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use rustc_data_structures::fx::FxHashMap;
use rustc_errors::struct_span_err;
use rustc_hir as hir;
use rustc_hir::def::{DefKind, Res};
use rustc_hir::def_id::{DefId, LocalDefId};
use rustc_lint_defs::Applicability;
use rustc_middle::ty::{self as ty, Ty, TypeVisitableExt};
use rustc_span::symbol::Ident;
use rustc_span::{ErrorGuaranteed, Span};
use rustc_trait_selection::traits;
use crate::astconv::{
AstConv, ConvertedBinding, ConvertedBindingKind, OnlySelfBounds, PredicateFilter,
};
use crate::bounds::Bounds;
use crate::errors;
impl<'tcx> dyn AstConv<'tcx> + '_ {
/// Sets `implicitly_sized` to true on `Bounds` if necessary
pub(crate) fn add_implicitly_sized(
&self,
bounds: &mut Bounds<'tcx>,
self_ty: Ty<'tcx>,
ast_bounds: &'tcx [hir::GenericBound<'tcx>],
self_ty_where_predicates: Option<(LocalDefId, &'tcx [hir::WherePredicate<'tcx>])>,
span: Span,
) {
let tcx = self.tcx();
// Try to find an unbound in bounds.
let mut unbound = None;
let mut search_bounds = |ast_bounds: &'tcx [hir::GenericBound<'tcx>]| {
for ab in ast_bounds {
if let hir::GenericBound::Trait(ptr, hir::TraitBoundModifier::Maybe) = ab {
if unbound.is_none() {
unbound = Some(&ptr.trait_ref);
} else {
tcx.sess.emit_err(errors::MultipleRelaxedDefaultBounds { span });
}
}
}
};
search_bounds(ast_bounds);
if let Some((self_ty, where_clause)) = self_ty_where_predicates {
for clause in where_clause {
if let hir::WherePredicate::BoundPredicate(pred) = clause {
if pred.is_param_bound(self_ty.to_def_id()) {
search_bounds(pred.bounds);
}
}
}
}
let sized_def_id = tcx.lang_items().sized_trait();
match (&sized_def_id, unbound) {
(Some(sized_def_id), Some(tpb))
if tpb.path.res == Res::Def(DefKind::Trait, *sized_def_id) =>
{
// There was in fact a `?Sized` bound, return without doing anything
return;
}
(_, Some(_)) => {
// There was a `?Trait` bound, but it was not `?Sized`; warn.
tcx.sess.span_warn(
span,
"default bound relaxed for a type parameter, but \
this does nothing because the given bound is not \
a default; only `?Sized` is supported",
);
// Otherwise, add implicitly sized if `Sized` is available.
}
_ => {
// There was no `?Sized` bound; add implicitly sized if `Sized` is available.
}
}
if sized_def_id.is_none() {
// No lang item for `Sized`, so we can't add it as a bound.
return;
}
bounds.push_sized(tcx, self_ty, span);
}
/// This helper takes a *converted* parameter type (`param_ty`)
/// and an *unconverted* list of bounds:
///
/// ```text
/// fn foo<T: Debug>
/// ^ ^^^^^ `ast_bounds` parameter, in HIR form
/// |
/// `param_ty`, in ty form
/// ```
///
/// It adds these `ast_bounds` into the `bounds` structure.
///
/// **A note on binders:** there is an implied binder around
/// `param_ty` and `ast_bounds`. See `instantiate_poly_trait_ref`
/// for more details.
