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wfcheck.rs
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wfcheck.rs
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use crate::check::{Inherited, FnCtxt};
use crate::constrained_generic_params::{identify_constrained_generic_params, Parameter};
use crate::hir::def_id::DefId;
use rustc::traits::{self, ObligationCauseCode};
use rustc::ty::{self, Lift, Ty, TyCtxt, TyKind, GenericParamDefKind, TypeFoldable, ToPredicate};
use rustc::ty::subst::{Subst, InternalSubsts};
use rustc::util::nodemap::{FxHashSet, FxHashMap};
use rustc::mir::interpret::ConstValue;
use rustc::middle::lang_items;
use rustc::infer::opaque_types::may_define_existential_type;
use syntax::ast;
use syntax::feature_gate::{self, GateIssue};
use syntax_pos::Span;
use errors::{DiagnosticBuilder, DiagnosticId};
use rustc::hir::itemlikevisit::ParItemLikeVisitor;
use rustc::hir;
/// Helper type of a temporary returned by `.for_item(...)`.
/// Necessary because we can't write the following bound:
/// `F: for<'b, 'tcx> where 'gcx: 'tcx FnOnce(FnCtxt<'b, 'gcx, 'tcx>)`.
struct CheckWfFcxBuilder<'a, 'gcx: 'a+'tcx, 'tcx: 'a> {
inherited: super::InheritedBuilder<'a, 'gcx, 'tcx>,
id: hir::HirId,
span: Span,
param_env: ty::ParamEnv<'tcx>,
}
impl<'a, 'gcx, 'tcx> CheckWfFcxBuilder<'a, 'gcx, 'tcx> {
fn with_fcx<F>(&'tcx mut self, f: F) where
F: for<'b> FnOnce(&FnCtxt<'b, 'gcx, 'tcx>,
TyCtxt<'b, 'gcx, 'gcx>) -> Vec<Ty<'tcx>>
{
let id = self.id;
let span = self.span;
let param_env = self.param_env;
self.inherited.enter(|inh| {
let fcx = FnCtxt::new(&inh, param_env, id);
if !inh.tcx.features().trivial_bounds {
// As predicates are cached rather than obligations, this
// needsto be called first so that they are checked with an
// empty param_env.
check_false_global_bounds(&fcx, span, id);
}
let wf_tys = f(&fcx, fcx.tcx.global_tcx());
fcx.select_all_obligations_or_error();
fcx.regionck_item(id, span, &wf_tys);
});
}
}
/// Checks that the field types (in a struct def'n) or argument types (in an enum def'n) are
/// well-formed, meaning that they do not require any constraints not declared in the struct
/// definition itself. For example, this definition would be illegal:
///
/// struct Ref<'a, T> { x: &'a T }
///
/// because the type did not declare that `T:'a`.
///
/// We do this check as a pre-pass before checking fn bodies because if these constraints are
/// not included it frequently leads to confusing errors in fn bodies. So it's better to check
/// the types first.
pub fn check_item_well_formed<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>, def_id: DefId) {
let hir_id = tcx.hir().as_local_hir_id(def_id).unwrap();
let item = tcx.hir().expect_item_by_hir_id(hir_id);
debug!("check_item_well_formed(it.hir_id={:?}, it.name={})",
item.hir_id,
tcx.def_path_str(def_id));
match item.node {
// Right now we check that every default trait implementation
// has an implementation of itself. Basically, a case like:
//
// `impl Trait for T {}`
//
// has a requirement of `T: Trait` which was required for default
// method implementations. Although this could be improved now that
// there's a better infrastructure in place for this, it's being left
// for a follow-up work.
//
// Since there's such a requirement, we need to check *just* positive
// implementations, otherwise things like:
//
// impl !Send for T {}
//
// won't be allowed unless there's an *explicit* implementation of `Send`
// for `T`
hir::ItemKind::Impl(_, polarity, defaultness, _, ref trait_ref, ref self_ty, _) => {
let is_auto = tcx.impl_trait_ref(tcx.hir().local_def_id_from_hir_id(item.hir_id))
.map_or(false, |trait_ref| tcx.trait_is_auto(trait_ref.def_id));
if let (hir::Defaultness::Default { .. }, true) = (defaultness, is_auto) {
tcx.sess.span_err(item.span, "impls of auto traits cannot be default");
}
if polarity == hir::ImplPolarity::Positive {
check_impl(tcx, item, self_ty, trait_ref);
} else {
// FIXME(#27579) what amount of WF checking do we need for neg impls?
