compiler/rustc_infer/src/infer/error_reporting/nice_region_error/util.rs

   1 //! Helper functions corresponding to lifetime errors due to
   2 //! anonymous regions.
   3
   4 use crate::infer::error_reporting::nice_region_error::NiceRegionError;
   5 use crate::infer::TyCtxt;
   6 use rustc_hir as hir;
   7 use rustc_hir::def_id::LocalDefId;
   8 use rustc_middle::ty::{self, Binder, DefIdTree, Region, Ty, TypeFoldable};
   9 use rustc_span::Span;
  10
  11 /// Information about the anonymous region we are searching for.
  12 #[derive(Debug)]
  13 pub struct AnonymousParamInfo<'tcx> {
  14     /// The parameter corresponding to the anonymous region.
  15     pub param: &'tcx hir::Param<'tcx>,
  16     /// The type corresponding to the anonymous region parameter.
  17     pub param_ty: Ty<'tcx>,
  18     /// The ty::BoundRegionKind corresponding to the anonymous region.
  19     pub bound_region: ty::BoundRegionKind,
  20     /// The `Span` of the parameter type.
  21     pub param_ty_span: Span,
  22     /// Signals that the argument is the first parameter in the declaration.
  23     pub is_first: bool,
  24 }
  25
  26 // This method walks the Type of the function body parameters using
  27 // `fold_regions()` function and returns the
  28 // &hir::Param of the function parameter corresponding to the anonymous
  29 // region and the Ty corresponding to the named region.
  30 // Currently only the case where the function declaration consists of
  31 // one named region and one anonymous region is handled.
  32 // Consider the example `fn foo<'a>(x: &'a i32, y: &i32) -> &'a i32`
  33 // Here, we would return the hir::Param for y, we return the type &'a
  34 // i32, which is the type of y but with the anonymous region replaced
  35 // with 'a, the corresponding bound region and is_first which is true if
  36 // the hir::Param is the first parameter in the function declaration.
  37 pub fn find_param_with_region<'tcx>(
  38     tcx: TyCtxt<'tcx>,
  39     anon_region: Region<'tcx>,
  40     replace_region: Region<'tcx>,
  41 ) -> Option<AnonymousParamInfo<'tcx>> {
  42     let (id, bound_region) = match *anon_region {
  43         ty::ReFree(ref free_region) => (free_region.scope, free_region.bound_region),
  44         ty::ReEarlyBound(ebr) => {
  45             (tcx.parent(ebr.def_id), ty::BoundRegionKind::BrNamed(ebr.def_id, ebr.name))
  46         }
  47         _ => return None, // not a free region
  48     };
  49
  50     let hir = &tcx.hir();
  51     let hir_id = hir.local_def_id_to_hir_id(id.as_local()?);
  52     let body_id = hir.maybe_body_owned_by(hir_id)?;
  53     let body = hir.body(body_id);
  54     let owner_id = hir.body_owner(body_id);
  55     let fn_decl = hir.fn_decl_by_hir_id(owner_id).unwrap();
  56     let poly_fn_sig = tcx.fn_sig(id);
  57     let fn_sig = tcx.liberate_late_bound_regions(id, poly_fn_sig);
  58     body.params
  59         .iter()
  60         .take(if fn_sig.c_variadic {
  61             fn_sig.inputs().len()
  62         } else {
  63             assert_eq!(fn_sig.inputs().len(), body.params.len());
  64             body.params.len()
  65         })
  66         .enumerate()
  67         .find_map(|(index, param)| {
  68             // May return None; sometimes the tables are not yet populated.
  69             let ty = fn_sig.inputs()[index];
  70             let mut found_anon_region = false;
  71             let new_param_ty = tcx.fold_regions(ty, &mut false, |r, _| {
  72                 if r == anon_region {
  73                     found_anon_region = true;
  74                     replace_region
  75                 } else {
  76                     r
  77                 }
  78             });
  79             if found_anon_region {
  80                 let ty_hir_id = fn_decl.inputs[index].hir_id;
  81                 let param_ty_span = hir.span(ty_hir_id);
  82                 let is_first = index == 0;
  83                 Some(AnonymousParamInfo {
  84                     param,
  85                     param_ty: new_param_ty,
  86                     param_ty_span,
  87                     bound_region,
  88                     is_first,
  89                 })
  90             } else {
  91                 None
  92             }
  93         })
  94 }
  95
  96 impl<'a, 'tcx> NiceRegionError<'a, 'tcx> {
  97     pub(super) fn find_param_with_region(
  98         &self,
  99         anon_region: Region<'tcx>,
 100         replace_region: Region<'tcx>,
 101     ) -> Option<AnonymousParamInfo<'_>> {
 102         find_param_with_region(self.tcx(), anon_region, replace_region)
 103     }
 104
 105     // Here, we check for the case where the anonymous region
 106     // is in the return type as written by the user.
 107     // FIXME(#42703) - Need to handle certain cases here.
 108     pub(super) fn is_return_type_anon(
 109         &self,
 110         scope_def_id: LocalDefId,
 111         br: ty::BoundRegionKind,
 112         hir_sig: &hir::FnSig<'_>,
 113     ) -> Option<Span> {
 114         let fn_ty = self.tcx().type_of(scope_def_id);
 115         if let ty::FnDef(_, _) = fn_ty.kind() {
 116             let ret_ty = fn_ty.fn_sig(self.tcx()).output();
 117             let span = hir_sig.decl.output.span();
 118             let future_output = if hir_sig.header.is_async() {
 119                 ret_ty.map_bound(|ty| self.infcx.get_impl_future_output_ty(ty)).transpose()
 120             } else {
 121                 None
 122             };
 123             return match future_output {
 124                 Some(output) if self.includes_region(output, br) => Some(span),
 125                 None if self.includes_region(ret_ty, br) => Some(span),
 126                 _ => None,
 127             };
 128         }
 129         None
 130     }
 131
 132     fn includes_region(
 133         &self,
 134         ty: Binder<'tcx, impl TypeFoldable<'tcx>>,
 135         region: ty::BoundRegionKind,
 136     ) -> bool {
 137         let late_bound_regions = self.tcx().collect_referenced_late_bound_regions(&ty);
 138         late_bound_regions.iter().any(|r| *r == region)
 139     }
 140
 141     // Here we check for the case where anonymous region
 142     // corresponds to self and if yes, we display E0312.
 143     // FIXME(#42700) - Need to format self properly to
 144     // enable E0621 for it.
 145     pub(super) fn is_self_anon(&self, is_first: bool, scope_def_id: LocalDefId) -> bool {
 146         is_first
 147             && self
 148                 .tcx()
 149                 .opt_associated_item(scope_def_id.to_def_id())
 150                 .map(|i| i.fn_has_self_parameter)
 151                 == Some(true)
 152     }
 153 }