self.push_op(OpCode::OpJump(JumpOffset(0)), node);
self.patch_jump(then_idx); // patch jump *to* else_body
self.push_op(OpCode::OpPop, node); // discard condition value
self.compile(slot, node.else_body().unwrap());
self.patch_jump(else_idx); // patch jump *over* else body
}
/// Compile `with` expressions by emitting instructions that
/// pop/remove the indices of attribute sets that are implicitly
/// in scope through `with` on the "with-stack".
fn compile_with(&mut self, slot: LocalIdx, node: &ast::With) {
self.scope_mut().begin_scope();
// TODO: Detect if the namespace is just an identifier, and
// resolve that directly (thus avoiding duplication on the
// stack).
self.compile(slot, node.namespace().unwrap());
let span = self.span_for(&node.namespace().unwrap());
// The attribute set from which `with` inherits values
// occupies a slot on the stack, but this stack slot is not
// directly accessible. As it must be accounted for to
// calculate correct offsets, what we call a "phantom" local
// is declared here.
let local_idx = self.scope_mut().declare_phantom(span, true);
let with_idx = self.scope().stack_index(local_idx);
self.scope_mut().push_with();
self.push_op(OpCode::OpPushWith(with_idx), &node.namespace().unwrap());
self.compile(slot, node.body().unwrap());
self.push_op(OpCode::OpPopWith, node);
self.scope_mut().pop_with();
self.cleanup_scope(node);
}
/// Compiles pattern function arguments, such as `{ a, b }: ...`.
///
/// These patterns are treated as a special case of locals binding
/// where the attribute set itself is placed on the first stack
/// slot of the call frame (either as a phantom, or named in case
/// of an `@` binding), and the function call sets up the rest of
/// the stack as if the parameters were rewritten into a `let`
/// binding.
///
/// For example:
///
/// ```nix
/// ({ a, b ? 2, c ? a * b, ... }@args: <body>) { a = 10; }
/// ```
///
/// would be compiled similarly to a binding such as
///
/// ```nix
/// let args = { a = 10; };
/// in let a = args.a;
/// b = args.a or 2;
/// c = args.c or a * b;
/// in <body>
/// ```
///
/// The only tricky bit being that bindings have to fail if too
/// many arguments are provided. This is done by emitting a
/// special instruction that checks the set of keys from a
/// constant containing the expected keys.
fn compile_param_pattern(&mut self, pattern: &ast::Pattern) -> Formals {
let span = self.span_for(pattern);
let set_idx = match pattern.pat_bind() {
Some(name) => self.declare_local(&name, name.ident().unwrap().to_string()),
None => self.scope_mut().declare_phantom(span, true),
};
// At call time, the attribute set is already at the top of
// the stack.
self.scope_mut().mark_initialised(set_idx);
self.emit_force(pattern);
let ellipsis = pattern.ellipsis_token().is_some();
if !ellipsis {
self.push_op(OpCode::OpValidateClosedFormals, pattern);
}
// Similar to `let ... in ...`, we now do multiple passes over
// the bindings to first declare them, then populate them, and
// then finalise any necessary recursion into the scope.
let mut entries: Vec<(LocalIdx, ast::PatEntry)> = vec![];
let mut indices: Vec<LocalIdx> = vec![];
let mut arguments = HashMap::default();
for entry in pattern.pat_entries() {
let ident = entry.ident().unwrap();
let idx = self.declare_local(&ident, ident.to_string());
let has_default = entry.default().is_some();
entries.push((idx, entry));
indices.push(idx);
arguments.insert(ident.into(), has_default);
}
// For each of the bindings, push the set on the stack and
// attempt to select from it.
let stack_idx = self.scope().stack_index(set_idx);
for (idx, entry) in entries.into_iter() {
self.push_op(OpCode::OpGetLocal(stack_idx), pattern);
self.emit_literal_ident(&entry.ident().unwrap());
// Use the same mechanism as `compile_select_or` if a
// default value was provided, or simply select otherwise.
