//! This module implements compiler logic related to name/value binding
//! definitions (that is, attribute sets and let-expressions).
//!
//! In the case of recursive scopes these cases share almost all of their
//! (fairly complex) logic.
use std::iter::Peekable;
use rnix::ast::HasEntry;
use rowan::ast::AstChildren;
use super::*;
type PeekableAttrs = Peekable<AstChildren<ast::Attr>>;
/// What kind of bindings scope is being compiled?
#[derive(Clone, Copy, PartialEq)]
enum BindingsKind {
/// Standard `let ... in ...`-expression.
LetIn,
/// Non-recursive attribute set.
Attrs,
/// Recursive attribute set.
RecAttrs,
}
impl BindingsKind {
fn is_attrs(&self) -> bool {
matches!(self, BindingsKind::Attrs | BindingsKind::RecAttrs)
}
}
// Internal representation of an attribute set used for merging sets, or
// inserting nested keys.
#[derive(Clone)]
struct AttributeSet {
/// Original span at which this set was first encountered.
span: Span,
/// Tracks the kind of set (rec or not).
kind: BindingsKind,
/// All inherited entries
inherits: Vec<ast::Inherit>,
/// All internal entries
entries: Vec<(Span, PeekableAttrs, ast::Expr)>,
}
impl ToSpan for AttributeSet {
fn span_for(&self, _: &codemap::File) -> Span {
self.span
}
}
impl AttributeSet {
fn from_ast(c: &Compiler, node: &ast::AttrSet) -> Self {
AttributeSet {
span: c.span_for(node),
// Kind of the attrs depends on the first time it is
// encountered. We actually believe this to be a Nix
// bug: https://github.com/NixOS/nix/issues/7111
kind: if node.rec_token().is_some() {
BindingsKind::RecAttrs
} else {
BindingsKind::Attrs
},
inherits: ast::HasEntry::inherits(node).collect(),
entries: ast::HasEntry::attrpath_values(node)
.map(|entry| {
let span = c.span_for(&entry);
(
span,
entry.attrpath().unwrap().attrs().peekable(),
entry.value().unwrap(),
)
})
.collect(),
}
}
}
// Data structures to track the bindings observed in the second pass, and
// forward the information needed to compile their value.
enum Binding {
InheritFrom {
namespace: ast::Expr,
name: SmolStr,
span: Span,
},
Plain {
expr: ast::Expr,
},
Set(AttributeSet),
}
impl Binding {
/// Merge the provided value into the current binding, or emit an
/// error if this turns out to be impossible.
fn merge(
&mut self,
c: &mut Compiler,
span: Span,
mut remaining_path: PeekableAttrs,
value: ast::Expr,
) {
match self {
Binding::InheritFrom { name, ref span, .. } => {
c.emit_error(span, ErrorKind::UnmergeableInherit { name: name.clone() })
}
// If the value is not yet a nested binding, flip the representation
// and recurse.
Binding::Plain { expr } => match expr {
ast::Expr::AttrSet(existing) => {
let nested = AttributeSet::from_ast(c, existing);
*self = Binding::Set(nested);
self.merge(c, span, remaining_path, value);
}
_ => c.emit_error(&value, ErrorKind::UnmergeableValue),
},
// If the value is nested further, it is simply inserted into the
// bindings with its full path and resolved recursively further
// down.
Binding::Set(existing) if remaining_path.peek().is_some() => {
existing.entries.push((span, remaining_path, value))
}
Binding::Set(existing) => {
if let ast::Expr::AttrSet(new) = value {
existing.inherits.extend(ast::HasEntry::inherits(&new));
existing
.entries
.extend(ast::HasEntry::attrpath_values(&new).map(|entry| {
let span = c.span_for(&entry);
(
span,
entry.attrpath().unwrap().attrs().peekable(),
entry.value().unwrap(),
)
}));
} else {
// This branch is unreachable because in cases where the
// path is empty (i.e. there is no further nesting), the
// previous try_merge function already verified that the
// expression is an attribute set.
// TODO(tazjin): Consider making this branch live by
// shuffling that check around and emitting a static error
// here instead of a runtime error.
unreachable!()
}
}
}
}
}
enum KeySlot {
/// There is no key slot (`let`-expressions do not emit their key).
None { name: SmolStr },
/// The key is statically known and has a slot.
Static { slot: LocalIdx, name: SmolStr },
/// The key is dynamic, i.e. only known at runtime, and must be compiled
/// into its slot.
