From 18e9c4f175ac3f2c3f474edca3ab9212890fbaea Mon Sep 17 00:00:00 2001 From: Michael Goulet Date: Mon, 27 Nov 2023 21:29:29 +0000 Subject: [PATCH 1/3] Add redundant_lifetime_args lint --- compiler/rustc_errors/src/diagnostic_impls.rs | 1 + compiler/rustc_lint/messages.ftl | 2 + compiler/rustc_lint/src/lib.rs | 3 + .../rustc_lint/src/redundant_lifetime_args.rs | 160 ++++++++++++++++++ compiler/rustc_middle/src/ty/diagnostics.rs | 18 +- 5 files changed, 176 insertions(+), 8 deletions(-) create mode 100644 compiler/rustc_lint/src/redundant_lifetime_args.rs diff --git a/compiler/rustc_errors/src/diagnostic_impls.rs b/compiler/rustc_errors/src/diagnostic_impls.rs index 4f77f09b26ec4..642c3a5a19329 100644 --- a/compiler/rustc_errors/src/diagnostic_impls.rs +++ b/compiler/rustc_errors/src/diagnostic_impls.rs @@ -44,6 +44,7 @@ impl<'a, T: Clone + IntoDiagnosticArg> IntoDiagnosticArg for &'a T { } } +#[macro_export] macro_rules! into_diagnostic_arg_using_display { ($( $ty:ty ),+ $(,)?) => { $( diff --git a/compiler/rustc_lint/messages.ftl b/compiler/rustc_lint/messages.ftl index 2db610d640c29..1dd3fd594d534 100644 --- a/compiler/rustc_lint/messages.ftl +++ b/compiler/rustc_lint/messages.ftl @@ -470,6 +470,8 @@ lint_reason_must_be_string_literal = reason must be a string literal lint_reason_must_come_last = reason in lint attribute must come last +lint_redundant_lifetime_args = lifetime `{$victim}` is required to be equal to `{$candidate}`, and is redundant and can be removed + lint_redundant_semicolons = unnecessary trailing {$multiple -> [true] semicolons diff --git a/compiler/rustc_lint/src/lib.rs b/compiler/rustc_lint/src/lib.rs index 8e95a71e11f1e..a48767139bb07 100644 --- a/compiler/rustc_lint/src/lib.rs +++ b/compiler/rustc_lint/src/lib.rs @@ -82,6 +82,7 @@ mod opaque_hidden_inferred_bound; mod pass_by_value; mod passes; mod ptr_nulls; +mod redundant_lifetime_args; mod redundant_semicolon; mod reference_casting; mod traits; @@ -119,6 +120,7 @@ use noop_method_call::*; use opaque_hidden_inferred_bound::*; use pass_by_value::*; use ptr_nulls::*; +use redundant_lifetime_args::RedundantLifetimeArgs; use redundant_semicolon::*; use reference_casting::*; use traits::*; @@ -240,6 +242,7 @@ late_lint_methods!( MissingDebugImplementations: MissingDebugImplementations, MissingDoc: MissingDoc, AsyncFnInTrait: AsyncFnInTrait, + RedundantLifetimeArgs: RedundantLifetimeArgs, ] ] ); diff --git a/compiler/rustc_lint/src/redundant_lifetime_args.rs b/compiler/rustc_lint/src/redundant_lifetime_args.rs new file mode 100644 index 0000000000000..7a7c5387369ea --- /dev/null +++ b/compiler/rustc_lint/src/redundant_lifetime_args.rs @@ -0,0 +1,160 @@ +#![allow(rustc::diagnostic_outside_of_impl)] +#![allow(rustc::untranslatable_diagnostic)] + +use rustc_data_structures::fx::FxHashSet; +use rustc_hir as hir; +use rustc_hir::def::DefKind; +use rustc_infer::infer::outlives::env::OutlivesEnvironment; +use rustc_infer::infer::{SubregionOrigin, TyCtxtInferExt}; +use rustc_macros::LintDiagnostic; +use rustc_middle::ty::{self, TyCtxt}; +use rustc_span::DUMMY_SP; +use rustc_trait_selection::traits::{outlives_bounds::InferCtxtExt, ObligationCtxt}; + +use crate::{LateContext, LateLintPass}; + +declare_lint! { + /// Docs + pub REDUNDANT_LIFETIME_ARGS, + Allow, + "do something" +} + +declare_lint_pass!