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-rw-r--r--compiler/rustc_typeck/src/coherence/builtin.rs603
1 files changed, 603 insertions, 0 deletions
diff --git a/compiler/rustc_typeck/src/coherence/builtin.rs b/compiler/rustc_typeck/src/coherence/builtin.rs
new file mode 100644
index 000000000..50946cc1d
--- /dev/null
+++ b/compiler/rustc_typeck/src/coherence/builtin.rs
@@ -0,0 +1,603 @@
+//! Check properties that are required by built-in traits and set
+//! up data structures required by type-checking/codegen.
+
+use crate::errors::{CopyImplOnNonAdt, CopyImplOnTypeWithDtor, DropImplOnWrongItem};
+use rustc_errors::{struct_span_err, MultiSpan};
+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;
+use rustc_middle::ty::{self, suggest_constraining_type_params, Ty, TyCtxt, TypeVisitable};
+use rustc_trait_selection::traits::error_reporting::InferCtxtExt;
+use rustc_trait_selection::traits::misc::{can_type_implement_copy, CopyImplementationError};
+use rustc_trait_selection::traits::predicate_for_trait_def;
+use rustc_trait_selection::traits::{self, ObligationCause, TraitEngine, TraitEngineExt};
+use std::collections::BTreeMap;
+
+pub fn check_trait(tcx: TyCtxt<'_>, trait_def_id: DefId) {
+ let lang_items = tcx.lang_items();
+ Checker { tcx, trait_def_id }
+ .check(lang_items.drop_trait(), visit_implementation_of_drop)
+ .check(lang_items.copy_trait(), visit_implementation_of_copy)
+ .check(lang_items.coerce_unsized_trait(), visit_implementation_of_coerce_unsized)
+ .check(lang_items.dispatch_from_dyn_trait(), visit_implementation_of_dispatch_from_dyn);
+}
+
+struct Checker<'tcx> {
+ tcx: TyCtxt<'tcx>,
+ trait_def_id: DefId,
+}
+
+impl<'tcx> Checker<'tcx> {
+ fn check<F>(&self, trait_def_id: Option<DefId>, mut f: F) -> &Self
+ where
+ F: FnMut(TyCtxt<'tcx>, LocalDefId),
+ {
+ if Some(self.trait_def_id) == trait_def_id {
+ for &impl_def_id in self.tcx.hir().trait_impls(self.trait_def_id) {
+ f(self.tcx, impl_def_id);
+ }
+ }
+ self
+ }
+}
+
+fn visit_implementation_of_drop(tcx: TyCtxt<'_>, impl_did: LocalDefId) {
+ // Destructors only work on nominal types.
+ if let ty::Adt(..) | ty::Error(_) = tcx.type_of(impl_did).kind() {
+ return;
+ }
+
+ let sp = match tcx.hir().expect_item(impl_did).kind {
+ ItemKind::Impl(ref impl_) => impl_.self_ty.span,
+ _ => bug!("expected Drop impl item"),
+ };
+
+ tcx.sess.emit_err(DropImplOnWrongItem { span: sp });
+}
+
+fn visit_implementation_of_copy(tcx: TyCtxt<'_>, impl_did: LocalDefId) {
+ debug!("visit_implementation_of_copy: impl_did={:?}", impl_did);
+
+ let impl_hir_id = tcx.hir().local_def_id_to_hir_id(impl_did);
+
+ let self_type = tcx.type_of(impl_did);
+ debug!("visit_implementation_of_copy: self_type={:?} (bound)", self_type);
+
+ let span = tcx.hir().span(impl_hir_id);
+ let param_env = tcx.param_env(impl_did);
+ assert!(!self_type.has_escaping_bound_vars());
+
+ debug!("visit_implementation_of_copy: self_type={:?} (free)", self_type);
+
+ let cause = traits::ObligationCause::misc(span, impl_hir_id);
+ match can_type_implement_copy(tcx, param_env, self_type, cause) {
+ Ok(()) => {}
+ Err(CopyImplementationError::InfrigingFields(fields)) => {
+ let item = tcx.hir().expect_item(impl_did);
+ let span = if let ItemKind::Impl(hir::Impl { of_trait: Some(ref tr), .. }) = item.kind {
+ tr.path.span
+ } else {
+ span
+ };
+
+ let mut err = struct_span_err!(
+ tcx.sess,
+ span,
+ E0204,
+ "the trait `Copy` may not be implemented for this type"
+ );
+
+ // We'll try to suggest constraining type parameters to fulfill the requirements of
+ // their `Copy` implementation.
