bjoernager/rust
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Suggest impl Iterator when possible for _ return type

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Address #106096.
This commit is contained in:
Esteban Küber 2022-12-26 17:44:16 -08:00
parent caa64e5b5e
commit 1b341fe8a1
5 changed files with 96 additions and 3 deletions
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66
compiler/rustc_hir_analysis/src/collect.rs
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@ -24,14 +24,20 @@ use rustc_hir as hir;
use rustc_hir::def_id::{DefId, LocalDefId};
use rustc_hir::intravisit::{self, Visitor};
use rustc_hir::{GenericParamKind, Node};
use rustc_infer::infer::type_variable::{TypeVariableOrigin, TypeVariableOriginKind};
use rustc_infer::infer::TyCtxtInferExt;
use rustc_middle::hir::nested_filter;
use rustc_middle::ty::query::Providers;
use rustc_middle::ty::util::{Discr, IntTypeExt};
use rustc_middle::ty::{self, AdtKind, Const, IsSuggestable, ToPredicate, Ty, TyCtxt};
use rustc_middle::ty::{
self, AdtKind, Const, IsSuggestable, ToPredicate, Ty, TyCtxt, TypeVisitable,
};
use rustc_span::symbol::{kw, sym, Ident, Symbol};
use rustc_span::Span;
use rustc_target::spec::abi;
use rustc_trait_selection::infer::InferCtxtExt;
use rustc_trait_selection::traits::error_reporting::suggestions::NextTypeParamName;
use rustc_trait_selection::traits::ObligationCtxt;
use std::iter;
mod generics_of;
@ -1224,7 +1230,17 @@ fn infer_return_ty_for_fn_sig<'tcx>(
// to prevent the user from getting a papercut while trying to use the unique closure
// syntax (e.g. `[closure@src/lib.rs:2:5: 2:9]`).
diag.help("consider using an `Fn`, `FnMut`, or `FnOnce` trait bound");
diag.note("for more information on `Fn` traits and closure types, see https://doc.rust-lang.org/book/ch13-01-closures.html");
diag.note(
"for more information on `Fn` traits and closure types, see \
https://doc.rust-lang.org/book/ch13-01-closures.html",
);
} else if let Some(i_ty) = suggest_impl_iterator(tcx, ret_ty, ty.span, hir_id, def_id) {
diag.span_suggestion(
ty.span,
"replace with an appropriate return type",
format!("impl Iterator<Item = {}>", i_ty),
Applicability::MachineApplicable,
);
}
diag.emit();
@ -1242,6 +1258,52 @@ fn infer_return_ty_for_fn_sig<'tcx>(
}
}
fn suggest_impl_iterator<'tcx>(
tcx: TyCtxt<'tcx>,
ret_ty: Ty<'tcx>,
span: Span,
hir_id: hir::HirId,
def_id: LocalDefId,
) -> Option<Ty<'tcx>> {
let Some(iter_trait) = tcx.get_diagnostic_item(sym::Iterator) else { return None; };
let Some(iterator_item) = tcx.get_diagnostic_item(sym::IteratorItem) else { return None; };
if !tcx
.infer_ctxt()
.build()
.type_implements_trait(iter_trait, [ret_ty], tcx.param_env(iter_trait))
.must_apply_modulo_regions()
{
return None;
}
let infcx = tcx.infer_ctxt().build();
let ocx = ObligationCtxt::new_in_snapshot(&infcx);
// Find the type of `Iterator::Item`.
let origin = TypeVariableOrigin { kind: TypeVariableOriginKind::TypeInference, span };
let ty_var = infcx.next_ty_var(origin);
let projection = ty::Binder::dummy(ty::PredicateKind::Clause(ty::Clause::Projection(
ty::ProjectionPredicate {
projection_ty: tcx.mk_alias_ty(iterator_item, tcx.mk_substs([ret_ty.into()].iter())),
term: ty_var.into(),
},
)));
// Add `<ret_ty as Iterator>::Item = _` obligation.
ocx.register_obligation(crate::traits::Obligation::misc(
tcx,
span,
hir_id,
tcx.param_env(def_id),
projection,
));
if ocx.select_where_possible().is_empty()
&& let item_ty = infcx.resolve_vars_if_possible(ty_var)
&& !item_ty.references_error()
&& !item_ty.has_placeholders()
{
return Some(item_ty);
}
None
}
fn impl_trait_ref(tcx: TyCtxt<'_>, def_id: DefId) -> Option<ty::TraitRef<'_>> {
let icx = ItemCtxt::new(tcx, def_id);
let item = tcx.hir().expect_item(def_id.expect_local());