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Auto merge of #131186 - compiler-errors:precise-capturing-borrowck, r…
…=estebank Try to point out when edition 2024 lifetime capture rules cause borrowck issues Lifetime capture rules in 2024 are modified to capture more lifetimes, which sometimes lead to some non-local borrowck errors. This PR attempts to link these back together with a useful note pointing out the capture rule changes. This is not a blocking concern, but I'd appreciate feedback (though, again, I'd like to stress that I don't want to block this PR on this): I'm worried about this note drowning in the sea of other diagnostics that borrowck emits. I was tempted to change the level of the note to `.span_warn` just so it would show up in a different color. Thoughts? Fixes #130545 Opening as a draft first since it's stacked on #131183. r? `@ghost`
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224
compiler/rustc_borrowck/src/diagnostics/opaque_suggestions.rs
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,224 @@ | ||
| #![allow(rustc::diagnostic_outside_of_impl)] | ||
| #![allow(rustc::untranslatable_diagnostic)] | ||
|
|
||
| use std::ops::ControlFlow; | ||
|
|
||
| use either::Either; | ||
| use rustc_data_structures::fx::FxIndexSet; | ||
| use rustc_errors::{Applicability, Diag}; | ||
| use rustc_hir as hir; | ||
| use rustc_hir::def_id::DefId; | ||
| use rustc_middle::mir::{self, ConstraintCategory, Location}; | ||
| use rustc_middle::ty::{ | ||
| self, Ty, TyCtxt, TypeSuperVisitable, TypeVisitable, TypeVisitableExt, TypeVisitor, | ||
| }; | ||
| use rustc_span::Symbol; | ||
|
|
||
| use crate::MirBorrowckCtxt; | ||
| use crate::borrow_set::BorrowData; | ||
| use crate::consumers::RegionInferenceContext; | ||
| use crate::type_check::Locations; | ||
|
|
||
| impl<'infcx, 'tcx> MirBorrowckCtxt<'_, 'infcx, 'tcx> { | ||
| /// Try to note when an opaque is involved in a borrowck error and that | ||
| /// opaque captures lifetimes due to edition 2024. | ||
| // FIXME: This code is otherwise somewhat general, and could easily be adapted | ||
| // to explain why other things overcapture... like async fn and RPITITs. | ||
| pub(crate) fn note_due_to_edition_2024_opaque_capture_rules( | ||
| &self, | ||
| borrow: &BorrowData<'tcx>, | ||
| diag: &mut Diag<'_>, | ||
| ) { | ||
| // We look at all the locals. Why locals? Because it's the best thing | ||
| // I could think of that's correlated with the *instantiated* higer-ranked | ||
| // binder for calls, since we don't really store those anywhere else. | ||
| for ty in self.body.local_decls.iter().map(|local| local.ty) { | ||
| if !ty.has_opaque_types() { | ||
| continue; | ||
| } | ||
|
|
||
| let tcx = self.infcx.tcx; | ||
| let ControlFlow::Break((opaque_def_id, offending_region_idx, location)) = ty | ||
| .visit_with(&mut FindOpaqueRegion { | ||
| regioncx: &self.regioncx, | ||
| tcx, | ||
| borrow_region: borrow.region, | ||
| }) | ||
| else { | ||
| continue; | ||
| }; | ||
|
|
||
| // If an opaque explicitly captures a lifetime, then no need to point it out. | ||
| // FIXME: We should be using a better heuristic for `use<>`. | ||
| if tcx.rendered_precise_capturing_args(opaque_def_id).is_some() { | ||
| continue; | ||
| } | ||
|
|
||
| // If one of the opaque's bounds mentions the region, then no need to | ||
| // point it out, since it would've been captured on edition 2021 as well. | ||
| // | ||
| // Also, while we're at it, collect all the lifetimes that the opaque | ||
| // *does* mention. We'll use that for the `+ use<'a>` suggestion below. | ||
| let mut visitor = CheckExplicitRegionMentionAndCollectGenerics { | ||
| tcx, | ||
| offending_region_idx, | ||
| seen_opaques: [opaque_def_id].into_iter().collect(), | ||
| seen_lifetimes: Default::default(), | ||
| }; | ||
| if tcx | ||
| .explicit_item_bounds(opaque_def_id) | ||
| .skip_binder() | ||
| .visit_with(&mut visitor) | ||
| .is_break() | ||
| { | ||
| continue; | ||
| } | ||
|
|
||
| // If we successfully located a terminator, then point it out | ||
| // and provide a suggestion if it's local. | ||
| match self.body.stmt_at(location) { | ||
| Either::Right(mir::Terminator { source_info, .. }) => { | ||
| diag.span_note( | ||
| source_info.span, | ||
| "this call may capture more lifetimes than intended, \ | ||
| because Rust 2024 has adjusted the `impl Trait` lifetime capture rules", | ||
| ); | ||
| let mut seen_generics: Vec<_> = | ||
| visitor.seen_lifetimes.iter().map(ToString::to_string).collect(); | ||
| // Capture all in-scope ty/const params. | ||
