443 lines
13 KiB
Rust
443 lines
13 KiB
Rust
use std::collections::HashMap;
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use crate::{
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ast::{ExprNode, FunDecl, ProgramNode, StmtNode, VariableExpr},
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errors::{ErrorKind, SloxError, SloxResult},
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tokens::Token,
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};
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/// Resolved variables. Pointers to the AST nodes using the variables are
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/// associated with the relative depth at which the variable definition will be
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/// found.
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pub type ResolvedVariables = HashMap<usize, usize>;
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/// Resolve all variables in a program's AST.
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pub fn resolve_variables(program: &ProgramNode) -> SloxResult<ResolvedVariables> {
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let mut state = ResolverState::default();
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state
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.with_scope(|rs| program.resolve(rs), ScopeType::TopLevel)
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.map(|_| state.resolved)
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}
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type ResolverResult = SloxResult<()>;
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/// The state of a symbol in a scope.
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#[derive(Clone, Copy, Debug, PartialEq, Eq)]
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enum SymState {
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/// The symbol has been declared but no value has been assigned to it.
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Declared,
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/// The symbol has been defined, but it hasn't been accessed.
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Defined,
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/// The symbol has been used.
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Used,
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}
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/// The kind of a symbol.
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#[derive(Clone, Copy, Debug, PartialEq, Eq)]
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enum SymKind {
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Variable,
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Function,
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Class,
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This,
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}
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/// The type of a scope
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#[derive(Clone, Copy, Debug, PartialEq, Eq)]
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enum ScopeType {
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TopLevel,
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Function,
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Method,
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}
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/// General information about a symbol.
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#[derive(Clone, Debug)]
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struct SymInfo<'a> {
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decl: Option<&'a Token>,
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kind: SymKind,
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state: SymState,
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}
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/// A resolver scope.
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#[derive(Clone, Debug)]
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struct SymScope<'a> {
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/// The type of scope we are in.
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scope_type: ScopeType,
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/// The symbols that are defined inside the current scope.
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symbols: HashMap<String, SymInfo<'a>>,
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}
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/// The state of the resolver.
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#[derive(Default)]
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struct ResolverState<'a> {
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/// The stack of scopes. Each scope maps symbols to information which
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/// includes the kind of symbol it is and its current state.
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scopes: Vec<SymScope<'a>>,
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/// The result of the resolver pass.
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resolved: ResolvedVariables,
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}
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impl<'a> SymScope<'a> {
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/// Initialize a new scope of the specified type.
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fn new(scope_type: ScopeType) -> Self {
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Self {
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scope_type,
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symbols: HashMap::default(),
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}
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}
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}
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impl<'a> ResolverState<'a> {
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/// Execute some function with a new scope. The scope will be disposed
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/// of after the function has been executed.
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fn with_scope<F>(&mut self, f: F, scope_type: ScopeType) -> ResolverResult
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where
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F: FnOnce(&mut Self) -> ResolverResult,
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{
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self.scopes.push(SymScope::new(scope_type));
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let result = f(self).and_then(|_| self.check_unused());
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self.scopes.pop();
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result
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}
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/// Get the type of the current scope.
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fn current_type(&self) -> ScopeType {
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let pos = self.scopes.len() - 1;
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self.scopes[pos].scope_type
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}
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/// Check for unused symbols in the scope. If an unused symbol is found and
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/// its name does not begin with an underscore, generate an error.
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fn check_unused(&self) -> ResolverResult {
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self.scopes[self.scopes.len() - 1]
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.symbols
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.values()
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.filter(|v| v.state != SymState::Used)
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.filter(|v| v.decl.is_some())
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.find(|v| !v.decl.unwrap().lexeme.starts_with('_'))
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.map_or(Ok(()), |v| {
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self.error(
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v.decl.unwrap(),
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"unused symbol; prefix its name with '_' to avoid this error",
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)
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})
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}
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/// Try to declare a symbol. If the scope already contains a declaration
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/// for the same name, return an error.
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fn declare<'b>(&mut self, name: &'b Token, kind: SymKind) -> ResolverResult
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where
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'b: 'a,
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{
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assert!(!self.scopes.is_empty());
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let idx = self.scopes.len() - 1;
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let scope = &mut self.scopes[idx];
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if scope.symbols.contains_key(&name.lexeme as &str) {
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Err(SloxError::with_token(
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ErrorKind::Parse,
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name,
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"already a symbol with this name in this scope".to_owned(),
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))
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} else {
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scope.symbols.insert(
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name.lexeme.clone(),
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SymInfo {
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decl: Some(name),
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kind,
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state: SymState::Declared,
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},
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);
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Ok(())
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}
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}
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/// Mark a symbol as defined. If the symbol has already been defined or
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/// used, its state isn't affected.
