diff options
8 files changed, 132 insertions, 11 deletions
diff --git a/compiler/rustc_borrowck/src/diagnostics/explain_borrow.rs b/compiler/rustc_borrowck/src/diagnostics/explain_borrow.rs index 8a930ca59a3..78e9e104bda 100644 --- a/compiler/rustc_borrowck/src/diagnostics/explain_borrow.rs +++ b/compiler/rustc_borrowck/src/diagnostics/explain_borrow.rs @@ -5,12 +5,13 @@ use rustc_hir as hir; use rustc_hir::intravisit::Visitor; use rustc_index::IndexSlice; use rustc_infer::infer::NllRegionVariableOrigin; +use rustc_middle::middle::resolve_bound_vars::ObjectLifetimeDefault; use rustc_middle::mir::{ Body, CallSource, CastKind, ConstraintCategory, FakeReadCause, Local, LocalInfo, Location, Operand, Place, Rvalue, Statement, StatementKind, TerminatorKind, }; use rustc_middle::ty::adjustment::PointerCoercion; -use rustc_middle::ty::{self, RegionVid, TyCtxt}; +use rustc_middle::ty::{self, RegionVid, Ty, TyCtxt}; use rustc_span::symbol::{kw, Symbol}; use rustc_span::{sym, DesugaringKind, Span}; use rustc_trait_selection::traits::error_reporting::FindExprBySpan; @@ -290,12 +291,69 @@ impl<'tcx> BorrowExplanation<'tcx> { } } + if let ConstraintCategory::Cast { unsize_to: Some(unsize_ty) } = category { + self.add_object_lifetime_default_note(tcx, err, unsize_ty); + } self.add_lifetime_bound_suggestion_to_diagnostic(err, &category, span, region_name); } _ => {} } } + fn add_object_lifetime_default_note( + &self, + tcx: TyCtxt<'tcx>, + err: &mut Diagnostic, + unsize_ty: Ty<'tcx>, + ) { + if let ty::Adt(def, args) = unsize_ty.kind() { + // We try to elaborate the object lifetime defaults and present those to the user. This should + // make it clear where the region constraint is coming from. + let generics = tcx.generics_of(def.did()); + + let mut has_dyn = false; + let mut failed = false; + + let elaborated_args = std::iter::zip(*args, &generics.params).map(|(arg, param)| { + if let Some(ty::Dynamic(obj, _, ty::DynKind::Dyn)) = arg.as_type().map(Ty::kind) { + let default = tcx.object_lifetime_default(param.def_id); + + let re_static = tcx.lifetimes.re_static; + + let implied_region = match default { + // This is not entirely precise. + ObjectLifetimeDefault::Empty => re_static, + ObjectLifetimeDefault::Ambiguous => { + failed = true; + re_static + } + ObjectLifetimeDefault::Param(param_def_id) => { + let index = generics.param_def_id_to_index[¶m_def_id] as usize; + args.get(index).and_then(|arg| arg.as_region()).unwrap_or_else(|| { + failed = true; + re_static + }) + } + ObjectLifetimeDefault::Static => re_static, + }; + + has_dyn = true; + + Ty::new_dynamic(tcx, obj, implied_region, ty::DynKind::Dyn).into() + } else { + arg + } + }); + let elaborated_ty = Ty::new_adt(tcx, *def, tcx.mk_args_from_iter(elaborated_args)); + + if has_dyn && !failed { + err.note(format!( + "due to object lifetime defaults, `{unsize_ty}` actually means `{elaborated_ty}`" + )); + } + } + } + fn add_lifetime_bound_suggestion_to_diagnostic( &self, err: &mut Diagnostic, diff --git a/compiler/rustc_borrowck/src/diagnostics/region_errors.rs b/compiler/rustc_borrowck/src/diagnostics/region_errors.rs index a0a809123c0..230c22045c7 100644 --- a/compiler/rustc_borrowck/src/diagnostics/region_errors.rs +++ b/compiler/rustc_borrowck/src/diagnostics/region_errors.rs @@ -53,7 +53,7 @@ impl<'tcx> ConstraintDescription for ConstraintCategory<'tcx> { ConstraintCategory::Yield => "yielding this value ", ConstraintCategory::UseAsConst => "using this value as a constant ", ConstraintCategory::UseAsStatic => "using this value as a static ", - ConstraintCategory::Cast => "cast ", + ConstraintCategory::Cast { .. } => "cast ", ConstraintCategory::CallArgument(_) => "argument ", ConstraintCategory::TypeAnnotation => "type annotation ", ConstraintCategory::ClosureBounds => "closure body ", diff --git a/compiler/rustc_borrowck/src/type_check/mod.rs b/compiler/rustc_borrowck/src/type_check/mod.rs index 608d010394f..9d05b0ec699 100644 --- a/compiler/rustc_borrowck/src/type_check/mod.rs +++ b/compiler/rustc_borrowck/src/type_check/mod.rs @@ -1934,7 +1934,7 @@ impl<'a, 'tcx> TypeChecker<'a, 'tcx> { *ty, ty_fn_ptr_from, location.to_locations(), - ConstraintCategory::Cast, + ConstraintCategory::Cast { unsize_to: None }, ) { span_mirbug!