diff options
Diffstat (limited to '')
| -rw-r--r-- | compiler/rustc_borrowck/src/diagnostics/explain_borrow.rs | 218 |
1 files changed, 56 insertions, 162 deletions
diff --git a/compiler/rustc_borrowck/src/diagnostics/explain_borrow.rs b/compiler/rustc_borrowck/src/diagnostics/explain_borrow.rs index 72aee0267..582d683dd 100644 --- a/compiler/rustc_borrowck/src/diagnostics/explain_borrow.rs +++ b/compiler/rustc_borrowck/src/diagnostics/explain_borrow.rs @@ -1,8 +1,5 @@ //! Print diagnostics to explain why values are borrowed. -use std::collections::VecDeque; - -use rustc_data_structures::fx::FxHashSet; use rustc_errors::{Applicability, Diagnostic}; use rustc_index::vec::IndexVec; use rustc_infer::infer::NllRegionVariableOrigin; @@ -15,7 +12,7 @@ use rustc_middle::ty::{self, RegionVid, TyCtxt}; use rustc_span::symbol::{kw, Symbol}; use rustc_span::{sym, DesugaringKind, Span}; -use crate::region_infer::BlameConstraint; +use crate::region_infer::{BlameConstraint, ExtraConstraintInfo}; use crate::{ borrow_set::BorrowData, nll::ConstraintDescription, region_infer::Cause, MirBorrowckCtxt, WriteKind, @@ -38,6 +35,7 @@ pub(crate) enum BorrowExplanation<'tcx> { span: Span, region_name: RegionName, opt_place_desc: Option<String>, + extra_info: Vec<ExtraConstraintInfo>, }, Unexplained, } @@ -243,6 +241,7 @@ impl<'tcx> BorrowExplanation<'tcx> { ref region_name, ref opt_place_desc, from_closure: _, + ref extra_info, } => { region_name.highlight_region_name(err); @@ -268,18 +267,30 @@ impl<'tcx> BorrowExplanation<'tcx> { ); }; + for extra in extra_info { + match extra { + ExtraConstraintInfo::PlaceholderFromPredicate(span) => { + err.span_note(*span, format!("due to current limitations in the borrow checker, this implies a `'static` lifetime")); + } + } + } + self.add_lifetime_bound_suggestion_to_diagnostic(err, &category, span, region_name); } _ => {} } } - pub(crate) fn add_lifetime_bound_suggestion_to_diagnostic( + + fn add_lifetime_bound_suggestion_to_diagnostic( &self, err: &mut Diagnostic, category: &ConstraintCategory<'tcx>, span: Span, region_name: &RegionName, ) { + if !span.is_desugaring(DesugaringKind::OpaqueTy) { + return; + } if let ConstraintCategory::OpaqueType = category { let suggestable_name = if region_name.was_named() { region_name.name } else { kw::UnderscoreLifetime }; @@ -305,18 +316,17 @@ impl<'cx, 'tcx> MirBorrowckCtxt<'cx, 'tcx> { &self, borrow_region: RegionVid, outlived_region: RegionVid, - ) -> (ConstraintCategory<'tcx>, bool, Span, Option<RegionName>) { - let BlameConstraint { category, from_closure, cause, variance_info: _ } = - self.regioncx.best_blame_constraint( - &self.body, - borrow_region, - NllRegionVariableOrigin::FreeRegion, - |r| self.regioncx.provides_universal_region(r, borrow_region, outlived_region), - ); + ) -> (ConstraintCategory<'tcx>, bool, Span, Option<RegionName>, Vec<ExtraConstraintInfo>) { + let (blame_constraint, extra_info) = self.regioncx.best_blame_constraint( + borrow_region, + NllRegionVariableOrigin::FreeRegion, + |r| self.regioncx.provides_universal_region(r, borrow_region, outlived_region), + ); + let BlameConstraint { category, from_closure, cause, .. } = blame_constraint; let outlived_fr_name = self.give_region_a_name(outlived_region); - (category, from_closure, cause.span, outlived_fr_name) + (category, from_closure, cause.span, outlived_fr_name, extra_info) } /// Returns structured explanation for *why* the borrow contains the @@ -332,37 +342,51 @@ impl<'cx, 'tcx> MirBorrowckCtxt<'cx, 'tcx> { /// - second half is the place being accessed /// /// [d]: https://rust-lang.github.io/rfcs/2094-nll.html#leveraging-intuition-framing-errors-in-terms-of-points + #[instrument(level = "debug", skip(self))] pub(crate) fn explain_why_borrow_contains_point( &self, location: Location, borrow: &BorrowData<'tcx>, kind_place: Option<(WriteKind, Place<'tcx>)>, ) -> BorrowExplanation<'tcx> { - debug!