//! 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 attrs;
mod scope;
use path_clean::PathClean;
use rnix::ast::{self, AstToken, HasEntry};
use rowan::ast::{AstChildren, AstNode};
use std::collections::HashMap;
use std::path::{Path, PathBuf};
use std::rc::Rc;
use crate::chunk::Chunk;
use crate::errors::{Error, ErrorKind, EvalResult};
use crate::observer::Observer;
use crate::opcode::{CodeIdx, Count, JumpOffset, OpCode, UpvalueIdx};
use crate::value::{Closure, Lambda, Thunk, Value};
use crate::warnings::{EvalWarning, WarningKind};
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>,
}
/// Represents the lambda currently being compiled.
struct LambdaCtx {
lambda: Lambda,
scope: Scope,
captures_with_stack: bool,
}
impl LambdaCtx {
fn new() -> Self {
LambdaCtx {
lambda: Lambda::new_anonymous(),
scope: Default::default(),
captures_with_stack: false,
}
}
fn inherit(&self) -> Self {
LambdaCtx {
lambda: Lambda::new_anonymous(),
scope: self.scope.inherit(),
captures_with_stack: false,
}
}
}
/// Alias for the map of globally available functions that should
/// implicitly be resolvable in the global scope.
type GlobalsMap = HashMap<&'static str, Rc<dyn Fn(&mut Compiler, rnix::ast::Ident)>>;
struct Compiler<'code, '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: GlobalsMap,
/// File reference in the codemap contains all known source code
/// and is used to track the spans from which instructions where
/// derived.
file: &'code codemap::File,
/// Carry an observer for the compilation process, which is called
/// whenever a chunk is emitted.
observer: &'observer mut dyn Observer,
}
// 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
}
fn span_for<N: AstNode>(&self, node: &N) -> codemap::Span {
let rowan_span = node.syntax().text_range();
self.file.span.subspan(
u32::from(rowan_span.start()) as u64,
u32::from(rowan_span.end()) as u64,
)
}
/// Push a single instruction to the current bytecode chunk and
/// track the source span from which it was compiled.
fn push_op<T: AstNode>(&mut self, data: OpCode, node: &T) -> CodeIdx {
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.
fn emit_constant<T: AstNode>(&mut self, value: Value, node: &T) {
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) {
match expr {
ast::Expr::Literal(literal) => self.compile_literal(literal),
ast::Expr::Path(path) => self.compile_path(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, o, s| c.compile_binop(s, o.clone()))
}
ast::Expr::HasAttr(has_attr) => self.compile_has_attr(slot, has_attr),
ast::Expr::List(list) => {
self.thunk(slot, &list, move |c, l, s| c.compile_list(s, l.clone()))
}
ast::Expr::AttrSet(attrs) => self.thunk(slot, &attrs, move |c, a, s| {
c.compile_attr_set(s, a.clone())
}),
ast::Expr::Select(select) => self.thunk(slot, &select, move |c, sel, s| {
c.compile_select(s, sel.clone())
}),
ast::Expr::Assert(assert) => {
self.thunk(slot, &assert, move |c, a, s| c.compile_assert(s, a.clone()))
}
ast::Expr::IfElse(if_else) => self.compile_if_else(slot, if_else),
ast::Expr::LetIn(let_in) => self.compile_let_in(slot, let_in),
ast::Expr::Ident(ident) => self.compile_ident(slot, ident),
ast::Expr::With(with) => {
self.thunk(slot, &with, |c, w, s| c.compile_with(s, w.clone()))
}
ast::Expr::Lambda(lambda) => self.compile_lambda(slot, lambda),
ast::Expr::Apply(apply) => {
self.thunk(slot, &apply, move |c, a, s| c.compile_apply(s, a.clone()))
}
// Parenthesized expressions are simply unwrapped, leaving
// their value on the stack.
