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