Fix overly restrictive lifetime in core::panic::Location::file return type

[ijchen]

Fixes #131770 by relaxing the lifetime to match what's stored in the struct. See that issue for more details and discussion.

Since this is a breaking change, I think a crater run is in order. Since this change should only have an effect at compile-time, I think just a check run is sufficient.

[rustbot]

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[SpriteOvO]

Maybe adding a regression test in library/core/tests/panic/location.rs would be nice.

[ijchen]

Maybe adding a regression test in library/core/tests/panic/location.rs would be nice.

That's a great idea! I'll implement that.

UPDATE: Implemented. It's a bit of a strange test, since it fails through a compiler error instead of a runtime panic, but I think that's necessary considering lifetimes and the borrow checker only exists at compile time.

[cuviper]

Hmm, this is "overly restrictive" in the current implementation, but sometimes that's on purpose to give implementation freedom. For instance, we couldn't use Cow<'a, str> internally after your change. (ignoring core/alloc for a moment)

The breaking change of the function type is unlikely to be a problem IMO, but the API team should review it overall.

@rustbot label -T-libs +T-libs-api
r? libs-api

[bors]

☔ The latest upstream changes (presumably #135937) made this pull request unmergeable. Please resolve the merge conflicts.

[Dylan-DPC]

@ijchen any updates on this? this requires resolving conflicts in order to move ahead and if you are ready for a review you can click on »Ready for review« so it changes it from a draft.

[ijchen]

Thanks for the poke! I've resolved merge conflicts, although it looks like the source code has changed a bit since I left off. There's some unsafe that I want to investigate more, so I'm going to hold off marking this ready for a bit.

[Amanieu]

@rfcbot merge

[rfcbot]

Team member @Amanieu has proposed to merge this. The next step is review by the rest of the tagged team members:

• @Amanieu
• @BurntSushi
• @dtolnay
• @joshtriplett
• @m-ou-se

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[rfcbot]

🔔 This is now entering its final comment period, as per the review above. 🔔