+ let mut errors: BTreeMap<_, Vec<_>> = Default::default();
+ let mut bounds = vec![];
+
+ for (field, ty) in fields {
+ let field_span = tcx.def_span(field.did);
+ let field_ty_span = match tcx.hir().get_if_local(field.did) {
+ Some(hir::Node::Field(field_def)) => field_def.ty.span,
+ _ => field_span,
+ };
+ err.span_label(field_span, "this field does not implement `Copy`");
+ // Spin up a new FulfillmentContext, so we can get the _precise_ reason
+ // why this field does not implement Copy. This is useful because sometimes
+ // it is not immediately clear why Copy is not implemented for a field, since
+ // all we point at is the field itself.
+ tcx.infer_ctxt().ignoring_regions().enter(|infcx| {
+ let mut fulfill_cx = <dyn TraitEngine<'_>>::new(tcx);
+ fulfill_cx.register_bound(
+ &infcx,
+ param_env,
+ ty,
+ tcx.lang_items().copy_trait().unwrap(),
+ traits::ObligationCause::dummy_with_span(field_ty_span),
+ );
+ for error in fulfill_cx.select_all_or_error(&infcx) {
+ let error_predicate = error.obligation.predicate;
+ // Only note if it's not the root obligation, otherwise it's trivial and
+ // should be self-explanatory (i.e. a field literally doesn't implement Copy).
+
+ // FIXME: This error could be more descriptive, especially if the error_predicate
+ // contains a foreign type or if it's a deeply nested type...
+ if error_predicate != error.root_obligation.predicate {
+ errors
+ .entry((ty.to_string(), error_predicate.to_string()))
+ .or_default()
+ .push(error.obligation.cause.span);
+ }
+ if let ty::PredicateKind::Trait(ty::TraitPredicate {
+ trait_ref,
+ polarity: ty::ImplPolarity::Positive,
+ ..
+ }) = error_predicate.kind().skip_binder()
+ {
+ let ty = trait_ref.self_ty();
+ if let ty::Param(_) = ty.kind() {
+ bounds.push((
+ format!("{ty}"),
+ trait_ref.print_only_trait_path().to_string(),
+ Some(trait_ref.def_id),
+ ));
+ }
+ }
+ }
+ });
+ }
+ for ((ty, error_predicate), spans) in errors {
+ let span: MultiSpan = spans.into();
+ err.span_note(
+ span,
+ &format!("the `Copy` impl for `{}` requires that `{}`", ty, error_predicate),
+ );
+ }
+ suggest_constraining_type_params(
+ tcx,
+ tcx.hir().get_generics(impl_did).expect("impls always have generics"),
+ &mut err,
+ bounds.iter().map(|(param, constraint, def_id)| {
+ (param.as_str(), constraint.as_str(), *def_id)
+ }),
+ );
+ err.emit();
+ }
+ Err(CopyImplementationError::NotAnAdt) => {
+ let item = tcx.hir().expect_item(impl_did);
+ let span =
+ if let ItemKind::Impl(ref impl_) = item.kind { impl_.self_ty.span } else { span };
+
+ tcx.sess.emit_err(CopyImplOnNonAdt { span });
+ }
+ Err(CopyImplementationError::HasDestructor) => {
+ tcx.sess.emit_err(CopyImplOnTypeWithDtor { span });
+ }
+ }
+}
+
+fn visit_implementation_of_coerce_unsized<'tcx>(tcx: TyCtxt<'tcx>, impl_did: LocalDefId) {
+ debug!("visit_implementation_of_coerce_unsized: impl_did={:?}", impl_did);
+
+ // Just compute this for the side-effects, in particular reporting
+ // errors; other parts of the code may demand it for the info of
+ // course.
