Wrap tracing spans in #[cfg(feature = "trace")]

[CrazyRoka]

Objective

• Reducing tracing overhead.
• Ensure that heavy info_span! calls and their associated logic are only compiled and executed when the trace feature is enabled.
• Fixes a memory leak on web, per Memory leak due to LogPlugin #23949.

Solution

• Wrapped info_span! entries with #[cfg(feature = "trace")].

Testing

• cargo check

---

Showcase

I observed in flamegraph profiling that certain span creations were consuming ~1.5% of total CPU time.

[mgi388]

@CrazyRoka I thought these are compiled out already when you configure your tracing log level feature: https://docs.rs/tracing/latest/tracing/level_filters/index.html#compile-time-filters

I could be missing something though.

[CrazyRoka]

@mgi388 I think we are using the default configuration, which according to https://docs.rs/tracing/latest/tracing/level_filters/index.html#compile-time-filters

By default, no levels are disabled.

During profiling I was running an example with this command:

CARGO_PROFILE_RELEASE_DEBUG=true cargo flamegraph -F 97 --example many_shadow_lights -- -l 50 -m 50

[alice-i-cecile]

@jakemoran, we use a open review process here at Bevy, where we weight everyone's reviews when deciding what to do with a PR. Can you please take a look and offer your opinion?

[jakemoran]

LGTM!