Libs Meeting 2023-06-07

tags: Libs Meetings Minutes

Meeting Link: https://meet.jit.si/rust-libs-meeting-ujepnbwg2lzqgt6wvrndwimi
Attendees: Amanieu, The 8472, Mara, joboet

Agenda

• Triage
• Anything else?

Triage

FCPs

1 rust-lang/rust T-libs FCPs

• merge rust.tf/104385 Raise minimum supported Apple OS versions - (9 checkboxes left)

(Backports) rust.tf/112292 Avoid unwind across `extern "C"` in `thread_local::fast_local`

This 'technically UB' doesn't really result in actual issues, it seems.

Not a recent regression, so might not be a good backport candidate.

Left a comment.

(Nominated) rust.tf/84187 Tracking Issue for restructuring `sys_common`

Discussed last time. Still need to respond. Mara to respond.

(Nominated) rust.tf/110708 Consider documenting that (parts of?) stdlib must not be used before/after main

Discussed last time. Amanieu replied, saying the main issue is thread::current(), which is only used in a few places.

For LocalKey::with we already document it: https://doc.rust-lang.org/stable/std/thread/struct.LocalKey.html#method.with
(And also have a try_with.)

Only for thread::current() (and a few APIs that use that) we don't provide any panic docs (or a try_current() etc.).

Pre-main seems like it's rarely a problem, it's post-main that is more interesting.

(Nominated) rust.tf/111071 assert_eq! message format (take 2a)

Summary: https://github.com/rust-lang/rust/pull/111071#issuecomment-1576734594

Question 1: Change the default panic handler output format?

Possible answers:

1. No
2. Yes, as proposed, but only for multi-line messages
3. Yes, as proposed, but for all messages

3 seems like a nice option, because the current "at {message}, {location}" feels flipped/swapped.

Crater run could check how widely people depend on the exact output.

We can do an FCP to make it show up in TWiR.

Split this into a separate PR to focus first on just the panic_handler output, independent from assert_eq.

Question 2: Change the panic message of assert_eq?

• Put the message on a separate line?
• Call it "error" or "message" or "description" or … ?
• Put message on the first line?

assertion failed: `left == right`
 error: message goes here
  left: `1`
 right: `2`

assertion failed: `left == right`, message goes here
  left: `1`
 right: `2`

assertion failed: message goes here
 check: left == right
  left: 1
 right: 2

Leave this for after the PR for question 1.

(Waiting on team) rust.tf/103126 Add cfg(no_128_bit) to core: removes u128/i128 formatting

Discussed and responded last time. FCP close in progress. Removed label.

(Regressions) rust.tf/109064 P-high `+outline-atomics` violates "core shall not depend on libc"

Resolutions: Either:

• remove outline-atomics, or
• allow core to depend on libc.

The 'can core depend on libc' discussion is a complicated one, probably needs an RFC for a resolution.

Amanieu to write up that RFC.

(Regressions) rust.tf/112180 assertion failed: key as usize != KEY_SENTVAL in DragonFly BSD

Might have already been broken but simply not resulted in a panic.

Tier 3, so not high priority.