if trait_ref.is_some() && !is_auto {
span_err!(tcx.sess, item.span, E0192,
"negative impls are only allowed for \
auto traits (e.g., `Send` and `Sync`)")
}
}
}
hir::ItemKind::Fn(..) => {
check_item_fn(tcx, item);
}
hir::ItemKind::Static(ref ty, ..) => {
check_item_type(tcx, item.hir_id, ty.span, false);
}
hir::ItemKind::Const(ref ty, ..) => {
check_item_type(tcx, item.hir_id, ty.span, false);
}
hir::ItemKind::ForeignMod(ref module) => for it in module.items.iter() {
if let hir::ForeignItemKind::Static(ref ty, ..) = it.node {
check_item_type(tcx, it.hir_id, ty.span, true);
}
},
hir::ItemKind::Struct(ref struct_def, ref ast_generics) => {
check_type_defn(tcx, item, false, |fcx| {
vec![fcx.non_enum_variant(struct_def)]
});
check_variances_for_type_defn(tcx, item, ast_generics);
}
hir::ItemKind::Union(ref struct_def, ref ast_generics) => {
check_type_defn(tcx, item, true, |fcx| {
vec![fcx.non_enum_variant(struct_def)]
});
check_variances_for_type_defn(tcx, item, ast_generics);
}
hir::ItemKind::Enum(ref enum_def, ref ast_generics) => {
check_type_defn(tcx, item, true, |fcx| {
fcx.enum_variants(enum_def)
});
check_variances_for_type_defn(tcx, item, ast_generics);
}
hir::ItemKind::Trait(..) => {
check_trait(tcx, item);
}
hir::ItemKind::TraitAlias(..) => {
check_trait(tcx, item);
}
_ => {}
}
}
pub fn check_trait_item<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>, def_id: DefId) {
let hir_id = tcx.hir().as_local_hir_id(def_id).unwrap();
let trait_item = tcx.hir().expect_trait_item(hir_id);
let method_sig = match trait_item.node {
hir::TraitItemKind::Method(ref sig, _) => Some(sig),
_ => None
};
check_associated_item(tcx, trait_item.hir_id, trait_item.span, method_sig);
}
pub fn check_impl_item<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>, def_id: DefId) {
let hir_id = tcx.hir().as_local_hir_id(def_id).unwrap();
let impl_item = tcx.hir().expect_impl_item(hir_id);
let method_sig = match impl_item.node {
hir::ImplItemKind::Method(ref sig, _) => Some(sig),
_ => None
};
check_associated_item(tcx, impl_item.hir_id, impl_item.span, method_sig);
}
fn check_associated_item<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
item_id: hir::HirId,
span: Span,
sig_if_method: Option<&hir::MethodSig>) {
debug!("check_associated_item: {:?}", item_id);
let code = ObligationCauseCode::MiscObligation;
for_id(tcx, item_id, span).with_fcx(|fcx, tcx| {
let item = fcx.tcx.associated_item(fcx.tcx.hir().local_def_id_from_hir_id(item_id));
let (mut implied_bounds, self_ty) = match item.container {
ty::TraitContainer(_) => (vec![], fcx.tcx.mk_self_type()),
ty::ImplContainer(def_id) => (fcx.impl_implied_bounds(def_id, span),
fcx.tcx.type_of(def_id))
};
match item.kind {
ty::AssociatedKind::Const => {
let ty = fcx.tcx.type_of(item.def_id);
let ty = fcx.normalize_associated_types_in(span, &ty);
fcx.register_wf_obligation(ty, span, code.clone());
}
ty::AssociatedKind::Method => {
reject_shadowing_parameters(fcx.tcx, item.def_id);
let sig = fcx.tcx.fn_sig(item.def_id);
let sig = fcx.normalize_associated_types_in(span, &sig);
check_fn_or_method(tcx, fcx, span, sig,
item.def_id, &mut implied_bounds);
let sig_if_method = sig_if_method.expect("bad signature for method");
check_method_receiver(fcx, sig_if_method, &item, self_ty);
}
ty::AssociatedKind::Type => {
if item.defaultness.has_value() {
let ty = fcx.tcx.type_of(item.def_id);
let ty = fcx.normalize_associated_types_in(span, &ty);
fcx.register_wf_obligation(ty, span, code.clone());
}
}
ty::AssociatedKind::Existential => {
// do nothing, existential types check themselves
}
}
implied_bounds
})
}
fn for_item<'a, 'gcx, 'tcx>(tcx: TyCtxt<'a, 'gcx, 'gcx>, item: &hir::Item)
-> CheckWfFcxBuilder<'a, 'gcx, 'tcx> {
for_id(tcx, item.hir_id, item.span)
}
fn for_id<'a, 'gcx, 'tcx>(tcx: TyCtxt<'a, 'gcx, 'gcx>, id: hir::HirId, span: Span)
-> CheckWfFcxBuilder<'a, 'gcx, 'tcx> {
let def_id = tcx.hir().local_def_id_from_hir_id(id);
CheckWfFcxBuilder {
inherited: Inherited::build(tcx, def_id),
id,
span,
param_env: tcx.param_env(def_id),
}
}
/// In a type definition, we check that to ensure that the types of the fields are well-formed.
