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};
  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         mut expected: &Ty,
  98         mut default_bm: BindingMode,
  99     ) -> Ty {
 100         let body = Arc::clone(&self.body); // avoid borrow checker problem
 101
 102         if is_non_ref_pat(&body, pat) {
 103             while let Some((inner, _lifetime, mutability)) = expected.as_reference() {
 104                 expected = inner;
 105                 default_bm = match default_bm {
 106                     BindingMode::Move => BindingMode::Ref(mutability),
 107                     BindingMode::Ref(Mutability::Not) => BindingMode::Ref(Mutability::Not),
 108                     BindingMode::Ref(Mutability::Mut) => BindingMode::Ref(mutability),
 109                 }
 110             }
 111         } else if let Pat::Ref { .. } = &body[pat] {
 112             cov_mark::hit!(match_ergonomics_ref);
 113             // When you encounter a `&pat` pattern, reset to Move.
 114             // This is so that `w` is by value: `let (_, &w) = &(1, &2);`
 115             default_bm = BindingMode::Move;
 116         }
 117
 118         // Lose mutability.
 119         let default_bm = default_bm;
 120         let expected = expected;
 121
 122         let ty = match &body[pat] {
 123             &Pat::Tuple { ref args, ellipsis } => {
 124                 let expectations = match expected.as_tuple() {
 125                     Some(parameters) => &*parameters.as_slice(&Interner),
 126                     _ => &[],
 127                 };
 128
 129                 let ((pre, post), n_uncovered_patterns) = match ellipsis {
 130                     Some(idx) => {
 131                         (args.split_at(idx), expectations.len().saturating_sub(args.len()))
 132                     }
 133                     None => ((&args[..], &[][..]), 0),
 134                 };
 135                 let err_ty = self.err_ty();
 136                 let mut expectations_iter =
 137                     expectations.iter().map(|a| a.assert_ty_ref(&Interner)).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::from_iter(&Interner, inner_tys))
 146                     .intern(&Interner)
 147             }
 148             Pat::Or(ref pats) => {
 149                 if let Some((first_pat, rest)) = pats.split_first() {
 150                     let ty = self.infer_pat(*first_pat, expected, default_bm);
 151                     for pat in rest {
 152                         self.infer_pat(*pat, expected, default_bm);
 153                     }
 154                     ty
 155                 } else {
 156                     self.err_ty()
 157                 }
 158             }
 159             Pat::Ref { pat, mutability } => {
 160                 let mutability = lower_to_chalk_mutability(*mutability);
 161                 let expectation = match expected.as_reference() {
 162                     Some((inner_ty, _lifetime, exp_mut)) => {
 163                         if mutability != exp_mut {
 164                             // FIXME: emit type error?
 165                         }
 166                         inner_ty.clone()
 167                     }
 168                     _ => self.result.standard_types.unknown.clone(),
 169                 };
 170                 let subty = self.infer_pat(*pat, &expectation, default_bm);
 171                 TyKind::Ref(mutability, static_lifetime(), subty).intern(&Interner)
 172             }
 173             Pat::TupleStruct { path: p, args: subpats, ellipsis } => self.infer_tuple_struct_pat(
 174                 p.as_deref(),
 175                 subpats,
 176                 expected,
 177                 default_bm,
 178                 pat,
 179                 *ellipsis,
 180             ),
 181             Pat::Record { path: p, args: fields, ellipsis: _ } => {
 182                 self.infer_record_pat(p.as_deref(), fields, expected, default_bm, pat)
 183             }
 184             Pat::Path(path) => {
 185                 // FIXME use correct resolver for the surrounding expression
 186                 let resolver = self.resolver.clone();
 187                 self.infer_path(&resolver, &path, pat.into()).unwrap_or(self.err_ty())
 188             }
 189             Pat::Bind { mode, name: _, subpat } => {
 190                 let mode = if mode == &BindingAnnotation::Unannotated {
 191                     default_bm
 192                 } else {
 193                     BindingMode::convert(*mode)
 194                 };
 195                 let inner_ty = if let Some(subpat) = subpat {
 196                     self.infer_pat(*subpat, expected, default_bm)
 197                 } else {
 198                     expected.clone()
 199                 };
 200                 let inner_ty = self.insert_type_vars_shallow(inner_ty);
 201
 202                 let bound_ty = match mode {
 203                     BindingMode::Ref(mutability) => {
 204                         TyKind::Ref(mutability, static_lifetime(), inner_ty.clone())
 205                             .intern(&Interner)
 206                     }
 207                     BindingMode::Move => inner_ty.clone(),
 208                 };
 209                 let bound_ty = self.resolve_ty_as_possible(bound_ty);
 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             // FIXME record mismatch, we need to change the type of self.type_mismatches for that
 270         }
 271         let ty = self.resolve_ty_as_possible(ty);
 272         self.write_pat_ty(pat, ty.clone());
 273         ty
 274     }
 275 }
 276
 277 fn is_non_ref_pat(body: &hir_def::body::Body, pat: PatId) -> bool {
 278     match &body[pat] {
 279         Pat::Tuple { .. }
 280         | Pat::TupleStruct { .. }
 281         | Pat::Record { .. }
 282         | Pat::Range { .. }
 283         | Pat::Slice { .. } => true,
 284         Pat::Or(pats) => pats.iter().all(|p| is_non_ref_pat(body, *p)),
 285         // FIXME: ConstBlock/Path/Lit might actually evaluate to ref, but inference is unimplemented.
 286         Pat::Path(..) => true,
 287         Pat::ConstBlock(..) => true,
 288         Pat::Lit(expr) => match body[*expr] {
 289             Expr::Literal(Literal::String(..)) => false,
 290             _ => true,
 291         },
 292         Pat::Wild | Pat::Bind { .. } | Pat::Ref { .. } | Pat::Box { .. } | Pat::Missing => false,
 293     }
 294 }