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 hir_def::{
   7     expr::{BindingAnnotation, Expr, Literal, Pat, PatId, RecordFieldPat},
   8     path::Path,
   9     type_ref::Mutability,
  10     FieldId,
  11 };
  12 use hir_expand::name::Name;
  13 use test_utils::mark;
  14
  15 use super::{BindingMode, Expectation, InferenceContext};
  16 use crate::{utils::variant_data, Substs, Ty, TypeCtor};
  17
  18 impl<'a> InferenceContext<'a> {
  19     fn infer_tuple_struct_pat(
  20         &mut self,
  21         path: Option<&Path>,
  22         subpats: &[PatId],
  23         expected: &Ty,
  24         default_bm: BindingMode,
  25         id: PatId,
  26         ellipsis: Option<usize>,
  27     ) -> Ty {
  28         let (ty, def) = self.resolve_variant(path);
  29         let var_data = def.map(|it| variant_data(self.db.upcast(), it));
  30         if let Some(variant) = def {
  31             self.write_variant_resolution(id.into(), variant);
  32         }
  33         self.unify(&ty, expected);
  34
  35         let substs = ty.substs().unwrap_or_else(Substs::empty);
  36
  37         let field_tys = def.map(|it| self.db.field_types(it)).unwrap_or_default();
  38         let (pre, post) = match ellipsis {
  39             Some(idx) => subpats.split_at(idx),
  40             None => (&subpats[..], &[][..]),
  41         };
  42         let post_idx_offset = field_tys.iter().count() - post.len();
  43
  44         let pre_iter = pre.iter().enumerate();
  45         let post_iter = (post_idx_offset..).zip(post.iter());
  46         for (i, &subpat) in pre_iter.chain(post_iter) {
  47             let expected_ty = var_data
  48                 .as_ref()
  49                 .and_then(|d| d.field(&Name::new_tuple_field(i)))
  50                 .map_or(Ty::Unknown, |field| field_tys[field].clone().subst(&substs));
  51             let expected_ty = self.normalize_associated_types_in(expected_ty);
  52             self.infer_pat(subpat, &expected_ty, default_bm);
  53         }
  54
  55         ty
  56     }
  57
  58     fn infer_record_pat(
  59         &mut self,
  60         path: Option<&Path>,
  61         subpats: &[RecordFieldPat],
  62         expected: &Ty,
  63         default_bm: BindingMode,
  64         id: PatId,
  65     ) -> Ty {
  66         let (ty, def) = self.resolve_variant(path);
  67         let var_data = def.map(|it| variant_data(self.db.upcast(), it));
  68         if let Some(variant) = def {
  69             self.write_variant_resolution(id.into(), variant);
  70         }
  71
  72         self.unify(&ty, expected);
  73
  74         let substs = ty.substs().unwrap_or_else(Substs::empty);
  75
  76         let field_tys = def.map(|it| self.db.field_types(it)).unwrap_or_default();
  77         for subpat in subpats {
  78             let matching_field = var_data.as_ref().and_then(|it| it.field(&subpat.name));
  79             if let Some(local_id) = matching_field {
  80                 let field_def = FieldId { parent: def.unwrap(), local_id };
  81                 self.result.record_pat_field_resolutions.insert(subpat.pat, field_def);
  82             }
  83
  84             let expected_ty =
  85                 matching_field.map_or(Ty::Unknown, |field| field_tys[field].clone().subst(&substs));
  86             let expected_ty = self.normalize_associated_types_in(expected_ty);
  87             self.infer_pat(subpat.pat, &expected_ty, default_bm);
  88         }
  89
  90         ty
  91     }
  92
  93     pub(super) fn infer_pat(
  94         &mut self,
  95         pat: PatId,
  96         mut expected: &Ty,
  97         mut default_bm: BindingMode,
  98     ) -> Ty {
  99         let body = Arc::clone(&self.body); // avoid borrow checker problem
 100
 101         if is_non_ref_pat(&body, pat) {
 102             while let Some((inner, mutability)) = expected.as_reference() {
 103                 expected = inner;
 104                 default_bm = match default_bm {
 105                     BindingMode::Move => BindingMode::Ref(mutability),
 106                     BindingMode::Ref(Mutability::Shared) => BindingMode::Ref(Mutability::Shared),
 107                     BindingMode::Ref(Mutability::Mut) => BindingMode::Ref(mutability),
 108                 }
 109             }
 110         } else if let Pat::Ref { .. } = &body[pat] {
 111             mark::hit!(match_ergonomics_ref);
 112             // When you encounter a `&pat` pattern, reset to Move.