ast::Expr::Paren(paren) => self.compile(slot, paren.expr().unwrap()),
ast::Expr::LegacyLet(_) => todo!("legacy let"),
ast::Expr::Root(_) => unreachable!("there cannot be more than one root"),
ast::Expr::Error(_) => unreachable!("compile is only called on validated trees"),
}
}
fn compile_literal(&mut self, node: ast::Literal) {
match node.kind() {
ast::LiteralKind::Float(f) => {
self.emit_constant(Value::Float(f.value().unwrap()), &node);
}
ast::LiteralKind::Integer(i) => {
self.emit_constant(Value::Integer(i.value().unwrap()), &node);
}
ast::LiteralKind::Uri(u) => {
self.emit_warning(self.span_for(&node), WarningKind::DeprecatedLiteralURL);
self.emit_constant(Value::String(u.syntax().text().into()), &node);
}
}
}
fn compile_path(&mut self, 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('~') {
let mut buf = match dirs::home_dir() {
Some(buf) => buf,
None => {
self.emit_error(
self.span_for(&node),
ErrorKind::PathResolution("failed to determine home directory".into()),
);
return;
}
};
buf.push(&raw_path);
buf
} else if raw_path.starts_with('.') {
let mut buf = self.root_dir.clone();
buf.push(&raw_path);
buf
} else {
// TODO: decide what to do with findFile
todo!("other path types (e.g. <...> lookups) not yet implemented")
};
// TODO: Use https://github.com/rust-lang/rfcs/issues/2208
// once it is available
let value = Value::Path(path.clean());
self.emit_constant(value, &node);
}
fn compile_str(&mut self, slot: LocalIdx, node: ast::Str) {
let mut count = 0;
// 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 node.normalized_parts().into_iter().rev() {
count += 1;
match part {
// Interpolated expressions are compiled as normal and
// dealt with by the VM before being assembled into
// the final string.
ast::InterpolPart::Interpolation(node) => self.compile(slot, node.expr().unwrap()),
ast::InterpolPart::Literal(lit) => {
self.emit_constant(Value::String(lit.into()), &node);
}
}
}
if count != 1 {
self.push_op(OpCode::OpInterpolate(Count(count)), &node);
}
}
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.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();
}
/// Compiles inherited values in an attribute set. Inherited
/// values are *always* inherited from the outer scope, even if
/// there is a matching name within a recursive attribute set.
fn compile_inherit_attrs(
&mut self,
slot: LocalIdx,
inherits: AstChildren<ast::Inherit>,
) -> usize {
// Count the number of inherited values, so that the outer
// constructor can emit the correct number of pairs when
// constructing attribute sets.
let mut count = 0;
for inherit in inherits {
match inherit.from() {
Some(from) => {
for ident in inherit.idents() {
count += 1;
// First emit the identifier itself (this
// becomes the new key).
self.emit_literal_ident(&ident);
let ident_span = self.span_for(&ident);
self.scope_mut().declare_phantom(ident_span, true);
// Then emit the node that we're inheriting
// from.
//
// TODO: Likely significant optimisation
// potential in having a multi-select
// instruction followed by a merge, rather
// than pushing/popping the same attrs
// potentially a lot of times.
let val_idx = self.scope_mut().declare_phantom(ident_span, false);
self.compile(val_idx, from.expr().unwrap());
self.emit_force(&from.expr().unwrap());
self.emit_literal_ident(&ident);
self.push_op(OpCode::OpAttrsSelect, &ident);
self.scope_mut().mark_initialised(val_idx);
}
}
None => {
for ident in inherit.idents() {
let ident_span = self.span_for(&ident);
count += 1;
// Emit the key to use for OpAttrs
self.emit_literal_ident(&ident);
self.scope_mut().declare_phantom(ident_span, true);
// Emit the value.
self.compile_ident(slot, ident);
self.scope_mut().declare_phantom(ident_span, true);
}
}
}
}
count
}
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.push_op(OpCode::OpAssert, &node);
// The runtime will abort evaluation at this point if the
// assertion failed, if not the body simply continues on like
// normal.
self.compile(slot, node.body().unwrap());
}
/// 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 a standard `let ...; in ...` statement.
///
/// Unless in a non-standard scope, the encountered values are
/// simply pushed on the stack and their indices noted in the
/// entries vector.
fn compile_let_in(&mut self, slot: LocalIdx, node: ast::LetIn) {
self.begin_scope();
// First pass to find all plain inherits (if they are not useless).
