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Rollup merge of rust-lang#66960 - wesleywiser:fix_66787_take2, r=oli-…
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…obk,RalfJung

[const-prop] Fix ICE calculating enum discriminant

Fixes rust-lang#66787

Different approach than rust-lang#66857

r? @oli-obk
cc @RalfJung @eddyb
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Centril authored Dec 3, 2019
2 parents 69f1323 + 0be80f2 commit ded9885
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Showing 2 changed files with 52 additions and 10 deletions.
23 changes: 13 additions & 10 deletions src/librustc_mir/interpret/place.rs
Original file line number Diff line number Diff line change
Expand Up @@ -1065,23 +1065,26 @@ where
variant_index: VariantIdx,
dest: PlaceTy<'tcx, M::PointerTag>,
) -> InterpResult<'tcx> {
let variant_scalar = Scalar::from_u32(variant_index.as_u32()).into();

// Layout computation excludes uninhabited variants from consideration
// therefore there's no way to represent those variants in the given layout.
if dest.layout.for_variant(self, variant_index).abi.is_uninhabited() {
throw_ub!(Unreachable);
}

match dest.layout.variants {
layout::Variants::Single { index } => {
if index != variant_index {
throw_ub!(InvalidDiscriminant(variant_scalar));
}
assert_eq!(index, variant_index);
}
layout::Variants::Multiple {
discr_kind: layout::DiscriminantKind::Tag,
discr: ref discr_layout,
discr_index,
..
} => {
if !dest.layout.ty.variant_range(*self.tcx).unwrap().contains(&variant_index) {
throw_ub!(InvalidDiscriminant(variant_scalar));
}
// No need to validate that the discriminant here because the
// `TyLayout::for_variant()` call earlier already checks the variant is valid.

let discr_val =
dest.layout.ty.discriminant_for_variant(*self.tcx, variant_index).unwrap().val;

Expand All @@ -1104,9 +1107,9 @@ where
discr_index,
..
} => {
if !variant_index.as_usize() < dest.layout.ty.ty_adt_def().unwrap().variants.len() {
throw_ub!(InvalidDiscriminant(variant_scalar));
}
// No need to validate that the discriminant here because the
// `TyLayout::for_variant()` call earlier already checks the variant is valid.

if variant_index != dataful_variant {
let variants_start = niche_variants.start().as_u32();
let variant_index_relative = variant_index.as_u32()
Expand Down
39 changes: 39 additions & 0 deletions src/test/ui/consts/issue-66787.rs
Original file line number Diff line number Diff line change
@@ -0,0 +1,39 @@
// build-pass
// compile-flags: --crate-type lib

// Regression test for ICE which occurred when const propagating an enum with three variants
// one of which is uninhabited.

pub enum ApiError {}
#[allow(dead_code)]
pub struct TokioError {
b: bool,
}
pub enum Error {
Api {
source: ApiError,
},
Ethereum,
Tokio {
source: TokioError,
},
}
struct Api;
impl IntoError<Error> for Api
{
type Source = ApiError;
fn into_error(self, error: Self::Source) -> Error {
Error::Api {
source: (|v| v)(error),
}
}
}

pub trait IntoError<E>
{
/// The underlying error
type Source;

/// Combine the information to produce the error
fn into_error(self, source: Self::Source) -> E;
}

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