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| 1 | +#![allow(rustc::diagnostic_outside_of_impl)] |
| 2 | +#![allow(rustc::untranslatable_diagnostic)] |
| 3 | + |
| 4 | +use rustc_data_structures::fx::FxHashSet; |
| 5 | +use rustc_hir as hir; |
| 6 | +use rustc_hir::def::DefKind; |
| 7 | +use rustc_infer::infer::outlives::env::OutlivesEnvironment; |
| 8 | +use rustc_infer::infer::{SubregionOrigin, TyCtxtInferExt}; |
| 9 | +use rustc_macros::LintDiagnostic; |
| 10 | +use rustc_middle::ty::{self, TyCtxt}; |
| 11 | +use rustc_session::lint::builtin::UNUSED_LIFETIMES; |
| 12 | +use rustc_span::DUMMY_SP; |
| 13 | +use rustc_trait_selection::traits::{outlives_bounds::InferCtxtExt, ObligationCtxt}; |
| 14 | + |
| 15 | +use crate::{LateContext, LateLintPass}; |
| 16 | + |
| 17 | +declare_lint_pass!(RedundantLifetimeArgs => []); |
| 18 | + |
| 19 | +impl<'tcx> LateLintPass<'tcx> for RedundantLifetimeArgs { |
| 20 | + fn check_item(&mut self, cx: &LateContext<'tcx>, item: &'tcx hir::Item<'tcx>) { |
| 21 | + check(cx.tcx, cx.param_env, item.owner_id); |
| 22 | + } |
| 23 | + |
| 24 | + fn check_trait_item(&mut self, cx: &LateContext<'tcx>, item: &'tcx hir::TraitItem<'tcx>) { |
| 25 | + check(cx.tcx, cx.param_env, item.owner_id); |
| 26 | + } |
| 27 | + |
| 28 | + fn check_impl_item(&mut self, cx: &LateContext<'tcx>, item: &'tcx hir::ImplItem<'tcx>) { |
| 29 | + if cx |
| 30 | + .tcx |
| 31 | + .hir() |
| 32 | + .expect_item(cx.tcx.local_parent(item.owner_id.def_id)) |
| 33 | + .expect_impl() |
| 34 | + .of_trait |
| 35 | + .is_some() |
| 36 | + { |
| 37 | + // Don't check for redundant lifetimes for trait implementations, |
| 38 | + // since the signature is required to be compatible with the trait. |
| 39 | + return; |
| 40 | + } |
| 41 | + |
| 42 | + check(cx.tcx, cx.param_env, item.owner_id); |
| 43 | + } |
| 44 | +} |
| 45 | + |
| 46 | +fn check<'tcx>(tcx: TyCtxt<'tcx>, param_env: ty::ParamEnv<'tcx>, owner_id: hir::OwnerId) { |
| 47 | + let def_kind = tcx.def_kind(owner_id); |
| 48 | + match def_kind { |
| 49 | + DefKind::Struct |
| 50 | + | DefKind::Union |
| 51 | + | DefKind::Enum |
| 52 | + | DefKind::Trait |
| 53 | + | DefKind::TraitAlias |
| 54 | + | DefKind::AssocTy |
| 55 | + | DefKind::Fn |
| 56 | + | DefKind::Const |
| 57 | + | DefKind::AssocFn |
| 58 | + | DefKind::AssocConst |
| 59 | + | DefKind::Impl { of_trait: _ } => { |
| 60 | + // Proceed |
| 61 | + } |
| 62 | + DefKind::Mod |
| 63 | + | DefKind::Variant |
| 64 | + | DefKind::TyAlias |
| 65 | + | DefKind::ForeignTy |
| 66 | + | DefKind::TyParam |
| 67 | + | DefKind::ConstParam |
| 68 | + | DefKind::Static(_) |
| 69 | + | DefKind::Ctor(_, _) |
| 70 | + | DefKind::Macro(_) |
| 71 | + | DefKind::ExternCrate |
| 72 | + | DefKind::Use |
| 73 | + | DefKind::ForeignMod |
| 74 | + | DefKind::AnonConst |
| 75 | + | DefKind::InlineConst |
| 76 | + | DefKind::OpaqueTy |
| 77 | + | DefKind::Field |
| 78 | + | DefKind::LifetimeParam |
| 79 | + | DefKind::GlobalAsm |
| 80 | + | DefKind::Closure => return, |
| 81 | + } |
| 82 | + |
| 83 | + let infcx = &tcx.infer_ctxt().build(); |
| 84 | + let ocx = ObligationCtxt::new(infcx); |
| 85 | + |
| 86 | + // Compute the implied outlives bounds for the item. This ensures that we treat |
| 87 | + // a signature with an argument like `&'a &'b ()` as implicitly having `'b: 'a`. |
| 88 | + let Ok(assumed_wf_types) = ocx.assumed_wf_types(param_env, owner_id.def_id) else { |
| 89 | + return; |
| 90 | + }; |
| 91 | + let implied_bounds = infcx.implied_bounds_tys(param_env, owner_id.def_id, assumed_wf_types); |
| 92 | + let outlives_env = &OutlivesEnvironment::with_bounds(param_env, implied_bounds); |
| 93 | + |
| 94 | + // The ordering of this lifetime map is a bit subtle. |
| 95 | + // |
| 96 | + // Specifically, we want to find a "candidate" lifetime that precedes a "victim" lifetime, |
