From: Matthew Jasper Date: Mon, 22 Apr 2019 17:20:19 +0000 (+0100) Subject: Explain error when yielding a reference to a local variable X-Git-Url: https://git.lizzy.rs/?a=commitdiff_plain;h=d9ea132b7322cebd595598a0639cf6018816d454;p=rust.git Explain error when yielding a reference to a local variable --- diff --git a/src/librustc_mir/borrow_check/error_reporting.rs b/src/librustc_mir/borrow_check/error_reporting.rs index 3ab0996d3a1..956e8c56272 100644 --- a/src/librustc_mir/borrow_check/error_reporting.rs +++ b/src/librustc_mir/borrow_check/error_reporting.rs @@ -826,18 +826,21 @@ fn report_local_value_does_not_live_long_enough( let borrow_span = borrow_spans.var_or_use(); if let BorrowExplanation::MustBeValidFor { - category: ConstraintCategory::Return, + category, span, ref opt_place_desc, from_closure: false, .. } = explanation { - return self.report_cannot_return_reference_to_local( + if let Some(diag) = self.try_report_cannot_return_reference_to_local( borrow, borrow_span, span, + category, opt_place_desc.as_ref(), - ); + ) { + return diag; + } } let mut err = self.infcx.tcx.path_does_not_live_long_enough( @@ -1015,17 +1018,20 @@ fn report_temporary_value_does_not_live_long_enough( ); if let BorrowExplanation::MustBeValidFor { - category: ConstraintCategory::Return, + category, span, from_closure: false, .. } = explanation { - return self.report_cannot_return_reference_to_local( + if let Some(diag) = self.try_report_cannot_return_reference_to_local( borrow, proper_span, span, + category, None, - ); + ) { + return diag; + } } let tcx = self.infcx.tcx; @@ -1064,15 +1070,22 @@ fn report_temporary_value_does_not_live_long_enough( err } - fn report_cannot_return_reference_to_local( + fn try_report_cannot_return_reference_to_local( &self, borrow: &BorrowData<'tcx>, borrow_span: Span, return_span: Span, + category: ConstraintCategory, opt_place_desc: Option<&String>, - ) -> DiagnosticBuilder<'cx> { + ) -> Option> { let tcx = self.infcx.tcx; + let return_kind = match category { + ConstraintCategory::Return => "return", + ConstraintCategory::Yield => "yield", + _ => return None, + }; + // FIXME use a better heuristic than Spans let reference_desc = if return_span == self.mir.source_info(borrow.reserve_location).span { "reference to" @@ -1110,7 +1123,7 @@ fn report_cannot_return_reference_to_local( let local = if let Place::Base(PlaceBase::Local(local)) = *root_place { local } else { - bug!("report_cannot_return_reference_to_local: not a local") + bug!("try_report_cannot_return_reference_to_local: not a local") }; match self.mir.local_kind(local) { LocalKind::ReturnPointer | LocalKind::Temp => { @@ -1131,6 +1144,7 @@ fn report_cannot_return_reference_to_local( let mut err = tcx.cannot_return_reference_to_local( return_span, + return_kind, reference_desc, &place_desc, Origin::Mir, @@ -1140,7 +1154,7 @@ fn report_cannot_return_reference_to_local( err.span_label(borrow_span, note); } - err + Some(err) } fn report_escaping_closure_capture( diff --git a/src/librustc_mir/borrow_check/nll/explain_borrow/mod.rs b/src/librustc_mir/borrow_check/nll/explain_borrow/mod.rs index 5ad54080c5a..5b1c64039be 100644 --- a/src/librustc_mir/borrow_check/nll/explain_borrow/mod.rs +++ b/src/librustc_mir/borrow_check/nll/explain_borrow/mod.rs @@ -313,9 +313,13 @@ pub(in crate::borrow_check) fn explain_why_borrow_contains_point( opt_place_desc, } } else { + debug!("explain_why_borrow_contains_point: \ + Could not generate a region name"); BorrowExplanation::Unexplained } } else { + debug!("explain_why_borrow_contains_point: \ + Could not generate an error region vid"); BorrowExplanation::Unexplained } } diff --git a/src/librustc_mir/borrow_check/nll/region_infer/error_reporting/region_name.rs b/src/librustc_mir/borrow_check/nll/region_infer/error_reporting/region_name.rs index 362214d3257..e72d4c9e3d5 100644 --- a/src/librustc_mir/borrow_check/nll/region_infer/error_reporting/region_name.rs +++ b/src/librustc_mir/borrow_check/nll/region_infer/error_reporting/region_name.rs @@ -32,6 +32,7 @@ MatchedAdtAndSegment(Span), AnonRegionFromUpvar(Span, String), AnonRegionFromOutput(Span, String, String), + AnonRegionFromYieldTy(Span, String), } impl RegionName { @@ -46,7 +47,8 @@ impl RegionName { RegionNameSource::MatchedHirTy(..) | RegionNameSource::MatchedAdtAndSegment(..) | RegionNameSource::AnonRegionFromUpvar(..) | - RegionNameSource::AnonRegionFromOutput(..) => false, + RegionNameSource::AnonRegionFromOutput(..) | + RegionNameSource::AnonRegionFromYieldTy(..) => false, } } @@ -103,6 +105,12 @@ impl RegionName { format!("return type{} is {}", mir_description, type_name), ); }, + RegionNameSource::AnonRegionFromYieldTy(span, type_name) => { + diag.span_label( + *span, + format!