Dynamic { slot: LocalIdx, attr: ast::Attr },
}
struct TrackedBinding {
key_slot: KeySlot,
value_slot: LocalIdx,
binding: Binding,
}
impl TrackedBinding {
/// Does this binding match the given key?
///
/// Used to determine which binding to merge another one into.
fn matches(&self, key: &str) -> bool {
match &self.key_slot {
KeySlot::None { name } => name == key,
KeySlot::Static { name, .. } => name == key,
KeySlot::Dynamic { .. } => false,
}
}
}
struct TrackedBindings {
bindings: Vec<TrackedBinding>,
}
impl TrackedBindings {
fn new() -> Self {
TrackedBindings { bindings: vec![] }
}
/// Attempt to merge an entry into an existing matching binding, assuming
/// that the provided binding is mergable (i.e. either a nested key or an
/// attribute set literal).
///
/// Returns true if the binding was merged, false if it needs to be compiled
/// separately as a new binding.
fn try_merge(
&mut self,
c: &mut Compiler,
span: Span,
name: &ast::Attr,
mut remaining_path: PeekableAttrs,
value: ast::Expr,
) -> bool {
// If the path has no more entries, and if the entry is not an
// attribute set literal, the entry can not be merged.
if remaining_path.peek().is_none() && !matches!(value, ast::Expr::AttrSet(_)) {
return false;
}
// If the first element of the path is not statically known, the entry
// can not be merged.
let name = match expr_static_attr_str(name) {
Some(name) => name,
None => return false,
};
// If there is no existing binding with this key, the entry can not be
// merged.
// TODO: benchmark whether using a map or something is useful over the
// `find` here
let binding = match self.bindings.iter_mut().find(|b| b.matches(&name)) {
Some(b) => b,
None => return false,
};
// No more excuses ... the binding can be merged!
binding.binding.merge(c, span, remaining_path, value);
true
}
/// Add a completely new binding to the tracked bindings.
fn track_new(&mut self, key_slot: KeySlot, value_slot: LocalIdx, binding: Binding) {
self.bindings.push(TrackedBinding {
key_slot,
value_slot,
binding,
});
}
}
/// Wrapper around the `ast::HasEntry` trait as that trait can not be
/// implemented for custom types.
trait HasEntryProxy {
fn inherits(&self) -> Box<dyn Iterator<Item = ast::Inherit>>;
fn attributes(
&self,
file: Arc<codemap::File>,
) -> Box<dyn Iterator<Item = (Span, PeekableAttrs, ast::Expr)>>;
}
impl<N: HasEntry> HasEntryProxy for N {
fn inherits(&self) -> Box<dyn Iterator<Item = ast::Inherit>> {
Box::new(ast::HasEntry::inherits(self))
}
fn attributes(
&self,
file: Arc<codemap::File>,
) -> Box<dyn Iterator<Item = (Span, PeekableAttrs, ast::Expr)>> {
Box::new(ast::HasEntry::attrpath_values(self).map(move |entry| {
(
entry.span_for(&file),
entry.attrpath().unwrap().attrs().peekable(),
entry.value().unwrap(),
)
}))
}
}
impl HasEntryProxy for AttributeSet {
fn inherits(&self) -> Box<dyn Iterator<Item = ast::Inherit>> {
Box::new(self.inherits.clone().into_iter())
}
fn attributes(
&self,
_: Arc<codemap::File>,
) -> Box<dyn Iterator<Item = (Span, PeekableAttrs, ast::Expr)>> {
Box::new(self.entries.clone().into_iter())
}
}
/// AST-traversing functions related to bindings.
impl Compiler<'_> {
/// Compile all inherits of a node with entries that do *not* have a
/// namespace to inherit from, and return the remaining ones that do.
fn compile_plain_inherits<N>(
&mut self,
slot: LocalIdx,
kind: BindingsKind,
count: &mut usize,
node: &N,
) -> Vec<(ast::Expr, SmolStr, Span)>
where
N: ToSpan + HasEntryProxy,
{
// Pass over all inherits, resolving only those without namespaces.
// Since they always resolve in a higher scope, we can just compile and
// declare them immediately.
//
// Inherits with namespaces are returned to the caller.
let mut inherit_froms: Vec<(ast::Expr, SmolStr, Span)> = vec![];
for inherit in node.inherits() {
if inherit.attrs().peekable().peek().is_none() {
self.emit_warning(&inherit, WarningKind::EmptyInherit);
continue;
}
match inherit.from() {
// Within a `let` binding, inheriting from the outer scope is a
// no-op *if* there are no dynamic bindings.
