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remove unreachable error code E0476 #106840

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remove unreachable error code E0476 #106840

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2 changes: 1 addition & 1 deletion compiler/rustc_error_codes/src/error_codes.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -607,7 +607,7 @@ E0791: include_str!("./error_codes/E0791.md"),
// E0473, // dereference of reference outside its lifetime
// E0474, // captured variable `..` does not outlive the enclosing closure
// E0475, // index of slice outside its lifetime
E0476, // lifetime of the source pointer does not outlive lifetime bound...
// E0476, // removed: unreachable
// E0479, // the type `..` (provided as the value of a type parameter) is...
// E0480, // lifetime of method receiver does not outlive the method call
// E0481, // lifetime of function argument does not outlive the function call
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4 changes: 1 addition & 3 deletions compiler/rustc_hir_analysis/src/coherence/builtin.rs
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Expand Up @@ -7,7 +7,6 @@ use rustc_hir as hir;
use rustc_hir::def_id::{DefId, LocalDefId};
use rustc_hir::lang_items::LangItem;
use rustc_hir::ItemKind;
use rustc_infer::infer;
use rustc_infer::infer::outlives::env::OutlivesEnvironment;
use rustc_infer::infer::TyCtxtInferExt;
use rustc_middle::ty::adjustment::CoerceUnsizedInfo;
Expand Down Expand Up @@ -386,8 +385,7 @@ pub fn coerce_unsized_info<'tcx>(tcx: TyCtxt<'tcx>, impl_did: DefId) -> CoerceUn
(mt_a.ty, mt_b.ty, unsize_trait, None)
};
let (source, target, trait_def_id, kind) = match (source.kind(), target.kind()) {
(&ty::Ref(r_a, ty_a, mutbl_a), &ty::Ref(r_b, ty_b, mutbl_b)) => {
infcx.sub_regions(infer::RelateObjectBound(span), r_b, r_a);
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Why is this line removed? This has side-effects.

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You could give it a different subregion origin, but this is required for soundness 😓

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@compiler-errors compiler-errors Jan 14, 2023 •
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This code reproduces this error:

#![feature(coerce_unsized)]
#![feature(unsize)]

use core::marker::Unsize;
use core::ops::CoerceUnsized;

struct Wrapper<T>(T);

impl<'a, 'b, T, S> CoerceUnsized<&'a Wrapper<T>> for &'b Wrapper<S> where S: Unsize<T> {}

Although it has a coherence error as well. Presumably if you made https://doc.rust-lang.org/src/core/ops/unsize.rs.html#55 this implementation unsound by removing 'b: 'a, then it would also trigger there.

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Ahh, my mistake, I assumed that this error code was no longer used. I'll close this PR and document/test it instead.

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@compiler-errors compiler-errors Jan 14, 2023 •
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It's alright -- in general, I would never remove side-effect-ful logic just because you think it's dead code. Sometimes people just forget to add a UI test for an error code.

Replace it with a delay_span_bug or bug!() if necessary, but unless you can statically prove that something is unreachable, you're very likely to introduce unsoundness or other subtle bugs into the compiler.

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Hmm, I was kind of naive. I assumed that untested error codes (basically all of them are like this) were from old Rust versions and had never been formally removed.

(&ty::Ref(_, ty_a, mutbl_a), &ty::Ref(r_b, ty_b, mutbl_b)) => {
let mt_a = ty::TypeAndMut { ty: ty_a, mutbl: mutbl_a };
let mt_b = ty::TypeAndMut { ty: ty_b, mutbl: mutbl_b };
check_mutbl(mt_a, mt_b, &|ty| tcx.mk_imm_ref(r_b, ty))
Expand Down
30 changes: 0 additions & 30 deletions compiler/rustc_infer/src/infer/error_reporting/note.rs
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Expand Up @@ -25,10 +25,6 @@ impl<'tcx> TypeErrCtxt<'_, 'tcx> {
infer::Reborrow(span) => {
RegionOriginNote::Plain { span, msg: fluent::infer_reborrow }.add_to_diagnostic(err)
}
infer::RelateObjectBound(span) => {
RegionOriginNote::Plain { span, msg: fluent::infer_relate_object_bound }
.add_to_diagnostic(err);
}
infer::ReferenceOutlivesReferent(ty, span) => {
RegionOriginNote::WithName {
span,
Expand Down Expand Up @@ -143,32 +139,6 @@ impl<'tcx> TypeErrCtxt<'_, 'tcx> {
);
err
}
infer::RelateObjectBound(span) => {
let mut err = struct_span_err!(
self.tcx.sess,
span,
E0476,
"lifetime of the source pointer does not outlive lifetime bound of the \
object type"
);
note_and_explain_region(
self.tcx,
&mut err,
"object type is valid for ",
sub,
"",
None,
);
note_and_explain_region(
self.tcx,
&mut err,
"source pointer is only valid for ",
sup,
"",
None,
);
err
}
infer::RelateParamBound(span, ty, opt_span) => {
let mut err = struct_span_err!(
self.tcx.sess,
Expand Down
5 changes: 0 additions & 5 deletions compiler/rustc_infer/src/infer/mod.rs
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Expand Up @@ -395,10 +395,6 @@ pub enum SubregionOrigin<'tcx> {
/// Arose from a subtyping relation
Subtype(Box<TypeTrace<'tcx>>),

/// When casting `&'a T` to an `&'b Trait` object,
/// relating `'a` to `'b`
RelateObjectBound(Span),

/// Some type parameter was instantiated with the given type,
/// and that type must outlive some region.
RelateParamBound(Span, Ty<'tcx>, Option<Span>),
Expand Down Expand Up @@ -1971,7 +1967,6 @@ impl<'tcx> SubregionOrigin<'tcx> {
pub fn span(&self) -> Span {
match *self {
Subtype(ref a) => a.span(),
RelateObjectBound(a) => a,
RelateParamBound(a, ..) => a,
RelateRegionParamBound(a) => a,
Reborrow(a) => a,
Expand Down
2 changes: 1 addition & 1 deletion src/tools/tidy/src/error_codes.rs
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Expand Up @@ -32,7 +32,7 @@ const IGNORE_DOCTEST_CHECK: &[&str] =

// Error codes that don't yet have a UI test. This list will eventually be removed.
const IGNORE_UI_TEST_CHECK: &[&str] =
&["E0461", "E0465", "E0476", "E0514", "E0523", "E0554", "E0640", "E0717", "E0729", "E0789"];
&["E0461", "E0465", "E0514", "E0523", "E0554", "E0640", "E0717", "E0729", "E0789"];

macro_rules! verbose_print {
($verbose:expr, $($fmt:tt)*) => {
Expand Down