compiler/rustc_borrowck/src/type_check/input_output.rs

   1 //! This module contains code to equate the input/output types appearing
   2 //! in the MIR with the expected input/output types from the function
   3 //! signature. This requires a bit of processing, as the expected types
   4 //! are supplied to us before normalization and may contain opaque
   5 //! `impl Trait` instances. In contrast, the input/output types found in
   6 //! the MIR (specifically, in the special local variables for the
   7 //! `RETURN_PLACE` the MIR arguments) are always fully normalized (and
   8 //! contain revealed `impl Trait` values).
   9
  10 use rustc_index::vec::Idx;
  11 use rustc_infer::infer::LateBoundRegionConversionTime;
  12 use rustc_middle::mir::*;
  13 use rustc_middle::ty::Ty;
  14 use rustc_span::Span;
  15
  16 use crate::universal_regions::UniversalRegions;
  17
  18 use super::{Locations, TypeChecker};
  19
  20 impl<'a, 'tcx> TypeChecker<'a, 'tcx> {
  21     #[instrument(skip(self, body, universal_regions), level = "debug")]
  22     pub(super) fn equate_inputs_and_outputs(
  23         &mut self,
  24         body: &Body<'tcx>,
  25         universal_regions: &UniversalRegions<'tcx>,
  26         normalized_inputs_and_output: &[Ty<'tcx>],
  27     ) {
  28         let (&normalized_output_ty, normalized_input_tys) =
  29             normalized_inputs_and_output.split_last().unwrap();
  30
  31         debug!(?normalized_output_ty);
  32         debug!(?normalized_input_tys);
  33
  34         let mir_def_id = body.source.def_id().expect_local();
  35
  36         // If the user explicitly annotated the input types, extract
  37         // those.
  38         //
  39         // e.g., `|x: FxHashMap<_, &'static u32>| ...`
  40         let user_provided_sig = if !self.tcx().is_closure(mir_def_id.to_def_id()) {
  41             None
  42         } else {
  43             let typeck_results = self.tcx().typeck(mir_def_id);
  44
  45             typeck_results.user_provided_sigs.get(&mir_def_id).map(|user_provided_poly_sig| {
  46                 // Instantiate the canonicalized variables from
  47                 // user-provided signature (e.g., the `_` in the code
  48                 // above) with fresh variables.
  49                 let poly_sig = self.instantiate_canonical_with_fresh_inference_vars(
  50                     body.span,
  51                     &user_provided_poly_sig,
  52                 );
  53
  54                 // Replace the bound items in the fn sig with fresh
  55                 // variables, so that they represent the view from
  56                 // "inside" the closure.
  57                 self.infcx.replace_bound_vars_with_fresh_vars(
  58                     body.span,
  59                     LateBoundRegionConversionTime::FnCall,
  60                     poly_sig,
  61                 )
  62             })
  63         };
  64
  65         debug!(?normalized_input_tys, ?body.local_decls);
  66
  67         // Equate expected input tys with those in the MIR.
  68         for (argument_index, &normalized_input_ty) in normalized_input_tys.iter().enumerate() {
  69             if argument_index + 1 >= body.local_decls.len() {
  70                 self.tcx()
  71                     .sess
  72                     .delay_span_bug(body.span, "found more normalized_input_ty than local_decls");
  73                 break;
  74             }
  75
  76             // In MIR, argument N is stored in local N+1.
  77             let local = Local::new(argument_index + 1);
  78
  79             let mir_input_ty = body.local_decls[local].ty;
  80
  81             let mir_input_span = body.local_decls[local].source_info.span;
  82             self.equate_normalized_input_or_output(
  83                 normalized_input_ty,
  84                 mir_input_ty,
  85                 mir_input_span,
  86             );
  87         }
  88
  89         if let Some(user_provided_sig) = user_provided_sig {
  90             for (argument_index, &user_provided_input_ty) in
  91                 user_provided_sig.inputs().iter().enumerate()
  92             {
  93                 // In MIR, closures begin an implicit `self`, so
  94                 // argument N is stored in local N+2.
  95                 let local = Local::new(argument_index + 2);
  96                 let mir_input_ty = body.local_decls[local].ty;
  97                 let mir_input_span = body.local_decls[local].source_info.span;
  98
  99                 // If the user explicitly annotated the input types, enforce those.
