compiler/rustc_mir/src/borrow_check/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_infer::infer::LateBoundRegionConversionTime;
  11 use rustc_middle::mir::*;
  12 use rustc_middle::ty::Ty;
  13
  14 use rustc_index::vec::Idx;
  15 use rustc_span::Span;
  16
  17 use crate::borrow_check::universal_regions::UniversalRegions;
  18
  19 use super::{Locations, TypeChecker};
  20
  21 impl<'a, 'tcx> TypeChecker<'a, 'tcx> {
  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         let mir_def_id = body.source.def_id().expect_local();
  32
  33         // If the user explicitly annotated the input types, extract
  34         // those.
  35         //
  36         // e.g., `|x: FxHashMap<_, &'static u32>| ...`
  37         let user_provided_sig;
  38         if !self.tcx().is_closure(mir_def_id.to_def_id()) {
  39             user_provided_sig = None;
  40         } else {
  41             let typeck_results = self.tcx().typeck(mir_def_id);
  42             user_provided_sig = typeck_results.user_provided_sigs.get(&mir_def_id.to_def_id()).map(
  43                 |user_provided_poly_sig| {
  44                     // Instantiate the canonicalized variables from
  45                     // user-provided signature (e.g., the `_` in the code
  46                     // above) with fresh variables.
  47                     let (poly_sig, _) = self.infcx.instantiate_canonical_with_fresh_inference_vars(
  48                         body.span,
  49                         &user_provided_poly_sig,
  50                     );
  51
  52                     // Replace the bound items in the fn sig with fresh
  53                     // variables, so that they represent the view from
  54                     // "inside" the closure.
  55                     self.infcx
  56                         .replace_bound_vars_with_fresh_vars(
  57                             body.span,
  58                             LateBoundRegionConversionTime::FnCall,
  59                             poly_sig,
  60                         )
  61                         .0
  62                 },
  63             );
  64         }
  65
  66         debug!(
  67             "equate_inputs_and_outputs: normalized_input_tys = {:?}, local_decls = {:?}",
  68             normalized_input_tys, body.local_decls
  69         );
  70
  71         // Equate expected input tys with those in the MIR.
  72         for (argument_index, &normalized_input_ty) in normalized_input_tys.iter().enumerate() {
  73             // In MIR, argument N is stored in local N+1.
  74             let local = Local::new(argument_index + 1);
  75
  76             let mir_input_ty = body.local_decls[local].ty;
  77             let mir_input_span = body.local_decls[local].source_info.span;
  78             self.equate_normalized_input_or_output(
  79                 normalized_input_ty,
  80                 mir_input_ty,
  81                 mir_input_span,
  82             );
  83         }
  84
  85         if let Some(user_provided_sig) = user_provided_sig {
  86             for (argument_index, &user_provided_input_ty) in
  87                 user_provided_sig.inputs().iter().enumerate()
  88             {
  89                 // In MIR, closures begin an implicit `self`, so
  90                 // argument N is stored in local N+2.
  91                 let local = Local::new(argument_index + 2);
  92                 let mir_input_ty = body.local_decls[local].ty;
  93                 let mir_input_span = body.local_decls[local].source_info.span;
  94
  95                 // If the user explicitly annotated the input types, enforce those.
  96                 let user_provided_input_ty =
  97                     self.normalize(user_provided_input_ty, Locations::All(mir_input_span));
  98                 self.equate_normalized_input_or_output(
  99                     user_provided_input_ty,
 100                     mir_input_ty,
 101                     mir_input_span,
 102                 );
 103             }
 104         }
 105
 106         assert!(
 107             body.yield_ty.is_some() && universal_regions.yield_ty.is_some()
 108                 || body.yield_ty.is_none() && universal_regions.yield_ty.is_none()
 109         );
 110         if let Some(mir_yield_ty) = body.yield_ty {
 111             let ur_yield_ty = universal_regions.yield_ty.unwrap();
 112             let yield_span = body.local_decls[RETURN_PLACE].source_info.span;
 113             self.equate_normalized_input_or_output(ur_yield_ty, mir_yield_ty, yield_span);
 114         }
 115
 116         // Return types are a bit more complex. They may contain opaque `impl Trait` types.
 117         let mir_output_ty = body.local_decls[RETURN_PLACE].ty;
 118         let output_span = body.local_decls[RETURN_PLACE].source_info.span;
 119         if let Err(terr) = self.eq_opaque_type_and_type(
 120             mir_output_ty,
 121             normalized_output_ty,
 122             mir_def_id,
 123             Locations::All(output_span),
 124             ConstraintCategory::BoringNoLocation,
 125         ) {
 126             span_mirbug!(
 127                 self,
 128                 Location::START,
 129                 "equate_inputs_and_outputs: `{:?}=={:?}` failed with `{:?}`",
 130                 normalized_output_ty,
 131                 mir_output_ty,
 132                 terr
 133             );
 134         };
 135
 136         // If the user explicitly annotated the output types, enforce those.
 137         // Note that this only happens for closures.
 138         if let Some(user_provided_sig) = user_provided_sig {
 139             let user_provided_output_ty = user_provided_sig.output();
 140             let user_provided_output_ty =
 141                 self.normalize(user_provided_output_ty, Locations::All(output_span));
 142             if let Err(err) = self.eq_opaque_type_and_type(
 143                 mir_output_ty,
 144                 user_provided_output_ty,
 145                 mir_def_id,
 146                 Locations::All(output_span),
 147                 ConstraintCategory::BoringNoLocation,
 148             ) {
 149                 span_mirbug!(
 150                     self,
 151                     Location::START,
 152                     "equate_inputs_and_outputs: `{:?}=={:?}` failed with `{:?}`",
 153                     mir_output_ty,
 154                     user_provided_output_ty,
 155                     err
 156                 );
 157             }
 158         }
 159     }
 160
 161     fn equate_normalized_input_or_output(&mut self, a: Ty<'tcx>, b: Ty<'tcx>, span: Span) {
 162         debug!("equate_normalized_input_or_output(a={:?}, b={:?})", a, b);
 163
 164         if let Err(terr) =
 165             self.eq_types(a, b, Locations::All(span), ConstraintCategory::BoringNoLocation)
 166         {
 167             span_mirbug!(
 168                 self,
 169                 Location::START,
 170                 "equate_normalized_input_or_output: `{:?}=={:?}` failed with `{:?}`",
 171                 a,
 172                 b,
 173                 terr
 174             );
 175         }
 176     }
 177 }