1 use crate::check::FnCtxt;
2 use crate::util::nodemap::FxHashMap;
3 use errors::{pluralize, Applicability, DiagnosticBuilder};
4 use rustc::hir::def::{CtorKind, DefKind, Res};
5 use rustc::hir::pat_util::EnumerateAndAdjustIterator;
6 use rustc::hir::{self, HirId, Pat, PatKind};
8 use rustc::infer::type_variable::{TypeVariableOrigin, TypeVariableOriginKind};
9 use rustc::traits::Pattern;
10 use rustc::ty::subst::GenericArg;
11 use rustc::ty::{self, BindingMode, Ty, TypeFoldable};
13 use syntax::util::lev_distance::find_best_match_for_name;
14 use syntax_pos::hygiene::DesugaringKind;
17 use rustc_error_codes::*;
20 use std::collections::hash_map::Entry::{Occupied, Vacant};
22 use super::report_unexpected_variant_res;
24 const CANNOT_IMPLICITLY_DEREF_POINTER_TRAIT_OBJ: &str = "\
25 This error indicates that a pointer to a trait type cannot be implicitly dereferenced by a \
26 pattern. Every trait defines a type, but because the size of trait implementors isn't fixed, \
27 this type has no compile-time size. Therefore, all accesses to trait types must be through \
28 pointers. If you encounter this error you should try to avoid dereferencing the pointer.
30 You can read more about trait objects in the Trait Objects section of the Reference: \
31 https://doc.rust-lang.org/reference/types.html#trait-objects";
33 impl<'tcx> FnCtxt<'_, 'tcx> {
34 fn demand_eqtype_pat_diag(
39 match_expr_span: Option<Span>,
40 ) -> Option<DiagnosticBuilder<'tcx>> {
41 let cause = if let Some(span) = match_expr_span {
42 self.cause(cause_span, Pattern { span, ty: expected })
46 self.demand_eqtype_with_origin(&cause, expected, actual)
54 match_expr_span: Option<Span>,
56 self.demand_eqtype_pat_diag(cause_span, expected, actual, match_expr_span)
57 .map(|mut err| err.emit());
61 impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
62 pub fn check_pat_top(&self, pat: &'tcx Pat<'tcx>, expected: Ty<'tcx>, span: Option<Span>) {
63 let def_bm = BindingMode::BindByValue(hir::Mutability::Not);
64 self.check_pat(pat, expected, def_bm, span);
67 /// `discrim_span` argument having a `Span` indicates that this pattern is part of a match
68 /// expression arm guard, and it points to the match discriminant to add context in type errors.
69 /// In the following example, `discrim_span` corresponds to the `a + b` expression:
72 /// error[E0308]: mismatched types
73 /// --> src/main.rs:5:9
75 /// 4 | let temp: usize = match a + b {
76 /// | ----- this expression has type `usize`
77 /// 5 | Ok(num) => num,
78 /// | ^^^^^^^ expected `usize`, found enum `std::result::Result`
80 /// = note: expected type `usize`
81 /// found type `std::result::Result<_, _>`
88 discrim_span: Option<Span>,
90 debug!("check_pat(pat={:?},expected={:?},def_bm={:?})", pat, expected, def_bm);
92 let path_resolution = match &pat.kind {
93 PatKind::Path(qpath) => Some(self.resolve_ty_and_res_ufcs(qpath, pat.hir_id, pat.span)),
96 let is_nrp = self.is_non_ref_pat(pat, path_resolution.map(|(res, ..)| res));
97 let (expected, def_bm) = self.calc_default_binding_mode(pat, expected, def_bm, is_nrp);
99 let ty = match pat.kind {
100 PatKind::Wild => expected,
101 PatKind::Lit(lt) => self.check_pat_lit(pat.span, lt, expected, discrim_span),
102 PatKind::Range(begin, end, _) => {
103 match self.check_pat_range(pat.span, begin, end, expected, discrim_span) {
108 PatKind::Binding(ba, var_id, _, sub) => {
109 self.check_pat_ident(pat, ba, var_id, sub, expected, def_bm, discrim_span)
111 PatKind::TupleStruct(ref qpath, subpats, ddpos) => self.check_pat_tuple_struct(
120 PatKind::Path(ref qpath) => {
121 self.check_pat_path(pat, path_resolution.unwrap(), qpath, expected)
123 PatKind::Struct(ref qpath, fields, etc) => {
124 self.check_pat_struct(pat, qpath, fields, etc, expected, def_bm, discrim_span)
126 PatKind::Or(pats) => {
128 self.check_pat(pat, expected, def_bm, discrim_span);
132 PatKind::Tuple(elements, ddpos) => {
133 self.check_pat_tuple(pat.span, elements, ddpos, expected, def_bm, discrim_span)
135 PatKind::Box(inner) => {
136 self.check_pat_box(pat.span, inner, expected, def_bm, discrim_span)
138 PatKind::Ref(inner, mutbl) => {
139 self.check_pat_ref(pat, inner, mutbl, expected, def_bm, discrim_span)
141 PatKind::Slice(before, slice, after) => {
142 self.check_pat_slice(pat.span, before, slice, after, expected, def_bm, discrim_span)
146 self.write_ty(pat.hir_id, ty);
148 // (note_1): In most of the cases where (note_1) is referenced
149 // (literals and constants being the exception), we relate types
150 // using strict equality, even though subtyping would be sufficient.