 100                 let user_provided_input_ty =
 101                     self.normalize(user_provided_input_ty, Locations::All(mir_input_span));
 102
 103                 self.equate_normalized_input_or_output(
 104                     user_provided_input_ty,
 105                     mir_input_ty,
 106                     mir_input_span,
 107                 );
 108             }
 109         }
 110
 111         debug!(
 112             "equate_inputs_and_outputs: body.yield_ty {:?}, universal_regions.yield_ty {:?}",
 113             body.yield_ty(),
 114             universal_regions.yield_ty
 115         );
 116
 117         // We will not have a universal_regions.yield_ty if we yield (by accident)
 118         // outside of a generator and return an `impl Trait`, so emit a delay_span_bug
 119         // because we don't want to panic in an assert here if we've already got errors.
 120         if body.yield_ty().is_some() != universal_regions.yield_ty.is_some() {
 121             self.tcx().sess.delay_span_bug(
 122                 body.span,
 123                 &format!(
 124                     "Expected body to have yield_ty ({:?}) iff we have a UR yield_ty ({:?})",
 125                     body.yield_ty(),
 126                     universal_regions.yield_ty,
 127                 ),
 128             );
 129         }
 130
 131         if let (Some(mir_yield_ty), Some(ur_yield_ty)) =
 132             (body.yield_ty(), universal_regions.yield_ty)
 133         {
 134             let yield_span = body.local_decls[RETURN_PLACE].source_info.span;
 135             self.equate_normalized_input_or_output(ur_yield_ty, mir_yield_ty, yield_span);
 136         }
 137
 138         // Return types are a bit more complex. They may contain opaque `impl Trait` types.
 139         let mir_output_ty = body.local_decls[RETURN_PLACE].ty;
 140         let output_span = body.local_decls[RETURN_PLACE].source_info.span;
 141         if let Err(terr) = self.eq_types(
 142             normalized_output_ty,
 143             mir_output_ty,
 144             Locations::All(output_span),
 145             ConstraintCategory::BoringNoLocation,
 146         ) {
 147             span_mirbug!(
 148                 self,
 149                 Location::START,
 150                 "equate_inputs_and_outputs: `{:?}=={:?}` failed with `{:?}`",
 151                 normalized_output_ty,
 152                 mir_output_ty,
 153                 terr
 154             );
 155         };
 156
 157         // If the user explicitly annotated the output types, enforce those.
 158         // Note that this only happens for closures.
 159         if let Some(user_provided_sig) = user_provided_sig {
 160             let user_provided_output_ty = user_provided_sig.output();
 161             let user_provided_output_ty =
 162                 self.normalize(user_provided_output_ty, Locations::All(output_span));
 163             if let Err(err) = self.eq_types(
 164                 user_provided_output_ty,
 165                 mir_output_ty,
 166                 Locations::All(output_span),
 167                 ConstraintCategory::BoringNoLocation,
 168             ) {
 169                 span_mirbug!(
 170                     self,
 171                     Location::START,
 172                     "equate_inputs_and_outputs: `{:?}=={:?}` failed with `{:?}`",
 173                     mir_output_ty,
 174                     user_provided_output_ty,
 175                     err
 176                 );
 177             }
 178         }
 179     }
 180
 181     #[instrument(skip(self), level = "debug")]
 182     fn equate_normalized_input_or_output(&mut self, a: Ty<'tcx>, b: Ty<'tcx>, span: Span) {
 183         if let Err(_) =
 184             self.eq_types(a, b, Locations::All(span), ConstraintCategory::BoringNoLocation)
 185         {
 186             // FIXME(jackh726): This is a hack. It's somewhat like
 187             // `rustc_traits::normalize_after_erasing_regions`. Ideally, we'd
 188             // like to normalize *before* inserting into `local_decls`, but
 189             // doing so ends up causing some other trouble.
 190             let b = self.normalize(b, Locations::All(span));
 191
 192             // Note: if we have to introduce new placeholders during normalization above, then we won't have
 193             // added those universes to the universe info, which we would want in `relate_tys`.
 194             if let Err(terr) =
 195                 self.eq_types(a, b, Locations::All(span), ConstraintCategory::BoringNoLocation)
 196             {
 197                 span_mirbug!(
 198                     self,
 199                     Location::START,
 200                     "equate_normalized_input_or_output: `{:?}=={:?}` failed with `{:?}`",
 201                     a,
 202                     b,
 203                     terr
 204                 );
 205             }
 206         }
 207     }
 208 }