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check all GATs at once

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This commit is contained in:
Michael Goulet 2022-02-11 00:08:17 -08:00
parent 764839320c
commit 453d2dbbd4
1 changed files with 90 additions and 99 deletions
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189
compiler/rustc_typeck/src/check/wfcheck.rs
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@ -3,7 +3,7 @@ use crate::check::{FnCtxt, Inherited};
use crate::constrained_generic_params::{identify_constrained_generic_params, Parameter}; use crate::constrained_generic_params::{identify_constrained_generic_params, Parameter};
use rustc_ast as ast; use rustc_ast as ast;
use rustc_data_structures::fx::FxHashSet; use rustc_data_structures::fx::{FxHashMap, FxHashSet};
use rustc_errors::{struct_span_err, Applicability, DiagnosticBuilder}; use rustc_errors::{struct_span_err, Applicability, DiagnosticBuilder};
use rustc_hir as hir; use rustc_hir as hir;
use rustc_hir::def_id::{DefId, LocalDefId}; use rustc_hir::def_id::{DefId, LocalDefId};
@ -258,145 +258,131 @@ pub fn check_trait_item(tcx: TyCtxt<'_>, def_id: LocalDefId) {
.emit(); .emit();
} }
} }
check_gat_where_clauses(tcx, trait_item, encl_trait_def_id);
} }
/// Require that the user writes where clauses on GATs for the implicit /// Require that the user writes where clauses on GATs for the implicit
/// outlives bounds involving trait parameters in trait functions and /// outlives bounds involving trait parameters in trait functions and
/// lifetimes passed as GAT substs. See `self-outlives-lint` test. /// lifetimes passed as GAT substs. See `self-outlives-lint` test.
///
/// This trait will be our running example. We are currently WF checking the `Item` item...
///
/// ```rust
/// trait LendingIterator {
/// type Item<'me>; // <-- WF checking this trait item
///
/// fn next<'a>(&'a mut self) -> Option<Self::Item<'a>>;
/// }
/// ``` /// ```
fn check_gat_where_clauses(tcx: TyCtxt<'_>, gat_hir: &hir::TraitItem<'_>, gat_def_id: DefId) { fn check_gat_where_clauses(tcx: TyCtxt<'_>, associated_items: &[hir::TraitItemRef]) {
let gat_item = tcx.associated_item(gat_def_id); let mut required_bounds_by_item = FxHashMap::default();
let gat_def_id = gat_hir.def_id;
// If the current trait item isn't a type, it isn't a GAT
if !matches!(gat_item.kind, ty::AssocKind::Type) {
return;
}
let gat_generics: &ty::Generics = tcx.generics_of(gat_def_id);
// If the current associated type doesn't have any (own) params, it's not a GAT
// FIXME(jackh726): we can also warn in the more general case
if gat_generics.params.len() == 0 {
return;
}
let associated_items: &ty::AssocItems<'_> = tcx.associated_items(gat_def_id);
let mut clauses: Option<FxHashSet<ty::Predicate<'_>>> = None;
// For every function in this trait...
// In our example, this would be the `next` method
for item in
associated_items.in_definition_order().filter(|item| matches!(item.kind, ty::AssocKind::Fn))
{
let item_hir_id = hir::HirId::make_owner(item.def_id.expect_local());
let param_env = tcx.param_env(item.def_id.expect_local());
// Get the signature using placeholders. In our example, this would for gat_item in associated_items {
// convert the late-bound 'a into a free region. let gat_def_id = gat_item.id.def_id;
let sig = tcx.liberate_late_bound_regions(item.def_id, tcx.fn_sig(item.def_id)); let gat_item = tcx.associated_item(gat_def_id);
// If this item is not an assoc ty, or has no substs, then it's not a GAT
if gat_item.kind != ty::AssocKind::Type {
continue;
}
let gat_generics = tcx.generics_of(gat_def_id);
if gat_generics.params.is_empty() {
continue;
}
// The types we can assume to be well-formed. In our example, this let mut new_required_bounds: Option<FxHashSet<ty::Predicate<'_>>> = None;
// would be &'a mut Self, from the first argument. for item in associated_items {
let mut wf_tys = FxHashSet::default(); if !matches!(&item.kind, hir::AssocItemKind::Fn { .. }) {
wf_tys.extend(sig.inputs()); // FIXME: next commit will add items...
continue;
}
// The clauses we that we would require from this function let item_def_id = item.id.def_id;
let function_clauses = gather_gat_bounds( // Skip our own GAT, since it would blow away the required bounds
tcx, if item_def_id == gat_def_id {
param_env, continue;
item_hir_id, }
sig.output(),
&wf_tys,
gat_def_id,
gat_generics,
);
if let Some(function_clauses) = function_clauses { let item_hir_id = item.id.hir_id();
// Imagine we have: let param_env = tcx.param_env(item_def_id);
// ```
// trait Foo { // Get the signature using placeholders. In our example, this would
// type Bar<'me>; // convert the late-bound 'a into a free region.
// fn gimme(&self) -> Self::Bar<'_>; let sig = tcx.liberate_late_bound_regions(
// fn gimme_default(&self) -> Self::Bar<'static>; item_def_id.to_def_id(),
// } tcx.fn_sig(item_def_id.to_def_id()),
// ``` );
// We only want to require clauses on `Bar` that we can prove from *all* functions (in this
// case, `'me` can be `static` from `gimme_default`) // The types we can assume to be well-formed. In our example, this
match clauses.as_mut() { // would be &'a mut Self, from the first argument.