fn check_type_defn<'a, 'tcx, F>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
item: &hir::Item, all_sized: bool, mut lookup_fields: F)
where F: for<'fcx, 'gcx, 'tcx2> FnMut(&FnCtxt<'fcx, 'gcx, 'tcx2>) -> Vec<AdtVariant<'tcx2>>
{
for_item(tcx, item).with_fcx(|fcx, fcx_tcx| {
let variants = lookup_fields(fcx);
let def_id = fcx.tcx.hir().local_def_id_from_hir_id(item.hir_id);
let packed = fcx.tcx.adt_def(def_id).repr.packed();
for variant in &variants {
// For DST, or when drop needs to copy things around, all
// intermediate types must be sized.
let needs_drop_copy = || {
packed && {
let ty = variant.fields.last().unwrap().ty;
fcx.tcx.erase_regions(&ty).lift_to_tcx(fcx_tcx)
.map(|ty| ty.needs_drop(fcx_tcx, fcx_tcx.param_env(def_id)))
.unwrap_or_else(|| {
fcx_tcx.sess.delay_span_bug(
item.span, &format!("inference variables in {:?}", ty));
// Just treat unresolved type expression as if it needs drop.
true
})
}
};
let all_sized =
all_sized ||
variant.fields.is_empty() ||
needs_drop_copy();
let unsized_len = if all_sized {
0
} else {
1
};
for (idx, field) in variant.fields[..variant.fields.len() - unsized_len]
.iter()
.enumerate()
{
let last = idx == variant.fields.len() - 1;
fcx.register_bound(
field.ty,
fcx.tcx.require_lang_item(lang_items::SizedTraitLangItem),
traits::ObligationCause::new(
field.span,
fcx.body_id,
traits::FieldSized {
adt_kind: match item.node.adt_kind() {
Some(i) => i,
None => bug!(),
},
last
}
)
);
}
// All field types must be well-formed.
for field in &variant.fields {
fcx.register_wf_obligation(field.ty, field.span,
ObligationCauseCode::MiscObligation)
}
}
check_where_clauses(tcx, fcx, item.span, def_id, None);
vec![] // no implied bounds in a struct def'n
});
}
fn check_trait<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>, item: &hir::Item) {
debug!("check_trait: {:?}", item.hir_id);
let trait_def_id = tcx.hir().local_def_id_from_hir_id(item.hir_id);
let trait_def = tcx.trait_def(trait_def_id);
if trait_def.is_marker {
for associated_def_id in &*tcx.associated_item_def_ids(trait_def_id) {
struct_span_err!(
tcx.sess,
tcx.def_span(*associated_def_id),
E0714,
"marker traits cannot have associated items",
).emit();
}
}
for_item(tcx, item).with_fcx(|fcx, _| {
check_where_clauses(tcx, fcx, item.span, trait_def_id, None);
vec![]
});
}
fn check_item_fn<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>, item: &hir::Item) {
for_item(tcx, item).with_fcx(|fcx, tcx| {
let def_id = fcx.tcx.hir().local_def_id_from_hir_id(item.hir_id);
let sig = fcx.tcx.fn_sig(def_id);
let sig = fcx.normalize_associated_types_in(item.span, &sig);
let mut implied_bounds = vec![];
check_fn_or_method(tcx, fcx, item.span, sig,
def_id, &mut implied_bounds);
implied_bounds
})
}
fn check_item_type<'a, 'tcx>(
tcx: TyCtxt<'a, 'tcx, 'tcx>,
item_id: hir::HirId,
ty_span: Span,
allow_foreign_ty: bool,
) {
debug!("check_item_type: {:?}", item_id);
for_id(tcx, item_id, ty_span).with_fcx(|fcx, gcx| {
let ty = gcx.type_of(gcx.hir().local_def_id_from_hir_id(item_id));
let item_ty = fcx.normalize_associated_types_in(ty_span, &ty);
let mut forbid_unsized = true;
if allow_foreign_ty {
if let TyKind::Foreign(_) = fcx.tcx.struct_tail(item_ty).sty {
