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Diffstat (limited to 'tvix/eval/src/compiler')
| -rw-r--r-- | tvix/eval/src/compiler/mod.rs | 1093 |
1 files changed, 1093 insertions, 0 deletions
diff --git a/tvix/eval/src/compiler/mod.rs b/tvix/eval/src/compiler/mod.rs new file mode 100644 index 000000000000..5cb02a66b96a --- /dev/null +++ b/tvix/eval/src/compiler/mod.rs @@ -0,0 +1,1093 @@ +//! 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. + +use path_clean::PathClean; +use rnix::ast::{self, AstToken, HasEntry}; +use rowan::ast::AstNode; +use std::collections::{hash_map, HashMap}; +use std::path::{Path, PathBuf}; +use std::rc::Rc; + +use crate::chunk::Chunk; +use crate::errors::{Error, ErrorKind, EvalResult}; +use crate::opcode::{CodeIdx, OpCode}; +use crate::value::{Lambda, Value}; +use crate::warnings::{EvalWarning, WarningKind}; + +/// 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 CompilationResult { + pub lambda: Lambda, + pub warnings: Vec<EvalWarning>, + pub errors: Vec<Error>, +} + +/// Represents a single local already known to the compiler. +struct Local { + // Definition name, which can be different kinds of tokens (plain + // string or identifier). Nix does not allow dynamic names inside + // of `let`-expressions. + name: String, + + // Syntax node at which this local was declared. + node: Option<rnix::SyntaxNode>, + + // Scope depth of this local. + depth: usize, + + // Phantom locals are not actually accessible by users (e.g. + // intermediate values used for `with`). + phantom: bool, + + // Is this local known to have been used at all? + used: bool, +} + +/// Represents a stack offset containing keys which are currently +/// in-scope through a with expression. +#[derive(Debug)] +struct With { + depth: usize, +} + +/// Represents a scope known during compilation, which can be resolved +/// directly to stack indices. +/// +/// TODO(tazjin): `with`-stack +/// TODO(tazjin): flag "specials" (e.g. note depth if builtins are +/// overridden) +#[derive(Default)] +struct Scope { + locals: Vec<Local>, + + // How many scopes "deep" are these locals? + scope_depth: usize, + + // Stack indices of attribute sets currently in scope through + // `with`. + with_stack: Vec<With>, + + // Users are allowed to override globally defined symbols like + // `true`, `false` or `null` in scopes. We call this "scope + // poisoning", as it requires runtime resolution of those tokens. + // + // To support this efficiently, the depth at which a poisoning + // occured is tracked here. + poisoned_tokens: HashMap<&'static str, usize>, +} + +impl Scope { + /// Mark a globally defined token as poisoned. + fn poison(&mut self, name: &'static str, depth: usize) { + match self.poisoned_tokens.entry(name) { + hash_map::Entry::Occupied(_) => { + /* do nothing, as the token is already poisoned at a + * lower scope depth */ + } + hash_map::Entry::Vacant(entry) => { + entry.insert(depth); + } + } + } + + /// Check whether a given token is poisoned. + fn is_poisoned(&self, name: &str) -> bool { + self.poisoned_tokens.contains_key(name) + } + + /// "Unpoison" tokens that were poisoned at a given depth. Used + /// when scopes are closed. + fn unpoison(&mut self, depth: usize) { + self.poisoned_tokens + .retain(|_, poisoned_at| *poisoned_at != depth); + } +} + +/// Represents the lambda currently being compiled. +struct LambdaCtx { + lambda: Lambda, + scope: Scope, +} + +impl LambdaCtx { + fn new() -> Self { + LambdaCtx { + lambda: Lambda::new_anonymous(), + scope: Default::default(), + } + } +} + +type GlobalsMap = HashMap<&'static str, Rc<dyn Fn(&mut Compiler)>>; + +struct Compiler { + 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, +} + +// 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 { + Rc::<Chunk>::get_mut(self.context_mut().lambda.chunk()) + .expect("compiler flaw: long-lived chunk reference") + } + + fn scope(&self) -> &Scope { + &self.context().scope + } + + fn scope_mut(&mut self) -> &mut Scope { + &mut self.context_mut().scope + } + + fn emit_constant(&mut self, value: Value) { + let idx = self.chunk().push_constant(value); + self.chunk().push_op(OpCode::OpConstant(idx)); + } +} + +// Actual code-emitting AST traversal methods. +impl Compiler { + fn compile(&mut self, 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(s), + ast::Expr::UnaryOp(op) => self.compile_unary_op(op), + ast::Expr::BinOp(op) => self.compile_binop(op), + ast::Expr::HasAttr(has_attr) => self.compile_has_attr(has_attr), + ast::Expr::List(list) => self.compile_list(list), + ast::Expr::AttrSet(attrs) => self.compile_attr_set(attrs), + ast::Expr::Select(select) => self.compile_select(select), + ast::Expr::Assert(assert) => self.compile_assert(assert), + ast::Expr::IfElse(if_else) => self.compile_if_else(if_else), + ast::Expr::LetIn(let_in) => self.compile_let_in(let_in), + ast::Expr::Ident(ident) => self.compile_ident(ident), + ast::Expr::With(with) => self.compile_with(with), + ast::Expr::Lambda(lambda) => self.compile_lambda(lambda), + ast::Expr::Apply(apply) => self.compile_apply(apply), + + // Parenthesized expressions are simply unwrapped, leaving + // their value on the stack. + ast::Expr::Paren(paren) => self.compile(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())); + } + + ast::LiteralKind::Integer(i) => { + self.emit_constant(Value::Integer(i.value().unwrap())); + } + ast::LiteralKind::Uri(u) => { + self.emit_warning(node.syntax().clone(), WarningKind::DeprecatedLiteralURL); + self.emit_constant(Value::String(u.syntax().text().into())); + } + } + } + + 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( + node.syntax().clone(), + 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); + } + + fn compile_str(&mut self, 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(node.expr().unwrap()), + + ast::InterpolPart::Literal(lit) => { + self.emit_constant(Value::String(lit.into())); + } + } + } + + if count != 1 { + self.chunk().push_op(OpCode::OpInterpolate(count)); + } + } + + fn compile_unary_op(&mut self, op: ast::UnaryOp) { + self.compile(op.expr().unwrap()); + + let opcode = match op.operator().unwrap() { + ast::UnaryOpKind::Invert => OpCode::OpInvert, + ast::UnaryOpKind::Negate => OpCode::OpNegate, + }; + + self.chunk().push_op(opcode); + } + + fn compile_binop(&mut self, 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(op), + BinOpKind::Or => return self.compile_or(op), + BinOpKind::Implication => return self.compile_implication(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(op.lhs().unwrap()); + self.compile(op.rhs().unwrap()); + + match op.operator().unwrap() { + BinOpKind::Add => self.chunk().push_op(OpCode::OpAdd), + BinOpKind::Sub => self.chunk().push_op(OpCode::OpSub), + BinOpKind::Mul => self.chunk().push_op(OpCode::OpMul), + BinOpKind::Div => self.chunk().push_op(OpCode::OpDiv), + BinOpKind::Update => self.chunk().push_op(OpCode::OpAttrsUpdate), + BinOpKind::Equal => self.chunk().push_op(OpCode::OpEqual), + BinOpKind::Less => self.chunk().push_op(OpCode::OpLess), + BinOpKind::LessOrEq => self.chunk().push_op(OpCode::OpLessOrEq), + BinOpKind::More => self.chunk().push_op(OpCode::OpMore), + BinOpKind::MoreOrEq => self.chunk().push_op(OpCode::OpMoreOrEq), + BinOpKind::Concat => self.chunk().push_op(OpCode::OpConcat), + + BinOpKind::NotEqual => { + self.chunk().push_op(OpCode::OpEqual); + self.chunk().push_op(OpCode::OpInvert) + } + + // Handled by separate branch above. + BinOpKind::And | BinOpKind::Implication | BinOpKind::Or => { + unreachable!