if let Some(default_expr) = entry.default() {
self.push_op(OpCode::OpAttrsTrySelect, &entry.ident().unwrap());
let jump_to_default =
self.push_op(OpCode::OpJumpIfNotFound(JumpOffset(0)), &default_expr);
let jump_over_default = self.push_op(OpCode::OpJump(JumpOffset(0)), &default_expr);
self.patch_jump(jump_to_default);
self.compile(idx, default_expr);
self.patch_jump(jump_over_default);
} else {
self.push_op(OpCode::OpAttrsSelect, &entry.ident().unwrap());
}
self.scope_mut().mark_initialised(idx);
}
for idx in indices {
if self.scope()[idx].needs_finaliser {
let stack_idx = self.scope().stack_index(idx);
self.push_op(OpCode::OpFinalise(stack_idx), pattern);
}
}
Formals {
arguments,
ellipsis,
span,
}
}
fn compile_lambda(&mut self, slot: LocalIdx, node: &ast::Lambda) {
// Compile the function itself, recording its formal arguments (if any)
// for later use
let formals = match node.param().unwrap() {
ast::Param::Pattern(pat) => Some(self.compile_param_pattern(&pat)),
ast::Param::IdentParam(param) => {
let name = param
.ident()
.unwrap()
.ident_token()
.unwrap()
.text()
.to_string();
let idx = self.declare_local(¶m, &name);
self.scope_mut().mark_initialised(idx);
None
}
};
self.compile(slot, node.body().unwrap());
self.context_mut().lambda.formals = formals;
}
fn thunk<N, F>(&mut self, outer_slot: LocalIdx, node: &N, content: F)
where
N: ToSpan,
F: FnOnce(&mut Compiler, LocalIdx),
{
self.compile_lambda_or_thunk(true, outer_slot, node, content)
}
/// Compile an expression into a runtime cloure or thunk
fn compile_lambda_or_thunk<N, F>(
&mut self,
is_suspended_thunk: bool,
outer_slot: LocalIdx,
node: &N,
content: F,
) where
N: ToSpan,
F: FnOnce(&mut Compiler, LocalIdx),
{
let name = self.scope()[outer_slot].name();
self.new_context();
// Set the (optional) name of the current slot on the lambda that is
// being compiled.
self.context_mut().lambda.name = name;
let span = self.span_for(node);
let slot = self.scope_mut().declare_phantom(span, false);
self.scope_mut().begin_scope();
content(self, slot);
self.cleanup_scope(node);
// TODO: determine and insert enclosing name, if available.
// Pop the lambda context back off, and emit the finished
// lambda as a constant.
let mut compiled = self.contexts.pop().unwrap();
// Check if tail-call optimisation is possible and perform it.
if self.dead_scope == 0 {
optimise_tail_call(&mut compiled.lambda.chunk);
}
// Capturing the with stack counts as an upvalue, as it is
// emitted as an upvalue data instruction.
if compiled.captures_with_stack {
compiled.lambda.upvalue_count += 1;
}
let lambda = Rc::new(compiled.lambda);
if is_suspended_thunk {
self.observer.observe_compiled_thunk(&lambda);
} else {
self.observer.observe_compiled_lambda(&lambda);
}
// If no upvalues are captured, emit directly and move on.
if lambda.upvalue_count == 0 {
self.emit_constant(
if is_suspended_thunk {
Value::Thunk(Thunk::new_suspended(lambda, LightSpan::new_actual(span)))
} else {
Value::Closure(Rc::new(Closure::new(lambda)))
},
node,
);
return;
}
// Otherwise, we need to emit the variable number of
// operands that allow the runtime to close over the
// upvalues and leave a blueprint in the constant index from
// which the result can be constructed.
let blueprint_idx = self.chunk().push_constant(Value::Blueprint(lambda));
let code_idx = self.push_op(
if is_suspended_thunk {
OpCode::OpThunkSuspended(blueprint_idx)
} else {
OpCode::OpThunkClosure(blueprint_idx)
},
node,
);
self.emit_upvalue_data(
outer_slot,
node,
compiled.scope.upvalues,
compiled.captures_with_stack,
);
if !is_suspended_thunk && !self.scope()[outer_slot].needs_finaliser {
if !self.scope()[outer_slot].must_thunk {
// The closure has upvalues, but is not recursive. Therefore no thunk is required,
// which saves us the overhead of Rc<RefCell<>>
self.chunk()[code_idx] = OpCode::OpClosure(blueprint_idx);
} else {
// This case occurs when a closure has upvalue-references to itself but does not need a
// finaliser. Since no OpFinalise will be emitted later on we synthesize one here.
// It is needed here only to set [`Closure::is_finalised`] which is used for sanity checks.
