crates/hir_ty/src/infer/pat.rs

   1 //! Type inference for patterns.
   2
   3 use std::iter::repeat;
   4 use std::sync::Arc;
   5
   6 use chalk_ir::Mutability;
   7 use hir_def::{
   8     expr::{BindingAnnotation, Expr, Literal, Pat, PatId, RecordFieldPat},
   9     path::Path,
  10     FieldId,
  11 };
  12 use hir_expand::name::Name;
  13
  14 use super::{BindingMode, Expectation, InferenceContext};
  15 use crate::{
  16     lower::lower_to_chalk_mutability,
  17     utils::{generics, variant_data},
  18     Interner, Substitution, Ty, TyKind,
  19 };
  20
  21 impl<'a> InferenceContext<'a> {
  22     fn infer_tuple_struct_pat(
  23         &mut self,
  24         path: Option<&Path>,
  25         subpats: &[PatId],
  26         expected: &Ty,
  27         default_bm: BindingMode,
  28         id: PatId,
  29         ellipsis: Option<usize>,
  30     ) -> Ty {
  31         let (ty, def) = self.resolve_variant(path);
  32         let var_data = def.map(|it| variant_data(self.db.upcast(), it));
  33         if let Some(variant) = def {
  34             self.write_variant_resolution(id.into(), variant);
  35         }
  36         self.unify(&ty, expected);
  37
  38         let substs = ty.substs().cloned().unwrap_or_else(Substitution::empty);
  39
  40         let field_tys = def.map(|it| self.db.field_types(it)).unwrap_or_default();
  41         let (pre, post) = match ellipsis {
  42             Some(idx) => subpats.split_at(idx),
  43             None => (subpats, &[][..]),
  44         };
  45         let post_idx_offset = field_tys.iter().count() - post.len();
  46
  47         let pre_iter = pre.iter().enumerate();
  48         let post_iter = (post_idx_offset..).zip(post.iter());
  49         for (i, &subpat) in pre_iter.chain(post_iter) {
  50             let expected_ty = var_data
  51                 .as_ref()
  52                 .and_then(|d| d.field(&Name::new_tuple_field(i)))
  53                 .map_or(self.err_ty(), |field| field_tys[field].clone().subst(&substs));
  54             let expected_ty = self.normalize_associated_types_in(expected_ty);
  55             self.infer_pat(subpat, &expected_ty, default_bm);
  56         }
  57
  58         ty
  59     }
  60
  61     fn infer_record_pat(
  62         &mut self,
  63         path: Option<&Path>,
  64         subpats: &[RecordFieldPat],
  65         expected: &Ty,
  66         default_bm: BindingMode,
  67         id: PatId,
  68     ) -> Ty {
  69         let (ty, def) = self.resolve_variant(path);
  70         let var_data = def.map(|it| variant_data(self.db.upcast(), it));
  71         if let Some(variant) = def {
  72             self.write_variant_resolution(id.into(), variant);
  73         }
  74
  75         self.unify(&ty, expected);
  76
  77         let substs = ty.substs().cloned().unwrap_or_else(Substitution::empty);
  78
  79         let field_tys = def.map(|it| self.db.field_types(it)).unwrap_or_default();
  80         for subpat in subpats {
  81             let matching_field = var_data.as_ref().and_then(|it| it.field(&subpat.name));
  82             if let Some(local_id) = matching_field {
  83                 let field_def = FieldId { parent: def.unwrap(), local_id };
  84                 self.result.record_pat_field_resolutions.insert(subpat.pat, field_def);
  85             }
  86
  87             let expected_ty = matching_field
  88                 .map_or(self.err_ty(), |field| field_tys[field].clone().subst(&substs));
  89             let expected_ty = self.normalize_associated_types_in(expected_ty);
  90             self.infer_pat(subpat.pat, &expected_ty, default_bm);
  91         }
  92
  93         ty
  94     }
  95
  96     pub(super) fn infer_pat(
  97         &mut self,
  98         pat: PatId,
  99         mut expected: &Ty,
 100         mut default_bm: BindingMode,
 101     ) -> Ty {
 102         let body = Arc::clone(&self.body); // avoid borrow checker problem
 103
 104         if is_non_ref_pat(&body, pat) {
 105             while let Some((inner, mutability)) = expected.as_reference() {
 106                 expected = inner;
 107                 default_bm = match default_bm {
 108                     BindingMode::Move => BindingMode::Ref(mutability),
 109                     BindingMode::Ref(Mutability::Not) => BindingMode::Ref(Mutability::Not),
 110                     BindingMode::Ref(Mutability::Mut) => BindingMode::Ref(mutability),
 111                 }
 112             }
 113         } else if let Pat::Ref { .. } = &body[pat] {
 114             cov_mark::hit!(match_ergonomics_ref);
 115             // When you encounter a `&pat` pattern, reset to Move.
