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Change flattened dependency graph from DiGraph<NodeId> to DiGraph<SystemKey> #20172

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Change flattened dependency graph from DiGraph<NodeId> to DiGraph<SystemKey> #20172

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ItsDoot
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@ItsDoot ItsDoot commented Jul 17, 2025

Objective

Semantically, the fully flattened dependency graph never contains SystemSetKeys, so lets encode that into its type.

Solution

  • Added GraphNodeId trait and its related traits GraphNodeIdPair and DirectedGraphNodeId.
    • The latter two traits are used to let us keep the space savings of CompactNodeIdAndDirection and CompactNodeIdPair.
  • Generalized DiGraph and UnGraph with a new GraphNodeId N type parameter.
  • Generalized most functions involving DiGraph/UnGraph to take a GraphNodeId type parameter.
  • Added Graph::try_into function to help us convert from DiGraph<NodeId> to DiGraph<SystemKey>. Does it look a bit gnarly? Yea.

Testing

Re-using current tests.

@ItsDoot ItsDoot added A-ECS Entities, components, systems, and events C-Code-Quality A section of code that is hard to understand or change D-Modest A "normal" level of difficulty; suitable for simple features or challenging fixes S-Needs-Review Needs reviewer attention (from anyone!) to move forward labels Jul 17, 2025
ItsDoot
ItsDoot commented Jul 17, 2025
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@ItsDoot ItsDoot requested review from chescock and hymm and removed request for chescock July 17, 2025 06:59
@ItsDoot ItsDoot mentioned this pull request Jul 13, 2025
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chescock
chescock approved these changes Jul 17, 2025
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alice-i-cecile
alice-i-cecile reviewed Jul 17, 2025
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ItsDoot commented Jul 18, 2025 •
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Thoughts on GraphNodeId now? I removed the two extra related traits as suggested by @chescock and also renamed the associated types to match their semantics.

EDIT: Since it's only a 16 line file now, I could also co-locate it in the same file as Graph.

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@alice-i-cecile alice-i-cecile requested a review from chescock July 18, 2025 04:10
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I appreciate the explictness about systems vs system sets. I think this is a net improvement as a result.

chescock
chescock approved these changes Jul 18, 2025
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crates/bevy_ecs/src/schedule/node.rs

impl From<CompactNodeIdPair> for (NodeId, NodeId) {
fn from(value: CompactNodeIdPair) -> Self {
let a = match value.is_system_a {
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Oh, I didn't notice the match bool before. It was like that before, and it does seem reasonable here for symmetry with the reverse impl, but ... but ... if!

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match on bool good! if bad!

@ItsDoot ItsDoot added S-Ready-For-Final-Review This PR has been approved by the community. It's ready for a maintainer to consider merging it and removed S-Needs-Review Needs reviewer attention (from anyone!) to move forward labels Jul 19, 2025
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@hymm hymm Awaiting requested review from hymm

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A-ECS Entities, components, systems, and events C-Code-Quality A section of code that is hard to understand or change D-Modest A "normal" level of difficulty; suitable for simple features or challenging fixes S-Ready-For-Final-Review This PR has been approved by the community. It's ready for a maintainer to consider merging it
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