// Since they always resolve to a higher scope, we can just compile and
// declare them immediately. This needs to happen *before* we declare
// any other locals in the scope or the stack order gets messed up.
// While we are looping through the inherits, already note all inherit
// (from) expressions, that may very well resolve recursively and need
// to be compiled like normal let in bindings.
let mut inherit_froms: Vec<(ast::Expr, ast::Ident)> = vec![];
for inherit in node.inherits() {
match inherit.from() {
// Within a `let` binding, inheriting from the outer
// scope is a no-op *if* the identifier can be
// statically resolved.
None if !self.scope().has_with() => {
self.emit_warning(self.span_for(&inherit), WarningKind::UselessInherit);
continue;
}
None => {
for ident in inherit.idents() {
// If the identifier resolves statically, it
// has precedence over dynamic bindings, and
// the inherit is useless.
if matches!(
self.scope_mut()
.resolve_local(ident.ident_token().unwrap().text()),
LocalPosition::Known(_)
) {
self.emit_warning(self.span_for(&ident), WarningKind::UselessInherit);
continue;
}
self.compile_ident(slot, ident.clone());
let idx = self.declare_local(&ident, ident.ident_token().unwrap().text());
self.scope_mut().mark_initialised(idx);
}
}
Some(from) => {
for ident in inherit.idents() {
inherit_froms.push((from.expr().unwrap(), ident));
}
}
}
}
// Second pass to ensure that all remaining identifiers (that may
// resolve recursively) are known.
// Track locals as an index, the expression of its values and optionally
// the ident of an attribute to select from it.
let mut entries: Vec<(LocalIdx, ast::Expr, Option<ast::Ident>)> = vec![];
// Begin with the inherit (from)s since they all become a thunk anyway
for (from, ident) in inherit_froms {
let idx = self.declare_local(&ident, ident.ident_token().unwrap().text());
entries.push((idx, from, Some(ident)))
}
// Declare all regular bindings
for entry in node.attrpath_values() {
let mut path = match self.normalise_ident_path(entry.attrpath().unwrap().attrs()) {
Ok(p) => p,
Err(err) => {
self.errors.push(err);
continue;
}
};
if path.len() != 1 {
todo!("nested bindings in let expressions :(")
}
let idx = self.declare_local(&entry.attrpath().unwrap(), path.pop().unwrap());
entries.push((idx, entry.value().unwrap(), None));
}
// Third pass to place the values in the correct stack slots.
let mut indices: Vec<LocalIdx> = vec![];
for (idx, value, path) in entries.into_iter() {
indices.push(idx);
// This entry is an inherit (from) expr, we need to select an attr
if let Some(ident) = path {
// Create a thunk wrapping value (which may be one as well) to
// avoid forcing the from expr too early.
self.thunk(idx, &value, move |c, n, s| {
c.compile(s, n.clone());
c.emit_force(n);
c.emit_literal_ident(&ident);
c.push_op(OpCode::OpAttrsSelect, &ident);
})
} else {
self.compile(idx, value);
}
// Any code after this point will observe the value in the
// right stack slot, so mark it as initialised.
self.scope_mut().mark_initialised(idx);
}
// Fourth pass to emit finaliser instructions if necessary.
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), &node);
}
}
// Deal with the body, then clean up the locals afterwards.
self.compile(slot, node.body().unwrap());
self.cleanup_scope(&node);
}
fn compile_ident(&mut self, slot: LocalIdx, node: ast::Ident) {
let ident = node.ident_token().unwrap();
// If the identifier is a global, and it is not poisoned, emit
// the global directly.
if let Some(global) = self.globals.get(ident.text()) {
if !self.scope().is_poisoned(ident.text()) {
global.clone()(self, node.clone());
return;
}
}
match self.scope_mut().resolve_local(ident.text()) {
LocalPosition::Unknown => {
// Are we possibly dealing with an upvalue?
if let Some(idx) =
self.resolve_upvalue(self.contexts.len() - 1, ident.text(), &node)
{
self.push_op(OpCode::OpGetUpvalue(idx), &node);
return;
}
// If there is a non-empty `with`-stack (or a parent
// context with one), emit a runtime dynamic
// resolution instruction.
if self.has_dynamic_ancestor() {
self.emit_literal_ident(&node);
self.push_op(OpCode::OpResolveWith, &node);
return;
}
// Otherwise, this variable is missing.
self.emit_error(self.span_for(&node), ErrorKind::UnknownStaticVariable);
return;
}
LocalPosition::Known(idx) => {
let stack_idx = self.scope().stack_index(idx);
self.push_op(OpCode::OpGetLocal(stack_idx), &node);
}
// This identifier is referring to a value from the same
// scope which is not yet defined. This identifier access
// must be thunked.
