Make std::env::{set_var, remove_var} unsafe in edition 2024

[tbu-]

Allow calling these functions without unsafe blocks in editions up until 2021, but don't trigger the unused_unsafe lint for unsafe blocks containing these functions.

Fixes #27970.
Fixes #90308.
CC #124866.

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[rustbot]

Some changes occurred in src/tools/clippy

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Some changes occurred in src/tools/rustfmt

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Some changes occurred in src/tools/compiletest

cc @jieyouxu

The Miri subtree was changed

cc @rust-lang/miri

[rustbot]

Some changes occurred in src/tools/rustfmt

cc @rust-lang/rustfmt

The Miri subtree was changed

cc @rust-lang/miri

Some changes occurred in src/tools/clippy

cc @rust-lang/clippy

Some changes occurred in src/tools/compiletest

cc @jieyouxu

[RalfJung]

Should there be a warning on older editions, to make this not come entirely out of the blue when doing edition migration?

[tbu-]

Should there be a warning on older editions, to make this not come entirely out of the blue when doing edition migration?

I agree that this would be quite useful. It seems hard to do right now, though, because a stage 0 compiler will detect a lot of unused unsafe blocks because it doesn't know about the std::env::set_var unsafety. Perhaps this could be postponed until after one bootstrap cycle?

[RalfJung]

I agree that this would be quite useful. It seems hard to do right now, though, because a stage 0 compiler will detect a lot of unused unsafe blocks because it doesn't know about the std::env::set_var unsafety. Perhaps this could be postponed until after one bootstrap cycle?

I wasn't talking about unused_unsafe, but a lint that warns against using set_var/remove_var outside an unsafe block on old editions.

Also, I am not sure if it's the best idea to add new lang items for these functions. In the past the proposal was to add an attribute for "deprecating safety". Then we could e.g. also add that attribute to before_exec.

[Amanieu]

FCP for making these functions unsafe in edition 2024. For the actual implementation, this could be reviewed by the compiler team.

@rfcbot fcp merge

[rfcbot]

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

• @Amanieu
• @cuviper
• @joshtriplett
• @m-ou-se
• @the8472
• @thomcc

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!

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[the8472]

@Amanieu shouldn't this be a libs-API FCP?

[Amanieu]

Yes, it should.

@rfcbot cancel

[rfcbot]

@Amanieu proposal cancelled.

[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

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!

See this document for info about what commands tagged team members can give me.

[rfcbot]

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