1 use crate::check::FnCtxt;
4 use rustc_data_structures::fx::FxHashMap;
6 pluralize, struct_span_err, Applicability, Diagnostic, DiagnosticBuilder, ErrorGuaranteed,
9 use rustc_hir::def::{CtorKind, DefKind, Res};
10 use rustc_hir::pat_util::EnumerateAndAdjustIterator;
11 use rustc_hir::{HirId, Pat, PatKind};
12 use rustc_infer::infer;
13 use rustc_infer::infer::type_variable::{TypeVariableOrigin, TypeVariableOriginKind};
14 use rustc_middle::middle::stability::EvalResult;
15 use rustc_middle::ty::{self, Adt, BindingMode, Ty, TypeFoldable};
16 use rustc_session::lint::builtin::NON_EXHAUSTIVE_OMITTED_PATTERNS;
17 use rustc_span::hygiene::DesugaringKind;
18 use rustc_span::lev_distance::find_best_match_for_name;
19 use rustc_span::source_map::{Span, Spanned};
20 use rustc_span::symbol::{kw, sym, Ident};
21 use rustc_span::{BytePos, MultiSpan, DUMMY_SP};
22 use rustc_trait_selection::autoderef::Autoderef;
23 use rustc_trait_selection::traits::{ObligationCause, Pattern};
27 use std::collections::hash_map::Entry::{Occupied, Vacant};
29 use super::report_unexpected_variant_res;
31 const CANNOT_IMPLICITLY_DEREF_POINTER_TRAIT_OBJ: &str = "\
32 This error indicates that a pointer to a trait type cannot be implicitly dereferenced by a \
33 pattern. Every trait defines a type, but because the size of trait implementors isn't fixed, \
34 this type has no compile-time size. Therefore, all accesses to trait types must be through \
35 pointers. If you encounter this error you should try to avoid dereferencing the pointer.
37 You can read more about trait objects in the Trait Objects section of the Reference: \
38 https://doc.rust-lang.org/reference/types.html#trait-objects";
40 /// Information about the expected type at the top level of type checking a pattern.
42 /// **NOTE:** This is only for use by diagnostics. Do NOT use for type checking logic!
43 #[derive(Copy, Clone)]
44 struct TopInfo<'tcx> {
45 /// The `expected` type at the top level of type checking a pattern.
47 /// Was the origin of the `span` from a scrutinee expression?
49 /// Otherwise there is no scrutinee and it could be e.g. from the type of a formal parameter.
51 /// The span giving rise to the `expected` type, if one could be provided.
53 /// If `origin_expr` is `true`, then this is the span of the scrutinee as in:
55 /// - `match scrutinee { ... }`
56 /// - `let _ = scrutinee;`
58 /// This is used to point to add context in type errors.
59 /// In the following example, `span` corresponds to the `a + b` expression:
62 /// error[E0308]: mismatched types
63 /// --> src/main.rs:L:C
65 /// L | let temp: usize = match a + b {
66 /// | ----- this expression has type `usize`
67 /// L | Ok(num) => num,
68 /// | ^^^^^^^ expected `usize`, found enum `std::result::Result`
70 /// = note: expected type `usize`
71 /// found type `std::result::Result<_, _>`
74 /// This refers to the parent pattern. Used to provide extra diagnostic information on errors.
76 /// error[E0308]: mismatched types
77 /// --> $DIR/const-in-struct-pat.rs:8:17
80 /// | --------- unit struct defined here
82 /// L | let Thing { f } = t;
85 /// | expected struct `std::string::String`, found struct `f`
86 /// | `f` is interpreted as a unit struct, not a new binding
87 /// | help: bind the struct field to a different name instead: `f: other_f`
89 parent_pat: Option<&'tcx Pat<'tcx>>,
92 impl<'tcx> FnCtxt<'_, 'tcx> {
93 fn pattern_cause(&self, ti: TopInfo<'tcx>, cause_span: Span) -> ObligationCause<'tcx> {
94 let code = Pattern { span: ti.span, root_ty: ti.expected, origin_expr: ti.origin_expr };
95 self.cause(cause_span, code)
98 fn demand_eqtype_pat_diag(
104 ) -> Option<DiagnosticBuilder<'tcx, ErrorGuaranteed>> {
105 self.demand_eqtype_with_origin(&self.pattern_cause(ti, cause_span), expected, actual)
108 fn demand_eqtype_pat(
115 if let Some(mut err) = self.demand_eqtype_pat_diag(cause_span, expected, actual, ti) {
121 const INITIAL_BM: BindingMode = BindingMode::BindByValue(hir::Mutability::Not);
123 /// Mode for adjusting the expected type and binding mode.
