1 //! Type inference for patterns.
3 use std::{iter::repeat, sync::Arc};
5 use chalk_ir::Mutability;
7 expr::{BindingAnnotation, Expr, Literal, Pat, PatId, RecordFieldPat},
11 use hir_expand::name::Name;
15 Adjust, Adjustment, AutoBorrow, BindingMode, Expectation, InferenceContext, TypeMismatch,
17 lower::lower_to_chalk_mutability,
18 static_lifetime, ConcreteConst, ConstValue, Interner, Substitution, Ty, TyBuilder, TyExt,
22 impl<'a> InferenceContext<'a> {
23 fn infer_tuple_struct_pat(
28 default_bm: BindingMode,
30 ellipsis: Option<usize>,
32 let (ty, def) = self.resolve_variant(path, true);
33 let var_data = def.map(|it| it.variant_data(self.db.upcast()));
34 if let Some(variant) = def {
35 self.write_variant_resolution(id.into(), variant);
37 self.unify(&ty, expected);
40 ty.as_adt().map(|(_, s)| s.clone()).unwrap_or_else(|| Substitution::empty(Interner));
42 let field_tys = def.map(|it| self.db.field_types(it)).unwrap_or_default();
43 let (pre, post) = match ellipsis {
44 Some(idx) => subpats.split_at(idx),
45 None => (subpats, &[][..]),
47 let post_idx_offset = field_tys.iter().count() - post.len();
49 let pre_iter = pre.iter().enumerate();
50 let post_iter = (post_idx_offset..).zip(post.iter());
51 for (i, &subpat) in pre_iter.chain(post_iter) {
52 let expected_ty = var_data
54 .and_then(|d| d.field(&Name::new_tuple_field(i)))
55 .map_or(self.err_ty(), |field| {
56 field_tys[field].clone().substitute(Interner, &substs)
58 let expected_ty = self.normalize_associated_types_in(expected_ty);
59 self.infer_pat(subpat, &expected_ty, default_bm);
68 subpats: &[RecordFieldPat],
70 default_bm: BindingMode,
73 let (ty, def) = self.resolve_variant(path, false);
74 let var_data = def.map(|it| it.variant_data(self.db.upcast()));
75 if let Some(variant) = def {
76 self.write_variant_resolution(id.into(), variant);
79 self.unify(&ty, expected);
82 ty.as_adt().map(|(_, s)| s.clone()).unwrap_or_else(|| Substitution::empty(Interner));
84 let field_tys = def.map(|it| self.db.field_types(it)).unwrap_or_default();
85 for subpat in subpats {
86 let matching_field = var_data.as_ref().and_then(|it| it.field(&subpat.name));
87 let expected_ty = matching_field.map_or(self.err_ty(), |field| {
88 field_tys[field].clone().substitute(Interner, &substs)
90 let expected_ty = self.normalize_associated_types_in(expected_ty);
91 self.infer_pat(subpat.pat, &expected_ty, default_bm);
97 pub(super) fn infer_pat(
101 mut default_bm: BindingMode,
103 let body = Arc::clone(&self.body); // avoid borrow checker problem
104 let mut expected = self.resolve_ty_shallow(expected);
106 if is_non_ref_pat(&body, pat) {
107 let mut pat_adjustments = Vec::new();
108 while let Some((inner, _lifetime, mutability)) = expected.as_reference() {
109 pat_adjustments.push(Adjustment {
110 target: expected.clone(),
111 kind: Adjust::Borrow(AutoBorrow::Ref(mutability)),
113 expected = self.resolve_ty_shallow(inner);
114 default_bm = match default_bm {
115 BindingMode::Move => BindingMode::Ref(mutability),
116 BindingMode::Ref(Mutability::Not) => BindingMode::Ref(Mutability::Not),
117 BindingMode::Ref(Mutability::Mut) => BindingMode::Ref(mutability),
121 if !pat_adjustments.is_empty() {
122 pat_adjustments.shrink_to_fit();
123 self.result.pat_adjustments.insert(pat, pat_adjustments);
125 } else if let Pat::Ref { .. } = &body[pat] {
126 cov_mark::hit!(match_ergonomics_ref);
127 // When you encounter a `&pat` pattern, reset to Move.
128 // This is so that `w` is by value: `let (_, &w) = &(1, &2);`
129 default_bm = BindingMode::Move;
133 let default_bm = default_bm;
134 let expected = expected;
136 let ty = match &body[pat] {
137 Pat::Tuple { args, ellipsis } => {
138 let expectations = match expected.as_tuple() {
139 Some(parameters) => &*parameters.as_slice(Interner),
143 let ((pre, post), n_uncovered_patterns) = match ellipsis {
145 (args.split_at(*idx), expectations.len().saturating_sub(args.len()))
147 None => ((&args[..], &[][..]), 0),
149 let err_ty = self.err_ty();
150 let mut expectations_iter =
151 expectations.iter().map(|a| a.assert_ty_ref(Interner)).chain(repeat(&err_ty));
152 let mut infer_pat = |(&pat, ty)| self.infer_pat(pat, ty, default_bm);
154 let mut inner_tys = Vec::with_capacity(n_uncovered_patterns + args.len());
155 inner_tys.extend(pre.iter().zip(expectations_iter.by_ref()).map(&mut infer_pat));
156 inner_tys.extend(expectations_iter.by_ref().take(n_uncovered_patterns).cloned());
157 inner_tys.extend(post.iter().zip(expectations_iter).map(infer_pat));
159 TyKind::Tuple(inner_tys.len(), Substitution::from_iter(Interner, inner_tys))
163 if let Some((first_pat, rest)) = pats.split_first() {
164 let ty = self.infer_pat(*first_pat, &expected, default_bm);
166 self.infer_pat(*pat, &expected, default_bm);
173 Pat::Ref { pat, mutability } => {
174 let mutability = lower_to_chalk_mutability(*mutability);
175 let expectation = match expected.as_reference() {
176 Some((inner_ty, _lifetime, exp_mut)) => {
177 if mutability != exp_mut {
178 // FIXME: emit type error?