( self, @@ -1959,7 +1959,7 @@ impl<'a, 'tcx> TypeChecker<'a, 'tcx> { *ty, ty_fn_ptr_from, location.to_locations(), - ConstraintCategory::Cast, + ConstraintCategory::Cast { unsize_to: None }, ) { span_mirbug!( self, @@ -1988,7 +1988,7 @@ impl<'a, 'tcx> TypeChecker<'a, 'tcx> { *ty, ty_fn_ptr_from, location.to_locations(), - ConstraintCategory::Cast, + ConstraintCategory::Cast { unsize_to: None }, ) { span_mirbug!( self, @@ -2013,7 +2013,15 @@ impl<'a, 'tcx> TypeChecker<'a, 'tcx> { self.prove_trait_ref( trait_ref, location.to_locations(), - ConstraintCategory::Cast, + ConstraintCategory::Cast { + unsize_to: Some(tcx.fold_regions(ty, |r, _| { + if let ty::ReVar(_) = r.kind() { + tcx.lifetimes.re_erased + } else { + r + } + })), + }, ); } @@ -2033,7 +2041,7 @@ impl<'a, 'tcx> TypeChecker<'a, 'tcx> { .iter() .map(|predicate| predicate.with_self_ty(tcx, self_ty)), location.to_locations(), - ConstraintCategory::Cast, + ConstraintCategory::Cast { unsize_to: None }, ); let outlives_predicate = tcx.mk_predicate(Binder::dummy( @@ -2044,7 +2052,7 @@ impl<'a, 'tcx> TypeChecker<'a, 'tcx> { self.prove_predicate( outlives_predicate, location.to_locations(), - ConstraintCategory::Cast, + ConstraintCategory::Cast { unsize_to: None }, ); } @@ -2065,7 +2073,7 @@ impl<'a, 'tcx> TypeChecker<'a, 'tcx> { *ty_from, *ty_to, location.to_locations(), - ConstraintCategory::Cast, + ConstraintCategory::Cast { unsize_to: None }, ) { span_mirbug!( self, @@ -2131,7 +2139,7 @@ impl<'a, 'tcx> TypeChecker<'a, 'tcx> { *ty_elem, *ty_to, location.to_locations(), - ConstraintCategory::Cast, + ConstraintCategory::Cast { unsize_to: None }, ) { span_mirbug!( self, diff --git a/compiler/rustc_middle/src/mir/query.rs b/compiler/rustc_middle/src/mir/query.rs index 0540eb0efd6..078923ab5be 100644 --- a/compiler/rustc_middle/src/mir/query.rs +++ b/compiler/rustc_middle/src/mir/query.rs @@ -341,7 +341,11 @@ pub enum ConstraintCategory<'tcx> { UseAsConst, UseAsStatic, TypeAnnotation, - Cast, + Cast { + /// Whether this is an unsizing cast and if yes, this contains the target type. + /// Region variables are erased to ReErased. + unsize_to: Option<Ty<'tcx>>, + }, /// A constraint that came from checking the body of a closure. /// diff --git a/tests/ui/borrowck/two-phase-surprise-no-conflict.stderr b/tests/ui/borrowck/two-phase-surprise-no-conflict.stderr index 9f9d4bd8d6c..b3bf2f924fc 100644 --- a/tests/ui/borrowck/two-phase-surprise-no-conflict.stderr +++ b/tests/ui/borrowck/two-phase-surprise-no-conflict.stderr @@ -77,6 +77,8 @@ LL | reg.register_univ(Box::new(CapturePass::new(®.sess_mut))); | | | immutable borrow occurs here | | cast requires that `reg.sess_mut` is borrowed for `'a` | mutable borrow occurs here + | + = note: due to object lifetime defaults, `Box<dyn for<'b> LateLintPass<'b>>` actually means `Box<(dyn for<'b> LateLintPass<'b> + 'static)>` error[E0502]: cannot borrow `*reg` as mutable because it is also borrowed as immutable --> $DIR/two-phase-surprise-no-conflict.rs:144:5 @@ -119,6 +121,8 @@ LL | reg.register_univ(Box::new(CapturePass::new_mut(&mut reg.sess_mut))); | | | first mutable borrow occurs here | | cast requires that `reg.sess_mut` is borrowed for `'a` | second mutable borrow occurs here + | + = note: due to object lifetime defaults, `Box<dyn for<'b> LateLintPass<'b>>` actually means `Box<(dyn for<'b> LateLintPass<'b> + 'static)>` error[E0499]: cannot borrow `reg.sess_mut` as mutable more than once at a time --> $DIR/two-phase-surprise-no-conflict.rs:158:53 diff --git a/tests/ui/dropck/dropck_trait_cycle_checked.stderr b/tests/ui/dropck/dropck_trait_cycle_checked.stderr index 4d4f7b9df11..63fd07a9163 100644 --- a/tests/ui/dropck/dropck_trait_cycle_checked.stderr +++ b/tests/ui/dropck/dropck_trait_cycle_checked.stderr @@ -8,6 +8,8 @@ LL | o1.set0(&o2); ... LL | } | - `o2` dropped here while still borrowed + | + = note: due to object lifetime defaults, `Box<dyn Obj<'_>>` actually means `Box<(dyn Obj<'_> + 'static)>` error[E0597]: `o3` does not live long enough --> $DIR/dropck_trait_cycle_checked.rs:112:13 @@ -20,6 +22,8 @@ LL | o1.set1(&o3); ... LL | } | - `o3` dropped here while still borrowed + | + = note: due to object lifetime defaults, `Box<dyn Obj<'_>>` actually means `Box<(dyn Obj<'_> + 'static)>` error[E0597]: `o2` does not live long enough --> $DIR/dropck_trait_cycle_checked.rs:113:13 @@ -32,6 +36,8 @@ LL | o2.set0(&o2); ... LL | } | - `o2` dropped here while still borrowed + | + = note: due to object lifetime defaults, `Box<dyn Obj<'_>>` actually means `Box<(dyn Obj<'_> + 'static)>` error[E0597]: `o3` does not live long enough --> $DIR/dropck_trait_cycle_checked.rs:114:13 @@ -44,6 +50,8 @@ LL | o2.set1(&o3); ... LL | } | - `o3` dropped here while still borrowed + | + = note: due to object lifetime defaults, `Box<dyn Obj<'_>>` actually means `Box<(dyn Obj<'_> + 'static)>` error[E0597]: `o1` does not live long enough --> $DIR/dropck_trait_cycle_checked.rs:115:13 @@ -56,6 +64,8 @@ LL | o3.set0(&o1); LL | o3.set1(&o2); LL | } | - `o1` dropped here while still borrowed + | + = note: due to object lifetime defaults, `Box<dyn Obj<'_>>` actually means `Box<(dyn Obj<'_> + 'static)>` error[E0597]: `o2` does not live long enough --> $DIR/dropck_trait_cycle_checked.rs:116:13 @@ -67,6 +77,8 @@ LL | o3.set1(&o2); | ^^^ borrowed value does not live long enough LL | } | - `o2` dropped here while still borrowed + | + = note: due to object lifetime defaults, `Box<dyn Obj<'_>>` actually means `Box<(dyn Obj<'_> + 'static)>` error: aborting due to 6 previous errors diff --git a/tests/ui/traits/trait-object-lifetime-default-note.rs b/tests/ui/traits/trait-object-lifetime-default-note.rs new file mode 100644 index 00000000000..31e3eb4ba41 --- /dev/null +++ b/tests/ui/traits/trait-object-lifetime-default-note.rs @@ -0,0 +1,16 @@ +trait A {} + +impl<T> A for T {} + +fn main() { + let local = 0; //~ NOTE binding `local` declared here + let r = &local; //~ ERROR `local` does not live long enough + //~| NOTE borrowed value does not live long enough + //~| NOTE due to object lifetime defaults, `Box<dyn A>` actually means `Box<(dyn A + 'static)>` + require_box(Box::new(r)); + //~^ NOTE cast requires that `local` is borrowed for `'static` + + let _ = 0; +} //~ NOTE `local` dropped here while still borrowed + +fn require_box(_a: Box<dyn A>) {} diff --git a/tests/ui/traits/trait-object-lifetime-default-note.stderr b/tests/ui/traits/trait-object-lifetime-default-note.stderr new file mode 100644 index 00000000000..b6dd6753899 --- /dev/null +++ b/tests/ui/traits/trait-object-lifetime-default-note.stderr @@ -0,0 +1,19 @@ +error[E0597]: `local` does not live long enough + --> $DIR/trait-object-lifetime-default-note.rs:7:13 + | +LL | let local = 0; + | ----- binding `local` declared here +LL | let r = &local; + | ^^^^^^ borrowed value does not live long enough +... +LL | require_box(Box::new(r)); + | ----------- cast requires that `local` is borrowed for `'static` +... +LL | } + | - `local` dropped here while still borrowed + | + = note: due to object lifetime defaults, `Box<dyn A>` actually means `Box<(dyn A + 'static)>` + +error: aborting due to previous error + +For more information about this error, try `rustc --explain E0597`. |