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;
  41         if !self.tcx().is_closure(mir_def_id.to_def_id()) {
  42             user_provided_sig = None;
  43         } else {
  44             let typeck_results = self.tcx().typeck(mir_def_id);
  45             user_provided_sig =
  46                 typeck_results.user_provided_sigs.get(&mir_def_id).map(|user_provided_poly_sig| {
  47                     // Instantiate the canonicalized variables from
  48                     // user-provided signature (e.g., the `_` in the code
  49                     // above) with fresh variables.
  50                     let poly_sig = self.instantiate_canonical_with_fresh_inference_vars(
  51                         body.span,
  52                         &user_provided_poly_sig,
  53                     );
  54
  55                     // Replace the bound items in the fn sig with fresh
  56                     // variables, so that they represent the view from
  57                     // "inside" the closure.
  58                     self.infcx.replace_bound_vars_with_fresh_vars(
  59                         body.span,
  60                         LateBoundRegionConversionTime::FnCall,
  61                         poly_sig,
  62                     )
  63                 });
  64         }
  65
  66         debug!(?normalized_input_tys, ?body.local_decls);
  67
  68         // Equate expected input tys with those in the MIR.
  69         for (argument_index, &normalized_input_ty) in normalized_input_tys.iter().enumerate() {
  70             if argument_index + 1 >= body.local_decls.len() {
  71                 self.tcx()
  72                     .sess
  73                     .delay_span_bug(body.span, "found more normalized_input_ty than local_decls");
  74                 break;
  75             }
  76
  77             // In MIR, argument N is stored in local N+1.
  78             let local = Local::new(argument_index + 1);
  79
  80             let mir_input_ty = body.local_decls[local].ty;
  81
  82             let mir_input_span = body.local_decls[local].source_info.span;
  83             self.equate_normalized_input_or_output(
  84                 normalized_input_ty,
  85                 mir_input_ty,
  86                 mir_input_span,
  87             );
  88         }
  89
  90         if let Some(user_provided_sig) = user_provided_sig {
  91             for (argument_index, &user_provided_input_ty) in
  92                 user_provided_sig.inputs().iter().enumerate()
  93             {
  94                 // In MIR, closures begin an implicit `self`, so
  95                 // argument N is stored in local N+2.
  96                 let local = Local::new(argument_index + 2);
  97                 let mir_input_ty = body.local_decls[local].ty;
  98                 let mir_input_span = body.local_decls[local].source_info.span;
  99
 100                 // If the user explicitly annotated the input types, enforce those.
 101                 let user_provided_input_ty =
 102                     self.normalize(user_provided_input_ty, Locations::All(mir_input_span));
 103
 104                 self.equate_normalized_input_or_output(
 105                     user_provided_input_ty,
 106                     mir_input_ty,
 107                     mir_input_span,
 108                 );
 109             }
 110         }
 111
 112         debug!(
 113             "equate_inputs_and_outputs: body.yield_ty {:?}, universal_regions.yield_ty {:?}",
 114             body.yield_ty(),
 115             universal_regions.yield_ty
 116         );
 117
 118         // We will not have a universal_regions.yield_ty if we yield (by accident)
 119         // outside of a generator and return an `impl Trait`, so emit a delay_span_bug
 120         // because we don't want to panic in an assert here if we've already got errors.
 121         if body.yield_ty().is_some() != universal_regions.yield_ty.is_some() {
 122             self.tcx().sess.delay_span_bug(
 123                 body.span,
 124                 &format!(
 125                     "Expected body to have yield_ty ({:?}) iff we have a UR yield_ty ({:?})",
 126                     body.yield_ty(),
 127                     universal_regions.yield_ty,
 128                 ),
 129             );
 130         }
 131
 132         if let (Some(mir_yield_ty), Some(ur_yield_ty)) =
 133             (body.yield_ty(), universal_regions.yield_ty)
 134         {
 135             let yield_span = body.local_decls[RETURN_PLACE].source_info.span;
 136             self.equate_normalized_input_or_output(ur_yield_ty, mir_yield_ty, yield_span);
 137         }
 138
 139         // Return types are a bit more complex. They may contain opaque `impl Trait` types.
 140         let mir_output_ty = body.local_decls[RETURN_PLACE].ty;
 141         let output_span = body.local_decls[RETURN_PLACE].source_info.span;
 142         if let Err(terr) = self.eq_types(
 143             normalized_output_ty,
 144             mir_output_ty,
 145             Locations::All(output_span),
 146             ConstraintCategory::BoringNoLocation,
 147         ) {
 148             span_mirbug!(
 149                 self,
 150                 Location::START,
 151                 "equate_inputs_and_outputs: `{:?}=={:?}` failed with `{:?}`",
 152                 normalized_output_ty,
 153                 mir_output_ty,
 154                 terr
 155             );
 156         };
 157
 158         // If the user explicitly annotated the output types, enforce those.
 159         // Note that this only happens for closures.
 160         if let Some(user_provided_sig) = user_provided_sig {
 161             let user_provided_output_ty = user_provided_sig.output();
 162             let user_provided_output_ty =
 163                 self.normalize(user_provided_output_ty, Locations::All(output_span));
 164             if let Err(err) = self.eq_types(
 165                 user_provided_output_ty,
 166                 mir_output_ty,
 167                 Locations::All(output_span),
 168                 ConstraintCategory::BoringNoLocation,
 169             ) {
 170                 span_mirbug!(
 171                     self,
 172                     Location::START,
 173                     "equate_inputs_and_outputs: `{:?}=={:?}` failed with `{:?}`",
 174                     mir_output_ty,
 175                     user_provided_output_ty,
 176                     err
 177                 );
 178             }
 179         }
 180     }
 181
 182     #[instrument(skip(self), level = "debug")]
 183     fn equate_normalized_input_or_output(&mut self, a: Ty<'tcx>, b: Ty<'tcx>, span: Span) {
 184         if let Err(_) =
 185             self.eq_types(a, b, Locations::All(span), ConstraintCategory::BoringNoLocation)
 186         {
 187             // FIXME(jackh726): This is a hack. It's somewhat like
 188             // `rustc_traits::normalize_after_erasing_regions`. Ideally, we'd
 189             // like to normalize *before* inserting into `local_decls`, but
 190             // doing so ends up causing some other trouble.
 191             let b = self.normalize(b, Locations::All(span));
 192
 193             // Note: if we have to introduce new placeholders during normalization above, then we won't have
 194             // added those universes to the universe info, which we would want in `relate_tys`.
 195             if let Err(terr) =
 196                 self.eq_types(a, b, Locations::All(span), ConstraintCategory::BoringNoLocation)
 197             {
 198                 span_mirbug!(
 199                     self,
 200                     Location::START,
 201                     "equate_normalized_input_or_output: `{:?}=={:?}` failed with `{:?}`",
 202                     a,
 203                     b,
 204                     terr
 205                 );
 206             }
 207         }
 208     }
 209 }