+ let span = tcx.def_span(impl_did);
+ tcx.at(span).coerce_unsized_info(impl_did);
+}
+
+fn visit_implementation_of_dispatch_from_dyn<'tcx>(tcx: TyCtxt<'tcx>, impl_did: LocalDefId) {
+ debug!("visit_implementation_of_dispatch_from_dyn: impl_did={:?}", impl_did);
+
+ let impl_hir_id = tcx.hir().local_def_id_to_hir_id(impl_did);
+ let span = tcx.hir().span(impl_hir_id);
+
+ let dispatch_from_dyn_trait = tcx.require_lang_item(LangItem::DispatchFromDyn, Some(span));
+
+ let source = tcx.type_of(impl_did);
+ assert!(!source.has_escaping_bound_vars());
+ let target = {
+ let trait_ref = tcx.impl_trait_ref(impl_did).unwrap();
+ assert_eq!(trait_ref.def_id, dispatch_from_dyn_trait);
+
+ trait_ref.substs.type_at(1)
+ };
+
+ debug!("visit_implementation_of_dispatch_from_dyn: {:?} -> {:?}", source, target);
+
+ let param_env = tcx.param_env(impl_did);
+
+ let create_err = |msg: &str| struct_span_err!(tcx.sess, span, E0378, "{}", msg);
+
+ tcx.infer_ctxt().enter(|infcx| {
+ let cause = ObligationCause::misc(span, impl_hir_id);
+
+ use rustc_type_ir::sty::TyKind::*;
+ match (source.kind(), target.kind()) {
+ (&Ref(r_a, _, mutbl_a), Ref(r_b, _, mutbl_b))
+ if infcx.at(&cause, param_env).eq(r_a, *r_b).is_ok() && mutbl_a == *mutbl_b => {}
+ (&RawPtr(tm_a), &RawPtr(tm_b)) if tm_a.mutbl == tm_b.mutbl => (),
+ (&Adt(def_a, substs_a), &Adt(def_b, substs_b))
+ if def_a.is_struct() && def_b.is_struct() =>
+ {
+ if def_a != def_b {
+ let source_path = tcx.def_path_str(def_a.did());
+ let target_path = tcx.def_path_str(def_b.did());
+
+ create_err(&format!(
+ "the trait `DispatchFromDyn` may only be implemented \
+ for a coercion between structures with the same \
+ definition; expected `{}`, found `{}`",
+ source_path, target_path,
+ ))
+ .emit();
+
+ return;
+ }
+
+ if def_a.repr().c() || def_a.repr().packed() {
+ create_err(
+ "structs implementing `DispatchFromDyn` may not have \
+ `#[repr(packed)]` or `#[repr(C)]`",
+ )
+ .emit();
+ }
+
+ let fields = &def_a.non_enum_variant().fields;
+
+ let coerced_fields = fields
+ .iter()
+ .filter(|field| {
+ let ty_a = field.ty(tcx, substs_a);
+ let ty_b = field.ty(tcx, substs_b);
+
+ if let Ok(layout) = tcx.layout_of(param_env.and(ty_a)) {
+ if layout.is_zst() && layout.align.abi.bytes() == 1 {
+ // ignore ZST fields with alignment of 1 byte
+ return false;
+ }
+ }
+
+ if let Ok(ok) = infcx.at(&cause, param_env).eq(ty_a, ty_b) {
+ if ok.obligations.is_empty() {
+ create_err(
+ "the trait `DispatchFromDyn` may only be implemented \
+ for structs containing the field being coerced, \
+ ZST fields with 1 byte alignment, and nothing else",
+ )
+ .note(&format!(
+ "extra field `{}` of type `{}` is not allowed",
+ field.name, ty_a,
+ ))
+ .emit();
+
+ return false;
+ }
+ }
+
+ return true;
+ })
+ .collect::<Vec<_>>();
+
+ if coerced_fields.is_empty() {
+ create_err(
+ "the trait `DispatchFromDyn` may only be implemented \
