src/librustc_infer/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::ty::{self, DefIdTree, Region, Ty};
   6 use rustc_hir as hir;
   7 use rustc_hir::def_id::DefId;
   8 use rustc_span::Span;
   9
  10 // The struct contains the information about the anonymous region
  11 // we are searching for.
  12 #[derive(Debug)]
  13 pub(super) struct AnonymousParamInfo<'tcx> {
  14     // the parameter corresponding to the anonymous region
  15     pub param: &'tcx hir::Param<'tcx>,
  16     // the type corresponding to the anonymopus region parameter
  17     pub param_ty: Ty<'tcx>,
  18     // the ty::BoundRegion corresponding to the anonymous region
  19     pub bound_region: ty::BoundRegion,
  20     // param_ty_span contains span of parameter type
  21     pub param_ty_span: Span,
  22     // corresponds to id the argument is the first parameter
  23     // in the declaration
  24     pub is_first: bool,
  25 }
  26
  27 impl<'a, 'tcx> NiceRegionError<'a, 'tcx> {
  28     // This method walks the Type of the function body parameters using
  29     // `fold_regions()` function and returns the
  30     // &hir::Param of the function parameter corresponding to the anonymous
  31     // region and the Ty corresponding to the named region.
  32     // Currently only the case where the function declaration consists of
  33     // one named region and one anonymous region is handled.
  34     // Consider the example `fn foo<'a>(x: &'a i32, y: &i32) -> &'a i32`
  35     // Here, we would return the hir::Param for y, we return the type &'a
  36     // i32, which is the type of y but with the anonymous region replaced
  37     // with 'a, the corresponding bound region and is_first which is true if
  38     // the hir::Param is the first parameter in the function declaration.
  39     pub(super) fn find_param_with_region(
  40         &self,
  41         anon_region: Region<'tcx>,
  42         replace_region: Region<'tcx>,
  43     ) -> Option<AnonymousParamInfo<'_>> {
  44         let (id, bound_region) = match *anon_region {
  45             ty::ReFree(ref free_region) => (free_region.scope, free_region.bound_region),
  46             ty::ReEarlyBound(ebr) => (
  47                 self.tcx().parent(ebr.def_id).unwrap(),
  48                 ty::BoundRegion::BrNamed(ebr.def_id, ebr.name),
  49             ),
  50             _ => return None, // not a free region
  51         };
  52
  53         let hir = &self.tcx().hir();
  54         if let Some(hir_id) = hir.as_local_hir_id(id) {
  55             if let Some(body_id) = hir.maybe_body_owned_by(hir_id) {
  56                 let body = hir.body(body_id);
  57                 let owner_id = hir.body_owner(body_id);
  58                 let fn_decl = hir.fn_decl_by_hir_id(owner_id).unwrap();
  59                 if let Some(tables) = self.tables {
  60                     body.params
  61                         .iter()
  62                         .enumerate()
  63                         .filter_map(|(index, param)| {
  64                             // May return None; sometimes the tables are not yet populated.
  65                             let ty_hir_id = fn_decl.inputs[index].hir_id;
  66                             let param_ty_span = hir.span(ty_hir_id);
  67                             let ty = tables.node_type_opt(param.hir_id)?;
  68                             let mut found_anon_region = false;
  69                             let new_param_ty = self.tcx().fold_regions(&ty, &mut false, |r, _| {
  70                                 if *r == *anon_region {
  71                                     found_anon_region = true;
  72                                     replace_region
  73                                 } else {
  74                                     r
  75                                 }
  76                             });
  77                             if found_anon_region {
  78                                 let is_first = index == 0;
  79                                 Some(AnonymousParamInfo {
  80                                     param,
  81                                     param_ty: new_param_ty,
  82                                     param_ty_span,
  83                                     bound_region,
  84                                     is_first,
  85                                 })
  86                             } else {
  87                                 None
  88                             }
  89                         })
  90                         .next()
  91                 } else {
  92                     None
  93                 }
  94             } else {
  95                 None
  96             }
  97         } else {
  98             None
  99         }
 100     }
 101
 102     // Here, we check for the case where the anonymous region
 103     // is in the return type.
 104     // FIXME(#42703) - Need to handle certain cases here.
 105     pub(super) fn is_return_type_anon(
 106         &self,
 107         scope_def_id: DefId,
 108         br: ty::BoundRegion,
 109         decl: &hir::FnDecl<'_>,
 110     ) -> Option<Span> {
 111         let ret_ty = self.tcx().type_of(scope_def_id);
 112         if let ty::FnDef(_, _) = ret_ty.kind {
 113             let sig = ret_ty.fn_sig(self.tcx());
 114             let late_bound_regions =
 115                 self.tcx().collect_referenced_late_bound_regions(&sig.output());
 116             if late_bound_regions.iter().any(|r| *r == br) {
 117                 return Some(decl.output.span());
 118             }
 119         }
 120         None
 121     }
 122
 123     // Here we check for the case where anonymous region
 124     // corresponds to self and if yes, we display E0312.
 125     // FIXME(#42700) - Need to format self properly to
 126     // enable E0621 for it.
 127     pub(super) fn is_self_anon(&self, is_first: bool, scope_def_id: DefId) -> bool {
 128         is_first
 129             && self.tcx().opt_associated_item(scope_def_id).map(|i| i.method_has_self_argument)
 130                 == Some(true)
 131     }
 132 }