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::{lower::lower_to_chalk_mutability, utils::variant_data, Interner, Substs, Ty, TyKind};
  16
  17 impl<'a> InferenceContext<'a> {
  18     fn infer_tuple_struct_pat(
  19         &mut self,
  20         path: Option<&Path>,
  21         subpats: &[PatId],
  22         expected: &Ty,
  23         default_bm: BindingMode,
  24         id: PatId,
  25         ellipsis: Option<usize>,
  26     ) -> Ty {
  27         let (ty, def) = self.resolve_variant(path);
  28         let var_data = def.map(|it| variant_data(self.db.upcast(), it));
  29         if let Some(variant) = def {
  30             self.write_variant_resolution(id.into(), variant);
  31         }
  32         self.unify(&ty, expected);
  33
  34         let substs = ty.substs().cloned().unwrap_or_else(Substs::empty);
  35
  36         let field_tys = def.map(|it| self.db.field_types(it)).unwrap_or_default();
  37         let (pre, post) = match ellipsis {
  38             Some(idx) => subpats.split_at(idx),
  39             None => (&subpats[..], &[][..]),
  40         };
  41         let post_idx_offset = field_tys.iter().count() - post.len();
  42
  43         let pre_iter = pre.iter().enumerate();
  44         let post_iter = (post_idx_offset..).zip(post.iter());
  45         for (i, &subpat) in pre_iter.chain(post_iter) {
  46             let expected_ty = var_data
  47                 .as_ref()
  48                 .and_then(|d| d.field(&Name::new_tuple_field(i)))
  49                 .map_or(self.err_ty(), |field| field_tys[field].clone().subst(&substs));
  50             let expected_ty = self.normalize_associated_types_in(expected_ty);
  51             self.infer_pat(subpat, &expected_ty, default_bm);
  52         }
  53
  54         ty
  55     }
  56
  57     fn infer_record_pat(
  58         &mut self,
  59         path: Option<&Path>,
  60         subpats: &[RecordFieldPat],
  61         expected: &Ty,
  62         default_bm: BindingMode,
  63         id: PatId,
  64     ) -> Ty {
  65         let (ty, def) = self.resolve_variant(path);
  66         let var_data = def.map(|it| variant_data(self.db.upcast(), it));
  67         if let Some(variant) = def {
  68             self.write_variant_resolution(id.into(), variant);
  69         }
  70
  71         self.unify(&ty, expected);
  72
  73         let substs = ty.substs().cloned().unwrap_or_else(Substs::empty);
  74
  75         let field_tys = def.map(|it| self.db.field_types(it)).unwrap_or_default();
  76         for subpat in subpats {
  77             let matching_field = var_data.as_ref().and_then(|it| it.field(&subpat.name));
  78             if let Some(local_id) = matching_field {
  79                 let field_def = FieldId { parent: def.unwrap(), local_id };
  80                 self.result.record_pat_field_resolutions.insert(subpat.pat, field_def);
  81             }
  82
  83             let expected_ty = matching_field
  84                 .map_or(self.err_ty(), |field| field_tys[field].clone().subst(&substs));
  85             let expected_ty = self.normalize_associated_types_in(expected_ty);
  86             self.infer_pat(subpat.pat, &expected_ty, default_bm);
  87         }
  88
  89         ty
  90     }
  91
  92     pub(super) fn infer_pat(
  93         &mut self,
  94         pat: PatId,
  95         mut expected: &Ty,
  96         mut default_bm: BindingMode,
  97     ) -> Ty {
  98         let body = Arc::clone(&self.body); // avoid borrow checker problem
  99
 100         if is_non_ref_pat(&body, pat) {
 101             while let Some((inner, mutability)) = expected.as_reference() {
 102                 expected = inner;
 103                 default_bm = match default_bm {
 104                     BindingMode::Move => BindingMode::Ref(mutability),
 105                     BindingMode::Ref(Mutability::Not) => BindingMode::Ref(Mutability::Not),
 106                     BindingMode::Ref(Mutability::Mut) => BindingMode::Ref(mutability),
 107                 }
 108             }
 109         } else if let Pat::Ref { .. } = &body[pat] {
 110             cov_mark::hit!(match_ergonomics_ref);
 111             // When you encounter a `&pat` pattern, reset to Move.
 112             // This is so that `w` is by value: `let (_, &w) = &(1, &2);`
 113             default_bm = BindingMode::Move;
 114         }
 115
 116         // Lose mutability.
 117         let default_bm = default_bm;
 118         let expected = expected;
 119
 120         let ty = match &body[pat] {
 121             &Pat::Tuple { ref args, ellipsis } => {
 122                 let expectations = match expected.as_tuple() {
 123                     Some(parameters) => &*parameters.0,
 124                     _ => &[],
 125                 };
 126
 127                 let (pre, post) = match ellipsis {
 128                     Some(idx) => args.split_at(idx),
 129                     None => (&args[..], &[][..]),
 130                 };
 131                 let n_uncovered_patterns = expectations.len().saturating_sub(args.len());
 132                 let err_ty = self.err_ty();
 133                 let mut expectations_iter = expectations.iter().chain(repeat(&err_ty));
 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                 TyKind::Tuple(inner_tys.len(), Substs(inner_tys.into())).intern(&Interner)
 142             }
 143             Pat::Or(ref pats) => {
 144                 if let Some((first_pat, rest)) = pats.split_first() {
 145                     let ty = self.infer_pat(*first_pat, expected, default_bm);
 146                     for pat in rest {
 147                         self.infer_pat(*pat, expected, default_bm);
 148                     }
 149                     ty
 150                 } else {
 151                     self.err_ty()
 152                 }
 153             }
 154             Pat::Ref { pat, mutability } => {
 155                 let mutability = lower_to_chalk_mutability(*mutability);
 156                 let expectation = match expected.as_reference() {
 157                     Some((inner_ty, exp_mut)) => {
 158                         if mutability != exp_mut {
 159                             // FIXME: emit type error?
