1 use crate::check::FnCtxt;
4 use rustc_data_structures::fx::FxHashMap;
5 use rustc_errors::{pluralize, struct_span_err, Applicability, DiagnosticBuilder};
7 use rustc_hir::def::{CtorKind, DefKind, Res};
8 use rustc_hir::pat_util::EnumerateAndAdjustIterator;
9 use rustc_hir::{HirId, Pat, PatKind};
10 use rustc_infer::infer;
11 use rustc_infer::infer::type_variable::{TypeVariableOrigin, TypeVariableOriginKind};
12 use rustc_middle::ty::subst::GenericArg;
13 use rustc_middle::ty::{self, Adt, BindingMode, Ty, TypeFoldable};
14 use rustc_span::hygiene::DesugaringKind;
15 use rustc_span::lev_distance::find_best_match_for_name;
16 use rustc_span::source_map::{Span, Spanned};
17 use rustc_span::symbol::Ident;
18 use rustc_span::{BytePos, DUMMY_SP};
19 use rustc_trait_selection::traits::{ObligationCause, Pattern};
22 use std::collections::hash_map::Entry::{Occupied, Vacant};
24 use super::report_unexpected_variant_res;
26 const CANNOT_IMPLICITLY_DEREF_POINTER_TRAIT_OBJ: &str = "\
27 This error indicates that a pointer to a trait type cannot be implicitly dereferenced by a \
28 pattern. Every trait defines a type, but because the size of trait implementors isn't fixed, \
29 this type has no compile-time size. Therefore, all accesses to trait types must be through \
30 pointers. If you encounter this error you should try to avoid dereferencing the pointer.
32 You can read more about trait objects in the Trait Objects section of the Reference: \
33 https://doc.rust-lang.org/reference/types.html#trait-objects";
35 /// Information about the expected type at the top level of type checking a pattern.
37 /// **NOTE:** This is only for use by diagnostics. Do NOT use for type checking logic!
38 #[derive(Copy, Clone)]
39 struct TopInfo<'tcx> {
40 /// The `expected` type at the top level of type checking a pattern.
42 /// Was the origin of the `span` from a scrutinee expression?
44 /// Otherwise there is no scrutinee and it could be e.g. from the type of a formal parameter.
46 /// The span giving rise to the `expected` type, if one could be provided.
48 /// If `origin_expr` is `true`, then this is the span of the scrutinee as in:
50 /// - `match scrutinee { ... }`
51 /// - `let _ = scrutinee;`
53 /// This is used to point to add context in type errors.
54 /// In the following example, `span` corresponds to the `a + b` expression:
57 /// error[E0308]: mismatched types
58 /// --> src/main.rs:L:C
60 /// L | let temp: usize = match a + b {
61 /// | ----- this expression has type `usize`
62 /// L | Ok(num) => num,
63 /// | ^^^^^^^ expected `usize`, found enum `std::result::Result`
65 /// = note: expected type `usize`
66 /// found type `std::result::Result<_, _>`
69 /// This refers to the parent pattern. Used to provide extra diagnostic information on errors.
71 /// error[E0308]: mismatched types
72 /// --> $DIR/const-in-struct-pat.rs:8:17
75 /// | --------- unit struct defined here
77 /// L | let Thing { f } = t;
80 /// | expected struct `std::string::String`, found struct `f`
81 /// | `f` is interpreted as a unit struct, not a new binding
82 /// | help: bind the struct field to a different name instead: `f: other_f`
84 parent_pat: Option<&'tcx Pat<'tcx>>,
87 impl<'tcx> FnCtxt<'_, 'tcx> {
88 fn pattern_cause(&self, ti: TopInfo<'tcx>, cause_span: Span) -> ObligationCause<'tcx> {
89 let code = Pattern { span: ti.span, root_ty: ti.expected, origin_expr: ti.origin_expr };
90 self.cause(cause_span, code)
93 fn demand_eqtype_pat_diag(
99 ) -> Option<DiagnosticBuilder<'tcx>> {
100 self.demand_eqtype_with_origin(&self.pattern_cause(ti, cause_span), expected, actual)
103 fn demand_eqtype_pat(
110 if let Some(mut err) = self.demand_eqtype_pat_diag(cause_span, expected, actual, ti) {
116 const INITIAL_BM: BindingMode = BindingMode::BindByValue(hir::Mutability::Not);
118 /// Mode for adjusting the expected type and binding mode.
120 /// Peel off all immediate reference types.
122 /// Reset binding mode to the initial mode.
124 /// Pass on the input binding mode and expected type.
128 impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
129 /// Type check the given top level pattern against the `expected` type.
131 /// If a `Some(span)` is provided and `origin_expr` holds,
132 /// then the `span` represents the scrutinee's span.
133 /// The scrutinee is found in e.g. `match scrutinee { ... }` and `let pat = scrutinee;`.
135 /// Otherwise, `Some(span)` represents the span of a type expression
136 /// which originated the `expected` type.
137 pub fn check_pat_top(
139 pat: &'tcx Pat<'tcx>,
144 let info = TopInfo { expected, origin_expr, span, parent_pat: None };
145 self.check_pat(pat, expected, INITIAL_BM, info);
148 /// Type check the given `pat` against the `expected` type
149 /// with the provided `def_bm` (default binding mode).
151 /// Outside of this module, `check_pat_top` should always be used.
152 /// Conversely, inside this module, `check_pat_top` should never be used.
153 #[instrument(skip(self, ti))]
156 pat: &'tcx Pat<'tcx>,
161 let path_res = match &pat.kind {
162 PatKind::Path(qpath) => Some(self.resolve_ty_and_res_ufcs(qpath, pat.hir_id, pat.span)),
165 let adjust_mode = self.calc_adjust_mode(pat, path_res.map(|(res, ..)| res));
166 let (expected, def_bm) = self.calc_default_binding_mode(pat, expected, def_bm, adjust_mode);
168 let ty = match pat.kind {
169 PatKind::Wild => expected,
170 PatKind::Lit(lt) => self.check_pat_lit(pat.span, lt, expected, ti),
171 PatKind::Range(lhs, rhs, _) => self.check_pat_range(pat.span, lhs, rhs, expected, ti),
172 PatKind::Binding(ba, var_id, _, sub) => {
173 self.check_pat_ident(pat, ba, var_id, sub, expected, def_bm, ti)
175 PatKind::TupleStruct(ref qpath, subpats, ddpos) => {
176 self.check_pat_tuple_struct(pat, qpath, subpats, ddpos, expected, def_bm, ti)
178 PatKind::Path(_) => self.check_pat_path(pat, path_res.unwrap(), expected, ti),
179 PatKind::Struct(ref qpath, fields, etc) => {
180 self.check_pat_struct(pat, qpath, fields, etc, expected, def_bm, ti)
182 PatKind::Or(pats) => {
183 let parent_pat = Some(pat);
185 self.check_pat(pat, expected, def_bm, TopInfo { parent_pat, ..ti });
189 PatKind::Tuple(elements, ddpos) => {
190 self.check_pat_tuple(pat.span, elements, ddpos, expected, def_bm, ti)
192 PatKind::Box(inner) => self.check_pat_box(pat.span, inner, expected, def_bm, ti),
193 PatKind::Ref(inner, mutbl) => {
194 self.check_pat_ref(pat, inner, mutbl, expected, def_bm, ti)
196 PatKind::Slice(before, slice, after) => {
197 self.check_pat_slice(pat.span, before, slice, after, expected, def_bm, ti)
201 self.write_ty(pat.hir_id, ty);
203 // (note_1): In most of the cases where (note_1) is referenced
204 // (literals and constants being the exception), we relate types
205 // using strict equality, even though subtyping would be sufficient.
