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Implement and use BikeshedGuaranteedNoDrop for union/unsafe field validity

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This commit is contained in:
Michael Goulet 2025-02-06 20:08:29 +00:00
parent c72d443cdd
commit 516afd557c
21 changed files with 365 additions and 66 deletions
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114
compiler/rustc_hir_analysis/src/check/check.rs
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@ -6,7 +6,7 @@ use rustc_data_structures::unord::{UnordMap, UnordSet};
use rustc_errors::MultiSpan;
use rustc_errors::codes::*;
use rustc_hir::def::{CtorKind, DefKind};
use rustc_hir::{Node, intravisit};
use rustc_hir::{LangItem, Node, intravisit};
use rustc_infer::infer::{RegionVariableOrigin, TyCtxtInferExt};
use rustc_infer::traits::{Obligation, ObligationCauseCode};
use rustc_lint_defs::builtin::{
@ -27,6 +27,7 @@ use rustc_session::lint::builtin::UNINHABITED_STATIC;
use rustc_trait_selection::error_reporting::InferCtxtErrorExt;
use rustc_trait_selection::error_reporting::traits::on_unimplemented::OnUnimplementedDirective;
use rustc_trait_selection::traits;
use rustc_trait_selection::traits::query::evaluate_obligation::InferCtxtExt;
use rustc_type_ir::fold::TypeFoldable;
use tracing::{debug, instrument};
use ty::TypingMode;
@ -87,89 +88,76 @@ fn allowed_union_or_unsafe_field<'tcx>(
typing_env: ty::TypingEnv<'tcx>,
span: Span,
) -> bool {
// We don't just accept all !needs_drop fields, due to semver concerns.
let allowed = match ty.kind() {
ty::Ref(..) => true, // references never drop (even mutable refs, which are non-Copy and hence fail the later check)
ty::Tuple(tys) => {
// allow tuples of allowed types
tys.iter().all(|ty| allowed_union_or_unsafe_field(tcx, ty, typing_env, span))
}
ty::Array(elem, _len) => {
// Like `Copy`, we do *not* special-case length 0.
allowed_union_or_unsafe_field(tcx, *elem, typing_env, span)
}
_ => {
// Fallback case: allow `ManuallyDrop` and things that are `Copy`,
// also no need to report an error if the type is unresolved.
ty.ty_adt_def().is_some_and(|adt_def| adt_def.is_manually_drop())
|| tcx.type_is_copy_modulo_regions(typing_env, ty)
|| ty.references_error()
}
};
if allowed && ty.needs_drop(tcx, typing_env) {
// This should never happen. But we can get here e.g. in case of name resolution errors.
tcx.dcx()
.span_delayed_bug(span, "we should never accept maybe-dropping union or unsafe fields");
// HACK (not that bad of a hack don't worry): Some codegen tests don't even define proper
// impls for `Copy`. Let's short-circuit here for this validity check, since a lot of them
// use unions. We should eventually fix all the tests to define that lang item or use
// minicore stubs.
if ty.is_trivially_pure_clone_copy() {
return true;
}
allowed
// If `BikeshedGuaranteedNoDrop` is not defined in a `#[no_core]` test, fall back to `Copy`.
// This is an underapproximation of `BikeshedGuaranteedNoDrop`,
let def_id = tcx
.lang_items()
.get(LangItem::BikeshedGuaranteedNoDrop)
.unwrap_or_else(|| tcx.require_lang_item(LangItem::Copy, Some(span)));
let Ok(ty) = tcx.try_normalize_erasing_regions(typing_env, ty) else {
tcx.dcx().span_delayed_bug(span, "could not normalize field type");
return true;
};
let (infcx, param_env) = tcx.infer_ctxt().build_with_typing_env(typing_env);
infcx.predicate_must_hold_modulo_regions(&Obligation::new(
tcx,
ObligationCause::dummy_with_span(span),
param_env,
ty::TraitRef::new(tcx, def_id, [ty]),
))
}
/// Check that the fields of the `union` do not need dropping.
fn check_union_fields(tcx: TyCtxt<'_>, span: Span, item_def_id: LocalDefId) -> bool {
let item_type = tcx.type_of(item_def_id).instantiate_identity();
if let ty::Adt(def, args) = item_type.kind() {
assert!(def.is_union());
let def = tcx.adt_def(item_def_id);
assert!(def.is_union());
let typing_env = ty::TypingEnv::non_body_analysis(tcx, item_def_id);
for field in &def.non_enum_variant().fields {
let Ok(field_ty) = tcx.try_normalize_erasing_regions(typing_env, field.ty(tcx, args))
else {
tcx.dcx().span_delayed_bug(span, "could not normalize field type");
continue;
let typing_env = ty::TypingEnv::non_body_analysis(tcx, item_def_id);
let args = ty::GenericArgs::identity_for_item(tcx, item_def_id);
for field in &def.non_enum_variant().fields {
if !allowed_union_or_unsafe_field(tcx, field.ty(tcx, args), typing_env, span) {
let (field_span, ty_span) = match tcx.hir().get_if_local(field.did) {
// We are currently checking the type this field came from, so it must be local.
Some(Node::Field(field)) => (field.span, field.ty.span),
_ => unreachable!("mir field has to correspond to hir field"),
};
if !allowed_union_or_unsafe_field(tcx, field_ty, typing_env, span) {
let (field_span, ty_span) = match tcx.hir().get_if_local(field.did) {
// We are currently checking the type this field came from, so it must be local.
Some(Node::Field(field)) => (field.span, field.ty.span),
_ => unreachable!("mir field has to correspond to hir field"),
};
tcx.dcx().emit_err(errors::InvalidUnionField {
field_span,
sugg: errors::InvalidUnionFieldSuggestion {
lo: ty_span.shrink_to_lo(),
hi: ty_span.shrink_to_hi(),
},
note: (),
});
return false;
}
tcx.dcx().emit_err(errors::InvalidUnionField {
field_span,
sugg: errors::InvalidUnionFieldSuggestion {
lo: ty_span.shrink_to_lo(),
hi: ty_span.shrink_to_hi(),
},
note: (),
});
return false;
}
} else {
span_bug!(span, "unions must be ty::Adt, but got {:?}", item_type.kind());
}
true
}
/// Check that the unsafe fields do not need dropping.
fn check_unsafe_fields(tcx: TyCtxt<'_>, item_def_id: LocalDefId) {
let span = tcx.def_span(item_def_id);
let item_type = tcx.type_of(item_def_id).instantiate_identity();
let ty::Adt(def, args) = item_type.kind() else {
span_bug!(span, "structs/enums must be ty::Adt, but got {:?}", item_type.kind());
};
let def = tcx.adt_def(item_def_id);
let typing_env = ty::TypingEnv::non_body_analysis(tcx, item_def_id);
let args = ty::GenericArgs::identity_for_item(tcx, item_def_id);
for field in def.all_fields() {
if !field.safety.is_unsafe() {
continue;
}
let Ok(field_ty) = tcx.try_normalize_erasing_regions(typing_env, field.ty(tcx, args))
else {
tcx.dcx().span_delayed_bug(span, "could not normalize field type");
continue;
};
if !allowed_union_or_unsafe_field(tcx, field_ty, typing_env, span) {
if !allowed_union_or_unsafe_field(tcx, field.ty(tcx, args), typing_env, span) {
let hir::Node::Field(field) = tcx.hir_node_by_def_id(field.did.expect_local()) else {
unreachable!("field has to correspond to hir field")
};