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 crate::type_check::constraint_conversion::ConstraintConversion;
  11 use rustc_index::vec::Idx;
  12 use rustc_infer::infer::LateBoundRegionConversionTime;
  13 use rustc_middle::mir::*;
  14 use rustc_middle::ty::Ty;
  15 use rustc_span::Span;
  16 use rustc_span::DUMMY_SP;
  17 use rustc_trait_selection::traits::query::type_op::{self, TypeOp};
  18 use rustc_trait_selection::traits::query::Fallible;
  19 use type_op::TypeOpOutput;
  20
  21 use crate::universal_regions::UniversalRegions;
  22
  23 use super::{Locations, TypeChecker};
  24
  25 impl<'a, 'tcx> TypeChecker<'a, 'tcx> {
  26     #[instrument(skip(self, body, universal_regions), level = "debug")]
  27     pub(super) fn equate_inputs_and_outputs(
  28         &mut self,
  29         body: &Body<'tcx>,
  30         universal_regions: &UniversalRegions<'tcx>,
  31         normalized_inputs_and_output: &[Ty<'tcx>],
  32     ) {
  33         let (&normalized_output_ty, normalized_input_tys) =
  34             normalized_inputs_and_output.split_last().unwrap();
  35
  36         debug!(?normalized_output_ty);
  37         debug!(?normalized_input_tys);
  38
  39         let mir_def_id = body.source.def_id().expect_local();
  40
  41         // If the user explicitly annotated the input types, extract
  42         // those.
  43         //
  44         // e.g., `|x: FxHashMap<_, &'static u32>| ...`
  45         let user_provided_sig;
  46         if !self.tcx().is_closure(mir_def_id.to_def_id()) {
  47             user_provided_sig = None;
  48         } else {
  49             let typeck_results = self.tcx().typeck(mir_def_id);
  50             user_provided_sig = typeck_results.user_provided_sigs.get(&mir_def_id.to_def_id()).map(
  51                 |user_provided_poly_sig| {
  52                     // Instantiate the canonicalized variables from
  53                     // user-provided signature (e.g., the `_` in the code
  54                     // above) with fresh variables.
  55                     let poly_sig = self.instantiate_canonical_with_fresh_inference_vars(
  56                         body.span,
  57                         &user_provided_poly_sig,
  58                     );
  59
  60                     // Replace the bound items in the fn sig with fresh
  61                     // variables, so that they represent the view from
  62                     // "inside" the closure.
  63                     self.infcx.replace_bound_vars_with_fresh_vars(
  64                         body.span,
  65                         LateBoundRegionConversionTime::FnCall,
  66                         poly_sig,
  67                     )
  68                 },
  69             );
  70         }
  71
  72         debug!(?normalized_input_tys, ?body.local_decls);
  73
  74         // Equate expected input tys with those in the MIR.
  75         for (argument_index, &normalized_input_ty) in normalized_input_tys.iter().enumerate() {
  76             if argument_index + 1 >= body.local_decls.len() {
  77                 self.tcx()
  78                     .sess
  79                     .delay_span_bug(body.span, "found more normalized_input_ty than local_decls");
  80                 break;
  81             }
  82
  83             // In MIR, argument N is stored in local N+1.
  84             let local = Local::new(argument_index + 1);
  85
  86             let mir_input_ty = body.local_decls[local].ty;
  87
  88             let mir_input_span = body.local_decls[local].source_info.span;
  89             self.equate_normalized_input_or_output(
  90                 normalized_input_ty,
  91                 mir_input_ty,
  92                 mir_input_span,
  93             );
  94         }
  95
  96         if let Some(user_provided_sig) = user_provided_sig {
  97             for (argument_index, &user_provided_input_ty) in
  98                 user_provided_sig.inputs().iter().enumerate()
  99             {
 100                 // In MIR, closures begin an implicit `self`, so
 101                 // argument N is stored in local N+2.
 102                 let local = Local::new(argument_index + 2);
 103                 let mir_input_ty = body.local_decls[local].ty;
 104                 let mir_input_span = body.local_decls[local].source_info.span;
 105
 106                 // If the user explicitly annotated the input types, enforce those.
 107                 let user_provided_input_ty =
 108                     self.normalize(user_provided_input_ty, Locations::All(mir_input_span));
 109
 110                 self.equate_normalized_input_or_output(
 111                     user_provided_input_ty,
 112                     mir_input_ty,
 113                     mir_input_span,
 114                 );
 115             }
 116         }
 117
 118         debug!(
 119             "equate_inputs_and_outputs: body.yield_ty {:?}, universal_regions.yield_ty {:?}",
 120             body.yield_ty(),
 121             universal_regions.yield_ty
 122         );
 123
 124         // We will not have a universal_regions.yield_ty if we yield (by accident)
 125         // outside of a generator and return an `impl Trait`, so emit a delay_span_bug
 126         // because we don't want to panic in an assert here if we've already got errors.