None if !kind.is_attrs() && !self.has_dynamic_ancestor() => {
self.emit_warning(&inherit, WarningKind::UselessInherit);
continue;
}
None => {
for attr in inherit.attrs() {
let name = match expr_static_attr_str(&attr) {
Some(name) => name,
None => {
self.emit_error(&attr, ErrorKind::DynamicKeyInScope("inherit"));
continue;
}
};
// If the identifier resolves statically in a `let`, it
// has precedence over dynamic bindings, and the inherit
// is useless.
if kind == BindingsKind::LetIn
&& matches!(
self.scope_mut().resolve_local(&name),
LocalPosition::Known(_)
)
{
self.emit_warning(&attr, WarningKind::UselessInherit);
continue;
}
*count += 1;
// Place key on the stack when compiling attribute sets.
if kind.is_attrs() {
self.emit_constant(Value::String(name.as_str().into()), &attr);
let span = self.span_for(&attr);
self.scope_mut().declare_phantom(span, true);
}
// Place the value on the stack. Note that because plain
// inherits are always in the outer scope, the slot of
// *this* scope itself is used.
self.compile_identifier_access(slot, &name, &attr);
// In non-recursive attribute sets, the key slot must be
// a phantom (i.e. the identifier can not be resolved in
// this scope).
let idx = if kind == BindingsKind::Attrs {
let span = self.span_for(&attr);
self.scope_mut().declare_phantom(span, false)
} else {
self.declare_local(&attr, name)
};
self.scope_mut().mark_initialised(idx);
}
}
Some(from) => {
for attr in inherit.attrs() {
let name = match expr_static_attr_str(&attr) {
Some(name) => name,
None => {
self.emit_error(&attr, ErrorKind::DynamicKeyInScope("inherit"));
continue;
}
};
*count += 1;
inherit_froms.push((from.expr().unwrap(), name, self.span_for(&attr)));
}
}
}
}
inherit_froms
}
/// Declare all namespaced inherits, that is inherits which are inheriting
/// values from an attribute set.
///
/// This only ensures that the locals stack is aware of the inherits, it
/// does not yet emit bytecode that places them on the stack. This is up to
/// the owner of the `bindings` vector, which this function will populate.
fn declare_namespaced_inherits(
&mut self,
kind: BindingsKind,
inherit_froms: Vec<(ast::Expr, SmolStr, Span)>,
bindings: &mut TrackedBindings,
) {
for (from, name, span) in inherit_froms {
let key_slot = if kind.is_attrs() {
// In an attribute set, the keys themselves are placed on the
// stack but their stack slot is inaccessible (it is only
// consumed by `OpAttrs`).
KeySlot::Static {
slot: self.scope_mut().declare_phantom(span, false),
name: name.clone(),
}
} else {
KeySlot::None { name: name.clone() }
};
let value_slot = match kind {
// In recursive scopes, the value needs to be accessible on the
// stack.
BindingsKind::LetIn | BindingsKind::RecAttrs => {
self.declare_local(&span, name.clone())
}
// In non-recursive attribute sets, the value is inaccessible
// (only consumed by `OpAttrs`).
BindingsKind::Attrs => self.scope_mut().declare_phantom(span, false),
};
bindings.track_new(
key_slot,
value_slot,
Binding::InheritFrom {
namespace: from,
name,
span,
},
);
}
}
/// Declare all regular bindings (i.e. `key = value;`) in a bindings scope,
/// but do not yet compile their values.
fn declare_bindings<N>(
&mut self,
kind: BindingsKind,
count: &mut usize,
bindings: &mut TrackedBindings,
node: &N,
) where
N: ToSpan + HasEntryProxy,
{
for (span, mut path, value) in node.attributes(self.file.clone()) {
let key = path.next().unwrap();
if bindings.try_merge(self, span, &key, path.clone(), value.clone()) {
// Binding is nested, or already exists and was merged, move on.
continue;
}
*count += 1;
let key_span = self.span_for(&key);
let key_slot = match expr_static_attr_str(&key) {
Some(name) if kind.is_attrs() => KeySlot::Static {
name,
slot: self.scope_mut().declare_phantom(key_span, false),
},
Some(name) => KeySlot::None { name },
None if kind.is_attrs() => KeySlot::Dynamic {
attr: key,
slot: self.scope_mut().declare_phantom(key_span, false),
},
None => {
self.emit_error(&key, ErrorKind::DynamicKeyInScope("let-expression"));
continue;
}
};
let value_slot = match kind {
BindingsKind::LetIn | BindingsKind::RecAttrs => match &key_slot {
// In recursive scopes, the value needs to be accessible on the
// stack if it is statically known
KeySlot::None { name } | KeySlot::Static { name, .. } => {
self.declare_local(&key_span, name.as_str())
}
// Dynamic values are never resolvable (as their names are
// of course only known at runtime).