() + } + }; + } + + fn compile_and(&mut self, 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(node.lhs().unwrap()); + + // If this value is false, jump over the right-hand side - the + // whole expression is false. + let end_idx = self.chunk().push_op(OpCode::OpJumpIfFalse(0)); + + // 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.chunk().push_op(OpCode::OpPop); + self.compile(node.rhs().unwrap()); + + self.patch_jump(end_idx); + self.chunk().push_op(OpCode::OpAssertBool); + } + + fn compile_or(&mut self, 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(node.lhs().unwrap()); + + // Opposite of above: If this value is **true**, we can + // short-circuit the right-hand side. + let end_idx = self.chunk().push_op(OpCode::OpJumpIfTrue(0)); + self.chunk().push_op(OpCode::OpPop); + self.compile(node.rhs().unwrap()); + self.patch_jump(end_idx); + self.chunk().push_op(OpCode::OpAssertBool); + } + + fn compile_implication(&mut self, 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(node.lhs().unwrap()); + self.chunk().push_op(OpCode::OpInvert); + + // Exactly as `||` (because `a -> b` = `!a || b`). + let end_idx = self.chunk().push_op(OpCode::OpJumpIfTrue(0)); + self.chunk().push_op(OpCode::OpPop); + self.compile(node.rhs().unwrap()); + self.patch_jump(end_idx); + self.chunk().push_op(OpCode::OpAssertBool); + } + + fn compile_has_attr(&mut self, node: ast::HasAttr) { + // Put the attribute set on the stack. + self.compile(node.expr().unwrap()); + let mut count = 0; + + // Push all path fragments with an operation for fetching the + // next nested element, for all fragments except the last one. + for fragment in node.attrpath().unwrap().attrs() { + if count > 0 { + self.chunk().push_op(OpCode::OpAttrOrNotFound); + } + count += 1; + self.compile_attr(fragment); + } + + // After the last fragment, emit the actual instruction that + // leaves a boolean on the stack. + self.chunk().push_op(OpCode::OpAttrsIsSet); + } + + fn compile_attr(&mut self, node: ast::Attr) { + match node { + ast::Attr::Dynamic(dynamic) => self.compile(dynamic.expr().unwrap()), + ast::Attr::Str(s) => self.compile_str(s), + ast::Attr::Ident(ident) => self.emit_literal_ident(&ident), + } + } + + // 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, node: ast::List) { + let mut count = 0; + + for item in node.items() { + count += 1; + self.compile(item); + } + + self.chunk().push_op(OpCode::OpList(count)); + } + + // 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. + fn compile_attr_set(&mut self, node: ast::AttrSet) { + if node.rec_token().is_some() { + todo!("recursive attribute sets are not yet implemented") + } + + let mut count = 0; + + // Inherits have to be evaluated before entering the scope of + // a potentially recursive attribute sets (i.e. we always + // inherit "from the outside"). + for inherit in node.inherits() { + match inherit.from() { + Some(from) => { + for ident in inherit.idents() { + count += 1; + + // First emit the identifier itself + self.emit_literal_ident(&ident); + + // 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. + self.compile(from.expr().unwrap()); + self.emit_literal_ident(&ident); + self.chunk().push_op(OpCode::OpAttrsSelect); + } + } + + None => { + for ident in inherit.idents() { + count += 1; + self.emit_literal_ident(&ident); + + match self.resolve_local(ident.ident_token().unwrap().text()) { + Some(idx) => self.chunk().push_op(OpCode::OpGetLocal(idx)), + None => { + self.emit_error( + ident.syntax().clone(), + ErrorKind::UnknownStaticVariable, + ); + continue; + } + }; + } + } + } + } + + for kv in node.attrpath_values() { + count += 1; + + // Because attribute set literals can contain nested keys, + // there is potentially more than one key fragment. If + // this is the case, a special operation to construct a + // runtime value representing the attribute path is + // emitted. + let mut key_count = 0; + for fragment in kv.attrpath().unwrap().attrs() { + key_count += 1; + self.compile_attr(fragment); + } + + // 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.chunk().push_op(OpCode::OpAttrPath(key_count)); + } + + // The value is just compiled as normal so that