leo_passes/common/graph/mod.rs
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// Copyright (C) 2019-2025 Provable Inc.
// This file is part of the Leo library.
// The Leo library is free software: you can redistribute it and/or modify
// it under the terms of the GNU General Public License as published by
// the Free Software Foundation, either version 3 of the License, or
// (at your option) any later version.
// The Leo library is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
// GNU General Public License for more details.
// You should have received a copy of the GNU General Public License
// along with the Leo library. If not, see <https://www.gnu.org/licenses/>.
use leo_span::Symbol;
use indexmap::{IndexMap, IndexSet};
use std::{fmt::Debug, hash::Hash};
/// A struct dependency graph.
pub type StructGraph = DiGraph<Symbol>;
/// A call graph.
pub type CallGraph = DiGraph<Symbol>;
/// An import dependency graph.
pub type ImportGraph = DiGraph<Symbol>;
/// A node in a graph.
pub trait Node: Copy + 'static + Eq + PartialEq + Debug + Hash {}
impl Node for Symbol {}
/// Errors in directed graph operations.
#[derive(Debug)]
pub enum DiGraphError<N: Node> {
/// An error that is emitted when a cycle is detected in the directed graph. Contains the path of the cycle.
CycleDetected(Vec<N>),
}
/// A directed graph.
#[derive(Debug, PartialEq, Eq)]
pub struct DiGraph<N: Node> {
/// The set of nodes in the graph.
nodes: IndexSet<N>,
/// The directed edges in the graph.
/// Each entry in the map is a node in the graph, and the set of nodes that it points to.
edges: IndexMap<N, IndexSet<N>>,
}
impl<N: Node> DiGraph<N> {
/// Initializes a new `DiGraph` from a vector of source nodes.
pub fn new(nodes: IndexSet<N>) -> Self {
Self { nodes, edges: IndexMap::new() }
}
/// Adds an edge to the graph.
pub fn add_edge(&mut self, from: N, to: N) {
// Add `from` and `to` to the set of nodes if they are not already in the set.
self.nodes.insert(from);
self.nodes.insert(to);
// Add the edge to the adjacency list.
let entry = self.edges.entry(from).or_default();
entry.insert(to);
}
/// Returns `true` if the graph contains the given node.
pub fn contains_node(&self, node: N) -> bool {
self.nodes.contains(&node)
}
/// Returns the post-order ordering of the graph.
/// Detects if there is a cycle in the graph.
pub fn post_order(&self) -> Result<IndexSet<N>, DiGraphError<N>> {
// The set of nodes that do not need to be visited again.
let mut finished: IndexSet<N> = IndexSet::with_capacity(self.nodes.len());
// Perform a depth-first search of the graph, starting from `node`, for each node in the graph.
for node in self.nodes.iter() {
// If the node has not been explored, explore it.
if !finished.contains(node) {
// The set of nodes that are on the path to the current node in the search.
let mut discovered: IndexSet<N> = IndexSet::new();
// Check if there is a cycle in the graph starting from `node`.
if let Some(node) = self.contains_cycle_from(*node, &mut discovered, &mut finished) {
let mut path = vec![node];
// Backtrack through the discovered nodes to find the cycle.
while let Some(next) = discovered.pop() {
// Add the node to the path.
path.push(next);
// If the node is the same as the first node in the path, we have found the cycle.
if next == node {
break;
}
}
// Reverse the path to get the cycle in the correct order.
path.reverse();
// A cycle was detected. Return the path of the cycle.
return Err(DiGraphError::CycleDetected(path));
}
}
}
// No cycle was found. Return the set of nodes in topological order.
Ok(finished)
}
/// Retains a subset of the nodes, and removes all edges in which the source or destination is not in the subset.
pub fn retain_nodes(&mut self, nodes: &IndexSet<N>) {
// Remove the nodes from the set of nodes.
self.nodes.retain(|node| nodes.contains(node));
self.edges.retain(|node, _| nodes.contains(node));
// Remove the edges that reference the nodes.
for (_, children) in self.edges.iter_mut() {
children.retain(|child| nodes.contains(child));
}
}
// Detects if there is a cycle in the graph starting from the given node, via a recursive depth-first search.
