add track_caller attribute to map_err and ok_or/_else

[yaahc]

Motivation unicode-org/icu4x#4048

This PR resolves a common edge case where users attempting to manually track std::panic::Locations of their callers in their Error types end up with irrelevant locations inside of std.

The main concern with this approach that I'm aware of is that #[track_caller] increases the stack sizes of the functions it is applied to, though I think this is a non-issue since we already have #[track_caller] on Result's FromResidual impl which is used far more frequently than any of these APIs when converting errors between different types. This change brings these functions in line with that impl.

example demonstrating the issue: https://play.rust-lang.org/?version=stable&mode=debug&edition=2024&gist=8205bcd02b380d9fd02b1f1153ac9c4e

[rustbot]

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[yaahc]

Relevant previous discussion: #91752

[tgross35]

@bors2 try @rust-timer queue

[rust-bors]

⌛ Trying commit 0eaeb6c with merge b52d9f8…

To cancel the try build, run the command @bors2 try cancel.

[rust-bors]

☀️ Try build successful (CI)
Build commit: b52d9f8 (b52d9f8ec0bb49a50d8e93315ac4e6b222cd971c, parent: 27eb2690f4d78f0f41eaa7193a06cd49d74b2eb0)

[rust-timer]

Finished benchmarking commit (b52d9f8): comparison URL.

Overall result: ❌ regressions - please read the text below

Benchmarking this pull request means it may be perf-sensitive – we'll automatically label it not fit for rolling up. You can override this, but we strongly advise not to, due to possible changes in compiler perf.

Next Steps: If you can justify the regressions found in this try perf run, please do so in sufficient writing along with @rustbot label: +perf-regression-triaged. If not, please fix the regressions and do another perf run. If its results are neutral or positive, the label will be automatically removed.

@bors rollup=never
@rustbot label: -S-waiting-on-perf +perf-regression

Instruction count

Our most reliable metric. Used to determine the overall result above. However, even this metric can be noisy.

	mean	range	count
Regressions ❌ (primary)	2.9%	[2.9%, 2.9%]	1
Regressions ❌ (secondary)	-	-	0
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	2.9%	[2.9%, 2.9%]	1

Max RSS (memory usage)

This benchmark run did not return any relevant results for this metric.

Cycles

Results (primary 2.5%)

A less reliable metric. May be of interest, but not used to determine the overall result above.

	mean	range	count
Regressions ❌ (primary)	2.5%	[2.5%, 2.5%]	1
Regressions ❌ (secondary)	-	-	0
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	2.5%	[2.5%, 2.5%]	1

Binary size

Results (primary 0.1%, secondary 0.1%)

A less reliable metric. May be of interest, but not used to determine the overall result above.

	mean	range	count
Regressions ❌ (primary)	0.1%	[0.0%, 0.1%]	19
Regressions ❌ (secondary)	0.1%	[0.0%, 0.2%]	11
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-0.0%	[-0.0%, -0.0%]	1
All ❌✅ (primary)	0.1%	[0.0%, 0.1%]	19

Bootstrap: 693.336s -> 692.254s (-0.16%)
Artifact size: 372.12 MiB -> 372.09 MiB (-0.01%)

[tgross35]

The only regression is for an incremental build of syn. Cc @dtolnay if you have any thoughts here (I seem to remember you using a match workaround somewhere to avoid #[track_caller] expense?) but I think this is probably fine to merge given the effect isn't all that bad and won't be visible for any consumers of syn.

[ogoffart]

Just curious: What's the reason to add track_caller on this function? ok_or does not panic nor call any user code that would track the caller. Or do you expect the Drop from E to track the caller? but that seems far fetched. Am I missing something or is this an oversight? (map_or_else seems like a better candidate)

[yaahc]

you're right, that's an oversight. The only one that matters is ok_or_else due to it taking a closure. Ill also look at adding it to map_or_else

[tgross35]

@rustbot author for those adjustments

[tgross35]

Been a few months, gentle nudge @yaahc if you're able to do the updates here.

[freitagfelipe]

Gentle nudge @yaahc, would really like to see this merged.

[tiberiusferreira]

I hit this today, would love to see this merged.

Thank you for all the work here. ❤️