crates/hir_ty/src/infer/pat.rs

   1 //! Type inference for patterns.
   2
   3 use std::{iter::repeat, sync::Arc};
   4
   5 use chalk_ir::Mutability;
   6 use hir_def::{
   7     expr::{BindingAnnotation, Expr, Literal, Pat, PatId, RecordFieldPat},
   8     path::Path,
   9     type_ref::ConstScalar,
  10 };
  11 use hir_expand::name::Name;
  12
  13 use crate::{
  14     infer::{
  15         Adjust, Adjustment, AutoBorrow, BindingMode, Expectation, InferenceContext, TypeMismatch,
  16     },
  17     lower::lower_to_chalk_mutability,
  18     static_lifetime, ConcreteConst, ConstValue, Interner, Substitution, Ty, TyBuilder, TyExt,
  19     TyKind,
  20 };
  21
  22 impl<'a> InferenceContext<'a> {
  23     fn infer_tuple_struct_pat(
  24         &mut self,
  25         path: Option<&Path>,
  26         subpats: &[PatId],
  27         expected: &Ty,
  28         default_bm: BindingMode,
  29         id: PatId,
  30         ellipsis: Option<usize>,
  31     ) -> Ty {
  32         let (ty, def) = self.resolve_variant(path, true);
  33         let var_data = def.map(|it| it.variant_data(self.db.upcast()));
  34         if let Some(variant) = def {
  35             self.write_variant_resolution(id.into(), variant);
  36         }
  37         self.unify(&ty, expected);
  38
  39         let substs =
  40             ty.as_adt().map(|(_, s)| s.clone()).unwrap_or_else(|| Substitution::empty(Interner));
  41
  42         let field_tys = def.map(|it| self.db.field_types(it)).unwrap_or_default();
  43         let (pre, post) = match ellipsis {
  44             Some(idx) => subpats.split_at(idx),
  45             None => (subpats, &[][..]),
  46         };
  47         let post_idx_offset = field_tys.iter().count() - post.len();
  48
  49         let pre_iter = pre.iter().enumerate();
  50         let post_iter = (post_idx_offset..).zip(post.iter());
  51         for (i, &subpat) in pre_iter.chain(post_iter) {
  52             let expected_ty = var_data
  53                 .as_ref()
  54                 .and_then(|d| d.field(&Name::new_tuple_field(i)))
  55                 .map_or(self.err_ty(), |field| {
  56                     field_tys[field].clone().substitute(Interner, &substs)
  57                 });
  58             let expected_ty = self.normalize_associated_types_in(expected_ty);
  59             self.infer_pat(subpat, &expected_ty, default_bm);
  60         }
  61
  62         ty
  63     }
  64
  65     fn infer_record_pat(
  66         &mut self,
  67         path: Option<&Path>,
  68         subpats: &[RecordFieldPat],
  69         expected: &Ty,
  70         default_bm: BindingMode,
  71         id: PatId,
  72     ) -> Ty {
  73         let (ty, def) = self.resolve_variant(path, false);
  74         let var_data = def.map(|it| it.variant_data(self.db.upcast()));
  75         if let Some(variant) = def {
  76             self.write_variant_resolution(id.into(), variant);
  77         }
  78
  79         self.unify(&ty, expected);
  80
  81         let substs =
  82             ty.as_adt().map(|(_, s)| s.clone()).unwrap_or_else(|| Substitution::empty(Interner));
  83
  84         let field_tys = def.map(|it| self.db.field_types(it)).unwrap_or_default();
  85         for subpat in subpats {
  86             let matching_field = var_data.as_ref().and_then(|it| it.field(&subpat.name));
  87             let expected_ty = matching_field.map_or(self.err_ty(), |field| {
  88                 field_tys[field].clone().substitute(Interner, &substs)
  89             });
  90             let expected_ty = self.normalize_associated_types_in(expected_ty);
  91             self.infer_pat(subpat.pat, &expected_ty, default_bm);
  92         }
  93
  94         ty
  95     }
  96
  97     pub(super) fn infer_pat(
  98         &mut self,
  99         pat: PatId,
 100         expected: &Ty,
 101         mut default_bm: BindingMode,
 102     ) -> Ty {
 103         let body = Arc::clone(&self.body); // avoid borrow checker problem
 104         let mut expected = self.resolve_ty_shallow(expected);
 105
 106         if is_non_ref_pat(&body, pat) {
 107             let mut pat_adjustments = Vec::new();
 108             while let Some((inner, _lifetime, mutability)) = expected.as_reference() {
 109                 pat_adjustments.push(Adjustment {
 110                     target: expected.clone(),
 111                     kind: Adjust::Borrow(AutoBorrow::Ref(mutability)),
 112                 });
 113                 expected = self.resolve_ty_shallow(inner);
 114                 default_bm = match default_bm {
 115                     BindingMode::Move => BindingMode::Ref(mutability),
 116                     BindingMode::Ref(Mutability::Not) => BindingMode::Ref(Mutability::Not),
 117                     BindingMode::Ref(Mutability::Mut) => BindingMode::Ref(mutability),
 118                 }
 119             }
 120
 121             if !pat_adjustments.is_empty() {
 122                 pat_adjustments.shrink_to_fit();
 123                 self.result.pat_adjustments.insert(pat, pat_adjustments);
 124             }
 125         } else if let Pat::Ref { .. } = &body[pat] {
 126             cov_mark::hit!(match_ergonomics_ref);
 127             // When you encounter a `&pat` pattern, reset to Move.
