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::ty::subst::GenericArg;
10 use rustc::ty::{self, BindingMode, Ty, TypeFoldable};
12 use syntax::util::lev_distance::find_best_match_for_name;
13 use syntax_pos::hygiene::DesugaringKind;
16 use rustc_error_codes::*;
19 use std::collections::hash_map::Entry::{Occupied, Vacant};
21 use super::report_unexpected_variant_res;
23 const CANNOT_IMPLICITLY_DEREF_POINTER_TRAIT_OBJ: &str = "\
24 This error indicates that a pointer to a trait type cannot be implicitly dereferenced by a \
25 pattern. Every trait defines a type, but because the size of trait implementors isn't fixed, \
26 this type has no compile-time size. Therefore, all accesses to trait types must be through \
27 pointers. If you encounter this error you should try to avoid dereferencing the pointer.
29 You can read more about trait objects in the Trait Objects section of the Reference: \
30 https://doc.rust-lang.org/reference/types.html#trait-objects";
32 impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
37 discrim_span: Option<Span>,
39 let def_bm = BindingMode::BindByValue(hir::Mutability::Not);
40 self.check_pat(pat, expected, def_bm, discrim_span);
43 /// `discrim_span` argument having a `Span` indicates that this pattern is part of a match
44 /// expression arm guard, and it points to the match discriminant to add context in type errors.
45 /// In the following example, `discrim_span` corresponds to the `a + b` expression:
48 /// error[E0308]: mismatched types
49 /// --> src/main.rs:5:9
51 /// 4 | let temp: usize = match a + b {
52 /// | ----- this expression has type `usize`
53 /// 5 | Ok(num) => num,
54 /// | ^^^^^^^ expected `usize`, found enum `std::result::Result`
56 /// = note: expected type `usize`
57 /// found type `std::result::Result<_, _>`
64 discrim_span: Option<Span>,
66 debug!("check_pat(pat={:?},expected={:?},def_bm={:?})", pat, expected, def_bm);
68 let path_resolution = match &pat.kind {
69 PatKind::Path(qpath) => Some(self.resolve_ty_and_res_ufcs(qpath, pat.hir_id, pat.span)),
72 let is_nrp = self.is_non_ref_pat(pat, path_resolution.map(|(res, ..)| res));
73 let (expected, def_bm) = self.calc_default_binding_mode(pat, expected, def_bm, is_nrp);
75 let ty = match pat.kind {
76 PatKind::Wild => expected,
77 PatKind::Lit(lt) => self.check_pat_lit(pat.span, lt, expected, discrim_span),
78 PatKind::Range(begin, end, _) => {
79 match self.check_pat_range(pat.span, begin, end, expected, discrim_span) {
84 PatKind::Binding(ba, var_id, _, sub) => {
85 self.check_pat_ident(pat, ba, var_id, sub, expected, def_bm, discrim_span)
87 PatKind::TupleStruct(ref qpath, subpats, ddpos) => self.check_pat_tuple_struct(
96 PatKind::Path(ref qpath) => {
97 self.check_pat_path(pat, path_resolution.unwrap(), qpath, expected)
99 PatKind::Struct(ref qpath, fields, etc) => {
100 self.check_pat_struct(pat, qpath, fields, etc, expected, def_bm, discrim_span)
102 PatKind::Or(pats) => {
104 self.check_pat(pat, expected, def_bm, discrim_span);
108 PatKind::Tuple(elements, ddpos) => {
109 self.check_pat_tuple(pat.span, elements, ddpos, expected, def_bm, discrim_span)
111 PatKind::Box(inner) => {
112 self.check_pat_box(pat.span, inner, expected, def_bm, discrim_span)
114 PatKind::Ref(inner, mutbl) => {
115 self.check_pat_ref(pat, inner, mutbl, expected, def_bm, discrim_span)
117 PatKind::Slice(before, slice, after) => {
118 self.check_pat_slice(pat.span, before, slice, after, expected, def_bm, discrim_span)
122 self.write_ty(pat.hir_id, ty);
124 // (note_1): In most of the cases where (note_1) is referenced
125 // (literals and constants being the exception), we relate types
126 // using strict equality, even though subtyping would be sufficient.
127 // There are a few reasons for this, some of which are fairly subtle
128 // and which cost me (nmatsakis) an hour or two debugging to remember,
129 // so I thought I'd write them down this time.
131 // 1. There is no loss of expressiveness here, though it does
132 // cause some inconvenience. What we are saying is that the type
133 // of `x` becomes *exactly* what is expected. This can cause unnecessary
134 // errors in some cases, such as this one:
137 // fn foo<'x>(x: &'x int) {
144 // The reason we might get an error is that `z` might be
145 // assigned a type like `&'x int`, and then we would have
146 // a problem when we try to assign `&a` to `z`, because
147 // the lifetime of `&a` (i.e., the enclosing block) is
148 // shorter than `'x`.
150 // HOWEVER, this code works fine. The reason is that the
151 // expected type here is whatever type the user wrote, not
152 // the initializer's type. In this case the user wrote
153 // nothing, so we are going to create a type variable `Z`.
