1 use crate::check::FnCtxt;
2 use errors::{pluralize, struct_span_err, Applicability, DiagnosticBuilder};
4 use rustc::infer::type_variable::{TypeVariableOrigin, TypeVariableOriginKind};
5 use rustc::traits::Pattern;
6 use rustc::ty::subst::GenericArg;
7 use rustc::ty::{self, BindingMode, Ty, TypeFoldable};
8 use rustc_data_structures::fx::FxHashMap;
10 use rustc_hir::def::{CtorKind, DefKind, Res};
11 use rustc_hir::pat_util::EnumerateAndAdjustIterator;
12 use rustc_hir::{HirId, Pat, PatKind};
13 use rustc_span::hygiene::DesugaringKind;
16 use syntax::util::lev_distance::find_best_match_for_name;
18 use rustc_error_codes::*;
21 use std::collections::hash_map::Entry::{Occupied, Vacant};
23 use super::report_unexpected_variant_res;
25 const CANNOT_IMPLICITLY_DEREF_POINTER_TRAIT_OBJ: &str = "\
26 This error indicates that a pointer to a trait type cannot be implicitly dereferenced by a \
27 pattern. Every trait defines a type, but because the size of trait implementors isn't fixed, \
28 this type has no compile-time size. Therefore, all accesses to trait types must be through \
29 pointers. If you encounter this error you should try to avoid dereferencing the pointer.
31 You can read more about trait objects in the Trait Objects section of the Reference: \
32 https://doc.rust-lang.org/reference/types.html#trait-objects";
34 /// Information about the expected type at the top level of type checking a pattern.
36 /// **NOTE:** This is only for use by diagnostics. Do NOT use for type checking logic!
37 #[derive(Copy, Clone)]
38 struct TopInfo<'tcx> {
39 /// The `expected` type at the top level of type checking a pattern.
41 /// Was the origin of the `span` from a scrutinee expression?
43 /// Otherwise there is no scrutinee and it could be e.g. from the type of a formal parameter.
45 /// The span giving rise to the `expected` type, if one could be provided.
47 /// If `origin_expr` is `true`, then this is the span of the scrutinee as in:
49 /// - `match scrutinee { ... }`
50 /// - `let _ = scrutinee;`
52 /// This is used to point to add context in type errors.
53 /// In the following example, `span` corresponds to the `a + b` expression:
56 /// error[E0308]: mismatched types
57 /// --> src/main.rs:L:C
59 /// L | let temp: usize = match a + b {
60 /// | ----- this expression has type `usize`
61 /// L | Ok(num) => num,
62 /// | ^^^^^^^ expected `usize`, found enum `std::result::Result`
64 /// = note: expected type `usize`
65 /// found type `std::result::Result<_, _>`
70 impl<'tcx> FnCtxt<'_, 'tcx> {
71 fn demand_eqtype_pat_diag(
77 ) -> Option<DiagnosticBuilder<'tcx>> {
78 let code = Pattern { span: ti.span, root_ty: ti.expected, origin_expr: ti.origin_expr };
79 let cause = self.cause(cause_span, code);
80 self.demand_eqtype_with_origin(&cause, expected, actual)
90 self.demand_eqtype_pat_diag(cause_span, expected, actual, ti).map(|mut err| err.emit());
94 impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
95 /// Type check the given top level pattern against the `expected` type.
97 /// If a `Some(span)` is provided and `origin_expr` holds,
98 /// then the `span` represents the scrutinee's span.
99 /// The scrutinee is found in e.g. `match scrutinee { ... }` and `let pat = scrutinee;`.
101 /// Otherwise, `Some(span)` represents the span of a type expression
102 /// which originated the `expected` type.
103 pub fn check_pat_top(
105 pat: &'tcx Pat<'tcx>,
110 let def_bm = BindingMode::BindByValue(hir::Mutability::Not);
111 self.check_pat(pat, expected, def_bm, TopInfo { expected, origin_expr, span });
114 /// Type check the given `pat` against the `expected` type
115 /// with the provided `def_bm` (default binding mode).
117 /// Outside of this module, `check_pat_top` should always be used.
118 /// Conversely, inside this module, `check_pat_top` should never be used.