LocalPosition::Recursive(idx) => self.thunk(slot, &node, move |compiler, node, _| {
let upvalue_idx = compiler.add_upvalue(
compiler.contexts.len() - 1,
node,
UpvalueKind::Local(idx),
);
compiler.push_op(OpCode::OpGetUpvalue(upvalue_idx), node);
}),
};
}
/// 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.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);
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) {
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);
// 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![];
for entry in pattern.pat_entries() {
let ident = entry.ident().unwrap();
let idx = self.declare_local(&ident, ident.to_string());
entries.push((idx, entry));
indices.push(idx);
}
// 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);
}
}
// TODO: strictly check if all keys have been consumed if
// there is no ellipsis.
if pattern.ellipsis_token().is_none() {
self.emit_warning(span, WarningKind::NotImplemented("closed formals"));
}
}
fn compile_lambda(&mut self, outer_slot: LocalIdx, node: ast::Lambda) {
self.new_context();
let span = self.span_for(&node);
let slot = self.scope_mut().declare_phantom(span, false);
self.begin_scope();
// Compile the function itself
match node.param().unwrap() {
ast::Param::Pattern(pat) => 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);
}
}
self.compile(slot, node.body().unwrap());
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.
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);
self.observer.observe_compiled_lambda(&lambda);
// If the function is not a closure, just emit it directly and
// move on.
if lambda.upvalue_count == 0 {
self.emit_constant(Value::Closure(Closure::new(lambda)), &node);
return;
}
// If the function is a closure, 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 runtime closure can be constructed.
let blueprint_idx = self.chunk().push_constant(Value::Blueprint(lambda));
self.push_op(OpCode::OpClosure(blueprint_idx), &node);
self.emit_upvalue_data(
outer_slot,
&node,
compiled.scope.upvalues,
compiled.captures_with_stack,
);
}
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);
}
/// Compile an expression into a runtime thunk which should be
/// lazily evaluated when accessed.
// TODO: almost the same as Compiler::compile_lambda; unify?
fn thunk<N, F>(&mut self, outer_slot: LocalIdx, node: &N, content: F)
where
N: AstNode + Clone,
F: FnOnce(&mut Compiler, &N, LocalIdx),
{
self.new_context();
let span = self.span_for(node);
let slot = self.scope_mut().declare_phantom(span, false);
self.begin_scope();
content(self, node, slot);
self.cleanup_scope(node);
let mut thunk = self.contexts.pop().unwrap();
optimise_tail_call(&mut thunk.lambda.chunk);
// Capturing the with stack counts as an upvalue, as it is
// emitted as an upvalue data instruction.
if thunk.captures_with_stack {
thunk.lambda.upvalue_count += 1;
}
let lambda = Rc::new(thunk.lambda);
self.observer.observe_compiled_thunk(&lambda);
// Emit the thunk directly if it does not close over the
// environment.
if lambda.upvalue_count == 0 {
self.emit_constant(Value::Thunk(Thunk::new(lambda)), node);
return;
}
// Otherwise prepare for runtime construction of the thunk.
let blueprint_idx = self.chunk().push_constant(Value::Blueprint(lambda));
self.push_op(OpCode::OpThunk(blueprint_idx), node);
self.emit_upvalue_data(
outer_slot,
node,
thunk.scope.upvalues,
thunk.captures_with_stack,
);
}
/// Emit the data instructions that the runtime needs to correctly
/// assemble the upvalues struct.