154 // Then we will assign the type of the initializer (`&'x
155 // int`) as a subtype of `Z`: `&'x int <: Z`. And hence we
156 // will instantiate `Z` as a type `&'0 int` where `'0` is
157 // a fresh region variable, with the constraint that `'x :
158 // '0`. So basically we're all set.
160 // Note that there are two tests to check that this remains true
161 // (`regions-reassign-{match,let}-bound-pointer.rs`).
163 // 2. Things go horribly wrong if we use subtype. The reason for
164 // THIS is a fairly subtle case involving bound regions. See the
165 // `givens` field in `region_constraints`, as well as the test
166 // `regions-relate-bound-regions-on-closures-to-inference-variables.rs`,
167 // for details. Short version is that we must sometimes detect
168 // relationships between specific region variables and regions
169 // bound in a closure signature, and that detection gets thrown
170 // off when we substitute fresh region variables here to enable
174 /// Compute the new expected type and default binding mode from the old ones
175 /// as well as the pattern form we are currently checking.
176 fn calc_default_binding_mode(
178 pat: &'tcx Pat<'tcx>,
181 is_non_ref_pat: bool,
182 ) -> (Ty<'tcx>, BindingMode) {
184 debug!("pattern is non reference pattern");
185 self.peel_off_references(pat, expected, def_bm)
187 // When you encounter a `&pat` pattern, reset to "by
188 // value". This is so that `x` and `y` here are by value,
189 // as they appear to be:
192 // match &(&22, &44) {
198 let def_bm = match pat.kind {
199 PatKind::Ref(..) => ty::BindByValue(hir::Mutability::Not),
206 /// Is the pattern a "non reference pattern"?
207 /// When the pattern is a path pattern, `opt_path_res` must be `Some(res)`.
208 fn is_non_ref_pat(&self, pat: &'tcx Pat<'tcx>, opt_path_res: Option<Res>) -> bool {
211 | PatKind::TupleStruct(..)
215 | PatKind::Slice(..) => true,
216 PatKind::Lit(ref lt) => {
217 let ty = self.check_expr(lt);
219 ty::Ref(..) => false,
223 PatKind::Path(_) => match opt_path_res.unwrap() {
224 Res::Def(DefKind::Const, _) | Res::Def(DefKind::AssocConst, _) => false,
227 // FIXME(or_patterns; Centril | dlrobertson): To keep things compiling
228 // for or-patterns at the top level, we need to make `p_0 | ... | p_n`
229 // a "non reference pattern". For example the following currently compiles:
232 // e @ &(1...2) | e @ &(3...4) => {}
237 // We should consider whether we should do something special in nested or-patterns.
238 PatKind::Or(_) | PatKind::Wild | PatKind::Binding(..) | PatKind::Ref(..) => false,
242 /// Peel off as many immediately nested `& mut?` from the expected type as possible
243 /// and return the new expected type and binding default binding mode.
244 /// The adjustments vector, if non-empty is stored in a table.
245 fn peel_off_references(
247 pat: &'tcx Pat<'tcx>,
249 mut def_bm: BindingMode,
250 ) -> (Ty<'tcx>, BindingMode) {
251 let mut expected = self.resolve_vars_with_obligations(&expected);
253 // Peel off as many `&` or `&mut` from the scrutinee type as possible. For example,
254 // for `match &&&mut Some(5)` the loop runs three times, aborting when it reaches
255 // the `Some(5)` which is not of type Ref.
257 // For each ampersand peeled off, update the binding mode and push the original
258 // type into the adjustments vector.
260 // See the examples in `ui/match-defbm*.rs`.
261 let mut pat_adjustments = vec![];
262 while let ty::Ref(_, inner_ty, inner_mutability) = expected.kind {
263 debug!("inspecting {:?}", expected);
265 debug!("current discriminant is Ref, inserting implicit deref");
266 // Preserve the reference type. We'll need it later during HAIR lowering.
267 pat_adjustments.push(expected);
270 def_bm = ty::BindByReference(match def_bm {
271 // If default binding mode is by value, make it `ref` or `ref mut`
272 // (depending on whether we observe `&` or `&mut`).
274 // When `ref mut`, stay a `ref mut` (on `&mut`) or downgrade to `ref` (on `&`).
275 ty::BindByReference(hir::Mutability::Mut) => inner_mutability,
276 // Once a `ref`, always a `ref`.
277 // This is because a `& &mut` cannot mutate the underlying value.
278 ty::BindByReference(m @ hir::Mutability::Not) => m,
282 if pat_adjustments.len() > 0 {
283 debug!("default binding mode is now {:?}", def_bm);
284 self.inh.tables.borrow_mut().pat_adjustments_mut().insert(pat.hir_id, pat_adjustments);
293 lt: &hir::Expr<'tcx>,
295 discrim_span: Option<Span>,
297 // We've already computed the type above (when checking for a non-ref pat),
298 // so avoid computing it again.
299 let ty = self.node_ty(lt.hir_id);
301 // Byte string patterns behave the same way as array patterns
302 // They can denote both statically and dynamically-sized byte arrays.