182 _ => self.result.standard_types.unknown.clone(),
184 let subty = self.infer_pat(*pat, &expectation, default_bm);
185 TyKind::Ref(mutability, static_lifetime(), subty).intern(Interner)
187 Pat::TupleStruct { path: p, args: subpats, ellipsis } => self.infer_tuple_struct_pat(
195 Pat::Record { path: p, args: fields, ellipsis: _ } => {
196 self.infer_record_pat(p.as_deref(), fields, &expected, default_bm, pat)
199 // FIXME use correct resolver for the surrounding expression
200 let resolver = self.resolver.clone();
201 self.infer_path(&resolver, path, pat.into()).unwrap_or_else(|| self.err_ty())
203 Pat::Bind { mode, name: _, subpat } => {
204 let mode = if mode == &BindingAnnotation::Unannotated {
207 BindingMode::convert(*mode)
209 self.result.pat_binding_modes.insert(pat, mode);
211 let inner_ty = match subpat {
212 Some(subpat) => self.infer_pat(*subpat, &expected, default_bm),
215 let inner_ty = self.insert_type_vars_shallow(inner_ty);
217 let bound_ty = match mode {
218 BindingMode::Ref(mutability) => {
219 TyKind::Ref(mutability, static_lifetime(), inner_ty.clone())
222 BindingMode::Move => inner_ty.clone(),
224 self.write_pat_ty(pat, bound_ty);
227 Pat::Slice { prefix, slice, suffix } => {
228 let elem_ty = match expected.kind(Interner) {
229 TyKind::Array(st, _) | TyKind::Slice(st) => st.clone(),
233 for &pat_id in prefix.iter().chain(suffix.iter()) {
234 self.infer_pat(pat_id, &elem_ty, default_bm);
237 if let &Some(slice_pat_id) = slice {
238 let rest_pat_ty = match expected.kind(Interner) {
239 TyKind::Array(_, length) => {
240 let length = match length.data(Interner).value {
241 ConstValue::Concrete(ConcreteConst {
242 interned: ConstScalar::Usize(length),
243 }) => length.checked_sub((prefix.len() + suffix.len()) as u64),
246 TyKind::Array(elem_ty.clone(), crate::consteval::usize_const(length))
248 _ => TyKind::Slice(elem_ty.clone()),
251 self.infer_pat(slice_pat_id, &rest_pat_ty, default_bm);
254 match expected.kind(Interner) {
255 TyKind::Array(_, const_) => TyKind::Array(elem_ty, const_.clone()),
256 _ => TyKind::Slice(elem_ty),
260 Pat::Wild => expected.clone(),
261 Pat::Range { start, end } => {
262 let start_ty = self.infer_expr(*start, &Expectation::has_type(expected.clone()));
263 self.infer_expr(*end, &Expectation::has_type(start_ty))
265 Pat::Lit(expr) => self.infer_expr(*expr, &Expectation::has_type(expected.clone())),
266 Pat::Box { inner } => match self.resolve_boxed_box() {
268 let (inner_ty, alloc_ty) = match expected.as_adt() {
269 Some((adt, subst)) if adt == box_adt => (
270 subst.at(Interner, 0).assert_ty_ref(Interner).clone(),
271 subst.as_slice(Interner).get(1).and_then(|a| a.ty(Interner).cloned()),
273 _ => (self.result.standard_types.unknown.clone(), None),
276 let inner_ty = self.infer_pat(*inner, &inner_ty, default_bm);
277 let mut b = TyBuilder::adt(self.db, box_adt).push(inner_ty);
279 if let Some(alloc_ty) = alloc_ty {
280 b = b.push(alloc_ty);
282 b.fill_with_defaults(self.db, || self.table.new_type_var()).build()
284 None => self.err_ty(),
286 Pat::ConstBlock(expr) => {
287 self.infer_expr(*expr, &Expectation::has_type(expected.clone()))
289 Pat::Missing => self.err_ty(),
291 // use a new type variable if we got error type here
292 let ty = self.insert_type_vars_shallow(ty);
293 if !self.unify(&ty, &expected) {
296 .insert(pat.into(), TypeMismatch { expected, actual: ty.clone() });
298 self.write_pat_ty(pat, ty.clone());
303 fn is_non_ref_pat(body: &hir_def::body::Body, pat: PatId) -> bool {
306 | Pat::TupleStruct { .. }
309 | Pat::Slice { .. } => true,
310 Pat::Or(pats) => pats.iter().all(|p| is_non_ref_pat(body, *p)),
311 // FIXME: ConstBlock/Path/Lit might actually evaluate to ref, but inference is unimplemented.
312 Pat::Path(..) => true,
313 Pat::ConstBlock(..) => true,
314 Pat::Lit(expr) => !matches!(body[*expr], Expr::Literal(Literal::String(..))),
316 mode: BindingAnnotation::Mutable | BindingAnnotation::Unannotated,
317 subpat: Some(subpat),
319 } => is_non_ref_pat(body, *subpat),
320 Pat::Wild | Pat::Bind { .. } | Pat::Ref { .. } | Pat::Box { .. } | Pat::Missing => false,