fn emit_upvalue_data<T: AstNode>(
&mut self,
slot: LocalIdx,
node: &T,
upvalues: Vec<Upvalue>,
capture_with: bool,
) {
let this_depth = self.scope()[slot].depth;
let this_stack_slot = self.scope().stack_index(slot);
for upvalue in upvalues {
match upvalue.kind {
UpvalueKind::Local(idx) => {
let target_depth = self.scope()[idx].depth;
let stack_idx = self.scope().stack_index(idx);
// If the upvalue slot is located at the same
// depth, but *after* the closure, the upvalue
// resolution must be deferred until the scope is
// fully initialised and can be finalised.
if this_depth == target_depth && this_stack_slot < stack_idx {
self.push_op(OpCode::DataDeferredLocal(stack_idx), &upvalue.node);
self.scope_mut().mark_needs_finaliser(slot);
} else {
self.push_op(OpCode::DataLocalIdx(stack_idx), &upvalue.node);
}
}
UpvalueKind::Upvalue(idx) => {
self.push_op(OpCode::DataUpvalueIdx(idx), &upvalue.node);
}
};
}
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.ident_token().unwrap().text().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),
}
}
/// Increase the scope depth of the current function (e.g. within
/// a new bindings block, or `with`-scope).
fn begin_scope(&mut self) {
self.scope_mut().scope_depth += 1;
}
/// Decrease scope depth of the current function and emit
/// instructions to clean up the stack at runtime.
fn cleanup_scope<N: AstNode>(&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);
}
self.scope_mut().scope_depth -= 1;
}
/// Open a new lambda context within which to compile a function,
/// closure or thunk.
fn new_context(&mut self) {
// This must inherit the scope-poisoning status of the parent
// in order for upvalue resolution to work correctly with
// poisoned identifiers.
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: AstNode>(&mut self, node: &N, name: S) -> LocalIdx {
let name = name.into();
let depth = self.scope().scope_depth;
// Do this little dance to get ahold of the *static* key and
// use it for poisoning if required.
let key: Option<&'static str> = match self.globals.get_key_value(name.as_str()) {
Some((key, _)) => Some(*key),
None => None,
};
if let Some(global_ident) = key {
self.emit_warning(
self.span_for(node),
WarningKind::ShadowedGlobal(global_ident),
);
self.scope_mut().poison(global_ident, depth);
}
let mut shadowed = false;
for other in self.scope().locals.iter().rev() {
if other.has_name(&name) && other.depth == depth {
shadowed = true;
break;
}
}
if shadowed {
self.emit_error(
self.span_for(node),
ErrorKind::VariableAlreadyDefined(name.clone()),
);
}
let span = self.span_for(node);
self.scope_mut().declare_local(name, span)
}
fn resolve_upvalue(
&mut self,
ctx_idx: usize,
name: &str,
node: &rnix::ast::Ident,
) -> Option<UpvalueIdx> {
if ctx_idx == 0 {
// There can not be any upvalue at the outermost context.
return None;
}
// Determine whether the upvalue is a local in the enclosing context.
match self.contexts[ctx_idx - 1].scope.resolve_local(name) {
// recursive upvalues are dealt with the same way as
// standard known ones, as thunks and closures are
// guaranteed to be placed on the stack (i.e. in the right
// position) *during* their runtime construction
LocalPosition::Known(idx) | LocalPosition::Recursive(idx) => {
return Some(self.add_upvalue(ctx_idx, node, UpvalueKind::Local(idx)))
}
LocalPosition::Unknown => { /* continue below */ }
};
// If the upvalue comes from even further up, we need to
// recurse to make sure that the upvalues are created at each
// level.
if let Some(idx) = self.resolve_upvalue(ctx_idx - 1, name, node) {
return Some(self.add_upvalue(ctx_idx, node, UpvalueKind::Upvalue(idx)));
}
None
}
/// 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 add_upvalue(
&mut self,
ctx_idx: usize,
node: &rnix::ast::Ident,
kind: UpvalueKind,
) -> UpvalueIdx {
// If there is already an upvalue closing over the specified
// index, retrieve that instead.