304 if let hir::ExprKind::Lit(ref lt) = lt.kind {
305 if let ast::LitKind::ByteStr(_) = lt.node {
306 let expected_ty = self.structurally_resolved_type(span, expected);
307 if let ty::Ref(_, r_ty, _) = expected_ty.kind {
308 if let ty::Slice(_) = r_ty.kind {
311 tcx.mk_imm_ref(tcx.lifetimes.re_static, tcx.mk_slice(tcx.types.u8));
317 // Somewhat surprising: in this case, the subtyping relation goes the
318 // opposite way as the other cases. Actually what we really want is not
319 // a subtyping relation at all but rather that there exists a LUB
320 // (so that they can be compared). However, in practice, constants are
321 // always scalars or strings. For scalars subtyping is irrelevant,
322 // and for strings `ty` is type is `&'static str`, so if we say that
324 // &'static str <: expected
326 // then that's equivalent to there existing a LUB.
327 if let Some(mut err) = self.demand_suptype_diag(span, expected, pat_ty) {
331 // In the case of `if`- and `while`-expressions we've already checked
332 // that `scrutinee: bool`. We know that the pattern is `true`,
333 // so an error here would be a duplicate and from the wrong POV.
334 s.is_desugaring(DesugaringKind::CondTemporary)
346 lhs: &'tcx hir::Expr<'tcx>,
347 rhs: &'tcx hir::Expr<'tcx>,
349 discrim_span: Option<Span>,
350 ) -> Option<Ty<'tcx>> {
351 let lhs_ty = self.check_expr(lhs);
352 let rhs_ty = self.check_expr(rhs);
354 // Check that both end-points are of numeric or char type.
355 let numeric_or_char = |ty: Ty<'_>| ty.is_numeric() || ty.is_char() || ty.references_error();
356 let lhs_fail = !numeric_or_char(lhs_ty);
357 let rhs_fail = !numeric_or_char(rhs_ty);
359 if lhs_fail || rhs_fail {
360 self.emit_err_pat_range(span, lhs.span, rhs.span, lhs_fail, rhs_fail, lhs_ty, rhs_ty);
364 // Now that we know the types can be unified we find the unified type and use
365 // it to type the entire expression.
366 let common_type = self.resolve_vars_if_possible(&lhs_ty);
368 // Subtyping doesn't matter here, as the value is some kind of scalar.
369 let demand_eqtype = |x_span, y_span, x_ty, y_ty| {
370 self.demand_eqtype_pat_diag(x_span, expected, x_ty, discrim_span).map(|mut err| {
371 self.endpoint_has_type(&mut err, y_span, y_ty);
375 demand_eqtype(lhs.span, rhs.span, lhs_ty, rhs_ty);
376 demand_eqtype(rhs.span, lhs.span, rhs_ty, lhs_ty);
381 fn endpoint_has_type(&self, err: &mut DiagnosticBuilder<'_>, span: Span, ty: Ty<'_>) {
382 if !ty.references_error() {
383 err.span_label(span, &format!("this is of type `{}`", ty));
387 fn emit_err_pat_range(
397 let span = if lhs_fail && rhs_fail {
405 let mut err = struct_span_err!(
409 "only char and numeric types are allowed in range patterns"
411 let msg = |ty| format!("this is of type `{}` but it should be `char` or numeric", ty);
412 let mut one_side_err = |first_span, first_ty, second_span, second_ty: Ty<'_>| {
413 err.span_label(first_span, &msg(first_ty));
414 self.endpoint_has_type(&mut err, second_span, second_ty);
416 if lhs_fail && rhs_fail {
417 err.span_label(begin_span, &msg(lhs_ty));
418 err.span_label(end_span, &msg(rhs_ty));
420 one_side_err(begin_span, lhs_ty, end_span, rhs_ty);
422 one_side_err(end_span, rhs_ty, begin_span, lhs_ty);
424 if self.tcx.sess.teach(&err.get_code().unwrap()) {
426 "In a match expression, only numbers and characters can be matched \
427 against a range. This is because the compiler checks that the range \
428 is non-empty at compile-time, and is unable to evaluate arbitrary \
429 comparison functions. If you want to capture values of an orderable \
430 type between two end-points, you can use a guard.",
439 ba: hir::BindingAnnotation,
441 sub: Option<&'tcx Pat<'tcx>>,
444 discrim_span: Option<Span>,
446 // Determine the binding mode...
448 hir::BindingAnnotation::Unannotated => def_bm,
449 _ => BindingMode::convert(ba),
451 // ...and store it in a side table:
452 self.inh.tables.borrow_mut().pat_binding_modes_mut().insert(pat.hir_id, bm);
454 debug!("check_pat_ident: pat.hir_id={:?} bm={:?}", pat.hir_id, bm);
456 let local_ty = self.local_ty(pat.span, pat.hir_id).decl_ty;
457 let eq_ty = match bm {
458 ty::BindByReference(mutbl) => {
459 // If the binding is like `ref x | ref const x | ref mut x`
460 // then `x` is assigned a value of type `&M T` where M is the
461 // mutability and T is the expected type.