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fn define(&mut self, name: &Token) {
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assert!(!self.scopes.is_empty());
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let idx = self.scopes.len() - 1;
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let top = &mut self.scopes[idx];
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if let Some(info) = top.symbols.get_mut(&name.lexeme as &str) {
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if info.state == SymState::Declared {
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info.state = SymState::Defined;
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}
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}
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}
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/// Declare and define the "this" value for the current scope.
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fn define_this(&mut self) {
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assert!(!self.scopes.is_empty());
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let idx = self.scopes.len() - 1;
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let scope = &mut self.scopes[idx];
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assert!(!scope.symbols.contains_key("this"));
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scope.symbols.insert(
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"this".to_owned(),
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SymInfo {
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decl: None,
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kind: SymKind::This,
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state: SymState::Defined,
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},
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);
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}
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/// Resolve a symbol when it is being used. If the symbol is local,
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/// the lookup distance will be stored to the resolution map.
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fn resolve_use(&mut self, expr: &VariableExpr) -> ResolverResult {
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let mut i = self.scopes.len();
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while i != 0 {
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i -= 1;
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if let Some(info) = self.scopes[i].symbols.get_mut(&expr.token.lexeme as &str) {
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if info.state == SymState::Declared {
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return self.error(&expr.token, "symbol accessed before definition");
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}
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info.state = SymState::Used;
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self.mark_resolved(&expr.id, i);
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return Ok(());
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}
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}
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self.symbol_not_found(&expr.token)
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}
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/// Resolve a symbol when it is being assigned to. If the symbol is local,
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/// the lookup distance will be stored to the resolution map. Trying to
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/// assign to something that isn't a variable will cause an error.
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fn resolve_assignment(&mut self, expr_id: &usize, name: &Token) -> ResolverResult {
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let mut i = self.scopes.len();
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while i != 0 {
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i -= 1;
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if let Some(info) = self.scopes[i].symbols.get_mut(&name.lexeme as &str) {
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if info.kind != SymKind::Variable {
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return self.error(name, "cannot assign to this symbol");
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}
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if info.state == SymState::Declared {
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info.state = SymState::Defined;
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}
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self.mark_resolved(expr_id, i);
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return Ok(());
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}
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}
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self.symbol_not_found(name)
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}
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/// Add an entry to the resolution map for an AST node.
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fn mark_resolved(&mut self, expr_id: &usize, depth: usize) {
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// Only mark symbols as locals if we're not at the top-level scope.
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if depth != 0 {
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self.resolved
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.insert(*expr_id, self.scopes.len() - 1 - depth);
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}
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}
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/// Return an error corresponding to an undeclared symbol.
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fn symbol_not_found(&mut self, name: &Token) -> ResolverResult {
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self.error(name, "undeclared symbol")
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}
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/// Return an error.
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fn error(&self, name: &Token, message: &str) -> ResolverResult {
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Err(SloxError::with_token(
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ErrorKind::Parse,
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name,
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message.to_owned(),
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))
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}
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}
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/// Process a function declaration.
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fn resolve_function<'a, 'b>(
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rs: &mut ResolverState<'a>,
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params: &'b [Token],
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body: &'b Vec<StmtNode>,
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) -> ResolverResult
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where
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'b: 'a,
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{
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for param in params {
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rs.declare(param, SymKind::Variable)?;
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rs.define(param);
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}
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// Unlike the original Lox, function arguments and function bodies do
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// not use the same environment.
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rs.with_scope(|rs| body.resolve(rs), ScopeType::Function)
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}
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/// Process all method definitions in a class.
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fn resolve_class<'a, 'b>(rs: &mut ResolverState<'a>, methods: &'b [FunDecl]) -> ResolverResult
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where
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'b: 'a,
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{
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rs.define_this();
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methods.iter().try_for_each(|method| {
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rs.with_scope(
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|rs| resolve_function(rs, &method.params, &method.body),
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ScopeType::Method,
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)
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})
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}
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/// Helper trait used to visit the various AST nodes with the resolver.
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trait VarResolver {
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/// Try to resolve local variables under some AST node.
