Module cycle_origins 

cycle-origins analysis — pinpoint the commit where each HEAD dependency cycle first formed.

dependency-cycles lists the import-graph cycles that exist now. This goes further: for each cycle it bisects history — reading source at past revisions via Repo::read_blob_at — to find the earliest commit where that exact cycle existed, i.e. the commit that closed the loop. Actionable archaeology: “the a ↔ b ↔ c tangle formed at abc1234 on 2026-03-15.”

Method

The HEAD cycles come from the shared SCC kernel applied to the import graph reconstructed at HEAD (via [architecture_trend::import_graph_at_rev], so the cycle definition and the bisect predicate use the exact same machinery). For each cycle, a binary search over the date-ordered commit list finds the transition from “cycle absent” to “cycle present”, rebuilding the import graph in memory at each probe and testing whether the cycle’s files sit in a single SCC there.

Binary search assumes a cycle, once formed, stays formed — its presence is monotonic over time. Cycles that form, break and reform are rare; for those the search still returns one valid formation point. Only the MAX_CYCLES largest cycles are traced (each costs ~log₂(commits) graph rebuilds), bounding cost on tangled repos.

Structs

CycleOriginRow

One traced dependency cycle and the commit where it first formed.

Constants

MAX_CYCLES

Maximum number of cycles to trace (largest first), bounding the historical-scan cost on heavily-tangled repositories.

Functions

run_cycle_origins

Run the cycle-origins analysis. Returns one row per traced HEAD cycle, largest first. Needs repository access (it reads historical blobs).