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paths.rs
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// -*- coding: utf-8 -*-
// ------------------------------------------------------------------------------------------------
// Copyright © 2021, stack-graphs authors.
// Licensed under either of Apache License, Version 2.0, or MIT license, at your option.
// Please see the LICENSE-APACHE or LICENSE-MIT files in this distribution for license details.
// ------------------------------------------------------------------------------------------------
//! Paths represent name bindings in a source language.
//!
//! With the set of rules we have for constructing stack graphs, bindings between references and
//! definitions are represented by paths within the graph. Each edge in the path must leave the
//! symbol and scopes stacks in a valid state — otherwise we have violated some name binding rule
//! in the source language. The symbol and scope stacks must be empty at the beginning and end of
//! the path. The reference's _push symbol_ node "seeds" the symbol stack with the first thing
//! that we want to look for, and once we (hopefully) reach the definition that reference refers
//! to, its pop node will remove that symbol from the symbol stack, leaving both stacks empty.
use std::collections::VecDeque;
/// Errors that can occur during the path resolution process.
#[derive(Debug)]
pub enum PathResolutionError {
/// The path is cyclic, and the cycle is disallowed.
DisallowedCycle,
/// The path contains a _jump to scope_ node, but there are no scopes on the scope stack to
/// jump to.
EmptyScopeStack,
/// The path contains a _pop symbol_ or _pop scoped symbol_ node, but there are no symbols on
/// the symbol stack to pop off.
EmptySymbolStack,
/// The partial path contains multiple references to a scope stack variable, and those
/// references can't unify on a single scope stack.
IncompatibleScopeStackVariables,
/// The partial path contains multiple references to a symbol stack variable, and those
/// references can't unify on a single symbol stack.
IncompatibleSymbolStackVariables,
/// The partial path contains edges from multiple files.
IncorrectFile,
/// The path contains a _pop symbol_ or _pop scoped symbol_ node, but the symbol at the top of
/// the symbol stack does not match.
IncorrectPoppedSymbol,
/// The path contains an edge whose source node does not match the sink node of the preceding
/// edge.
IncorrectSourceNode,
/// The path contains a _pop scoped symbol_ node, but the symbol at the top of the symbol stack
/// does not have an attached scope list to pop off.
MissingAttachedScopeList,
/// The path's scope stack does not satisfy the partial path's scope stack precondition.
ScopeStackUnsatisfied,
/// The path's symbol stack does not satisfy the partial path's symbol stack precondition.
SymbolStackUnsatisfied,
/// The partial path's postcondition references a symbol stack variable that isn't present in
/// the precondition.
UnboundSymbolStackVariable,
/// The partial path's postcondition references a scope stack variable that isn't present in
/// the precondition.
UnboundScopeStackVariable,
/// The path contains a _pop symbol_ node, but the symbol at the top of the symbol stack has an
/// attached scope list that we weren't expecting.
UnexpectedAttachedScopeList,
/// A _push scoped symbol_ node referes to an exported scope node that doesn't exist.
UnknownAttachedScope,
}
/// A collection that can be used to receive the results of the [`Path::extend`][] method.
///
/// Note: There's an [open issue][std-extend] to add these methods to std's `Extend` trait. If
/// that gets merged, we can drop this trait and use the std one instead.
///
/// [std-extend]: https://github.com/rust-lang/rust/issues/72631
pub trait Extend<T> {
/// Reserve space for `additional` elements in the collection.
fn reserve(&mut self, additional: usize);
/// Add a new element to the collection.
fn push(&mut self, item: T);
}
impl<T> Extend<T> for Vec<T> {
fn reserve(&mut self, additional: usize) {
self.reserve(additional);
}
fn push(&mut self, item: T) {
self.push(item);
}
}
impl<T> Extend<T> for VecDeque<T> {
fn reserve(&mut self, additional: usize) {
self.reserve(additional);
}
fn push(&mut self, item: T) {
self.push_back(item);
}
}