206 // There are a few reasons for this, some of which are fairly subtle
207 // and which cost me (nmatsakis) an hour or two debugging to remember,
208 // so I thought I'd write them down this time.
210 // 1. There is no loss of expressiveness here, though it does
211 // cause some inconvenience. What we are saying is that the type
212 // of `x` becomes *exactly* what is expected. This can cause unnecessary
213 // errors in some cases, such as this one:
216 // fn foo<'x>(x: &'x i32) {
223 // The reason we might get an error is that `z` might be
224 // assigned a type like `&'x i32`, and then we would have
225 // a problem when we try to assign `&a` to `z`, because
226 // the lifetime of `&a` (i.e., the enclosing block) is
227 // shorter than `'x`.
229 // HOWEVER, this code works fine. The reason is that the
230 // expected type here is whatever type the user wrote, not
231 // the initializer's type. In this case the user wrote
232 // nothing, so we are going to create a type variable `Z`.
233 // Then we will assign the type of the initializer (`&'x i32`)
234 // as a subtype of `Z`: `&'x i32 <: Z`. And hence we
235 // will instantiate `Z` as a type `&'0 i32` where `'0` is
236 // a fresh region variable, with the constraint that `'x : '0`.
237 // So basically we're all set.
239 // Note that there are two tests to check that this remains true
240 // (`regions-reassign-{match,let}-bound-pointer.rs`).
242 // 2. Things go horribly wrong if we use subtype. The reason for
243 // THIS is a fairly subtle case involving bound regions. See the
244 // `givens` field in `region_constraints`, as well as the test
245 // `regions-relate-bound-regions-on-closures-to-inference-variables.rs`,
246 // for details. Short version is that we must sometimes detect
247 // relationships between specific region variables and regions
248 // bound in a closure signature, and that detection gets thrown
249 // off when we substitute fresh region variables here to enable
253 /// Compute the new expected type and default binding mode from the old ones
254 /// as well as the pattern form we are currently checking.
255 fn calc_default_binding_mode(
257 pat: &'tcx Pat<'tcx>,
260 adjust_mode: AdjustMode,
261 ) -> (Ty<'tcx>, BindingMode) {
263 AdjustMode::Pass => (expected, def_bm),
264 AdjustMode::Reset => (expected, INITIAL_BM),
265 AdjustMode::Peel => self.peel_off_references(pat, expected, def_bm),
269 /// How should the binding mode and expected type be adjusted?
271 /// When the pattern is a path pattern, `opt_path_res` must be `Some(res)`.
272 fn calc_adjust_mode(&self, pat: &'tcx Pat<'tcx>, opt_path_res: Option<Res>) -> AdjustMode {
273 // When we perform destructuring assignment, we disable default match bindings, which are
274 // unintuitive in this context.
275 if !pat.default_binding_modes {
276 return AdjustMode::Reset;
279 // Type checking these product-like types successfully always require
280 // that the expected type be of those types and not reference types.
282 | PatKind::TupleStruct(..)
286 | PatKind::Slice(..) => AdjustMode::Peel,
287 // String and byte-string literals result in types `&str` and `&[u8]` respectively.
288 // All other literals result in non-reference types.
289 // As a result, we allow `if let 0 = &&0 {}` but not `if let "foo" = &&"foo {}`.
290 PatKind::Lit(lt) => match self.check_expr(lt).kind() {
291 ty::Ref(..) => AdjustMode::Pass,
292 _ => AdjustMode::Peel,
294 PatKind::Path(_) => match opt_path_res.unwrap() {
295 // These constants can be of a reference type, e.g. `const X: &u8 = &0;`.
296 // Peeling the reference types too early will cause type checking failures.
297 // Although it would be possible to *also* peel the types of the constants too.
298 Res::Def(DefKind::Const | DefKind::AssocConst, _) => AdjustMode::Pass,
299 // In the `ValueNS`, we have `SelfCtor(..) | Ctor(_, Const), _)` remaining which
300 // could successfully compile. The former being `Self` requires a unit struct.
301 // In either case, and unlike constants, the pattern itself cannot be
302 // a reference type wherefore peeling doesn't give up any expressivity.
303 _ => AdjustMode::Peel,
305 // When encountering a `& mut? pat` pattern, reset to "by value".
306 // This is so that `x` and `y` here are by value, as they appear to be:
309 // match &(&22, &44) {
315 PatKind::Ref(..) => AdjustMode::Reset,
316 // A `_` pattern works with any expected type, so there's no need to do anything.
318 // Bindings also work with whatever the expected type is,
319 // and moreover if we peel references off, that will give us the wrong binding type.
320 // Also, we can have a subpattern `binding @ pat`.
321 // Each side of the `@` should be treated independently (like with OR-patterns).
322 | PatKind::Binding(..)
323 // An OR-pattern just propagates to each individual alternative.
324 // This is maximally flexible, allowing e.g., `Some(mut x) | &Some(mut x)`.
325 // In that example, `Some(mut x)` results in `Peel` whereas `&Some(mut x)` in `Reset`.
326 | PatKind::Or(_) => AdjustMode::Pass,
330 /// Peel off as many immediately nested `& mut?` from the expected type as possible
331 /// and return the new expected type and binding default binding mode.
332 /// The adjustments vector, if non-empty is stored in a table.
333 fn peel_off_references(
335 pat: &'tcx Pat<'tcx>,
337 mut def_bm: BindingMode,
338 ) -> (Ty<'tcx>, BindingMode) {
339 let mut expected = self.resolve_vars_with_obligations(&expected);
341 // Peel off as many `&` or `&mut` from the scrutinee type as possible. For example,
342 // for `match &&&mut Some(5)` the loop runs three times, aborting when it reaches
343 // the `Some(5)` which is not of type Ref.
345 // For each ampersand peeled off, update the binding mode and push the original
346 // type into the adjustments vector.
348 // See the examples in `ui/match-defbm*.rs`.
349 let mut pat_adjustments = vec![];
350 while let ty::Ref(_, inner_ty, inner_mutability) = *expected.kind() {
351 debug!("inspecting {:?}", expected);
353 debug!("current discriminant is Ref, inserting implicit deref");
354 // Preserve the reference type. We'll need it later during THIR lowering.
355 pat_adjustments.push(expected);
358 def_bm = ty::BindByReference(match def_bm {
359 // If default binding mode is by value, make it `ref` or `ref mut`
360 // (depending on whether we observe `&` or `&mut`).
362 // When `ref mut`, stay a `ref mut` (on `&mut`) or downgrade to `ref` (on `&`).
363 ty::BindByReference(hir::Mutability::Mut) => inner_mutability,
364 // Once a `ref`, always a `ref`.
365 // This is because a `& &mut` cannot mutate the underlying value.