463 // `x` is assigned a value of type `&M T`, hence `&M T <: typeof(x)`
464 // is required. However, we use equality, which is stronger.
465 // See (note_1) for an explanation.
466 self.new_ref_ty(pat.span, mutbl, expected)
468 // Otherwise, the type of x is the expected type `T`.
469 ty::BindByValue(_) => {
470 // As above, `T <: typeof(x)` is required, but we use equality, see (note_1).
474 self.demand_eqtype_pat(pat.span, eq_ty, local_ty, discrim_span);
476 // If there are multiple arms, make sure they all agree on
477 // what the type of the binding `x` ought to be.
478 if var_id != pat.hir_id {
479 let vt = self.local_ty(pat.span, var_id).decl_ty;
480 self.demand_eqtype_pat(pat.span, vt, local_ty, discrim_span);
483 if let Some(p) = sub {
484 self.check_pat(&p, expected, def_bm, discrim_span);
490 fn borrow_pat_suggestion(
492 err: &mut DiagnosticBuilder<'_>,
498 if let PatKind::Binding(..) = inner.kind {
499 let binding_parent_id = tcx.hir().get_parent_node(pat.hir_id);
500 let binding_parent = tcx.hir().get(binding_parent_id);
501 debug!("inner {:?} pat {:?} parent {:?}", inner, pat, binding_parent);
502 match binding_parent {
503 hir::Node::Param(hir::Param { span, .. }) => {
504 if let Ok(snippet) = tcx.sess.source_map().span_to_snippet(inner.span) {
507 &format!("did you mean `{}`", snippet),
508 format!(" &{}", expected),
509 Applicability::MachineApplicable,
513 hir::Node::Arm(_) | hir::Node::Pat(_) => {
514 // rely on match ergonomics or it might be nested `&&pat`
515 if let Ok(snippet) = tcx.sess.source_map().span_to_snippet(inner.span) {
518 "you can probably remove the explicit borrow",
520 Applicability::MaybeIncorrect,
524 _ => {} // don't provide suggestions in other cases #55175
529 pub fn check_dereferenceable(&self, span: Span, expected: Ty<'tcx>, inner: &Pat<'_>) -> bool {
530 if let PatKind::Binding(..) = inner.kind {
531 if let Some(mt) = self.shallow_resolve(expected).builtin_deref(true) {
532 if let ty::Dynamic(..) = mt.ty.kind {
533 // This is "x = SomeTrait" being reduced from
534 // "let &x = &SomeTrait" or "let box x = Box<SomeTrait>", an error.
535 let type_str = self.ty_to_string(expected);
536 let mut err = struct_span_err!(
540 "type `{}` cannot be dereferenced",
543 err.span_label(span, format!("type `{}` cannot be dereferenced", type_str));
544 if self.tcx.sess.teach(&err.get_code().unwrap()) {
545 err.note(CANNOT_IMPLICITLY_DEREF_POINTER_TRAIT_OBJ);
557 pat: &'tcx Pat<'tcx>,
558 qpath: &hir::QPath<'_>,
559 fields: &'tcx [hir::FieldPat<'tcx>],
563 discrim_span: Option<Span>,
565 // Resolve the path and check the definition for errors.
566 let (variant, pat_ty) = if let Some(variant_ty) = self.check_struct_path(qpath, pat.hir_id)
570 for field in fields {
571 self.check_pat(&field.pat, self.tcx.types.err, def_bm, discrim_span);
573 return self.tcx.types.err;
576 // Type-check the path.
577 self.demand_eqtype_pat(pat.span, expected, pat_ty, discrim_span);
579 // Type-check subpatterns.
580 if self.check_struct_pat_fields(pat_ty, pat.hir_id, pat.span, variant, fields, etc, def_bm)
591 path_resolution: (Res, Option<Ty<'tcx>>, &'b [hir::PathSegment<'b>]),
592 qpath: &hir::QPath<'_>,
597 // We have already resolved the path.
598 let (res, opt_ty, segments) = path_resolution;
601 self.set_tainted_by_errors();
602 return tcx.types.err;
604 Res::Def(DefKind::Method, _)
605 | Res::Def(DefKind::Ctor(_, CtorKind::Fictive), _)
606 | Res::Def(DefKind::Ctor(_, CtorKind::Fn), _) => {
607 report_unexpected_variant_res(tcx, res, pat.span, qpath);
608 return tcx.types.err;
610 Res::Def(DefKind::Ctor(_, CtorKind::Const), _)
612 | Res::Def(DefKind::Const, _)
613 | Res::Def(DefKind::AssocConst, _) => {} // OK
614 _ => bug!("unexpected pattern resolution: {:?}", res),
617 // Type-check the path.