151 // There are a few reasons for this, some of which are fairly subtle
152 // and which cost me (nmatsakis) an hour or two debugging to remember,
153 // so I thought I'd write them down this time.
155 // 1. There is no loss of expressiveness here, though it does
156 // cause some inconvenience. What we are saying is that the type
157 // of `x` becomes *exactly* what is expected. This can cause unnecessary
158 // errors in some cases, such as this one:
161 // fn foo<'x>(x: &'x int) {
168 // The reason we might get an error is that `z` might be
169 // assigned a type like `&'x int`, and then we would have
170 // a problem when we try to assign `&a` to `z`, because
171 // the lifetime of `&a` (i.e., the enclosing block) is
172 // shorter than `'x`.
174 // HOWEVER, this code works fine. The reason is that the
175 // expected type here is whatever type the user wrote, not
176 // the initializer's type. In this case the user wrote
177 // nothing, so we are going to create a type variable `Z`.
178 // Then we will assign the type of the initializer (`&'x
179 // int`) as a subtype of `Z`: `&'x int <: Z`. And hence we
180 // will instantiate `Z` as a type `&'0 int` where `'0` is
181 // a fresh region variable, with the constraint that `'x :
182 // '0`. So basically we're all set.
184 // Note that there are two tests to check that this remains true
185 // (`regions-reassign-{match,let}-bound-pointer.rs`).
187 // 2. Things go horribly wrong if we use subtype. The reason for
188 // THIS is a fairly subtle case involving bound regions. See the
189 // `givens` field in `region_constraints`, as well as the test
190 // `regions-relate-bound-regions-on-closures-to-inference-variables.rs`,
191 // for details. Short version is that we must sometimes detect
192 // relationships between specific region variables and regions
193 // bound in a closure signature, and that detection gets thrown
194 // off when we substitute fresh region variables here to enable
198 /// Compute the new expected type and default binding mode from the old ones
199 /// as well as the pattern form we are currently checking.
200 fn calc_default_binding_mode(
202 pat: &'tcx Pat<'tcx>,
205 is_non_ref_pat: bool,
206 ) -> (Ty<'tcx>, BindingMode) {
208 debug!("pattern is non reference pattern");
209 self.peel_off_references(pat, expected, def_bm)
211 // When you encounter a `&pat` pattern, reset to "by
212 // value". This is so that `x` and `y` here are by value,
213 // as they appear to be:
216 // match &(&22, &44) {
222 let def_bm = match pat.kind {
223 PatKind::Ref(..) => ty::BindByValue(hir::Mutability::Not),
230 /// Is the pattern a "non reference pattern"?
231 /// When the pattern is a path pattern, `opt_path_res` must be `Some(res)`.
232 fn is_non_ref_pat(&self, pat: &'tcx Pat<'tcx>, opt_path_res: Option<Res>) -> bool {
235 | PatKind::TupleStruct(..)
239 | PatKind::Slice(..) => true,
240 PatKind::Lit(ref lt) => {
241 let ty = self.check_expr(lt);
243 ty::Ref(..) => false,
247 PatKind::Path(_) => match opt_path_res.unwrap() {
248 Res::Def(DefKind::Const, _) | Res::Def(DefKind::AssocConst, _) => false,
251 // FIXME(or_patterns; Centril | dlrobertson): To keep things compiling
252 // for or-patterns at the top level, we need to make `p_0 | ... | p_n`
253 // a "non reference pattern". For example the following currently compiles:
256 // e @ &(1...2) | e @ &(3...4) => {}
261 // We should consider whether we should do something special in nested or-patterns.
262 PatKind::Or(_) | PatKind::Wild | PatKind::Binding(..) | PatKind::Ref(..) => false,
266 /// Peel off as many immediately nested `& mut?` from the expected type as possible
267 /// and return the new expected type and binding default binding mode.
268 /// The adjustments vector, if non-empty is stored in a table.
269 fn peel_off_references(
271 pat: &'tcx Pat<'tcx>,
273 mut def_bm: BindingMode,
274 ) -> (Ty<'tcx>, BindingMode) {
275 let mut expected = self.resolve_vars_with_obligations(&expected);
277 // Peel off as many `&` or `&mut` from the scrutinee type as possible. For example,
278 // for `match &&&mut Some(5)` the loop runs three times, aborting when it reaches
279 // the `Some(5)` which is not of type Ref.
281 // For each ampersand peeled off, update the binding mode and push the original
282 // type into the adjustments vector.
284 // See the examples in `ui/match-defbm*.rs`.
285 let mut pat_adjustments = vec![];
286 while let ty::Ref(_, inner_ty, inner_mutability) = expected.kind {
287 debug!("inspecting {:?}", expected);
289 debug!("current discriminant is Ref, inserting implicit deref");
290 // Preserve the reference type. We'll need it later during HAIR lowering.
291 pat_adjustments.push(expected);
294 def_bm = ty::BindByReference(match def_bm {
295 // If default binding mode is by value, make it `ref` or `ref mut`
296 // (depending on whether we observe `&` or `&mut`).