366 ty::BindByReference(m @ hir::Mutability::Not) => m,
370 if !pat_adjustments.is_empty() {
371 debug!("default binding mode is now {:?}", def_bm);
375 .pat_adjustments_mut()
376 .insert(pat.hir_id, pat_adjustments);
385 lt: &hir::Expr<'tcx>,
389 // We've already computed the type above (when checking for a non-ref pat),
390 // so avoid computing it again.
391 let ty = self.node_ty(lt.hir_id);
393 // Byte string patterns behave the same way as array patterns
394 // They can denote both statically and dynamically-sized byte arrays.
396 if let hir::ExprKind::Lit(Spanned { node: ast::LitKind::ByteStr(_), .. }) = lt.kind {
397 let expected = self.structurally_resolved_type(span, expected);
398 if let ty::Ref(_, inner_ty, _) = expected.kind() {
399 if matches!(inner_ty.kind(), ty::Slice(_)) {
401 trace!(?lt.hir_id.local_id, "polymorphic byte string lit");
404 .treat_byte_string_as_slice
405 .insert(lt.hir_id.local_id);
406 pat_ty = tcx.mk_imm_ref(tcx.lifetimes.re_static, tcx.mk_slice(tcx.types.u8));
411 // Somewhat surprising: in this case, the subtyping relation goes the
412 // opposite way as the other cases. Actually what we really want is not
413 // a subtyping relation at all but rather that there exists a LUB
414 // (so that they can be compared). However, in practice, constants are
415 // always scalars or strings. For scalars subtyping is irrelevant,
416 // and for strings `ty` is type is `&'static str`, so if we say that
418 // &'static str <: expected
420 // then that's equivalent to there existing a LUB.
421 let cause = self.pattern_cause(ti, span);
422 if let Some(mut err) = self.demand_suptype_with_origin(&cause, expected, pat_ty) {
426 // In the case of `if`- and `while`-expressions we've already checked
427 // that `scrutinee: bool`. We know that the pattern is `true`,
428 // so an error here would be a duplicate and from the wrong POV.
429 s.is_desugaring(DesugaringKind::CondTemporary)
441 lhs: Option<&'tcx hir::Expr<'tcx>>,
442 rhs: Option<&'tcx hir::Expr<'tcx>>,
446 let calc_side = |opt_expr: Option<&'tcx hir::Expr<'tcx>>| match opt_expr {
447 None => (None, None),
449 let ty = self.check_expr(expr);
450 // Check that the end-point is of numeric or char type.
451 let fail = !(ty.is_numeric() || ty.is_char() || ty.references_error());
452 (Some(ty), Some((fail, ty, expr.span)))
455 let (lhs_ty, lhs) = calc_side(lhs);
456 let (rhs_ty, rhs) = calc_side(rhs);
458 if let (Some((true, ..)), _) | (_, Some((true, ..))) = (lhs, rhs) {
459 // There exists a side that didn't meet our criteria that the end-point
460 // be of a numeric or char type, as checked in `calc_side` above.
461 self.emit_err_pat_range(span, lhs, rhs);
462 return self.tcx.ty_error();
465 // Now that we know the types can be unified we find the unified type
466 // and use it to type the entire expression.
467 let common_type = self.resolve_vars_if_possible(lhs_ty.or(rhs_ty).unwrap_or(expected));
469 // Subtyping doesn't matter here, as the value is some kind of scalar.
470 let demand_eqtype = |x, y| {
471 if let Some((_, x_ty, x_span)) = x {
472 if let Some(mut err) = self.demand_eqtype_pat_diag(x_span, expected, x_ty, ti) {
473 if let Some((_, y_ty, y_span)) = y {
474 self.endpoint_has_type(&mut err, y_span, y_ty);
480 demand_eqtype(lhs, rhs);
481 demand_eqtype(rhs, lhs);
486 fn endpoint_has_type(&self, err: &mut DiagnosticBuilder<'_>, span: Span, ty: Ty<'_>) {
487 if !ty.references_error() {
488 err.span_label(span, &format!("this is of type `{}`", ty));
492 fn emit_err_pat_range(
495 lhs: Option<(bool, Ty<'tcx>, Span)>,
496 rhs: Option<(bool, Ty<'tcx>, Span)>,
498 let span = match (lhs, rhs) {
499 (Some((true, ..)), Some((true, ..))) => span,
500 (Some((true, _, sp)), _) => sp,
501 (_, Some((true, _, sp))) => sp,
502 _ => span_bug!(span, "emit_err_pat_range: no side failed or exists but still error?"),
504 let mut err = struct_span_err!(
508 "only `char` and numeric types are allowed in range patterns"
510 let msg = |ty| format!("this is of type `{}` but it should be `char` or numeric", ty);
511 let mut one_side_err = |first_span, first_ty, second: Option<(bool, Ty<'tcx>, Span)>| {
512 err.span_label(first_span, &msg(first_ty));
513 if let Some((_, ty, sp)) = second {
514 self.endpoint_has_type(&mut err, sp, ty);
518 (Some((true, lhs_ty, lhs_sp)), Some((true, rhs_ty, rhs_sp))) => {
519 err.span_label(lhs_sp, &msg(lhs_ty));
520 err.span_label(rhs_sp, &msg(rhs_ty));
522 (Some((true, lhs_ty, lhs_sp)), rhs) => one_side_err(lhs_sp, lhs_ty, rhs),
523 (lhs, Some((true, rhs_ty, rhs_sp))) => one_side_err(rhs_sp, rhs_ty, lhs),
524 _ => span_bug!(span, "Impossible, verified above."),
526 if self.tcx.sess.teach(&err.get_code().unwrap()) {
528 "In a match expression, only numbers and characters can be matched \
529 against a range. This is because the compiler checks that the range \
530 is non-empty at compile-time, and is unable to evaluate arbitrary \
531 comparison functions. If you want to capture values of an orderable \
532 type between two end-points, you can use a guard.",
540 pat: &'tcx Pat<'tcx>,
541 ba: hir::BindingAnnotation,
543 sub: Option<&'tcx Pat<'tcx>>,
548 // Determine the binding mode...
550 hir::BindingAnnotation::Unannotated => def_bm,
551 _ => BindingMode::convert(ba),
553 // ...and store it in a side table:
554 self.inh.typeck_results.borrow_mut().pat_binding_modes_mut().insert(pat.hir_id, bm);
556 debug!("check_pat_ident: pat.hir_id={:?} bm={:?}", pat.hir_id, bm);
558 let local_ty = self.local_ty(pat.span, pat.hir_id).decl_ty;
559 let eq_ty = match bm {
560 ty::BindByReference(mutbl) => {
561 // If the binding is like `ref x | ref mut x`,
562 // then `x` is assigned a value of type `&M T` where M is the
563 // mutability and T is the expected type.
565 // `x` is assigned a value of type `&M T`, hence `&M T <: typeof(x)`
566 // is required. However, we use equality, which is stronger.
567 // See (note_1) for an explanation.
568 self.new_ref_ty(pat.span, mutbl, expected)
570 // Otherwise, the type of x is the expected type `T`.
571 ty::BindByValue(_) => {
572 // As above, `T <: typeof(x)` is required, but we use equality, see (note_1).
576 self.demand_eqtype_pat(pat.span, eq_ty, local_ty, ti);
578 // If there are multiple arms, make sure they all agree on
579 // what the type of the binding `x` ought to be.
