diff options
Diffstat (limited to 'compiler/rustc_typeck/src/impl_wf_check.rs')
| -rw-r--r-- | compiler/rustc_typeck/src/impl_wf_check.rs | 228 |
1 files changed, 0 insertions, 228 deletions
diff --git a/compiler/rustc_typeck/src/impl_wf_check.rs b/compiler/rustc_typeck/src/impl_wf_check.rs deleted file mode 100644 index 9fee1eaae..000000000 --- a/compiler/rustc_typeck/src/impl_wf_check.rs +++ /dev/null @@ -1,228 +0,0 @@ -//! This pass enforces various "well-formedness constraints" on impls. -//! Logically, it is part of wfcheck -- but we do it early so that we -//! can stop compilation afterwards, since part of the trait matching -//! infrastructure gets very grumpy if these conditions don't hold. In -//! particular, if there are type parameters that are not part of the -//! impl, then coherence will report strange inference ambiguity -//! errors; if impls have duplicate items, we get misleading -//! specialization errors. These things can (and probably should) be -//! fixed, but for the moment it's easier to do these checks early. - -use crate::constrained_generic_params as cgp; -use min_specialization::check_min_specialization; - -use rustc_data_structures::fx::{FxHashMap, FxHashSet}; -use rustc_errors::struct_span_err; -use rustc_hir::def::DefKind; -use rustc_hir::def_id::LocalDefId; -use rustc_middle::ty::query::Providers; -use rustc_middle::ty::{self, TyCtxt, TypeVisitable}; -use rustc_span::{Span, Symbol}; - -use std::collections::hash_map::Entry::{Occupied, Vacant}; - -mod min_specialization; - -/// Checks that all the type/lifetime parameters on an impl also -/// appear in the trait ref or self type (or are constrained by a -/// where-clause). These rules are needed to ensure that, given a -/// trait ref like `<T as Trait<U>>`, we can derive the values of all -/// parameters on the impl (which is needed to make specialization -/// possible). -/// -/// However, in the case of lifetimes, we only enforce these rules if -/// the lifetime parameter is used in an associated type. This is a -/// concession to backwards compatibility; see comment at the end of -/// the fn for details. -/// -/// Example: -/// -/// ```rust,ignore (pseudo-Rust) -/// impl<T> Trait<Foo> for Bar { ... } -/// // ^ T does not appear in `Foo` or `Bar`, error! -/// -/// impl<T> Trait<Foo<T>> for Bar { ... } -/// // ^ T appears in `Foo<T>`, ok. -/// -/// impl<T> Trait<Foo> for Bar where Bar: Iterator<Item = T> { ... } -/// // ^ T is bound to `<Bar as Iterator>::Item`, ok. -/// -/// impl<'a> Trait<Foo> for Bar { } -/// // ^ 'a is unused, but for back-compat we allow it -/// -/// impl<'a> Trait<Foo> for Bar { type X = &'a i32; } -/// // ^ 'a is unused and appears in assoc type, error -/// ``` -fn check_mod_impl_wf(tcx: TyCtxt<'_>, module_def_id: LocalDefId) { - let min_specialization = tcx.features().min_specialization; - let module = tcx.hir_module_items(module_def_id); - for id in module.items() { - if matches!(tcx.def_kind(id.def_id), DefKind::Impl) { - enforce_impl_params_are_constrained(tcx, id.def_id); - enforce_impl_items_are_distinct(tcx, id.def_id); - if min_specialization { - check_min_specialization(tcx, id.def_id); - } - } - } -} - -pub fn provide(providers: &mut Providers) { - *providers = Providers { check_mod_impl_wf, ..*providers }; -} - -fn enforce_impl_params_are_constrained(tcx: TyCtxt<'_>, impl_def_id: LocalDefId) { - // Every lifetime used in an associated type must be constrained. - let impl_self_ty = tcx.type_of(impl_def_id); - if impl_self_ty.references_error() { - // Don't complain about unconstrained type params when self ty isn't known due to errors. - // (#36836) - tcx.sess.delay_span_bug( - tcx.def_span(impl_def_id), - &format!( - "potentially unconstrained type parameters weren't evaluated: {:?