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fn resolve<'a, 'b>(&'a self, rs: &mut ResolverState<'b>) -> ResolverResult
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where
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'a: 'b;
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}
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impl VarResolver for ProgramNode {
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fn resolve<'a, 'b>(&'a self, rs: &mut ResolverState<'b>) -> ResolverResult
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where
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'a: 'b,
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{
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self.0.resolve(rs)
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}
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}
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impl VarResolver for Vec<StmtNode> {
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fn resolve<'a, 'b>(&'a self, rs: &mut ResolverState<'b>) -> ResolverResult
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where
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'a: 'b,
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{
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for stmt in self.iter() {
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stmt.resolve(rs)?;
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}
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Ok(())
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}
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}
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impl VarResolver for StmtNode {
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fn resolve<'a, 'b>(&'a self, rs: &mut ResolverState<'b>) -> ResolverResult
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where
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'a: 'b,
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{
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match self {
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StmtNode::Block(stmts) => rs.with_scope(|rs| stmts.resolve(rs), rs.current_type()),
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StmtNode::VarDecl(name, None) => {
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rs.declare(name, SymKind::Variable)?;
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Ok(())
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}
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StmtNode::VarDecl(name, Some(init)) => {
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rs.declare(name, SymKind::Variable)?;
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init.resolve(rs)?;
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rs.define(name);
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Ok(())
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}
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StmtNode::FunDecl(decl) => {
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rs.declare(&decl.name, SymKind::Function)?;
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rs.define(&decl.name);
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rs.with_scope(
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|rs| resolve_function(rs, &decl.params, &decl.body),
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ScopeType::Function,
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)
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}
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StmtNode::ClassDecl(decl) => {
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rs.declare(&decl.name, SymKind::Class)?;
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rs.define(&decl.name);
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rs.with_scope(|rs| resolve_class(rs, &decl.methods), rs.current_type())
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}
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StmtNode::If {
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condition,
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then_branch,
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else_branch: None,
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} => condition.resolve(rs).and_then(|_| then_branch.resolve(rs)),
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StmtNode::If {
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condition,
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then_branch,
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else_branch: Some(else_branch),
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} => condition
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.resolve(rs)
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.and_then(|_| then_branch.resolve(rs))
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.and_then(|_| else_branch.resolve(rs)),
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StmtNode::Loop {
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label: _,
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condition,
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body,
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after_body,
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} => condition
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.resolve(rs)
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.and_then(|_| {
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if let Some(stmt) = after_body {
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stmt.resolve(rs)
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} else {
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Ok(())
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}
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})
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.and_then(|_| body.resolve(rs)),
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StmtNode::Return {
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token: _,
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value: None,
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} => Ok(()),
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StmtNode::Return {
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token: _,
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value: Some(expr),
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} => expr.resolve(rs),
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StmtNode::Expression(expr) => expr.resolve(rs),
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StmtNode::Print(expr) => expr.resolve(rs),
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StmtNode::LoopControl {
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is_break: _,
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loop_name: _,
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} => Ok(()),
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}
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}
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}
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impl VarResolver for ExprNode {
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fn resolve<'a, 'b>(&'a self, rs: &mut ResolverState<'b>) -> ResolverResult
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where
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'a: 'b,
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{
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match self {
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ExprNode::Variable(var_expr) | ExprNode::This(var_expr) => rs.resolve_use(var_expr),
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ExprNode::Assignment { name, value, id } => {
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value.resolve(rs)?;
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rs.resolve_assignment(id, name)
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}
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ExprNode::Lambda { params, body } => {
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rs.with_scope(|rs| resolve_function(rs, params, body), ScopeType::Function)
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}
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ExprNode::Logical(binary_expr) | ExprNode::Binary(binary_expr) => binary_expr
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.left
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.resolve(rs)
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.and_then(|_| binary_expr.right.resolve(rs)),
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ExprNode::Unary { operator: _, right } => right.resolve(rs),
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ExprNode::Grouping { expression } => expression.resolve(rs),
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ExprNode::Litteral { value: _ } => Ok(()),
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ExprNode::Call {
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callee,
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right_paren: _,
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arguments,
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} => callee.resolve(rs).and_then(|_| arguments.resolve(rs)),
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ExprNode::Get(get_expr) => get_expr.instance.resolve(rs),
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ExprNode::Set(set_expr) => set_expr
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.instance
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.resolve(rs)
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.and_then(|_| set_expr.value.resolve(rs)),
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}
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}
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}
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impl VarResolver for Vec<ExprNode> {
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fn resolve<'a, 'b>(&'a self, rs: &mut ResolverState<'b>) -> ResolverResult
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where
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'a: 'b,
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{
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for expr in self.iter() {
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expr.resolve(rs)?;
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}
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Ok(())
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}
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}
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