Cargo "cyclic package dependency" in CI

Cargo detected a dependency cycle: crate A depends on B which depends back on A. Normal dependencies cannot form a cycle, so cargo aborts resolution -- usually a dev-dependency edge closing a loop.

What this error means

cargo fails with error: cyclic package dependency: package A depends on itself and prints the cycle path. It is deterministic for the manifest set.

cargo

error: cyclic package dependency: package `core v0.1.0` depends on itself. Cycle:
package `core v0.1.0`
    ... which satisfies dependency `utils` of package `core v0.1.0`
package `utils v0.1.0`
    ... which satisfies dependency `core` of package `utils v0.1.0`

Common causes

Mutually dependent crates

Two workspace members list each other as dependencies, forming a cycle cargo cannot order.

Dev-dependency closing the loop

A [dev-dependencies] edge from a lower crate back up to a higher one creates a cycle, even if the normal deps are acyclic.

How to fix it

Break the cycle by extracting shared code

Identify the two crates in the printed cycle.
Move the shared types/functions into a third, lower-level crate both can depend on.
Remove the back-edge so the graph is a DAG again.

Cargo.toml

# crates/core -> depends on crates/shared
# crates/utils -> depends on crates/shared
# (neither depends on the other)

How to prevent it

Keep workspace crates layered; avoid back-edges.
Factor shared code into a low-level crate instead of cross-depending.
Watch dev-dependencies -- they count toward cycles.