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 rustc_hir as hir;
   6 use rustc_hir::def_id::LocalDefId;
   7 use rustc_middle::ty::{self, DefIdTree, Region, Ty};
   8 use rustc_span::Span;
   9
  10 /// Information about the anonymous region we are searching for.
  11 #[derive(Debug)]
  12 pub(super) struct AnonymousParamInfo<'tcx> {
  13     /// The parameter corresponding to the anonymous region.
  14     pub param: &'tcx hir::Param<'tcx>,
  15     /// The type corresponding to the anonymous region parameter.
  16     pub param_ty: Ty<'tcx>,
  17     /// The ty::BoundRegion corresponding to the anonymous region.
  18     pub bound_region: ty::BoundRegion,
  19     /// The `Span` of the parameter type.
  20     pub param_ty_span: Span,
  21     /// Signals that the argument is the first parameter in the declaration.
  22     pub is_first: bool,
  23 }
  24
  25 impl<'a, 'tcx> NiceRegionError<'a, 'tcx> {
  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(super) fn find_param_with_region(
  38         &self,
  39         anon_region: Region<'tcx>,
  40         replace_region: Region<'tcx>,
  41     ) -> Option<AnonymousParamInfo<'_>> {
  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                 self.tcx().parent(ebr.def_id).unwrap(),
  46                 ty::BoundRegion::BrNamed(ebr.def_id, ebr.name),
  47             ),
  48             _ => return None, // not a free region
  49         };
  50
  51         let hir = &self.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         let owner_id = hir.body_owner(body_id);
  56         let fn_decl = hir.fn_decl_by_hir_id(owner_id).unwrap();
  57         let poly_fn_sig = self.tcx().fn_sig(id);
  58         let fn_sig = self.tcx().liberate_late_bound_regions(id, &poly_fn_sig);
  59         body.params.iter().enumerate().find_map(|(index, param)| {
  60             // May return None; sometimes the tables are not yet populated.
  61             let ty = fn_sig.inputs()[index];
  62             let mut found_anon_region = false;
  63             let new_param_ty = self.tcx().fold_regions(&ty, &mut false, |r, _| {
  64                 if *r == *anon_region {
  65                     found_anon_region = true;
  66                     replace_region
  67                 } else {
  68                     r
  69                 }
  70             });
  71             if found_anon_region {
  72                 let ty_hir_id = fn_decl.inputs[index].hir_id;
  73                 let param_ty_span = hir.span(ty_hir_id);
  74                 let is_first = index == 0;
  75                 Some(AnonymousParamInfo {
  76                     param,
  77                     param_ty: new_param_ty,
  78                     param_ty_span,
  79                     bound_region,
  80                     is_first,
  81                 })
  82             } else {
  83                 None
  84             }
  85         })
  86     }
  87
  88     // Here, we check for the case where the anonymous region
  89     // is in the return type.
  90     // FIXME(#42703) - Need to handle certain cases here.
  91     pub(super) fn is_return_type_anon(
  92         &self,
  93         scope_def_id: LocalDefId,
  94         br: ty::BoundRegion,
  95         decl: &hir::FnDecl<'_>,
  96     ) -> Option<Span> {
  97         let ret_ty = self.tcx().type_of(scope_def_id);
  98         if let ty::FnDef(_, _) = ret_ty.kind() {
  99             let sig = ret_ty.fn_sig(self.tcx());
 100             let late_bound_regions =
 101                 self.tcx().collect_referenced_late_bound_regions(&sig.output());
 102             if late_bound_regions.iter().any(|r| *r == br) {
 103                 return Some(decl.output.span());
 104             }
 105         }
 106         None
 107     }
 108
 109     // Here we check for the case where anonymous region
 110     // corresponds to self and if yes, we display E0312.
 111     // FIXME(#42700) - Need to format self properly to
 112     // enable E0621 for it.
 113     pub(super) fn is_self_anon(&self, is_first: bool, scope_def_id: LocalDefId) -> bool {
 114         is_first
 115             && self
 116                 .tcx()
 117                 .opt_associated_item(scope_def_id.to_def_id())
 118                 .map(|i| i.fn_has_self_parameter)
 119                 == Some(true)
 120     }
 121 }