(RedundantLifetimeArgs => [REDUNDANT_LIFETIME_ARGS]); + +impl<'tcx> LateLintPass<'tcx> for RedundantLifetimeArgs { + fn check_item(&mut self, cx: &LateContext<'tcx>, item: &'tcx hir::Item<'tcx>) { + check(cx.tcx, cx.param_env, item.owner_id); + } + + fn check_trait_item(&mut self, cx: &LateContext<'tcx>, item: &'tcx hir::TraitItem<'tcx>) { + check(cx.tcx, cx.param_env, item.owner_id); + } + + fn check_impl_item(&mut self, cx: &LateContext<'tcx>, item: &'tcx hir::ImplItem<'tcx>) { + if cx + .tcx + .hir() + .expect_item(cx.tcx.local_parent(item.owner_id.def_id)) + .expect_impl() + .of_trait + .is_some() + { + // Don't check for redundant lifetimes for trait implementations, + // since the signature is required to be compatible with the trait. + return; + } + + check(cx.tcx, cx.param_env, item.owner_id); + } +} + +fn check<'tcx>(tcx: TyCtxt<'tcx>, param_env: ty::ParamEnv<'tcx>, owner_id: hir::OwnerId) { + let def_kind = tcx.def_kind(owner_id); + match def_kind { + DefKind::Struct + | DefKind::Union + | DefKind::Enum + | DefKind::Trait + | DefKind::TraitAlias + | DefKind::AssocTy + | DefKind::Fn + | DefKind::Const + | DefKind::AssocFn + | DefKind::AssocConst + | DefKind::Impl { of_trait: _ } => { + // Proceed + } + DefKind::Mod + | DefKind::Variant + | DefKind::TyAlias + | DefKind::ForeignTy + | DefKind::TyParam + | DefKind::ConstParam + | DefKind::Static(_) + | DefKind::Ctor(_, _) + | DefKind::Macro(_) + | DefKind::ExternCrate + | DefKind::Use + | DefKind::ForeignMod + | DefKind::AnonConst + | DefKind::InlineConst + | DefKind::OpaqueTy + | DefKind::Field + | DefKind::LifetimeParam + | DefKind::GlobalAsm + | DefKind::Closure => return, + } + + let infcx = &tcx.infer_ctxt().build(); + let ocx = ObligationCtxt::new(infcx); + 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); + + 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 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 }; + lifetimes.push(ty::Region::new_late_param(tcx, owner_id.to_def_id(), kind)); + } + } + + // Keep track of lifetimes which have already been replaced with other lifetimes. + let mut shadowed = FxHashSet::default(); + + for (idx, &candidate) in lifetimes.iter().enumerate() { + if shadowed.contains(&candidate) { + // Don't suggest removing a lifetime twice. + continue; + } + + if !candidate.has_name() { + // Can't rename a named lifetime with `'_` without ambiguity. + continue; + } + + for &victim in &lifetimes[(idx + 1)..] { + let (ty::ReEarlyParam(ty::EarlyParamRegion { def_id, .. }) + | ty::ReLateParam(ty::LateParamRegion { + bound_region: ty::BoundRegionKind::BrNamed(def_id, _), + .. + })) = victim.kind() + else { + continue; + }; + + 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(); + infcx.sub_regions(SubregionOrigin::RelateRegionParamBound(DUMMY_SP), candidate, victim); + infcx.sub_regions(SubregionOrigin::RelateRegionParamBound(DUMMY_SP), victim, candidate); + if infcx.resolve_regions(outlives_env).is_empty() { + shadowed.insert(victim); + tcx.emit_spanned_lint( + REDUNDANT_LIFETIME_ARGS, + tcx.local_def_id_to_hir_id(def_id.expect_local()), + tcx.def_span(def_id), + RedundantLifetimeArgsList { candidate, victim }, + ); + } + } + } +} + +#[derive(LintDiagnostic)] +#[diag(lint_redundant_lifetime_args)] +struct RedundantLifetimeArgsList<'tcx> { + candidate: ty::Region<'tcx>, + victim: ty::Region<'tcx>, +} diff --git a/compiler/rustc_middle/src/ty/diagnostics.rs b/compiler/rustc_middle/src/ty/diagnostics.rs