forbid_unsized = false;
}
}
fcx.register_wf_obligation(item_ty, ty_span, ObligationCauseCode::MiscObligation);
if forbid_unsized {
fcx.register_bound(
item_ty,
fcx.tcx.require_lang_item(lang_items::SizedTraitLangItem),
traits::ObligationCause::new(ty_span, fcx.body_id, traits::MiscObligation),
);
}
vec![] // no implied bounds in a const etc
});
}
fn check_impl<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
item: &hir::Item,
ast_self_ty: &hir::Ty,
ast_trait_ref: &Option<hir::TraitRef>)
{
debug!("check_impl: {:?}", item);
for_item(tcx, item).with_fcx(|fcx, tcx| {
let item_def_id = fcx.tcx.hir().local_def_id_from_hir_id(item.hir_id);
match *ast_trait_ref {
Some(ref ast_trait_ref) => {
let trait_ref = fcx.tcx.impl_trait_ref(item_def_id).unwrap();
let trait_ref =
fcx.normalize_associated_types_in(
ast_trait_ref.path.span, &trait_ref);
let obligations =
ty::wf::trait_obligations(fcx,
fcx.param_env,
fcx.body_id,
&trait_ref,
ast_trait_ref.path.span);
for obligation in obligations {
fcx.register_predicate(obligation);
}
}
None => {
let self_ty = fcx.tcx.type_of(item_def_id);
let self_ty = fcx.normalize_associated_types_in(item.span, &self_ty);
fcx.register_wf_obligation(self_ty, ast_self_ty.span,
ObligationCauseCode::MiscObligation);
}
}
check_where_clauses(tcx, fcx, item.span, item_def_id, None);
fcx.impl_implied_bounds(item_def_id, item.span)
});
}
/// Checks where-clauses and inline bounds that are declared on `def_id`.
fn check_where_clauses<'a, 'gcx, 'fcx, 'tcx>(
tcx: TyCtxt<'a, 'gcx, 'gcx>,
fcx: &FnCtxt<'fcx, 'gcx, 'tcx>,
span: Span,
def_id: DefId,
return_ty: Option<Ty<'tcx>>,
) {
use ty::subst::Subst;
use rustc::ty::TypeFoldable;
let predicates = fcx.tcx.predicates_of(def_id);
let generics = tcx.generics_of(def_id);
let is_our_default = |def: &ty::GenericParamDef| {
match def.kind {
GenericParamDefKind::Type { has_default, .. } => {
has_default && def.index >= generics.parent_count as u32
}
_ => unreachable!()
}
};
// Check that concrete defaults are well-formed. See test `type-check-defaults.rs`.
// For example this forbids the declaration:
// struct Foo<T = Vec<[u32]>> { .. }
// Here the default `Vec<[u32]>` is not WF because `[u32]: Sized` does not hold.
for param in &generics.params {
if let GenericParamDefKind::Type { .. } = param.kind {
if is_our_default(¶m) {
let ty = fcx.tcx.type_of(param.def_id);
// ignore dependent defaults -- that is, where the default of one type
// parameter includes another (e.g., <T, U = T>). In those cases, we can't
// be sure if it will error or not as user might always specify the other.
if !ty.needs_subst() {
fcx.register_wf_obligation(ty, fcx.tcx.def_span(param.def_id),
ObligationCauseCode::MiscObligation);
}
}
}
}
// Check that trait predicates are WF when params are substituted by their defaults.
// We don't want to overly constrain the predicates that may be written but we want to
// catch cases where a default my never be applied such as `struct Foo<T: Copy = String>`.
// Therefore we check if a predicate which contains a single type param
// with a concrete default is WF with that default substituted.
// For more examples see tests `defaults-well-formedness.rs` and `type-check-defaults.rs`.
