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, utils::variant_data, Interner, Substitution, Ty, TyBuilder,
  17     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| field_tys[field].clone().subst(&substs));
  53             let expected_ty = self.normalize_associated_types_in(expected_ty);
  54             self.infer_pat(subpat, &expected_ty, default_bm);
  55         }
  56
  57         ty
  58     }
  59
  60     fn infer_record_pat(
  61         &mut self,
  62         path: Option<&Path>,
  63         subpats: &[RecordFieldPat],
  64         expected: &Ty,
  65         default_bm: BindingMode,
  66         id: PatId,
  67     ) -> Ty {
  68         let (ty, def) = self.resolve_variant(path);
  69         let var_data = def.map(|it| variant_data(self.db.upcast(), it));
  70         if let Some(variant) = def {
  71             self.write_variant_resolution(id.into(), variant);
  72         }
  73
  74         self.unify(&ty, expected);
  75
  76         let substs = ty.substs().cloned().unwrap_or_else(|| Substitution::empty(&Interner));
  77
  78         let field_tys = def.map(|it| self.db.field_types(it)).unwrap_or_default();
  79         for subpat in subpats {
  80             let matching_field = var_data.as_ref().and_then(|it| it.field(&subpat.name));
  81             if let Some(local_id) = matching_field {
  82                 let field_def = FieldId { parent: def.unwrap(), local_id };
  83                 self.result.record_pat_field_resolutions.insert(subpat.pat, field_def);
  84             }
  85
  86             let expected_ty = matching_field
  87                 .map_or(self.err_ty(), |field| field_tys[field].clone().subst(&substs));
  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         mut expected: &Ty,
  99         mut default_bm: BindingMode,
 100     ) -> Ty {
 101         let body = Arc::clone(&self.body); // avoid borrow checker problem
 102
 103         if is_non_ref_pat(&body, pat) {
 104             while let Some((inner, mutability)) = expected.as_reference() {
 105                 expected = 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.0,
 127                     _ => &[],
 128                 };
 129
 130                 let (pre, post) = match ellipsis {
 131                     Some(idx) => args.split_at(idx),
 132                     None => (&args[..], &[][..]),
 133                 };
 134                 let n_uncovered_patterns = expectations.len().saturating_sub(args.len());
 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, 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, subty).intern(&Interner)
 172             }
 173             Pat::TupleStruct { path: p, args: subpats, ellipsis } => self.infer_tuple_struct_pat(
 174                 p.as_ref(),
 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_ref(), 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, inner_ty.clone()).intern(&Interner)
 205                     }
 206                     BindingMode::Move => inner_ty.clone(),
 207                 };
 208                 let bound_ty = self.resolve_ty_as_possible(bound_ty);
 209                 self.write_pat_ty(pat, bound_ty);
 210                 return inner_ty;
 211             }
 212             Pat::Slice { prefix, slice, suffix } => {
 213                 let (container_ty, elem_ty): (fn(_) -> _, _) = match expected.kind(&Interner) {
 214                     TyKind::Array(st) => (TyKind::Array, st.clone()),
 215                     TyKind::Slice(st) => (TyKind::Slice, st.clone()),
 216                     _ => (TyKind::Slice, 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 = container_ty(elem_ty).intern(&Interner);
 224                 if let Some(slice_pat_id) = slice {
 225                     self.infer_pat(*slice_pat_id, &pat_ty, default_bm);
 226                 }
 227
 228                 pat_ty
 229             }
 230             Pat::Wild => expected.clone(),
 231             Pat::Range { start, end } => {
 232                 let start_ty = self.infer_expr(*start, &Expectation::has_type(expected.clone()));
 233                 let end_ty = self.infer_expr(*end, &Expectation::has_type(start_ty));
 234                 end_ty
 235             }
 236             Pat::Lit(expr) => self.infer_expr(*expr, &Expectation::has_type(expected.clone())),
 237             Pat::Box { inner } => match self.resolve_boxed_box() {
 238                 Some(box_adt) => {
 239                     let (inner_ty, alloc_ty) = match expected.as_adt() {
 240                         Some((adt, subst)) if adt == box_adt => (
 241                             subst.at(&Interner, 0).assert_ty_ref(&Interner).clone(),
 242                             subst.interned(&Interner).get(1).and_then(|a| a.ty(&Interner).cloned()),
 243                         ),
 244                         _ => (self.result.standard_types.unknown.clone(), None),
 245                     };
 246
 247                     let inner_ty = self.infer_pat(*inner, &inner_ty, default_bm);
 248                     let mut b = TyBuilder::adt(self.db, box_adt).push(inner_ty);
 249
 250                     if let Some(alloc_ty) = alloc_ty {
 251                         b = b.push(alloc_ty);
 252                     }
 253                     b.fill_with_defaults(self.db, || self.table.new_type_var()).build()
 254                 }
 255                 None => self.err_ty(),
 256             },
 257             Pat::ConstBlock(expr) => {
 258                 self.infer_expr(*expr, &Expectation::has_type(expected.clone()))
 259             }
 260             Pat::Missing => self.err_ty(),
 261         };
 262         // use a new type variable if we got error type here
 263         let ty = self.insert_type_vars_shallow(ty);
 264         if !self.unify(&ty, expected) {
 265             // FIXME record mismatch, we need to change the type of self.type_mismatches for that
 266         }
 267         let ty = self.resolve_ty_as_possible(ty);
 268         self.write_pat_ty(pat, ty.clone());
 269         ty
 270     }
 271 }
 272
 273 fn is_non_ref_pat(body: &hir_def::body::Body, pat: PatId) -> bool {
 274     match &body[pat] {
 275         Pat::Tuple { .. }
 276         | Pat::TupleStruct { .. }
 277         | Pat::Record { .. }
 278         | Pat::Range { .. }
 279         | Pat::Slice { .. } => true,
 280         Pat::Or(pats) => pats.iter().all(|p| is_non_ref_pat(body, *p)),
 281         // FIXME: ConstBlock/Path/Lit might actually evaluate to ref, but inference is unimplemented.
 282         Pat::Path(..) => true,
 283         Pat::ConstBlock(..) => true,
 284         Pat::Lit(expr) => match body[*expr] {
 285             Expr::Literal(Literal::String(..)) => false,
 286             _ => true,
 287         },
 288         Pat::Wild | Pat::Bind { .. } | Pat::Ref { .. } | Pat::Box { .. } | Pat::Missing => false,
 289     }
 290 }