From f8f4d50aa34640906e0315adbf4c487712fab0cd Mon Sep 17 00:00:00 2001 From: Michael Goulet Date: Mon, 12 Aug 2024 17:56:49 -0400 Subject: [PATCH] Don't worry about uncaptured contravariant lifetimes if they outlive a captured lifetime --- .../rustc_lint/src/impl_trait_overcaptures.rs | 247 ++++++++++++++++-- .../overcaptures-2024-but-fine.rs | 15 ++ 2 files changed, 241 insertions(+), 21 deletions(-) create mode 100644 tests/ui/impl-trait/precise-capturing/overcaptures-2024-but-fine.rs diff --git a/compiler/rustc_lint/src/impl_trait_overcaptures.rs b/compiler/rustc_lint/src/impl_trait_overcaptures.rs index 8824e1dfe50..42c800a81af 100644 --- a/compiler/rustc_lint/src/impl_trait_overcaptures.rs +++ b/compiler/rustc_lint/src/impl_trait_overcaptures.rs @@ -1,19 +1,28 @@ -use rustc_data_structures::fx::FxIndexSet; +use std::cell::LazyCell; + +use rustc_data_structures::fx::{FxHashMap, FxIndexMap, FxIndexSet}; use rustc_data_structures::unord::UnordSet; use rustc_errors::{Applicability, LintDiagnostic}; use rustc_hir as hir; use rustc_hir::def::DefKind; use rustc_hir::def_id::{DefId, LocalDefId}; +use rustc_infer::infer::outlives::env::OutlivesEnvironment; +use rustc_infer::infer::TyCtxtInferExt; use rustc_macros::LintDiagnostic; -use rustc_middle::bug; use rustc_middle::middle::resolve_bound_vars::ResolvedArg; +use rustc_middle::ty::relate::{ + structurally_relate_consts, structurally_relate_tys, Relate, RelateResult, TypeRelation, +}; use rustc_middle::ty::{ self, Ty, TyCtxt, TypeSuperVisitable, TypeVisitable, TypeVisitableExt, TypeVisitor, }; +use rustc_middle::{bug, span_bug}; use rustc_session::lint::FutureIncompatibilityReason; use rustc_session::{declare_lint, declare_lint_pass}; use rustc_span::edition::Edition; -use rustc_span::Span; +use rustc_span::{Span, Symbol}; +use rustc_trait_selection::traits::outlives_bounds::InferCtxtExt; +use rustc_trait_selection::traits::ObligationCtxt; use crate::{fluent_generated as fluent, LateContext, LateLintPass}; @@ -119,20 +128,41 @@ fn check_trait_item(&mut self, cx: &LateContext<'tcx>, it: &'tcx hir::TraitItem< } } +#[derive(PartialEq, Eq, Hash, Debug, Copy, Clone)] +enum ParamKind { + // Early-bound var. + Early(Symbol, u32), + // Late-bound var on function, not within a binder. We can capture these. + Free(DefId, Symbol), + // Late-bound var in a binder. We can't capture these yet. + Late, +} + fn check_fn(tcx: TyCtxt<'_>, parent_def_id: LocalDefId) { let sig = tcx.fn_sig(parent_def_id).instantiate_identity(); - let mut in_scope_parameters = FxIndexSet::default(); + let mut in_scope_parameters = FxIndexMap::default(); // Populate the in_scope_parameters list first with all of the generics in scope let mut current_def_id = Some(parent_def_id.to_def_id()); while let Some(def_id) = current_def_id { let generics = tcx.generics_of(def_id); for param in &generics.own_params { - in_scope_parameters.insert(param.def_id); + in_scope_parameters.insert(param.def_id, ParamKind::Early(param.name, param.index)); } current_def_id = generics.parent; } + for bound_var in sig.bound_vars() { + let ty::BoundVariableKind::Region(ty::BoundRegionKind::BrNamed(def_id, name)) = bound_var + else { + span_bug!