("yield type is {}", type_name), + ); + } RegionNameSource::Static => {}, } } @@ -167,6 +175,11 @@ impl<'tcx> RegionInferenceContext<'tcx> { self.give_name_if_anonymous_region_appears_in_output( infcx, mir, mir_def_id, fr, counter, ) + }) + .or_else(|| { + self.give_name_if_anonymous_region_appears_in_yield_ty( + infcx, mir, mir_def_id, fr, counter, + ) }); debug!("give_region_a_name: gave name {:?}", value); @@ -673,10 +686,7 @@ fn give_name_if_anonymous_region_appears_in_output( "give_name_if_anonymous_region_appears_in_output: return_ty = {:?}", return_ty ); - if !infcx - .tcx - .any_free_region_meets(&return_ty, |r| r.to_region_vid() == fr) - { + if !tcx.any_free_region_meets(&return_ty, |r| r.to_region_vid() == fr) { return None; } @@ -721,6 +731,57 @@ fn give_name_if_anonymous_region_appears_in_output( }) } + fn give_name_if_anonymous_region_appears_in_yield_ty( + &self, + infcx: &InferCtxt<'_, '_, 'tcx>, + mir: &Mir<'tcx>, + mir_def_id: DefId, + fr: RegionVid, + counter: &mut usize, + ) -> Option { + // Note: generators from `async fn` yield `()`, so we don't have to + // worry about them here. + let yield_ty = self.universal_regions.yield_ty?; + debug!( + "give_name_if_anonymous_region_appears_in_yield_ty: yield_ty = {:?}", + yield_ty, + ); + + let tcx = infcx.tcx; + + if !tcx.any_free_region_meets(&yield_ty, |r| r.to_region_vid() == fr) { + return None; + } + + let mut highlight = RegionHighlightMode::default(); + highlight.highlighting_region_vid(fr, *counter); + let type_name = infcx.extract_type_name(&yield_ty, Some(highlight)); + + let mir_node_id = tcx.hir().as_local_node_id(mir_def_id).expect("non-local mir"); + + let yield_span = match tcx.hir().get(mir_node_id) { + hir::Node::Expr(hir::Expr { + node: hir::ExprKind::Closure(_, _, _, span, _), + .. + }) => ( + tcx.sess.source_map().end_point(*span) + ), + _ => mir.span, + }; + + debug!( + "give_name_if_anonymous_region_appears_in_yield_ty: \ + type_name = {:?}, yield_span = {:?}", + yield_span, + type_name, + ); + + Some(RegionName { + name: self.synthesize_region_name(counter), + source: RegionNameSource::AnonRegionFromYieldTy(yield_span, type_name), + }) + } + /// Creates a synthetic region named `'1`, incrementing the /// counter. fn synthesize_region_name(&self, counter: &mut usize) -> InternedString { diff --git a/src/librustc_mir/util/borrowck_errors.rs b/src/librustc_mir/util/borrowck_errors.rs index e334e27cc85..0cbe39ab6d4 100644 --- a/src/librustc_mir/util/borrowck_errors.rs +++ b/src/librustc_mir/util/borrowck_errors.rs @@ -650,6 +650,7 @@ fn path_does_not_live_long_enough( fn cannot_return_reference_to_local( self, span: Span, + return_kind: &str, reference_desc: &str, path_desc: &str, o: Origin, @@ -658,7 +659,8 @@ fn cannot_return_reference_to_local( self, span, E0515, - "cannot return {REFERENCE} {LOCAL}{OGN}", + "cannot {RETURN} {REFERENCE} {LOCAL}{OGN}", + RETURN=return_kind, REFERENCE=reference_desc, LOCAL=path_desc, OGN = o @@ -666,7 +668,7 @@ fn cannot_return_reference_to_local( err.span_label( span, - format!("returns a {} data owned by the current function", reference_desc), + format!("{}s a {} data owned by the current function", return_kind, reference_desc), ); self.cancel_if_wrong_origin(err, o) diff --git a/src/test/ui/nll/issue-55850.rs b/src/test/ui/nll/issue-55850.rs index 8a016bf8779..a8f7299f899 100644 --- a/src/test/ui/nll/issue-55850.rs +++ b/src/test/ui/nll/issue-55850.rs @@ -25,7 +25,7 @@ fn next(&mut self) -> Option { fn bug<'a>() -> impl Iterator { GenIter(move || { let mut s = String::new(); - yield &s[..] //~ ERROR `s` does not live long enough [E0597] + yield &s[..] //~ ERROR cannot yield value referencing local variable `s` [E0515] //~| ERROR borrow may still be in use when generator yields }) } diff --git a/src/test/ui/nll/issue-55850.stderr b/src/test/ui/nll/issue-55850.stderr index 66c2995efc8..86a8cdc42ff 100644 --- a/src/test/ui/nll/issue-55850.stderr +++ b/src/test/ui/nll/issue-55850.stderr @@ -1,11 +1,11 @@ -error[E0597]: `s` does not live long enough - --> $DIR/issue-55850.rs:28:16 +error[E0515]: cannot yield value referencing local variable `s` + --> $DIR/issue-55850.rs:28:9 | LL | yield &s[..] - | ^ borrowed value does not live long enough -LL | -LL | }) - | - `s` dropped here while still borrowed + | ^^^^^^^-^^^^ + | | | + | | `s` is borrowed here + | yields a value referencing data owned by the current function error[E0626]: borrow may still be in use when generator yields --> $DIR/issue-55850.rs:28:16 @@ -15,5 +15,5 @@ LL | yield &s[..] error: aborting due to 2 previous errors -Some errors have detailed explanations: E0597, E0626. -For more information about an error, try `rustc --explain E0597`. +Some errors have detailed explanations: E0515, E0626. +For more information about an error, try `rustc --explain E0515`.