298 // When `ref mut`, stay a `ref mut` (on `&mut`) or downgrade to `ref` (on `&`).
299 ty::BindByReference(hir::Mutability::Mut) => inner_mutability,
300 // Once a `ref`, always a `ref`.
301 // This is because a `& &mut` cannot mutate the underlying value.
302 ty::BindByReference(m @ hir::Mutability::Not) => m,
306 if pat_adjustments.len() > 0 {
307 debug!("default binding mode is now {:?}", def_bm);
308 self.inh.tables.borrow_mut().pat_adjustments_mut().insert(pat.hir_id, pat_adjustments);
317 lt: &hir::Expr<'tcx>,
319 discrim_span: Option<Span>,
321 // We've already computed the type above (when checking for a non-ref pat),
322 // so avoid computing it again.
323 let ty = self.node_ty(lt.hir_id);
325 // Byte string patterns behave the same way as array patterns
326 // They can denote both statically and dynamically-sized byte arrays.
328 if let hir::ExprKind::Lit(ref lt) = lt.kind {
329 if let ast::LitKind::ByteStr(_) = lt.node {
330 let expected_ty = self.structurally_resolved_type(span, expected);
331 if let ty::Ref(_, r_ty, _) = expected_ty.kind {
332 if let ty::Slice(_) = r_ty.kind {
335 tcx.mk_imm_ref(tcx.lifetimes.re_static, tcx.mk_slice(tcx.types.u8));
341 // Somewhat surprising: in this case, the subtyping relation goes the
342 // opposite way as the other cases. Actually what we really want is not
343 // a subtyping relation at all but rather that there exists a LUB
344 // (so that they can be compared). However, in practice, constants are
345 // always scalars or strings. For scalars subtyping is irrelevant,
346 // and for strings `ty` is type is `&'static str`, so if we say that
348 // &'static str <: expected
350 // then that's equivalent to there existing a LUB.
351 if let Some(mut err) = self.demand_suptype_diag(span, expected, pat_ty) {
355 // In the case of `if`- and `while`-expressions we've already checked
356 // that `scrutinee: bool`. We know that the pattern is `true`,
357 // so an error here would be a duplicate and from the wrong POV.
358 s.is_desugaring(DesugaringKind::CondTemporary)
370 lhs: &'tcx hir::Expr<'tcx>,
371 rhs: &'tcx hir::Expr<'tcx>,
373 discrim_span: Option<Span>,
374 ) -> Option<Ty<'tcx>> {
375 let lhs_ty = self.check_expr(lhs);
376 let rhs_ty = self.check_expr(rhs);
378 // Check that both end-points are of numeric or char type.
379 let numeric_or_char = |ty: Ty<'_>| ty.is_numeric() || ty.is_char() || ty.references_error();
380 let lhs_fail = !numeric_or_char(lhs_ty);
381 let rhs_fail = !numeric_or_char(rhs_ty);
383 if lhs_fail || rhs_fail {
384 self.emit_err_pat_range(span, lhs.span, rhs.span, lhs_fail, rhs_fail, lhs_ty, rhs_ty);
388 // Now that we know the types can be unified we find the unified type and use
389 // it to type the entire expression.
390 let common_type = self.resolve_vars_if_possible(&lhs_ty);
392 // Subtyping doesn't matter here, as the value is some kind of scalar.
393 let demand_eqtype = |x_span, y_span, x_ty, y_ty| {
394 self.demand_eqtype_pat_diag(x_span, expected, x_ty, discrim_span).map(|mut err| {
395 self.endpoint_has_type(&mut err, y_span, y_ty);
399 demand_eqtype(lhs.span, rhs.span, lhs_ty, rhs_ty);
400 demand_eqtype(rhs.span, lhs.span, rhs_ty, lhs_ty);
405 fn endpoint_has_type(&self, err: &mut DiagnosticBuilder<'_>, span: Span, ty: Ty<'_>) {
406 if !ty.references_error() {
407 err.span_label(span, &format!("this is of type `{}`", ty));
411 fn emit_err_pat_range(
421 let span = if lhs_fail && rhs_fail {
429 let mut err = struct_span_err!(
433 "only char and numeric types are allowed in range patterns"
435 let msg = |ty| format!("this is of type `{}` but it should be `char` or numeric", ty);
436 let mut one_side_err = |first_span, first_ty, second_span, second_ty: Ty<'_>| {
437 err.span_label(first_span, &msg(first_ty));
438 self.endpoint_has_type(&mut err, second_span, second_ty);
440 if lhs_fail && rhs_fail {
441 err.span_label(begin_span, &msg(lhs_ty));
442 err.span_label(end_span, &msg(rhs_ty));
444 one_side_err(begin_span, lhs_ty, end_span, rhs_ty);
446 one_side_err(end_span, rhs_ty, begin_span, lhs_ty);
448 if self.tcx.sess.teach(&err.get_code().unwrap()) {
450 "In a match expression, only numbers and characters can be matched \
451 against a range. This is because the compiler checks that the range \
452 is non-empty at compile-time, and is unable to evaluate arbitrary \
453 comparison functions. If you want to capture values of an orderable \
454 type between two end-points, you can use a guard.",
463 ba: hir::BindingAnnotation,
465 sub: Option<&'tcx Pat<'tcx>>,
468 discrim_span: Option<Span>,
470 // Determine the binding mode...