index 0094825fc70d4..6dc98c369bfa4 100644 --- a/compiler/rustc_middle/src/ty/diagnostics.rs +++ b/compiler/rustc_middle/src/ty/diagnostics.rs @@ -5,13 +5,16 @@ use std::fmt::Write; use std::ops::ControlFlow; use crate::ty::{ - AliasTy, Const, ConstKind, FallibleTypeFolder, InferConst, InferTy, Opaque, PolyTraitPredicate, - Projection, Ty, TyCtxt, TypeFoldable, TypeSuperFoldable, TypeSuperVisitable, TypeVisitable, - TypeVisitor, + self, AliasTy, Const, ConstKind, FallibleTypeFolder, InferConst, InferTy, Opaque, + PolyTraitPredicate, Projection, Ty, TyCtxt, TypeFoldable, TypeSuperFoldable, + TypeSuperVisitable, TypeVisitable, TypeVisitor, }; use rustc_data_structures::fx::FxHashMap; -use rustc_errors::{Applicability, Diagnostic, DiagnosticArgValue, IntoDiagnosticArg}; +use rustc_errors::{ + into_diagnostic_arg_using_display, Applicability, Diagnostic, DiagnosticArgValue, + IntoDiagnosticArg, +}; use rustc_hir as hir; use rustc_hir::def::DefKind; use rustc_hir::def_id::DefId; @@ -19,10 +22,9 @@ use rustc_hir::{PredicateOrigin, WherePredicate}; use rustc_span::{BytePos, Span}; use rustc_type_ir::TyKind::*; -impl<'tcx> IntoDiagnosticArg for Ty<'tcx> { - fn into_diagnostic_arg(self) -> DiagnosticArgValue<'static> { - self.to_string().into_diagnostic_arg() - } +into_diagnostic_arg_using_display! { + Ty<'_>, + ty::Region<'_>, } impl<'tcx> Ty<'tcx> { From 5e6f119d340f2504e294c328dabd21675529032b Mon Sep 17 00:00:00 2001 From: Michael Goulet Date: Mon, 27 Nov 2023 21:54:03 +0000 Subject: [PATCH 2/3] Actually, just reuse the UNUSED_LIFETIMES lint --- .../src/collect/resolve_bound_vars.rs | 26 ------------- compiler/rustc_lint/messages.ftl | 3 +- .../rustc_lint/src/redundant_lifetime_args.rs | 17 +++----- .../unsatisfied-item-lifetime-bound.rs | 3 -- .../unsatisfied-item-lifetime-bound.stderr | 31 +++++---------- ...on-outlives-static-outlives-free-region.rs | 4 +- ...utlives-static-outlives-free-region.stderr | 8 ++-- .../ui/regions/regions-static-bound-rpass.rs | 7 ++-- .../regions/regions-static-bound-rpass.stderr | 34 +++++++++------- tests/ui/regions/regions-static-bound.rs | 5 --- tests/ui/regions/regions-static-bound.stderr | 38 ++---------------- .../transitively-redundant-lifetimes.rs | 16 ++++++++ .../transitively-redundant-lifetimes.stderr | 39 +++++++++++++++++++ 13 files changed, 107 insertions(+), 124 deletions(-) create mode 100644 tests/ui/regions/transitively-redundant-lifetimes.rs create mode 100644 tests/ui/regions/transitively-redundant-lifetimes.stderr diff --git a/compiler/rustc_hir_analysis/src/collect/resolve_bound_vars.rs b/compiler/rustc_hir_analysis/src/collect/resolve_bound_vars.rs index e49bd0917a80f..8f22af944b910 100644 --- a/compiler/rustc_hir_analysis/src/collect/resolve_bound_vars.rs +++ b/compiler/rustc_hir_analysis/src/collect/resolve_bound_vars.rs @@ -19,7 +19,6 @@ use rustc_middle::hir::nested_filter; use rustc_middle::middle::resolve_bound_vars::*; use rustc_middle::query::Providers; use rustc_middle::ty::{self, TyCtxt, TypeSuperVisitable, TypeVisitor}; -use rustc_session::lint; use rustc_span::def_id::DefId; use rustc_span::symbol::{sym, Ident}; use rustc_span::{Span, DUMMY_SP}; @@ -905,31 +904,6 @@ impl<'a, 'tcx> Visitor<'tcx> for BoundVarContext<'a, 'tcx> { }) => { self.visit_lifetime(lifetime); walk_list!