121 pat: &'tcx Pat<'tcx>,
126 debug!("check_pat(pat={:?},expected={:?},def_bm={:?})", pat, expected, def_bm);
128 let path_resolution = match &pat.kind {
129 PatKind::Path(qpath) => Some(self.resolve_ty_and_res_ufcs(qpath, pat.hir_id, pat.span)),
132 let is_nrp = self.is_non_ref_pat(pat, path_resolution.map(|(res, ..)| res));
133 let (expected, def_bm) = self.calc_default_binding_mode(pat, expected, def_bm, is_nrp);
135 let ty = match pat.kind {
136 PatKind::Wild => expected,
137 PatKind::Lit(lt) => self.check_pat_lit(pat.span, lt, expected, ti),
138 PatKind::Range(begin, end, _) => {
139 match self.check_pat_range(pat.span, begin, end, expected, ti) {
144 PatKind::Binding(ba, var_id, _, sub) => {
145 self.check_pat_ident(pat, ba, var_id, sub, expected, def_bm, ti)
147 PatKind::TupleStruct(ref qpath, subpats, ddpos) => {
148 self.check_pat_tuple_struct(pat, qpath, subpats, ddpos, expected, def_bm, ti)
150 PatKind::Path(ref qpath) => {
151 self.check_pat_path(pat, path_resolution.unwrap(), qpath, expected)
153 PatKind::Struct(ref qpath, fields, etc) => {
154 self.check_pat_struct(pat, qpath, fields, etc, expected, def_bm, ti)
156 PatKind::Or(pats) => {
158 self.check_pat(pat, expected, def_bm, ti);
162 PatKind::Tuple(elements, ddpos) => {
163 self.check_pat_tuple(pat.span, elements, ddpos, expected, def_bm, ti)
165 PatKind::Box(inner) => self.check_pat_box(pat.span, inner, expected, def_bm, ti),
166 PatKind::Ref(inner, mutbl) => {
167 self.check_pat_ref(pat, inner, mutbl, expected, def_bm, ti)
169 PatKind::Slice(before, slice, after) => {
170 self.check_pat_slice(pat.span, before, slice, after, expected, def_bm, ti)
174 self.write_ty(pat.hir_id, ty);
176 // (note_1): In most of the cases where (note_1) is referenced
177 // (literals and constants being the exception), we relate types
178 // using strict equality, even though subtyping would be sufficient.
179 // There are a few reasons for this, some of which are fairly subtle
180 // and which cost me (nmatsakis) an hour or two debugging to remember,
181 // so I thought I'd write them down this time.
183 // 1. There is no loss of expressiveness here, though it does
184 // cause some inconvenience. What we are saying is that the type
185 // of `x` becomes *exactly* what is expected. This can cause unnecessary
186 // errors in some cases, such as this one:
189 // fn foo<'x>(x: &'x int) {
196 // The reason we might get an error is that `z` might be
197 // assigned a type like `&'x int`, and then we would have
198 // a problem when we try to assign `&a` to `z`, because
199 // the lifetime of `&a` (i.e., the enclosing block) is
200 // shorter than `'x`.
202 // HOWEVER, this code works fine. The reason is that the
203 // expected type here is whatever type the user wrote, not
204 // the initializer's type. In this case the user wrote
205 // nothing, so we are going to create a type variable `Z`.
206 // Then we will assign the type of the initializer (`&'x
207 // int`) as a subtype of `Z`: `&'x int <: Z`. And hence we
208 // will instantiate `Z` as a type `&'0 int` where `'0` is
209 // a fresh region variable, with the constraint that `'x :
210 // '0`. So basically we're all set.
212 // Note that there are two tests to check that this remains true
213 // (`regions-reassign-{match,let}-bound-pointer.rs`).
215 // 2. Things go horribly wrong if we use subtype. The reason for
216 // THIS is a fairly subtle case involving bound regions. See the
217 // `givens` field in `region_constraints`, as well as the test
218 // `regions-relate-bound-regions-on-closures-to-inference-variables.rs`,
219 // for details. Short version is that we must sometimes detect
220 // relationships between specific region variables and regions
221 // bound in a closure signature, and that detection gets thrown
222 // off when we substitute fresh region variables here to enable
226 /// Compute the new expected type and default binding mode from the old ones
227 /// as well as the pattern form we are currently checking.
228 fn calc_default_binding_mode(
230 pat: &'tcx Pat<'tcx>,
233 is_non_ref_pat: bool,
234 ) -> (Ty<'tcx>, BindingMode) {
236 debug!("pattern is non reference pattern");
237 self.peel_off_references(pat, expected, def_bm)
239 // When you encounter a `&pat` pattern, reset to "by
240 // value". This is so that `x` and `y` here are by value,
241 // as they appear to be:
244 // match &(&22, &44) {
250 let def_bm = match pat.kind {
251 PatKind::Ref(..) => ty::BindByValue(hir::Mutability::Not),
258 /// Is the pattern a "non reference pattern"?
259 /// When the pattern is a path pattern, `opt_path_res` must be `Some(res)`.
260 fn is_non_ref_pat(&self, pat: &'tcx Pat<'tcx>, opt_path_res: Option<Res>) -> bool {
263 | PatKind::TupleStruct(..)
267 | PatKind::Slice(..) => true,
268 PatKind::Lit(ref lt) => {
269 let ty = self.check_expr(lt);
271 ty::Ref(..) => false,
275 PatKind::Path(_) => match opt_path_res.unwrap() {
276 Res::Def(DefKind::Const, _) | Res::Def(DefKind::AssocConst, _) => false,
279 // FIXME(or_patterns; Centril | dlrobertson): To keep things compiling
280 // for or-patterns at the top level, we need to make `p_0 | ... | p_n`
281 // a "non reference pattern". For example the following currently compiles:
284 // e @ &(1...2) | e @ &(3...4) => {}
289 // We should consider whether we should do something special in nested or-patterns.
290 PatKind::Or(_) | PatKind::Wild | PatKind::Binding(..) | PatKind::Ref(..) => false,
294 /// Peel off as many immediately nested `& mut?` from the expected type as possible
295 /// and return the new expected type and binding default binding mode.
296 /// The adjustments vector, if non-empty is stored in a table.
