1.97 beta regression due to `TryFromIntError` changing size

[theemathas]

This regression was found by the 1.97 beta crater run.

[INFO] [stdout] error[E0512]: cannot transmute between types of different sizes, or dependently-sized types
[INFO] [stdout]   --> /opt/rustwide/cargo-home/registry/src/index.crates.io-1949cf8c6b5b557f/ethnum-1.5.2/src/error.rs:16:14
[INFO] [stdout]    |
[INFO] [stdout] 16 |     unsafe { mem::transmute(()) }
[INFO] [stdout]    |              ^^^^^^^^^^^^^^
[INFO] [stdout]    |
[INFO] [stdout]    = note: source type: `()` (0 bits)
[INFO] [stdout]    = note: target type: `TryFromIntError` (8 bits)

It affects 230 dependents of ethnum version 1.5.2 or earlier. (ethnum version 1.5.3 was released on April 20 to fix this.)

• https://crater-reports.s3.amazonaws.com/beta-1.97-3-v2/1.97.0-beta.1/gh/Akash9900.flowdesk/log.txt
• https://crater-reports.s3.amazonaws.com/beta-1.97-3-v2/1.97.0-beta.1/gh/0rd1r3hv.algs4/log.txt
• https://crater-reports.s3.amazonaws.com/beta-1.97-3-v2/1.97.0-beta.1/gh/0xh3rman.sui-types/log.txt
• etc.

Presumably regressed in #153178. cc @sorairolake, @tgross35

I assume this is acceptable breakage, but I'm filing this issue just in case some action is needed (e.g., a mention in the release notes).

[tgross35]

Opened an issue nlordell/ethnum-rs#60.

We make no guarantees about the internals of std types (unless specified) so I'm not sure we need a release note mention. Maybe this type should have a constructor if other crates want to make use of it?

[theemathas]

@tgross ethnum is already fixed. This regression affects only dependents of older versions.

[nlordell]

This should have been fixed here: nlordell/ethnum-rs#58 and released in 1.5.3.

[theemathas]

There's also another "regression" related to TryFromIntError. But this time, it's due to the Debug output changing:

[INFO] [stdout] note: panic did not contain expected string
[INFO] [stdout]       panic message: "index out of bounds: TryFromIntError(NegOverflow)"
[INFO] [stdout]  expected substring: "index out of bounds: TryFromIntError(())"

https://crater-reports.s3.amazonaws.com/beta-1.97-3-v2/1.97.0-beta.1/reg/univec-1.1.0/log.txt

---

Edit: Another crate had the same regression.

[INFO] [stdout] note: panic did not contain expected string
[INFO] [stdout]       panic message: "nanos_to_duration() overflowed seconds value for Duration: TryFromIntError(PosOverflow)"
[INFO] [stdout]  expected substring: "nanos_to_duration() overflowed seconds value for Duration: TryFromIntError(())"

https://crater-reports.s3.amazonaws.com/beta-1.97-3-v2/1.97.0-beta.1/reg/roundable-0.2.0/log.txt

---

Edit 2: Yet another crate.

[INFO] [stdout] note: panic did not contain expected string
[INFO] [stdout]       panic message: "called `Result::unwrap()` on an `Err` value: TryFromIntError(Zero)"
[INFO] [stdout]  expected substring: "called `Result::unwrap()` on an `Err` value: TryFromIntError(())"

https://crater-reports.s3.amazonaws.com/beta-1.97-3-v2/1.97.0-beta.1/gh/qter-project.puzzle-theory/log.txt

[cuviper]

https://doc.rust-lang.org/nightly/std/fmt/trait.Debug.html#stability

Derived Debug formats are not stable, and so may change with future Rust versions. Additionally, Debug implementations of types provided by the standard library (std, core, alloc, etc.) are not stable, and may also change with future Rust versions.

[the8472]

We discussed this during today's T-libs meeting and consider this acceptable breakage.