580 if var_id != pat.hir_id {
581 self.check_binding_alt_eq_ty(pat.span, var_id, local_ty, ti);
584 if let Some(p) = sub {
585 self.check_pat(&p, expected, def_bm, TopInfo { parent_pat: Some(&pat), ..ti });
591 fn check_binding_alt_eq_ty(&self, span: Span, var_id: HirId, ty: Ty<'tcx>, ti: TopInfo<'tcx>) {
592 let var_ty = self.local_ty(span, var_id).decl_ty;
593 if let Some(mut err) = self.demand_eqtype_pat_diag(span, var_ty, ty, ti) {
594 let hir = self.tcx.hir();
595 let var_ty = self.resolve_vars_with_obligations(var_ty);
596 let msg = format!("first introduced with type `{}` here", var_ty);
597 err.span_label(hir.span(var_id), msg);
598 let in_match = hir.parent_iter(var_id).any(|(_, n)| {
601 hir::Node::Expr(hir::Expr {
602 kind: hir::ExprKind::Match(.., hir::MatchSource::Normal),
607 let pre = if in_match { "in the same arm, " } else { "" };
608 err.note(&format!("{}a binding must have the same type in all alternatives", pre));
613 fn borrow_pat_suggestion(
615 err: &mut DiagnosticBuilder<'_>,
621 if let PatKind::Binding(..) = inner.kind {
622 let binding_parent_id = tcx.hir().get_parent_node(pat.hir_id);
623 let binding_parent = tcx.hir().get(binding_parent_id);
624 debug!("inner {:?} pat {:?} parent {:?}", inner, pat, binding_parent);
625 match binding_parent {
626 hir::Node::Param(hir::Param { span, .. }) => {
627 if let Ok(snippet) = tcx.sess.source_map().span_to_snippet(inner.span) {
630 &format!("did you mean `{}`", snippet),
631 format!(" &{}", expected),
632 Applicability::MachineApplicable,
636 hir::Node::Arm(_) | hir::Node::Pat(_) => {
637 // rely on match ergonomics or it might be nested `&&pat`
638 if let Ok(snippet) = tcx.sess.source_map().span_to_snippet(inner.span) {
641 "you can probably remove the explicit borrow",
643 Applicability::MaybeIncorrect,
647 _ => {} // don't provide suggestions in other cases #55175
652 pub fn check_dereferenceable(&self, span: Span, expected: Ty<'tcx>, inner: &Pat<'_>) -> bool {
653 if let PatKind::Binding(..) = inner.kind {
654 if let Some(mt) = self.shallow_resolve(expected).builtin_deref(true) {
655 if let ty::Dynamic(..) = mt.ty.kind() {
656 // This is "x = SomeTrait" being reduced from
657 // "let &x = &SomeTrait" or "let box x = Box<SomeTrait>", an error.
658 let type_str = self.ty_to_string(expected);
659 let mut err = struct_span_err!(
663 "type `{}` cannot be dereferenced",
666 err.span_label(span, format!("type `{}` cannot be dereferenced", type_str));
667 if self.tcx.sess.teach(&err.get_code().unwrap()) {
668 err.note(CANNOT_IMPLICITLY_DEREF_POINTER_TRAIT_OBJ);
680 pat: &'tcx Pat<'tcx>,
681 qpath: &hir::QPath<'_>,
682 fields: &'tcx [hir::FieldPat<'tcx>],
688 // Resolve the path and check the definition for errors.
689 let (variant, pat_ty) = if let Some(variant_ty) = self.check_struct_path(qpath, pat.hir_id)
693 let err = self.tcx.ty_error();
694 for field in fields {
695 let ti = TopInfo { parent_pat: Some(&pat), ..ti };
696 self.check_pat(&field.pat, err, def_bm, ti);
701 // Type-check the path.
702 self.demand_eqtype_pat(pat.span, expected, pat_ty, ti);
704 // Type-check subpatterns.
705 if self.check_struct_pat_fields(pat_ty, &pat, variant, fields, etc, def_bm, ti) {
715 path_resolution: (Res, Option<Ty<'tcx>>, &'b [hir::PathSegment<'b>]),
721 // We have already resolved the path.
722 let (res, opt_ty, segments) = path_resolution;
725 self.set_tainted_by_errors();
726 return tcx.ty_error();
728 Res::Def(DefKind::AssocFn | DefKind::Ctor(_, CtorKind::Fictive | CtorKind::Fn), _) => {
729 report_unexpected_variant_res(tcx, res, pat.span);
730 return tcx.ty_error();
734 DefKind::Ctor(_, CtorKind::Const)
736 | DefKind::AssocConst
737 | DefKind::ConstParam,
740 _ => bug!("unexpected pattern resolution: {:?}", res),
743 // Type-check the path.
744 let (pat_ty, pat_res) =
745 self.instantiate_value_path(segments, opt_ty, res, pat.span, pat.hir_id);
747 self.demand_suptype_with_origin(&self.pattern_cause(ti, pat.span), expected, pat_ty)
749 self.emit_bad_pat_path(err, pat.span, res, pat_res, pat_ty, segments, ti.parent_pat);
754 fn maybe_suggest_range_literal(
756 e: &mut DiagnosticBuilder<'_>,
757 opt_def_id: Option<hir::def_id::DefId>,
761 Some(def_id) => match self.tcx.hir().get_if_local(def_id) {
762 Some(hir::Node::Item(hir::Item {
763 kind: hir::ItemKind::Const(_, body_id), ..
764 })) => match self.tcx.hir().get(body_id.hir_id) {
765 hir::Node::Expr(expr) => {
766 if hir::is_range_literal(expr) {
767 let span = self.tcx.hir().span(body_id.hir_id);
768 if let Ok(snip) = self.tcx.sess.source_map().span_to_snippet(span) {
769 e.span_suggestion_verbose(
771 "you may want to move the range into the match block",
773 Applicability::MachineApplicable,
788 fn emit_bad_pat_path(
790 mut e: DiagnosticBuilder<'_>,
795 segments: &'b [hir::PathSegment<'b>],
796 parent_pat: Option<&Pat<'_>>,
798 if let Some(span) = self.tcx.hir().res_span(pat_res) {
799 e.span_label(span, &format!("{} defined here", res.descr()));
800 if let [hir::PathSegment { ident, .. }] = &*segments {
804 "`{}` is interpreted as {} {}, not a new binding",
811 Some(Pat { kind: hir::PatKind::Struct(..), .. }) => {
812 e.span_suggestion_verbose(
813 ident.span.shrink_to_hi(),
814 "bind the struct field to a different name instead",
815 format!(": other_{}", ident.as_str().to_lowercase()),
816 Applicability::HasPlaceholders,
820 let (type_def_id, item_def_id) = match pat_ty.kind() {
821 Adt(def, _) => match res {
822 Res::Def(DefKind::Const, def_id) => (Some(def.did), Some(def_id)),
829 self.tcx.lang_items().range_struct(),
830 self.tcx.lang_items().range_from_struct(),
831 self.tcx.lang_items().range_to_struct(),
832 self.tcx.lang_items().range_full_struct(),
833 self.tcx.lang_items().range_inclusive_struct(),
834 self.tcx.lang_items().range_to_inclusive_struct(),
836 if type_def_id != None && ranges.contains(&type_def_id) {
837 if !self.maybe_suggest_range_literal(&mut e, item_def_id, *ident) {
838 let msg = "constants only support matching by type, \
839 if you meant to match against a range of values, \
840 consider using a range pattern like `min ..= max` in the match block";
844 let msg = "introduce a new binding instead";
845 let sugg = format!("other_{}", ident.as_str().to_lowercase());
850 Applicability::HasPlaceholders,
860 fn check_pat_tuple_struct(
862 pat: &'tcx Pat<'tcx>,
863 qpath: &hir::QPath<'_>,
864 subpats: &'tcx [&'tcx Pat<'tcx>],
865 ddpos: Option<usize>,
872 let parent_pat = Some(pat);
874 self.check_pat(&pat, tcx.ty_error(), def_bm, TopInfo { parent_pat, ..ti });
877 let report_unexpected_res = |res: Res| {
878 let sm = tcx.sess.source_map();
880 .span_to_snippet(sm.span_until_char(pat.span, '('))
881 .map_or(String::new(), |s| format!(" `{}`", s.trim_end()));
883 "expected tuple struct or tuple variant, found {}{}",
888 let mut err = struct_span_err!(tcx.sess, pat.span, E0164, "{}", msg);
890 Res::Def(DefKind::Fn | DefKind::AssocFn, _) => {
891 err.span_label(pat.span, "`fn` calls are not allowed in patterns");
893 "for more information, visit \
894 https://doc.rust-lang.org/book/ch18-00-patterns.html",
898 err.span_label(pat.span, "not a tuple variant or struct");
905 // Resolve the path and check the definition for errors.