 116             // This is so that `w` is by value: `let (_, &w) = &(1, &2);`
 117             default_bm = BindingMode::Move;
 118         }
 119
 120         // Lose mutability.
 121         let default_bm = default_bm;
 122         let expected = expected;
 123
 124         let ty = match &body[pat] {
 125             &Pat::Tuple { ref args, ellipsis } => {
 126                 let expectations = match expected.as_tuple() {
 127                     Some(parameters) => &*parameters.0,
 128                     _ => &[],
 129                 };
 130
 131                 let (pre, post) = match ellipsis {
 132                     Some(idx) => args.split_at(idx),
 133                     None => (&args[..], &[][..]),
 134                 };
 135                 let n_uncovered_patterns = expectations.len().saturating_sub(args.len());
 136                 let err_ty = self.err_ty();
 137                 let mut expectations_iter = expectations.iter().chain(repeat(&err_ty));
 138                 let mut infer_pat = |(&pat, ty)| self.infer_pat(pat, ty, default_bm);
 139
 140                 let mut inner_tys = Vec::with_capacity(n_uncovered_patterns + args.len());
 141                 inner_tys.extend(pre.iter().zip(expectations_iter.by_ref()).map(&mut infer_pat));
 142                 inner_tys.extend(expectations_iter.by_ref().take(n_uncovered_patterns).cloned());
 143                 inner_tys.extend(post.iter().zip(expectations_iter).map(infer_pat));
 144
 145                 TyKind::Tuple(inner_tys.len(), Substitution(inner_tys.into())).intern(&Interner)
 146             }
 147             Pat::Or(ref pats) => {
 148                 if let Some((first_pat, rest)) = pats.split_first() {
 149                     let ty = self.infer_pat(*first_pat, expected, default_bm);
 150                     for pat in rest {
 151                         self.infer_pat(*pat, expected, default_bm);
 152                     }
 153                     ty
 154                 } else {
 155                     self.err_ty()
 156                 }
 157             }
 158             Pat::Ref { pat, mutability } => {
 159                 let mutability = lower_to_chalk_mutability(*mutability);
 160                 let expectation = match expected.as_reference() {
 161                     Some((inner_ty, exp_mut)) => {
 162                         if mutability != exp_mut {
 163                             // FIXME: emit type error?
 164                         }
 165                         inner_ty.clone()
 166                     }
 167                     _ => self.result.standard_types.unknown.clone(),
 168                 };
 169                 let subty = self.infer_pat(*pat, &expectation, default_bm);
 170                 TyKind::Ref(mutability, subty).intern(&Interner)
 171             }
 172             Pat::TupleStruct { path: p, args: subpats, ellipsis } => self.infer_tuple_struct_pat(
 173                 p.as_ref(),
 174                 subpats,
 175                 expected,
 176                 default_bm,
 177                 pat,
 178                 *ellipsis,
 179             ),
 180             Pat::Record { path: p, args: fields, ellipsis: _ } => {
 181                 self.infer_record_pat(p.as_ref(), fields, expected, default_bm, pat)
 182             }
 183             Pat::Path(path) => {
 184                 // FIXME use correct resolver for the surrounding expression
 185                 let resolver = self.resolver.clone();
 186                 self.infer_path(&resolver, &path, pat.into()).unwrap_or(self.err_ty())
 187             }
 188             Pat::Bind { mode, name: _, subpat } => {
 189                 let mode = if mode == &BindingAnnotation::Unannotated {
 190                     default_bm
 191                 } else {
 192                     BindingMode::convert(*mode)
 193                 };
 194                 let inner_ty = if let Some(subpat) = subpat {
 195                     self.infer_pat(*subpat, expected, default_bm)
 196                 } else {
 197                     expected.clone()
 198                 };
 199                 let inner_ty = self.insert_type_vars_shallow(inner_ty);
 200
 201                 let bound_ty = match mode {
 202                     BindingMode::Ref(mutability) => {
 203                         TyKind::Ref(mutability, inner_ty.clone()).intern(&Interner)
 204                     }
 205                     BindingMode::Move => inner_ty.clone(),
 206                 };
