578 lines
24 KiB
Rust
578 lines
24 KiB
Rust
//! Check properties that are required by built-in traits and set
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//! up data structures required by type-checking/codegen.
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use errors::struct_span_err;
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use rustc::infer;
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use rustc::infer::outlives::env::OutlivesEnvironment;
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use rustc::infer::SuppressRegionErrors;
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use rustc::middle::lang_items::UnsizeTraitLangItem;
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use rustc::middle::region;
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use rustc::traits::misc::{can_type_implement_copy, CopyImplementationError};
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use rustc::traits::predicate_for_trait_def;
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use rustc::traits::{self, ObligationCause, TraitEngine};
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use rustc::ty::adjustment::CoerceUnsizedInfo;
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use rustc::ty::TypeFoldable;
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use rustc::ty::{self, Ty, TyCtxt};
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use rustc_error_codes::*;
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use rustc_hir as hir;
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use rustc_hir::def_id::DefId;
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use rustc_hir::ItemKind;
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pub fn check_trait(tcx: TyCtxt<'_>, trait_def_id: DefId) {
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Checker { tcx, trait_def_id }
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.check(tcx.lang_items().drop_trait(), visit_implementation_of_drop)
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.check(tcx.lang_items().copy_trait(), visit_implementation_of_copy)
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.check(tcx.lang_items().coerce_unsized_trait(), visit_implementation_of_coerce_unsized)
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.check(
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tcx.lang_items().dispatch_from_dyn_trait(),
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visit_implementation_of_dispatch_from_dyn,
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);
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}
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struct Checker<'tcx> {
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tcx: TyCtxt<'tcx>,
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trait_def_id: DefId,
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}
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impl<'tcx> Checker<'tcx> {
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fn check<F>(&self, trait_def_id: Option<DefId>, mut f: F) -> &Self
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where
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F: FnMut(TyCtxt<'tcx>, DefId),
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{
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if Some(self.trait_def_id) == trait_def_id {
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for &impl_id in self.tcx.hir().trait_impls(self.trait_def_id) {
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let impl_def_id = self.tcx.hir().local_def_id(impl_id);
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f(self.tcx, impl_def_id);
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}
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}
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self
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}
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}
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fn visit_implementation_of_drop(tcx: TyCtxt<'_>, impl_did: DefId) {
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// Destructors only work on nominal types.
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if let ty::Adt(..) | ty::Error = tcx.type_of(impl_did).kind {
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return;
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}
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let impl_hir_id = tcx.hir().as_local_hir_id(impl_did).expect("foreign Drop impl on non-ADT");
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let sp = match tcx.hir().expect_item(impl_hir_id).kind {
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ItemKind::Impl(.., ty, _) => ty.span,
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_ => bug!("expected Drop impl item"),
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};
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struct_span_err!(
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tcx.sess,
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sp,
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E0120,
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"the `Drop` trait may only be implemented for structs, enums, and unions",
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)
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.span_label(sp, "must be a struct, enum, or union")
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.emit();
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}
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fn visit_implementation_of_copy(tcx: TyCtxt<'_>, impl_did: DefId) {
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debug!("visit_implementation_of_copy: impl_did={:?}", impl_did);
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let impl_hir_id = if let Some(n) = tcx.hir().as_local_hir_id(impl_did) {
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n
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} else {
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debug!("visit_implementation_of_copy(): impl not in this crate");
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return;
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};
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let self_type = tcx.type_of(impl_did);
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debug!("visit_implementation_of_copy: self_type={:?} (bound)", self_type);
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let span = tcx.hir().span(impl_hir_id);
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let param_env = tcx.param_env(impl_did);
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assert!(!self_type.has_escaping_bound_vars());
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debug!("visit_implementation_of_copy: self_type={:?} (free)", self_type);
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match can_type_implement_copy(tcx, param_env, self_type) {
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Ok(()) => {}
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Err(CopyImplementationError::InfrigingFields(fields)) => {
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let item = tcx.hir().expect_item(impl_hir_id);
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let span = if let ItemKind::Impl(.., Some(ref tr), _, _) = item.kind {
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tr.path.span
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} else {
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span
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};
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let mut err = struct_span_err!(
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tcx.sess,
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span,
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E0204,
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"the trait `Copy` may not be implemented for this type"
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);
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for span in fields.iter().map(|f| tcx.def_span(f.did)) {
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err.span_label(span, "this field does not implement `Copy`");
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}
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err.emit()
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}
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Err(CopyImplementationError::NotAnAdt) => {
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let item = tcx.hir().expect_item(impl_hir_id);
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let span = if let ItemKind::Impl(.., ref ty, _) = item.kind { ty.span } else { span };
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struct_span_err!(
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tcx.sess,
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span,
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E0206,
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"the trait `Copy` may not be implemented for this type"
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)
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.span_label(span, "type is not a structure or enumeration")
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.emit();
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}
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Err(CopyImplementationError::HasDestructor) => {
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struct_span_err!(
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tcx.sess,
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span,
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E0184,
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"the trait `Copy` may not be implemented for this type; the \
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type has a destructor"
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)
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.span_label(span, "Copy not allowed on types with destructors")
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.emit();
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}
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}
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}
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fn visit_implementation_of_coerce_unsized(tcx: TyCtxt<'tcx>, impl_did: DefId) {
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debug!("visit_implementation_of_coerce_unsized: impl_did={:?}", impl_did);
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// Just compute this for the side-effects, in particular reporting
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// errors; other parts of the code may demand it for the info of
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// course.