618 let pat_ty = self.instantiate_value_path(segments, opt_ty, res, pat.span, pat.hir_id).0;
619 self.demand_suptype(pat.span, expected, pat_ty);
623 fn check_pat_tuple_struct(
626 qpath: &hir::QPath<'_>,
627 subpats: &'tcx [&'tcx Pat<'tcx>],
628 ddpos: Option<usize>,
631 match_arm_pat_span: Option<Span>,
636 self.check_pat(&pat, tcx.types.err, def_bm, match_arm_pat_span);
639 let report_unexpected_res = |res: Res| {
641 "expected tuple struct or tuple variant, found {} `{}`",
643 hir::print::to_string(tcx.hir(), |s| s.print_qpath(qpath, false)),
645 let mut err = struct_span_err!(tcx.sess, pat.span, E0164, "{}", msg);
646 match (res, &pat.kind) {
647 (Res::Def(DefKind::Fn, _), _) | (Res::Def(DefKind::Method, _), _) => {
648 err.span_label(pat.span, "`fn` calls are not allowed in patterns");
650 "for more information, visit \
651 https://doc.rust-lang.org/book/ch18-00-patterns.html",
655 err.span_label(pat.span, "not a tuple variant or struct");
662 // Resolve the path and check the definition for errors.
663 let (res, opt_ty, segments) = self.resolve_ty_and_res_ufcs(qpath, pat.hir_id, pat.span);
665 self.set_tainted_by_errors();
667 return self.tcx.types.err;
670 // Type-check the path.
672 self.instantiate_value_path(segments, opt_ty, res, pat.span, pat.hir_id);
674 report_unexpected_res(res);
675 return tcx.types.err;
678 let variant = match res {
680 self.set_tainted_by_errors();
682 return tcx.types.err;
684 Res::Def(DefKind::AssocConst, _) | Res::Def(DefKind::Method, _) => {
685 report_unexpected_res(res);
686 return tcx.types.err;
688 Res::Def(DefKind::Ctor(_, CtorKind::Fn), _) => tcx.expect_variant_res(res),
689 _ => bug!("unexpected pattern resolution: {:?}", res),
692 // Replace constructor type with constructed type for tuple struct patterns.
693 let pat_ty = pat_ty.fn_sig(tcx).output();
694 let pat_ty = pat_ty.no_bound_vars().expect("expected fn type");
696 // Type-check the tuple struct pattern against the expected type.
697 let diag = self.demand_eqtype_pat_diag(pat.span, expected, pat_ty, match_arm_pat_span);
698 let had_err = diag.is_some();
699 diag.map(|mut err| err.emit());
701 // Type-check subpatterns.
702 if subpats.len() == variant.fields.len()
703 || subpats.len() < variant.fields.len() && ddpos.is_some()
705 let substs = match pat_ty.kind {
706 ty::Adt(_, substs) => substs,
707 _ => bug!("unexpected pattern type {:?}", pat_ty),
709 for (i, subpat) in subpats.iter().enumerate_and_adjust(variant.fields.len(), ddpos) {
710 let field_ty = self.field_ty(subpat.span, &variant.fields[i], substs);
711 self.check_pat(&subpat, field_ty, def_bm, match_arm_pat_span);
713 self.tcx.check_stability(variant.fields[i].did, Some(pat.hir_id), subpat.span);
716 // Pattern has wrong number of fields.
717 self.e0023(pat.span, res, qpath, subpats, &variant.fields, expected, had_err);
719 return tcx.types.err;
728 qpath: &hir::QPath<'_>,
729 subpats: &'tcx [&'tcx Pat<'tcx>],
730 fields: &'tcx [ty::FieldDef],
734 let subpats_ending = pluralize!(subpats.len());
735 let fields_ending = pluralize!(fields.len());
736 let res_span = self.tcx.def_span(res.def_id());
737 let mut err = struct_span_err!(
741 "this pattern has {} field{}, but the corresponding {} has {} field{}",
750 format!("expected {} field{}, found {}", fields.len(), fields_ending, subpats.len(),),
752 .span_label(res_span, format!("{} defined here", res.descr()));
754 // Identify the case `Some(x, y)` where the expected type is e.g. `Option<(T, U)>`.
755 // More generally, the expected type wants a tuple variant with one field of an
756 // N-arity-tuple, e.g., `V_i((p_0, .., p_N))`. Meanwhile, the user supplied a pattern
757 // with the subpatterns directly in the tuple variant pattern, e.g., `V_i(p_0, .., p_N)`.
758 let missing_parenthesis = match (&expected.kind, fields, had_err) {
759 // #67037: only do this if we could sucessfully type-check the expected type against
760 // the tuple struct pattern. Otherwise the substs could get out of range on e.g.,
761 // `let P() = U;` where `P != U` with `struct P<T>(T);`.
762 (ty::Adt(_, substs), [field], false) => {
763 let field_ty = self.field_ty(pat_span, field, substs);
764 match field_ty.kind {
765 ty::Tuple(_) => field_ty.tuple_fields().count() == subpats.len(),
771 if missing_parenthesis {
772 let (left, right) = match subpats {
773 // This is the zero case; we aim to get the "hi" part of the `QPath`'s
774 // span as the "lo" and then the "hi" part of the pattern's span as the "hi".