906 let (res, opt_ty, segments) = self.resolve_ty_and_res_ufcs(qpath, pat.hir_id, pat.span);
908 self.set_tainted_by_errors();
910 return self.tcx.ty_error();
913 // Type-check the path.
915 self.instantiate_value_path(segments, opt_ty, res, pat.span, pat.hir_id);
917 report_unexpected_res(res);
918 return tcx.ty_error();
921 let variant = match res {
923 self.set_tainted_by_errors();
925 return tcx.ty_error();
927 Res::Def(DefKind::AssocConst | DefKind::AssocFn, _) => {
928 report_unexpected_res(res);
929 return tcx.ty_error();
931 Res::Def(DefKind::Ctor(_, CtorKind::Fn), _) => tcx.expect_variant_res(res),
932 _ => bug!("unexpected pattern resolution: {:?}", res),
935 // Replace constructor type with constructed type for tuple struct patterns.
936 let pat_ty = pat_ty.fn_sig(tcx).output();
937 let pat_ty = pat_ty.no_bound_vars().expect("expected fn type");
939 // Type-check the tuple struct pattern against the expected type.
940 let diag = self.demand_eqtype_pat_diag(pat.span, expected, pat_ty, ti);
941 let had_err = if let Some(mut err) = diag {
948 // Type-check subpatterns.
949 if subpats.len() == variant.fields.len()
950 || subpats.len() < variant.fields.len() && ddpos.is_some()
952 let substs = match pat_ty.kind() {
953 ty::Adt(_, substs) => substs,
954 _ => bug!("unexpected pattern type {:?}", pat_ty),
956 for (i, subpat) in subpats.iter().enumerate_and_adjust(variant.fields.len(), ddpos) {
957 let field_ty = self.field_ty(subpat.span, &variant.fields[i], substs);
958 self.check_pat(&subpat, field_ty, def_bm, TopInfo { parent_pat: Some(&pat), ..ti });
960 self.tcx.check_stability(variant.fields[i].did, Some(pat.hir_id), subpat.span);
963 // Pattern has wrong number of fields.
964 self.e0023(pat.span, res, qpath, subpats, &variant.fields, expected, had_err);
966 return tcx.ty_error();
975 qpath: &hir::QPath<'_>,
976 subpats: &'tcx [&'tcx Pat<'tcx>],
977 fields: &'tcx [ty::FieldDef],
981 let subpats_ending = pluralize!(subpats.len());
982 let fields_ending = pluralize!(fields.len());
983 let res_span = self.tcx.def_span(res.def_id());
984 let mut err = struct_span_err!(
988 "this pattern has {} field{}, but the corresponding {} has {} field{}",
997 format!("expected {} field{}, found {}", fields.len(), fields_ending, subpats.len(),),
999 .span_label(res_span, format!("{} defined here", res.descr()));
1001 // Identify the case `Some(x, y)` where the expected type is e.g. `Option<(T, U)>`.
1002 // More generally, the expected type wants a tuple variant with one field of an
1003 // N-arity-tuple, e.g., `V_i((p_0, .., p_N))`. Meanwhile, the user supplied a pattern
1004 // with the subpatterns directly in the tuple variant pattern, e.g., `V_i(p_0, .., p_N)`.
1005 let missing_parentheses = match (&expected.kind(), fields, had_err) {
1006 // #67037: only do this if we could successfully type-check the expected type against
1007 // the tuple struct pattern. Otherwise the substs could get out of range on e.g.,
1008 // `let P() = U;` where `P != U` with `struct P<T>(T);`.
1009 (ty::Adt(_, substs), [field], false) => {
1010 let field_ty = self.field_ty(pat_span, field, substs);
1011 match field_ty.kind() {
1012 ty::Tuple(_) => field_ty.tuple_fields().count() == subpats.len(),
1018 if missing_parentheses {
1019 let (left, right) = match subpats {
1020 // This is the zero case; we aim to get the "hi" part of the `QPath`'s
1021 // span as the "lo" and then the "hi" part of the pattern's span as the "hi".
1024 // help: missing parentheses
1026 // L | let A(()) = A(());
1028 [] => (qpath.span().shrink_to_hi(), pat_span),
1029 // Easy case. Just take the "lo" of the first sub-pattern and the "hi" of the
1030 // last sub-pattern. In the case of `A(x)` the first and last may coincide.
1033 // help: missing parentheses
1035 // L | let A((x, y)) = A((1, 2));
1037 [first, ..] => (first.span.shrink_to_lo(), subpats.last().unwrap().span),
1039 err.multipart_suggestion(
1040 "missing parentheses",
1041 vec![(left, "(".to_string()), (right.shrink_to_hi(), ")".to_string())],
1042 Applicability::MachineApplicable,
1044 } else if fields.len() > subpats.len() {
1045 let after_fields_span = if pat_span == DUMMY_SP {
1048 pat_span.with_hi(pat_span.hi() - BytePos(1)).shrink_to_hi()
1050 let all_fields_span = match subpats {
1051 [] => after_fields_span,
1052 [field] => field.span,
1053 [first, .., last] => first.span.to(last.span),
1056 // Check if all the fields in the pattern are wildcards.
1057 let all_wildcards = subpats.iter().all(|pat| matches!(pat.kind, PatKind::Wild));
1059 let mut wildcard_sugg = vec!["_"; fields.len() - subpats.len()].join(", ");
1060 if !subpats.is_empty() {
1061 wildcard_sugg = String::from(", ") + &wildcard_sugg;
1064 err.span_suggestion(
1066 "use `_` to explicitly ignore each field",
1068 Applicability::MaybeIncorrect,
1071 if subpats.is_empty() || all_wildcards {
1072 err.span_suggestion(
1074 "use `..` to ignore all unmentioned fields",
1076 Applicability::MaybeIncorrect,
1079 err.span_suggestion(
1081 "use `..` to ignore all unmentioned fields",
1082 String::from(", .."),
1083 Applicability::MaybeIncorrect,
1094 elements: &'tcx [&'tcx Pat<'tcx>],
1095 ddpos: Option<usize>,
1097 def_bm: BindingMode,
1101 let mut expected_len = elements.len();
1102 if ddpos.is_some() {
1103 // Require known type only when `..` is present.