#[instrument(level = "debug", skip(self, ast_bounds, bounds))]
pub(crate) fn add_bounds<'hir, I: Iterator<Item = &'hir hir::GenericBound<'hir>>>(
&self,
param_ty: Ty<'tcx>,
ast_bounds: I,
bounds: &mut Bounds<'tcx>,
bound_vars: &'tcx ty::List<ty::BoundVariableKind>,
only_self_bounds: OnlySelfBounds,
) {
for ast_bound in ast_bounds {
match ast_bound {
hir::GenericBound::Trait(poly_trait_ref, modifier) => {
let (constness, polarity) = match modifier {
hir::TraitBoundModifier::MaybeConst => {
(ty::BoundConstness::ConstIfConst, ty::ImplPolarity::Positive)
}
hir::TraitBoundModifier::None => {
(ty::BoundConstness::NotConst, ty::ImplPolarity::Positive)
}
hir::TraitBoundModifier::Negative => {
(ty::BoundConstness::NotConst, ty::ImplPolarity::Negative)
}
hir::TraitBoundModifier::Maybe => continue,
};
let _ = self.instantiate_poly_trait_ref(
&poly_trait_ref.trait_ref,
poly_trait_ref.span,
constness,
polarity,
param_ty,
bounds,
false,
only_self_bounds,
);
}
&hir::GenericBound::LangItemTrait(lang_item, span, hir_id, args) => {
self.instantiate_lang_item_trait_ref(
lang_item,
span,
hir_id,
args,
param_ty,
bounds,
only_self_bounds,
);
}
hir::GenericBound::Outlives(lifetime) => {
let region = self.ast_region_to_region(lifetime, None);
bounds.push_region_bound(
self.tcx(),
ty::Binder::bind_with_vars(
ty::OutlivesPredicate(param_ty, region),
bound_vars,
),
lifetime.ident.span,
);
}
}
}
}
/// Translates a list of bounds from the HIR into the `Bounds` data structure.
/// The self-type for the bounds is given by `param_ty`.
///
/// Example:
///
/// ```ignore (illustrative)
/// fn foo<T: Bar + Baz>() { }
/// // ^ ^^^^^^^^^ ast_bounds
/// // param_ty
/// ```
///
/// The `sized_by_default` parameter indicates if, in this context, the `param_ty` should be
/// considered `Sized` unless there is an explicit `?Sized` bound. This would be true in the
/// example above, but is not true in supertrait listings like `trait Foo: Bar + Baz`.
///
/// `span` should be the declaration size of the parameter.
pub(crate) fn compute_bounds(
&self,
param_ty: Ty<'tcx>,
ast_bounds: &[hir::GenericBound<'_>],
filter: PredicateFilter,
) -> Bounds<'tcx> {
let mut bounds = Bounds::default();
let only_self_bounds = match filter {
PredicateFilter::All | PredicateFilter::SelfAndAssociatedTypeBounds => {
OnlySelfBounds(false)
}
PredicateFilter::SelfOnly | PredicateFilter::SelfThatDefines(_) => OnlySelfBounds(true),
};
self.add_bounds(
param_ty,
ast_bounds.iter().filter(|bound| {
match filter {
PredicateFilter::All
| PredicateFilter::SelfOnly
| PredicateFilter::SelfAndAssociatedTypeBounds => true,
PredicateFilter::SelfThatDefines(assoc_name) => {
if let Some(trait_ref) = bound.trait_ref()
&& let Some(trait_did) = trait_ref.trait_def_id()
&& self.tcx().trait_may_define_assoc_item(trait_did, assoc_name)
{
true
} else {
false
}
}
}
}),
&mut bounds,
ty::List::empty(),
only_self_bounds,
);
debug!(?bounds);
bounds
}
/// Given an HIR binding like `Item = Foo` or `Item: Foo`, pushes the corresponding predicates
/// onto `bounds`.
///
/// **A note on binders:** given something like `T: for<'a> Iterator<Item = &'a u32>`, the
/// `trait_ref` here will be `for<'a> T: Iterator`. The `binding` data however is from *inside*
/// the binder (e.g., `&'a u32`) and hence may reference bound regions.