(tcx.def_span(parent_def_id), "unexpected non-lifetime binder on fn sig"); + }; + + in_scope_parameters.insert(def_id, ParamKind::Free(def_id, name)); + } + + let sig = tcx.liberate_late_bound_regions(parent_def_id.to_def_id(), sig); + // Then visit the signature to walk through all the binders (incl. the late-bound // vars on the function itself, which we need to count too). sig.visit_with(&mut VisitOpaqueTypes { @@ -140,17 +170,44 @@ fn check_fn(tcx: TyCtxt<'_>, parent_def_id: LocalDefId) { parent_def_id, in_scope_parameters, seen: Default::default(), + // Lazily compute these two, since they're likely a bit expensive. + variances: LazyCell::new(|| { + let mut functional_variances = FunctionalVariances { + tcx: tcx, + variances: FxHashMap::default(), + ambient_variance: ty::Covariant, + generics: tcx.generics_of(parent_def_id), + }; + let _ = functional_variances.relate(sig, sig); + functional_variances.variances + }), + outlives_env: LazyCell::new(|| { + let param_env = tcx.param_env(parent_def_id); + let infcx = tcx.infer_ctxt().build(); + let ocx = ObligationCtxt::new(&infcx); + let assumed_wf_tys = ocx.assumed_wf_types(param_env, parent_def_id).unwrap_or_default(); + let implied_bounds = + infcx.implied_bounds_tys_compat(param_env, parent_def_id, &assumed_wf_tys, false); + OutlivesEnvironment::with_bounds(param_env, implied_bounds) + }), }); } -struct VisitOpaqueTypes<'tcx> { +struct VisitOpaqueTypes<'tcx, VarFn, OutlivesFn> { tcx: TyCtxt<'tcx>, parent_def_id: LocalDefId, - in_scope_parameters: FxIndexSet, + in_scope_parameters: FxIndexMap, + variances: LazyCell, VarFn>, + outlives_env: LazyCell, OutlivesFn>, seen: FxIndexSet, } -impl<'tcx> TypeVisitor> for VisitOpaqueTypes<'tcx> { +impl<'tcx, VarFn, OutlivesFn> TypeVisitor> + for VisitOpaqueTypes<'tcx, VarFn, OutlivesFn> +where + VarFn: FnOnce() -> FxHashMap, + OutlivesFn: FnOnce() -> OutlivesEnvironment<'tcx>, +{ fn visit_binder>>( &mut self, t: &ty::Binder<'tcx, T>, @@ -163,8 +220,8 @@ fn visit_binder>>( ty::BoundVariableKind::Region(ty::BoundRegionKind::BrNamed(def_id, ..)) | ty::BoundVariableKind::Ty(ty::BoundTyKind::Param(def_id, _)) => { added.push(def_id); - let unique = self.in_scope_parameters.insert(def_id); - assert!(unique); + let unique = self.in_scope_parameters.insert(def_id, ParamKind::Late); + assert_eq!(unique, None); } _ => { self.tcx.dcx().span_delayed_bug( @@ -209,6 +266,7 @@ fn visit_ty(&mut self, t: Ty<'tcx>) -> Self::Result { { // Compute the set of args that are captured by the opaque... let mut captured = FxIndexSet::default(); + let mut captured_regions = FxIndexSet::default(); let variances = self.tcx.variances_of(opaque_def_id); let mut current_def_id = Some(opaque_def_id.to_def_id()); while let Some(def_id) = current_def_id { @@ -218,26 +276,61 @@ fn visit_ty(&mut self, t: Ty<'tcx>) -> Self::Result { if variances[param.index as usize] != ty::Invariant { continue; } + + let arg = opaque_ty.args[param.index as usize]; // We need to turn all `ty::Param`/`ConstKind::Param` and // `ReEarlyParam`/`ReBound` into def ids. - captured.insert(extract_def_id_from_arg( - self.tcx, - generics, - opaque_ty.args[param.index as usize], - )); + captured.insert(extract_def_id_from_arg(self.tcx, generics, arg)); + + captured_regions.extend(arg.as_region()); } current_def_id = generics.parent; } // Compute the set of in scope params that are not captured. Get their spans, // since