 128             // This is so that `w` is by value: `let (_, &w) = &(1, &2);`
 129             default_bm = BindingMode::Move;
 130         }
 131
 132         // Lose mutability.
 133         let default_bm = default_bm;
 134         let expected = expected;
 135
 136         let ty = match &body[pat] {
 137             Pat::Tuple { args, ellipsis } => {
 138                 let expectations = match expected.as_tuple() {
 139                     Some(parameters) => &*parameters.as_slice(Interner),
 140                     _ => &[],
 141                 };
 142
 143                 let ((pre, post), n_uncovered_patterns) = match ellipsis {
 144                     Some(idx) => {
 145                         (args.split_at(*idx), expectations.len().saturating_sub(args.len()))
 146                     }
 147                     None => ((&args[..], &[][..]), 0),
 148                 };
 149                 let err_ty = self.err_ty();
 150                 let mut expectations_iter =
 151                     expectations.iter().map(|a| a.assert_ty_ref(Interner)).chain(repeat(&err_ty));
 152                 let mut infer_pat = |(&pat, ty)| self.infer_pat(pat, ty, default_bm);
 153
 154                 let mut inner_tys = Vec::with_capacity(n_uncovered_patterns + args.len());
 155                 inner_tys.extend(pre.iter().zip(expectations_iter.by_ref()).map(&mut infer_pat));
 156                 inner_tys.extend(expectations_iter.by_ref().take(n_uncovered_patterns).cloned());
 157                 inner_tys.extend(post.iter().zip(expectations_iter).map(infer_pat));
 158
 159                 TyKind::Tuple(inner_tys.len(), Substitution::from_iter(Interner, inner_tys))
 160                     .intern(Interner)
 161             }
 162             Pat::Or(pats) => {
 163                 if let Some((first_pat, rest)) = pats.split_first() {
 164                     let ty = self.infer_pat(*first_pat, &expected, default_bm);
 165                     for pat in rest {
 166                         self.infer_pat(*pat, &expected, default_bm);
 167                     }
 168                     ty
 169                 } else {
 170                     self.err_ty()
 171                 }
 172             }
 173             Pat::Ref { pat, mutability } => {
 174                 let mutability = lower_to_chalk_mutability(*mutability);
 175                 let expectation = match expected.as_reference() {
 176                     Some((inner_ty, _lifetime, exp_mut)) => {
 177                         if mutability != exp_mut {
 178                             // FIXME: emit type error?
 179                         }
 180                         inner_ty.clone()
 181                     }
 182                     _ => self.result.standard_types.unknown.clone(),
 183                 };
 184                 let subty = self.infer_pat(*pat, &expectation, default_bm);
 185                 TyKind::Ref(mutability, static_lifetime(), subty).intern(Interner)
 186             }
 187             Pat::TupleStruct { path: p, args: subpats, ellipsis } => self.infer_tuple_struct_pat(
 188                 p.as_deref(),
 189                 subpats,
 190                 &expected,
 191                 default_bm,
 192                 pat,
 193                 *ellipsis,
 194             ),
 195             Pat::Record { path: p, args: fields, ellipsis: _ } => {
 196                 self.infer_record_pat(p.as_deref(), fields, &expected, default_bm, pat)
 197             }
 198             Pat::Path(path) => {
 199                 // FIXME use correct resolver for the surrounding expression
 200                 let resolver = self.resolver.clone();
 201                 self.infer_path(&resolver, path, pat.into()).unwrap_or_else(|| self.err_ty())
 202             }
 203             Pat::Bind { mode, name: _, subpat } => {
 204                 let mode = if mode == &BindingAnnotation::Unannotated {
 205                     default_bm
 206                 } else {
 207                     BindingMode::convert(*mode)
 208                 };
 209                 self.result.pat_binding_modes.insert(pat, mode);
 210
 211                 let inner_ty = match subpat {
 212                     Some(subpat) => self.infer_pat(*subpat, &expected, default_bm),
 213                     None => expected,
 214                 };
 215                 let inner_ty = self.insert_type_vars_shallow(inner_ty);
 216
 217                 let bound_ty = match mode {
 218                     BindingMode::Ref(mutability) => {
 219                         TyKind::Ref(mutability, static_lifetime(), inner_ty.clone())
 220                             .intern(Interner)
 221                     }
 222                     BindingMode::Move => inner_ty.clone(),
 223                 };
 224                 self.write_pat_ty(pat, bound_ty);
