Module blockers 

Dependency inventory for blocked tasks.

[crate::daemon::resolve_blockers] frees a task when its dependency is done (or its question answered) and quarantines it when the dependency no longer exists. It has nothing to say about a dependency that is alive but stuck: a held task never becomes done on its own, so everything waiting on it waits forever, and nothing shows why. Inventory answers that from one snapshot of the queue and the questions:

• Inventory::waits_on - what a blocked task waits on and each dependency’s state, following a chain of blocked dependencies (4135 (blocked → 9db7 held)), for magi task list and the web UI.
• Inventory::stuck_roots - the tasks nothing in the loop will ever run that a blocked task is frozen behind. crate::triage asks about each such root once, naming everything it freezes.

A blocked task is stuck when it has at least one unresolved dependency and every one of them is either held or itself a stuck blocked task. Anything that can still make progress - a queued, running or failed (retried) task, an open question, a dependency that no longer exists (which resolve_blockers quarantines) - makes it not stuck. A dependency cycle terminates: its members are stuck, and the smallest id in the cycle is its root.

Structs

Inventory

One snapshot of the tasks and questions a blocked_by id can name.