Comprehensive Source Tracking

[NthTensor]

Bevy code can get very spread out. It's not uncommon for very well separated pieces of machinery to have to coordinate, often across crate boundaries. Bevy has great tools to accomplish this sort of coordination, but it is often hard to inspect.

The first attempt at improving runtime inspection was made in #14034, which added optional tracking of exactly where every component is accessed or mutated, as an extension of the change detection system. But there's still several other places we don't track this information.

• Event Source Tracking #16776
• Track callsite for observers & hooks #15607
• track_change_detection: Also track spawns/despawns #16047
• Add source location tracking to resource access.
• Rename track_change_detection to track_source_hints or similar.
• Expose source tracking through the remote protocol.

[alice-i-cecile]

Each of these work items should be tackled one PR at a time to help them get merged in smoothly :)

[SpecificProtagonist]

Another aspect to add source location tracking to: Spawns/Despawn (PR: #16047).

[NthTensor]

Thanks for helping with triage & de-duplication @SpecificProtagonist <3.

[SpecificProtagonist]

Another potential issue: Currently, custom commands cannot preserve source location tracking. A simple solution would be to expose all *_with_caller functions, but that would lead to a lot of API duplication.

[NthTensor]

The location would point back to the custom commands though, right? That seems acceptable, it can still help users debug their code.

It just shouldn't return locations pointing to the core engine crates.

[SpecificProtagonist]

Another missing feature: This info should be accessible via the Bevy Remote Protocol.