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Fully destructure slice and array constants into patterns #77390

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Fully destructure slice and array constants into patterns #77390

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002a1c2
Destructure byte array constants to array patterns instead of keeping…
oli-obk Sep 29, 2020
14a0b10
Destructure byte slices and remove all the workarounds
oli-obk Oct 1, 2020
e0e48ac
Treat booleans as integers with valid range 0..=1
oli-obk Oct 2, 2020
523b752
Stop passing opaque constants around in the exhaustiveness checks and…
oli-obk Oct 2, 2020
6553d38
Document new (or new uses) of enum variants
Oct 12, 2020
d0bb77d
Update comment
Oct 15, 2020
0915063
WIP: Add opaque constructor
Oct 15, 2020
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7 changes: 3 additions & 4 deletions compiler/rustc_mir_build/src/thir/pattern/_match.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -1485,9 +1485,7 @@ fn all_constructors<'a, 'tcx>(
)
};
match *pcx.ty.kind() {
ty::Bool => {
[true, false].iter().map(|&b| ConstantValue(ty::Const::from_bool(cx.tcx, b))).collect()
}
ty::Bool => vec![make_range(0, 1)],
ty::Array(ref sub_ty, len) if len.try_eval_usize(cx.tcx, cx.param_env).is_some() => {
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@Nadrieril Nadrieril Oct 12, 2020 •
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Doesn't this affect diagnostics? I'd expect this would display "pattern 0 not covered" instead of "pattern false not covered", but that would clearly be caught by the tests. I don't understand what piece of code makes it so it doesn't.

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I had also wondered this, but assumed this would be caught by tests, so it must have been okay. But you're right that it would be better to understand this (and add a comment).

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This is because while decisions are made on Constructors, they do not directly flow into diagnostics. Instead diagnostics are reported on Pats in https://github.com/rust-lang/rust/blob/6553d38bcb0c9193808ae93db8bd95bcf4c4824a/compiler/rustc_mir_build/src/thir/pattern/check_match.rs

let len = len.eval_usize(cx.tcx, cx.param_env);
if len != 0 && cx.is_uninhabited(sub_ty) {
Expand Down Expand Up @@ -1600,7 +1598,7 @@ impl<'tcx> IntRange<'tcx> {
#[inline]
fn is_integral(ty: Ty<'_>) -> bool {
match ty.kind() {
ty::Char | ty::Int(_) | ty::Uint(_) => true,
ty::Char | ty::Int(_) | ty::Uint(_) | ty::Bool => true,
_ => false,
}
}
Expand All @@ -1622,6 +1620,7 @@ impl<'tcx> IntRange<'tcx> {
#[inline]
fn integral_size_and_signed_bias(tcx: TyCtxt<'tcx>, ty: Ty<'_>) -> Option<(Size, u128)> {
match *ty.kind() {
ty::Bool => Some((Size::from_bytes(1), 0)),
ty::Char => Some((Size::from_bytes(4), 0)),
ty::Int(ity) => {
let size = Integer::from_attr(&tcx, SignedInt(ity)).size();
Expand Down