472 hir::BindingAnnotation::Unannotated => def_bm,
473 _ => BindingMode::convert(ba),
475 // ...and store it in a side table:
476 self.inh.tables.borrow_mut().pat_binding_modes_mut().insert(pat.hir_id, bm);
478 debug!("check_pat_ident: pat.hir_id={:?} bm={:?}", pat.hir_id, bm);
480 let local_ty = self.local_ty(pat.span, pat.hir_id).decl_ty;
481 let eq_ty = match bm {
482 ty::BindByReference(mutbl) => {
483 // If the binding is like `ref x | ref const x | ref mut x`
484 // then `x` is assigned a value of type `&M T` where M is the
485 // mutability and T is the expected type.
487 // `x` is assigned a value of type `&M T`, hence `&M T <: typeof(x)`
488 // is required. However, we use equality, which is stronger.
489 // See (note_1) for an explanation.
490 self.new_ref_ty(pat.span, mutbl, expected)
492 // Otherwise, the type of x is the expected type `T`.
493 ty::BindByValue(_) => {
494 // As above, `T <: typeof(x)` is required, but we use equality, see (note_1).
498 self.demand_eqtype_pat(pat.span, eq_ty, local_ty, discrim_span);
500 // If there are multiple arms, make sure they all agree on
501 // what the type of the binding `x` ought to be.
502 if var_id != pat.hir_id {
503 let vt = self.local_ty(pat.span, var_id).decl_ty;
504 self.demand_eqtype_pat(pat.span, vt, local_ty, discrim_span);
507 if let Some(p) = sub {
508 self.check_pat(&p, expected, def_bm, discrim_span);
514 fn borrow_pat_suggestion(
516 err: &mut DiagnosticBuilder<'_>,
522 if let PatKind::Binding(..) = inner.kind {
523 let binding_parent_id = tcx.hir().get_parent_node(pat.hir_id);
524 let binding_parent = tcx.hir().get(binding_parent_id);
525 debug!("inner {:?} pat {:?} parent {:?}", inner, pat, binding_parent);
526 match binding_parent {
527 hir::Node::Param(hir::Param { span, .. }) => {
528 if let Ok(snippet) = tcx.sess.source_map().span_to_snippet(inner.span) {
531 &format!("did you mean `{}`", snippet),
532 format!(" &{}", expected),
533 Applicability::MachineApplicable,
537 hir::Node::Arm(_) | hir::Node::Pat(_) => {
538 // rely on match ergonomics or it might be nested `&&pat`
539 if let Ok(snippet) = tcx.sess.source_map().span_to_snippet(inner.span) {
542 "you can probably remove the explicit borrow",
544 Applicability::MaybeIncorrect,
548 _ => {} // don't provide suggestions in other cases #55175
553 pub fn check_dereferenceable(&self, span: Span, expected: Ty<'tcx>, inner: &Pat<'_>) -> bool {
554 if let PatKind::Binding(..) = inner.kind {
555 if let Some(mt) = self.shallow_resolve(expected).builtin_deref(true) {
556 if let ty::Dynamic(..) = mt.ty.kind {
557 // This is "x = SomeTrait" being reduced from
558 // "let &x = &SomeTrait" or "let box x = Box<SomeTrait>", an error.
559 let type_str = self.ty_to_string(expected);
560 let mut err = struct_span_err!(
564 "type `{}` cannot be dereferenced",
567 err.span_label(span, format!("type `{}` cannot be dereferenced", type_str));
568 if self.tcx.sess.teach(&err.get_code().unwrap()) {
569 err.note(CANNOT_IMPLICITLY_DEREF_POINTER_TRAIT_OBJ);
581 pat: &'tcx Pat<'tcx>,
582 qpath: &hir::QPath<'_>,
583 fields: &'tcx [hir::FieldPat<'tcx>],
587 discrim_span: Option<Span>,
589 // Resolve the path and check the definition for errors.
590 let (variant, pat_ty) = if let Some(variant_ty) = self.check_struct_path(qpath, pat.hir_id)
594 for field in fields {
595 self.check_pat(&field.pat, self.tcx.types.err, def_bm, discrim_span);
597 return self.tcx.types.err;
600 // Type-check the path.
601 self.demand_eqtype_pat(pat.span, expected, pat_ty, discrim_span);
603 // Type-check subpatterns.
604 if self.check_struct_pat_fields(
623 path_resolution: (Res, Option<Ty<'tcx>>, &'b [hir::PathSegment<'b>]),
624 qpath: &hir::QPath<'_>,
629 // We have already resolved the path.
630 let (res, opt_ty, segments) = path_resolution;
633 self.set_tainted_by_errors();
634 return tcx.types.err;
636 Res::Def(DefKind::Method, _)
637 | Res::Def(DefKind::Ctor(_, CtorKind::Fictive), _)
638 | Res::Def(DefKind::Ctor(_, CtorKind::Fn), _) => {
639 report_unexpected_variant_res(tcx, res, pat.span, qpath);
640 return tcx.types.err;
642 Res::Def(DefKind::Ctor(_, CtorKind::Const), _)
644 | Res::Def(DefKind::Const, _)
645 | Res::Def(DefKind::AssocConst, _) => {} // OK
646 _ => bug!("unexpected pattern resolution: {:?}", res),
649 // Type-check the path.