}", - impl_self_ty, - ), - ); - return; - } - let impl_generics = tcx.generics_of(impl_def_id); - let impl_predicates = tcx.predicates_of(impl_def_id); - let impl_trait_ref = tcx.impl_trait_ref(impl_def_id); - - let mut input_parameters = cgp::parameters_for_impl(impl_self_ty, impl_trait_ref); - cgp::identify_constrained_generic_params( - tcx, - impl_predicates, - impl_trait_ref, - &mut input_parameters, - ); - - // Disallow unconstrained lifetimes, but only if they appear in assoc types. - let lifetimes_in_associated_types: FxHashSet<_> = tcx - .associated_item_def_ids(impl_def_id) - .iter() - .flat_map(|def_id| { - let item = tcx.associated_item(def_id); - match item.kind { - ty::AssocKind::Type => { - if item.defaultness(tcx).has_value() { - cgp::parameters_for(&tcx.type_of(def_id), true) - } else { - Vec::new() - } - } - ty::AssocKind::Fn | ty::AssocKind::Const => Vec::new(), - } - }) - .collect(); - - for param in &impl_generics.params { - match param.kind { - // Disallow ANY unconstrained type parameters. - ty::GenericParamDefKind::Type { .. } => { - let param_ty = ty::ParamTy::for_def(param); - if !input_parameters.contains(&cgp::Parameter::from(param_ty)) { - report_unused_parameter(tcx, tcx.def_span(param.def_id), "type", param_ty.name); - } - } - ty::GenericParamDefKind::Lifetime => { - let param_lt = cgp::Parameter::from(param.to_early_bound_region_data()); - if lifetimes_in_associated_types.contains(¶m_lt) && // (*) - !input_parameters.contains(¶m_lt) - { - report_unused_parameter( - tcx, - tcx.def_span(param.def_id), - "lifetime", - param.name, - ); - } - } - ty::GenericParamDefKind::Const { .. } => { - let param_ct = ty::ParamConst::for_def(param); - if !input_parameters.contains(&cgp::Parameter::from(param_ct)) { - report_unused_parameter( - tcx, - tcx.def_span(param.def_id), - "const", - param_ct.name, - ); - } - } - } - } - - // (*) This is a horrible concession to reality. I think it'd be - // better to just ban unconstrained lifetimes outright, but in - // practice people do non-hygienic macros like: - // - // ``` - // macro_rules! __impl_slice_eq1 { - // ($Lhs: ty, $Rhs: ty, $Bound: ident) => { - // impl<'a, 'b, A: $Bound, B> PartialEq<$Rhs> for $Lhs where A: PartialEq<B> { - // .... - // } - // } - // } - // ``` - // - // In a concession to backwards compatibility, we continue to - // permit those, so long as the lifetimes aren't used in - // associated types. I believe this is sound, because lifetimes - // used elsewhere are not projected back out. -} - -fn report_unused_parameter(tcx: TyCtxt<'_>, span: Span, kind: &str, name: Symbol) { - let mut err = struct_span_err!( - tcx.sess, - span, - E0207, - "the {} parameter `{}` is not constrained by the \ - impl trait, self type, or predicates", - kind, - name - ); - err.span_label(span, format!("unconstrained {} parameter", kind)); - if kind == "const" { - err.note( - "expressions using a const parameter must map each value to a distinct output value", - ); - err.note( - "proving the result of expressions other than the parameter are unique is not supported", - ); - } - err.emit(); -} - -/// Enforce that we do not have two items in an impl with the same name. -fn enforce_impl_items_are_distinct(tcx: TyCtxt<'_>, impl_def_id: LocalDefId) { - let mut seen_type_items = FxHashMap::default(); - let mut seen_value_items = FxHashMap::default(); - for &impl_item_ref in tcx.associated_item_def_ids(impl_def_id) { - let impl_item = tcx.associated_item(impl_item_ref); - let seen_items = match impl_item.kind { - ty::AssocKind::Type => &mut seen_type_items, - _ => &mut seen_value_items, - }; - let span = tcx.def_span(impl_item_ref); - let ident = impl_item.ident(tcx); - match seen_items.entry(ident.normalize_to_macros_2_0()) { - Occupied(entry) => { - let mut err = struct_span_err!( - tcx.sess, - span, - E0201, - "duplicate definitions with name `{}`:", - ident - ); - err.span_label(*entry.get(), format!("previous definition of `{}` here", ident)); - err.span_label(span, "duplicate definition"); - err.emit(); - } - Vacant(entry) => { - entry.insert(span); - } - } - } -} |