Add #[track_caller] to Query methods

[BD103]

Objective

• Closes Resolve #[track_caller] inconsistency in bevy's Query types. #12958

Solution

• Find all methods under Query that mention panicking, and add #[track_caller] to them.

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Changelog

• Added #[track_caller] to Query::many, Query::many_mut, Query::transmute_lens, and Query::transmute_lens_filtered.

For reviewers

I'm unfamiliar with the depths of the Query struct. Please check whether it makes since for the updated methods to have #[track_caller], and if I missed any!

[BD103]

cc @Themayu

[cart]

Iirc track_caller does introduce some minor runtime overhead. For high frequency usage this might show up on benchmarks. Can we do a sanity check here with before / after benches.

[BD103]

I created a benchmark comparing the overhead of #[track_caller] on my M1 MacBook. (See the gist.) There appears to be little to no overhead whatsoever.

tracked false           time:   [1.5369 ns 1.5376 ns 1.5383 ns]
Found 8 outliers among 100 measurements (8.00%)
  5 (5.00%) high mild
  3 (3.00%) high severe

untracked false         time:   [1.5371 ns 1.5376 ns 1.5382 ns]
Found 5 outliers among 100 measurements (5.00%)
  3 (3.00%) high mild
  2 (2.00%) high severe

If you look at the average time, they both take 1.5376 nanoseconds. The #[track_caller] has a greater deviation, with both a lower minimum and greater maximum, but this is sub-nanosecond behavior.

Furthermore, you can compare the generated assembly here.

untracked:
  test edi, edi
  jne .LBB7_2
  ret
.LBB7_2: ; panicking code, no `#[track_caller]`
  push rax
  lea rdi, [rip + .L__unnamed_3] ; returns panic message
  lea rdx, [rip + .L__unnamed_4] ; different
  mov esi, 9
  call _ZN3std9panicking11begin_panic17he275593115e721e6E

tracked:
  test edi, edi
  jne .LBB8_2
  ret
.LBB8_2: ; panicking code, with `#[track_caller]`
  push rax
  mov rdx, rsi ; different
  lea rdi, [rip + .L__unnamed_5] ; returns panic message
  mov esi, 7
  call _ZN3std9panicking11begin_panic17he275593115e721e6E

The only difference in the generated code is a lea instruction being replaced with a mov instruction. This change is only noticeable when the function panics, where time is not an issue.