297 fn peel_off_references(
299 pat: &'tcx Pat<'tcx>,
301 mut def_bm: BindingMode,
302 ) -> (Ty<'tcx>, BindingMode) {
303 let mut expected = self.resolve_vars_with_obligations(&expected);
305 // Peel off as many `&` or `&mut` from the scrutinee type as possible. For example,
306 // for `match &&&mut Some(5)` the loop runs three times, aborting when it reaches
307 // the `Some(5)` which is not of type Ref.
309 // For each ampersand peeled off, update the binding mode and push the original
310 // type into the adjustments vector.
312 // See the examples in `ui/match-defbm*.rs`.
313 let mut pat_adjustments = vec![];
314 while let ty::Ref(_, inner_ty, inner_mutability) = expected.kind {
315 debug!("inspecting {:?}", expected);
317 debug!("current discriminant is Ref, inserting implicit deref");
318 // Preserve the reference type. We'll need it later during HAIR lowering.
319 pat_adjustments.push(expected);
322 def_bm = ty::BindByReference(match def_bm {
323 // If default binding mode is by value, make it `ref` or `ref mut`
324 // (depending on whether we observe `&` or `&mut`).
326 // When `ref mut`, stay a `ref mut` (on `&mut`) or downgrade to `ref` (on `&`).
327 ty::BindByReference(hir::Mutability::Mut) => inner_mutability,
328 // Once a `ref`, always a `ref`.
329 // This is because a `& &mut` cannot mutate the underlying value.
330 ty::BindByReference(m @ hir::Mutability::Not) => m,
334 if pat_adjustments.len() > 0 {
335 debug!("default binding mode is now {:?}", def_bm);
336 self.inh.tables.borrow_mut().pat_adjustments_mut().insert(pat.hir_id, pat_adjustments);
345 lt: &hir::Expr<'tcx>,
349 // We've already computed the type above (when checking for a non-ref pat),
350 // so avoid computing it again.
351 let ty = self.node_ty(lt.hir_id);
353 // Byte string patterns behave the same way as array patterns
354 // They can denote both statically and dynamically-sized byte arrays.
356 if let hir::ExprKind::Lit(ref lt) = lt.kind {
357 if let ast::LitKind::ByteStr(_) = lt.node {
358 let expected_ty = self.structurally_resolved_type(span, expected);
359 if let ty::Ref(_, r_ty, _) = expected_ty.kind {
360 if let ty::Slice(_) = r_ty.kind {
363 tcx.mk_imm_ref(tcx.lifetimes.re_static, tcx.mk_slice(tcx.types.u8));
369 // Somewhat surprising: in this case, the subtyping relation goes the
370 // opposite way as the other cases. Actually what we really want is not
371 // a subtyping relation at all but rather that there exists a LUB
372 // (so that they can be compared). However, in practice, constants are
373 // always scalars or strings. For scalars subtyping is irrelevant,
374 // and for strings `ty` is type is `&'static str`, so if we say that
376 // &'static str <: expected
378 // then that's equivalent to there existing a LUB.
379 if let Some(mut err) = self.demand_suptype_diag(span, expected, pat_ty) {
383 // In the case of `if`- and `while`-expressions we've already checked
384 // that `scrutinee: bool`. We know that the pattern is `true`,
385 // so an error here would be a duplicate and from the wrong POV.
386 s.is_desugaring(DesugaringKind::CondTemporary)
398 lhs: &'tcx hir::Expr<'tcx>,
399 rhs: &'tcx hir::Expr<'tcx>,
402 ) -> Option<Ty<'tcx>> {
403 let lhs_ty = self.check_expr(lhs);
404 let rhs_ty = self.check_expr(rhs);
406 // Check that both end-points are of numeric or char type.
407 let numeric_or_char = |ty: Ty<'_>| ty.is_numeric() || ty.is_char() || ty.references_error();
408 let lhs_fail = !numeric_or_char(lhs_ty);
409 let rhs_fail = !numeric_or_char(rhs_ty);
411 if lhs_fail || rhs_fail {
412 self.emit_err_pat_range(span, lhs.span, rhs.span, lhs_fail, rhs_fail, lhs_ty, rhs_ty);
416 // Now that we know the types can be unified we find the unified type and use
417 // it to type the entire expression.
418 let common_type = self.resolve_vars_if_possible(&lhs_ty);
420 // Subtyping doesn't matter here, as the value is some kind of scalar.
421 let demand_eqtype = |x_span, y_span, x_ty, y_ty| {
422 self.demand_eqtype_pat_diag(x_span, expected, x_ty, ti).map(|mut err| {
423 self.endpoint_has_type(&mut err, y_span, y_ty);
427 demand_eqtype(lhs.span, rhs.span, lhs_ty, rhs_ty);
428 demand_eqtype(rhs.span, lhs.span, rhs_ty, lhs_ty);
433 fn endpoint_has_type(&self, err: &mut DiagnosticBuilder<'_>, span: Span, ty: Ty<'_>) {
434 if !ty.references_error() {
435 err.span_label(span, &format!("this is of type `{}`", ty));
439 fn emit_err_pat_range(
449 let span = if lhs_fail && rhs_fail {
457 let mut err = struct_span_err!(
461 "only char and numeric types are allowed in range patterns"
463 let msg = |ty| format!("this is of type `{}` but it should be `char` or numeric", ty);
464 let mut one_side_err = |first_span, first_ty, second_span, second_ty: Ty<'_>| {
465 err.span_label(first_span, &msg(first_ty));
466 self.endpoint_has_type(&mut err, second_span, second_ty);
468 if lhs_fail && rhs_fail {
469 err.span_label(begin_span, &msg(lhs_ty));
470 err.span_label(end_span, &msg(rhs_ty));
472 one_side_err(begin_span, lhs_ty, end_span, rhs_ty);
474 one_side_err(end_span, rhs_ty, begin_span, lhs_ty);
476 if self.tcx.sess.teach(&err.get_code().unwrap()) {
478 "In a match expression, only numbers and characters can be matched \
479 against a range. This is because the compiler checks that the range \
480 is non-empty at compile-time, and is unable to evaluate arbitrary \
481 comparison functions. If you want to capture values of an orderable \
482 type between two end-points, you can use a guard.",
491 ba: hir::BindingAnnotation,
493 sub: Option<&'tcx Pat<'tcx>>,
498 // Determine the binding mode...