Some(clauses) => { let mut wf_tys = FxHashSet::default();
clauses.drain_filter(|p| !function_clauses.contains(p)); wf_tys.extend(sig.inputs());
}
None => { // The clauses we that we would require from this function
clauses = Some(function_clauses); let item_required_bounds = gather_gat_bounds(
tcx,
param_env,
item_hir_id,
sig.output(),
&wf_tys,
gat_def_id,
gat_generics,
);
if let Some(item_required_bounds) = item_required_bounds {
// Take the intersection of the new_required_bounds and the item_required_bounds
// for this item. This is why we use an Option<_>, since we need to distinguish
// the empty set of bounds from the uninitialized set of bounds.
if let Some(new_required_bounds) = &mut new_required_bounds {
new_required_bounds.retain(|b| item_required_bounds.contains(b));
} else {
new_required_bounds = Some(item_required_bounds);
} }
} }
} }
if let Some(required_bounds) = new_required_bounds {
required_bounds_by_item.insert(gat_def_id, required_bounds);
}
} }
// If there are any clauses that aren't provable, emit an error for (gat_def_id, required_bounds) in required_bounds_by_item {
let clauses = clauses.unwrap_or_default(); let gat_item_hir = tcx.hir().expect_trait_item(gat_def_id);
debug!(?clauses); debug!(?required_bounds);
if !clauses.is_empty() {
let param_env = tcx.param_env(gat_def_id); let param_env = tcx.param_env(gat_def_id);
let gat_hir = gat_item_hir.hir_id();
let mut clauses: Vec<_> = clauses let mut unsatisfied_bounds: Vec<_> = required_bounds
.into_iter() .into_iter()
.filter(|clause| match clause.kind().skip_binder() { .filter(|clause| match clause.kind().skip_binder() {
ty::PredicateKind::RegionOutlives(ty::OutlivesPredicate(a, b)) => { ty::PredicateKind::RegionOutlives(ty::OutlivesPredicate(a, b)) => {
!region_known_to_outlive( !region_known_to_outlive(tcx, gat_hir, param_env, &FxHashSet::default(), a, b)
tcx,
gat_hir.hir_id(),
param_env,
&FxHashSet::default(),
a,
b,
)
} }
ty::PredicateKind::TypeOutlives(ty::OutlivesPredicate(a, b)) => { ty::PredicateKind::TypeOutlives(ty::OutlivesPredicate(a, b)) => {
!ty_known_to_outlive( !ty_known_to_outlive(tcx, gat_hir, param_env, &FxHashSet::default(), a, b)
tcx,
gat_hir.hir_id(),
param_env,
&FxHashSet::default(),
a,
b,
)
} }
_ => bug!("Unexpected PredicateKind"), _ => bug!("Unexpected PredicateKind"),
}) })
.map(|clause| format!("{}", clause)) .map(|clause| clause.to_string())
.collect(); .collect();
// We sort so that order is predictable // We sort so that order is predictable
clauses.sort(); unsatisfied_bounds.sort();
if !clauses.is_empty() { if !unsatisfied_bounds.is_empty() {
let plural = if clauses.len() > 1 { "s" } else { "" }; let plural = if unsatisfied_bounds.len() > 1 { "s" } else { "" };
let mut err = tcx.sess.struct_span_err( let mut err = tcx.sess.struct_span_err(
gat_hir.span, gat_item_hir.span,
&format!("missing required bound{} on `{}`", plural, gat_hir.ident), &format!("missing required bound{} on `{}`", plural, gat_item_hir.ident),
); );
let suggestion = format!( let suggestion = format!(
"{} {}", "{} {}",
if !gat_hir.generics.where_clause.predicates.is_empty() { "," } else { " where" }, if !gat_item_hir.generics.where_clause.predicates.is_empty() {
clauses.join(", "), ","
} else {
" where"
},
unsatisfied_bounds.join(", "),
); );
err.span_suggestion( err.span_suggestion(
gat_hir.generics.where_clause.tail_span_for_suggestion(), gat_item_hir.generics.where_clause.tail_span_for_suggestion(),
&format!("add the required where clause{}", plural), &format!("add the required where clause{}", plural),
suggestion, suggestion,
Applicability::MachineApplicable, Applicability::MachineApplicable,
); );
let bound = if clauses.len() > 1 { "these bounds are" } else { "this bound is" }; let bound =
if unsatisfied_bounds.len() > 1 { "these bounds are" } else { "this bound is" };
err.note(&format!( err.note(&format!(
"{} currently required to ensure that impls have maximum flexibility", "{} currently required to ensure that impls have maximum flexibility",
bound bound
@ -1025,6 +1011,11 @@ fn check_trait(tcx: TyCtxt<'_>, item: &hir::Item<'_>) {
FxHashSet::default() FxHashSet::default()
}); });
// Only check traits, don't check trait aliases
if let hir::ItemKind::Trait(_, _, _, _, items) = item.kind {
check_gat_where_clauses(tcx, items);
}
} }
/// Checks all associated type defaults of trait `trait_def_id`. /// Checks all associated type defaults of trait `trait_def_id`.