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, 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| variant_data(self.db.upcast(), it));
  31         if let Some(variant) = def {
  32             self.write_variant_resolution(id.into(), variant);
  33         }
  34         self.unify(&ty, expected);
  35
  36         let substs = ty.substs().cloned().unwrap_or_else(Substitution::empty);
  37
  38         let field_tys = def.map(|it| self.db.field_types(it)).unwrap_or_default();
  39         let (pre, post) = match ellipsis {
  40             Some(idx) => subpats.split_at(idx),
  41             None => (&subpats[..], &[][..]),
  42         };
  43         let post_idx_offset = field_tys.iter().count() - post.len();
  44
  45         let pre_iter = pre.iter().enumerate();
  46         let post_iter = (post_idx_offset..).zip(post.iter());
  47         for (i, &subpat) in pre_iter.chain(post_iter) {
  48             let expected_ty = var_data
  49                 .as_ref()
  50                 .and_then(|d| d.field(&Name::new_tuple_field(i)))
  51                 .map_or(self.err_ty(), |field| field_tys[field].clone().subst(&substs));
  52             let expected_ty = self.normalize_associated_types_in(expected_ty);
  53             self.infer_pat(subpat, &expected_ty, default_bm);
  54         }
  55
  56         ty
  57     }
  58
  59     fn infer_record_pat(
  60         &mut self,
  61         path: Option<&Path>,
  62         subpats: &[RecordFieldPat],
  63         expected: &Ty,
  64         default_bm: BindingMode,
  65         id: PatId,
  66     ) -> Ty {
  67         let (ty, def) = self.resolve_variant(path);
  68         let var_data = def.map(|it| variant_data(self.db.upcast(), it));
  69         if let Some(variant) = def {
  70             self.write_variant_resolution(id.into(), variant);
  71         }
  72
  73         self.unify(&ty, expected);
  74
  75         let substs = ty.substs().cloned().unwrap_or_else(Substitution::empty);
  76
  77         let field_tys = def.map(|it| self.db.field_types(it)).unwrap_or_default();
  78         for subpat in subpats {
  79             let matching_field = var_data.as_ref().and_then(|it| it.field(&subpat.name));
  80             if let Some(local_id) = matching_field {
  81                 let field_def = FieldId { parent: def.unwrap(), local_id };
  82                 self.result.record_pat_field_resolutions.insert(subpat.pat, field_def);
  83             }
  84
  85             let expected_ty = matching_field
  86                 .map_or(self.err_ty(), |field| field_tys[field].clone().subst(&substs));
  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, 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.0,
 126                     _ => &[],
 127                 };
 128
 129                 let (pre, post) = match ellipsis {
 130                     Some(idx) => args.split_at(idx),
 131                     None => (&args[..], &[][..]),
 132                 };
 133                 let n_uncovered_patterns = expectations.len().saturating_sub(args.len());
 134                 let err_ty = self.err_ty();
 135                 let mut expectations_iter = expectations.iter().chain(repeat(&err_ty));
 136                 let mut infer_pat = |(&pat, ty)| self.infer_pat(pat, ty, default_bm);
 137
 138                 let mut inner_tys = Vec::with_capacity(n_uncovered_patterns + args.len());
 139                 inner_tys.extend(pre.iter().zip(expectations_iter.by_ref()).map(&mut infer_pat));
 140                 inner_tys.extend(expectations_iter.by_ref().take(n_uncovered_patterns).cloned());
 141                 inner_tys.extend(post.iter().zip(expectations_iter).map(infer_pat));
 142
 143                 TyKind::Tuple(inner_tys.len(), Substitution(inner_tys.into())).intern(&Interner)
 144             }
 145             Pat::Or(ref pats) => {
 146                 if let Some((first_pat, rest)) = pats.split_first() {
 147                     let ty = self.infer_pat(*first_pat, expected, default_bm);
 148                     for pat in rest {
 149                         self.infer_pat(*pat, expected, default_bm);
 150                     }
 151                     ty
 152                 } else {
 153                     self.err_ty()
 154                 }
 155             }
 156             Pat::Ref { pat, mutability } => {
 157                 let mutability = lower_to_chalk_mutability(*mutability);
 158                 let expectation = match expected.as_reference() {
 159                     Some((inner_ty, exp_mut)) => {
 160                         if mutability != exp_mut {
 161                             // FIXME: emit type error?
