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Update some comment/docs related to "extern intrinsic" removal #139490

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Merged
merged 3 commits into from
Apr 8, 2025
Merged

Update some comment/docs related to "extern intrinsic" removal #139490

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e1a69da
unstable-book/intrinsics: wordsmith MIR-lowering intrinsic docs
RalfJung Apr 7, 2025
a7400a8
update intrinsics/mod.rs comment about const intrinsics
RalfJung Apr 7, 2025
742b378
make hover_feature test less fragile
RalfJung Apr 8, 2025
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12 changes: 4 additions & 8 deletions library/core/src/intrinsics/mod.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -5,15 +5,11 @@
//!
//! # Const intrinsics
//!
//! Note: any changes to the constness of intrinsics should be discussed with the language team.
//! This includes changes in the stability of the constness.
//!
//! //FIXME(#132735) "old" style intrinsics support has been removed
//! In order to make an intrinsic usable at compile-time, it needs to be declared in the "new"
//! style, i.e. as a `#[rustc_intrinsic]` function, not inside an `extern` block. Then copy the
//! implementation from <https://github.com/rust-lang/miri/blob/master/src/intrinsics> to
//! In order to make an intrinsic unstable usable at compile-time, copy the implementation from
//! <https://github.com/rust-lang/miri/blob/master/src/intrinsics> to
//! <https://github.com/rust-lang/rust/blob/master/compiler/rustc_const_eval/src/interpret/intrinsics.rs>
//! and make the intrinsic declaration a `const fn`.
//! and make the intrinsic declaration below a `const fn`. This should be done in coordination with
//! wg-const-eval.
//!
//! If an intrinsic is supposed to be used from a `const fn` with a `rustc_const_stable` attribute,
//! `#[rustc_intrinsic_const_stable_indirect]` needs to be added to the intrinsic. Such a change requires
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3 changes: 2 additions & 1 deletion src/doc/unstable-book/src/language-features/intrinsics.md
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Expand Up @@ -53,7 +53,8 @@ Various intrinsics have native MIR operations that they correspond to. Instead o
backends to implement both the intrinsic and the MIR operation, the `lower_intrinsics` pass
will convert the calls to the MIR operation. Backends do not need to know about these intrinsics
at all. These intrinsics only make sense without a body, and can be declared as a `#[rustc_intrinsic]`.
The body is never used, as calls to the intrinsic do not exist anymore after MIR analyses.
The body is never used as the lowering pass implements support for all backends, so we never have to
use the fallback logic.
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@rust-lang/rust-analyzer I guess this PR will fail to land since RA has a copy of this file for the hover_feature test. How can I adjust the test to not require such a hard-to-maintain full copy?

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Is there a feature that won't really ever change maybe that we can just swap to?

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Ah well, replacing the hover test with

#[test]
fn hover_feature() {
    let (analysis, position) = fixture::position(r#"#![feature(intrinsics$0)]"#);
    analysis
        .hover(
            &HoverConfig { links_in_hover: true, ..HOVER_BASE_CONFIG },
            FileRange { file_id: position.file_id, range: TextRange::empty(position.offset) },
        )
        .unwrap()
        .unwrap();
}

should suffice

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@RalfJung RalfJung Apr 8, 2025 •
edited
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As someone who has ran into tests relying on "surely this unstable feature will never change" about a dozen times over the years, and each time had to do a frustrating search for what this test actually cared about and what was entirely incidental reliance on a feature -- I'd prefer if we didn't go down that route. Why does the test need to compare the full string for equality? There's no reason for that that I can think of.

If absolutely necessary we could probably have a dedicated feature that exists solely for the purpose of testing.

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Ah well, replacing the hover test with

Ah, that's great, thanks a lot. :)


## Intrinsics without fallback logic

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