777 // help: missing parenthesis
779 // L | let A(()) = A(());
782 let qpath_span = match qpath {
783 hir::QPath::Resolved(_, path) => path.span,
784 hir::QPath::TypeRelative(_, ps) => ps.ident.span,
786 (qpath_span.shrink_to_hi(), pat_span)
788 // Easy case. Just take the "lo" of the first sub-pattern and the "hi" of the
789 // last sub-pattern. In the case of `A(x)` the first and last may coincide.
792 // help: missing parenthesis
794 // L | let A((x, y)) = A((1, 2));
796 [first, ..] => (first.span.shrink_to_lo(), subpats.last().unwrap().span),
798 err.multipart_suggestion(
799 "missing parenthesis",
800 vec![(left, "(".to_string()), (right.shrink_to_hi(), ")".to_string())],
801 Applicability::MachineApplicable,
811 elements: &'tcx [&'tcx Pat<'tcx>],
812 ddpos: Option<usize>,
815 discrim_span: Option<Span>,
818 let mut expected_len = elements.len();
820 // Require known type only when `..` is present.
821 if let ty::Tuple(ref tys) = self.structurally_resolved_type(span, expected).kind {
822 expected_len = tys.len();
825 let max_len = cmp::max(expected_len, elements.len());
827 let element_tys_iter = (0..max_len).map(|_| {
828 GenericArg::from(self.next_ty_var(
829 // FIXME: `MiscVariable` for now -- obtaining the span and name information
830 // from all tuple elements isn't trivial.
831 TypeVariableOrigin { kind: TypeVariableOriginKind::TypeInference, span },
834 let element_tys = tcx.mk_substs(element_tys_iter);
835 let pat_ty = tcx.mk_ty(ty::Tuple(element_tys));
836 if let Some(mut err) = self.demand_eqtype_diag(span, expected, pat_ty) {
838 // Walk subpatterns with an expected type of `err` in this case to silence
839 // further errors being emitted when using the bindings. #50333
840 let element_tys_iter = (0..max_len).map(|_| tcx.types.err);
841 for (_, elem) in elements.iter().enumerate_and_adjust(max_len, ddpos) {
842 self.check_pat(elem, &tcx.types.err, def_bm, discrim_span);
844 tcx.mk_tup(element_tys_iter)
846 for (i, elem) in elements.iter().enumerate_and_adjust(max_len, ddpos) {
847 self.check_pat(elem, &element_tys[i].expect_ty(), def_bm, discrim_span);
853 fn check_struct_pat_fields(
858 variant: &'tcx ty::VariantDef,
859 fields: &'tcx [hir::FieldPat<'tcx>],
865 let (substs, adt) = match adt_ty.kind {
866 ty::Adt(adt, substs) => (substs, adt),
867 _ => span_bug!(span, "struct pattern is not an ADT"),
869 let kind_name = adt.variant_descr();
871 // Index the struct fields' types.
872 let field_map = variant
876 .map(|(i, field)| (field.ident.modern(), (i, field)))
877 .collect::<FxHashMap<_, _>>();
879 // Keep track of which fields have already appeared in the pattern.
880 let mut used_fields = FxHashMap::default();
881 let mut no_field_errors = true;
883 let mut inexistent_fields = vec![];
884 // Typecheck each field.
885 for field in fields {
886 let span = field.span;
887 let ident = tcx.adjust_ident(field.ident, variant.def_id);
888 let field_ty = match used_fields.entry(ident) {
889 Occupied(occupied) => {
890 self.error_field_already_bound(span, field.ident, *occupied.get());
891 no_field_errors = false;
899 self.write_field_index(field.hir_id, *i);
900 self.tcx.check_stability(f.did, Some(pat_id), span);
901 self.field_ty(span, f, substs)
904 inexistent_fields.push(field.ident);
905 no_field_errors = false;
911 self.check_pat(&field.pat, field_ty, def_bm, None);
914 let mut unmentioned_fields = variant
917 .map(|field| field.ident.modern())
918 .filter(|ident| !used_fields.contains_key(&ident))
919 .collect::<Vec<_>>();
921 if inexistent_fields.len() > 0 && !variant.recovered {
922 self.error_inexistent_fields(
925 &mut unmentioned_fields,
930 // Require `..` if struct has non_exhaustive attribute.
931 if variant.is_field_list_non_exhaustive() && !adt.did.is_local() && !etc {
936 "`..` required with {} marked as non-exhaustive",
941 // Report an error if incorrect number of the fields were specified.
