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//! Regression: community density must not overflow for very large communities.
//!
//! `CommunityDetector::community_stats` computes `max_internal = nc * (nc - 1)`
//! where `nc: u32` is the community node count. When m1nd ingests a large repo
//! and Louvain collapses >= 65_537 nodes into one community, `nc * (nc - 1)`
//! exceeds `u32::MAX` and overflows (debug: panic; release: a wrong, wrapped
//! density). This builds exactly that community and asserts a finite, in-range
//! density instead.
//! (Surfaced by the X-RAY adversarial bug hunt.)
use m1nd_core::graph::Graph;
use m1nd_core::topology::{CommunityDetector, CommunityResult};
use m1nd_core::types::{CommunityId, FiniteF32, NodeType};
#[test]
fn community_density_does_not_overflow_for_huge_community() {
// 65_537 is the smallest count where nc * (nc - 1) exceeds u32::MAX:
// 65_537 * 65_536 = 4_295_032_832 > 4_294_967_295.
let n: u32 = 65_537;
let mut g = Graph::new();
for i in 0..n {
g.add_node(&format!("n{i}"), "n", NodeType::Function, &[], 0.0, 0.0)
.expect("add_node");
}
g.finalize().expect("finalize");
// Every node in a single community — what Louvain yields when a dense graph
// fully collapses. No edges are needed: the overflow is in the max-internal
// term, which is computed before any density division.
let result = CommunityResult {
assignments: vec![CommunityId(0); n as usize],
num_communities: 1,
modularity: FiniteF32::new(0.0),
passes: 1,
};
let stats = CommunityDetector::community_stats(&g, &result);
assert_eq!(stats.len(), 1, "exactly one community expected");
let density = stats[0].density.get();
assert!(density.is_finite(), "density must be finite, got {density}");
assert!(
(0.0..=1.0).contains(&density),
"density must stay in [0, 1], got {density}"
);
assert_eq!(
stats[0].node_count, n,
"node_count must match the community"