//
// Note: This branch is unreachable in `let`-expressions.
KeySlot::Dynamic { .. } => self.scope_mut().declare_phantom(key_span, false),
},
// In non-recursive attribute sets, the value is inaccessible
// (only consumed by `OpAttrs`).
BindingsKind::Attrs => self.scope_mut().declare_phantom(key_span, false),
};
let binding = if path.peek().is_some() {
Binding::Set(AttributeSet {
span,
kind: BindingsKind::Attrs,
inherits: vec![],
entries: vec![(span, path, value)],
})
} else {
Binding::Plain { expr: value }
};
bindings.track_new(key_slot, value_slot, binding);
}
}
/// Compile attribute set literals into equivalent bytecode.
///
/// This is complicated by a number of features specific to Nix attribute
/// sets, most importantly:
///
/// 1. Keys can be dynamically constructed through interpolation.
/// 2. Keys can refer to nested attribute sets.
/// 3. Attribute sets can (optionally) be recursive.
pub(super) fn compile_attr_set(&mut self, slot: LocalIdx, node: &ast::AttrSet) {
// Open a scope to track the positions of the temporaries used by the
// `OpAttrs` instruction.
self.scope_mut().begin_scope();
let kind = if node.rec_token().is_some() {
BindingsKind::RecAttrs
} else {
BindingsKind::Attrs
};
self.compile_bindings(slot, kind, node);
// Remove the temporary scope, but do not emit any additional cleanup
// (OpAttrs consumes all of these locals).
self.scope_mut().end_scope();
}
/// Actually binds all tracked bindings by emitting the bytecode that places
/// them in their stack slots.
fn bind_values(&mut self, bindings: TrackedBindings) {
let mut value_indices: Vec<LocalIdx> = vec![];
for binding in bindings.bindings.into_iter() {
value_indices.push(binding.value_slot);
match binding.key_slot {
KeySlot::None { .. } => {} // nothing to do here
KeySlot::Static { slot, name } => {
let span = self.scope()[slot].span;
self.emit_constant(Value::String(name.as_str().into()), &span);
self.scope_mut().mark_initialised(slot);
}
KeySlot::Dynamic { slot, attr } => {
self.compile_attr(slot, &attr);
self.scope_mut().mark_initialised(slot);
}
}
match binding.binding {
// This entry is an inherit (from) expr. The value is placed on
// the stack by selecting an attribute.
Binding::InheritFrom {
namespace,
name,
span,
} => {
// Create a thunk wrapping value (which may be one as well)
// to avoid forcing the from expr too early.
self.thunk(binding.value_slot, &namespace, |c, s| {
c.compile(s, namespace.clone());
c.emit_force(&namespace);
c.emit_constant(Value::String(name.as_str().into()), &span);
c.push_op(OpCode::OpAttrsSelect, &span);
})
}
// Binding is "just" a plain expression that needs to be
// compiled.
Binding::Plain { expr } => self.compile(binding.value_slot, expr),
// Binding is a merged or nested attribute set, and needs to be
// recursively compiled as another binding.
Binding::Set(set) => self.thunk(binding.value_slot, &set, |c, _| {
c.scope_mut().begin_scope();
c.compile_bindings(binding.value_slot, set.kind, &set);
c.scope_mut().end_scope();
}),
}
// Any code after this point will observe the value in the right
// stack slot, so mark it as initialised.
self.scope_mut().mark_initialised(binding.value_slot);
}
// Final pass to emit finaliser instructions if necessary.
for idx in value_indices {
if self.scope()[idx].needs_finaliser {
let stack_idx = self.scope().stack_index(idx);
let span = self.scope()[idx].span;
self.push_op(OpCode::OpFinalise(stack_idx), &span);
}
}
}
fn compile_bindings<N>(&mut self, slot: LocalIdx, kind: BindingsKind, node: &N)
where
N: ToSpan + HasEntryProxy,
{
let mut count = 0;
self.scope_mut().begin_scope();
// Vector to track all observed bindings.