#[instrument(level = "debug", skip(self, bounds, speculative, dup_bindings, path_span))]
pub(super) fn add_predicates_for_ast_type_binding(
&self,
hir_ref_id: hir::HirId,
trait_ref: ty::PolyTraitRef<'tcx>,
binding: &ConvertedBinding<'_, 'tcx>,
bounds: &mut Bounds<'tcx>,
speculative: bool,
dup_bindings: &mut FxHashMap<DefId, Span>,
path_span: Span,
constness: ty::BoundConstness,
only_self_bounds: OnlySelfBounds,
polarity: ty::ImplPolarity,
) -> Result<(), ErrorGuaranteed> {
// Given something like `U: SomeTrait<T = X>`, we want to produce a
// predicate like `<U as SomeTrait>::T = X`. This is somewhat
// subtle in the event that `T` is defined in a supertrait of
// `SomeTrait`, because in that case we need to upcast.
//
// That is, consider this case:
//
// ```
// trait SubTrait: SuperTrait<i32> { }
// trait SuperTrait<A> { type T; }
//
// ... B: SubTrait<T = foo> ...
// ```
//
// We want to produce `<B as SuperTrait<i32>>::T == foo`.
let tcx = self.tcx();
let return_type_notation =
binding.gen_args.parenthesized == hir::GenericArgsParentheses::ReturnTypeNotation;
let candidate = if return_type_notation {
if self.trait_defines_associated_item_named(
trait_ref.def_id(),
ty::AssocKind::Fn,
binding.item_name,
) {
trait_ref
} else {
self.one_bound_for_assoc_method(
traits::supertraits(tcx, trait_ref),
trait_ref.print_only_trait_path(),
binding.item_name,
path_span,
)?
}
} else if self.trait_defines_associated_item_named(
trait_ref.def_id(),
ty::AssocKind::Type,
binding.item_name,
) {
// Simple case: X is defined in the current trait.
trait_ref
} else {
// Otherwise, we have to walk through the supertraits to find
// those that do.
self.one_bound_for_assoc_type(
|| traits::supertraits(tcx, trait_ref),
trait_ref.skip_binder().print_only_trait_name(),
binding.item_name,
path_span,
match binding.kind {
ConvertedBindingKind::Equality(term) => Some(term),
_ => None,
},
)?
};
let (assoc_ident, def_scope) =
tcx.adjust_ident_and_get_scope(binding.item_name, candidate.def_id(), hir_ref_id);
// We have already adjusted the item name above, so compare with `ident.normalize_to_macros_2_0()` instead
// of calling `filter_by_name_and_kind`.
let find_item_of_kind = |kind| {
tcx.associated_items(candidate.def_id())
.filter_by_name_unhygienic(assoc_ident.name)
.find(|i| i.kind == kind && i.ident(tcx).normalize_to_macros_2_0() == assoc_ident)
};
let assoc_item = if return_type_notation {
find_item_of_kind(ty::AssocKind::Fn)
} else {
find_item_of_kind(ty::AssocKind::Type)
.or_else(|| find_item_of_kind(ty::AssocKind::Const))
}
.expect("missing associated type");
if !assoc_item.visibility(tcx).is_accessible_from(def_scope, tcx) {
tcx.sess
.struct_span_err(
binding.span,
format!("{} `{}` is private", assoc_item.kind, binding.item_name),
)
.span_label(binding.span, format!("private {}", assoc_item.kind))
.emit();
}
tcx.check_stability(assoc_item.def_id, Some(hir_ref_id), binding.span, None);
if !speculative {
dup_bindings
.entry(assoc_item.def_id)
.and_modify(|prev_span| {
tcx.sess.emit_err(errors::ValueOfAssociatedStructAlreadySpecified {
span: binding.span,
prev_span: *prev_span,
item_name: binding.item_name,
def_path: tcx.def_path_str(assoc_item.container_id(tcx)),
});
})
.or_insert(binding.span);
}
let projection_ty = if return_type_notation {
let mut emitted_bad_param_err = false;
// If we have an method return type bound, then we need to substitute
// the method's early bound params with suitable late-bound params.