 162                         }
 163                         inner_ty.clone()
 164                     }
 165                     _ => self.result.standard_types.unknown.clone(),
 166                 };
 167                 let subty = self.infer_pat(*pat, &expectation, default_bm);
 168                 TyKind::Ref(mutability, subty).intern(&Interner)
 169             }
 170             Pat::TupleStruct { path: p, args: subpats, ellipsis } => self.infer_tuple_struct_pat(
 171                 p.as_ref(),
 172                 subpats,
 173                 expected,
 174                 default_bm,
 175                 pat,
 176                 *ellipsis,
 177             ),
 178             Pat::Record { path: p, args: fields, ellipsis: _ } => {
 179                 self.infer_record_pat(p.as_ref(), fields, expected, default_bm, pat)
 180             }
 181             Pat::Path(path) => {
 182                 // FIXME use correct resolver for the surrounding expression
 183                 let resolver = self.resolver.clone();
 184                 self.infer_path(&resolver, &path, pat.into()).unwrap_or(self.err_ty())
 185             }
 186             Pat::Bind { mode, name: _, subpat } => {
 187                 let mode = if mode == &BindingAnnotation::Unannotated {
 188                     default_bm
 189                 } else {
 190                     BindingMode::convert(*mode)
 191                 };
 192                 let inner_ty = if let Some(subpat) = subpat {
 193                     self.infer_pat(*subpat, expected, default_bm)
 194                 } else {
 195                     expected.clone()
 196                 };
 197                 let inner_ty = self.insert_type_vars_shallow(inner_ty);
 198
 199                 let bound_ty = match mode {
 200                     BindingMode::Ref(mutability) => {
 201                         TyKind::Ref(mutability, inner_ty.clone()).intern(&Interner)
 202                     }
 203                     BindingMode::Move => inner_ty.clone(),
 204                 };
 205                 let bound_ty = self.resolve_ty_as_possible(bound_ty);
 206                 self.write_pat_ty(pat, bound_ty);
 207                 return inner_ty;
 208             }
 209             Pat::Slice { prefix, slice, suffix } => {
 210                 let (container_ty, elem_ty): (fn(_) -> _, _) = match expected.interned(&Interner) {
 211                     TyKind::Array(st) => (TyKind::Array, st.clone()),
 212                     TyKind::Slice(st) => (TyKind::Slice, st.clone()),
 213                     _ => (TyKind::Slice, self.err_ty()),
 214                 };
 215
 216                 for pat_id in prefix.iter().chain(suffix) {
 217                     self.infer_pat(*pat_id, &elem_ty, default_bm);
 218                 }
 219
 220                 let pat_ty = container_ty(elem_ty).intern(&Interner);
 221                 if let Some(slice_pat_id) = slice {
 222                     self.infer_pat(*slice_pat_id, &pat_ty, default_bm);
 223                 }
 224
 225                 pat_ty
 226             }
 227             Pat::Wild => expected.clone(),
 228             Pat::Range { start, end } => {
 229                 let start_ty = self.infer_expr(*start, &Expectation::has_type(expected.clone()));
 230                 let end_ty = self.infer_expr(*end, &Expectation::has_type(start_ty));
 231                 end_ty
 232             }
 233             Pat::Lit(expr) => self.infer_expr(*expr, &Expectation::has_type(expected.clone())),
 234             Pat::Box { inner } => match self.resolve_boxed_box() {
 235                 Some(box_adt) => {
 236                     let inner_expected = match expected.as_adt() {
 237                         Some((adt, substs)) if adt == box_adt => substs.as_single().clone(),
 238                         _ => self.result.standard_types.unknown.clone(),
 239                     };
 240
 241                     let inner_ty = self.infer_pat(*inner, &inner_expected, default_bm);
 242                     Ty::adt_ty(box_adt, Substitution::single(inner_ty))
 243                 }
 244                 None => self.err_ty(),
 245             },
 246             Pat::ConstBlock(expr) => {
 247                 self.infer_expr(*expr, &Expectation::has_type(expected.clone()))
 248             }
 249             Pat::Missing => self.err_ty(),
 250         };
 251         // use a new type variable if we got error type here
 252         let ty = self.insert_type_vars_shallow(ty);
 253         if !self.unify(&ty, expected) {
 254             // FIXME record mismatch, we need to change the type of self.type_mismatches for that
 255         }
 256         let ty = self.resolve_ty_as_possible(ty);
 257         self.write_pat_ty(pat, ty.clone());
 258         ty
 259     }
 260 }
 261
 262 fn is_non_ref_pat(body: &hir_def::body::Body, pat: PatId) -> bool {
 263     match &body[pat] {
 264         Pat::Tuple { .. }
 265         | Pat::TupleStruct { .. }
 266         | Pat::Record { .. }
 267         | Pat::Range { .. }
 268         | Pat::Slice { .. } => true,
 269         Pat::Or(pats) => pats.iter().all(|p| is_non_ref_pat(body, *p)),
 270         // FIXME: ConstBlock/Path/Lit might actually evaluate to ref, but inference is unimplemented.
 271         Pat::Path(..) => true,
 272         Pat::ConstBlock(..) => true,
 273         Pat::Lit(expr) => match body[*expr] {
 274             Expr::Literal(Literal::String(..)) => false,
 275             _ => true,
 276         },
 277         Pat::Wild | Pat::Bind { .. } | Pat::Ref { .. } | Pat::Box { .. } | Pat::Missing => false,
 278     }
 279 }