its + // resulting value is on the stack when the attribute set + // is constructed at runtime. + self.compile(kv.value().unwrap()); + } + + self.chunk().push_op(OpCode::OpAttrs(count)); + } + + fn compile_select(&mut self, node: ast::Select) { + let set = node.expr().unwrap(); + let path = node.attrpath().unwrap(); + + if node.or_token().is_some() { + self.compile_select_or(set, path, node.default_expr().unwrap()); + return; + } + + // Push the set onto the stack + self.compile(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() { + self.compile_attr(fragment); + self.chunk().push_op(OpCode::OpAttrsSelect); + } + } + + /// 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 + /// ┌────────────────────────────┐ ┌─────────────────────────┐ + /// │ ... │ │ ... │ + /// │ 5 OP_ATTRS(1) │ → │ 5 [ { a.b = 1; } ] │ + /// │ 6 OP_CONSTANT("a") │ → │ 6 [ { a.b = 1; } "a" ] │ + /// │ 7 OP_ATTR_OR_NOT_FOUND │ → │ 7 [ { b = 1; } ] │ + /// │ 8 JUMP_IF_NOT_FOUND(13) │ → │ 8 [ { b = 1; } ] │ + /// │ 9 OP_CONSTANT("C") │ → │ 9 [ { b = 1; } "c" ] │ + /// │ 10 OP_ATTR_OR_NOT_FOUND │ → │ 10 [ NOT_FOUND ] │ + /// │ 11 JUMP_IF_NOT_FOUND(13) │ → │ 11 [ ] │ + /// │ 12 JUMP(14) │ │ .. jumped over │ + /// │ 13 CONSTANT(42) │ → │ 12 [ 42 ] │ + /// │ 14 ... │ │ .. .... │ + /// └────────────────────────────┘ └─────────────────────────┘ + /// ``` + fn compile_select_or(&mut self, set: ast::Expr, path: ast::Attrpath, default: ast::Expr) { + self.compile(set); + let mut jumps = vec![]; + + for fragment in path.attrs() { + self.compile_attr(fragment); + self.chunk().push_op(OpCode::OpAttrOrNotFound); + jumps.push(self.chunk().push_op(OpCode::OpJumpIfNotFound(0))); + } + + let final_jump = self.chunk().push_op(OpCode::OpJump(0)); + + for jump in jumps { + self.patch_jump(jump); + } + + // Compile the default value expression and patch the final + // jump to point *beyond* it. + self.compile(default); + self.patch_jump(final_jump); + } + + fn compile_assert(&mut self, node: ast::Assert) { + // Compile the assertion condition to leave its value on the stack. + self.compile(node.condition().unwrap()); + self.chunk().push_op(OpCode::OpAssert); + + // The runtime will abort evaluation at this point if the + // assertion failed, if not the body simply continues on like + // normal. + self.compile(node.body().unwrap()); + } + + // Compile conditional expressions using jumping instructions in the VM. + // + // ┌────────────────────┐ + // │ 0 [ conditional ] │ + // │ 1 JUMP_IF_FALSE →┼─┐ + // │ 2 [ main body ] │ │ Jump to else body if + // ┌┼─3─← JUMP │ │ condition is false. + // Jump over else body ││ 4 [ else body ]←┼─┘ + // if condition is true.└┼─5─→ ... │ + // └────────────────────┘ + fn compile_if_else(&mut self, node: ast::IfElse) { + self.compile(node.condition().unwrap()); + + let then_idx = self.chunk().push_op(OpCode::OpJumpIfFalse(0)); + + self.chunk().push_op(OpCode::OpPop); // discard condition value + self.compile(node.body().unwrap()); + + let else_idx = self.chunk().push_op(OpCode::OpJump(0)); + + self.patch_jump(then_idx); // patch jump *to* else_body + self.chunk().push_op(OpCode::OpPop); // discard condition value + self.compile(node.else_body().unwrap()); + + self.patch_jump(else_idx); // patch jump *over* else body + } + + // Compile an `inherit` node of a `let`-expression. + fn compile_let_inherit<I: Iterator<Item = ast::Inherit>>(&mut self, inherits: I) { + for inherit in 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().with_stack.is_empty() => { + self.emit_warning(inherit.syntax().clone(), 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 self + .resolve_local(ident.ident_token().unwrap().text()) + .is_some() + { + self.emit_warning(ident.syntax().clone(), WarningKind::UselessInherit); + continue; + } + + self.compile_ident(ident.clone()); + self.declare_local( + ident.syntax().clone(), + ident.ident_token().unwrap().text(), + ); + } + } + + Some(from) => { + for