let mut num_bound_vars = candidate.bound_vars().len();
let args =
candidate.skip_binder().args.extend_to(tcx, assoc_item.def_id, |param, _| {
let subst = match param.kind {
ty::GenericParamDefKind::Lifetime => ty::Region::new_late_bound(
tcx,
ty::INNERMOST,
ty::BoundRegion {
var: ty::BoundVar::from_usize(num_bound_vars),
kind: ty::BoundRegionKind::BrNamed(param.def_id, param.name),
},
)
.into(),
ty::GenericParamDefKind::Type { .. } => {
if !emitted_bad_param_err {
tcx.sess.emit_err(
crate::errors::ReturnTypeNotationIllegalParam::Type {
span: path_span,
param_span: tcx.def_span(param.def_id),
},
);
emitted_bad_param_err = true;
}
Ty::new_bound(
tcx,
ty::INNERMOST,
ty::BoundTy {
var: ty::BoundVar::from_usize(num_bound_vars),
kind: ty::BoundTyKind::Param(param.def_id, param.name),
},
)
.into()
}
ty::GenericParamDefKind::Const { .. } => {
if !emitted_bad_param_err {
tcx.sess.emit_err(
crate::errors::ReturnTypeNotationIllegalParam::Const {
span: path_span,
param_span: tcx.def_span(param.def_id),
},
);
emitted_bad_param_err = true;
}
let ty = tcx
.type_of(param.def_id)
.no_bound_vars()
.expect("ct params cannot have early bound vars");
ty::Const::new_bound(
tcx,
ty::INNERMOST,
ty::BoundVar::from_usize(num_bound_vars),
ty,
)
.into()
}
};
num_bound_vars += 1;
subst
});
// Next, we need to check that the return-type notation is being used on
// an RPITIT (return-position impl trait in trait) or AFIT (async fn in trait).
let output = tcx.fn_sig(assoc_item.def_id).skip_binder().output();
let output = if let ty::Alias(ty::Projection, alias_ty) = *output.skip_binder().kind()
&& tcx.is_impl_trait_in_trait(alias_ty.def_id)
{
alias_ty
} else {
return Err(self.tcx().sess.emit_err(
crate::errors::ReturnTypeNotationOnNonRpitit {
span: binding.span,
ty: tcx.liberate_late_bound_regions(assoc_item.def_id, output),
fn_span: tcx.hir().span_if_local(assoc_item.def_id),
note: (),
},
));
};
// Finally, move the fn return type's bound vars over to account for the early bound
// params (and trait ref's late bound params). This logic is very similar to
// `Predicate::subst_supertrait`, and it's no coincidence why.
let shifted_output = tcx.shift_bound_var_indices(num_bound_vars, output);
let subst_output = ty::EarlyBinder::bind(shifted_output).instantiate(tcx, args);
let bound_vars = tcx.late_bound_vars(binding.hir_id);
ty::Binder::bind_with_vars(subst_output, bound_vars)
} else {
// Append the generic arguments of the associated type to the `trait_ref`.
candidate.map_bound(|trait_ref| {
let ident = Ident::new(assoc_item.name, binding.item_name.span);
let item_segment = hir::PathSegment {
ident,
hir_id: binding.hir_id,
res: Res::Err,
args: Some(binding.gen_args),
infer_args: false,
};
let args_trait_ref_and_assoc_item = self.create_args_for_associated_item(
path_span,
assoc_item.def_id,
&item_segment,
trait_ref.args,
);
debug!(?args_trait_ref_and_assoc_item);
tcx.mk_alias_ty(assoc_item.def_id, args_trait_ref_and_assoc_item)
})
};
if !speculative {
// Find any late-bound regions declared in `ty` that are not
// declared in the trait-ref or assoc_item. These are not well-formed.