( - "explain_why_borrow_contains_point(location={:?}, borrow={:?}, kind_place={:?})", - location, borrow, kind_place - ); - let regioncx = &self.regioncx; let body: &Body<'_> = &self.body; let tcx = self.infcx.tcx; let borrow_region_vid = borrow.region; - debug!("explain_why_borrow_contains_point: borrow_region_vid={:?}", borrow_region_vid); - - let region_sub = self.regioncx.find_sub_region_live_at(borrow_region_vid, location); - debug!("explain_why_borrow_contains_point: region_sub={:?}", region_sub); + debug!(?borrow_region_vid); + + let mut region_sub = self.regioncx.find_sub_region_live_at(borrow_region_vid, location); + debug!(?region_sub); + + let mut use_location = location; + let mut use_in_later_iteration_of_loop = false; + + if region_sub == borrow_region_vid { + // When `region_sub` is the same as `borrow_region_vid` (the location where the borrow is + // issued is the same location that invalidates the reference), this is likely a loop iteration + // - in this case, try using the loop terminator location in `find_sub_region_live_at`. + if let Some(loop_terminator_location) = + regioncx.find_loop_terminator_location(borrow.region, body) + { + region_sub = self + .regioncx + .find_sub_region_live_at(borrow_region_vid, loop_terminator_location); + debug!("explain_why_borrow_contains_point: region_sub in loop={:?}", region_sub); + use_location = loop_terminator_location; + use_in_later_iteration_of_loop = true; + } + } - match find_use::find(body, regioncx, tcx, region_sub, location) { + match find_use::find(body, regioncx, tcx, region_sub, use_location) { Some(Cause::LiveVar(local, location)) => { let span = body.source_info(location).span; let spans = self .move_spans(Place::from(local).as_ref(), location) .or_else(|| self.borrow_spans(span, location)); - let borrow_location = location; - if self.is_use_in_later_iteration_of_loop(borrow_location, location) { - let later_use = self.later_use_kind(borrow, spans, location); + if use_in_later_iteration_of_loop { + let later_use = self.later_use_kind(borrow, spans, use_location); BorrowExplanation::UsedLaterInLoop(later_use.0, later_use.1, later_use.2) } else { // Check if the location represents a `FakeRead`, and adapt the error @@ -392,7 +416,7 @@ impl<'cx, 'tcx> MirBorrowckCtxt<'cx, 'tcx> { None => { if let Some(region) = self.to_error_region_vid(borrow_region_vid) { - let (category, from_closure, span, region_name) = + let (category, from_closure, span, region_name, extra_info) = self.free_region_constraint_info(borrow_region_vid, region); if let Some(region_name) = region_name { let opt_place_desc = self.describe_place(borrow.borrowed_place.as_ref()); @@ -402,150 +426,20 @@ impl<'cx, 'tcx> MirBorrowckCtxt<'cx, 'tcx> { span, region_name, opt_place_desc, + extra_info, } } else { - debug!( - "explain_why_borrow_contains_point: \ - Could not generate a region name" - ); + debug!("Could not generate a region name"); BorrowExplanation::Unexplained } } else { - debug!( - "explain_why_borrow_contains_point: \ - Could not generate an error region vid" - ); + debug!