for (idx, existing) in self.contexts[ctx_idx].scope.upvalues.iter().enumerate() {
if existing.kind == kind {
return UpvalueIdx(idx);
}
}
self.contexts[ctx_idx].scope.upvalues.push(Upvalue {
kind,
node: node.clone(),
});
let idx = UpvalueIdx(self.contexts[ctx_idx].lambda.upvalue_count);
self.contexts[ctx_idx].lambda.upvalue_count += 1;
idx
}
fn emit_force<N: AstNode>(&mut self, node: &N) {
self.push_op(OpCode::OpForce, node);
}
fn emit_warning(&mut self, span: codemap::Span, kind: WarningKind) {
self.warnings.push(EvalWarning { kind, span })
}
fn emit_error(&mut self, span: codemap::Span, kind: ErrorKind) {
self.errors.push(Error { kind, span })
}
/// Convert a non-dynamic string expression to a string if possible,
/// or raise an error.
fn expr_str_to_string(&self, expr: ast::Str) -> EvalResult<String> {
if expr.normalized_parts().len() == 1 {
if let ast::InterpolPart::Literal(s) = expr.normalized_parts().pop().unwrap() {
return Ok(s);
}
}
return Err(Error {
kind: ErrorKind::DynamicKeyInLet(expr.syntax().clone()),
span: self.span_for(&expr),
});
}
/// Convert a single identifier path fragment to a string if possible,
/// or raise an error about the node being dynamic.
fn attr_to_string(&self, node: ast::Attr) -> EvalResult<String> {
match node {
ast::Attr::Ident(ident) => Ok(ident.ident_token().unwrap().text().into()),
ast::Attr::Str(s) => self.expr_str_to_string(s),
// The dynamic node type is just a wrapper. C++ Nix does not
// care about the dynamic wrapper when determining whether the
// node itself is dynamic, it depends solely on the expression
// inside (i.e. `let ${"a"} = 1; in a` is valid).
ast::Attr::Dynamic(ref dynamic) => match dynamic.expr().unwrap() {
ast::Expr::Str(s) => self.expr_str_to_string(s),
_ => Err(Error {
kind: ErrorKind::DynamicKeyInLet(node.syntax().clone()),
span: self.span_for(&node),
}),
},
}
}
/// Normalises identifier fragments into a single string vector
/// for `let`-expressions; fails if fragments requiring dynamic
/// computation are encountered.
fn normalise_ident_path<I: Iterator<Item = ast::Attr>>(
&self,
path: I,
) -> EvalResult<Vec<String>> {
path.map(|node| self.attr_to_string(node)).collect()
}
}
/// 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 from additional globals supplied
/// by the caller of the compiler, as well as the built-in globals
/// that are always part of the language.
///
/// Note that all builtin functions are *not* considered part of the
/// language in this sense and MUST be supplied as additional global
/// values, including the `builtins` set itself.
fn prepare_globals(additional: HashMap<&'static str, Value>) -> GlobalsMap {
let mut globals: GlobalsMap = HashMap::new();
globals.insert(
"true",
Rc::new(|compiler, node| {
compiler.push_op(OpCode::OpTrue, &node);
}),
);
globals.insert(
"false",
Rc::new(|compiler, node| {
compiler.push_op(OpCode::OpFalse, &node);
}),
);
globals.insert(
"null",
Rc::new(|compiler, node| {
compiler.push_op(OpCode::OpNull, &node);
}),
);
for (ident, value) in additional.into_iter() {
globals.insert(
ident,
Rc::new(move |compiler, node| compiler.emit_constant(value.clone(), &node)),
);
}
globals
}
pub fn compile(
expr: ast::Expr,
location: Option<PathBuf>,
file: &codemap::File,
globals: HashMap<&'static str, Value>,
observer: &mut dyn Observer,
) -> EvalResult<CompilationOutput> {
let mut root_dir = match location {
Some(dir) => Ok(dir),
None => std::env::current_dir().map_err(|e| Error {
kind: ErrorKind::PathResolution(format!(
"could not determine current directory: {}",
e
)),
span: file.span,
}),
}?;
// 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();
}
let mut c = Compiler {
root_dir,
file,
observer,
globals: prepare_globals(globals),
contexts: vec![LambdaCtx::new()],
warnings: vec![],
errors: vec![],
};
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,
})
}