 207                 let bound_ty = self.resolve_ty_as_possible(bound_ty);
 208                 self.write_pat_ty(pat, bound_ty);
 209                 return inner_ty;
 210             }
 211             Pat::Slice { prefix, slice, suffix } => {
 212                 let (container_ty, elem_ty): (fn(_) -> _, _) = match expected.interned(&Interner) {
 213                     TyKind::Array(st) => (TyKind::Array, st.clone()),
 214                     TyKind::Slice(st) => (TyKind::Slice, st.clone()),
 215                     _ => (TyKind::Slice, self.err_ty()),
 216                 };
 217
 218                 for pat_id in prefix.iter().chain(suffix) {
 219                     self.infer_pat(*pat_id, &elem_ty, default_bm);
 220                 }
 221
 222                 let pat_ty = container_ty(elem_ty).intern(&Interner);
 223                 if let Some(slice_pat_id) = slice {
 224                     self.infer_pat(*slice_pat_id, &pat_ty, default_bm);
 225                 }
 226
 227                 pat_ty
 228             }
 229             Pat::Wild => expected.clone(),
 230             Pat::Range { start, end } => {
 231                 let start_ty = self.infer_expr(*start, &Expectation::has_type(expected.clone()));
 232                 let end_ty = self.infer_expr(*end, &Expectation::has_type(start_ty));
 233                 end_ty
 234             }
 235             Pat::Lit(expr) => self.infer_expr(*expr, &Expectation::has_type(expected.clone())),
 236             Pat::Box { inner } => match self.resolve_boxed_box() {
 237                 Some(box_adt) => {
 238                     let (inner_ty, alloc_ty) = match expected.as_adt() {
 239                         Some((adt, subst)) if adt == box_adt => {
 240                             (subst[0].clone(), subst.get(1).cloned())
 241                         }
 242                         _ => (self.result.standard_types.unknown.clone(), None),
 243                     };
 244
 245                     let inner_ty = self.infer_pat(*inner, &inner_ty, default_bm);
 246                     let mut sb = Substitution::build_for_generics(&generics(
 247                         self.db.upcast(),
 248                         box_adt.into(),
 249                     ));
 250                     sb = sb.push(inner_ty);
 251                     if sb.remaining() == 1 {
 252                         sb = sb.push(match alloc_ty {
 253                             Some(alloc_ty) if !alloc_ty.is_unknown() => alloc_ty,
 254                             _ => match self.db.generic_defaults(box_adt.into()).get(1) {
 255                                 Some(alloc_ty) if !alloc_ty.value.is_unknown() => {
 256                                     alloc_ty.value.clone()
 257                                 }
 258                                 _ => self.table.new_type_var(),
 259                             },
 260                         });
 261                     }
 262                     Ty::adt_ty(box_adt, sb.build())
 263                 }
 264                 None => self.err_ty(),
 265             },
 266             Pat::ConstBlock(expr) => {
 267                 self.infer_expr(*expr, &Expectation::has_type(expected.clone()))
 268             }
 269             Pat::Missing => self.err_ty(),
 270         };
 271         // use a new type variable if we got error type here
 272         let ty = self.insert_type_vars_shallow(ty);
 273         if !self.unify(&ty, expected) {
 274             // FIXME record mismatch, we need to change the type of self.type_mismatches for that
 275         }
 276         let ty = self.resolve_ty_as_possible(ty);
 277         self.write_pat_ty(pat, ty.clone());
 278         ty
 279     }
 280 }
 281
 282 fn is_non_ref_pat(body: &hir_def::body::Body, pat: PatId) -> bool {
 283     match &body[pat] {
 284         Pat::Tuple { .. }
 285         | Pat::TupleStruct { .. }
 286         | Pat::Record { .. }
 287         | Pat::Range { .. }
 288         | Pat::Slice { .. } => true,
 289         Pat::Or(pats) => pats.iter().all(|p| is_non_ref_pat(body, *p)),
 290         // FIXME: ConstBlock/Path/Lit might actually evaluate to ref, but inference is unimplemented.
 291         Pat::Path(..) => true,
 292         Pat::ConstBlock(..) => true,
 293         Pat::Lit(expr) => match body[*expr] {
 294             Expr::Literal(Literal::String(..)) => false,
 295             _ => true,
 296         },
 297         Pat::Wild | Pat::Bind { .. } | Pat::Ref { .. } | Pat::Box { .. } | Pat::Missing => false,
 298     }
 299 }