("Could not generate an error region vid"); BorrowExplanation::Unexplained } } } } - /// true if `borrow_location` can reach `use_location` by going through a loop and - /// `use_location` is also inside of that loop - fn is_use_in_later_iteration_of_loop( - &self, - borrow_location: Location, - use_location: Location, - ) -> bool { - let back_edge = self.reach_through_backedge(borrow_location, use_location); - back_edge.map_or(false, |back_edge| self.can_reach_head_of_loop(use_location, back_edge)) - } - - /// Returns the outmost back edge if `from` location can reach `to` location passing through - /// that back edge - fn reach_through_backedge(&self, from: Location, to: Location) -> Option<Location> { - let mut visited_locations = FxHashSet::default(); - let mut pending_locations = VecDeque::new(); - visited_locations.insert(from); - pending_locations.push_back(from); - debug!("reach_through_backedge: from={:?} to={:?}", from, to,); - - let mut outmost_back_edge = None; - while let Some(location) = pending_locations.pop_front() { - debug!( - "reach_through_backedge: location={:?} outmost_back_edge={:?} - pending_locations={:?} visited_locations={:?}", - location, outmost_back_edge, pending_locations, visited_locations - ); - - if location == to && outmost_back_edge.is_some() { - // We've managed to reach the use location - debug!("reach_through_backedge: found!"); - return outmost_back_edge; - } - - let block = &self.body.basic_blocks()[location.block]; - - if location.statement_index < block.statements.len() { - let successor = location.successor_within_block(); - if visited_locations.insert(successor) { - pending_locations.push_back(successor); - } - } else { - pending_locations.extend( - block - .terminator() - .successors() - .map(|bb| Location { statement_index: 0, block: bb }) - .filter(|s| visited_locations.insert(*s)) - .map(|s| { - if self.is_back_edge(location, s) { - match outmost_back_edge { - None => { - outmost_back_edge = Some(location); - } - - Some(back_edge) - if location.dominates(back_edge, &self.dominators) => - { - outmost_back_edge = Some(location); - } - - Some(_) => {} - } - } - - s - }), - ); - } - } - - None - } - - /// true if `from` location can reach `loop_head` location and `loop_head` dominates all the - /// intermediate nodes - fn can_reach_head_of_loop(&self, from: Location, loop_head: Location) -> bool { - self.find_loop_head_dfs(from, loop_head, &mut FxHashSet::default()) - } - - fn find_loop_head_dfs( - &self, - from: Location, - loop_head: Location, - visited_locations: &mut FxHashSet<Location>, - ) -> bool { - visited_locations.insert(from); - - if from == loop_head { - return true; - } - - if loop_head.dominates(from, &self.dominators) { - let block = &self.body.basic_blocks()[from.block]; - - if from.statement_index < block.statements.len() { - let successor = from.successor_within_block(); - - if !visited_locations.contains(&successor) - && self.find_loop_head_dfs(successor, loop_head, visited_locations) - { - return true; - } - } else { - for bb in block.terminator().successors() { - let successor = Location { statement_index: 0, block: bb }; - - if !visited_locations.contains(&successor) - && self.find_loop_head_dfs(successor, loop_head, visited_locations) - { - return true; - } - } - } - } - - false - } - - /// True if an edge `source -> target` is a backedge -- in other words, if the target - /// dominates the source. - fn is_back_edge(&self, source: Location, target: Location) -> bool { - target.dominates(source, &self.dominators) - } - /// Determine how the borrow was later used. /// First span returned points to the location of the conflicting use /// Second span if `Some` is returned in the case of closures and points @@ -564,7 +458,7 @@ impl<'cx, 'tcx> MirBorrowckCtxt<'cx, 'tcx> { UseSpans::PatUse(span) | UseSpans::OtherUse(span) | UseSpans::FnSelfUse { var_span: span, .. } => { - let block = &self.body.basic_blocks()[location.block]; + let block = &self.body.basic_blocks[location.block]; let kind = if let Some(&Statement { kind: StatementKind::FakeRead(box (FakeReadCause::ForLet(_), _)), |