src/librustc_mir/borrow_check/nll/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 existential
   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 crate::borrow_check::nll::universal_regions::UniversalRegions;
  11 use rustc::infer::LateBoundRegionConversionTime;
  12 use rustc::mir::*;
  13 use rustc::ty::Ty;
  14
  15 use rustc_data_structures::indexed_vec::Idx;
  16 use syntax_pos::Span;
  17
  18 use super::{Locations, TypeChecker};
  19
  20 impl<'a, 'gcx, 'tcx> TypeChecker<'a, 'gcx, 'tcx> {
  21     pub(super) fn equate_inputs_and_outputs(
  22         &mut self,
  23         mir: &Body<'tcx>,
  24         universal_regions: &UniversalRegions<'tcx>,
  25         normalized_inputs_and_output: &[Ty<'tcx>],
  26     ) {
  27         let (&normalized_output_ty, normalized_input_tys) =
  28             normalized_inputs_and_output.split_last().unwrap();
  29
  30         // If the user explicitly annotated the input types, extract
  31         // those.
  32         //
  33         // e.g., `|x: FxHashMap<_, &'static u32>| ...`
  34         let user_provided_sig;
  35         if !self.tcx().is_closure(self.mir_def_id) {
  36             user_provided_sig = None;
  37         } else {
  38             let typeck_tables = self.tcx().typeck_tables_of(self.mir_def_id);
  39             user_provided_sig = match typeck_tables.user_provided_sigs.get(&self.mir_def_id) {
  40                 None => None,
  41                 Some(user_provided_poly_sig) => {
  42                     // Instantiate the canonicalized variables from
  43                     // user-provided signature (e.g., the `_` in the code
  44                     // above) with fresh variables.
  45                     let (poly_sig, _) = self.infcx.instantiate_canonical_with_fresh_inference_vars(
  46                         mir.span,
  47                         &user_provided_poly_sig,
  48                     );
  49
  50                     // Replace the bound items in the fn sig with fresh
  51                     // variables, so that they represent the view from
  52                     // "inside" the closure.
  53                     Some(
  54                         self.infcx
  55                             .replace_bound_vars_with_fresh_vars(
  56                                 mir.span,
  57                                 LateBoundRegionConversionTime::FnCall,
  58                                 &poly_sig,
  59                             )
  60                             .0,
  61                     )
  62                 }
  63             }
  64         };
  65
  66         // Equate expected input tys with those in the MIR.
  67         for (&normalized_input_ty, argument_index) in normalized_input_tys.iter().zip(0..) {
  68             // In MIR, argument N is stored in local N+1.
  69             let local = Local::new(argument_index + 1);
  70
  71             debug!(
  72                 "equate_inputs_and_outputs: normalized_input_ty = {:?}",
  73                 normalized_input_ty
  74             );
  75
  76             let mir_input_ty = mir.local_decls[local].ty;
  77             let mir_input_span = mir.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 (&user_provided_input_ty, argument_index) in
  87                 user_provided_sig.inputs().iter().zip(0..)
  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 = mir.local_decls[local].ty;
  93                 let mir_input_span = mir.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             mir.yield_ty.is_some() && universal_regions.yield_ty.is_some()
 108                 || mir.yield_ty.is_none() && universal_regions.yield_ty.is_none()
 109         );
 110         if let Some(mir_yield_ty) = mir.yield_ty {
 111             let ur_yield_ty = universal_regions.yield_ty.unwrap();
 112             let yield_span = mir.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 existential `impl Trait`
 117         // types.
 118         let mir_output_ty = mir.local_decls[RETURN_PLACE].ty;
 119         let output_span = mir.local_decls[RETURN_PLACE].source_info.span;
 120         if let Err(terr) = self.eq_opaque_type_and_type(
 121             mir_output_ty,
 122             normalized_output_ty,
 123             self.mir_def_id,
 124             Locations::All(output_span),
 125             ConstraintCategory::BoringNoLocation,
 126         ) {
 127             span_mirbug!(
 128                 self,
 129                 Location::START,
 130                 "equate_inputs_and_outputs: `{:?}=={:?}` failed with `{:?}`",
 131                 normalized_output_ty,
 132                 mir_output_ty,
 133                 terr
 134             );
 135         };
 136
 137         // If the user explicitly annotated the output types, enforce those.
 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             self.equate_normalized_input_or_output(
 143                 user_provided_output_ty,
 144                 mir_output_ty,
 145                 output_span,
 146             );
 147         }
 148     }
 149
 150     fn equate_normalized_input_or_output(&mut self, a: Ty<'tcx>, b: Ty<'tcx>, span: Span) {
 151         debug!("equate_normalized_input_or_output(a={:?}, b={:?})", a, b);
 152
 153         if let Err(terr) = self.eq_types(
 154             a,
 155             b,
 156             Locations::All(span),
 157             ConstraintCategory::BoringNoLocation,
 158         ) {
 159             span_mirbug!(
 160                 self,
 161                 Location::START,
 162                 "equate_normalized_input_or_output: `{:?}=={:?}` failed with `{:?}`",
 163                 a,
 164                 b,
 165                 terr
 166             );
 167         }
 168     }
 169 }