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if impl_did.is_local() {
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let span = tcx.def_span(impl_did);
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tcx.at(span).coerce_unsized_info(impl_did);
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}
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}
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fn visit_implementation_of_dispatch_from_dyn(tcx: TyCtxt<'_>, impl_did: DefId) {
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debug!("visit_implementation_of_dispatch_from_dyn: impl_did={:?}", impl_did);
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if impl_did.is_local() {
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let dispatch_from_dyn_trait = tcx.lang_items().dispatch_from_dyn_trait().unwrap();
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let impl_hir_id = tcx.hir().as_local_hir_id(impl_did).unwrap();
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let span = tcx.hir().span(impl_hir_id);
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let source = tcx.type_of(impl_did);
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assert!(!source.has_escaping_bound_vars());
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let target = {
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let trait_ref = tcx.impl_trait_ref(impl_did).unwrap();
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assert_eq!(trait_ref.def_id, dispatch_from_dyn_trait);
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trait_ref.substs.type_at(1)
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};
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debug!("visit_implementation_of_dispatch_from_dyn: {:?} -> {:?}", source, target);
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let param_env = tcx.param_env(impl_did);
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let create_err = |msg: &str| struct_span_err!(tcx.sess, span, E0378, "{}", msg);
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tcx.infer_ctxt().enter(|infcx| {
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let cause = ObligationCause::misc(span, impl_hir_id);
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use ty::TyKind::*;
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match (&source.kind, &target.kind) {
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(&Ref(r_a, _, mutbl_a), Ref(r_b, _, mutbl_b))
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if infcx.at(&cause, param_env).eq(r_a, r_b).is_ok() && mutbl_a == *mutbl_b =>
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{
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()
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}
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(&RawPtr(tm_a), &RawPtr(tm_b)) if tm_a.mutbl == tm_b.mutbl => (),
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(&Adt(def_a, substs_a), &Adt(def_b, substs_b))
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if def_a.is_struct() && def_b.is_struct() =>
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{
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if def_a != def_b {
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let source_path = tcx.def_path_str(def_a.did);
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let target_path = tcx.def_path_str(def_b.did);
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create_err(&format!(
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"the trait `DispatchFromDyn` may only be implemented \
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for a coercion between structures with the same \
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definition; expected `{}`, found `{}`",
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source_path, target_path,
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))
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.emit();
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return;
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}
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if def_a.repr.c() || def_a.repr.packed() {
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create_err(
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"structs implementing `DispatchFromDyn` may not have \
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`#[repr(packed)]` or `#[repr(C)]`",
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)
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.emit();
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}
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let fields = &def_a.non_enum_variant().fields;
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let coerced_fields = fields
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.iter()
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.filter_map(|field| {
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let ty_a = field.ty(tcx, substs_a);
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let ty_b = field.ty(tcx, substs_b);
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if let Ok(layout) = tcx.layout_of(param_env.and(ty_a)) {
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if layout.is_zst() && layout.details.align.abi.bytes() == 1 {
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// ignore ZST fields with alignment of 1 byte
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return None;
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}
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}
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if let Ok(ok) = infcx.at(&cause, param_env).eq(ty_a, ty_b) {
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if ok.obligations.is_empty() {
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create_err(
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"the trait `DispatchFromDyn` may only be implemented \
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for structs containing the field being coerced, \
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ZST fields with 1 byte alignment, and nothing else",
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)
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.note(&format!(
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"extra field `{}` of type `{}` is not allowed",
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field.ident, ty_a,
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))
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.emit();
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return None;
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}
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}
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Some(field)
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})
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.collect::<Vec<_>>();
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if coerced_fields.is_empty() {
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create_err(
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"the trait `DispatchFromDyn` may only be implemented \
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for a coercion between structures with a single field \
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being coerced, none found",
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)
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.emit();
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} else if coerced_fields.len() > 1 {
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create_err(
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"implementing the `DispatchFromDyn` trait requires multiple coercions",
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)
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.note(
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"the trait `DispatchFromDyn` may only be implemented \
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for a coercion between structures with a single field \
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being coerced",
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)
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.note(&format!(
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"currently, {} fields need coercions: {}",
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coerced_fields.len(),
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coerced_fields
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.iter()
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.map(|field| {
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format!(
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"`{}` (`{}` to `{}`)",
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field.ident,
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field.ty(tcx, substs_a),
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field.ty(tcx, substs_b),
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)
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})
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.collect::<Vec<_>>()
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.join(", ")
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))
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.emit();
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} else {
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let mut fulfill_cx = TraitEngine::new(infcx.tcx);
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for field in coerced_fields {
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let predicate = predicate_for_trait_def(
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tcx,
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param_env,
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cause.clone(),
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dispatch_from_dyn_trait,
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0,
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field.ty(tcx, substs_a),
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&[field.ty(tcx, substs_b).into()],
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);
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fulfill_cx.register_predicate_obligation(&infcx, predicate);
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}
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// Check that all transitive obligations are satisfied.
