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Try to point out when edition 2024 lifetime capture rules cause borrowck issues #131186
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Oct 31, 2024
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224 changes: 224 additions & 0 deletions
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) | ||
| } | ||
| } | ||
|
|
||
| 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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Why isn't this a structured suggestion? Edit: because it's checking if it's not the current crate, got it.