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Rollup merge of #135228 - compiler-errors:normalizes-ur-dispatch, r=BoxyUwU

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Improve `DispatchFromDyn` and `CoerceUnsized` impl validation

* Disallow arbitrary 1-ZST fields in `DispatchFromDyn` -- only `PhantomData`, and 1-ZSTs that mention no params (which is needed to support, e.g., the `Global` alloctor in `Box<T, U = Global>`).
* Don't allow coercing between non-ZSTs to ZSTs (since the previous check wasn't actually checking the field tys were the same before checking the layout...)
* Normalize the field before checking it's `PhantomData`.

Fixes #135215
Fixes #135214
Fixes #135220

r? ```@BoxyUwU``` or reassign
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Jubilee 2025-01-14 19:56:30 -08:00 • committed by GitHub
commit f256f9ef22
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8 changed files with 153 additions and 11 deletions
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42
compiler/rustc_hir_analysis/src/coherence/builtin.rs
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@ -259,19 +259,37 @@ fn visit_implementation_of_dispatch_from_dyn(checker: &Checker<'_>) -> Result<()
let coerced_fields = fields
.iter()
.filter(|field| {
// Ignore PhantomData fields
let unnormalized_ty = tcx.type_of(field.did).instantiate_identity();
if tcx
.try_normalize_erasing_regions(
ty::TypingEnv::non_body_analysis(tcx, def_a.did()),
unnormalized_ty,
)
.unwrap_or(unnormalized_ty)
.is_phantom_data()
{
return false;
}
let ty_a = field.ty(tcx, args_a);
let ty_b = field.ty(tcx, args_b);
if let Ok(layout) =
tcx.layout_of(infcx.typing_env(param_env).as_query_input(ty_a))
{
if layout.is_1zst() {
// FIXME: We could do normalization here, but is it really worth it?
if ty_a == ty_b {
// Allow 1-ZSTs that don't mention type params.
//
// Allowing type params here would allow us to possibly transmute
// between ZSTs, which may be used to create library unsoundness.
if let Ok(layout) =
tcx.layout_of(infcx.typing_env(param_env).as_query_input(ty_a))
&& layout.is_1zst()
&& !ty_a.has_non_region_param()
{
// ignore 1-ZST fields
return false;
}
}
if ty_a == ty_b {
res = Err(tcx.dcx().emit_err(errors::DispatchFromDynZST {
span,
name: field.name,
@ -460,8 +478,16 @@ pub(crate) fn coerce_unsized_info<'tcx>(
.filter_map(|(i, f)| {
let (a, b) = (f.ty(tcx, args_a), f.ty(tcx, args_b));
if tcx.type_of(f.did).instantiate_identity().is_phantom_data() {
// Ignore PhantomData fields
// Ignore PhantomData fields
let unnormalized_ty = tcx.type_of(f.did).instantiate_identity();
if tcx
.try_normalize_erasing_regions(
ty::TypingEnv::non_body_analysis(tcx, def_a.did()),
unnormalized_ty,
)
.unwrap_or(unnormalized_ty)
.is_phantom_data()
{
return None;
}