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[RFC] Explicit ABI in extern #3722

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[RFC] Explicit ABI in extern #3722

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@m-ou-se m-ou-se commented Oct 30, 2024 •
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@m-ou-se m-ou-se added T-lang Relevant to the language team, which will review and decide on the RFC. A-defaults Proposals relating to defaults / provided definitions I-lang-nominated Indicates that an issue has been nominated for prioritizing at the next lang team meeting. A-edition-2024 Area: The 2024 edition A-maybe-future-edition Changes of edition-relevance not targeted for a specific edition. T-edition Relevant to the edition team, which will review and decide on this RFC. labels Oct 30, 2024
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joshtriplett commented Oct 30, 2024 •
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Very much a fan of making this change. As noted in the RFC, it's very late for the 2024 edition. That said, I would personally not object to trying for 2024 if we can get the necessary migration lint in place.

One way or another, I personally think T-lang should approve this RFC, with the guidance of "whenever it's ready", and defer to those wrangling the edition to decide whether this happens in 2024 or 2027.

@m-ou-se m-ou-se mentioned this pull request Oct 30, 2024
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m-ou-se commented Oct 30, 2024

Implementation, including migration lint: rust-lang/rust#132357

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@rustbot labels -A-edition-2024

This makes sense to me as a language matter also.

With the edition hat on, though, and after consulting with the rest of the edition team, it's unfortunately just too late to accept a new language item like this for Rust 2024. This is due to the testing and release timeline, where we are in it, and how these kind of changes affect that.

Let's make sure it makes the next edition, assuming the rest of the lang team likes this also.

@rustbot rustbot removed the A-edition-2024 Area: The 2024 edition label Oct 30, 2024
@tmandry tmandry removed the T-edition Relevant to the edition team, which will review and decide on this RFC. label Oct 30, 2024
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tmandry commented Oct 30, 2024

The lang team discussed this in our meeting today and everyone was in favor of the change. Since it's too late for 2024 Edition, this RFC is not time sensitive, but we might as well approve it for the next edition.

Meanwhile, there is an existing missing_abi lint that we should upgrade to warn-by-default in all editions. We should do that in a separate FCP. (There was some discussion of rolling this out starting with 2024 – but that should not happen as part of the initial edition release, or it would fall under the testing and documentation requirements that we already said it was too late to do for 2024.)

@rfcbot fcp merge

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rfcbot commented Oct 30, 2024 •
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Team member @tmandry has proposed to merge this. The next step is review by the rest of the tagged team members:

No concerns currently listed.

Once a majority of reviewers approve (and at most 2 approvals are outstanding), this will enter its final comment period. If you spot a major issue that hasn't been raised at any point in this process, please speak up!

cc @rust-lang/lang-advisors: FCP proposed for lang, please feel free to register concerns.
See this document for info about what commands tagged team members can give me.

@rfcbot rfcbot added proposed-final-comment-period Currently awaiting signoff of all team members in order to enter the final comment period. disposition-merge This RFC is in PFCP or FCP with a disposition to merge it. labels Oct 30, 2024
@tmandry tmandry added the T-edition Relevant to the edition team, which will review and decide on this RFC. label Oct 30, 2024
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est31 reviewed Oct 30, 2024
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text/3722-explicit-abi.md
# Future possibilities

In the future, we might want to add a new default ABI.
For example, if `extern "stable-rust-abi"` becomes a thing and e.g. dynamically linking Rust from Rust becomes very popular, it might make sense to make that the default when writing `extern fn` without an ABI.
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I don't think, if there is a default, it should be anything other than "C" because it raises the stakes of getting the edition wrong.

It would mean that getting the edition parameter wrong causes a breakage in ABI. Which is fine if it's caught by an error but this is not guaranteed, it could also just lead to silent UB, segfaults, etc.

There is some such flags in Rust already, but flags have been removed with it affecting the ABI being one of the reasons.

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Sure. The future possibilities are a separate discussion if/when they are proposed. Definitely not part of what I'm proposing now. :)

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It is easy to read anything in the future possibilities section as an endorsement of that idea. It would be nice to either remove that paragraph or incorporate the known issues into the text.

Also I doubt that dynamically linking Rust to Rust will become more popular than interfacing with the non-Rust world, which (mostly) goes via the "C" ABI.

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I like being explicit here. The burden of also saying "C" is small compared to also having to have said extern, so might as well -- especially as more people actually want "C-unwind".

@rfcbot reviewed

I agree that we probably shouldn't change to a new default for some time, if ever.

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@rustbot labels -I-lang-nominated

We discussed this in lang triage today, resulting in tmandry's proposed FCP above, which sounds right to me.

@rustbot rustbot removed the I-lang-nominated Indicates that an issue has been nominated for prioritizing at the next lang team meeting. label Oct 30, 2024
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m-ou-se commented Oct 31, 2024

Meanwhile, there is an existing missing_abi lint that we should upgrade to warn-by-default in all editions. We should do that in a separate FCP.

This PR makes the lint warn-by-default: rust-lang/rust#132397

matthiaskrgr added a commit to matthiaskrgr/rust that referenced this pull request Oct 31, 2024
@matthiaskrgr
Rollup merge of rust-lang#132357 - m-ou-se:explicit-abi, r=compiler-e…
a7bdfe2 
…rrors

Improve missing_abi lint

This is for the migration lint for rust-lang/rfcs#3722

It is not yet marked as an edition migration lint, because `Edition2027` doesn't exist yet.

The lint now includes a machine applicable suggestion:

```
warning: extern declarations without an explicit ABI are deprecated
 --> src/main.rs:3:1
  |
3 | extern fn a() {}
  | ^^^^^^ help: explicitly specify the C ABI: `extern "C"`
  |
```
workingjubilee added a commit to workingjubilee/rustc that referenced this pull request Nov 1, 2024
@workingjubilee
Rollup merge of rust-lang#132357 - m-ou-se:explicit-abi, r=compiler-e…
6b0c8cf 
…rrors

Improve missing_abi lint

This is for the migration lint for rust-lang/rfcs#3722

It is not yet marked as an edition migration lint, because `Edition2027` doesn't exist yet.

The lint now includes a machine applicable suggestion:

```
warning: extern declarations without an explicit ABI are deprecated
 --> src/main.rs:3:1
  |
3 | extern fn a() {}
  | ^^^^^^ help: explicitly specify the C ABI: `extern "C"`
  |
```
rust-timer added a commit to rust-lang-ci/rust that referenced this pull request Nov 1, 2024
@rust-timer
Unrolled build for rust-lang#132357
913a219 
Rollup merge of rust-lang#132357 - m-ou-se:explicit-abi, r=compiler-errors

Improve missing_abi lint

This is for the migration lint for rust-lang/rfcs#3722

It is not yet marked as an edition migration lint, because `Edition2027` doesn't exist yet.

The lint now includes a machine applicable suggestion:

```
warning: extern declarations without an explicit ABI are deprecated
 --> src/main.rs:3:1
  |
3 | extern fn a() {}
  | ^^^^^^ help: explicitly specify the C ABI: `extern "C"`
  |
```
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