 225                 return inner_ty;
 226             }
 227             Pat::Slice { prefix, slice, suffix } => {
 228                 let elem_ty = match expected.kind(Interner) {
 229                     TyKind::Array(st, _) | TyKind::Slice(st) => st.clone(),
 230                     _ => self.err_ty(),
 231                 };
 232
 233                 for &pat_id in prefix.iter().chain(suffix.iter()) {
 234                     self.infer_pat(pat_id, &elem_ty, default_bm);
 235                 }
 236
 237                 if let &Some(slice_pat_id) = slice {
 238                     let rest_pat_ty = match expected.kind(Interner) {
 239                         TyKind::Array(_, length) => {
 240                             let length = match length.data(Interner).value {
 241                                 ConstValue::Concrete(ConcreteConst {
 242                                     interned: ConstScalar::Usize(length),
 243                                 }) => length.checked_sub((prefix.len() + suffix.len()) as u64),
 244                                 _ => None,
 245                             };
 246                             TyKind::Array(elem_ty.clone(), crate::consteval::usize_const(length))
 247                         }
 248                         _ => TyKind::Slice(elem_ty.clone()),
 249                     }
 250                     .intern(Interner);
 251                     self.infer_pat(slice_pat_id, &rest_pat_ty, default_bm);
 252                 }
 253
 254                 match expected.kind(Interner) {
 255                     TyKind::Array(_, const_) => TyKind::Array(elem_ty, const_.clone()),
 256                     _ => TyKind::Slice(elem_ty),
 257                 }
 258                 .intern(Interner)
 259             }
 260             Pat::Wild => expected.clone(),
 261             Pat::Range { start, end } => {
 262                 let start_ty = self.infer_expr(*start, &Expectation::has_type(expected.clone()));
 263                 self.infer_expr(*end, &Expectation::has_type(start_ty))
 264             }
 265             Pat::Lit(expr) => self.infer_expr(*expr, &Expectation::has_type(expected.clone())),
 266             Pat::Box { inner } => match self.resolve_boxed_box() {
 267                 Some(box_adt) => {
 268                     let (inner_ty, alloc_ty) = match expected.as_adt() {
 269                         Some((adt, subst)) if adt == box_adt => (
 270                             subst.at(Interner, 0).assert_ty_ref(Interner).clone(),
 271                             subst.as_slice(Interner).get(1).and_then(|a| a.ty(Interner).cloned()),
 272                         ),
 273                         _ => (self.result.standard_types.unknown.clone(), None),
 274                     };
 275
 276                     let inner_ty = self.infer_pat(*inner, &inner_ty, default_bm);
 277                     let mut b = TyBuilder::adt(self.db, box_adt).push(inner_ty);
 278
 279                     if let Some(alloc_ty) = alloc_ty {
 280                         b = b.push(alloc_ty);
 281                     }
 282                     b.fill_with_defaults(self.db, || self.table.new_type_var()).build()
 283                 }
 284                 None => self.err_ty(),
 285             },
 286             Pat::ConstBlock(expr) => {
 287                 self.infer_expr(*expr, &Expectation::has_type(expected.clone()))
 288             }
 289             Pat::Missing => self.err_ty(),
 290         };
 291         // use a new type variable if we got error type here
 292         let ty = self.insert_type_vars_shallow(ty);
 293         if !self.unify(&ty, &expected) {
 294             self.result
 295                 .type_mismatches
 296                 .insert(pat.into(), TypeMismatch { expected, actual: ty.clone() });
 297         }
 298         self.write_pat_ty(pat, ty.clone());
 299         ty
 300     }
 301 }
 302
 303 fn is_non_ref_pat(body: &hir_def::body::Body, pat: PatId) -> bool {
 304     match &body[pat] {
 305         Pat::Tuple { .. }
 306         | Pat::TupleStruct { .. }
 307         | Pat::Record { .. }
 308         | Pat::Range { .. }
 309         | Pat::Slice { .. } => true,
 310         Pat::Or(pats) => pats.iter().all(|p| is_non_ref_pat(body, *p)),
 311         // FIXME: ConstBlock/Path/Lit might actually evaluate to ref, but inference is unimplemented.
 312         Pat::Path(..) => true,
 313         Pat::ConstBlock(..) => true,
 314         Pat::Lit(expr) => !matches!(body[*expr], Expr::Literal(Literal::String(..))),
 315         Pat::Bind {
 316             mode: BindingAnnotation::Mutable | BindingAnnotation::Unannotated,
 317             subpat: Some(subpat),
 318             ..
 319         } => is_non_ref_pat(body, *subpat),
 320         Pat::Wild | Pat::Bind { .. } | Pat::Ref { .. } | Pat::Box { .. } | Pat::Missing => false,
 321     }
 322 }