let mut bindings = TrackedBindings::new();
let inherit_froms = self.compile_plain_inherits(slot, kind, &mut count, node);
self.declare_namespaced_inherits(kind, inherit_froms, &mut bindings);
self.declare_bindings(kind, &mut count, &mut bindings, node);
// Check if we can bail out on empty bindings
if count == 0 {
// still need an attrset to exist, but it is empty.
if kind.is_attrs() {
self.emit_constant(Value::Attrs(Box::new(NixAttrs::empty())), node);
return;
}
self.emit_warning(node, WarningKind::EmptyLet);
return;
}
// Actually bind values and ensure they are on the stack.
self.bind_values(bindings);
if kind.is_attrs() {
self.push_op(OpCode::OpAttrs(Count(count)), node);
}
if count == 0 {
self.unthunk();
}
}
/// Compile a standard `let ...; in ...` expression.
///
/// Unless in a non-standard scope, the encountered values are simply pushed
/// on the stack and their indices noted in the entries vector.
pub(super) fn compile_let_in(&mut self, slot: LocalIdx, node: &ast::LetIn) {
self.compile_bindings(slot, BindingsKind::LetIn, node);
// Deal with the body, then clean up the locals afterwards.
self.compile(slot, node.body().unwrap());
self.cleanup_scope(node);
}
pub(super) fn compile_legacy_let(&mut self, slot: LocalIdx, node: &ast::LegacyLet) {
self.emit_warning(node, WarningKind::DeprecatedLegacyLet);
self.scope_mut().begin_scope();
self.compile_bindings(slot, BindingsKind::RecAttrs, node);
// Remove the temporary scope, but do not emit any additional cleanup
// (OpAttrs consumes all of these locals).
self.scope_mut().end_scope();
self.emit_constant(Value::String("body".into()), node);
self.push_op(OpCode::OpAttrsSelect, node);
}
/// Is the given identifier defined *by the user* in any current scope?
pub(super) fn is_user_defined(&mut self, ident: &str) -> bool {
matches!(
self.scope_mut().resolve_local(ident),
LocalPosition::Known(_) | LocalPosition::Recursive(_)
)
}
/// Resolve and compile access to an identifier in the scope.
fn compile_identifier_access<N: ToSpan + Clone>(
&mut self,
slot: LocalIdx,
ident: &str,
node: &N,
) {
match self.scope_mut().resolve_local(ident) {
LocalPosition::Unknown => {
// Are we possibly dealing with an upvalue?
if let Some(idx) = self.resolve_upvalue(self.contexts.len() - 1, ident, node) {
self.push_op(OpCode::OpGetUpvalue(idx), node);
return;
}
// Globals are the "upmost upvalues": they behave
// exactly like a `let ... in` prepended to the
// program's text, and the global scope is nothing
// more than the parent scope of the root scope.
if let Some(global) = self.globals.get(ident) {
self.emit_constant(global.clone(), &self.span_for(node));
return;
}
// If there is a non-empty `with`-stack (or a parent context
// with one), emit a runtime dynamic resolution instruction.
//
// Since it is possible for users to e.g. assign a variable to a
// dynamic resolution without actually using it, this operation
// is wrapped in an extra thunk.
if self.has_dynamic_ancestor() {
self.thunk(slot, node, |c, _| {
c.context_mut().captures_with_stack = true;
c.emit_constant(Value::String(ident.into()), node);
c.push_op(OpCode::OpResolveWith, node);
});
return;
}
// Otherwise, this variable is missing.
self.emit_error(node, ErrorKind::UnknownStaticVariable);
}
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, _| {
let upvalue_idx = compiler.add_upvalue(
compiler.contexts.len() - 1,
node,
UpvalueKind::Local(idx),
);
compiler.push_op(OpCode::OpGetUpvalue(upvalue_idx), node);
}),
};
}
pub(super) fn compile_ident(&mut self, slot: LocalIdx, node: &ast::Ident) {
let ident = node.ident_token().unwrap();
self.compile_identifier_access(slot, ident.text(), node);
}
}
/// Private compiler helpers related to bindings.
impl Compiler<'_> {
fn resolve_upvalue<N: ToSpan>(
&mut self,
ctx_idx: usize,
name: &str,
node: &N,
) -> 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
}
fn add_upvalue<N: ToSpan>(
&mut self,
ctx_idx: usize,
node: &N,
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);
}
}
let span = self.span_for(node);
self.contexts[ctx_idx]
.scope
.upvalues
.push(Upvalue { kind, span });
let idx = UpvalueIdx(self.contexts[ctx_idx].lambda.upvalue_count);
self.contexts[ctx_idx].lambda.upvalue_count += 1;
idx
}
}