500 hir::BindingAnnotation::Unannotated => def_bm,
501 _ => BindingMode::convert(ba),
503 // ...and store it in a side table:
504 self.inh.tables.borrow_mut().pat_binding_modes_mut().insert(pat.hir_id, bm);
506 debug!("check_pat_ident: pat.hir_id={:?} bm={:?}", pat.hir_id, bm);
508 let local_ty = self.local_ty(pat.span, pat.hir_id).decl_ty;
509 let eq_ty = match bm {
510 ty::BindByReference(mutbl) => {
511 // If the binding is like `ref x | ref const x | ref mut x`
512 // then `x` is assigned a value of type `&M T` where M is the
513 // mutability and T is the expected type.
515 // `x` is assigned a value of type `&M T`, hence `&M T <: typeof(x)`
516 // is required. However, we use equality, which is stronger.
517 // See (note_1) for an explanation.
518 self.new_ref_ty(pat.span, mutbl, expected)
520 // Otherwise, the type of x is the expected type `T`.
521 ty::BindByValue(_) => {
522 // As above, `T <: typeof(x)` is required, but we use equality, see (note_1).
526 self.demand_eqtype_pat(pat.span, eq_ty, local_ty, ti);
528 // If there are multiple arms, make sure they all agree on
529 // what the type of the binding `x` ought to be.
530 if var_id != pat.hir_id {
531 let vt = self.local_ty(pat.span, var_id).decl_ty;
532 self.demand_eqtype_pat(pat.span, vt, local_ty, ti);
535 if let Some(p) = sub {
536 self.check_pat(&p, expected, def_bm, ti);
542 fn borrow_pat_suggestion(
544 err: &mut DiagnosticBuilder<'_>,
550 if let PatKind::Binding(..) = inner.kind {
551 let binding_parent_id = tcx.hir().get_parent_node(pat.hir_id);
552 let binding_parent = tcx.hir().get(binding_parent_id);
553 debug!("inner {:?} pat {:?} parent {:?}", inner, pat, binding_parent);
554 match binding_parent {
555 hir::Node::Param(hir::Param { span, .. }) => {
556 if let Ok(snippet) = tcx.sess.source_map().span_to_snippet(inner.span) {
559 &format!("did you mean `{}`", snippet),
560 format!(" &{}", expected),
561 Applicability::MachineApplicable,
565 hir::Node::Arm(_) | hir::Node::Pat(_) => {
566 // rely on match ergonomics or it might be nested `&&pat`
567 if let Ok(snippet) = tcx.sess.source_map().span_to_snippet(inner.span) {
570 "you can probably remove the explicit borrow",
572 Applicability::MaybeIncorrect,
576 _ => {} // don't provide suggestions in other cases #55175
581 pub fn check_dereferenceable(&self, span: Span, expected: Ty<'tcx>, inner: &Pat<'_>) -> bool {
582 if let PatKind::Binding(..) = inner.kind {
583 if let Some(mt) = self.shallow_resolve(expected).builtin_deref(true) {
584 if let ty::Dynamic(..) = mt.ty.kind {
585 // This is "x = SomeTrait" being reduced from
586 // "let &x = &SomeTrait" or "let box x = Box<SomeTrait>", an error.
587 let type_str = self.ty_to_string(expected);
588 let mut err = struct_span_err!(
592 "type `{}` cannot be dereferenced",
595 err.span_label(span, format!("type `{}` cannot be dereferenced", type_str));
596 if self.tcx.sess.teach(&err.get_code().unwrap()) {
597 err.note(CANNOT_IMPLICITLY_DEREF_POINTER_TRAIT_OBJ);
609 pat: &'tcx Pat<'tcx>,
610 qpath: &hir::QPath<'_>,
611 fields: &'tcx [hir::FieldPat<'tcx>],
617 // Resolve the path and check the definition for errors.
618 let (variant, pat_ty) = if let Some(variant_ty) = self.check_struct_path(qpath, pat.hir_id)
622 for field in fields {
623 self.check_pat(&field.pat, self.tcx.types.err, def_bm, ti);
625 return self.tcx.types.err;
628 // Type-check the path.
629 self.demand_eqtype_pat(pat.span, expected, pat_ty, ti);
631 // Type-check subpatterns.