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if let Err(errors) = fulfill_cx.select_all_or_error(&infcx) {
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infcx.report_fulfillment_errors(&errors, None, false);
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}
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// Finally, resolve all regions.
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let region_scope_tree = region::ScopeTree::default();
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let outlives_env = OutlivesEnvironment::new(param_env);
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infcx.resolve_regions_and_report_errors(
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impl_did,
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®ion_scope_tree,
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&outlives_env,
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SuppressRegionErrors::default(),
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);
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}
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}
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_ => {
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create_err(
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"the trait `DispatchFromDyn` may only be implemented \
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for a coercion between structures",
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)
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.emit();
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}
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}
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})
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}
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}
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pub fn coerce_unsized_info<'tcx>(tcx: TyCtxt<'tcx>, impl_did: DefId) -> CoerceUnsizedInfo {
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debug!("compute_coerce_unsized_info(impl_did={:?})", impl_did);
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let coerce_unsized_trait = tcx.lang_items().coerce_unsized_trait().unwrap();
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let unsize_trait = tcx.lang_items().require(UnsizeTraitLangItem).unwrap_or_else(|err| {
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tcx.sess.fatal(&format!("`CoerceUnsized` implementation {}", err));
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});
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// this provider should only get invoked for local def-ids
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let impl_hir_id = tcx.hir().as_local_hir_id(impl_did).unwrap_or_else(|| {
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bug!("coerce_unsized_info: invoked for non-local def-id {:?}", impl_did)
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});
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let source = tcx.type_of(impl_did);
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let trait_ref = tcx.impl_trait_ref(impl_did).unwrap();
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assert_eq!(trait_ref.def_id, coerce_unsized_trait);
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let target = trait_ref.substs.type_at(1);
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debug!("visit_implementation_of_coerce_unsized: {:?} -> {:?} (bound)", source, target);
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let span = tcx.hir().span(impl_hir_id);
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let param_env = tcx.param_env(impl_did);
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assert!(!source.has_escaping_bound_vars());
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let err_info = CoerceUnsizedInfo { custom_kind: None };
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debug!("visit_implementation_of_coerce_unsized: {:?} -> {:?} (free)", source, target);
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tcx.infer_ctxt().enter(|infcx| {
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let cause = ObligationCause::misc(span, impl_hir_id);
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let check_mutbl = |mt_a: ty::TypeAndMut<'tcx>,
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mt_b: ty::TypeAndMut<'tcx>,
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mk_ptr: &dyn Fn(Ty<'tcx>) -> Ty<'tcx>| {
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if (mt_a.mutbl, mt_b.mutbl) == (hir::Mutability::Not, hir::Mutability::Mut) {
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infcx
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.report_mismatched_types(
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&cause,
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mk_ptr(mt_b.ty),
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target,
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ty::error::TypeError::Mutability,
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)
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.emit();
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}
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(mt_a.ty, mt_b.ty, unsize_trait, None)
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};
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let (source, target, trait_def_id, kind) = match (&source.kind, &target.kind) {
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(&ty::Ref(r_a, ty_a, mutbl_a), &ty::Ref(r_b, ty_b, mutbl_b)) => {
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infcx.sub_regions(infer::RelateObjectBound(span), r_b, r_a);
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let mt_a = ty::TypeAndMut { ty: ty_a, mutbl: mutbl_a };
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let mt_b = ty::TypeAndMut { ty: ty_b, mutbl: mutbl_b };
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check_mutbl(mt_a, mt_b, &|ty| tcx.mk_imm_ref(r_b, ty))
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}
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(&ty::Ref(_, ty_a, mutbl_a), &ty::RawPtr(mt_b)) => {
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let mt_a = ty::TypeAndMut { ty: ty_a, mutbl: mutbl_a };
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check_mutbl(mt_a, mt_b, &|ty| tcx.mk_imm_ptr(ty))
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}
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(&ty::RawPtr(mt_a), &ty::RawPtr(mt_b)) => {
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check_mutbl(mt_a, mt_b, &|ty| tcx.mk_imm_ptr(ty))
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}