that's all we really care about them for emitting the diagnostic. - let uncaptured_spans: Vec<_> = self + let mut uncaptured_args: FxIndexSet<_> = self .in_scope_parameters .iter() - .filter(|def_id| !captured.contains(*def_id)) - .map(|def_id| self.tcx.def_span(def_id)) + .filter(|&(def_id, _)| !captured.contains(def_id)) .collect(); + // These are args that we know are likely fine to "overcapture", since they can be + // contravariantly shortened to one of the already-captured lifetimes that they + // outlive. + let covariant_long_args: FxIndexSet<_> = uncaptured_args + .iter() + .copied() + .filter(|&(def_id, kind)| { + let Some(ty::Bivariant | ty::Contravariant) = self.variances.get(def_id) else { + return false; + }; + let DefKind::LifetimeParam = self.tcx.def_kind(def_id) else { + return false; + }; + let uncaptured = match *kind { + ParamKind::Early(name, index) => ty::Region::new_early_param( + self.tcx, + ty::EarlyParamRegion { name, index }, + ), + ParamKind::Free(def_id, name) => ty::Region::new_late_param( + self.tcx, + self.parent_def_id.to_def_id(), + ty::BoundRegionKind::BrNamed(def_id, name), + ), + ParamKind::Late => return false, + }; + // Does this region outlive any captured region? + captured_regions.iter().any(|r| { + self.outlives_env + .free_region_map() + .sub_free_regions(self.tcx, *r, uncaptured) + }) + }) + .collect(); + // We don't care to warn on these args. + uncaptured_args.retain(|arg| !covariant_long_args.contains(arg)); + let opaque_span = self.tcx.def_span(opaque_def_id); let new_capture_rules = opaque_span.at_least_rust_2024() || self.tcx.features().lifetime_capture_rules_2024; @@ -246,7 +339,7 @@ fn visit_ty(&mut self, t: Ty<'tcx>) -> Self::Result { // `use<>` syntax on it, and we're < edition 2024, then warn the user. if !new_capture_rules && !opaque.bounds.iter().any(|bound| matches!(bound, hir::GenericBound::Use(..))) - && !uncaptured_spans.is_empty() + && !uncaptured_args.is_empty() { let suggestion = if let Ok(snippet) = self.tcx.sess.source_map().span_to_snippet(opaque_span) @@ -274,6 +367,11 @@ fn visit_ty(&mut self, t: Ty<'tcx>) -> Self::Result { None }; + let uncaptured_spans: Vec<_> = uncaptured_args + .into_iter() + .map(|(def_id, _)| self.tcx.def_span(def_id)) + .collect(); + self.tcx.emit_node_span_lint( IMPL_TRAIT_OVERCAPTURES, self.tcx.local_def_id_to_hir_id(opaque_def_id), @@ -327,7 +425,7 @@ fn visit_ty(&mut self, t: Ty<'tcx>) -> Self::Result { if self .in_scope_parameters .iter() - .all(|def_id| explicitly_captured.contains(def_id)) + .all(|(def_id, _)| explicitly_captured.contains(def_id)) { self.tcx.emit_node_span_lint( IMPL_TRAIT_REDUNDANT_CAPTURES, @@ -396,7 +494,11 @@ fn extract_def_id_from_arg<'tcx>( ty::ReBound( _, ty::BoundRegion { kind: ty::BoundRegionKind::BrNamed(def_id, ..), .. }, - ) => def_id, + ) + | ty::ReLateParam(ty::LateParamRegion { + scope: _, + bound_region: ty::BoundRegionKind::BrNamed(def_id, ..), + }) => def_id, _ => unreachable!