//
// First we build the defaulted substitution.
let substs = InternalSubsts::for_item(fcx.tcx, def_id, |param, _| {
match param.kind {
GenericParamDefKind::Lifetime => {
// All regions are identity.
fcx.tcx.mk_param_from_def(param)
}
GenericParamDefKind::Type { .. } => {
// If the param has a default,
if is_our_default(param) {
let default_ty = fcx.tcx.type_of(param.def_id);
// and it's not a dependent default
if !default_ty.needs_subst() {
// then substitute with the default.
return default_ty.into();
}
}
// Mark unwanted params as err.
fcx.tcx.types.err.into()
}
GenericParamDefKind::Const => {
// FIXME(const_generics:defaults)
fcx.tcx.types.err.into()
}
}
});
// Now we build the substituted predicates.
let default_obligations = predicates.predicates.iter().flat_map(|&(pred, _)| {
#[derive(Default)]
struct CountParams { params: FxHashSet<u32> }
impl<'tcx> ty::fold::TypeVisitor<'tcx> for CountParams {
fn visit_ty(&mut self, t: Ty<'tcx>) -> bool {
match t.sty {
ty::Param(p) => {
self.params.insert(p.idx);
t.super_visit_with(self)
}
_ => t.super_visit_with(self)
}
}
fn visit_region(&mut self, _: ty::Region<'tcx>) -> bool {
true
}
fn visit_const(&mut self, c: &'tcx ty::Const<'tcx>) -> bool {
if let ConstValue::Param(param) = c.val {
self.params.insert(param.index);
}
c.super_visit_with(self)
}
}
let mut param_count = CountParams::default();
let has_region = pred.visit_with(&mut param_count);
let substituted_pred = pred.subst(fcx.tcx, substs);
// Don't check non-defaulted params, dependent defaults (including lifetimes)
// or preds with multiple params.
if substituted_pred.references_error() || param_count.params.len() > 1 || has_region {
None
} else if predicates.predicates.iter().any(|&(p, _)| p == substituted_pred) {
// Avoid duplication of predicates that contain no parameters, for example.
None
} else {
Some(substituted_pred)
}
}).map(|pred| {
// convert each of those into an obligation. So if you have
// something like `struct Foo<T: Copy = String>`, we would
// take that predicate `T: Copy`, substitute to `String: Copy`
// (actually that happens in the previous `flat_map` call),
// and then try to prove it (in this case, we'll fail).
//
// Note the subtle difference from how we handle `predicates`
// below: there, we are not trying to prove those predicates
// to be *true* but merely *well-formed*.
let pred = fcx.normalize_associated_types_in(span, &pred);
let cause = traits::ObligationCause::new(span, fcx.body_id, traits::ItemObligation(def_id));
traits::Obligation::new(cause, fcx.param_env, pred)
});
let mut predicates = predicates.instantiate_identity(fcx.tcx);
if let Some(return_ty) = return_ty {
predicates.predicates.extend(check_existential_types(tcx, fcx, def_id, span, return_ty));
}
let predicates = fcx.normalize_associated_types_in(span, &predicates);
debug!("check_where_clauses: predicates={:?}", predicates.predicates);
let wf_obligations =
predicates.predicates
.iter()
.flat_map(|p| ty::wf::predicate_obligations(fcx,
fcx.param_env,
fcx.body_id,
p,
span));
for obligation in wf_obligations.chain(default_obligations) {
debug!("next obligation cause: {:?}", obligation.cause);
fcx.register_predicate(obligation);
}
}
fn check_fn_or_method<'a, 'fcx, 'gcx, 'tcx>(tcx: TyCtxt<'a, 'gcx, 'gcx>,
fcx: &FnCtxt<'fcx, 'gcx, 'tcx>,
span: Span,
sig: ty::PolyFnSig<'tcx>,
def_id: DefId,
implied_bounds: &mut Vec<Ty<'tcx>>)
{
let sig = fcx.normalize_associated_types_in(span, &sig);
let sig = fcx.tcx.liberate_late_bound_regions(def_id, &sig);
for input_ty in sig.inputs() {
fcx.register_wf_obligation(&input_ty, span, ObligationCauseCode::MiscObligation);
}
implied_bounds.extend(sig.inputs());
fcx.register_wf_obligation(sig.output(), span, ObligationCauseCode::MiscObligation);
// FIXME(#25759) return types should not be implied bounds
implied_bounds.push(sig.output());
check_where_clauses(tcx, fcx, span, def_id, Some(sig.output()));
}
/// Checks "defining uses" of existential types to ensure that they meet the restrictions laid for
/// "higher-order pattern unification".
/// This ensures that inference is tractable.