(self, visit_param_bound, bounds); - - if lifetime.res != hir::LifetimeName::Static { - for bound in bounds { - let hir::GenericBound::Outlives(lt) = bound else { - continue; - }; - if lt.res != hir::LifetimeName::Static { - continue; - } - self.insert_lifetime(lt, ResolvedArg::StaticLifetime); - self.tcx.struct_span_lint_hir( - lint::builtin::UNUSED_LIFETIMES, - lifetime.hir_id, - lifetime.ident.span, - format!("unnecessary lifetime parameter `{}`", lifetime.ident), - |lint| { - let help = format!( - "you can use the `'static` lifetime directly, in place of `{}`", - lifetime.ident, - ); - lint.help(help) - }, - ); - } - } } &hir::WherePredicate::EqPredicate(hir::WhereEqPredicate { lhs_ty, rhs_ty, .. }) => { self.visit_ty(lhs_ty); diff --git a/compiler/rustc_lint/messages.ftl b/compiler/rustc_lint/messages.ftl index 1dd3fd594d534..6289a0f747a8f 100644 --- a/compiler/rustc_lint/messages.ftl +++ b/compiler/rustc_lint/messages.ftl @@ -470,7 +470,8 @@ lint_reason_must_be_string_literal = reason must be a string literal lint_reason_must_come_last = reason in lint attribute must come last -lint_redundant_lifetime_args = lifetime `{$victim}` is required to be equal to `{$candidate}`, and is redundant and can be removed +lint_redundant_lifetime_args = unnecessary lifetime parameter `{$victim}` + .note = you can use the `{$candidate}` lifetime directly, in place of `{$victim}` lint_redundant_semicolons = unnecessary trailing {$multiple -> diff --git a/compiler/rustc_lint/src/redundant_lifetime_args.rs b/compiler/rustc_lint/src/redundant_lifetime_args.rs index 7a7c5387369ea..59d2edba124af 100644 --- a/compiler/rustc_lint/src/redundant_lifetime_args.rs +++ b/compiler/rustc_lint/src/redundant_lifetime_args.rs @@ -8,19 +8,13 @@ use rustc_infer::infer::outlives::env::OutlivesEnvironment; use rustc_infer::infer::{SubregionOrigin, TyCtxtInferExt}; use rustc_macros::LintDiagnostic; use rustc_middle::ty::{self, TyCtxt}; +use rustc_session::lint::builtin::UNUSED_LIFETIMES; use rustc_span::DUMMY_SP; use rustc_trait_selection::traits::{outlives_bounds::InferCtxtExt, ObligationCtxt}; use crate::{LateContext, LateLintPass}; -declare_lint! { - /// Docs - pub REDUNDANT_LIFETIME_ARGS, - Allow, - "do something" -} - -declare_lint_pass!(RedundantLifetimeArgs => [REDUNDANT_LIFETIME_ARGS]); +declare_lint_pass!(RedundantLifetimeArgs => []); impl<'tcx> LateLintPass<'tcx> for RedundantLifetimeArgs { fn check_item(&mut self, cx: &LateContext<'tcx>, item: &'tcx hir::Item<'tcx>) { @@ -142,10 +136,10 @@ fn check<'tcx>(tcx: TyCtxt<'tcx>, param_env: ty::ParamEnv<'tcx>, owner_id: hir:: if infcx.resolve_regions(outlives_env).is_empty() { shadowed.insert(victim); tcx.emit_spanned_lint( - REDUNDANT_LIFETIME_ARGS, + UNUSED_LIFETIMES, tcx.local_def_id_to_hir_id(def_id.expect_local()), tcx.def_span(def_id), - RedundantLifetimeArgsList { candidate, victim }, + RedundantLifetimeArgsLint { candidate, victim }, ); } } @@ -154,7 +148,8 @@ fn check<'tcx>(tcx: TyCtxt<'tcx>, param_env: ty::ParamEnv<'tcx>, owner_id: hir:: #[derive(LintDiagnostic)] #[diag(lint_redundant_lifetime_args)] -struct RedundantLifetimeArgsList<'tcx> { +#[note] +struct RedundantLifetimeArgsLint<'tcx> { candidate: ty::Region<'tcx>, victim: ty::Region<'tcx>, } diff --git a/tests/ui/generic-associated-types/unsatisfied-item-lifetime-bound.rs b/tests/ui/generic-associated-types/unsatisfied-item-lifetime-bound.rs index a3f3b1a6d4d9a..1d427e89c21d8 100644 --- a/tests/ui/generic-associated-types/unsatisfied-item-lifetime-bound.rs +++ b/tests/ui/generic-associated-types/unsatisfied-item-lifetime-bound.rs @@ -1,8 +1,5 @@ -#![warn(unused_lifetimes)] - pub trait X { type Y<'a: 'static>; - //~^ WARNING unnecessary lifetime parameter } impl X for () { diff --git a/tests/ui/generic-associated-types/unsatisfied-item-lifetime-bound.stderr b/tests/ui/generic-associated-types/unsatisfied-item-lifetime-bound.stderr index f73ed5956da21..483bb9e1167be 100644 --- a/tests/ui/generic-associated-types/unsatisfied-item-lifetime-bound.stderr +++ b/tests/ui/generic-associated-types/unsatisfied-item-lifetime-bound.stderr @@ -1,57 +1,44 @@ -warning: unnecessary lifetime parameter `'a` - --> $DIR/unsatisfied-item-lifetime-bound.rs:4:12 - | -LL | type Y<'a: 'static>; - | ^^ - | - = help: you can use the `'static` lifetime directly, in place of `'a` -note: the lint level is defined here - --> $DIR/unsatisfied-item-lifetime-bound.rs:1:9 - | -LL | #![warn(unused_lifetimes)] - | ^^^^^^^^^^^^^^^^ - error[E0478]: lifetime bound not satisfied - --> $DIR/unsatisfied-item-lifetime-bound.rs:14:8 + --> $DIR/unsatisfied-item-lifetime-bound.rs:11:8 | LL | f: ::Y<'a>, | ^^^^^^^^^^^^^^^ | note: lifetime parameter instantiated with the lifetime `'a` as defined here - --> $DIR/unsatisfied-item-lifetime-bound.rs:13:10 + --> $DIR/unsatisfied-item-lifetime-bound.rs:10:10 | LL | struct B<'a, T: for<'r> X = &'r ()>> { | ^^ = note: but lifetime parameter must outlive the static lifetime error[E0478]: lifetime bound not satisfied - --> $DIR/unsatisfied-item-lifetime-bound.rs:19:8 + --> $DIR/unsatisfied-item-lifetime-bound.rs:16:8 | LL | f: ::Y<'a>, | ^^^^^^^^^^^^^^^ | note: lifetime parameter instantiated with the lifetime `'a` as defined here - --> $DIR/unsatisfied-item-lifetime-bound.rs:18:10 + --> $DIR/unsatisfied-item-lifetime-bound.rs:15:10 | LL | struct C<'a, T: X> { | ^^ = note: but lifetime parameter must outlive the static lifetime error[E0478]: lifetime bound not satisfied - --> $DIR/unsatisfied-item-lifetime-bound.rs:24:8 + --> $DIR/unsatisfied-item-lifetime-bound.rs:21:8 | LL | f: <() as X>::Y<'a>, | ^^^^^^^^^^^^^^^^ | note: lifetime parameter instantiated with the lifetime `'a` as defined here - --> $DIR/unsatisfied-item-lifetime-bound.rs:23:10 + --> $DIR/unsatisfied-item-lifetime-bound.rs:20:10 | LL | struct D<'a> { | ^^ = note: but lifetime parameter must outlive the static lifetime error[E0478]: lifetime bound not satisfied - --> $DIR/unsatisfied-item-lifetime-bound.rs:9:18 + --> $DIR/unsatisfied-item-lifetime-bound.rs:6:18 | LL | type Y<'a: 'static>; | ------------------- definition of `Y` from trait @@ -60,7 +47,7 @@ LL | type Y<'a> = &'a (); | ^^^^^^ | note: lifetime parameter instantiated with the lifetime `'a` as defined here - --> $DIR/unsatisfied-item-lifetime-bound.rs:9:12 + --> $DIR/unsatisfied-item-lifetime-bound.rs:6:12 | LL | type Y<'a> = &'a (); | ^^ @@ -70,6 +57,6 @@ help: copy the `where` clause predicates from the trait LL | type Y<'a> = &'a () where 'a: 'static; | +++++++++++++++++ -error: aborting due to 4 previous errors; 1 warning emitted +error: aborting due to 4 previous errors For more information about this error, try `rustc --explain E0478`. diff --git a/tests/ui/regions/regions-free-region-outlives-static-outlives-free-region.rs b/tests/ui/regions/regions-free-region-outlives-static-outlives-free-region.rs index 