650 let pat_ty = self.instantiate_value_path(segments, opt_ty, res, pat.span, pat.hir_id).0;
651 self.demand_suptype(pat.span, expected, pat_ty);
655 fn check_pat_tuple_struct(
658 qpath: &hir::QPath<'_>,
659 subpats: &'tcx [&'tcx Pat<'tcx>],
660 ddpos: Option<usize>,
663 match_arm_pat_span: Option<Span>,
668 self.check_pat(&pat, tcx.types.err, def_bm, match_arm_pat_span);
671 let report_unexpected_res = |res: Res| {
673 "expected tuple struct or tuple variant, found {} `{}`",
675 hir::print::to_string(tcx.hir(), |s| s.print_qpath(qpath, false)),
677 let mut err = struct_span_err!(tcx.sess, pat.span, E0164, "{}", msg);
678 match (res, &pat.kind) {
679 (Res::Def(DefKind::Fn, _), _) | (Res::Def(DefKind::Method, _), _) => {
680 err.span_label(pat.span, "`fn` calls are not allowed in patterns");
682 "for more information, visit \
683 https://doc.rust-lang.org/book/ch18-00-patterns.html",
687 err.span_label(pat.span, "not a tuple variant or struct");
694 // Resolve the path and check the definition for errors.
695 let (res, opt_ty, segments) = self.resolve_ty_and_res_ufcs(qpath, pat.hir_id, pat.span);
697 self.set_tainted_by_errors();
699 return self.tcx.types.err;
702 // Type-check the path.
704 self.instantiate_value_path(segments, opt_ty, res, pat.span, pat.hir_id);
706 report_unexpected_res(res);
707 return tcx.types.err;
710 let variant = match res {
712 self.set_tainted_by_errors();
714 return tcx.types.err;
716 Res::Def(DefKind::AssocConst, _) | Res::Def(DefKind::Method, _) => {
717 report_unexpected_res(res);
718 return tcx.types.err;
720 Res::Def(DefKind::Ctor(_, CtorKind::Fn), _) => tcx.expect_variant_res(res),
721 _ => bug!("unexpected pattern resolution: {:?}", res),
724 // Replace constructor type with constructed type for tuple struct patterns.
725 let pat_ty = pat_ty.fn_sig(tcx).output();
726 let pat_ty = pat_ty.no_bound_vars().expect("expected fn type");
728 // Type-check the tuple struct pattern against the expected type.
729 let diag = self.demand_eqtype_pat_diag(pat.span, expected, pat_ty, match_arm_pat_span);
730 let had_err = diag.is_some();
731 diag.map(|mut err| err.emit());
733 // Type-check subpatterns.
734 if subpats.len() == variant.fields.len()
735 || subpats.len() < variant.fields.len() && ddpos.is_some()
737 let substs = match pat_ty.kind {
738 ty::Adt(_, substs) => substs,
739 _ => bug!("unexpected pattern type {:?}", pat_ty),
741 for (i, subpat) in subpats.iter().enumerate_and_adjust(variant.fields.len(), ddpos) {
742 let field_ty = self.field_ty(subpat.span, &variant.fields[i], substs);
743 self.check_pat(&subpat, field_ty, def_bm, match_arm_pat_span);
745 self.tcx.check_stability(variant.fields[i].did, Some(pat.hir_id), subpat.span);
748 // Pattern has wrong number of fields.
749 self.e0023(pat.span, res, qpath, subpats, &variant.fields, expected, had_err);
751 return tcx.types.err;
760 qpath: &hir::QPath<'_>,
761 subpats: &'tcx [&'tcx Pat<'tcx>],
762 fields: &'tcx [ty::FieldDef],
766 let subpats_ending = pluralize!(subpats.len());
767 let fields_ending = pluralize!(fields.len());
768 let res_span = self.tcx.def_span(res.def_id());
769 let mut err = struct_span_err!(
773 "this pattern has {} field{}, but the corresponding {} has {} field{}",
782 format!("expected {} field{}, found {}", fields.len(), fields_ending, subpats.len(),),
784 .span_label(res_span, format!("{} defined here", res.descr()));
786 // Identify the case `Some(x, y)` where the expected type is e.g. `Option<(T, U)>`.
787 // More generally, the expected type wants a tuple variant with one field of an
788 // N-arity-tuple, e.g., `V_i((p_0, .., p_N))`. Meanwhile, the user supplied a pattern
789 // with the subpatterns directly in the tuple variant pattern, e.g., `V_i(p_0, .., p_N)`.
790 let missing_parenthesis = match (&expected.kind, fields, had_err) {
791 // #67037: only do this if we could sucessfully type-check the expected type against
792 // the tuple struct pattern. Otherwise the substs could get out of range on e.g.,
793 // `let P() = U;` where `P != U` with `struct P<T>(T);`.