#[cfg(debug_assertions)]
self.push_op(
OpCode::OpFinalise(self.scope().stack_index(outer_slot)),
&self.span_for(node),
);
}
}
}
fn compile_apply(&mut self, slot: LocalIdx, node: &ast::Apply) {
// To call a function, we leave its arguments on the stack,
// followed by the function expression itself, and then emit a
// call instruction. This way, the stack is perfectly laid out
// to enter the function call straight away.
self.compile(slot, node.argument().unwrap());
self.compile(slot, node.lambda().unwrap());
self.emit_force(&node.lambda().unwrap());
self.push_op(OpCode::OpCall, node);
}
/// Emit the data instructions that the runtime needs to correctly
/// assemble the upvalues struct.
fn emit_upvalue_data<T: ToSpan>(
&mut self,
slot: LocalIdx,
node: &T,
upvalues: Vec<Upvalue>,
capture_with: bool,
) {
for upvalue in upvalues {
match upvalue.kind {
UpvalueKind::Local(idx) => {
let target = &self.scope()[idx];
let stack_idx = self.scope().stack_index(idx);
// If the target is not yet initialised, we need to defer
// the local access
if !target.initialised {
self.push_op(OpCode::DataDeferredLocal(stack_idx), &upvalue.span);
self.scope_mut().mark_needs_finaliser(slot);
} else {
// a self-reference
if slot == idx {
self.scope_mut().mark_must_thunk(slot);
}
self.push_op(OpCode::DataStackIdx(stack_idx), &upvalue.span);
}
}
UpvalueKind::Upvalue(idx) => {
self.push_op(OpCode::DataUpvalueIdx(idx), &upvalue.span);
}
};
}
if capture_with {
// TODO(tazjin): probably better to emit span for the ident that caused this
self.push_op(OpCode::DataCaptureWith, node);
}
}
/// Emit the literal string value of an identifier. Required for
/// several operations related to attribute sets, where
/// identifiers are used as string keys.
fn emit_literal_ident(&mut self, ident: &ast::Ident) {
self.emit_constant(Value::String(ident.clone().into()), ident);
}
/// Patch the jump instruction at the given index, setting its
/// jump offset from the placeholder to the current code position.
///
/// This is required because the actual target offset of jumps is
/// not known at the time when the jump operation itself is
/// emitted.
fn patch_jump(&mut self, idx: CodeIdx) {
let offset = JumpOffset(self.chunk().code.len() - 1 - idx.0);
match &mut self.chunk().code[idx.0] {
OpCode::OpJump(n)
| OpCode::OpJumpIfFalse(n)
| OpCode::OpJumpIfTrue(n)
| OpCode::OpJumpIfNotFound(n) => {
*n = offset;
}
op => panic!("attempted to patch unsupported op: {:?}", op),
}
}
/// Decrease scope depth of the current function and emit
/// instructions to clean up the stack at runtime.
fn cleanup_scope<N: ToSpan>(&mut self, node: &N) {
// When ending a scope, all corresponding locals need to be
// removed, but the value of the body needs to remain on the
// stack. This is implemented by a separate instruction.
let (popcount, unused_spans) = self.scope_mut().end_scope();
for span in &unused_spans {
self.emit_warning(span, WarningKind::UnusedBinding);
}
if popcount > 0 {
self.push_op(OpCode::OpCloseScope(Count(popcount)), node);
}
}
/// Open a new lambda context within which to compile a function,
/// closure or thunk.
fn new_context(&mut self) {
self.contexts.push(self.context().inherit());
}
/// Declare a local variable known in the scope that is being
/// compiled by pushing it to the locals. This is used to
/// determine the stack offset of variables.
fn declare_local<S: Into<String>, N: ToSpan>(&mut self, node: &N, name: S) -> LocalIdx {
let name = name.into();
let depth = self.scope().scope_depth();
// Do this little dance to turn name:&'a str into the same
// string with &'static lifetime, as required by WarningKind
if let Some((global_ident, _)) = self.globals.get_key_value(name.as_str()) {
self.emit_warning(node, WarningKind::ShadowedGlobal(global_ident));
}
let span = self.span_for(node);
let (idx, shadowed) = self.scope_mut().declare_local(name, span);
if let Some(shadow_idx) = shadowed {
let other = &self.scope()[shadow_idx];
if other.depth == depth {
self.emit_error(node, ErrorKind::VariableAlreadyDefined(other.span));
}
}
idx
}
/// Determine whether the current lambda context has any ancestors
/// that use dynamic scope resolution, and mark contexts as
/// needing to capture their enclosing `with`-stack in their
/// upvalues.
fn has_dynamic_ancestor(&mut self) -> bool {
let mut ancestor_has_with = false;
for ctx in self.contexts.iter_mut() {
if ancestor_has_with {
// If the ancestor has an active with stack, mark this
// lambda context as needing to capture it.