942 if kind_name == "union" {
943 if fields.len() != 1 {
944 tcx.sess.span_err(span, "union patterns should have exactly one field");
947 tcx.sess.span_err(span, "`..` cannot be used in union patterns");
949 } else if !etc && unmentioned_fields.len() > 0 {
950 self.error_unmentioned_fields(span, &unmentioned_fields, variant);
955 fn error_field_already_bound(&self, span: Span, ident: ast::Ident, other_field: Span) {
960 "field `{}` bound multiple times in the pattern",
963 .span_label(span, format!("multiple uses of `{}` in pattern", ident))
964 .span_label(other_field, format!("first use of `{}`", ident))
968 fn error_inexistent_fields(
971 inexistent_fields: &[ast::Ident],
972 unmentioned_fields: &mut Vec<ast::Ident>,
973 variant: &ty::VariantDef,
976 let (field_names, t, plural) = if inexistent_fields.len() == 1 {
977 (format!("a field named `{}`", inexistent_fields[0]), "this", "")
984 .map(|ident| format!("`{}`", ident))
985 .collect::<Vec<String>>()
992 let spans = inexistent_fields.iter().map(|ident| ident.span).collect::<Vec<_>>();
993 let mut err = struct_span_err!(
997 "{} `{}` does not have {}",
999 tcx.def_path_str(variant.def_id),
1002 if let Some(ident) = inexistent_fields.last() {
1006 "{} `{}` does not have {} field{}",
1008 tcx.def_path_str(variant.def_id),
1014 let input = unmentioned_fields.iter().map(|field| &field.name);
1015 let suggested_name = find_best_match_for_name(input, &ident.as_str(), None);
1016 if let Some(suggested_name) = suggested_name {
1017 err.span_suggestion(
1019 "a field with a similar name exists",
1020 suggested_name.to_string(),
1021 Applicability::MaybeIncorrect,
1024 // we don't want to throw `E0027` in case we have thrown `E0026` for them
1025 unmentioned_fields.retain(|&x| x.name != suggested_name);
1029 if tcx.sess.teach(&err.get_code().unwrap()) {
1031 "This error indicates that a struct pattern attempted to \
1032 extract a non-existent field from a struct. Struct fields \
1033 are identified by the name used before the colon : so struct \
1034 patterns should resemble the declaration of the struct type \
1036 If you are using shorthand field patterns but want to refer \
1037 to the struct field by a different name, you should rename \
1044 fn error_unmentioned_fields(
1047 unmentioned_fields: &[ast::Ident],
1048 variant: &ty::VariantDef,
1050 let field_names = if unmentioned_fields.len() == 1 {
1051 format!("field `{}`", unmentioned_fields[0])
1053 let fields = unmentioned_fields
1055 .map(|name| format!("`{}`", name))
1056 .collect::<Vec<String>>()
1058 format!("fields {}", fields)
1060 let mut diag = struct_span_err!(
1064 "pattern does not mention {}",
1067 diag.span_label(span, format!("missing {}", field_names));
1068 if variant.ctor_kind == CtorKind::Fn {
1069 diag.note("trying to match a tuple variant with a struct variant pattern");
1071 if self.tcx.sess.teach(&diag.get_code().unwrap()) {
1073 "This error indicates that a pattern for a struct fails to specify a \
1074 sub-pattern for every one of the struct's fields. Ensure that each field \
1075 from the struct's definition is mentioned in the pattern, or use `..` to \
1076 ignore unwanted fields.",
1085 inner: &'tcx Pat<'tcx>,
1087 def_bm: BindingMode,
1088 discrim_span: Option<Span>,
1091 let (box_ty, inner_ty) = if self.check_dereferenceable(span, expected, &inner) {
1092 // Here, `demand::subtype` is good enough, but I don't
1093 // think any errors can be introduced by using `demand::eqtype`.
1094 let inner_ty = self.next_ty_var(TypeVariableOrigin {
1095 kind: TypeVariableOriginKind::TypeInference,
1098 let box_ty = tcx.mk_box(inner_ty);
1099 self.demand_eqtype_pat(span, expected, box_ty, discrim_span);
1102 (tcx.types.err, tcx.types.err)
1104 self.check_pat(&inner, inner_ty, def_bm, discrim_span);
1111 inner: &'tcx Pat<'tcx>,
1112 mutbl: hir::Mutability,
1114 def_bm: BindingMode,
1115 discrim_span: Option<Span>,
1118 let expected = self.shallow_resolve(expected);
1119 let (rptr_ty, inner_ty) = if self.check_dereferenceable(pat.span, expected, &inner) {
1120 // `demand::subtype` would be good enough, but using `eqtype` turns
1121 // out to be equally general. See (note_1) for details.
1123 // Take region, inner-type from expected type if we can,
1124 // to avoid creating needless variables. This also helps with
1125 // the bad interactions of the given hack detailed in (note_1).
1126 debug!("check_pat_ref: expected={:?}", expected);
1127 match expected.kind {
1128 ty::Ref(_, r_ty, r_mutbl) if r_mutbl == mutbl => (expected, r_ty),
1130 let inner_ty = self.next_ty_var(TypeVariableOrigin {
1131 kind: TypeVariableOriginKind::TypeInference,
1134 let rptr_ty = self.new_ref_ty(pat.span, mutbl, inner_ty);
1135 debug!("check_pat_ref: demanding {:?} = {:?}", expected, rptr_ty);
1136 let err = self.demand_eqtype_diag(pat.span, expected, rptr_ty);
1138 // Look for a case like `fn foo(&foo: u32)` and suggest
1139 // `fn foo(foo: &u32)`
1140 if let Some(mut err) = err {
1141 self.borrow_pat_suggestion(&mut err, &pat, &inner, &expected);
1148 (tcx.types.err, tcx.types.err)
1150 self.check_pat(&inner, inner_ty, def_bm, discrim_span);
1154 /// Create a reference type with a fresh region variable.