46462c432a8c7..5ccc75409bdc5 100644 --- a/tests/ui/regions/regions-free-region-outlives-static-outlives-free-region.rs +++ b/tests/ui/regions/regions-free-region-outlives-static-outlives-free-region.rs @@ -10,8 +10,8 @@ #![warn(unused_lifetimes)] -fn test<'a,'b>(x: &'a i32) -> &'b i32 - where 'a: 'static //~ WARN unnecessary lifetime parameter `'a` +fn test<'a,'b>(x: &'a i32) -> &'b i32 //~ WARN unnecessary lifetime parameter `'a` + where 'a: 'static { x } diff --git a/tests/ui/regions/regions-free-region-outlives-static-outlives-free-region.stderr b/tests/ui/regions/regions-free-region-outlives-static-outlives-free-region.stderr index 9f03a6553ba83..69f409f436e9e 100644 --- a/tests/ui/regions/regions-free-region-outlives-static-outlives-free-region.stderr +++ b/tests/ui/regions/regions-free-region-outlives-static-outlives-free-region.stderr @@ -1,10 +1,10 @@ warning: unnecessary lifetime parameter `'a` - --> $DIR/regions-free-region-outlives-static-outlives-free-region.rs:14:11 + --> $DIR/regions-free-region-outlives-static-outlives-free-region.rs:13:9 | -LL | where 'a: 'static - | ^^ +LL | fn test<'a,'b>(x: &'a i32) -> &'b i32 + | ^^ | - = help: you can use the `'static` lifetime directly, in place of `'a` + = note: you can use the `'static` lifetime directly, in place of `'a` note: the lint level is defined here --> $DIR/regions-free-region-outlives-static-outlives-free-region.rs:11:9 | diff --git a/tests/ui/regions/regions-static-bound-rpass.rs b/tests/ui/regions/regions-static-bound-rpass.rs index e2ebb394d0ad2..72312b86db56b 100644 --- a/tests/ui/regions/regions-static-bound-rpass.rs +++ b/tests/ui/regions/regions-static-bound-rpass.rs @@ -3,16 +3,17 @@ #![warn(unused_lifetimes)] fn invariant_id<'a,'b>(t: &'b mut &'static ()) -> &'b mut &'a () - where 'a: 'static { t } //~^ WARN unnecessary lifetime parameter `'a` + where 'a: 'static { t } fn static_id<'a>(t: &'a ()) -> &'static () - where 'a: 'static { t } //~^ WARN unnecessary lifetime parameter `'a` + where 'a: 'static { t } fn static_id_indirect<'a,'b>(t: &'a ()) -> &'static () +//~^ WARN unnecessary lifetime parameter `'a` +//~| WARN unnecessary lifetime parameter `'b` where 'a: 'b, 'b: 'static { t } -//~^ WARN unnecessary lifetime parameter `'b` fn ref_id<'a>(t: &'a ()) -> &'a () where 'static: 'a { t } diff --git a/tests/ui/regions/regions-static-bound-rpass.stderr b/tests/ui/regions/regions-static-bound-rpass.stderr index f0f3a4c5261aa..d197266380a5a 100644 --- a/tests/ui/regions/regions-static-bound-rpass.stderr +++ b/tests/ui/regions/regions-static-bound-rpass.stderr @@ -1,10 +1,10 @@ warning: unnecessary lifetime parameter `'a` - --> $DIR/regions-static-bound-rpass.rs:6:11 + --> $DIR/regions-static-bound-rpass.rs:5:17 | -LL | where 'a: 'static { t } - | ^^ +LL | fn invariant_id<'a,'b>(t: &'b mut &'static ()) -> &'b mut &'a () + | ^^ | - = help: you can use the `'static` lifetime directly, in place of `'a` + = note: you can use the `'static` lifetime directly, in place of `'a` note: the lint level is defined here --> $DIR/regions-static-bound-rpass.rs:3:9 | @@ -12,20 +12,28 @@ LL | #![warn(unused_lifetimes)] | ^^^^^^^^^^^^^^^^ warning: unnecessary lifetime parameter `'a` - --> $DIR/regions-static-bound-rpass.rs:10:11 + --> $DIR/regions-static-bound-rpass.rs:9:14 | -LL | where 'a: 'static { t } - | ^^ +LL | fn static_id<'a>(t: &'a ()) -> &'static () + | ^^ | - = help: you