| 97 | + // where we can prove that `'candidate = 'victim`. |
| 98 | + // |
| 99 | + // `'static` must come first in this list because we can never replace `'static` with |
| 100 | + // something else, but if we find some lifetime `'a` where `'a = 'static`, we want to |
| 101 | + // suggest replacing `'a` with `'static`. |
| 102 | + let mut lifetimes = vec![tcx.lifetimes.re_static]; |
| 103 | + lifetimes.extend( |
| 104 | + ty::GenericArgs::identity_for_item(tcx, owner_id).iter().filter_map(|arg| arg.as_region()), |
| 105 | + ); |
| 106 | + // If we are in a function, add its late-bound lifetimes too. |
| 107 | + if matches!(def_kind, DefKind::Fn | DefKind::AssocFn) { |
| 108 | + for var in tcx.fn_sig(owner_id).instantiate_identity().bound_vars() { |
| 109 | + let ty::BoundVariableKind::Region(kind) = var else { continue }; |
| 110 | + lifetimes.push(ty::Region::new_late_param(tcx, owner_id.to_def_id(), kind)); |
| 111 | + } |
| 112 | + } |
| 113 | + |
| 114 | + // Keep track of lifetimes which have already been replaced with other lifetimes. |
| 115 | + // This makes sure that if `'a = 'b = 'c`, we don't say `'c` should be replaced by |
| 116 | + // both `'a` and `'b`. |
| 117 | + let mut shadowed = FxHashSet::default(); |
| 118 | + |
| 119 | + for (idx, &candidate) in lifetimes.iter().enumerate() { |
| 120 | + // Don't suggest removing a lifetime twice. |
| 121 | + if shadowed.contains(&candidate) { |
| 122 | + continue; |
| 123 | + } |
| 124 | + |
| 125 | + // Can't rename a named lifetime named `'_` without ambiguity. |
| 126 | + if !candidate.has_name() { |
| 127 | + continue; |
| 128 | + } |
| 129 | + |
| 130 | + for &victim in &lifetimes[(idx + 1)..] { |
| 131 | + // We only care about lifetimes that are "real", i.e. that have a def-id. |
| 132 | + let (ty::ReEarlyParam(ty::EarlyParamRegion { def_id, .. }) |
| 133 | + | ty::ReLateParam(ty::LateParamRegion { |
| 134 | + bound_region: ty::BoundRegionKind::BrNamed(def_id, _), |
| 135 | + .. |
| 136 | + })) = victim.kind() |
| 137 | + else { |
| 138 | + continue; |
| 139 | + }; |
| 140 | + |
| 141 | + // Do not rename lifetimes not local to this item since they'll overlap |
| 142 | + // with the lint running on the parent. We still want to consider parent |
| 143 | + // lifetimes which make child lifetimes redundant, otherwise we would |
| 144 | + // have truncated the `identity_for_item` args above. |
| 145 | + if tcx.parent(def_id) != owner_id.to_def_id() { |
| 146 | + continue; |
| 147 | + } |
| 148 | + |
| 149 | + let infcx = infcx.fork(); |
| 150 | + |
| 151 | + // Require that `'candidate = 'victim` |
| 152 | + infcx.sub_regions(SubregionOrigin::RelateRegionParamBound(DUMMY_SP), candidate, victim); |
| 153 | + infcx.sub_regions(SubregionOrigin::RelateRegionParamBound(DUMMY_SP), victim, candidate); |
| 154 | + |
| 155 | + // If there are no lifetime errors, then we have proven that `'candidate = 'victim`! |
| 156 | + if infcx.resolve_regions(outlives_env).is_empty() { |
| 157 | + shadowed.insert(victim); |
| 158 | + tcx.emit_spanned_lint( |
| 159 | + UNUSED_LIFETIMES, |
| 160 | + tcx.local_def_id_to_hir_id(def_id.expect_local()), |
| 161 | + tcx.def_span(def_id), |
| 162 | + RedundantLifetimeArgsLint { candidate, victim }, |
| 163 | + ); |
| 164 | + } |
| 165 | + } |
| 166 | + } |
| 167 | +} |
| 168 | + |
| 169 | +#[derive(LintDiagnostic)] |
| 170 | +#[diag(lint_redundant_lifetime_args)] |
| 171 | +#[note] |
| 172 | +struct RedundantLifetimeArgsLint<'tcx> { |
| 173 | + /// The lifetime we have found to be redundant. |
| 174 | + victim: ty::Region<'tcx>, |
| 175 | + // The lifetime we can replace the victim with. |
| 176 | + candidate: ty::Region<'tcx>, |
| 177 | +} |
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