Rollup merge of #76199 - Mark-Simulacrum:void-zero, r=nikomatsakis

Permit uninhabited enums to cast into ints

This essentially reverts part of #6204; it is unclear why that [commit](c0f587de34) was introduced, and I suspect no one remembers.

The changed code was only called from casting checks and appears to not affect any callers of that code (other than permitting this one case).

Fixes #75647.
This commit is contained in:
Dylan DPC 2020-10-17 03:27:12 +02:00 committed by GitHub
commit 496e2feed6
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4 changed files with 12 additions and 12 deletions

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@ -2436,8 +2436,10 @@ impl<'tcx> AdtDef {
self.variants.iter().flat_map(|v| v.fields.iter())
}
/// Whether the ADT lacks fields. Note that this includes uninhabited enums,
/// e.g., `enum Void {}` is considered payload free as well.
pub fn is_payloadfree(&self) -> bool {
!self.variants.is_empty() && self.variants.iter().all(|v| v.fields.is_empty())
self.variants.iter().all(|v| v.fields.is_empty())
}
/// Return a `VariantDef` given a variant id.

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@ -139,9 +139,14 @@ impl<'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
// # First handle non-scalar source values.
// Handle cast from a univariant (ZST) enum.
// Handle cast from a ZST enum (0 or 1 variants).
match src.layout.variants {
Variants::Single { index } => {
if src.layout.abi.is_uninhabited() {
// This is dead code, because an uninhabited enum is UB to
// instantiate.
throw_ub!(Unreachable);
}
if let Some(discr) = src.layout.ty.discriminant_for_variant(*self.tcx, index) {
assert!(src.layout.is_zst());
let discr_layout = self.layout_of(discr.ty)?;

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@ -1,7 +1,9 @@
// check-pass
enum E {}
fn f(e: E) {
println!("{}", (e as isize).to_string()); //~ ERROR non-primitive cast
println!("{}", (e as isize).to_string());
}
fn main() {}

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@ -1,9 +0,0 @@
error[E0605]: non-primitive cast: `E` as `isize`
--> $DIR/uninhabited-enum-cast.rs:4:20
|
LL | println!("{}", (e as isize).to_string());
| ^^^^^^^^^^^^ an `as` expression can only be used to convert between primitive types or to coerce to a specific trait object
error: aborting due to previous error
For more information about this error, try `rustc --explain E0605`.