+ for a coercion between structures with a single field \
+ being coerced, none found",
+ )
+ .emit();
+ } else if coerced_fields.len() > 1 {
+ create_err(
+ "implementing the `DispatchFromDyn` trait requires multiple coercions",
+ )
+ .note(
+ "the trait `DispatchFromDyn` may only be implemented \
+ for a coercion between structures with a single field \
+ being coerced",
+ )
+ .note(&format!(
+ "currently, {} fields need coercions: {}",
+ coerced_fields.len(),
+ coerced_fields
+ .iter()
+ .map(|field| {
+ format!(
+ "`{}` (`{}` to `{}`)",
+ field.name,
+ field.ty(tcx, substs_a),
+ field.ty(tcx, substs_b),
+ )
+ })
+ .collect::<Vec<_>>()
+ .join(", ")
+ ))
+ .emit();
+ } else {
+ let mut fulfill_cx = <dyn TraitEngine<'_>>::new(infcx.tcx);
+
+ for field in coerced_fields {
+ let predicate = predicate_for_trait_def(
+ tcx,
+ param_env,
+ cause.clone(),
+ dispatch_from_dyn_trait,
+ 0,
+ field.ty(tcx, substs_a),
+ &[field.ty(tcx, substs_b).into()],
+ );
+
+ fulfill_cx.register_predicate_obligation(&infcx, predicate);
+ }
+
+ // Check that all transitive obligations are satisfied.
+ let errors = fulfill_cx.select_all_or_error(&infcx);
+ if !errors.is_empty() {
+ infcx.report_fulfillment_errors(&errors, None, false);
+ }
+
+ // Finally, resolve all regions.
+ let outlives_env = OutlivesEnvironment::new(param_env);
+ infcx.check_region_obligations_and_report_errors(impl_did, &outlives_env);
+ }
+ }
+ _ => {
+ create_err(
+ "the trait `DispatchFromDyn` may only be implemented \
+ for a coercion between structures",
+ )
+ .emit();
+ }
+ }
+ })
+}
+
+pub fn coerce_unsized_info<'tcx>(tcx: TyCtxt<'tcx>, impl_did: DefId) -> CoerceUnsizedInfo {
+ debug!("compute_coerce_unsized_info(impl_did={:?})", impl_did);
+
+ // this provider should only get invoked for local def-ids
+ let impl_did = impl_did.expect_local();
+ let span = tcx.def_span(impl_did);
+
+ let coerce_unsized_trait = tcx.require_lang_item(LangItem::CoerceUnsized, Some(span));
+
+ let unsize_trait = tcx.lang_items().require(LangItem::Unsize).unwrap_or_else(|err| {
+ tcx.sess.fatal(&format!("`CoerceUnsized` implementation {}", err));
+ });
+
+ let source = tcx.type_of(impl_did);
+ let trait_ref = tcx.impl_trait_ref(impl_did).unwrap();
+ assert_eq!(trait_ref.def_id, coerce_unsized_trait);
+ let target = trait_ref.substs.type_at(1);
+ debug!("visit_implementation_of_coerce_unsized: {:?} -> {:?} (bound)", source, target);
+
+ let param_env = tcx.param_env(impl_did);
+ assert!(!source.has_escaping_bound_vars());
+
+ let err_info = CoerceUnsizedInfo { custom_kind: None };
+
+ debug!("visit_implementation_of_coerce_unsized: {:?} -> {:?} (free)", source, target);
+
+ tcx.infer_ctxt().enter(|infcx| {
+ let impl_hir_id = tcx.hir().local_def_id_to_hir_id(impl_did);
+ let cause = ObligationCause::misc(span, impl_hir_id);
+ let check_mutbl = |mt_a: ty::TypeAndMut<'tcx>,