 160                         }
 161                         inner_ty.clone()
 162                     }
 163                     _ => self.result.standard_types.unknown.clone(),
 164                 };
 165                 let subty = self.infer_pat(*pat, &expectation, default_bm);
 166                 TyKind::Ref(mutability, subty).intern(&Interner)
 167             }
 168             Pat::TupleStruct { path: p, args: subpats, ellipsis } => self.infer_tuple_struct_pat(
 169                 p.as_ref(),
 170                 subpats,
 171                 expected,
 172                 default_bm,
 173                 pat,
 174                 *ellipsis,
 175             ),
 176             Pat::Record { path: p, args: fields, ellipsis: _ } => {
 177                 self.infer_record_pat(p.as_ref(), fields, expected, default_bm, pat)
 178             }
 179             Pat::Path(path) => {
 180                 // FIXME use correct resolver for the surrounding expression
 181                 let resolver = self.resolver.clone();
 182                 self.infer_path(&resolver, &path, pat.into()).unwrap_or(self.err_ty())
 183             }
 184             Pat::Bind { mode, name: _, subpat } => {
 185                 let mode = if mode == &BindingAnnotation::Unannotated {
 186                     default_bm
 187                 } else {
 188                     BindingMode::convert(*mode)
 189                 };
 190                 let inner_ty = if let Some(subpat) = subpat {
 191                     self.infer_pat(*subpat, expected, default_bm)
 192                 } else {
 193                     expected.clone()
 194                 };
 195                 let inner_ty = self.insert_type_vars_shallow(inner_ty);
 196
 197                 let bound_ty = match mode {
 198                     BindingMode::Ref(mutability) => {
 199                         TyKind::Ref(mutability, inner_ty.clone()).intern(&Interner)
 200                     }
 201                     BindingMode::Move => inner_ty.clone(),
 202                 };
 203                 let bound_ty = self.resolve_ty_as_possible(bound_ty);
 204                 self.write_pat_ty(pat, bound_ty);
 205                 return inner_ty;
 206             }
 207             Pat::Slice { prefix, slice, suffix } => {
 208                 let (container_ty, elem_ty): (fn(_) -> _, _) = match expected.interned(&Interner) {
 209                     TyKind::Array(st) => (TyKind::Array, st.clone()),
 210                     TyKind::Slice(st) => (TyKind::Slice, st.clone()),
 211                     _ => (TyKind::Slice, self.err_ty()),
 212                 };
 213
 214                 for pat_id in prefix.iter().chain(suffix) {
 215                     self.infer_pat(*pat_id, &elem_ty, default_bm);
 216                 }
 217
 218                 let pat_ty = container_ty(elem_ty).intern(&Interner);
 219                 if let Some(slice_pat_id) = slice {
 220                     self.infer_pat(*slice_pat_id, &pat_ty, default_bm);
 221                 }
 222
 223                 pat_ty
 224             }
 225             Pat::Wild => expected.clone(),
 226             Pat::Range { start, end } => {
 227                 let start_ty = self.infer_expr(*start, &Expectation::has_type(expected.clone()));
 228                 let end_ty = self.infer_expr(*end, &Expectation::has_type(start_ty));
 229                 end_ty
 230             }
 231             Pat::Lit(expr) => self.infer_expr(*expr, &Expectation::has_type(expected.clone())),
 232             Pat::Box { inner } => match self.resolve_boxed_box() {
 233                 Some(box_adt) => {
 234                     let inner_expected = match expected.as_adt() {
 235                         Some((adt, substs)) if adt == box_adt => substs.as_single().clone(),
 236                         _ => self.result.standard_types.unknown.clone(),
 237                     };
 238
 239                     let inner_ty = self.infer_pat(*inner, &inner_expected, default_bm);
 240                     Ty::adt_ty(box_adt, Substs::single(inner_ty))
 241                 }
 242                 None => self.err_ty(),
 243             },
 244             Pat::ConstBlock(expr) => {
 245                 self.infer_expr(*expr, &Expectation::has_type(expected.clone()))
 246             }
 247             Pat::Missing => self.err_ty(),
 248         };
 249         // use a new type variable if we got error type here
 250         let ty = self.insert_type_vars_shallow(ty);
 251         if !self.unify(&ty, expected) {
 252             // FIXME record mismatch, we need to change the type of self.type_mismatches for that
 253         }
 254         let ty = self.resolve_ty_as_possible(ty);
 255         self.write_pat_ty(pat, ty.clone());
 256         ty
 257     }
 258 }
 259
 260 fn is_non_ref_pat(body: &hir_def::body::Body, pat: PatId) -> bool {
 261     match &body[pat] {
 262         Pat::Tuple { .. }
 263         | Pat::TupleStruct { .. }
 264         | Pat::Record { .. }
 265         | Pat::Range { .. }
 266         | Pat::Slice { .. } => true,
 267         Pat::Or(pats) => pats.iter().all(|p| is_non_ref_pat(body, *p)),
 268         // FIXME: ConstBlock/Path/Lit might actually evaluate to ref, but inference is unimplemented.
 269         Pat::Path(..) => true,
 270         Pat::ConstBlock(..) => true,
 271         Pat::Lit(expr) => match body[*expr] {
 272             Expr::Literal(Literal::String(..)) => false,
 273             _ => true,
 274         },
 275         Pat::Wild | Pat::Bind { .. } | Pat::Ref { .. } | Pat::Box { .. } | Pat::Missing => false,
 276     }
 277 }