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Diffstat (limited to 'tvix/eval/src/compiler/bindings.rs')
| -rw-r--r-- | tvix/eval/src/compiler/bindings.rs | 689 |
1 files changed, 689 insertions, 0 deletions
diff --git a/tvix/eval/src/compiler/bindings.rs b/tvix/eval/src/compiler/bindings.rs new file mode 100644 index 0000000000..55621aa0d8 --- /dev/null +++ b/tvix/eval/src/compiler/bindings.rs @@ -0,0 +1,689 @@ +//! 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 super::*; + +// Data structures to track the bindings observed in the +// second pass, and forward the information needed to compile +// their value. +enum BindingKind { + InheritFrom { + namespace: ast::Expr, + name: SmolStr, + span: Span, + }, + + Plain { + expr: ast::Expr, + }, +} + +struct KeySlot { + slot: LocalIdx, + name: SmolStr, +} + +struct TrackedBinding { + key_slot: Option<KeySlot>, + value_slot: LocalIdx, + kind: BindingKind, +} + +/// AST-traversing functions related to bindings. +impl Compiler<'_> { + /// 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 attr in inherit.attrs() { + count += 1; + + let name = match self.expr_static_attr_str(&attr) { + Some(name) => name, + None => { + // TODO(tazjin): error variant for dynamic + // key in *inherit* (or generalise it) + self.emit_error(&attr, ErrorKind::DynamicKeyInLet); + continue; + } + }; + + let name_span = self.span_for(&attr); + + // First emit the identifier itself (this + // becomes the new key). + self.emit_constant(Value::String(SmolStr::new(&name).into()), &attr); + self.scope_mut().declare_phantom(name_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(name_span, false); + self.compile(val_idx, from.expr().unwrap()); + self.emit_force(&from.expr().unwrap()); + self.emit_constant(Value::String(name.into()), &attr); + self.push_op(OpCode::OpAttrsSelect, &attr); + self.scope_mut().mark_initialised(val_idx); + } + } + + None => { + for attr in inherit.attrs() { + count += 1; + + // Emit the key to use for OpAttrs + let name = match self.expr_static_attr_str(&attr) { + Some(name) => name, + None => { + // TODO(tazjin): error variant for dynamic + // key in *inherit* (or generalise it) + self.emit_error(&attr, ErrorKind::DynamicKeyInLet); + continue; + } + }; + + let name_span = self.span_for(&attr); + self.emit_constant(Value::String(SmolStr::new(&name).into()), &attr); + self.scope_mut().declare_phantom(name_span, true); + + // Emit the value. + self.compile_identifier_access(slot, &name, &attr); + self.scope_mut().declare_phantom(name_span, true); + } + } + } + } + + count + } + + /// Compile the statically known entries of an attribute set. Which + /// keys are which is not known from the iterator, so discovered + /// dynamic keys are returned from here. + fn compile_static_attr_entries( + &mut self, + count: &mut usize, + entries: AstChildren<ast::AttrpathValue>, + ) -> Vec<ast::AttrpathValue> { + let mut dynamic_attrs: Vec<ast::AttrpathValue> = vec![]; + + 'entries: for kv in entries { + // Attempt to turn the attrpath into a list of static + // strings, but abort this process if any dynamic + // fragments are encountered. + let static_attrpath: Option<Vec<String>> = kv + .attrpath() + .unwrap() + .attrs() + .map(|a| self.expr_static_attr_str(&a)) + .collect(); + + let fragments = match static_attrpath { + Some(fragments) => fragments, + None => { + dynamic_attrs.push(kv); + continue 'entries; + } + }; + + // At this point we can increase the counter because we + // know that this particular attribute is static and can + // thus be processed here. + *count += 1; + + let key_count = fragments.len(); + for fragment in fragments.into_iter() { + self.emit_constant(Value::String(fragment.into()), &kv.attrpath().unwrap()); + } + + // We're done with the key if there was only one fragment, + // otherwise we need to emit an instruction to construct + // the attribute path. + if key_count > 1 { + self.push_op( + OpCode::OpAttrPath(Count(key_count)), + &kv.attrpath().unwrap(), + ); + } + + // The value is just compiled as normal so that its + // resulting value is on the stack when the attribute set + // is constructed at runtime. + let value_span = self.span_for(&kv.value().unwrap()); + let value_slot = self.scope_mut().declare_phantom(value_span, false); + self.compile(value_slot, kv.value().unwrap()); + self.scope_mut().mark_initialised(value_slot); + } + + dynamic_attrs + } + + /// Compile the dynamic entries of an attribute set, where keys + /// are only known at runtime. + fn compile_dynamic_attr_entries( + &mut self, + count: &mut usize, + entries: Vec<ast::AttrpathValue>, + ) { + for entry in