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