1104 if let ty::Tuple(ref tys) = self.structurally_resolved_type(span, expected).kind() {
1105 expected_len = tys.len();
1108 let max_len = cmp::max(expected_len, elements.len());
1110 let element_tys_iter = (0..max_len).map(|_| {
1111 GenericArg::from(self.next_ty_var(
1112 // FIXME: `MiscVariable` for now -- obtaining the span and name information
1113 // from all tuple elements isn't trivial.
1114 TypeVariableOrigin { kind: TypeVariableOriginKind::TypeInference, span },
1117 let element_tys = tcx.mk_substs(element_tys_iter);
1118 let pat_ty = tcx.mk_ty(ty::Tuple(element_tys));
1119 if let Some(mut err) = self.demand_eqtype_pat_diag(span, expected, pat_ty, ti) {
1121 // Walk subpatterns with an expected type of `err` in this case to silence
1122 // further errors being emitted when using the bindings. #50333
1123 let element_tys_iter = (0..max_len).map(|_| tcx.ty_error());
1124 for (_, elem) in elements.iter().enumerate_and_adjust(max_len, ddpos) {
1125 self.check_pat(elem, &tcx.ty_error(), def_bm, ti);
1127 tcx.mk_tup(element_tys_iter)
1129 for (i, elem) in elements.iter().enumerate_and_adjust(max_len, ddpos) {
1130 self.check_pat(elem, &element_tys[i].expect_ty(), def_bm, ti);
1136 fn check_struct_pat_fields(
1139 pat: &'tcx Pat<'tcx>,
1140 variant: &'tcx ty::VariantDef,
1141 fields: &'tcx [hir::FieldPat<'tcx>],
1143 def_bm: BindingMode,
1148 let (substs, adt) = match adt_ty.kind() {
1149 ty::Adt(adt, substs) => (substs, adt),
1150 _ => span_bug!(pat.span, "struct pattern is not an ADT"),
1153 // Index the struct fields' types.
1154 let field_map = variant
1158 .map(|(i, field)| (field.ident.normalize_to_macros_2_0(), (i, field)))
1159 .collect::<FxHashMap<_, _>>();
1161 // Keep track of which fields have already appeared in the pattern.
1162 let mut used_fields = FxHashMap::default();
1163 let mut no_field_errors = true;
1165 let mut inexistent_fields = vec![];
1166 // Typecheck each field.
1167 for field in fields {
1168 let span = field.span;
1169 let ident = tcx.adjust_ident(field.ident, variant.def_id);
1170 let field_ty = match used_fields.entry(ident) {
1171 Occupied(occupied) => {
1172 self.error_field_already_bound(span, field.ident, *occupied.get());
1173 no_field_errors = false;
1177 vacant.insert(span);
1181 self.write_field_index(field.hir_id, *i);
1182 self.tcx.check_stability(f.did, Some(pat.hir_id), span);
1183 self.field_ty(span, f, substs)
1185 .unwrap_or_else(|| {
1186 inexistent_fields.push(field.ident);
1187 no_field_errors = false;
1193 self.check_pat(&field.pat, field_ty, def_bm, TopInfo { parent_pat: Some(&pat), ..ti });
1196 let mut unmentioned_fields = variant
1199 .map(|field| (field, field.ident.normalize_to_macros_2_0()))
1200 .filter(|(_, ident)| !used_fields.contains_key(&ident))
1201 .collect::<Vec<_>>();
1203 let inexistent_fields_err = if !(inexistent_fields.is_empty() || variant.is_recovered()) {
1204 Some(self.error_inexistent_fields(
1205 adt.variant_descr(),
1207 &mut unmentioned_fields,
1214 // Require `..` if struct has non_exhaustive attribute.
1215 if variant.is_field_list_non_exhaustive() && !adt.did.is_local() && !etc {
1216 self.error_foreign_non_exhaustive_spat(pat, adt.variant_descr(), fields.is_empty());
1219 let mut unmentioned_err = None;
1220 // Report an error if an incorrect number of fields was specified.
1222 if fields.len() != 1 {
1224 .struct_span_err(pat.span, "union patterns should have exactly one field")
1228 tcx.sess.struct_span_err(pat.span, "`..` cannot be used in union patterns").emit();
1230 } else if !etc && !unmentioned_fields.is_empty() {
1231 let no_accessible_unmentioned_fields = !unmentioned_fields.iter().any(|(field, _)| {
1232 field.vis.is_accessible_from(tcx.parent_module(pat.hir_id).to_def_id(), tcx)
1235 if no_accessible_unmentioned_fields {
1236 unmentioned_err = Some(self.error_no_accessible_fields(pat, &fields));
1239 Some(self.error_unmentioned_fields(pat, &unmentioned_fields, &fields));
1242 match (inexistent_fields_err, unmentioned_err) {
1243 (Some(mut i), Some(mut u)) => {
1244 if let Some(mut e) = self.error_tuple_variant_as_struct_pat(pat, fields, variant) {
1245 // We don't want to show the inexistent fields error when this was
1246 // `Foo { a, b }` when it should have been `Foo(a, b)`.
1255 (None, Some(mut err)) | (Some(mut err), None) => {
1263 fn error_foreign_non_exhaustive_spat(&self, pat: &Pat<'_>, descr: &str, no_fields: bool) {
1264 let sess = self.tcx.sess;
1265 let sm = sess.source_map();
1266 let sp_brace = sm.end_point(pat.span);
1267 let sp_comma = sm.end_point(pat.span.with_hi(sp_brace.hi()));
1268 let sugg = if no_fields || sp_brace != sp_comma { ".. }" } else { ", .. }" };
1270 let mut err = struct_span_err!(
1274 "`..` required with {} marked as non-exhaustive",
1277 err.span_suggestion_verbose(
1279 "add `..` at the end of the field list to ignore all other fields",
1281 Applicability::MachineApplicable,
1286 fn error_field_already_bound(&self, span: Span, ident: Ident, other_field: Span) {
1291 "field `{}` bound multiple times in the pattern",
1294 .span_label(span, format!("multiple uses of `{}` in pattern", ident))
1295 .span_label(other_field, format!("first use of `{}`", ident))
1299 fn error_inexistent_fields(
1302 inexistent_fields: &[Ident],
1303 unmentioned_fields: &mut Vec<(&ty::FieldDef, Ident)>,
1304 variant: &ty::VariantDef,
1305 ) -> DiagnosticBuilder<'tcx> {
1307 let (field_names, t, plural) = if inexistent_fields.len() == 1 {
1308 (format!("a field named `{}`", inexistent_fields[0]), "this", "")
1315 .map(|ident| format!("`{}`", ident))
1316 .collect::<Vec<String>>()
1323 let spans = inexistent_fields.iter().map(|ident| ident.span).collect::<Vec<_>>();
1324 let mut err = struct_span_err!(
1328 "{} `{}` does not have {}",
1330 tcx.def_path_str(variant.def_id),
1333 if let Some(ident) = inexistent_fields.last() {
1337 "{} `{}` does not have {} field{}",
1339 tcx.def_path_str(variant.def_id),
1346 unmentioned_fields.iter().map(|(_, field)| field.name).collect::<Vec<_>>();
1347 let suggested_name = find_best_match_for_name(&input, ident.name, None);
1348 if let Some(suggested_name) = suggested_name {
1349 err.span_suggestion(
1351 "a field with a similar name exists",
1352 suggested_name.to_string(),
1353 Applicability::MaybeIncorrect,
1356 // When we have a tuple struct used with struct we don't want to suggest using
1357 // the (valid) struct syntax with numeric field names. Instead we want to
1358 // suggest the expected syntax. We infer that this is the case by parsing the
1359 // `Ident` into an unsized integer. The suggestion will be emitted elsewhere in
1360 // `smart_resolve_context_dependent_help`.