633 .check_struct_pat_fields(pat_ty, pat.hir_id, pat.span, variant, fields, etc, def_bm, ti)
644 path_resolution: (Res, Option<Ty<'tcx>>, &'b [hir::PathSegment<'b>]),
645 qpath: &hir::QPath<'_>,
650 // We have already resolved the path.
651 let (res, opt_ty, segments) = path_resolution;
654 self.set_tainted_by_errors();
655 return tcx.types.err;
657 Res::Def(DefKind::Method, _)
658 | Res::Def(DefKind::Ctor(_, CtorKind::Fictive), _)
659 | Res::Def(DefKind::Ctor(_, CtorKind::Fn), _) => {
660 report_unexpected_variant_res(tcx, res, pat.span, qpath);
661 return tcx.types.err;
663 Res::Def(DefKind::Ctor(_, CtorKind::Const), _)
665 | Res::Def(DefKind::Const, _)
666 | Res::Def(DefKind::AssocConst, _) => {} // OK
667 _ => bug!("unexpected pattern resolution: {:?}", res),
670 // Type-check the path.
671 let pat_ty = self.instantiate_value_path(segments, opt_ty, res, pat.span, pat.hir_id).0;
672 self.demand_suptype(pat.span, expected, pat_ty);
676 fn check_pat_tuple_struct(
679 qpath: &hir::QPath<'_>,
680 subpats: &'tcx [&'tcx Pat<'tcx>],
681 ddpos: Option<usize>,
689 self.check_pat(&pat, tcx.types.err, def_bm, ti);
692 let report_unexpected_res = |res: Res| {
694 "expected tuple struct or tuple variant, found {} `{}`",
696 hir::print::to_string(tcx.hir(), |s| s.print_qpath(qpath, false)),
698 let mut err = struct_span_err!(tcx.sess, pat.span, E0164, "{}", msg);
699 match (res, &pat.kind) {
700 (Res::Def(DefKind::Fn, _), _) | (Res::Def(DefKind::Method, _), _) => {
701 err.span_label(pat.span, "`fn` calls are not allowed in patterns");
703 "for more information, visit \
704 https://doc.rust-lang.org/book/ch18-00-patterns.html",
708 err.span_label(pat.span, "not a tuple variant or struct");
715 // Resolve the path and check the definition for errors.
716 let (res, opt_ty, segments) = self.resolve_ty_and_res_ufcs(qpath, pat.hir_id, pat.span);
718 self.set_tainted_by_errors();
720 return self.tcx.types.err;
723 // Type-check the path.
725 self.instantiate_value_path(segments, opt_ty, res, pat.span, pat.hir_id);
727 report_unexpected_res(res);
728 return tcx.types.err;
731 let variant = match res {
733 self.set_tainted_by_errors();
735 return tcx.types.err;
737 Res::Def(DefKind::AssocConst, _) | Res::Def(DefKind::Method, _) => {
738 report_unexpected_res(res);
739 return tcx.types.err;
741 Res::Def(DefKind::Ctor(_, CtorKind::Fn), _) => tcx.expect_variant_res(res),
742 _ => bug!("unexpected pattern resolution: {:?}", res),
745 // Replace constructor type with constructed type for tuple struct patterns.
746 let pat_ty = pat_ty.fn_sig(tcx).output();
747 let pat_ty = pat_ty.no_bound_vars().expect("expected fn type");
749 // Type-check the tuple struct pattern against the expected type.
750 let diag = self.demand_eqtype_pat_diag(pat.span, expected, pat_ty, ti);
751 let had_err = diag.is_some();
752 diag.map(|mut err| err.emit());
754 // Type-check subpatterns.
755 if subpats.len() == variant.fields.len()
756 || subpats.len() < variant.fields.len() && ddpos.is_some()
758 let substs = match pat_ty.kind {
759 ty::Adt(_, substs) => substs,
760 _ => bug!("unexpected pattern type {:?}", pat_ty),
762 for (i, subpat) in subpats.iter().enumerate_and_adjust(variant.fields.len(), ddpos) {
763 let field_ty = self.field_ty(subpat.span, &variant.fields[i], substs);
764 self.check_pat(&subpat, field_ty, def_bm, ti);
766 self.tcx.check_stability(variant.fields[i].did, Some(pat.hir_id), subpat.span);
769 // Pattern has wrong number of fields.
770 self.e0023(pat.span, res, qpath, subpats, &variant.fields, expected, had_err);
772 return tcx.types.err;
781 qpath: &hir::QPath<'_>,
782 subpats: &'tcx [&'tcx Pat<'tcx>],
783 fields: &'tcx [ty::FieldDef],
787 let subpats_ending = pluralize!(subpats.len());
788 let fields_ending = pluralize!(fields.len());
789 let res_span = self.tcx.def_span(res.def_id());
790 let mut err = struct_span_err!(
794 "this pattern has {} field{}, but the corresponding {} has {} field{}",
803 format!("expected {} field{}, found {}", fields.len(), fields_ending, subpats.len(),),
805 .span_label(res_span, format!("{} defined here", res.descr()));
807 // Identify the case `Some(x, y)` where the expected type is e.g. `Option<(T, U)>`.
808 // More generally, the expected type wants a tuple variant with one field of an
809 // N-arity-tuple, e.g., `V_i((p_0, .., p_N))`. Meanwhile, the user supplied a pattern
810 // with the subpatterns directly in the tuple variant pattern, e.g., `V_i(p_0, .., p_N)`.
