|
| 1 | +use rustc_hir as hir; |
| 2 | +use rustc_infer::infer::TyCtxtInferExt; |
| 3 | +use rustc_macros::LintDiagnostic; |
| 4 | +use rustc_middle::ty::{self, fold::BottomUpFolder, Ty, TypeFoldable}; |
| 5 | +use rustc_span::Span; |
| 6 | +use rustc_trait_selection::traits; |
| 7 | +use rustc_trait_selection::traits::query::evaluate_obligation::InferCtxtExt; |
| 8 | + |
| 9 | +use crate::{LateContext, LateLintPass, LintContext}; |
| 10 | + |
| 11 | +declare_lint! { |
| 12 | + /// The `opaque_hidden_inferred_bound` lint detects cases in which nested |
| 13 | + /// `impl Trait` in associated type bounds are not written generally enough |
| 14 | + /// to satisfy the bounds of the associated type. This functionality was |
| 15 | + /// removed in #97346, but then rolled back in #99860 because it was made |
| 16 | + /// into a hard error too quickly. |
| 17 | + /// |
| 18 | + /// We plan on reintroducing this as a hard error, but in the mean time, this |
| 19 | + /// lint serves to warn and suggest fixes for any use-cases which rely on this |
| 20 | + /// behavior. |
| 21 | + pub OPAQUE_HIDDEN_INFERRED_BOUND, |
| 22 | + Warn, |
| 23 | + "detects the use of nested `impl Trait` types in associated type bounds that are not general enough" |
| 24 | +} |
| 25 | + |
| 26 | +declare_lint_pass!(OpaqueHiddenInferredBound => [OPAQUE_HIDDEN_INFERRED_BOUND]); |
| 27 | + |
| 28 | +impl<'tcx> LateLintPass<'tcx> for OpaqueHiddenInferredBound { |
| 29 | + fn check_item(&mut self, cx: &LateContext<'tcx>, item: &'tcx hir::Item<'tcx>) { |
| 30 | + let hir::ItemKind::OpaqueTy(_) = &item.kind else { return; }; |
| 31 | + let def_id = item.def_id.def_id.to_def_id(); |
| 32 | + cx.tcx.infer_ctxt().enter(|ref infcx| { |
| 33 | + // For every projection predicate in the opaque type's explicit bounds, |
| 34 | + // check that the type that we're assigning actually satisfies the bounds |
| 35 | + // of the associated type. |
| 36 | + for &(pred, pred_span) in cx.tcx.explicit_item_bounds(def_id) { |
| 37 | + // Liberate bound regions in the predicate since we |
| 38 | + // don't actually care about lifetimes in this check. |
| 39 | + let predicate = cx.tcx.liberate_late_bound_regions( |
| 40 | + def_id, |
| 41 | + pred.kind(), |
| 42 | + ); |
| 43 | + let ty::PredicateKind::Projection(proj) = predicate else { |
| 44 | + continue; |
| 45 | + }; |
| 46 | + // Only check types, since those are the only things that may |
| 47 | + // have opaques in them anyways. |
| 48 | + let Some(proj_term) = proj.term.ty() else { continue }; |
| 49 | + |
| 50 | + let proj_ty = |
| 51 | + cx |
| 52 | + .tcx |
| 53 | + .mk_projection(proj.projection_ty.item_def_id, proj.projection_ty.substs); |
| 54 | + // For every instance of the projection type in the bounds, |
| 55 | + // replace them with the term we're assigning to the associated |
| 56 | + // type in our opaque type. |
| 57 | + let proj_replacer = &mut BottomUpFolder { |
| 58 | + tcx: cx.tcx, |
| 59 | + ty_op: |ty| if ty == proj_ty { proj_term } else { ty }, |
| 60 | + lt_op: |lt| lt, |
| 61 | + ct_op: |ct| ct, |
| 62 | + }; |
| 63 | + // For example, in `impl Trait<Assoc = impl Send>`, for all of the bounds on `Assoc`, |
| 64 | + // e.g. `type Assoc: OtherTrait`, replace `<impl Trait as Trait>::Assoc: OtherTrait` |
| 65 | + // with `impl Send: OtherTrait`. |
| 66 | + for assoc_pred_and_span in cx |
| 67 | + .tcx |
| 68 | + .bound_explicit_item_bounds(proj.projection_ty.item_def_id) |
| 69 | + .transpose_iter() |
| 70 | + { |
| 71 | + let assoc_pred_span = assoc_pred_and_span.0.1; |
| 72 | + let assoc_pred = assoc_pred_and_span |
| 73 | + .map_bound(|(pred, _)| *pred) |
| 74 | + .subst(cx.tcx, &proj.projection_ty.substs) |
| 75 | + .fold_with(proj_replacer); |
| 76 | + let Ok(assoc_pred) = traits::fully_normalize(infcx, traits::ObligationCause::dummy(), cx.param_env, assoc_pred) else { |
| 77 | + continue; |
| 78 | + }; |
| 79 | + // If that predicate doesn't hold modulo regions (but passed during type-check), |
| 80 | + // then we must've taken advantage of the hack in `project_and_unify_types` where |
| 81 | + // we replace opaques with inference vars. Emit a warning! |
| 82 | + if !infcx.predicate_must_hold_modulo_regions(&traits::Obligation::new( |
| 83 | + traits::ObligationCause::dummy(), |
| 84 | + cx.param_env, |
| 85 | + assoc_pred, |
| 86 | + )) { |
| 87 | + // If it's a trait bound and an opaque that doesn't satisfy it, |
| 88 | + // then we can emit a suggestion to add the bound. |
| 89 | + let (suggestion, suggest_span) = |
| 90 | + match (proj_term.kind(), assoc_pred.kind().skip_binder()) { |
| 91 | + (ty::Opaque(def_id, _), ty::PredicateKind::Trait(trait_pred)) => ( |
| 92 | + format!(" + {}", trait_pred.print_modifiers_and_trait_path()), |
| 93 | + Some(cx.tcx.def_span(def_id).shrink_to_hi()), |
| 94 | + ), |
| 95 | + _ => (String::new(), None), |
| 96 | + }; |
| 97 | + cx.emit_spanned_lint( |
| 98 | + OPAQUE_HIDDEN_INFERRED_BOUND, |
| 99 | + pred_span, |
| 100 | + OpaqueHiddenInferredBoundLint { |
| 101 | + ty: cx.tcx.mk_opaque(def_id, ty::InternalSubsts::identity_for_item(cx.tcx, def_id)), |
| 102 | + proj_ty: proj_term, |
| 103 | + assoc_pred_span, |
| 104 | + suggestion, |
| 105 | + suggest_span, |
| 106 | + }, |
| 107 | + ); |
| 108 | + } |
| 109 | + } |
| 110 | + } |
| 111 | + }); |
| 112 | + } |
| 113 | +} |
| 114 | + |
| 115 | +#[derive(LintDiagnostic)] |
| 116 | +#[diag(lint::opaque_hidden_inferred_bound)] |
| 117 | +struct OpaqueHiddenInferredBoundLint<'tcx> { |
| 118 | + ty: Ty<'tcx>, |
| 119 | + proj_ty: Ty<'tcx>, |
| 120 | + #[label(lint::specifically)] |
| 121 | + assoc_pred_span: Span, |
| 122 | + #[suggestion_verbose(applicability = "machine-applicable", code = "{suggestion}")] |
| 123 | + suggest_span: Option<Span>, |
| 124 | + suggestion: String, |
| 125 | +} |
0 commit comments