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Improve error message for lifetime error with dyn Trait
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140 changes: 140 additions & 0 deletions
140
src/librustc/infer/error_reporting/nice_region_error/static_dyn_trait.rs
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,140 @@ | ||
| #![allow(unused)] | ||
| //! Error Reporting for dyn Traits. | ||
| use crate::infer::error_reporting::nice_region_error::NiceRegionError; | ||
| use crate::infer::lexical_region_resolve::RegionResolutionError; | ||
| use crate::ty::{self, BoundRegion, FreeRegion, RegionKind, DefIdTree, ParamEnv}; | ||
| use crate::util::common::ErrorReported; | ||
| use errors::Applicability; | ||
| use crate::infer::{SubregionOrigin, ValuePairs, TypeTrace}; | ||
| use crate::ty::error::ExpectedFound; | ||
| use crate::hir; | ||
| use crate::hir::def_id::DefId; | ||
| use crate::traits::ObligationCauseCode::ExprAssignable; | ||
| use crate::traits::ObligationCause; | ||
| use crate::ty::{TyCtxt, TypeFoldable}; | ||
| use crate::ty::subst::{Subst, InternalSubsts, SubstsRef}; | ||
| use syntax_pos::Span; | ||
|
|
||
| impl<'a, 'tcx> NiceRegionError<'a, 'tcx> { | ||
| /// Print the error message for lifetime errors when a static ref to a trait object is required | ||
| /// because of a `dyn Trait` impl. | ||
| pub(super) fn try_report_static_dyn_trait(&self) -> Option<ErrorReported> { | ||
| let (span, sub, sup) = self.regions(); | ||
|
|
||
| debug!( | ||
| "try_report_static_dyn_trait: sub={:?}, sup={:?}, error={:?}", | ||
| sub, | ||
| sup, | ||
| self.error, | ||
| ); | ||
|
|
||
| if let Some(ref error) = self.error { | ||
| let (found, origin_span) = match error { | ||
| RegionResolutionError::ConcreteFailure(SubregionOrigin::Subtype(box TypeTrace { | ||
| cause, | ||
| values: ValuePairs::TraitRefs(ExpectedFound { expected, found }), | ||
| }), _, _) => { | ||
| (found, cause.span) | ||
| }, | ||
| // FIXME there is also the other region origin! | ||
| RegionResolutionError::SubSupConflict(_, _, SubregionOrigin::Subtype(box TypeTrace { | ||
| cause, | ||
| values: ValuePairs::TraitRefs(ExpectedFound { expected, found }), | ||
| }), _, _, _) => { | ||
| (found, cause.span) | ||
| } | ||
| _ => { | ||
| return None; | ||
| } | ||
| }; | ||
|
|
||
| debug!( | ||
| "try_report_static_dyn_trait: found={:?} origin_span={:?}", | ||
| found, origin_span, | ||
| ); | ||
|
|
||
| let found = self.infcx.resolve_vars_if_possible(found); | ||
| let dyn_static_ty = found.self_ty().walk().find(|ty| | ||
| if let ty::Dynamic(_, _) = ty.kind { true } else { false }); | ||
|
|
||
| debug!( | ||
| "try_report_static_dyn_trait: dyn_static_ty={:?} dyn_static_ty.kind={:?}", | ||
| dyn_static_ty, dyn_static_ty.map(|dyn_static_ty| &dyn_static_ty.kind), | ||
| ); | ||
|
|
||
| let dyn_trait_name = if let Some(dyn_static_ty) = dyn_static_ty { | ||
| if let ty::Dynamic(binder, _) = dyn_static_ty.kind { | ||
| binder.skip_binder().to_string() | ||
| } else { | ||
| return None; | ||
| } | ||
| } else { | ||
| return None; | ||
| }; | ||
|
|
||
| let mut trait_impl = None; | ||
|
|
||
| self.tcx().for_each_relevant_impl( | ||
| found.def_id, | ||
| found.self_ty(), | ||
| |impl_def_id| { | ||
| debug!( | ||
| "try_report_static_dyn_trait: for_each_relevant_impl impl_def_id={:?}", | ||
| impl_def_id, | ||
| ); | ||
|
|
||
| trait_impl = Some(impl_def_id); | ||
| }); | ||
|
|
||
| debug!( | ||
| "try_report_static_dyn_trait: trait_impl={:?}", trait_impl, | ||
| ); | ||
|
|
||
| if let Some(impl_def_id) = trait_impl { | ||
| self.emit_dyn_trait_err(origin_span, &dyn_trait_name, impl_def_id); | ||
| return Some(ErrorReported); | ||
| } | ||
| } | ||
| None | ||
| } | ||
|
|
||
| fn emit_dyn_trait_err(&self, | ||
| expr_span: Span, | ||
| dyn_trait_name: &String, | ||
| impl_def_id: DefId, | ||
| ) { | ||
| let (_, sub, sup) = self.regions(); | ||
|
|
||
| debug!( | ||
| "emit_dyn_trait_err: sup={:?} sub={:?} expr_span={:?} dyn_trait_name={:?}", | ||
| sup, sub, expr_span, dyn_trait_name, | ||
| ); | ||
|
|
||
| let item_span = self.tcx().sess.source_map() | ||
| .def_span(self.tcx().def_span(impl_def_id)); | ||
|
|
||
| let (lifetime_description, lt_sp_opt) = self.tcx().msg_span_from_free_region(sup); | ||
|
|
||
| let impl_span = item_span; | ||
|
|
||
| let mut err = self.tcx().sess.struct_span_err( | ||
| expr_span, | ||
| "cannot infer an appropriate lifetime", | ||
| ); | ||
|
|
||
| if let Some(lt_sp_opt) = lt_sp_opt { | ||
| err.span_note( | ||
| lt_sp_opt, | ||
| &format!("first, the lifetime cannot outlive {}...", lifetime_description), | ||
| ); | ||
| } | ||
|
|
||
| err.span_note(expr_span, | ||
| &format!("but, the lifetime must be valid for the {} lifetime...", sub)); | ||
|
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||
|
|
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| self.infcx.note_dyn_impl_and_suggest_anon_lifetime(&mut err, impl_def_id, dyn_trait_name); | ||
|
|
||
| err.emit(); | ||
| } | ||
| } |
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I don't have time to do an in-depth review right now, but we should try to come up with a different way of doing this. Fiddling with the textual representation of the code is a recipe for pain later on. It produces output that isn't always correct (like the problem with the missing parens and some incorrect suggestions I noticed below), and is brittle and affected by whitespace. I'll take another look later to see if I can have more actionable feedback on what to do instead.