125 /// Peel off all immediate reference types.
127 /// Reset binding mode to the initial mode.
129 /// Pass on the input binding mode and expected type.
133 impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
134 /// Type check the given top level pattern against the `expected` type.
136 /// If a `Some(span)` is provided and `origin_expr` holds,
137 /// then the `span` represents the scrutinee's span.
138 /// The scrutinee is found in e.g. `match scrutinee { ... }` and `let pat = scrutinee;`.
140 /// Otherwise, `Some(span)` represents the span of a type expression
141 /// which originated the `expected` type.
142 pub fn check_pat_top(
144 pat: &'tcx Pat<'tcx>,
149 let info = TopInfo { expected, origin_expr, span, parent_pat: None };
150 self.check_pat(pat, expected, INITIAL_BM, info);
153 /// Type check the given `pat` against the `expected` type
154 /// with the provided `def_bm` (default binding mode).
156 /// Outside of this module, `check_pat_top` should always be used.
157 /// Conversely, inside this module, `check_pat_top` should never be used.
158 #[instrument(level = "debug", skip(self, ti))]
161 pat: &'tcx Pat<'tcx>,
166 let path_res = match &pat.kind {
167 PatKind::Path(qpath) => {
168 Some(self.resolve_ty_and_res_fully_qualified_call(qpath, pat.hir_id, pat.span))
172 let adjust_mode = self.calc_adjust_mode(pat, path_res.map(|(res, ..)| res));
173 let (expected, def_bm) = self.calc_default_binding_mode(pat, expected, def_bm, adjust_mode);
175 let ty = match pat.kind {
176 PatKind::Wild => expected,
177 PatKind::Lit(lt) => self.check_pat_lit(pat.span, lt, expected, ti),
178 PatKind::Range(lhs, rhs, _) => self.check_pat_range(pat.span, lhs, rhs, expected, ti),
179 PatKind::Binding(ba, var_id, _, sub) => {
180 self.check_pat_ident(pat, ba, var_id, sub, expected, def_bm, ti)
182 PatKind::TupleStruct(ref qpath, subpats, ddpos) => {
183 self.check_pat_tuple_struct(pat, qpath, subpats, ddpos, expected, def_bm, ti)
185 PatKind::Path(_) => self.check_pat_path(pat, path_res.unwrap(), expected, ti),
186 PatKind::Struct(ref qpath, fields, has_rest_pat) => {
187 self.check_pat_struct(pat, qpath, fields, has_rest_pat, expected, def_bm, ti)
189 PatKind::Or(pats) => {
190 let parent_pat = Some(pat);
192 self.check_pat(pat, expected, def_bm, TopInfo { parent_pat, ..ti });
196 PatKind::Tuple(elements, ddpos) => {
197 self.check_pat_tuple(pat.span, elements, ddpos, expected, def_bm, ti)
199 PatKind::Box(inner) => self.check_pat_box(pat.span, inner, expected, def_bm, ti),
200 PatKind::Ref(inner, mutbl) => {
201 self.check_pat_ref(pat, inner, mutbl, expected, def_bm, ti)
203 PatKind::Slice(before, slice, after) => {
204 self.check_pat_slice(pat.span, before, slice, after, expected, def_bm, ti)
208 self.write_ty(pat.hir_id, ty);
210 // (note_1): In most of the cases where (note_1) is referenced
211 // (literals and constants being the exception), we relate types
212 // using strict equality, even though subtyping would be sufficient.