 127         if body.yield_ty().is_some() != universal_regions.yield_ty.is_some() {
 128             self.tcx().sess.delay_span_bug(
 129                 body.span,
 130                 &format!(
 131                     "Expected body to have yield_ty ({:?}) iff we have a UR yield_ty ({:?})",
 132                     body.yield_ty(),
 133                     universal_regions.yield_ty,
 134                 ),
 135             );
 136         }
 137
 138         if let (Some(mir_yield_ty), Some(ur_yield_ty)) =
 139             (body.yield_ty(), universal_regions.yield_ty)
 140         {
 141             let yield_span = body.local_decls[RETURN_PLACE].source_info.span;
 142             self.equate_normalized_input_or_output(ur_yield_ty, mir_yield_ty, yield_span);
 143         }
 144
 145         // Return types are a bit more complex. They may contain opaque `impl Trait` types.
 146         let mir_output_ty = body.local_decls[RETURN_PLACE].ty;
 147         let output_span = body.local_decls[RETURN_PLACE].source_info.span;
 148         if let Err(terr) = self.eq_types(
 149             normalized_output_ty,
 150             mir_output_ty,
 151             Locations::All(output_span),
 152             ConstraintCategory::BoringNoLocation,
 153         ) {
 154             span_mirbug!(
 155                 self,
 156                 Location::START,
 157                 "equate_inputs_and_outputs: `{:?}=={:?}` failed with `{:?}`",
 158                 normalized_output_ty,
 159                 mir_output_ty,
 160                 terr
 161             );
 162         };
 163
 164         // If the user explicitly annotated the output types, enforce those.
 165         // Note that this only happens for closures.
 166         if let Some(user_provided_sig) = user_provided_sig {
 167             let user_provided_output_ty = user_provided_sig.output();
 168             let user_provided_output_ty =
 169                 self.normalize(user_provided_output_ty, Locations::All(output_span));
 170             if let Err(err) = self.eq_types(
 171                 user_provided_output_ty,
 172                 mir_output_ty,
 173                 Locations::All(output_span),
 174                 ConstraintCategory::BoringNoLocation,
 175             ) {
 176                 span_mirbug!(
 177                     self,
 178                     Location::START,
 179                     "equate_inputs_and_outputs: `{:?}=={:?}` failed with `{:?}`",
 180                     mir_output_ty,
 181                     user_provided_output_ty,
 182                     err
 183                 );
 184             }
 185         }
 186     }
 187
 188     #[instrument(skip(self, span), level = "debug")]
 189     fn equate_normalized_input_or_output(&mut self, a: Ty<'tcx>, b: Ty<'tcx>, span: Span) {
 190         if let Err(_) =
 191             self.eq_types(a, b, Locations::All(span), ConstraintCategory::BoringNoLocation)
 192         {
 193             // FIXME(jackh726): This is a hack. It's somewhat like
 194             // `rustc_traits::normalize_after_erasing_regions`. Ideally, we'd
 195             // like to normalize *before* inserting into `local_decls`, but
 196             // doing so ends up causing some other trouble.
 197             let b = match self.normalize_and_add_constraints(b) {
 198                 Ok(n) => n,
 199                 Err(_) => {
 200                     debug!("equate_inputs_and_outputs: NoSolution");
 201                     b
 202                 }
 203             };
 204
 205             // Note: if we have to introduce new placeholders during normalization above, then we won't have
 206             // added those universes to the universe info, which we would want in `relate_tys`.
 207             if let Err(terr) =
 208                 self.eq_types(a, b, Locations::All(span), ConstraintCategory::BoringNoLocation)
 209             {
 210                 span_mirbug!(
 211                     self,
 212                     Location::START,
 213                     "equate_normalized_input_or_output: `{:?}=={:?}` failed with `{:?}`",
 214                     a,
 215                     b,
 216                     terr
 217                 );
 218             }
 219         }
 220     }
 221
 222     pub(crate) fn normalize_and_add_constraints(&mut self, t: Ty<'tcx>) -> Fallible<Ty<'tcx>> {
 223         let TypeOpOutput { output: norm_ty, constraints, .. } =
 224             self.param_env.and(type_op::normalize::Normalize::new(t)).fully_perform(self.infcx)?;
 225
 226         debug!("{:?} normalized to {:?}", t, norm_ty);
 227
 228         for data in constraints.into_iter().collect::<Vec<_>>() {
 229             ConstraintConversion::new(
 230                 self.infcx,
 231                 &self.borrowck_context.universal_regions,
 232                 &self.region_bound_pairs,
 233                 Some(self.implicit_region_bound),
 234                 self.param_env,
 235                 Locations::All(DUMMY_SP),
 236                 DUMMY_SP,
 237                 ConstraintCategory::Internal,
 238                 &mut self.borrowck_context.constraints,
 239             )
 240             .convert_all(&*data);
 241         }
 242
 243         Ok(norm_ty)
 244     }
 245 }