/// In particular, definitions of existential types can only use other generics as arguments,
/// and they cannot repeat an argument. Example:
///
/// ```rust
/// existential type Foo<A, B>;
///
/// // ok -- `Foo` is applied to two distinct, generic types.
/// fn a<T, U>() -> Foo<T, U> { .. }
///
/// // not ok -- `Foo` is applied to `T` twice.
/// fn b<T>() -> Foo<T, T> { .. }
///
///
/// // not ok -- `Foo` is applied to a non-generic type.
/// fn b<T>() -> Foo<T, u32> { .. }
/// ```
///
fn check_existential_types<'a, 'fcx, 'gcx, 'tcx>(
tcx: TyCtxt<'a, 'gcx, 'gcx>,
fcx: &FnCtxt<'fcx, 'gcx, 'tcx>,
fn_def_id: DefId,
span: Span,
ty: Ty<'tcx>,
) -> Vec<ty::Predicate<'tcx>> {
trace!("check_existential_types: {:?}", ty);
let mut substituted_predicates = Vec::new();
ty.fold_with(&mut ty::fold::BottomUpFolder {
tcx: fcx.tcx,
fldop: |ty| {
if let ty::Opaque(def_id, substs) = ty.sty {
trace!("check_existential_types: opaque_ty, {:?}, {:?}", def_id, substs);
let generics = tcx.generics_of(def_id);
// only check named existential types defined in this crate
if generics.parent.is_none() && def_id.is_local() {
let opaque_hir_id = tcx.hir().as_local_hir_id(def_id).unwrap();
if may_define_existential_type(tcx, fn_def_id, opaque_hir_id) {
trace!("check_existential_types may define. Generics: {:#?}", generics);
let mut seen: FxHashMap<_, Vec<_>> = FxHashMap::default();
for (subst, param) in substs.iter().zip(&generics.params) {
match subst.unpack() {
ty::subst::UnpackedKind::Type(ty) => match ty.sty {
ty::Param(..) => {}
// prevent `fn foo() -> Foo<u32>` from being defining
_ => {
tcx.sess
.struct_span_err(
span,
"non-defining existential type use \
in defining scope",
)
.span_note(
tcx.def_span(param.def_id),
&format!(
"used non-generic type {} for \
generic parameter",
ty,
),
)
.emit();
}
}
ty::subst::UnpackedKind::Lifetime(region) => {
let param_span = tcx.def_span(param.def_id);
if let ty::ReStatic = region {
tcx
.sess
.struct_span_err(
span,
"non-defining existential type use \
in defining scope",
)
.span_label(
param_span,
"cannot use static lifetime, use a bound lifetime \
instead or remove the lifetime parameter from the \
existential type",
)
.emit();
} else {
seen.entry(region).or_default().push(param_span);
}
}
ty::subst::UnpackedKind::Const(ct) => match ct.val {
ConstValue::Param(_) => {}
_ => {
tcx.sess
.struct_span_err(
span,
"non-defining existential type use \
in defining scope",
)
.span_note(
tcx.def_span(param.def_id),
&format!(
"used non-generic const {} for \
generic parameter",
ty,
),
)
.emit();
}
}
} // match subst
} // for (subst, param)
for (_, spans) in seen {
if spans.len() > 1 {
tcx
.sess
.struct_span_err(
span,
"non-defining existential type use \
in defining scope",
).
span_note(
spans,
"lifetime used multiple times",
)
.emit();
}
}
} // if may_define_existential_type
// now register the bounds on the parameters of the existential type
// so the parameters given by the function need to fulfill them
// ```rust
// existential type Foo<T: Bar>: 'static;
// fn foo<U>() -> Foo<U> { .. *}
// ```
// becomes
// ```rust
// existential type Foo<T: Bar>: 'static;
// fn foo<U: Bar>() -> Foo<U> { .. *}
// ```
let predicates = tcx.predicates_of(def_id);
trace!(
"check_existential_types may define. adding predicates: {:#?}",
predicates,
);
for &(pred, _) in predicates.predicates.iter() {
let substituted_pred = pred.subst(fcx.tcx, substs);
// Avoid duplication of predicates that contain no parameters, for example.