ident in inherit.idents() { + self.compile(from.expr().unwrap()); + self.emit_literal_ident(&ident); + self.chunk().push_op(OpCode::OpAttrsSelect); + self.declare_local( + ident.syntax().clone(), + ident.ident_token().unwrap().text(), + ); + } + } + } + } + } + + // 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, node: ast::LetIn) { + self.begin_scope(); + + self.compile_let_inherit(node.inherits()); + + for entry in node.attrpath_values() { + let mut path = match 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 :(") + } + + self.compile(entry.value().unwrap()); + self.declare_local( + entry.attrpath().unwrap().syntax().clone(), + path.pop().unwrap(), + ); + } + + // Deal with the body, then clean up the locals afterwards. + self.compile(node.body().unwrap()); + self.end_scope(); + } + + fn compile_ident(&mut self, 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); + return; + } + } + + match self.resolve_local(ident.text()) { + Some(idx) => self.chunk().push_op(OpCode::OpGetLocal(idx)), + None => { + if self.scope().with_stack.is_empty() { + self.emit_error(node.syntax().clone(), ErrorKind::UnknownStaticVariable); + return; + } + + // Variable needs to be dynamically resolved + // at runtime. + self.emit_constant(Value::String(ident.text().into())); + self.chunk().push_op(OpCode::OpResolveWith) + } + }; + } + + // 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, node: ast::With) { + // TODO: Detect if the namespace is just an identifier, and + // resolve that directly (thus avoiding duplication on the + // stack). + self.compile(node.namespace().unwrap()); + + self.declare_phantom(); + let depth = self.scope().scope_depth; + self.scope_mut().with_stack.push(With { depth }); + + let with_idx = self.scope().locals.len() - 1; + self.chunk().push_op(OpCode::OpPushWith(with_idx)); + + self.compile(node.body().unwrap()); + } + + fn compile_lambda(&mut self, node: ast::Lambda) { + // Open new lambda context in compiler, which has its own + // scope etc. + self.contexts.push(LambdaCtx::new()); + self.begin_scope(); + + // Compile the function itself + match node.param().unwrap() { + ast::Param::Pattern(_) => todo!("formals function definitions"), + ast::Param::IdentParam(param) => { + let name = param + .ident() + .unwrap() + .ident_token() + .unwrap() + .text() + .to_string(); + + self.declare_local(param.syntax().clone(), name); + } + } + + self.compile(node.body().unwrap()); + self.end_scope(); + + // TODO: determine and insert enclosing name, if available. + + // Pop the lambda context back off, and emit the finished + // lambda as a constant. + let compiled = self.contexts.pop().unwrap(); + + #[cfg(feature = "disassembler")] + { + crate::disassembler::disassemble_chunk(&compiled.lambda.chunk); + } + + self.emit_constant(Value::Lambda(compiled.lambda)); + } + + fn compile_apply(&mut self, 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(node.argument().unwrap()); + self.compile(node.lambda().unwrap()); + self.chunk().push_op(OpCode::OpCall); + } + + /// 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())); + } + + fn patch_jump(&mut self, idx: CodeIdx) { + let offset = 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), + } + } + + fn begin_scope(&mut self) { + self.scope_mut().scope_depth += 1; + } + + fn end_scope(&mut self) { + debug_assert!