diff options
Diffstat (limited to 'compiler')
| -rw-r--r-- | compiler/rustc_hir_typeck/src/expr.rs | 97 |
1 files changed, 97 insertions, 0 deletions
diff --git a/compiler/rustc_hir_typeck/src/expr.rs b/compiler/rustc_hir_typeck/src/expr.rs index ffc73d64fc0..5c45e8f9d94 100644 --- a/compiler/rustc_hir_typeck/src/expr.rs +++ b/compiler/rustc_hir_typeck/src/expr.rs @@ -38,6 +38,7 @@ use rustc_infer::infer; use rustc_infer::infer::type_variable::{TypeVariableOrigin, TypeVariableOriginKind}; use rustc_infer::infer::DefineOpaqueTypes; use rustc_infer::infer::InferOk; +use rustc_infer::traits::query::NoSolution; use rustc_infer::traits::ObligationCause; use rustc_middle::middle::stability; use rustc_middle::ty::adjustment::{Adjust, Adjustment, AllowTwoPhase}; @@ -53,6 +54,8 @@ use rustc_span::symbol::{kw, sym, Ident, Symbol}; use rustc_target::abi::FieldIdx; use rustc_target::spec::abi::Abi::RustIntrinsic; use rustc_trait_selection::infer::InferCtxtExt; +use rustc_trait_selection::traits::error_reporting::TypeErrCtxtExt; +use rustc_trait_selection::traits::ObligationCtxt; use rustc_trait_selection::traits::{self, ObligationCauseCode}; impl<'a, 'tcx> FnCtxt<'a, 'tcx> { @@ -2800,6 +2803,17 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> { element_ty } None => { + // Attempt to *shallowly* search for an impl which matches, + // but has nested obligations which are unsatisfied. + for (base_t, _) in self.autoderef(base.span, base_t).silence_errors() { + if let Some((_, index_ty, element_ty)) = + self.find_and_report_unsatisfied_index_impl(expr.hir_id, base, base_t) + { + self.demand_coerce(idx, idx_t, index_ty, None, AllowTwoPhase::No); + return element_ty; + } + } + let mut err = type_error_struct!( self.tcx.sess, expr.span, @@ -2843,6 +2857,89 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> { } } + /// Try to match an implementation of `Index` against a self type, and report + /// the unsatisfied predicates that result from confirming this impl. + /// + /// Given an index expression, sometimes the `Self` type shallowly but does not + /// deeply satisfy an impl predicate. Instead of simply saying that the type + /// does not support being indexed, we want to point out exactly what nested + /// predicates cause this to be, so that the user can add them to fix their code. + fn find_and_report_unsatisfied_index_impl( + &self, + index_expr_hir_id: HirId, + base_expr: &hir::Expr<'_>, + base_ty: Ty<'tcx>, + ) -> Option<(ErrorGuaranteed, Ty<'tcx>, Ty<'tcx>)> { + let index_trait_def_id = self.tcx.lang_items().index_trait()?; + + let mut relevant_impls = vec![]; + self.tcx.for_each_relevant_impl(index_trait_def_id, base_ty, |impl_def_id| { + relevant_impls.push(impl_def_id); + }); + let [impl_def_id] = relevant_impls[..] else { + // Only report unsatisfied impl predicates if there's one impl + return None; + }; + + self.commit_if_ok(|_| { + let ocx = ObligationCtxt::new_in_snapshot(self); + let impl_substs = self.fresh_substs_for_item(base_expr.span, impl_def_id); + let impl_trait_ref = + self.tcx.impl_trait_ref(impl_def_id).unwrap().subst(self.tcx, impl_substs); + let cause = self.misc(base_expr.span); + + // Match the impl self type against the base ty. If this fails, + // we just skip this impl, since it's not particularly useful. + let impl_trait_ref = ocx.normalize(&cause, self.param_env, impl_trait_ref); + ocx.eq(&cause, self.param_env, impl_trait_ref.self_ty(), base_ty)?; + + // Register the impl's predicates. One of these predicates + // must be unsatisfied, or else we wouldn't have gotten here + // in the first place. + ocx.register_obligations(traits::predicates_for_generics( + |idx, span| { + traits::ObligationCause::new( + base_expr.span, + self.body_id, + if span.is_dummy() { + traits::ExprItemObligation(impl_def_id, index_expr_hir_id, idx) + } else { + traits::ExprBindingObligation(impl_def_id, span, index_expr_hir_id, idx) + }, + ) + }, + self.param_env, + self.tcx.predicates_of(impl_def_id).instantiate(self.tcx, impl_substs), + )); + + // Normalize the output type, which we can use later on as the + // return type of the index expression... + let element_ty = ocx.normalize( + &cause, + self.param_env, + self.tcx.mk_projection( + self.tcx + .associated_items(index_trait_def_id) + .filter_by_name_unhygienic(sym::Output) + .next() + .unwrap() + .def_id, + impl_trait_ref.substs, + ), + ); + + let errors = ocx.select_where_possible(); + // There should be at least one error reported. If not, we + // will still delay a span bug in `report_fulfillment_errors`. + Ok::<_, NoSolution>(( + self.err_ctxt().report_fulfillment_errors(&errors), + impl_trait_ref.substs.type_at(1), + element_ty, + )) + }) + .ok() + } + fn point_at_index_if_possible( &self, errors: &mut Vec<traits::FulfillmentError<'tcx>>, |