+ mt_b: ty::TypeAndMut<'tcx>,
+ mk_ptr: &dyn Fn(Ty<'tcx>) -> Ty<'tcx>| {
+ if (mt_a.mutbl, mt_b.mutbl) == (hir::Mutability::Not, hir::Mutability::Mut) {
+ infcx
+ .report_mismatched_types(
+ &cause,
+ mk_ptr(mt_b.ty),
+ target,
+ ty::error::TypeError::Mutability,
+ )
+ .emit();
+ }
+ (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);
+ 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))
+ }
+
+ (&ty::Ref(_, ty_a, mutbl_a), &ty::RawPtr(mt_b)) => {
+ let mt_a = ty::TypeAndMut { ty: ty_a, mutbl: mutbl_a };
+ check_mutbl(mt_a, mt_b, &|ty| tcx.mk_imm_ptr(ty))
+ }
+
+ (&ty::RawPtr(mt_a), &ty::RawPtr(mt_b)) => {
+ check_mutbl(mt_a, mt_b, &|ty| tcx.mk_imm_ptr(ty))
+ }
+
+ (&ty::Adt(def_a, substs_a), &ty::Adt(def_b, substs_b))
+ if def_a.is_struct() && def_b.is_struct() =>
+ {
+ if def_a != def_b {
+ let source_path = tcx.def_path_str(def_a.did());
+ let target_path = tcx.def_path_str(def_b.did());
+ struct_span_err!(
+ tcx.sess,
+ span,
+ E0377,
+ "the trait `CoerceUnsized` may only be implemented \
+ for a coercion between structures with the same \
+ definition; expected `{}`, found `{}`",
+ source_path,
+ target_path
+ )
+ .emit();
+ return err_info;
+ }
+
+ // Here we are considering a case of converting
+ // `S<P0...Pn>` to S<Q0...Qn>`. As an example, let's imagine a struct `Foo<T, U>`,
+ // which acts like a pointer to `U`, but carries along some extra data of type `T`:
+ //
+ // struct Foo<T, U> {
+ // extra: T,
+ // ptr: *mut U,
+ // }
+ //
+ // We might have an impl that allows (e.g.) `Foo<T, [i32; 3]>` to be unsized
+ // to `Foo<T, [i32]>`. That impl would look like:
+ //
+ // impl<T, U: Unsize<V>, V> CoerceUnsized<Foo<T, V>> for Foo<T, U> {}
+ //
+ // Here `U = [i32; 3]` and `V = [i32]`. At runtime,
+ // when this coercion occurs, we would be changing the
+ // field `ptr` from a thin pointer of type `*mut [i32;
+ // 3]` to a fat pointer of type `*mut [i32]` (with
+ // extra data `3`). **The purpose of this check is to
+ // make sure that we know how to do this conversion.**
+ //
+ // To check if this impl is legal, we would walk down
+ // the fields of `Foo` and consider their types with
+ // both substitutes. We are looking to find that
+ // exactly one (non-phantom) field has changed its
+ // type, which we will expect to be the pointer that
+ // is becoming fat (we could probably generalize this
+ // to multiple thin pointers of the same type becoming
+ // fat, but we don't). In this case:
+ //
+ // - `extra` has type `T` before and type `T` after
+ // - `ptr` has type `*mut U` before and type `*mut V` after
+ //
+ // Since just one field changed, we would then check
+ // that `*mut U: CoerceUnsized<*mut V>` is implemented
+ // (in other words, that we know how to do this
+ // conversion). This will work out because `U:
+ // Unsize<V>`, and we have a builtin rule that `*mut
+ // U` can be coerced to `*mut V` if `U: Unsize<V>`.
