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Rollup merge of #118598 - Nadrieril:remove_precise_pointer_size_matching, r=davidtwco

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Remove the `precise_pointer_size_matching` feature gate

`usize` and `isize` are special for pattern matching because their range might depend on the platform. To make code portable across platforms, the following is never considered exhaustive:
```rust
let x: usize = ...;
match x {
    0..=18446744073709551615 => {}
}
```
Because of how rust handles constants, this also unfortunately counts `0..=usize::MAX` as non-exhaustive. The [`precise_pointer_size_matching`](https://github.com/rust-lang/rust/issues/56354) feature gate was introduced both for this convenience and for the possibility that the lang team could decide to allow the above.

Since then, [half-open range patterns](https://github.com/rust-lang/rust/issues/67264) have been implemented, and since #116692 they correctly support `usize`/`isize`:
```rust
match 0usize { // exhaustive!
    0..5 => {}
    5.. => {}
}
```
I believe this subsumes all the use cases of the feature gate. Moreover no attempt has been made to stabilize it in the 5 years of its existence. I therefore propose we retire this feature gate.

Closes https://github.com/rust-lang/rust/issues/56354
This commit is contained in:
Matthias Krüger 2023-12-05 16:08:35 +01:00 • committed by GitHub
commit 81b6263dd0
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10 changed files with 33 additions and 86 deletions
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6
compiler/rustc_mir_build/src/thir/pattern/check_match.rs
View file

@ -867,12 +867,6 @@ fn report_non_exhaustive_match<'p, 'tcx>(
exhaustively",
));
}
if cx.tcx.sess.is_nightly_build() {
err.help(format!(
"add `#![feature(precise_pointer_size_matching)]` to the crate attributes to \
enable precise `{ty}` matching",
));
}
} else if ty == cx.tcx.types.str_ {
err.note("`&str` cannot be matched exhaustively, so a wildcard `_` is necessary");
} else if cx.is_foreign_non_exhaustive_enum(ty) {

19
compiler/rustc_mir_build/src/thir/pattern/deconstruct_pat.rs
View file

@ -326,8 +326,7 @@ impl IntRange {
/// `NegInfinity..PosInfinity`. In other words, as far as `IntRange` is concerned, there are
/// values before `isize::MIN` and after `usize::MAX`/`isize::MAX`.
/// This is to avoid e.g. `0..(u32::MAX as usize)` from being exhaustive on one architecture and
/// not others. See discussions around the `precise_pointer_size_matching` feature for more
/// details.
/// not others. This was decided in <https://github.com/rust-lang/rfcs/pull/2591>.
///
/// These infinities affect splitting subtly: it is possible to get `NegInfinity..0` and
/// `usize::MAX+1..PosInfinity` in the output. Diagnostics must be careful to handle these
@ -380,7 +379,7 @@ impl IntRange {
/// Whether the range denotes the fictitious values before `isize::MIN` or after
/// `usize::MAX`/`isize::MAX` (see doc of [`IntRange::split`] for why these exist).
pub(crate) fn is_beyond_boundaries<'tcx>(&self, ty: Ty<'tcx>, tcx: TyCtxt<'tcx>) -> bool {
ty.is_ptr_sized_integral() && !tcx.features().precise_pointer_size_matching && {
ty.is_ptr_sized_integral() && {
// The two invalid ranges are `NegInfinity..isize::MIN` (represented as
// `NegInfinity..0`), and `{u,i}size::MAX+1..PosInfinity`. `to_diagnostic_pat_range_bdy`
// converts `MAX+1` to `PosInfinity`, and we couldn't have `PosInfinity` in `self.lo`
@ -941,11 +940,8 @@ impl ConstructorSet {
}
}
&ty::Int(ity) => {
let range = if ty.is_ptr_sized_integral()
&& !cx.tcx.features().precise_pointer_size_matching
{
// The min/max values of `isize` are not allowed to be observed unless the
// `precise_pointer_size_matching` feature is enabled.
let range = if ty.is_ptr_sized_integral() {
// The min/max values of `isize` are not allowed to be observed.
IntRange { lo: NegInfinity, hi: PosInfinity }
} else {
let bits = Integer::from_int_ty(&cx.tcx, ity).size().bits() as u128;
@ -956,11 +952,8 @@ impl ConstructorSet {
Self::Integers { range_1: range, range_2: None }
}
&ty::Uint(uty) => {
let range = if ty.is_ptr_sized_integral()
&& !cx.tcx.features().precise_pointer_size_matching
{
// The max value of `usize` is not allowed to be observed unless the
// `precise_pointer_size_matching` feature is enabled.
let range = if ty.is_ptr_sized_integral() {
// The max value of `usize` is not allowed to be observed.
let lo = MaybeInfiniteInt::new_finite(cx.tcx, ty, 0);
IntRange { lo, hi: PosInfinity }
} else {