ctx.captures_with_stack = true;
} else {
// otherwise, check this context and move on
ancestor_has_with = ctx.scope.has_with();
}
}
ancestor_has_with
}
fn emit_force<N: ToSpan>(&mut self, node: &N) {
self.push_op(OpCode::OpForce, node);
}
fn emit_warning<N: ToSpan>(&mut self, node: &N, kind: WarningKind) {
let span = self.span_for(node);
self.warnings.push(EvalWarning { kind, span })
}
fn emit_error<N: ToSpan>(&mut self, node: &N, kind: ErrorKind) {
let span = self.span_for(node);
self.errors.push(Error::new(kind, span))
}
}
/// Perform tail-call optimisation if the last call within a
/// compiled chunk is another call.
fn optimise_tail_call(chunk: &mut Chunk) {
let last_op = chunk
.code
.last_mut()
.expect("compiler bug: chunk should never be empty");
if matches!(last_op, OpCode::OpCall) {
*last_op = OpCode::OpTailCall;
}
}
/// Prepare the full set of globals available in evaluated code. These
/// are constructed from the set of builtins supplied by the caller,
/// which are made available globally under the `builtins` identifier.
///
/// A subset of builtins (specified by [`GLOBAL_BUILTINS`]) is
/// available globally *iff* they are set.
///
/// Optionally adds the `import` feature if desired by the caller.
pub fn prepare_globals(
builtins: Vec<(&'static str, Value)>,
source: SourceCode,
enable_import: bool,
) -> Rc<GlobalsMap> {
Rc::new_cyclic(Box::new(move |weak: &Weak<GlobalsMap>| {
// First step is to construct the builtins themselves as
// `NixAttrs`.
let mut builtins: GlobalsMap = HashMap::from_iter(builtins.into_iter());
// At this point, optionally insert `import` if enabled. To
// "tie the knot" of `import` needing the full set of globals
// to instantiate its compiler, the `Weak` reference is passed
// here.
if enable_import {
let import = Value::Builtin(import::builtins_import(weak, source.clone()));
builtins.insert("import", import);
}
// Next, the actual map of globals is constructed and
// populated with (copies) of the values that should be
// available in the global scope (see [`GLOBAL_BUILTINS`]).
let mut globals: GlobalsMap = HashMap::new();
for global in GLOBAL_BUILTINS {
if let Some(builtin) = builtins.get(global).cloned() {
globals.insert(global, builtin);
}
}
// builtins contain themselves (`builtins.builtins`), which we
// can resolve by manually constructing a suspended thunk that
// dereferences the same weak pointer as above.
//
// This is an inefficient hack, but *if* anyone was to use
// `builtins.builtins`, it would only happen once as the thunk
// is then resolved.
let weak_globals = weak.clone();
builtins.insert(
"builtins",
Value::Thunk(Thunk::new_suspended_native(Rc::new(move |_| {
Ok(weak_globals
.upgrade()
.unwrap()
.get("builtins")
.cloned()
.unwrap())
}))),
);
// This is followed by the actual `builtins` attribute set
// being constructed and inserted in the global scope.
globals.insert(
"builtins",
Value::attrs(NixAttrs::from_iter(builtins.into_iter())),
);
// Finally insert the compiler-internal "magic" builtins for top-level values.
globals.insert("true", Value::Bool(true));
globals.insert("false", Value::Bool(false));
globals.insert("null", Value::Null);
globals
}))
}
pub fn compile(
expr: &ast::Expr,
location: Option<PathBuf>,
file: Arc<codemap::File>,
globals: Rc<GlobalsMap>,
observer: &mut dyn CompilerObserver,
) -> EvalResult<CompilationOutput> {
let mut c = Compiler::new(location, file, globals.clone(), observer)?;
let root_span = c.span_for(expr);
let root_slot = c.scope_mut().declare_phantom(root_span, false);
c.compile(root_slot, expr.clone());
// The final operation of any top-level Nix program must always be
// `OpForce`. A thunk should not be returned to the user in an
// unevaluated state (though in practice, a value *containing* a
// thunk might be returned).
c.emit_force(expr);
let lambda = Rc::new(c.contexts.pop().unwrap().lambda);
c.observer.observe_compiled_toplevel(&lambda);
Ok(CompilationOutput {
lambda,
warnings: c.warnings,
errors: c.errors,
globals,
})
}