(), }, ty::GenericArgKind::Type(ty) => { @@ -413,3 +515,106 @@ fn extract_def_id_from_arg<'tcx>( } } } + +/// Computes the variances of regions that appear in the type, but considering +/// late-bound regions too, which don't have their variance computed usually. +/// +/// Like generalization, this is a unary operation implemented on top of the binary +/// relation infrastructure, mostly because it's much easier to have the relation +/// track the variance for you, rather than having to do it yourself. +struct FunctionalVariances<'tcx> { + tcx: TyCtxt<'tcx>, + variances: FxHashMap, + ambient_variance: ty::Variance, + generics: &'tcx ty::Generics, +} + +impl<'tcx> TypeRelation> for FunctionalVariances<'tcx> { + fn cx(&self) -> TyCtxt<'tcx> { + self.tcx + } + + fn relate_with_variance>>( + &mut self, + variance: rustc_type_ir::Variance, + _: ty::VarianceDiagInfo>, + a: T, + b: T, + ) -> RelateResult<'tcx, T> { + let old_variance = self.ambient_variance; + self.ambient_variance = self.ambient_variance.xform(variance); + self.relate(a, b)?; + self.ambient_variance = old_variance; + Ok(a) + } + + fn tys(&mut self, a: Ty<'tcx>, b: Ty<'tcx>) -> RelateResult<'tcx, Ty<'tcx>> { + structurally_relate_tys(self, a, b)?; + Ok(a) + } + + fn regions( + &mut self, + a: ty::Region<'tcx>, + _: ty::Region<'tcx>, + ) -> RelateResult<'tcx, ty::Region<'tcx>> { + let def_id = match *a { + ty::ReEarlyParam(ebr) => self.generics.region_param(ebr, self.tcx).def_id, + ty::ReBound( + _, + ty::BoundRegion { kind: ty::BoundRegionKind::BrNamed(def_id, ..), .. }, + ) + | ty::ReLateParam(ty::LateParamRegion { + scope: _, + bound_region: ty::BoundRegionKind::BrNamed(def_id, ..), + }) => def_id, + _ => { + return Ok(a); + } + }; + + if let Some(variance) = self.variances.get_mut(&def_id) { + *variance = unify(*variance, self.ambient_variance); + } else { + self.variances.insert(def_id, self.ambient_variance); + } + + Ok(a) + } + + fn consts( + &mut self, + a: ty::Const<'tcx>, + b: ty::Const<'tcx>, + ) -> RelateResult<'tcx, ty::Const<'tcx>> { + structurally_relate_consts(self, a, b)?; + Ok(a) + } + + fn binders( + &mut self, + a: ty::Binder<'tcx, T>, + b: ty::Binder<'tcx, T>, + ) -> RelateResult<'tcx, ty::Binder<'tcx, T>> + where + T: Relate>, + { + self.relate(a.skip_binder(), b.skip_binder())?; + Ok(a) + } +} + +/// What is the variance that satisfies the two variances? +fn unify(a: ty::Variance, b: ty::Variance) -> ty::Variance { + match (a, b) { + // Bivariance is lattice bottom. + (ty::Bivariant, other) | (other, ty::Bivariant) => other, + // Invariant is lattice top. + (ty::Invariant, _) | (_, ty::Invariant) => ty::Invariant, + // If type is required to be covariant and contravariant, then it's invariant. + (ty::Contravariant, ty::Covariant) | (ty::Covariant, ty::Contravariant) => ty::Invariant, + // Otherwise, co + co = co, contra + contra = contra. + (ty::Contravariant, ty::Contravariant) => ty::Contravariant, + (ty::Covariant, ty::Covariant) => ty::Covariant, + } +} diff --git a/tests/ui/impl-trait/precise-capturing/overcaptures-2024-but-fine.rs b/tests/ui/impl-trait/precise-capturing/overcaptures-2024-but-fine.rs new file mode 100644 index 00000000000..e30f785b0ae --- /dev/null +++ b/tests/ui/impl-trait/precise-capturing/overcaptures-2024-but-fine.rs @@ -0,0 +1,15 @@ +//@ check-pass + +#![deny(impl_trait_overcaptures)] + +struct Ctxt<'tcx>(&'tcx ()); + +// In `compute`, we don't care that we're "overcapturing" `'tcx` +// in edition 2024, because it can be shortened at the call site +// and we know it outlives `'_`. + +impl<'tcx> Ctxt<'tcx> { + fn compute(&self) -> impl Sized + '_ {} +} + +fn main() {}