1361 if suggested_name.to_ident_string().parse::<usize>().is_err() {
1362 // We don't want to throw `E0027` in case we have thrown `E0026` for them.
1363 unmentioned_fields.retain(|&(_, x)| x.name != suggested_name);
1368 if tcx.sess.teach(&err.get_code().unwrap()) {
1370 "This error indicates that a struct pattern attempted to \
1371 extract a non-existent field from a struct. Struct fields \
1372 are identified by the name used before the colon : so struct \
1373 patterns should resemble the declaration of the struct type \
1375 If you are using shorthand field patterns but want to refer \
1376 to the struct field by a different name, you should rename \
1383 fn error_tuple_variant_as_struct_pat(
1386 fields: &'tcx [hir::FieldPat<'tcx>],
1387 variant: &ty::VariantDef,
1388 ) -> Option<DiagnosticBuilder<'tcx>> {
1389 if let (CtorKind::Fn, PatKind::Struct(qpath, ..)) = (variant.ctor_kind, &pat.kind) {
1390 let path = rustc_hir_pretty::to_string(rustc_hir_pretty::NO_ANN, |s| {
1391 s.print_qpath(qpath, false)
1393 let mut err = struct_span_err!(
1397 "tuple variant `{}` written as struct variant",
1400 let (sugg, appl) = if fields.len() == variant.fields.len() {
1404 .map(|f| match self.tcx.sess.source_map().span_to_snippet(f.pat.span) {
1406 Err(_) => rustc_hir_pretty::to_string(rustc_hir_pretty::NO_ANN, |s| {
1410 .collect::<Vec<String>>()
1412 Applicability::MachineApplicable,
1416 variant.fields.iter().map(|_| "_").collect::<Vec<&str>>().join(", "),
1417 Applicability::MaybeIncorrect,
1420 err.span_suggestion(
1422 "use the tuple variant pattern syntax instead",
1423 format!("{}({})", path, sugg),
1431 /// Returns a diagnostic reporting a struct pattern which is missing an `..` due to
1432 /// inaccessible fields.
1435 /// error: pattern requires `..` due to inaccessible fields
1436 /// --> src/main.rs:10:9
1438 /// LL | let foo::Foo {} = foo::Foo::default();
1441 /// help: add a `..`
1443 /// LL | let foo::Foo { .. } = foo::Foo::default();
1446 fn error_no_accessible_fields(
1449 fields: &'tcx [hir::FieldPat<'tcx>],
1450 ) -> DiagnosticBuilder<'tcx> {
1454 .struct_span_err(pat.span, "pattern requires `..` due to inaccessible fields");
1456 if let Some(field) = fields.last() {
1457 err.span_suggestion_verbose(
1458 field.span.shrink_to_hi(),
1459 "ignore the inaccessible and unused fields",
1461 Applicability::MachineApplicable,
1464 let qpath_span = if let PatKind::Struct(qpath, ..) = &pat.kind {
1467 bug!("`error_no_accessible_fields` called on non-struct pattern");
1470 // Shrink the span to exclude the `foo:Foo` in `foo::Foo { }`.
1471 let span = pat.span.with_lo(qpath_span.shrink_to_hi().hi());
1472 err.span_suggestion_verbose(
1474 "ignore the inaccessible and unused fields",
1475 " { .. }".to_string(),
1476 Applicability::MachineApplicable,
1482 /// Returns a diagnostic reporting a struct pattern which does not mention some fields.
1485 /// error[E0027]: pattern does not mention field `you_cant_use_this_field`
1486 /// --> src/main.rs:15:9
1488 /// LL | let foo::Foo {} = foo::Foo::new();
1489 /// | ^^^^^^^^^^^ missing field `you_cant_use_this_field`
1491 fn error_unmentioned_fields(
1494 unmentioned_fields: &[(&ty::FieldDef, Ident)],
1495 fields: &'tcx [hir::FieldPat<'tcx>],
1496 ) -> DiagnosticBuilder<'tcx> {
1497 let field_names = if unmentioned_fields.len() == 1 {
1498 format!("field `{}`", unmentioned_fields[0].1)
1500 let fields = unmentioned_fields
1502 .map(|(_, name)| format!("`{}`", name))
1503 .collect::<Vec<String>>()
1505 format!("fields {}", fields)
1507 let mut err = struct_span_err!(
1511 "pattern does not mention {}",
1514 err.span_label(pat.span, format!("missing {}", field_names));
1515 let len = unmentioned_fields.len();
1516 let (prefix, postfix, sp) = match fields {
1517 [] => match &pat.kind {
1518 PatKind::Struct(path, [], false) => {
1519 (" { ", " }", path.span().shrink_to_hi().until(pat.span.shrink_to_hi()))
1525 PatKind::Struct(_, [_, ..], _) => ", ",
1529 field.span.shrink_to_hi(),
1532 err.span_suggestion(
1535 "include the missing field{} in the pattern",
1536 if len == 1 { "" } else { "s" },
1543 .map(|(_, name)| name.to_string())
1544 .collect::<Vec<_>>()
1548 Applicability::MachineApplicable,
1550 err.span_suggestion(
1553 "if you don't care about {} missing field{}, you can explicitly ignore {}",
1554 if len == 1 { "this" } else { "these" },
1555 if len == 1 { "" } else { "s" },
1556 if len == 1 { "it" } else { "them" },
1558 format!("{}..{}", prefix, postfix),
1559 Applicability::MachineApplicable,
1567 inner: &'tcx Pat<'tcx>,
1569 def_bm: BindingMode,
1573 let (box_ty, inner_ty) = if self.check_dereferenceable(span, expected, &inner) {
1574 // Here, `demand::subtype` is good enough, but I don't
1575 // think any errors can be introduced by using `demand::eqtype`.
1576 let inner_ty = self.next_ty_var(TypeVariableOrigin {
1577 kind: TypeVariableOriginKind::TypeInference,
1580 let box_ty = tcx.mk_box(inner_ty);
1581 self.demand_eqtype_pat(span, expected, box_ty, ti);
1584 let err = tcx.ty_error();
1587 self.check_pat(&inner, inner_ty, def_bm, ti);
1593 pat: &'tcx Pat<'tcx>,
1594 inner: &'tcx Pat<'tcx>,
1595 mutbl: hir::Mutability,
1597 def_bm: BindingMode,
1601 let expected = self.shallow_resolve(expected);
1602 let (rptr_ty, inner_ty) = if self.check_dereferenceable(pat.span, expected, &inner) {
1603 // `demand::subtype` would be good enough, but using `eqtype` turns
1604 // out to be equally general. See (note_1) for details.