// If there is no cycle, returns `None`.
// If there is a cycle, returns the node that was most recently discovered.
// Nodes are added to `finished` in post-order order.
fn contains_cycle_from(&self, node: N, discovered: &mut IndexSet<N>, finished: &mut IndexSet<N>) -> Option<N> {
// Add the node to the set of discovered nodes.
discovered.insert(node);
// Check each outgoing edge of the node.
if let Some(children) = self.edges.get(&node) {
for child in children.iter() {
// If the node already been discovered, there is a cycle.
if discovered.contains(child) {
// Insert the child node into the set of discovered nodes; this is used to reconstruct the cycle.
// Note that this case is always hit when there is a cycle.
return Some(*child);
}
// If the node has not been explored, explore it.
if !finished.contains(child) {
if let Some(child) = self.contains_cycle_from(*child, discovered, finished) {
return Some(child);
}
}
}
}
// Remove the node from the set of discovered nodes.
discovered.pop();
// Add the node to the set of finished nodes.
finished.insert(node);
None
}
}
#[cfg(test)]
mod test {
use super::*;
impl Node for u32 {}
fn check_post_order<N: Node>(graph: &DiGraph<N>, expected: &[N]) {
let result = graph.post_order();
assert!(result.is_ok());
let order: Vec<N> = result.unwrap().into_iter().collect();
assert_eq!(order, expected);
}
#[test]
fn test_post_order() {
let mut graph = DiGraph::<u32>::new(IndexSet::new());
graph.add_edge(1, 2);
graph.add_edge(1, 3);
graph.add_edge(2, 4);
graph.add_edge(3, 4);
graph.add_edge(4, 5);
check_post_order(&graph, &[5, 4, 2, 3, 1]);
let mut graph = DiGraph::<u32>::new(IndexSet::new());
// F -> B
graph.add_edge(6, 2);
// B -> A
graph.add_edge(2, 1);
// B -> D
graph.add_edge(2, 4);
// D -> C
graph.add_edge(4, 3);
// D -> E
graph.add_edge(4, 5);
// F -> G
graph.add_edge(6, 7);
// G -> I
graph.add_edge(7, 9);
// I -> H
graph.add_edge(9, 8);
// A, C, E, D, B, H, I, G, F.
check_post_order(&graph, &[1, 3, 5, 4, 2, 8, 9, 7, 6]);
}
#[test]
fn test_cycle() {
let mut graph = DiGraph::<u32>::new(IndexSet::new());
graph.add_edge(1, 2);
graph.add_edge(2, 3);
graph.add_edge(2, 4);
graph.add_edge(4, 1);
let result = graph.post_order();
assert!(result.is_err());
let DiGraphError::CycleDetected(cycle) = result.unwrap_err();
let expected = Vec::from([1u32, 2, 4, 1]);
assert_eq!(cycle, expected);
}
#[test]
fn test_unconnected_graph() {
let graph = DiGraph::<u32>::new(IndexSet::from([1, 2, 3, 4, 5]));
check_post_order(&graph, &[1, 2, 3, 4, 5]);
}
#[test]
fn test_retain_nodes() {
let mut graph = DiGraph::<u32>::new(IndexSet::new());
graph.add_edge(1, 2);
graph.add_edge(1, 3);
graph.add_edge(1, 5);
graph.add_edge(2, 3);
graph.add_edge(2, 4);
graph.add_edge(2, 5);
graph.add_edge(3, 4);
graph.add_edge(4, 5);
let mut nodes = IndexSet::new();
nodes.insert(1);
nodes.insert(2);
nodes.insert(3);
graph.retain_nodes(&nodes);
let mut expected = DiGraph::<u32>::new(IndexSet::new());
expected.add_edge(1, 2);
expected.add_edge(1, 3);
expected.add_edge(2, 3);
expected.edges.insert(3, IndexSet::new());
assert_eq!(graph, expected);
}
}