+ let fields = &def_a.non_enum_variant().fields;
+ let diff_fields = fields
+ .iter()
+ .enumerate()
+ .filter_map(|(i, f)| {
+ let (a, b) = (f.ty(tcx, substs_a), f.ty(tcx, substs_b));
+
+ if tcx.type_of(f.did).is_phantom_data() {
+ // Ignore PhantomData fields
+ return None;
+ }
+
+ // Ignore fields that aren't changed; it may
+ // be that we could get away with subtyping or
+ // something more accepting, but we use
+ // equality because we want to be able to
+ // perform this check without computing
+ // variance where possible. (This is because
+ // we may have to evaluate constraint
+ // expressions in the course of execution.)
+ // See e.g., #41936.
+ if let Ok(ok) = infcx.at(&cause, param_env).eq(a, b) {
+ if ok.obligations.is_empty() {
+ return None;
+ }
+ }
+
+ // Collect up all fields that were significantly changed
+ // i.e., those that contain T in coerce_unsized T -> U
+ Some((i, a, b))
+ })
+ .collect::<Vec<_>>();
+
+ if diff_fields.is_empty() {
+ struct_span_err!(
+ tcx.sess,
+ span,
+ E0374,
+ "the trait `CoerceUnsized` may only be implemented \
+ for a coercion between structures with one field \
+ being coerced, none found"
+ )
+ .emit();
+ return err_info;
+ } else if diff_fields.len() > 1 {
+ let item = tcx.hir().expect_item(impl_did);
+ let span = if let ItemKind::Impl(hir::Impl { of_trait: Some(ref t), .. }) =
+ item.kind
+ {
+ t.path.span
+ } else {
+ tcx.def_span(impl_did)
+ };
+
+ struct_span_err!(
+ tcx.sess,
+ span,
+ E0375,
+ "implementing the trait \
+ `CoerceUnsized` requires multiple \
+ coercions"
+ )
+ .note(
+ "`CoerceUnsized` may only be implemented for \
+ a coercion between structures with one field being coerced",
+ )
+ .note(&format!(
+ "currently, {} fields need coercions: {}",
+ diff_fields.len(),
+ diff_fields
+ .iter()
+ .map(|&(i, a, b)| {
+ format!("`{}` (`{}` to `{}`)", fields[i].name, a, b)
+ })
+ .collect::<Vec<_>>()
+ .join(", ")
+ ))
+ .span_label(span, "requires multiple coercions")
+ .emit();
+ return err_info;
+ }
+
+ let (i, a, b) = diff_fields[0];
+ let kind = ty::adjustment::CustomCoerceUnsized::Struct(i);
+ (a, b, coerce_unsized_trait, Some(kind))
+ }
+
+ _ => {
+ struct_span_err!(
+ tcx.sess,
+ span,
+ E0376,
+ "the trait `CoerceUnsized` may only be implemented \
+ for a coercion between structures"
+ )
+ .emit();
+ return err_info;
+ }
+ };
+
+ let mut fulfill_cx = <dyn TraitEngine<'_>>::new(infcx.tcx);
+
+ // Register an obligation for `A: Trait<B>`.
+ let cause = traits::ObligationCause::misc(span, impl_hir_id);
+ let predicate = predicate_for_trait_def(
+ tcx,
+ param_env,
+ cause,
+ trait_def_id,
+ 0,
+ source,
+ &[target.into()],
+ );
+ fulfill_cx.register_predicate_obligation(&infcx, predicate);
+
+ // Check that all transitive obligations are satisfied.
+ let errors = fulfill_cx.select_all_or_error(&infcx);
+ if !errors.is_empty() {
+ infcx.report_fulfillment_errors(&errors, None, false);
+ }
+
+ // Finally, resolve all regions.
+ let outlives_env = OutlivesEnvironment::new(param_env);
+ infcx.check_region_obligations_and_report_errors(impl_did, &outlives_env);
+
+ CoerceUnsizedInfo { custom_kind: kind }
+ })
+}
generated by cgit v1.2.3 (git 2.39.1) at 2024-06-12 14:15:34 +0000