if !predicates.predicates.iter().any(|&(p, _)| p == substituted_pred) {
substituted_predicates.push(substituted_pred);
}
}
} // if is_named_existential_type
} // if let Opaque
ty
},
reg_op: |reg| reg,
});
substituted_predicates
}
fn check_method_receiver<'fcx, 'gcx, 'tcx>(fcx: &FnCtxt<'fcx, 'gcx, 'tcx>,
method_sig: &hir::MethodSig,
method: &ty::AssociatedItem,
self_ty: Ty<'tcx>)
{
// check that the method has a valid receiver type, given the type `Self`
debug!("check_method_receiver({:?}, self_ty={:?})",
method, self_ty);
if !method.method_has_self_argument {
return;
}
let span = method_sig.decl.inputs[0].span;
let sig = fcx.tcx.fn_sig(method.def_id);
let sig = fcx.normalize_associated_types_in(span, &sig);
let sig = fcx.tcx.liberate_late_bound_regions(method.def_id, &sig);
debug!("check_method_receiver: sig={:?}", sig);
let self_ty = fcx.normalize_associated_types_in(span, &self_ty);
let self_ty = fcx.tcx.liberate_late_bound_regions(
method.def_id,
&ty::Binder::bind(self_ty)
);
let receiver_ty = sig.inputs()[0];
let receiver_ty = fcx.normalize_associated_types_in(span, &receiver_ty);
let receiver_ty = fcx.tcx.liberate_late_bound_regions(
method.def_id,
&ty::Binder::bind(receiver_ty)
);
if fcx.tcx.features().arbitrary_self_types {
if !receiver_is_valid(fcx, span, receiver_ty, self_ty, true) {
// report error, arbitrary_self_types was enabled
fcx.tcx.sess.diagnostic().mut_span_err(
span, &format!("invalid method receiver type: {:?}", receiver_ty)
).note("type of `self` must be `Self` or a type that dereferences to it")
.help("consider changing to `self`, `&self`, `&mut self`, or `self: Box<Self>`")
.code(DiagnosticId::Error("E0307".into()))
.emit();
}
} else {
if !receiver_is_valid(fcx, span, receiver_ty, self_ty, false) {
if receiver_is_valid(fcx, span, receiver_ty, self_ty, true) {
// report error, would have worked with arbitrary_self_types
feature_gate::feature_err(
&fcx.tcx.sess.parse_sess,
"arbitrary_self_types",
span,
GateIssue::Language,
&format!(
"`{}` cannot be used as the type of `self` without \
the `arbitrary_self_types` feature",
receiver_ty,
),
).help("consider changing to `self`, `&self`, `&mut self`, or `self: Box<Self>`")
.emit();
} else {
// report error, would not have worked with arbitrary_self_types
fcx.tcx.sess.diagnostic().mut_span_err(
span, &format!("invalid method receiver type: {:?}", receiver_ty)
).note("type must be `Self` or a type that dereferences to it")
.help("consider changing to `self`, `&self`, `&mut self`, or `self: Box<Self>`")
.code(DiagnosticId::Error("E0307".into()))
.emit();
}
}
}
}
/// returns true if `receiver_ty` would be considered a valid receiver type for `self_ty`. If
/// `arbitrary_self_types` is enabled, `receiver_ty` must transitively deref to `self_ty`, possibly
/// through a `*const/mut T` raw pointer. If the feature is not enabled, the requirements are more
/// strict: `receiver_ty` must implement `Receiver` and directly implement `Deref<Target=self_ty>`.
///
/// N.B., there are cases this function returns `true` but causes an error to be emitted,
/// particularly when `receiver_ty` derefs to a type that is the same as `self_ty` but has the
/// wrong lifetime. Be careful of this if you are calling this function speculatively.
fn receiver_is_valid<'fcx, 'tcx, 'gcx>(
fcx: &FnCtxt<'fcx, 'gcx, 'tcx>,
span: Span,
receiver_ty: Ty<'tcx>,
self_ty: Ty<'tcx>,
arbitrary_self_types_enabled: bool,
) -> bool {
let cause = fcx.cause(span, traits::ObligationCauseCode::MethodReceiver);
let can_eq_self = |ty| fcx.infcx.can_eq(fcx.param_env, self_ty, ty).is_ok();
// `self: Self` is always valid
if can_eq_self(receiver_ty) {
if let Some(mut err) = fcx.demand_eqtype_with_origin(&cause, self_ty, receiver_ty) {
err.emit();
}
return true
}
let mut autoderef = fcx.autoderef(span, receiver_ty);
// the `arbitrary_self_types` feature allows raw pointer receivers like `self: *const Self`
if arbitrary_self_types_enabled {
autoderef = autoderef.include_raw_pointers();
}
// the first type is `receiver_ty`, which we know its not equal to `self_ty`. skip it.