can use the `'static` lifetime directly, in place of `'a` + = note: you can use the `'static` lifetime directly, in place of `'a` + +warning: unnecessary lifetime parameter `'a` + --> $DIR/regions-static-bound-rpass.rs:13:23 + | +LL | fn static_id_indirect<'a,'b>(t: &'a ()) -> &'static () + | ^^ + | + = note: you can use the `'static` lifetime directly, in place of `'a` warning: unnecessary lifetime parameter `'b` - --> $DIR/regions-static-bound-rpass.rs:14:19 + --> $DIR/regions-static-bound-rpass.rs:13:26 | -LL | where 'a: 'b, 'b: 'static { t } - | ^^ +LL | fn static_id_indirect<'a,'b>(t: &'a ()) -> &'static () + | ^^ | - = help: you can use the `'static` lifetime directly, in place of `'b` + = note: you can use the `'static` lifetime directly, in place of `'b` -warning: 3 warnings emitted +warning: 4 warnings emitted diff --git a/tests/ui/regions/regions-static-bound.rs b/tests/ui/regions/regions-static-bound.rs index e7aa8795f01a6..af6425971bd12 100644 --- a/tests/ui/regions/regions-static-bound.rs +++ b/tests/ui/regions/regions-static-bound.rs @@ -1,12 +1,7 @@ -#![warn(unused_lifetimes)] - fn static_id<'a,'b>(t: &'a ()) -> &'static () where 'a: 'static { t } -//~^ WARN lifetime parameter `'b` never used -//~| WARN unnecessary lifetime parameter `'a` fn static_id_indirect<'a,'b>(t: &'a ()) -> &'static () where 'a: 'b, 'b: 'static { t } -//~^ WARN unnecessary lifetime parameter `'b` fn static_id_wrong_way<'a>(t: &'a ()) -> &'static () where 'static: 'a { t diff --git a/tests/ui/regions/regions-static-bound.stderr b/tests/ui/regions/regions-static-bound.stderr index b314e9fe85d4e..f7b48349e4a3f 100644 --- a/tests/ui/regions/regions-static-bound.stderr +++ b/tests/ui/regions/regions-static-bound.stderr @@ -1,35 +1,5 @@ -warning: lifetime parameter `'b` never used - --> $DIR/regions-static-bound.rs:3:17 - | -LL | fn static_id<'a,'b>(t: &'a ()) -> &'static () where 'a: 'static { t } - | -^^ - | | - | help: elide the unused lifetime - | -note: the lint level is defined here - --> $DIR/regions-static-bound.rs:1:9 - | -LL | #![warn(unused_lifetimes)] - | ^^^^^^^^^^^^^^^^ - -warning: unnecessary lifetime parameter `'a` - --> $DIR/regions-static-bound.rs:3:53 - | -LL | fn static_id<'a,'b>(t: &'a ()) -> &'static () where 'a: 'static { t } - | ^^ - | - = help: you can use the `'static` lifetime directly, in place of `'a` - -warning: unnecessary lifetime parameter `'b` - --> $DIR/regions-static-bound.rs:8:19 - | -LL | where 'a: 'b, 'b: 'static { t } - | ^^ - | - = help: you can use the `'static` lifetime directly, in place of `'b` - error: lifetime may not live long enough - --> $DIR/regions-static-bound.rs:12:5 + --> $DIR/regions-static-bound.rs:7:5 | LL | fn static_id_wrong_way<'a>(t: &'a ()) -> &'static () where 'static: 'a { | -- lifetime `'a` defined here @@ -37,7 +7,7 @@ LL | t | ^ returning this value requires that `'a` must outlive `'static` error[E0521]: borrowed data escapes outside of function - --> $DIR/regions-static-bound.rs:17:5 + --> $DIR/regions-static-bound.rs:12:5 | LL | fn error(u: &(), v: &()) { | - - let's call the lifetime of this reference `'1` @@ -50,7 +20,7 @@ LL | static_id(&u); | argument requires that `'1` must outlive `'static` error[E0521]: borrowed data escapes outside of function - --> $DIR/regions-static-bound.rs:19:5 + --> $DIR/regions-static-bound.rs:14:5 | LL | fn error(u: &(), v: &()) { | - - let's