811 let missing_parenthesis = match (&expected.kind, fields, had_err) {
812 // #67037: only do this if we could sucessfully type-check the expected type against
813 // the tuple struct pattern. Otherwise the substs could get out of range on e.g.,
814 // `let P() = U;` where `P != U` with `struct P<T>(T);`.
815 (ty::Adt(_, substs), [field], false) => {
816 let field_ty = self.field_ty(pat_span, field, substs);
817 match field_ty.kind {
818 ty::Tuple(_) => field_ty.tuple_fields().count() == subpats.len(),
824 if missing_parenthesis {
825 let (left, right) = match subpats {
826 // This is the zero case; we aim to get the "hi" part of the `QPath`'s
827 // span as the "lo" and then the "hi" part of the pattern's span as the "hi".
830 // help: missing parenthesis
832 // L | let A(()) = A(());
835 let qpath_span = match qpath {
836 hir::QPath::Resolved(_, path) => path.span,
837 hir::QPath::TypeRelative(_, ps) => ps.ident.span,
839 (qpath_span.shrink_to_hi(), pat_span)
841 // Easy case. Just take the "lo" of the first sub-pattern and the "hi" of the
842 // last sub-pattern. In the case of `A(x)` the first and last may coincide.
845 // help: missing parenthesis
847 // L | let A((x, y)) = A((1, 2));
849 [first, ..] => (first.span.shrink_to_lo(), subpats.last().unwrap().span),
851 err.multipart_suggestion(
852 "missing parenthesis",
853 vec![(left, "(".to_string()), (right.shrink_to_hi(), ")".to_string())],
854 Applicability::MachineApplicable,
864 elements: &'tcx [&'tcx Pat<'tcx>],
865 ddpos: Option<usize>,
871 let mut expected_len = elements.len();
873 // Require known type only when `..` is present.
874 if let ty::Tuple(ref tys) = self.structurally_resolved_type(span, expected).kind {
875 expected_len = tys.len();
878 let max_len = cmp::max(expected_len, elements.len());
880 let element_tys_iter = (0..max_len).map(|_| {
881 GenericArg::from(self.next_ty_var(
882 // FIXME: `MiscVariable` for now -- obtaining the span and name information
883 // from all tuple elements isn't trivial.
884 TypeVariableOrigin { kind: TypeVariableOriginKind::TypeInference, span },
887 let element_tys = tcx.mk_substs(element_tys_iter);
888 let pat_ty = tcx.mk_ty(ty::Tuple(element_tys));
889 if let Some(mut err) = self.demand_eqtype_diag(span, expected, pat_ty) {
891 // Walk subpatterns with an expected type of `err` in this case to silence
892 // further errors being emitted when using the bindings. #50333
893 let element_tys_iter = (0..max_len).map(|_| tcx.types.err);
894 for (_, elem) in elements.iter().enumerate_and_adjust(max_len, ddpos) {
895 self.check_pat(elem, &tcx.types.err, def_bm, ti);
897 tcx.mk_tup(element_tys_iter)
899 for (i, elem) in elements.iter().enumerate_and_adjust(max_len, ddpos) {
900 self.check_pat(elem, &element_tys[i].expect_ty(), def_bm, ti);
906 fn check_struct_pat_fields(
911 variant: &'tcx ty::VariantDef,
912 fields: &'tcx [hir::FieldPat<'tcx>],
919 let (substs, adt) = match adt_ty.kind {
920 ty::Adt(adt, substs) => (substs, adt),
921 _ => span_bug!(span, "struct pattern is not an ADT"),
923 let kind_name = adt.variant_descr();
925 // Index the struct fields' types.
926 let field_map = variant
930 .map(|(i, field)| (field.ident.modern(), (i, field)))
931 .collect::<FxHashMap<_, _>>();
933 // Keep track of which fields have already appeared in the pattern.
934 let mut used_fields = FxHashMap::default();
935 let mut no_field_errors = true;
937 let mut inexistent_fields = vec![];
938 // Typecheck each field.
939 for field in fields {
940 let span = field.span;
941 let ident = tcx.adjust_ident(field.ident, variant.def_id);
942 let field_ty = match used_fields.entry(ident) {
943 Occupied(occupied) => {
944 self.error_field_already_bound(span, field.ident, *occupied.get());
945 no_field_errors = false;
953 self.write_field_index(field.hir_id, *i);
954 self.tcx.check_stability(f.did, Some(pat_id), span);
955 self.field_ty(span, f, substs)
958 inexistent_fields.push(field.ident);
959 no_field_errors = false;
965 self.check_pat(&field.pat, field_ty, def_bm, ti);
968 let mut unmentioned_fields = variant
971 .map(|field| field.ident.modern())
972 .filter(|ident| !used_fields.contains_key(&ident))
973 .collect::<Vec<_>>();
975 if inexistent_fields.len() > 0 && !variant.recovered {
976 self.error_inexistent_fields(
979 &mut unmentioned_fields,
984 // Require `..` if struct has non_exhaustive attribute.
985 if variant.is_field_list_non_exhaustive() && !adt.did.is_local() && !etc {
990 "`..` required with {} marked as non-exhaustive",
996 // Report an error if incorrect number of the fields were specified.