794 (ty::Adt(_, substs), [field], false) => {
795 let field_ty = self.field_ty(pat_span, field, substs);
796 match field_ty.kind {
797 ty::Tuple(_) => field_ty.tuple_fields().count() == subpats.len(),
803 if missing_parenthesis {
804 let (left, right) = match subpats {
805 // This is the zero case; we aim to get the "hi" part of the `QPath`'s
806 // span as the "lo" and then the "hi" part of the pattern's span as the "hi".
809 // help: missing parenthesis
811 // L | let A(()) = A(());
814 let qpath_span = match qpath {
815 hir::QPath::Resolved(_, path) => path.span,
816 hir::QPath::TypeRelative(_, ps) => ps.ident.span,
818 (qpath_span.shrink_to_hi(), pat_span)
820 // Easy case. Just take the "lo" of the first sub-pattern and the "hi" of the
821 // last sub-pattern. In the case of `A(x)` the first and last may coincide.
824 // help: missing parenthesis
826 // L | let A((x, y)) = A((1, 2));
828 [first, ..] => (first.span.shrink_to_lo(), subpats.last().unwrap().span),
830 err.multipart_suggestion(
831 "missing parenthesis",
832 vec![(left, "(".to_string()), (right.shrink_to_hi(), ")".to_string())],
833 Applicability::MachineApplicable,
843 elements: &'tcx [&'tcx Pat<'tcx>],
844 ddpos: Option<usize>,
847 discrim_span: Option<Span>,
850 let mut expected_len = elements.len();
852 // Require known type only when `..` is present.
853 if let ty::Tuple(ref tys) = self.structurally_resolved_type(span, expected).kind {
854 expected_len = tys.len();
857 let max_len = cmp::max(expected_len, elements.len());
859 let element_tys_iter = (0..max_len).map(|_| {
860 GenericArg::from(self.next_ty_var(
861 // FIXME: `MiscVariable` for now -- obtaining the span and name information
862 // from all tuple elements isn't trivial.
863 TypeVariableOrigin { kind: TypeVariableOriginKind::TypeInference, span },
866 let element_tys = tcx.mk_substs(element_tys_iter);
867 let pat_ty = tcx.mk_ty(ty::Tuple(element_tys));
868 if let Some(mut err) = self.demand_eqtype_diag(span, expected, pat_ty) {
870 // Walk subpatterns with an expected type of `err` in this case to silence
871 // further errors being emitted when using the bindings. #50333
872 let element_tys_iter = (0..max_len).map(|_| tcx.types.err);
873 for (_, elem) in elements.iter().enumerate_and_adjust(max_len, ddpos) {
874 self.check_pat(elem, &tcx.types.err, def_bm, discrim_span);
876 tcx.mk_tup(element_tys_iter)
878 for (i, elem) in elements.iter().enumerate_and_adjust(max_len, ddpos) {
879 self.check_pat(elem, &element_tys[i].expect_ty(), def_bm, discrim_span);
885 fn check_struct_pat_fields(
890 variant: &'tcx ty::VariantDef,
891 fields: &'tcx [hir::FieldPat<'tcx>],
894 discrim_span: Option<Span>,
898 let (substs, adt) = match adt_ty.kind {
899 ty::Adt(adt, substs) => (substs, adt),
900 _ => span_bug!(span, "struct pattern is not an ADT"),
902 let kind_name = adt.variant_descr();
904 // Index the struct fields' types.
905 let field_map = variant
909 .map(|(i, field)| (field.ident.modern(), (i, field)))
910 .collect::<FxHashMap<_, _>>();
912 // Keep track of which fields have already appeared in the pattern.
913 let mut used_fields = FxHashMap::default();
914 let mut no_field_errors = true;
916 let mut inexistent_fields = vec![];
917 // Typecheck each field.
918 for field in fields {
919 let span = field.span;
920 let ident = tcx.adjust_ident(field.ident, variant.def_id);
921 let field_ty = match used_fields.entry(ident) {
922 Occupied(occupied) => {
923 self.error_field_already_bound(span, field.ident, *occupied.get());
924 no_field_errors = false;
932 self.write_field_index(field.hir_id, *i);
933 self.tcx.check_stability(f.did, Some(pat_id), span);
934 self.field_ty(span, f, substs)
937 inexistent_fields.push(field.ident);
938 no_field_errors = false;
944 self.check_pat(&field.pat, field_ty, def_bm, discrim_span);
947 let mut unmentioned_fields = variant
950 .map(|field| field.ident.modern())
951 .filter(|ident| !used_fields.contains_key(&ident))
952 .collect::<Vec<_>>();
954 if inexistent_fields.len() > 0 && !variant.recovered {
955 self.error_inexistent_fields(
958 &mut unmentioned_fields,
963 // Require `..` if struct has non_exhaustive attribute.
964 if variant.is_field_list_non_exhaustive() && !adt.did.is_local() && !etc {
969 "`..` required with {} marked as non-exhaustive",
974 // Report an error if incorrect number of the fields were specified.