//
// Example:
//
// for<'a> <T as Iterator>::Item = &'a str // <-- 'a is bad
// for<'a> <T as FnMut<(&'a u32,)>>::Output = &'a str // <-- 'a is ok
if let ConvertedBindingKind::Equality(ty) = binding.kind {
let late_bound_in_trait_ref =
tcx.collect_constrained_late_bound_regions(&projection_ty);
let late_bound_in_ty =
tcx.collect_referenced_late_bound_regions(&trait_ref.rebind(ty));
debug!(?late_bound_in_trait_ref);
debug!(?late_bound_in_ty);
// FIXME: point at the type params that don't have appropriate lifetimes:
// struct S1<F: for<'a> Fn(&i32, &i32) -> &'a i32>(F);
// ---- ---- ^^^^^^^
self.validate_late_bound_regions(
late_bound_in_trait_ref,
late_bound_in_ty,
|br_name| {
struct_span_err!(
tcx.sess,
binding.span,
E0582,
"binding for associated type `{}` references {}, \
which does not appear in the trait input types",
binding.item_name,
br_name
)
},
);
}
}
let assoc_item_def_id = projection_ty.skip_binder().def_id;
let def_kind = tcx.def_kind(assoc_item_def_id);
match binding.kind {
ConvertedBindingKind::Equality(..) if return_type_notation => {
return Err(self.tcx().sess.emit_err(
crate::errors::ReturnTypeNotationEqualityBound { span: binding.span },
));
}
ConvertedBindingKind::Equality(mut term) => {
// "Desugar" a constraint like `T: Iterator<Item = u32>` this to
// the "projection predicate" for:
//
// `<T as Iterator>::Item = u32`
match (def_kind, term.unpack()) {
(DefKind::AssocTy, ty::TermKind::Ty(_))
| (DefKind::AssocConst, ty::TermKind::Const(_)) => (),
(_, _) => {
let got = if let Some(_) = term.ty() { "type" } else { "constant" };
let expected = tcx.def_descr(assoc_item_def_id);
let mut err = tcx.sess.struct_span_err(
binding.span,
format!("expected {expected} bound, found {got}"),
);
err.span_note(
tcx.def_span(assoc_item_def_id),
format!("{expected} defined here"),
);
if let DefKind::AssocConst = def_kind
&& let Some(t) = term.ty() && (t.is_enum() || t.references_error())
&& tcx.features().associated_const_equality {
err.span_suggestion(
binding.span,
"if equating a const, try wrapping with braces",
format!("{} = {{ const }}", binding.item_name),
Applicability::HasPlaceholders,
);
}
let reported = err.emit();
term = match def_kind {
DefKind::AssocTy => Ty::new_error(tcx, reported).into(),
DefKind::AssocConst => ty::Const::new_error(
tcx,
reported,
tcx.type_of(assoc_item_def_id)
.instantiate(tcx, projection_ty.skip_binder().args),
)
.into(),
_ => unreachable!(),
};
}
}
bounds.push_projection_bound(
tcx,
projection_ty
.map_bound(|projection_ty| ty::ProjectionPredicate { projection_ty, term }),
binding.span,
);
}
ConvertedBindingKind::Constraint(ast_bounds) => {
match def_kind {
DefKind::AssocTy => {}
_ => {
return Err(tcx.sess.emit_err(errors::AssocBoundOnConst {
span: assoc_ident.span,
descr: tcx.def_descr(assoc_item_def_id),
}));
}
}
// "Desugar" a constraint like `T: Iterator<Item: Debug>` to
//
// `<T as Iterator>::Item: Debug`
//
// Calling `skip_binder` is okay, because `add_bounds` expects the `param_ty`
// parameter to have a skipped binder.
//
// NOTE: If `only_self_bounds` is true, do NOT expand this associated
// type bound into a trait predicate, since we only want to add predicates
// for the `Self` type.
if !only_self_bounds.0 {
let param_ty = Ty::new_alias(tcx, ty::Projection, projection_ty.skip_binder());
self.add_bounds(
param_ty,
ast_bounds.iter(),
bounds,
projection_ty.bound_vars(),
only_self_bounds,
);
}
}
}
Ok(())
}
}