997 if kind_name == "union" {
998 if fields.len() != 1 {
1000 .struct_span_err(span, "union patterns should have exactly one field")
1004 tcx.sess.struct_span_err(span, "`..` cannot be used in union patterns").emit();
1006 } else if !etc && unmentioned_fields.len() > 0 {
1007 self.error_unmentioned_fields(span, &unmentioned_fields, variant);
1012 fn error_field_already_bound(&self, span: Span, ident: ast::Ident, other_field: Span) {
1017 "field `{}` bound multiple times in the pattern",
1020 .span_label(span, format!("multiple uses of `{}` in pattern", ident))
1021 .span_label(other_field, format!("first use of `{}`", ident))
1025 fn error_inexistent_fields(
1028 inexistent_fields: &[ast::Ident],
1029 unmentioned_fields: &mut Vec<ast::Ident>,
1030 variant: &ty::VariantDef,
1033 let (field_names, t, plural) = if inexistent_fields.len() == 1 {
1034 (format!("a field named `{}`", inexistent_fields[0]), "this", "")
1041 .map(|ident| format!("`{}`", ident))
1042 .collect::<Vec<String>>()
1049 let spans = inexistent_fields.iter().map(|ident| ident.span).collect::<Vec<_>>();
1050 let mut err = struct_span_err!(
1054 "{} `{}` does not have {}",
1056 tcx.def_path_str(variant.def_id),
1059 if let Some(ident) = inexistent_fields.last() {
1063 "{} `{}` does not have {} field{}",
1065 tcx.def_path_str(variant.def_id),
1071 let input = unmentioned_fields.iter().map(|field| &field.name);
1072 let suggested_name = find_best_match_for_name(input, &ident.as_str(), None);
1073 if let Some(suggested_name) = suggested_name {
1074 err.span_suggestion(
1076 "a field with a similar name exists",
1077 suggested_name.to_string(),
1078 Applicability::MaybeIncorrect,
1081 // we don't want to throw `E0027` in case we have thrown `E0026` for them
1082 unmentioned_fields.retain(|&x| x.name != suggested_name);
1086 if tcx.sess.teach(&err.get_code().unwrap()) {
1088 "This error indicates that a struct pattern attempted to \
1089 extract a non-existent field from a struct. Struct fields \
1090 are identified by the name used before the colon : so struct \
1091 patterns should resemble the declaration of the struct type \
1093 If you are using shorthand field patterns but want to refer \
1094 to the struct field by a different name, you should rename \
1101 fn error_unmentioned_fields(
1104 unmentioned_fields: &[ast::Ident],
1105 variant: &ty::VariantDef,
1107 let field_names = if unmentioned_fields.len() == 1 {
1108 format!("field `{}`", unmentioned_fields[0])
1110 let fields = unmentioned_fields
1112 .map(|name| format!("`{}`", name))
1113 .collect::<Vec<String>>()
1115 format!("fields {}", fields)
1117 let mut diag = struct_span_err!(
1121 "pattern does not mention {}",
1124 diag.span_label(span, format!("missing {}", field_names));
1125 if variant.ctor_kind == CtorKind::Fn {
1126 diag.note("trying to match a tuple variant with a struct variant pattern");
1128 if self.tcx.sess.teach(&diag.get_code().unwrap()) {
1130 "This error indicates that a pattern for a struct fails to specify a \
1131 sub-pattern for every one of the struct's fields. Ensure that each field \
1132 from the struct's definition is mentioned in the pattern, or use `..` to \
1133 ignore unwanted fields.",
1142 inner: &'tcx Pat<'tcx>,
1144 def_bm: BindingMode,
1148 let (box_ty, inner_ty) = if self.check_dereferenceable(span, expected, &inner) {
1149 // Here, `demand::subtype` is good enough, but I don't
1150 // think any errors can be introduced by using `demand::eqtype`.
1151 let inner_ty = self.next_ty_var(TypeVariableOrigin {
1152 kind: TypeVariableOriginKind::TypeInference,
1155 let box_ty = tcx.mk_box(inner_ty);
1156 self.demand_eqtype_pat(span, expected, box_ty, ti);
1159 (tcx.types.err, tcx.types.err)
1161 self.check_pat(&inner, inner_ty, def_bm, ti);
1168 inner: &'tcx Pat<'tcx>,
1169 mutbl: hir::Mutability,
1171 def_bm: BindingMode,
1175 let expected = self.shallow_resolve(expected);
1176 let (rptr_ty, inner_ty) = if self.check_dereferenceable(pat.span, expected, &inner) {
1177 // `demand::subtype` would be good enough, but using `eqtype` turns
1178 // out to be equally general. See (note_1) for details.
1180 // Take region, inner-type from expected type if we can,
1181 // to avoid creating needless variables. This also helps with
1182 // the bad interactions of the given hack detailed in (note_1).