entries.into_iter() { + *count += 1; + + let mut key_count = 0; + let key_span = self.span_for(&entry.attrpath().unwrap()); + let key_idx = self.scope_mut().declare_phantom(key_span, false); + + for fragment in entry.attrpath().unwrap().attrs() { + // Key fragments can contain dynamic expressions, + // which makes accounting for their stack slots very + // tricky. + // + // In order to ensure the locals are correctly cleaned + // up, we essentially treat any key fragment after the + // first one (which has a locals index that will + // become that of the final key itself) as being part + // of a separate scope, which results in the somewhat + // annoying setup logic below. + let fragment_slot = match key_count { + 0 => key_idx, + 1 => { + self.scope_mut().begin_scope(); + self.scope_mut().declare_phantom(key_span, false) + } + _ => self.scope_mut().declare_phantom(key_span, false), + }; + + key_count += 1; + self.compile_attr(fragment_slot, fragment); + self.scope_mut().mark_initialised(fragment_slot); + } + + // We're done with the key if there was only one fragment, + // otherwise we need to emit an instruction to construct + // the attribute path. + if key_count > 1 { + self.push_op( + OpCode::OpAttrPath(Count(key_count)), + &entry.attrpath().unwrap(), + ); + + // Close the temporary scope that was set up for the + // key fragments. + self.scope_mut().end_scope(); + } + + // The value is just compiled as normal so that its + // resulting value is on the stack when the attribute set + // is constructed at runtime. + let value_span = self.span_for(&entry.value().unwrap()); + let value_slot = self.scope_mut().declare_phantom(value_span, false); + self.compile(value_slot, entry.value().unwrap()); + self.scope_mut().mark_initialised(value_slot); + } + } + + /// 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(); + + if node.rec_token().is_some() { + let count = self.compile_recursive_scope(slot, true, &node); + self.push_op(OpCode::OpAttrs(Count(count)), &node); + } else { + let mut count = self.compile_inherit_attrs(slot, node.inherits()); + + let dynamic_entries = + self.compile_static_attr_entries(&mut count, node.attrpath_values()); + + self.compile_dynamic_attr_entries(&mut count, dynamic_entries); + + self.push_op(OpCode::OpAttrs(Count(count)), &node); + } + + // Remove the temporary scope, but do not emit any additional + // cleanup (OpAttrs consumes all of these locals). + self.scope_mut().end_scope(); + } + + fn compile_recursive_scope<N>(&mut self, slot: LocalIdx, rec_attrs: bool, node: &N) -> usize + where + N: ToSpan + ast::HasEntry, + { + let mut count = 0; + self.scope_mut().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, String, Span)> = 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 !rec_attrs && !self.scope().has_with() => { + self.emit_warning(&inherit, WarningKind::UselessInherit); + continue; + } + + None => { + for attr in inherit.attrs() { + let name = match self.expr_static_attr_str(&attr) { + Some(name) => name, + None => { + // TODO(tazjin): error variant for dynamic + // key in *inherit* (or generalise it) + self.emit_error(&attr, ErrorKind::DynamicKeyInLet); + continue; + } + }; + + count += 1; + + // If the identifier resolves statically in a + // `let`, it has precedence over dynamic + // bindings, and the inherit is useless. + if !rec_attrs + && matches!( + self.scope_mut().resolve_local(&name), + LocalPosition::Known(_) + ) + { + self.emit_warning(&attr, WarningKind::UselessInherit); + continue; + } + + if rec_attrs { + self.emit_constant(Value::String(SmolStr::new(&name).into()), &attr); + let span = self.span_for(&attr); + self.scope_mut().declare_phantom(span, true); + } + + self.compile_identifier_access(slot, &name, &attr); + let idx = self.declare_local(&attr, &name); + self.scope_mut().mark_initialised(idx); + } + } + + Some(from) => { + for attr in inherit.attrs() { + let name = match self.expr_static_attr_str(&attr) { + Some(name) => name, + None => { + // TODO(tazjin): error variant for dynamic + // key in *inherit* (or generalise it) + self.emit_error(&attr, ErrorKind::DynamicKeyInLet); + continue; + } + }; + + count += 1; + inherit_froms.push((from.expr().unwrap(), name, self.span_for(&attr))); + } + } + } + } + + // Vector to track these observed bindings. + let mut bindings: Vec<TrackedBinding> = vec![]; + + // Begin second pass to ensure that all remaining identifiers + // (that may resolve recursively) are known. + + // Begin with the inherit (from)s since they all become a thunk anyway + for (from, name, span) in inherit_froms { + let key_slot = if rec_attrs { + Some(KeySlot { + slot: self.scope_mut().declare_phantom(span, false), + name: SmolStr::new(&name), + }) + } else { + None + }; + + let value_slot = self.declare_local(&span, &name); + + bindings.push(TrackedBinding { + key_slot, + value_slot, + kind: BindingKind::InheritFrom { + namespace: from, + name: SmolStr::new(&name), + span, + }, + }); + } + + // Declare all regular bindings + for entry in node.attrpath_values() { + count += 1; + + 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 { + self.emit_error( + &entry, + ErrorKind::NotImplemented("nested bindings in recursive scope :("), + ); + continue; + } + + let key_slot = if rec_attrs { + let span = self.span_for(&entry.attrpath().unwrap()); + Some(KeySlot { + slot: self.scope_mut().declare_phantom(span, false), + name: SmolStr::new(&path[0]), + }) + } else { + None + }; + + let value_slot = self.declare_local(&entry.attrpath().unwrap(), path.pop().unwrap()); + + bindings.push(TrackedBinding { + key_slot, + value_slot, + kind: BindingKind::Plain { + expr: entry.value().unwrap(), + }, + }); + } + + // Third pass to place the values in the correct stack slots. + let mut value_indices: Vec<LocalIdx> = vec![]; + for binding in bindings.into_iter() { + value_indices.push(binding.value_slot); + + if let Some(key_slot) = binding.key_slot { + let span = self.scope()[key_slot.slot].span; + self.emit_constant(Value::String(key_slot.name.into()), &span); + self.scope_mut().mark_initialised(key_slot.slot); + } + + match binding.kind { + // This entry is an inherit (from) expr. The value is + // placed on the stack by selecting an attribute. + BindingKind::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, move |c, n, s| { + c.compile(s, n.clone()); + c.emit_force(n); + + c.emit_constant(Value::String(name.into()), &span); + c.push_op(OpCode::OpAttrsSelect, &span); + }) + } + + // Binding is "just" a plain expression that needs to + // be compiled. + BindingKind::Plain { expr } => self.compile(binding.value_slot, expr), + } + + // 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); + } + + // Fourth 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); + self.push_op(OpCode::OpFinalise(stack_idx), node); + } + } + + count + } + + /// 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_recursive_scope(slot, false, &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_recursive_scope(slot, true, &node); + self.push_op(OpCode::OpAttrs(Count(node.entries().count())), &node); + self.emit_constant(Value::String(SmolStr::new_inline("body").into()), &node); + self.push_op(OpCode::OpAttrsSelect, &node); + } + + /// 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, + ) { + // If the identifier is a global, and it is not poisoned, emit + // the global directly. + if let Some(global) = self.globals.get(ident) { + if !self.scope().is_poisoned(ident) { + global.clone()(self, self.span_for(node)); + return; + } + } + + 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; + } + + // 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_constant(Value::String(SmolStr::new(ident).into()), node); + self.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, node, _| { + 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 + } + + /// Convert a single identifier path fragment of a let binding to + /// a string if possible, or raise an error about the node being + /// dynamic. + fn binding_name(&self, node: ast::Attr) -> EvalResult<String> { + self.expr_static_attr_str(&node) + .ok_or_else(|| self.dynamic_key_error(&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.binding_name(node)).collect() + } + + /// Construct the error returned when a dynamic attribute is found + /// in a `let`-expression. + fn dynamic_key_error<N>(&self, node: &N) -> Error + where + N: ToSpan, + { + Error { + kind: ErrorKind::DynamicKeyInLet, + span: self.span_for(node), + } + } + + /// Convert a non-dynamic string expression to a string if possible. + fn expr_static_str(&self, node: &ast::Str) -> Option<String> { + let mut parts = node.normalized_parts(); + + if parts.len() != 1 { + return None; + } + + if let Some(ast::InterpolPart::Literal(lit)) = parts.pop() { + return Some(lit); + } + + None + } + + /// Convert the provided `ast::Attr` into a statically known + /// string if possible. + // TODO(tazjin): these should probably be SmolStr + fn expr_static_attr_str(&self, node: &ast::Attr) -> Option<String> { + match node { + ast::Attr::Ident(ident) => Some(ident.ident_token().unwrap().text().into()), + ast::Attr::Str(s) => self.expr_static_str(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_static_str(&s), + _ => None, + }, + } + } +} |