1606 // Take region, inner-type from expected type if we can,
1607 // to avoid creating needless variables. This also helps with
1608 // the bad interactions of the given hack detailed in (note_1).
1609 debug!("check_pat_ref: expected={:?}", expected);
1610 match *expected.kind() {
1611 ty::Ref(_, r_ty, r_mutbl) if r_mutbl == mutbl => (expected, r_ty),
1613 let inner_ty = self.next_ty_var(TypeVariableOrigin {
1614 kind: TypeVariableOriginKind::TypeInference,
1617 let rptr_ty = self.new_ref_ty(pat.span, mutbl, inner_ty);
1618 debug!("check_pat_ref: demanding {:?} = {:?}", expected, rptr_ty);
1619 let err = self.demand_eqtype_pat_diag(pat.span, expected, rptr_ty, ti);
1621 // Look for a case like `fn foo(&foo: u32)` and suggest
1622 // `fn foo(foo: &u32)`
1623 if let Some(mut err) = err {
1624 self.borrow_pat_suggestion(&mut err, &pat, &inner, &expected);
1631 let err = tcx.ty_error();
1634 self.check_pat(&inner, inner_ty, def_bm, TopInfo { parent_pat: Some(&pat), ..ti });
1638 /// Create a reference type with a fresh region variable.
1639 fn new_ref_ty(&self, span: Span, mutbl: hir::Mutability, ty: Ty<'tcx>) -> Ty<'tcx> {
1640 let region = self.next_region_var(infer::PatternRegion(span));
1641 let mt = ty::TypeAndMut { ty, mutbl };
1642 self.tcx.mk_ref(region, mt)
1645 /// Type check a slice pattern.
1647 /// Syntactically, these look like `[pat_0, ..., pat_n]`.
1648 /// Semantically, we are type checking a pattern with structure:
1650 /// [before_0, ..., before_n, (slice, after_0, ... after_n)?]
1652 /// The type of `slice`, if it is present, depends on the `expected` type.
1653 /// If `slice` is missing, then so is `after_i`.
1654 /// If `slice` is present, it can still represent 0 elements.
1658 before: &'tcx [&'tcx Pat<'tcx>],
1659 slice: Option<&'tcx Pat<'tcx>>,
1660 after: &'tcx [&'tcx Pat<'tcx>],
1662 def_bm: BindingMode,
1665 let expected = self.structurally_resolved_type(span, expected);
1666 let (element_ty, opt_slice_ty, inferred) = match *expected.kind() {
1667 // An array, so we might have something like `let [a, b, c] = [0, 1, 2];`.
1668 ty::Array(element_ty, len) => {
1669 let min = before.len() as u64 + after.len() as u64;
1670 let (opt_slice_ty, expected) =
1671 self.check_array_pat_len(span, element_ty, expected, slice, len, min);
1672 // `opt_slice_ty.is_none()` => `slice.is_none()`.
1673 // Note, though, that opt_slice_ty could be `Some(error_ty)`.
1674 assert!(opt_slice_ty.is_some() || slice.is_none());
1675 (element_ty, opt_slice_ty, expected)
1677 ty::Slice(element_ty) => (element_ty, Some(expected), expected),
1678 // The expected type must be an array or slice, but was neither, so error.
1680 if !expected.references_error() {
1681 self.error_expected_array_or_slice(span, expected);
1683 let err = self.tcx.ty_error();
1684 (err, Some(err), err)
1688 // Type check all the patterns before `slice`.
1690 self.check_pat(&elt, element_ty, def_bm, ti);
1692 // Type check the `slice`, if present, against its expected type.
1693 if let Some(slice) = slice {
1694 self.check_pat(&slice, opt_slice_ty.unwrap(), def_bm, ti);
1696 // Type check the elements after `slice`, if present.
1698 self.check_pat(&elt, element_ty, def_bm, ti);
1703 /// Type check the length of an array pattern.
1705 /// Returns both the type of the variable length pattern (or `None`), and the potentially
1706 /// inferred array type. We only return `None` for the slice type if `slice.is_none()`.
1707 fn check_array_pat_len(
1710 element_ty: Ty<'tcx>,
1712 slice: Option<&'tcx Pat<'tcx>>,
1713 len: &ty::Const<'tcx>,
1715 ) -> (Option<Ty<'tcx>>, Ty<'tcx>) {
1716 if let Some(len) = len.try_eval_usize(self.tcx, self.param_env) {
1717 // Now we know the length...
1718 if slice.is_none() {
1719 // ...and since there is no variable-length pattern,
1720 // we require an exact match between the number of elements
1721 // in the array pattern and as provided by the matched type.
1723 return (None, arr_ty);
1726 self.error_scrutinee_inconsistent_length(span, min_len, len);
1727 } else if let Some(pat_len) = len.checked_sub(min_len) {
1728 // The variable-length pattern was there,
1729 // so it has an array type with the remaining elements left as its size...
1730 return (Some(self.tcx.mk_array(element_ty, pat_len)), arr_ty);
1732 // ...however, in this case, there were no remaining elements.
1733 // That is, the slice pattern requires more than the array type offers.
1734 self.error_scrutinee_with_rest_inconsistent_length(span, min_len, len);
1736 } else if slice.is_none() {
1737 // We have a pattern with a fixed length,
1738 // which we can use to infer the length of the array.
1739 let updated_arr_ty = self.tcx.mk_array(element_ty, min_len);
1740 self.demand_eqtype(span, updated_arr_ty, arr_ty);
1741 return (None, updated_arr_ty);
1743 // We have a variable-length pattern and don't know the array length.
1744 // This happens if we have e.g.,
1745 // `let [a, b, ..] = arr` where `arr: [T; N]` where `const N: usize`.
1746 self.error_scrutinee_unfixed_length(span);
1749 // If we get here, we must have emitted an error.
1750 (Some(self.tcx.ty_error()), arr_ty)
1753 fn error_scrutinee_inconsistent_length(&self, span: Span, min_len: u64, size: u64) {
1758 "pattern requires {} element{} but array has {}",
1760 pluralize!(min_len),
1763 .span_label(span, format!("expected {} element{}", size, pluralize!(size)))
1767 fn error_scrutinee_with_rest_inconsistent_length(&self, span: Span, min_len: u64, size: u64) {
1772 "pattern requires at least {} element{} but array has {}",
1774 pluralize!(min_len),
1779 format!("pattern cannot match array of {} element{}", size, pluralize!(size),),
1784 fn error_scrutinee_unfixed_length(&self, span: Span) {
1789 "cannot pattern-match on an array without a fixed length",
1794 fn error_expected_array_or_slice(&self, span: Span, expected_ty: Ty<'tcx>) {
1795 let mut err = struct_span_err!(
1799 "expected an array or slice, found `{}`",
1802 if let ty::Ref(_, ty, _) = expected_ty.kind() {
1803 if let ty::Array(..) | ty::Slice(..) = ty.kind() {
1804 err.help("the semantics of slice patterns changed recently; see issue #62254");
1807 err.span_label(span, format!("pattern cannot match with input type `{}`", expected_ty));