975 if kind_name == "union" {
976 if fields.len() != 1 {
977 tcx.sess.span_err(span, "union patterns should have exactly one field");
980 tcx.sess.span_err(span, "`..` cannot be used in union patterns");
982 } else if !etc && unmentioned_fields.len() > 0 {
983 self.error_unmentioned_fields(span, &unmentioned_fields, variant);
988 fn error_field_already_bound(&self, span: Span, ident: ast::Ident, other_field: Span) {
993 "field `{}` bound multiple times in the pattern",
996 .span_label(span, format!("multiple uses of `{}` in pattern", ident))
997 .span_label(other_field, format!("first use of `{}`", ident))
1001 fn error_inexistent_fields(
1004 inexistent_fields: &[ast::Ident],
1005 unmentioned_fields: &mut Vec<ast::Ident>,
1006 variant: &ty::VariantDef,
1009 let (field_names, t, plural) = if inexistent_fields.len() == 1 {
1010 (format!("a field named `{}`", inexistent_fields[0]), "this", "")
1017 .map(|ident| format!("`{}`", ident))
1018 .collect::<Vec<String>>()
1025 let spans = inexistent_fields.iter().map(|ident| ident.span).collect::<Vec<_>>();
1026 let mut err = struct_span_err!(
1030 "{} `{}` does not have {}",
1032 tcx.def_path_str(variant.def_id),
1035 if let Some(ident) = inexistent_fields.last() {
1039 "{} `{}` does not have {} field{}",
1041 tcx.def_path_str(variant.def_id),
1047 let input = unmentioned_fields.iter().map(|field| &field.name);
1048 let suggested_name = find_best_match_for_name(input, &ident.as_str(), None);
1049 if let Some(suggested_name) = suggested_name {
1050 err.span_suggestion(
1052 "a field with a similar name exists",
1053 suggested_name.to_string(),
1054 Applicability::MaybeIncorrect,
1057 // we don't want to throw `E0027` in case we have thrown `E0026` for them
1058 unmentioned_fields.retain(|&x| x.name != suggested_name);
1062 if tcx.sess.teach(&err.get_code().unwrap()) {
1064 "This error indicates that a struct pattern attempted to \
1065 extract a non-existent field from a struct. Struct fields \
1066 are identified by the name used before the colon : so struct \
1067 patterns should resemble the declaration of the struct type \
1069 If you are using shorthand field patterns but want to refer \
1070 to the struct field by a different name, you should rename \
1077 fn error_unmentioned_fields(
1080 unmentioned_fields: &[ast::Ident],
1081 variant: &ty::VariantDef,
1083 let field_names = if unmentioned_fields.len() == 1 {
1084 format!("field `{}`", unmentioned_fields[0])
1086 let fields = unmentioned_fields
1088 .map(|name| format!("`{}`", name))
1089 .collect::<Vec<String>>()
1091 format!("fields {}", fields)
1093 let mut diag = struct_span_err!(
1097 "pattern does not mention {}",
1100 diag.span_label(span, format!("missing {}", field_names));
1101 if variant.ctor_kind == CtorKind::Fn {
1102 diag.note("trying to match a tuple variant with a struct variant pattern");
1104 if self.tcx.sess.teach(&diag.get_code().unwrap()) {
1106 "This error indicates that a pattern for a struct fails to specify a \
1107 sub-pattern for every one of the struct's fields. Ensure that each field \
1108 from the struct's definition is mentioned in the pattern, or use `..` to \
1109 ignore unwanted fields.",
1118 inner: &'tcx Pat<'tcx>,
1120 def_bm: BindingMode,
1121 discrim_span: Option<Span>,
1124 let (box_ty, inner_ty) = if self.check_dereferenceable(span, expected, &inner) {
1125 // Here, `demand::subtype` is good enough, but I don't
1126 // think any errors can be introduced by using `demand::eqtype`.
1127 let inner_ty = self.next_ty_var(TypeVariableOrigin {
1128 kind: TypeVariableOriginKind::TypeInference,
1131 let box_ty = tcx.mk_box(inner_ty);
1132 self.demand_eqtype_pat(span, expected, box_ty, discrim_span);
1135 (tcx.types.err, tcx.types.err)
1137 self.check_pat(&inner, inner_ty, def_bm, discrim_span);
1144 inner: &'tcx Pat<'tcx>,
1145 mutbl: hir::Mutability,
1147 def_bm: BindingMode,
1148 discrim_span: Option<Span>,
1151 let expected = self.shallow_resolve(expected);
1152 let (rptr_ty, inner_ty) = if self.check_dereferenceable(pat.span, expected, &inner) {
1153 // `demand::subtype` would be good enough, but using `eqtype` turns
1154 // out to be equally general. See (note_1) for details.
1156 // Take region, inner-type from expected type if we can,
1157 // to avoid creating needless variables. This also helps with
1158 // the bad interactions of the given hack detailed in (note_1).
1159 debug!("check_pat_ref: expected={:?}", expected);
1160 match expected.kind {
1161 ty::Ref(_, r_ty, r_mutbl) if r_mutbl == mutbl => (expected, r_ty),
1163 let inner_ty = self.next_ty_var(TypeVariableOrigin {
1164 kind: TypeVariableOriginKind::TypeInference,
1167 let rptr_ty = self.new_ref_ty(pat.span, mutbl, inner_ty);
1168 debug!("check_pat_ref: demanding {:?} = {:?}", expected, rptr_ty);
1169 let err = self.demand_eqtype_diag(pat.span, expected, rptr_ty);
1171 // Look for a case like `fn foo(&foo: u32)` and suggest
1172 // `fn foo(foo: &u32)`
1173 if let Some(mut err) = err {
1174 self.borrow_pat_suggestion(&mut err, &pat, &inner, &expected);
1181 (tcx.types.err, tcx.types.err)
1183 self.check_pat(&inner, inner_ty, def_bm, discrim_span);
1187 /// Create a reference type with a fresh region variable.