1155 fn new_ref_ty(&self, span: Span, mutbl: hir::Mutability, ty: Ty<'tcx>) -> Ty<'tcx> {
1156 let region = self.next_region_var(infer::PatternRegion(span));
1157 let mt = ty::TypeAndMut { ty, mutbl };
1158 self.tcx.mk_ref(region, mt)
1161 /// Type check a slice pattern.
1163 /// Syntactically, these look like `[pat_0, ..., pat_n]`.
1164 /// Semantically, we are type checking a pattern with structure:
1166 /// [before_0, ..., before_n, (slice, after_0, ... after_n)?]
1168 /// The type of `slice`, if it is present, depends on the `expected` type.
1169 /// If `slice` is missing, then so is `after_i`.
1170 /// If `slice` is present, it can still represent 0 elements.
1174 before: &'tcx [&'tcx Pat<'tcx>],
1175 slice: Option<&'tcx Pat<'tcx>>,
1176 after: &'tcx [&'tcx Pat<'tcx>],
1178 def_bm: BindingMode,
1179 discrim_span: Option<Span>,
1181 let err = self.tcx.types.err;
1182 let expected = self.structurally_resolved_type(span, expected);
1183 let (inner_ty, slice_ty, expected) = match expected.kind {
1184 // An array, so we might have something like `let [a, b, c] = [0, 1, 2];`.
1185 ty::Array(inner_ty, len) => {
1186 let min = before.len() as u64 + after.len() as u64;
1188 .check_array_pat_len(span, slice, len, min)
1189 .map_or(err, |len| self.tcx.mk_array(inner_ty, len));
1190 (inner_ty, slice_ty, expected)
1192 ty::Slice(inner_ty) => (inner_ty, expected, expected),
1193 // The expected type must be an array or slice, but was neither, so error.
1195 if !expected.references_error() {
1196 self.error_expected_array_or_slice(span, expected);
1202 // Type check all the patterns before `slice`.
1204 self.check_pat(&elt, inner_ty, def_bm, discrim_span);
1206 // Type check the `slice`, if present, against its expected type.
1207 if let Some(slice) = slice {
1208 self.check_pat(&slice, slice_ty, def_bm, discrim_span);
1210 // Type check the elements after `slice`, if present.
1212 self.check_pat(&elt, inner_ty, def_bm, discrim_span);
1217 /// Type check the length of an array pattern.
1219 /// Return the length of the variable length pattern,
1220 /// if it exists and there are no errors.
1221 fn check_array_pat_len(
1224 slice: Option<&'tcx Pat<'tcx>>,
1225 len: &ty::Const<'tcx>,
1228 if let Some(len) = len.try_eval_usize(self.tcx, self.param_env) {
1229 // Now we know the length...
1230 if slice.is_none() {
1231 // ...and since there is no variable-length pattern,
1232 // we require an exact match between the number of elements
1233 // in the array pattern and as provided by the matched type.
1235 self.error_scrutinee_inconsistent_length(span, min_len, len);
1237 } else if let r @ Some(_) = len.checked_sub(min_len) {
1238 // The variable-length pattern was there,
1239 // so it has an array type with the remaining elements left as its size...
1242 // ...however, in this case, there were no remaining elements.
1243 // That is, the slice pattern requires more than the array type offers.
1244 self.error_scrutinee_with_rest_inconsistent_length(span, min_len, len);
1247 // No idea what the length is, which happens if we have e.g.,
1248 // `let [a, b] = arr` where `arr: [T; N]` where `const N: usize`.
1249 self.error_scrutinee_unfixed_length(span);
1254 fn error_scrutinee_inconsistent_length(&self, span: Span, min_len: u64, size: u64) {
1259 "pattern requires {} element{} but array has {}",
1261 pluralize!(min_len),
1264 .span_label(span, format!("expected {} element{}", size, pluralize!(size)))
1268 fn error_scrutinee_with_rest_inconsistent_length(&self, span: Span, min_len: u64, size: u64) {
1273 "pattern requires at least {} element{} but array has {}",
1275 pluralize!(min_len),
1280 format!("pattern cannot match array of {} element{}", size, pluralize!(size),),
1285 fn error_scrutinee_unfixed_length(&self, span: Span) {
1290 "cannot pattern-match on an array without a fixed length",
1295 fn error_expected_array_or_slice(&self, span: Span, expected_ty: Ty<'tcx>) {
1296 let mut err = struct_span_err!(
1300 "expected an array or slice, found `{}`",
1303 if let ty::Ref(_, ty, _) = expected_ty.kind {
1304 if let ty::Array(..) | ty::Slice(..) = ty.kind {
1305 err.help("the semantics of slice patterns changed recently; see issue #62254");
1308 err.span_label(span, format!("pattern cannot match with input type `{}`", expected_ty));