call the lifetime of this reference `'2` @@ -63,6 +33,6 @@ LL | static_id_indirect(&v); | `v` escapes the function body here | argument requires that `'2` must outlive `'static` -error: aborting due to 3 previous errors; 3 warnings emitted +error: aborting due to 3 previous errors For more information about this error, try `rustc --explain E0521`. diff --git a/tests/ui/regions/transitively-redundant-lifetimes.rs b/tests/ui/regions/transitively-redundant-lifetimes.rs new file mode 100644 index 0000000000000..3baf2a88abb40 --- /dev/null +++ b/tests/ui/regions/transitively-redundant-lifetimes.rs @@ -0,0 +1,16 @@ +#![allow(unused)] +#![deny(unused_lifetimes)] + +fn a<'a, 'b>(x: &'a &'b &'a ()) {} //~ ERROR unnecessary lifetime parameter `'b` + +fn b<'a: 'b, 'b: 'a>() {} //~ ERROR unnecessary lifetime parameter `'b` + +struct Foo(T); +fn c<'a>(_: Foo<&'a ()>) {} //~ ERROR unnecessary lifetime parameter `'a` + +struct Bar<'a>(&'a ()); +impl<'a> Bar<'a> { + fn d<'b: 'a>(&'b self) {} //~ ERROR unnecessary lifetime parameter `'b` +} + +fn main() {} diff --git a/tests/ui/regions/transitively-redundant-lifetimes.stderr b/tests/ui/regions/transitively-redundant-lifetimes.stderr new file mode 100644 index 0000000000000..22a27115f7ae2 --- /dev/null +++ b/tests/ui/regions/transitively-redundant-lifetimes.stderr @@ -0,0 +1,39 @@ +error: unnecessary lifetime parameter `'b` + --> $DIR/transitively-redundant-lifetimes.rs:4:10 + | +LL | fn a<'a, 'b>(x: &'a &'b &'a ()) {} + | ^^ + | + = note: you can use the `'a` lifetime directly, in place of `'b` +note: the lint level is defined here + --> $DIR/transitively-redundant-lifetimes.rs:2:9 + | +LL | #![deny(unused_lifetimes)] + | ^^^^^^^^^^^^^^^^ + +error: unnecessary lifetime parameter `'b` + --> $DIR/transitively-redundant-lifetimes.rs:6:14 + | +LL | fn b<'a: 'b, 'b: 'a>() {} + | ^^ + | + = note: you can use the `'a` lifetime directly, in place of `'b` + +error: unnecessary lifetime parameter `'a` + --> $DIR/transitively-redundant-lifetimes.rs:9:6 + | +LL | fn c<'a>(_: Foo<&'a ()>) {} + | ^^ + | + = note: you can use the `'static` lifetime directly, in place of `'a` + +error: unnecessary lifetime parameter `'b` + --> $DIR/transitively-redundant-lifetimes.rs:13:10 + | +LL | fn d<'b: 'a>(&'b self) {} + | ^^ + | + = note: you can use the `'a` lifetime directly, in place of `'b` + +error: aborting due to 4 previous errors + From b2c18d9d01e27768b915764aa1f99da89cb4d148 Mon Sep 17 00:00:00 2001 From: Michael Goulet Date: Mon, 27 Nov 2023 22:05:46 +0000 Subject: [PATCH 3/3] Add comments --- .../rustc_lint/src/redundant_lifetime_args.rs | 34 +++++++++++++++---- compiler/rustc_lint_defs/src/builtin.rs | 8 ++++- 2 files changed, 35 insertions(+), 7 deletions(-) diff --git a/compiler/rustc_lint/src/redundant_lifetime_args.rs b/compiler/rustc_lint/src/redundant_lifetime_args.rs index 59d2edba124af..34ff5e9dfe98b 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 a2243817df95f..1ac21607df75b 100644 --- a/compiler/rustc_lint_defs/src/builtin.rs +++ b/compiler/rustc_lint_defs/src/builtin.rs @@ -1532,7 +1532,7 @@ declare_lint! { declare_lint! { /// The `unused_lifetimes` lint detects lifetime parameters that are never - /// used. + /// used, or are redundant because they are equal to another named lifetime. /// /// ### Example /// @@ -1540,6 +1540,12 @@ 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}}