| seen_generics.extend( | ||
| ty::GenericArgs::identity_for_item(tcx, opaque_def_id) | ||
| .iter() | ||
| .filter(|arg| { | ||
| matches!( | ||
| arg.unpack(), | ||
| ty::GenericArgKind::Type(_) | ty::GenericArgKind::Const(_) | ||
| ) | ||
| }) | ||
| .map(|arg| arg.to_string()), | ||
| ); | ||
| if opaque_def_id.is_local() { | ||
| diag.span_suggestion_verbose( | ||
| tcx.def_span(opaque_def_id).shrink_to_hi(), | ||
| "add a precise capturing bound to avoid overcapturing", | ||
| format!(" + use<{}>", seen_generics.join(", ")), | ||
| Applicability::MaybeIncorrect, | ||
| ); | ||
| } else { | ||
| diag.span_help( | ||
| tcx.def_span(opaque_def_id), | ||
| format!( | ||
| "if you can modify this crate, add a precise \ | ||
| capturing bound to avoid overcapturing: `+ use<{}>`", | ||
| seen_generics.join(", ") | ||
| ), | ||
| ); | ||
| } | ||
| return; | ||
| } | ||
| Either::Left(_) => {} | ||
| } | ||
| } | ||
| } | ||
| } | ||
|
|
||
| /// This visitor contains the bulk of the logic for this lint. | ||
| struct FindOpaqueRegion<'a, 'tcx> { | ||
| tcx: TyCtxt<'tcx>, | ||
| regioncx: &'a RegionInferenceContext<'tcx>, | ||
| borrow_region: ty::RegionVid, | ||
| } | ||
|
|
||
| impl<'tcx> TypeVisitor<TyCtxt<'tcx>> for FindOpaqueRegion<'_, 'tcx> { | ||
| type Result = ControlFlow<(DefId, usize, Location), ()>; | ||
|
|
||
| fn visit_ty(&mut self, ty: Ty<'tcx>) -> Self::Result { | ||
| // If we find an opaque in a local ty, then for each of its captured regions, | ||
| // try to find a path between that captured regions and our borrow region... | ||
| if let ty::Alias(ty::Opaque, opaque) = *ty.kind() | ||
| && let hir::OpaqueTyOrigin::FnReturn { parent, in_trait_or_impl: None } = | ||
| self.tcx.opaque_ty_origin(opaque.def_id) | ||
| { | ||
| let variances = self.tcx.variances_of(opaque.def_id); | ||
| for (idx, (arg, variance)) in std::iter::zip(opaque.args, variances).enumerate() { | ||
| // Skip uncaptured args. | ||
| if *variance == ty::Bivariant { | ||
| continue; | ||
| } | ||
| // We only care about regions. | ||
| let Some(opaque_region) = arg.as_region() else { | ||
| continue; | ||
| }; | ||
| // Don't try to convert a late-bound region, which shouldn't exist anyways (yet). | ||
| if opaque_region.is_bound() { | ||
| continue; | ||
| } | ||
| let opaque_region_vid = self.regioncx.to_region_vid(opaque_region); | ||
|
|
||
| // Find a path between the borrow region and our opaque capture. | ||
| if let Some((path, _)) = | ||
| self.regioncx.find_constraint_paths_between_regions(self.borrow_region, |r| { | ||
| r == opaque_region_vid | ||
| }) | ||
| { | ||
| for constraint in path { | ||
| // If we find a call in this path, then check if it defines the opaque. | ||
| if let ConstraintCategory::CallArgument(Some(call_ty)) = constraint.category | ||
| && let ty::FnDef(call_def_id, _) = *call_ty.kind() | ||
| // This function defines the opaque :D | ||
| && call_def_id == parent | ||
| && let Locations::Single(location) = constraint.locations | ||
| { | ||
| return ControlFlow::Break((opaque.def_id, idx, location)); | ||
| } | ||
| } | ||
| } | ||
| } | ||
| } | ||
|
|
||
| ty.super_visit_with(self) | ||
| } | ||
| } | ||
|
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||
| struct CheckExplicitRegionMentionAndCollectGenerics<'tcx> { | ||
| tcx: TyCtxt<'tcx>, | ||
| offending_region_idx: usize, | ||
| seen_opaques: FxIndexSet<DefId>, | ||
| seen_lifetimes: FxIndexSet<Symbol>, | ||
| } | ||
|
|
||
| impl<'tcx> TypeVisitor<TyCtxt<'tcx>> for CheckExplicitRegionMentionAndCollectGenerics<'tcx> { | ||
| type Result = ControlFlow<(), ()>; | ||
|
|
||
| fn visit_ty(&mut self, ty: Ty<'tcx>) -> Self::Result { | ||
| match *ty.kind() { | ||
| ty::Alias(ty::Opaque, opaque) => { | ||
| if self.seen_opaques.insert(opaque.def_id) { | ||
| for (bound, _) in self | ||
| .tcx | ||
| .explicit_item_bounds(opaque.def_id) | ||
| .iter_instantiated_copied(self.tcx, opaque.args) | ||
| { | ||
| bound.visit_with(self)?; | ||
| } | ||
| } | ||
| ControlFlow::Continue(()) | ||
| } | ||
| _ => ty.super_visit_with(self), | ||
| } | ||
| } | ||
|
|
||
| fn visit_region(&mut self, r: ty::Region<'tcx>) -> Self::Result { | ||
| match r.kind() { | ||
| ty::ReEarlyParam(param) => { | ||
| if param.index as usize == self.offending_region_idx { | ||
| ControlFlow::Break(()) | ||
| } else { | ||
| self.seen_lifetimes.insert(param.name); | ||
| ControlFlow::Continue(()) | ||
| } | ||
| } | ||
| _ => ControlFlow::Continue(()), | ||
| } | ||
| } | ||
| } |
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