 113             // This is so that `w` is by value: `let (_, &w) = &(1, &2);`
 114             default_bm = BindingMode::Move;
 115         }
 116
 117         // Lose mutability.
 118         let default_bm = default_bm;
 119         let expected = expected;
 120
 121         let ty = match &body[pat] {
 122             &Pat::Tuple { ref args, ellipsis } => {
 123                 let expectations = match expected.as_tuple() {
 124                     Some(parameters) => &*parameters.0,
 125                     _ => &[],
 126                 };
 127
 128                 let (pre, post) = match ellipsis {
 129                     Some(idx) => args.split_at(idx),
 130                     None => (&args[..], &[][..]),
 131                 };
 132                 let n_uncovered_patterns = expectations.len().saturating_sub(args.len());
 133                 let mut expectations_iter = expectations.iter().chain(repeat(&Ty::Unknown));
 134                 let mut infer_pat = |(&pat, ty)| self.infer_pat(pat, ty, default_bm);
 135
 136                 let mut inner_tys = Vec::with_capacity(n_uncovered_patterns + args.len());
 137                 inner_tys.extend(pre.iter().zip(expectations_iter.by_ref()).map(&mut infer_pat));
 138                 inner_tys.extend(expectations_iter.by_ref().take(n_uncovered_patterns).cloned());
 139                 inner_tys.extend(post.iter().zip(expectations_iter).map(infer_pat));
 140
 141                 Ty::apply(
 142                     TypeCtor::Tuple { cardinality: inner_tys.len() as u16 },
 143                     Substs(inner_tys.into()),
 144                 )
 145             }
 146             Pat::Or(ref pats) => {
 147                 if let Some((first_pat, rest)) = pats.split_first() {
 148                     let ty = self.infer_pat(*first_pat, expected, default_bm);
 149                     for pat in rest {
 150                         self.infer_pat(*pat, expected, default_bm);
 151                     }
 152                     ty
 153                 } else {
 154                     Ty::Unknown
 155                 }
 156             }
 157             Pat::Ref { pat, 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
 164                     }
 165                     _ => &Ty::Unknown,
 166                 };
 167                 let subty = self.infer_pat(*pat, expectation, default_bm);
 168                 Ty::apply_one(TypeCtor::Ref(*mutability), subty)
 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(Ty::Unknown)
 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                         Ty::apply_one(TypeCtor::Ref(mutability), inner_ty.clone())
 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) = match &expected {
 211                     ty_app!(TypeCtor::Array, st) => (TypeCtor::Array, st.as_single().clone()),
 212                     ty_app!(TypeCtor::Slice, st) => (TypeCtor::Slice, st.as_single().clone()),
 213                     _ => (TypeCtor::Slice, Ty::Unknown),
 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 = Ty::apply_one(container_ty, elem_ty);
 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(),
 238                         _ => &Ty::Unknown,
 239                     };
 240
 241                     let inner_ty = self.infer_pat(*inner, inner_expected, default_bm);
 242                     Ty::apply_one(TypeCtor::Adt(box_adt), inner_ty)
 243                 }
 244                 None => Ty::Unknown,
 245             },
 246             Pat::ConstBlock(expr) => {
 247                 self.infer_expr(*expr, &Expectation::has_type(expected.clone()))
 248             }
 249             Pat::Missing => Ty::Unknown,
 250         };
 251         // use a new type variable if we got Ty::Unknown 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 }