213 // There are a few reasons for this, some of which are fairly subtle
214 // and which cost me (nmatsakis) an hour or two debugging to remember,
215 // so I thought I'd write them down this time.
217 // 1. There is no loss of expressiveness here, though it does
218 // cause some inconvenience. What we are saying is that the type
219 // of `x` becomes *exactly* what is expected. This can cause unnecessary
220 // errors in some cases, such as this one:
223 // fn foo<'x>(x: &'x i32) {
230 // The reason we might get an error is that `z` might be
231 // assigned a type like `&'x i32`, and then we would have
232 // a problem when we try to assign `&a` to `z`, because
233 // the lifetime of `&a` (i.e., the enclosing block) is
234 // shorter than `'x`.
236 // HOWEVER, this code works fine. The reason is that the
237 // expected type here is whatever type the user wrote, not
238 // the initializer's type. In this case the user wrote
239 // nothing, so we are going to create a type variable `Z`.
240 // Then we will assign the type of the initializer (`&'x i32`)
241 // as a subtype of `Z`: `&'x i32 <: Z`. And hence we
242 // will instantiate `Z` as a type `&'0 i32` where `'0` is
243 // a fresh region variable, with the constraint that `'x : '0`.
244 // So basically we're all set.
246 // Note that there are two tests to check that this remains true
247 // (`regions-reassign-{match,let}-bound-pointer.rs`).
249 // 2. Things go horribly wrong if we use subtype. The reason for
250 // THIS is a fairly subtle case involving bound regions. See the
251 // `givens` field in `region_constraints`, as well as the test
252 // `regions-relate-bound-regions-on-closures-to-inference-variables.rs`,
253 // for details. Short version is that we must sometimes detect
254 // relationships between specific region variables and regions
255 // bound in a closure signature, and that detection gets thrown
256 // off when we substitute fresh region variables here to enable
260 /// Compute the new expected type and default binding mode from the old ones
261 /// as well as the pattern form we are currently checking.
262 fn calc_default_binding_mode(
264 pat: &'tcx Pat<'tcx>,
267 adjust_mode: AdjustMode,
268 ) -> (Ty<'tcx>, BindingMode) {
270 AdjustMode::Pass => (expected, def_bm),
271 AdjustMode::Reset => (expected, INITIAL_BM),
272 AdjustMode::Peel => self.peel_off_references(pat, expected, def_bm),
276 /// How should the binding mode and expected type be adjusted?
278 /// When the pattern is a path pattern, `opt_path_res` must be `Some(res)`.
279 fn calc_adjust_mode(&self, pat: &'tcx Pat<'tcx>, opt_path_res: Option<Res>) -> AdjustMode {
280 // When we perform destructuring assignment, we disable default match bindings, which are
281 // unintuitive in this context.
282 if !pat.default_binding_modes {
283 return AdjustMode::Reset;
286 // Type checking these product-like types successfully always require
287 // that the expected type be of those types and not reference types.
289 | PatKind::TupleStruct(..)
293 | PatKind::Slice(..) => AdjustMode::Peel,
294 // String and byte-string literals result in types `&str` and `&[u8]` respectively.
295 // All other literals result in non-reference types.
296 // As a result, we allow `if let 0 = &&0 {}` but not `if let "foo" = &&"foo {}`.
298 // Call `resolve_vars_if_possible` here for inline const blocks.
299 PatKind::Lit(lt) => match self.resolve_vars_if_possible(self.check_expr(lt)).kind() {
300 ty::Ref(..) => AdjustMode::Pass,
301 _ => AdjustMode::Peel,
303 PatKind::Path(_) => match opt_path_res.unwrap() {
304 // These constants can be of a reference type, e.g. `const X: &u8 = &0;`.
305 // Peeling the reference types too early will cause type checking failures.
306 // Although it would be possible to *also* peel the types of the constants too.