(self.scope().scope_depth != 0, "can not end top scope"); + + // If this scope poisoned any builtins or special identifiers, + // they need to be reset. + let depth = self.scope().scope_depth; + self.scope_mut().unpoison(depth); + + self.scope_mut().scope_depth -= 1; + + // 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 mut pops = 0; + + // TL;DR - iterate from the back while things belonging to the + // ended scope still exist. + while !self.scope().locals.is_empty() + && self.scope().locals[self.scope().locals.len() - 1].depth > self.scope().scope_depth + { + pops += 1; + + // While removing the local, analyse whether it has been + // accessed while it existed and emit a warning to the + // user otherwise. + if let Some(Local { + node: Some(node), + used, + .. + }) = self.scope_mut().locals.pop() + { + if !used { + self.emit_warning(node, WarningKind::UnusedBinding); + } + } + } + + if pops > 0 { + self.chunk().push_op(OpCode::OpCloseScope(pops)); + } + + while !self.scope().with_stack.is_empty() + && self.scope().with_stack[self.scope().with_stack.len() - 1].depth + > self.scope().scope_depth + { + self.chunk().push_op(OpCode::OpPopWith); + self.scope_mut().with_stack.pop(); + } + } + + /// 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>>(&mut self, node: rnix::SyntaxNode, name: S) { + 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(node.clone(), WarningKind::ShadowedGlobal(global_ident)); + self.scope_mut().poison(global_ident, depth); + } + + self.scope_mut().locals.push(Local { + depth, + name: name.into(), + node: Some(node), + phantom: false, + used: false, + }); + } + + fn declare_phantom(&mut self) { + let depth = self.scope().scope_depth; + self.scope_mut().locals.push(Local { + depth, + name: "".into(), + node: None, + phantom: true, + used: true, + }); + } + + fn resolve_local(&mut self, name: &str) -> Option<usize> { + let scope = self.scope_mut(); + + for (idx, local) in scope.locals.iter_mut().enumerate().rev() { + if !local.phantom && local.name == name { + local.used = true; + return Some(idx); + } + } + + None + } + + fn emit_warning(&mut self, node: rnix::SyntaxNode, kind: WarningKind) { + self.warnings.push(EvalWarning { node, kind }) + } + + fn emit_error(&mut self, node: rnix::SyntaxNode, kind: ErrorKind) { + self.errors.push(Error { + node: Some(node), + kind, + }) + } +} + +/// Convert a non-dynamic string expression to a string if possible, +/// or raise an error. +fn expr_str_to_string(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 { + node: Some(expr.syntax().clone()), + kind: ErrorKind::DynamicKeyInLet(expr.syntax().clone()), + }); +} + +/// Convert a single identifier path fragment to a string if possible, +/// or raise an error about the node being dynamic. +fn attr_to_string(node: ast::Attr) -> EvalResult<String> { + match node { + ast::Attr::Ident(ident) => Ok(ident.ident_token().unwrap().text().into()), + ast::Attr::Str(s) => 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) => expr_str_to_string(s), + _ => Err(ErrorKind::DynamicKeyInLet(node.syntax().clone()).into()), + }, + } +} + +// 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>>(path: I) -> EvalResult<Vec<String>> { + path.map(attr_to_string).collect() +} + +/// 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| { + compiler.chunk().push_op(OpCode::OpTrue); + }), + ); + + globals.insert( + "false", + Rc::new(|compiler| { + compiler.chunk().push_op(OpCode::OpFalse); + }), + ); + + globals.insert( + "null", + Rc::new(|compiler| { + compiler.chunk().push_op(OpCode::OpNull); + }), + ); + + for (ident, value) in additional.into_iter() { + globals.insert( + ident, + Rc::new(move |compiler| compiler.emit_constant(value.clone())), + ); + } + + globals +} + +pub fn compile( + expr: ast::Expr, + location: Option<PathBuf>, + globals: HashMap<&'static str, Value>, +) -> EvalResult<CompilationResult> { + let mut root_dir = match location { + Some(dir) => Ok(dir), + None => std::env::current_dir().map_err(|e| { + ErrorKind::PathResolution(format!("could not determine current directory: {}", e)) + }), + }?; + + // 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, + globals: prepare_globals(globals), + contexts: vec![LambdaCtx::new()], + warnings: vec![], + errors: vec![], + }; + + c.compile(expr); + + Ok(CompilationResult { + lambda: c.contexts.pop().unwrap().lambda, + warnings: c.warnings, + errors: c.errors, + }) +} |