Fix application freezing on macOS when trace_tracy is enabled

[xremming]

Objective

On macOS (26.3) enabling tracy for tracing causes Bevy to freeze here.

https://github.com/bevyengine/bevy/blob/release-0.18.1/crates/bevy_render/src/diagnostic/tracy_gpu.rs#L64

I assume this problem is likely related to the same root cause as #22365.

Solution

• Short circuit and return 0 on macOS.
  • It's probably not correct but it works. 🤷🏼‍♀️

Testing

• Tested locally by patching Bevy to the fixed version.

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[kfc35]

@xremming Just confirming that you meant to point this PR to be merged into the release-0.18.1 branch? Since 0.18.1 has been released already, I think it might be too late to merge a fix into that branch.

Does this issue appear on main? If so, I think it’s better to point this PR to be merged into main, and then we can tag it appropriately for inclusion in the correct milestone

[alice-i-cecile]

Indeed: we should point this to main, then cherrypick it to 0.18.2 if needed.

[xremming]

@kfc35 I did indeed point this to 0.18.1 branch for a reason, which is that it's where I made the fix at for myself for (and tested it). I can rebase this to main if that's preferable.

However 0.18.1 is not yet released at crates.io?

[alice-i-cecile]

I can rebase this to main if that's preferable.

Yes, this needs to be rebased :)

However 0.18.1 is not yet released at crates.io?

Correct; just waiting for final sign-off from fellow maintainers.

[xremming]

Rarely does a rebase work on the first try as intended... Nice.

Tested it out with and without the patch on main against the 3d_shapes example and can confirm the fix still works (and is still required).

[xremming]

Would be interesting if someone with an older macOS version could test this. Seeing that it has worked on macOS previously, at least based on the profiling.md that has a screenshot from macOS.

This also made me wonder if this will need to be gated on iOS too. 🤔 I remember seeing an issue about supporting Tracy on iOS and Android. Perhaps another PR will be required to rework the GPU profiling based on support for it.

[aevyrie]

Why do we even bother continuing if we hit an invalid backend - could we just make this function fallible and do nothing on unsupported platforms? Then we can stop worrying about these hacks.