307 Res::Def(DefKind::Const | DefKind::AssocConst, _) => AdjustMode::Pass,
308 // In the `ValueNS`, we have `SelfCtor(..) | Ctor(_, Const), _)` remaining which
309 // could successfully compile. The former being `Self` requires a unit struct.
310 // In either case, and unlike constants, the pattern itself cannot be
311 // a reference type wherefore peeling doesn't give up any expressivity.
312 _ => AdjustMode::Peel,
314 // When encountering a `& mut? pat` pattern, reset to "by value".
315 // This is so that `x` and `y` here are by value, as they appear to be:
318 // match &(&22, &44) {
324 PatKind::Ref(..) => AdjustMode::Reset,
325 // A `_` pattern works with any expected type, so there's no need to do anything.
327 // Bindings also work with whatever the expected type is,
328 // and moreover if we peel references off, that will give us the wrong binding type.
329 // Also, we can have a subpattern `binding @ pat`.
330 // Each side of the `@` should be treated independently (like with OR-patterns).
331 | PatKind::Binding(..)
332 // An OR-pattern just propagates to each individual alternative.
333 // This is maximally flexible, allowing e.g., `Some(mut x) | &Some(mut x)`.
334 // In that example, `Some(mut x)` results in `Peel` whereas `&Some(mut x)` in `Reset`.
335 | PatKind::Or(_) => AdjustMode::Pass,
339 /// Peel off as many immediately nested `& mut?` from the expected type as possible
340 /// and return the new expected type and binding default binding mode.
341 /// The adjustments vector, if non-empty is stored in a table.
342 fn peel_off_references(
344 pat: &'tcx Pat<'tcx>,
346 mut def_bm: BindingMode,
347 ) -> (Ty<'tcx>, BindingMode) {
348 let mut expected = self.resolve_vars_with_obligations(expected);
350 // Peel off as many `&` or `&mut` from the scrutinee type as possible. For example,
351 // for `match &&&mut Some(5)` the loop runs three times, aborting when it reaches
352 // the `Some(5)` which is not of type Ref.
354 // For each ampersand peeled off, update the binding mode and push the original
355 // type into the adjustments vector.
357 // See the examples in `ui/match-defbm*.rs`.
358 let mut pat_adjustments = vec![];
359 while let ty::Ref(_, inner_ty, inner_mutability) = *expected.kind() {
360 debug!("inspecting {:?}", expected);
362 debug!("current discriminant is Ref, inserting implicit deref");
363 // Preserve the reference type. We'll need it later during THIR lowering.
364 pat_adjustments.push(expected);
367 def_bm = ty::BindByReference(match def_bm {
368 // If default binding mode is by value, make it `ref` or `ref mut`
369 // (depending on whether we observe `&` or `&mut`).
371 // When `ref mut`, stay a `ref mut` (on `&mut`) or downgrade to `ref` (on `&`).
372 ty::BindByReference(hir::Mutability::Mut) => inner_mutability,
373 // Once a `ref`, always a `ref`.
374 // This is because a `& &mut` cannot mutate the underlying value.
375 ty::BindByReference(m @ hir::Mutability::Not) => m,
379 if !pat_adjustments.is_empty() {
380 debug!("default binding mode is now {:?}", def_bm);
384 .pat_adjustments_mut()
385 .insert(pat.hir_id, pat_adjustments);
394 lt: &hir::Expr<'tcx>,
398 // We've already computed the type above (when checking for a non-ref pat),
399 // so avoid computing it again.
400 let ty = self.node_ty(lt.hir_id);
402 // Byte string patterns behave the same way as array patterns
403 // They can denote both statically and dynamically-sized byte arrays.