1188 fn new_ref_ty(&self, span: Span, mutbl: hir::Mutability, ty: Ty<'tcx>) -> Ty<'tcx> {
1189 let region = self.next_region_var(infer::PatternRegion(span));
1190 let mt = ty::TypeAndMut { ty, mutbl };
1191 self.tcx.mk_ref(region, mt)
1194 /// Type check a slice pattern.
1196 /// Syntactically, these look like `[pat_0, ..., pat_n]`.
1197 /// Semantically, we are type checking a pattern with structure:
1199 /// [before_0, ..., before_n, (slice, after_0, ... after_n)?]
1201 /// The type of `slice`, if it is present, depends on the `expected` type.
1202 /// If `slice` is missing, then so is `after_i`.
1203 /// If `slice` is present, it can still represent 0 elements.
1207 before: &'tcx [&'tcx Pat<'tcx>],
1208 slice: Option<&'tcx Pat<'tcx>>,
1209 after: &'tcx [&'tcx Pat<'tcx>],
1211 def_bm: BindingMode,
1212 discrim_span: Option<Span>,
1214 let err = self.tcx.types.err;
1215 let expected = self.structurally_resolved_type(span, expected);
1216 let (inner_ty, slice_ty, expected) = match expected.kind {
1217 // An array, so we might have something like `let [a, b, c] = [0, 1, 2];`.
1218 ty::Array(inner_ty, len) => {
1219 let min = before.len() as u64 + after.len() as u64;
1221 .check_array_pat_len(span, slice, len, min)
1222 .map_or(err, |len| self.tcx.mk_array(inner_ty, len));
1223 (inner_ty, slice_ty, expected)
1225 ty::Slice(inner_ty) => (inner_ty, expected, expected),
1226 // The expected type must be an array or slice, but was neither, so error.
1228 if !expected.references_error() {
1229 self.error_expected_array_or_slice(span, expected);
1235 // Type check all the patterns before `slice`.
1237 self.check_pat(&elt, inner_ty, def_bm, discrim_span);
1239 // Type check the `slice`, if present, against its expected type.
1240 if let Some(slice) = slice {
1241 self.check_pat(&slice, slice_ty, def_bm, discrim_span);
1243 // Type check the elements after `slice`, if present.
1245 self.check_pat(&elt, inner_ty, def_bm, discrim_span);
1250 /// Type check the length of an array pattern.
1252 /// Return the length of the variable length pattern,
1253 /// if it exists and there are no errors.
1254 fn check_array_pat_len(
1257 slice: Option<&'tcx Pat<'tcx>>,
1258 len: &ty::Const<'tcx>,
1261 if let Some(len) = len.try_eval_usize(self.tcx, self.param_env) {
1262 // Now we know the length...
1263 if slice.is_none() {
1264 // ...and since there is no variable-length pattern,
1265 // we require an exact match between the number of elements
1266 // in the array pattern and as provided by the matched type.
1268 self.error_scrutinee_inconsistent_length(span, min_len, len);
1270 } else if let r @ Some(_) = len.checked_sub(min_len) {
1271 // The variable-length pattern was there,
1272 // so it has an array type with the remaining elements left as its size...
1275 // ...however, in this case, there were no remaining elements.
1276 // That is, the slice pattern requires more than the array type offers.
1277 self.error_scrutinee_with_rest_inconsistent_length(span, min_len, len);
1280 // No idea what the length is, which happens if we have e.g.,
1281 // `let [a, b] = arr` where `arr: [T; N]` where `const N: usize`.
1282 self.error_scrutinee_unfixed_length(span);
1287 fn error_scrutinee_inconsistent_length(&self, span: Span, min_len: u64, size: u64) {
1292 "pattern requires {} element{} but array has {}",
1294 pluralize!(min_len),
1297 .span_label(span, format!("expected {} element{}", size, pluralize!(size)))
1301 fn error_scrutinee_with_rest_inconsistent_length(&self, span: Span, min_len: u64, size: u64) {
1306 "pattern requires at least {} element{} but array has {}",
1308 pluralize!(min_len),
1313 format!("pattern cannot match array of {} element{}", size, pluralize!(size),),
1318 fn error_scrutinee_unfixed_length(&self, span: Span) {
1323 "cannot pattern-match on an array without a fixed length",
1328 fn error_expected_array_or_slice(&self, span: Span, expected_ty: Ty<'tcx>) {
1329 let mut err = struct_span_err!(
1333 "expected an array or slice, found `{}`",
1336 if let ty::Ref(_, ty, _) = expected_ty.kind {
1337 if let ty::Array(..) | ty::Slice(..) = ty.kind {
1338 err.help("the semantics of slice patterns changed recently; see issue #62254");
1341 err.span_label(span, format!("pattern cannot match with input type `{}`", expected_ty));