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Unrolled build for rust-lang#136179
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Rollup merge of rust-lang#136179 - oli-obk:push-vxvyttorquxw, r=BoxyUwU

Allow transmuting generic pattern types to and from their base

Pattern types always have the same size as their base type, so we can just ignore the pattern and look at the base type for figuring out whether transmuting is possible.
rust-timer authored Jan 30, 2025
2 parents a6434ef + a639e27 commit c24a00e
Showing 3 changed files with 56 additions and 0 deletions.
3 changes: 3 additions & 0 deletions compiler/rustc_middle/src/ty/layout.rs
Original file line number Diff line number Diff line change
@@ -504,6 +504,9 @@ impl<'tcx> SizeSkeleton<'tcx> {
}
}

// Pattern types are always the same size as their base.
ty::Pat(base, _) => SizeSkeleton::compute(base, tcx, typing_env),

_ => Err(err),
}
}
32 changes: 32 additions & 0 deletions tests/ui/type/pattern_types/transmute.rs
Original file line number Diff line number Diff line change
@@ -0,0 +1,32 @@
#![feature(pattern_types)]
#![feature(pattern_type_macro)]

use std::pat::pattern_type;

// ok
fn create<const S: u32, const E: u32>(x: u32) -> pattern_type!(u32 is S..=E) {
unsafe { std::mem::transmute(x) }
}

// ok
fn unwrap<const S: u32, const E: u32>(x: pattern_type!(u32 is S..=E)) -> u32 {
unsafe { std::mem::transmute(x) }
}

// bad, only when S != u32::MIN or E != u32::MAX will this ok
fn non_base_ty_transmute<const S: u32, const E: u32>(
x: Option<pattern_type!(u32 is S..=E)>,
) -> u32 {
unsafe { std::mem::transmute(x) }
//~^ ERROR types of different sizes
}

// bad, only when S = u32::MIN and E = u32::MAX will this ok
fn wrapped_transmute<const S: u32, const E: u32>(
x: Option<pattern_type!(u32 is S..=E)>,
) -> Option<u32> {
unsafe { std::mem::transmute(x) }
//~^ ERROR types of different sizes
}

fn main() {}
21 changes: 21 additions & 0 deletions tests/ui/type/pattern_types/transmute.stderr
Original file line number Diff line number Diff line change
@@ -0,0 +1,21 @@
error[E0512]: cannot transmute between types of different sizes, or dependently-sized types
--> $DIR/transmute.rs:20:14
|
LL | unsafe { std::mem::transmute(x) }
| ^^^^^^^^^^^^^^^^^^^
|
= note: source type: `Option<(u32) is S..=E>` (size can vary because of u32)
= note: target type: `u32` (32 bits)

error[E0512]: cannot transmute between types of different sizes, or dependently-sized types
--> $DIR/transmute.rs:28:14
|
LL | unsafe { std::mem::transmute(x) }
| ^^^^^^^^^^^^^^^^^^^
|
= note: source type: `Option<(u32) is S..=E>` (size can vary because of u32)
= note: target type: `Option<u32>` (64 bits)

error: aborting due to 2 previous errors

For more information about this error, try `rustc --explain E0512`.

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