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