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(&ty::Adt(def_a, substs_a), &ty::Adt(def_b, substs_b))
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if def_a.is_struct() && def_b.is_struct() =>
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{
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if def_a != def_b {
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let source_path = tcx.def_path_str(def_a.did);
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let target_path = tcx.def_path_str(def_b.did);
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struct_span_err!(
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tcx.sess,
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span,
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E0377,
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"the trait `CoerceUnsized` may only be implemented \
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for a coercion between structures with the same \
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definition; expected `{}`, found `{}`",
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source_path,
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target_path
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)
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.emit();
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return err_info;
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}
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// Here we are considering a case of converting
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// `S<P0...Pn>` to S<Q0...Qn>`. As an example, let's imagine a struct `Foo<T, U>`,
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// which acts like a pointer to `U`, but carries along some extra data of type `T`:
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//
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// struct Foo<T, U> {
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// extra: T,
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// ptr: *mut U,
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// }
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//
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// We might have an impl that allows (e.g.) `Foo<T, [i32; 3]>` to be unsized
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// to `Foo<T, [i32]>`. That impl would look like:
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//
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// impl<T, U: Unsize<V>, V> CoerceUnsized<Foo<T, V>> for Foo<T, U> {}
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//
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// Here `U = [i32; 3]` and `V = [i32]`. At runtime,
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// when this coercion occurs, we would be changing the
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// field `ptr` from a thin pointer of type `*mut [i32;
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// 3]` to a fat pointer of type `*mut [i32]` (with
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// extra data `3`). **The purpose of this check is to
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// make sure that we know how to do this conversion.**
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//
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// To check if this impl is legal, we would walk down
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// the fields of `Foo` and consider their types with
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// both substitutes. We are looking to find that
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// exactly one (non-phantom) field has changed its
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// type, which we will expect to be the pointer that
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// is becoming fat (we could probably generalize this
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// to multiple thin pointers of the same type becoming
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// fat, but we don't). In this case:
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//
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// - `extra` has type `T` before and type `T` after
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// - `ptr` has type `*mut U` before and type `*mut V` after
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//
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// Since just one field changed, we would then check
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// that `*mut U: CoerceUnsized<*mut V>` is implemented
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// (in other words, that we know how to do this
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// conversion). This will work out because `U:
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// Unsize<V>`, and we have a builtin rule that `*mut
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// U` can be coerced to `*mut V` if `U: Unsize<V>`.
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let fields = &def_a.non_enum_variant().fields;
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let diff_fields = fields
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.iter()
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.enumerate()
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.filter_map(|(i, f)| {
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let (a, b) = (f.ty(tcx, substs_a), f.ty(tcx, substs_b));
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if tcx.type_of(f.did).is_phantom_data() {
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// Ignore PhantomData fields
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return None;
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}
|
|
|
|
// 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_hir_id);
|
|
let span = if let ItemKind::Impl(.., Some(ref t), _, _) = item.kind {
|
|
t.path.span
|
|
} else {
|
|
tcx.hir().span(impl_hir_id)
|
|
};
|
|
|
|
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].ident, 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 = 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.
|
|
if let Err(errors) = fulfill_cx.select_all_or_error(&infcx) {
|
|
infcx.report_fulfillment_errors(&errors, None, false);
|
|
}
|
|
|
|
// Finally, resolve all regions.
|
|
let region_scope_tree = region::ScopeTree::default();
|
|
let outlives_env = OutlivesEnvironment::new(param_env);
|
|
infcx.resolve_regions_and_report_errors(
|
|
impl_did,
|
|
®ion_scope_tree,
|
|
&outlives_env,
|
|
SuppressRegionErrors::default(),
|
|
);
|
|
|
|
CoerceUnsizedInfo { custom_kind: kind }
|
|
})
|
|
}
|