1183 debug!("check_pat_ref: expected={:?}", expected);
1184 match expected.kind {
1185 ty::Ref(_, r_ty, r_mutbl) if r_mutbl == mutbl => (expected, r_ty),
1187 let inner_ty = self.next_ty_var(TypeVariableOrigin {
1188 kind: TypeVariableOriginKind::TypeInference,
1191 let rptr_ty = self.new_ref_ty(pat.span, mutbl, inner_ty);
1192 debug!("check_pat_ref: demanding {:?} = {:?}", expected, rptr_ty);
1193 let err = self.demand_eqtype_diag(pat.span, expected, rptr_ty);
1195 // Look for a case like `fn foo(&foo: u32)` and suggest
1196 // `fn foo(foo: &u32)`
1197 if let Some(mut err) = err {
1198 self.borrow_pat_suggestion(&mut err, &pat, &inner, &expected);
1205 (tcx.types.err, tcx.types.err)
1207 self.check_pat(&inner, inner_ty, def_bm, ti);
1211 /// Create a reference type with a fresh region variable.
1212 fn new_ref_ty(&self, span: Span, mutbl: hir::Mutability, ty: Ty<'tcx>) -> Ty<'tcx> {
1213 let region = self.next_region_var(infer::PatternRegion(span));
1214 let mt = ty::TypeAndMut { ty, mutbl };
1215 self.tcx.mk_ref(region, mt)
1218 /// Type check a slice pattern.
1220 /// Syntactically, these look like `[pat_0, ..., pat_n]`.
1221 /// Semantically, we are type checking a pattern with structure:
1223 /// [before_0, ..., before_n, (slice, after_0, ... after_n)?]
1225 /// The type of `slice`, if it is present, depends on the `expected` type.
1226 /// If `slice` is missing, then so is `after_i`.
1227 /// If `slice` is present, it can still represent 0 elements.
1231 before: &'tcx [&'tcx Pat<'tcx>],
1232 slice: Option<&'tcx Pat<'tcx>>,
1233 after: &'tcx [&'tcx Pat<'tcx>],
1235 def_bm: BindingMode,
1238 let err = self.tcx.types.err;
1239 let expected = self.structurally_resolved_type(span, expected);
1240 let (inner_ty, slice_ty, expected) = match expected.kind {
1241 // An array, so we might have something like `let [a, b, c] = [0, 1, 2];`.
1242 ty::Array(inner_ty, len) => {
1243 let min = before.len() as u64 + after.len() as u64;
1245 .check_array_pat_len(span, slice, len, min)
1246 .map_or(err, |len| self.tcx.mk_array(inner_ty, len));
1247 (inner_ty, slice_ty, expected)
1249 ty::Slice(inner_ty) => (inner_ty, expected, expected),
1250 // The expected type must be an array or slice, but was neither, so error.
1252 if !expected.references_error() {
1253 self.error_expected_array_or_slice(span, expected);
1259 // Type check all the patterns before `slice`.
1261 self.check_pat(&elt, inner_ty, def_bm, ti);
1263 // Type check the `slice`, if present, against its expected type.
1264 if let Some(slice) = slice {
1265 self.check_pat(&slice, slice_ty, def_bm, ti);
1267 // Type check the elements after `slice`, if present.
1269 self.check_pat(&elt, inner_ty, def_bm, ti);
1274 /// Type check the length of an array pattern.
1276 /// Return the length of the variable length pattern,
1277 /// if it exists and there are no errors.
1278 fn check_array_pat_len(
1281 slice: Option<&'tcx Pat<'tcx>>,
1282 len: &ty::Const<'tcx>,
1285 if let Some(len) = len.try_eval_usize(self.tcx, self.param_env) {
1286 // Now we know the length...
1287 if slice.is_none() {
1288 // ...and since there is no variable-length pattern,
1289 // we require an exact match between the number of elements
1290 // in the array pattern and as provided by the matched type.
1292 self.error_scrutinee_inconsistent_length(span, min_len, len);
1294 } else if let r @ Some(_) = len.checked_sub(min_len) {
1295 // The variable-length pattern was there,
1296 // so it has an array type with the remaining elements left as its size...
1299 // ...however, in this case, there were no remaining elements.
1300 // That is, the slice pattern requires more than the array type offers.
1301 self.error_scrutinee_with_rest_inconsistent_length(span, min_len, len);
1304 // No idea what the length is, which happens if we have e.g.,
1305 // `let [a, b] = arr` where `arr: [T; N]` where `const N: usize`.
1306 self.error_scrutinee_unfixed_length(span);
1311 fn error_scrutinee_inconsistent_length(&self, span: Span, min_len: u64, size: u64) {
1316 "pattern requires {} element{} but array has {}",
1318 pluralize!(min_len),
1321 .span_label(span, format!("expected {} element{}", size, pluralize!(size)))
1325 fn error_scrutinee_with_rest_inconsistent_length(&self, span: Span, min_len: u64, size: u64) {
1330 "pattern requires at least {} element{} but array has {}",
1332 pluralize!(min_len),
1337 format!("pattern cannot match array of {} element{}", size, pluralize!(size),),
1342 fn error_scrutinee_unfixed_length(&self, span: Span) {
1347 "cannot pattern-match on an array without a fixed length",
1352 fn error_expected_array_or_slice(&self, span: Span, expected_ty: Ty<'tcx>) {
1353 let mut err = struct_span_err!(
1357 "expected an array or slice, found `{}`",
1360 if let ty::Ref(_, ty, _) = expected_ty.kind {
1361 if let ty::Array(..) | ty::Slice(..) = ty.kind {
1362 err.help("the semantics of slice patterns changed recently; see issue #62254");
1365 err.span_label(span, format!("pattern cannot match with input type `{}`", expected_ty));