diff options
| -rw-r--r-- | compiler/rustc_lint/src/redundant_lifetime_args.rs | 34 | ||||
| -rw-r--r-- | compiler/rustc_lint_defs/src/builtin.rs | 6 |
2 files changed, 34 insertions, 6 deletions
diff --git a/compiler/rustc_lint/src/redundant_lifetime_args.rs b/compiler/rustc_lint/src/redundant_lifetime_args.rs index 59d2edba124..34ff5e9dfe9 100644 --- a/compiler/rustc_lint/src/redundant_lifetime_args.rs +++ b/compiler/rustc_lint/src/redundant_lifetime_args.rs @@ -82,17 +82,28 @@ fn check<'tcx>(tcx: TyCtxt<'tcx>, param_env: ty::ParamEnv<'tcx>, owner_id: hir:: let infcx = &tcx.infer_ctxt().build(); let ocx = ObligationCtxt::new(infcx); + + // Compute the implied outlives bounds for the item. This ensures that we treat + // a signature with an argument like `&'a &'b ()` as implicitly having `'b: 'a`. let Ok(assumed_wf_types) = ocx.assumed_wf_types(param_env, owner_id.def_id) else { return; }; - let implied_bounds = infcx.implied_bounds_tys(param_env, owner_id.def_id, assumed_wf_types); let outlives_env = &OutlivesEnvironment::with_bounds(param_env, implied_bounds); + // The ordering of this lifetime map is a bit subtle. + // + // Specifically, we want to find a "candidate" lifetime that precedes a "victim" lifetime, + // where we can prove that `'candidate = 'victim`. + // + // `'static` must come first in this list because we can never replace `'static` with + // something else, but if we find some lifetime `'a` where `'a = 'static`, we want to + // suggest replacing `'a` with `'static`. let mut lifetimes = vec![tcx.lifetimes.re_static]; lifetimes.extend( ty::GenericArgs::identity_for_item(tcx, owner_id).iter().filter_map(|arg| arg.as_region()), ); + // If we are in a function, add its late-bound lifetimes too. if matches!(def_kind, DefKind::Fn | DefKind::AssocFn) { for var in tcx.fn_sig(owner_id).instantiate_identity().bound_vars() { let ty::BoundVariableKind::Region(kind) = var else { continue }; @@ -101,20 +112,23 @@ fn check<'tcx>(tcx: TyCtxt<'tcx>, param_env: ty::ParamEnv<'tcx>, owner_id: hir:: } // Keep track of lifetimes which have already been replaced with other lifetimes. + // This makes sure that if `'a = 'b = 'c`, we don't say `'c` should be replaced by + // both `'a` and `'b`. let mut shadowed = FxHashSet::default(); for (idx, &candidate) in lifetimes.iter().enumerate() { + // Don't suggest removing a lifetime twice. if shadowed.contains(&candidate) { - // Don't suggest removing a lifetime twice. continue; } + // Can't rename a named lifetime named `'_` without ambiguity. if !candidate.has_name() { - // Can't rename a named lifetime with `'_` without ambiguity. continue; } for &victim in &lifetimes[(idx + 1)..] { + // We only care about lifetimes that are "real", i.e. that have a def-id. let (ty::ReEarlyParam(ty::EarlyParamRegion { def_id, .. }) | ty::ReLateParam(ty::LateParamRegion { bound_region: ty::BoundRegionKind::BrNamed(def_id, _), @@ -124,15 +138,21 @@ fn check<'tcx>(tcx: TyCtxt<'tcx>, param_env: ty::ParamEnv<'tcx>, owner_id: hir:: continue; }; + // Do not rename lifetimes not local to this item since they'll overlap + // with the lint running on the parent. We still want to consider parent + // lifetimes which make child lifetimes redundant, otherwise we would + // have truncated the `identity_for_item` args above. if tcx.parent(def_id) != owner_id.to_def_id() { - // Do not rename generics not local to this item since - // they'll overlap with this lint running on the parent. continue; } let infcx = infcx.fork(); + + // Require that `'candidate = 'victim` infcx.sub_regions(SubregionOrigin::RelateRegionParamBound(DUMMY_SP), candidate, victim); infcx.sub_regions(SubregionOrigin::RelateRegionParamBound(DUMMY_SP), victim, candidate); + + // If there are no lifetime errors, then we have proven that `'candidate = 'victim`! if infcx.resolve_regions(outlives_env).is_empty() { shadowed.insert(victim); tcx.emit_spanned_lint( @@ -150,6 +170,8 @@ fn check<'tcx>(tcx: TyCtxt<'tcx>, param_env: ty::ParamEnv<'tcx>, owner_id: hir:: #[diag(lint_redundant_lifetime_args)] #[note] struct RedundantLifetimeArgsLint<'tcx> { - candidate: ty::Region<'tcx>, + /// The lifetime we have found to be redundant. victim: ty::Region<'tcx>, + // The lifetime we can replace the victim with. + candidate: ty::Region<'tcx>, } diff --git a/compiler/rustc_lint_defs/src/builtin.rs b/compiler/rustc_lint_defs/src/builtin.rs index 53b5273803c..c2df3e1015f 100644 --- a/compiler/rustc_lint_defs/src/builtin.rs +++ b/compiler/rustc_lint_defs/src/builtin.rs @@ -1694,6 +1694,12 @@ declare_lint! { /// #[deny(unused_lifetimes)] /// /// pub fn foo<'a>() {} + /// + /// // `'a = 'static`, so all usages of `'a` can be replaced with `'static` + /// pub fn bar<'a: 'static>() {} + /// + /// // `'a = 'b`, so all usages of `'b` can be replaced with `'a` + /// pub fn bar<'a: 'b, 'b: 'a>() {} /// ``` /// /// {{produces}} |