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 #[instrument(skip(tcx), level = "debug")]
  38 pub fn find_param_with_region<'tcx>(
  39     tcx: TyCtxt<'tcx>,
  40     anon_region: Region<'tcx>,
  41     replace_region: Region<'tcx>,
  42 ) -> Option<AnonymousParamInfo<'tcx>> {
  43     let (id, bound_region) = match *anon_region {
  44         ty::ReFree(ref free_region) => (free_region.scope, free_region.bound_region),
  45         ty::ReEarlyBound(ebr) => {
  46             (tcx.parent(ebr.def_id), ty::BoundRegionKind::BrNamed(ebr.def_id, ebr.name))
  47         }
  48         _ => return None, // not a free region
  49     };
  50
  51     let hir = &tcx.hir();
  52     let hir_id = hir.local_def_id_to_hir_id(id.as_local()?);
  53     let body_id = hir.maybe_body_owned_by(hir_id)?;
  54     let body = hir.body(body_id);
  55
  56     // Don't perform this on closures
  57     match hir.get(hir_id) {
  58         hir::Node::Expr(&hir::Expr { kind: hir::ExprKind::Closure { .. }, .. }) => {
  59             return None;
  60         }
  61         _ => {}
  62     }
  63
  64     let owner_id = hir.body_owner(body_id);
  65     let fn_decl = hir.fn_decl_by_hir_id(owner_id).unwrap();
  66     let poly_fn_sig = tcx.fn_sig(id);
  67
  68     let fn_sig = tcx.liberate_late_bound_regions(id, poly_fn_sig);
  69     body.params
  70         .iter()
  71         .take(if fn_sig.c_variadic {
  72             fn_sig.inputs().len()
  73         } else {
  74             assert_eq!(fn_sig.inputs().len(), body.params.len());
  75             body.params.len()
  76         })
  77         .enumerate()
  78         .find_map(|(index, param)| {
  79             // May return None; sometimes the tables are not yet populated.
  80             let ty = fn_sig.inputs()[index];
  81             let mut found_anon_region = false;
  82             let new_param_ty = tcx.fold_regions(ty, &mut false, |r, _| {
  83                 if r == anon_region {
  84                     found_anon_region = true;
  85                     replace_region
  86                 } else {
  87                     r
  88                 }
  89             });
  90             if found_anon_region {
  91                 let ty_hir_id = fn_decl.inputs[index].hir_id;
  92                 let param_ty_span = hir.span(ty_hir_id);
  93                 let is_first = index == 0;
  94                 Some(AnonymousParamInfo {
  95                     param,
  96                     param_ty: new_param_ty,
  97                     param_ty_span,
  98                     bound_region,
  99                     is_first,
 100                 })
 101             } else {
 102                 None
 103             }
 104         })
 105 }
 106
 107 impl<'a, 'tcx> NiceRegionError<'a, 'tcx> {
 108     pub(super) fn find_param_with_region(
 109         &self,
 110         anon_region: Region<'tcx>,
 111         replace_region: Region<'tcx>,
 112     ) -> Option<AnonymousParamInfo<'tcx>> {
 113         find_param_with_region(self.tcx(), anon_region, replace_region)
 114     }
 115
 116     // Here, we check for the case where the anonymous region
 117     // is in the return type as written by the user.
 118     // FIXME(#42703) - Need to handle certain cases here.
 119     pub(super) fn is_return_type_anon(
 120         &self,
 121         scope_def_id: LocalDefId,
 122         br: ty::BoundRegionKind,
 123         hir_sig: &hir::FnSig<'_>,
 124     ) -> Option<Span> {
 125         let fn_ty = self.tcx().type_of(scope_def_id);
 126         if let ty::FnDef(_, _) = fn_ty.kind() {
 127             let ret_ty = fn_ty.fn_sig(self.tcx()).output();
 128             let span = hir_sig.decl.output.span();
 129             let future_output = if hir_sig.header.is_async() {
 130                 ret_ty.map_bound(|ty| self.infcx.get_impl_future_output_ty(ty)).transpose()
 131             } else {
 132                 None
 133             };
 134             return match future_output {
 135                 Some(output) if self.includes_region(output, br) => Some(span),
 136                 None if self.includes_region(ret_ty, br) => Some(span),
 137                 _ => None,
 138             };
 139         }
 140         None
 141     }
 142
 143     fn includes_region(
 144         &self,
 145         ty: Binder<'tcx, impl TypeFoldable<'tcx>>,
 146         region: ty::BoundRegionKind,
 147     ) -> bool {
 148         let late_bound_regions = self.tcx().collect_referenced_late_bound_regions(&ty);
 149         late_bound_regions.iter().any(|r| *r == region)
 150     }
 151
 152     // Here we check for the case where anonymous region
 153     // corresponds to self and if yes, we display E0312.
 154     // FIXME(#42700) - Need to format self properly to
 155     // enable E0621 for it.
 156     pub(super) fn is_self_anon(&self, is_first: bool, scope_def_id: LocalDefId) -> bool {
 157         is_first
 158             && self
 159                 .tcx()
 160                 .opt_associated_item(scope_def_id.to_def_id())
 161                 .map(|i| i.fn_has_self_parameter)
 162                 == Some(true)
 163     }
 164 }