autoderef.next();
// keep dereferencing `receiver_ty` until we get to `self_ty`
loop {
if let Some((potential_self_ty, _)) = autoderef.next() {
debug!("receiver_is_valid: potential self type `{:?}` to match `{:?}`",
potential_self_ty, self_ty);
if can_eq_self(potential_self_ty) {
autoderef.finalize(fcx);
if let Some(mut err) = fcx.demand_eqtype_with_origin(
&cause, self_ty, potential_self_ty
) {
err.emit();
}
break
}
} else {
debug!("receiver_is_valid: type `{:?}` does not deref to `{:?}`",
receiver_ty, self_ty);
// If he receiver already has errors reported due to it, consider it valid to avoid
// unecessary errors (#58712).
return receiver_ty.references_error();
}
// without the `arbitrary_self_types` feature, `receiver_ty` must directly deref to
// `self_ty`. Enforce this by only doing one iteration of the loop
if !arbitrary_self_types_enabled {
return false
}
}
// without `feature(arbitrary_self_types)`, we require that `receiver_ty` implements `Receiver`
if !arbitrary_self_types_enabled {
let trait_def_id = match fcx.tcx.lang_items().receiver_trait() {
Some(did) => did,
None => {
debug!("receiver_is_valid: missing Receiver trait");
return false
}
};
let trait_ref = ty::TraitRef{
def_id: trait_def_id,
substs: fcx.tcx.mk_substs_trait(receiver_ty, &[]),
};
let obligation = traits::Obligation::new(
cause.clone(),
fcx.param_env,
trait_ref.to_predicate()
);
if !fcx.predicate_must_hold_modulo_regions(&obligation) {
debug!("receiver_is_valid: type `{:?}` does not implement `Receiver` trait",
receiver_ty);
return false
}
}
true
}
fn check_variances_for_type_defn<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
item: &hir::Item,
hir_generics: &hir::Generics)
{
let item_def_id = tcx.hir().local_def_id_from_hir_id(item.hir_id);
let ty = tcx.type_of(item_def_id);
if tcx.has_error_field(ty) {
return;
}
let ty_predicates = tcx.predicates_of(item_def_id);
assert_eq!(ty_predicates.parent, None);
let variances = tcx.variances_of(item_def_id);
let mut constrained_parameters: FxHashSet<_> =
variances.iter().enumerate()
.filter(|&(_, &variance)| variance != ty::Bivariant)
.map(|(index, _)| Parameter(index as u32))
.collect();
identify_constrained_generic_params(tcx,
&ty_predicates,
None,
&mut constrained_parameters);
for (index, _) in variances.iter().enumerate() {
if constrained_parameters.contains(&Parameter(index as u32)) {
continue;
}
let param = &hir_generics.params[index];
match param.name {
hir::ParamName::Error => { }
_ => report_bivariance(tcx, param.span, param.name.ident().name),
}
}
}
fn report_bivariance<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
span: Span,
param_name: ast::Name)
{
let mut err = error_392(tcx, span, param_name);
let suggested_marker_id = tcx.lang_items().phantom_data();
// help is available only in presence of lang items
if let Some(def_id) = suggested_marker_id {
err.help(&format!("consider removing `{}` or using a marker such as `{}`",
param_name,
tcx.def_path_str(def_id)));
}
err.emit();
}
fn reject_shadowing_parameters(tcx: TyCtxt<'_, '_, '_>, def_id: DefId) {
let generics = tcx.generics_of(def_id);
let parent = tcx.generics_of(generics.parent.unwrap());
let impl_params: FxHashMap<_, _> = parent.params.iter().flat_map(|param| match param.kind {
GenericParamDefKind::Lifetime => None,
GenericParamDefKind::Type { .. } | GenericParamDefKind::Const => {
Some((param.name, param.def_id))
}
}).collect();
for method_param in &generics.params {
// Shadowing is checked in resolve_lifetime.
if let GenericParamDefKind::Lifetime = method_param.kind {
continue
}
if impl_params.contains_key(&method_param.name) {
// Tighten up the span to focus on only the shadowing type
let type_span = tcx.def_span(method_param.def_id);
// The expectation here is that the original trait declaration is
// local so it should be okay to just unwrap everything.
let trait_def_id = impl_params[&method_param.name];
let trait_decl_span = tcx.def_span(trait_def_id);