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C# codegen: generated `Equals(object)` on `[SpacetimeDB.Type]` structs recurses forever

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Assessment

Difficulty
2/5
Estimated time
1-3 hours
Newbie friendliness
72/100
Issue type
Bug
Clarity
Clearly specified
Activity status
Active
Tech stack
csharp
Domain
devtools

Research direction

The bug is in the C# source generator at crates/bindings-csharp/BSATN.Codegen/Type.cs, around lines 809-818, where the generated Equals(object) override for structs calls Equals(that_) on a Nullable and recurses. Start by reading that emitter code, then reproduce with the Cell struct and Equals(a, b) example from the issue. Done when the generated override unwraps the nullable value, for example by calling Equals(that_.Value), and the reducer no longer overflows the stack.

Written by the indexing model from the issue text.

Description

Version: SpacetimeDB.Runtime 2.11.*, still on master e596513
Where: crates/bindings-csharp/BSATN.Codegen/Type.cs ~L809-818

public override bool Equals(object? that) {
    if (that == null) return false;
    var that_ = that as VoipCellCoord?;          // for structs this is Nullable<T>
    if (((object?)that_) == null) return false;
    return Equals(that_);                        // binds to Equals(object?) again → infinite recursion
}

Repro:

[SpacetimeDB.Type] public partial struct Cell { public int X; public int Y; }

[SpacetimeDB.Reducer]
public static void Repro(ReducerContext ctx) {
    Cell a = new() { X = 1 }; Cell? b = new Cell { X = 1 };
    var same = Equals(a, b);   // object.Equals → Cell.Equals(object) → stack overflow, wasm trap
}

Actual: the reducer traps with a deep recursion through VoipCellCoord__Equals_0 (RhBox at the bottom). Anything
that goes through Equals(object) is affected: object.Equals, EqualityComparer<T>.Default on boxed values,
collections of boxed structs.
Fix: for structs, return Equals(that_.Value); (or that is T t && Equals(t)).

Dominant language
Rust
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