405 if let hir::ExprKind::Lit(Spanned { node: ast::LitKind::ByteStr(_), .. }) = lt.kind {
406 let expected = self.structurally_resolved_type(span, expected);
407 if let ty::Ref(_, inner_ty, _) = expected.kind() {
408 if matches!(inner_ty.kind(), ty::Slice(_)) {
410 trace!(?lt.hir_id.local_id, "polymorphic byte string lit");
413 .treat_byte_string_as_slice
414 .insert(lt.hir_id.local_id);
415 pat_ty = tcx.mk_imm_ref(tcx.lifetimes.re_static, tcx.mk_slice(tcx.types.u8));
420 // Somewhat surprising: in this case, the subtyping relation goes the
421 // opposite way as the other cases. Actually what we really want is not
422 // a subtyping relation at all but rather that there exists a LUB
423 // (so that they can be compared). However, in practice, constants are
424 // always scalars or strings. For scalars subtyping is irrelevant,
425 // and for strings `ty` is type is `&'static str`, so if we say that
427 // &'static str <: expected
429 // then that's equivalent to there existing a LUB.
430 let cause = self.pattern_cause(ti, span);
431 if let Some(mut err) = self.demand_suptype_with_origin(&cause, expected, pat_ty) {
435 // In the case of `if`- and `while`-expressions we've already checked
436 // that `scrutinee: bool`. We know that the pattern is `true`,
437 // so an error here would be a duplicate and from the wrong POV.
438 s.is_desugaring(DesugaringKind::CondTemporary)
450 lhs: Option<&'tcx hir::Expr<'tcx>>,
451 rhs: Option<&'tcx hir::Expr<'tcx>>,
455 let calc_side = |opt_expr: Option<&'tcx hir::Expr<'tcx>>| match opt_expr {
458 let ty = self.check_expr(expr);
459 // Check that the end-point is possibly of numeric or char type.
460 // The early check here is not for correctness, but rather better
461 // diagnostics (e.g. when `&str` is being matched, `expected` will
462 // be peeled to `str` while ty here is still `&str`, if we don't
463 // err ealy here, a rather confusing unification error will be
466 !(ty.is_numeric() || ty.is_char() || ty.is_ty_var() || ty.references_error());
467 Some((fail, ty, expr.span))
470 let mut lhs = calc_side(lhs);
471 let mut rhs = calc_side(rhs);
473 if let (Some((true, ..)), _) | (_, Some((true, ..))) = (lhs, rhs) {
474 // There exists a side that didn't meet our criteria that the end-point
475 // be of a numeric or char type, as checked in `calc_side` above.
476 self.emit_err_pat_range(span, lhs, rhs);
477 return self.tcx.ty_error();
480 // Unify each side with `expected`.
481 // Subtyping doesn't matter here, as the value is some kind of scalar.
482 let demand_eqtype = |x: &mut _, y| {
483 if let Some((ref mut fail, x_ty, x_span)) = *x {
484 if let Some(mut err) = self.demand_eqtype_pat_diag(x_span, expected, x_ty, ti) {
485 if let Some((_, y_ty, y_span)) = y {
486 self.endpoint_has_type(&mut err, y_span, y_ty);
493 demand_eqtype(&mut lhs, rhs);
494 demand_eqtype(&mut rhs, lhs);
496 if let (Some((true, ..)), _) | (_, Some((true, ..))) = (lhs, rhs) {
497 return self.tcx.ty_error();
500 // Find the unified type and check if it's of numeric or char type again.
501 // This check is needed if both sides are inference variables.
502 // We require types to be resolved here so that we emit inference failure
503 // rather than "_ is not a char or numeric".
504 let ty = self.structurally_resolved_type(span, expected);
505 if !(ty.is_numeric() || ty.is_char() || ty.references_error()) {
506 if let Some((ref mut fail, _, _)) = lhs {
509 if let Some((ref mut fail, _, _)) = rhs {
512 self.emit_err_pat_range(span, lhs, rhs);
513 return self.tcx.ty_error();
518 fn endpoint_has_type(&self, err: &mut Diagnostic, span: Span, ty: Ty<'_>) {
519 if !ty.references_error() {
520 err.span_label(span, &format!("this is of type `{}`", ty));
524 fn emit_err_pat_range(
527 lhs: Option<(bool, Ty<'tcx>, Span)>,
528 rhs: Option<(bool, Ty<'tcx>, Span)>,
530 let span = match (lhs, rhs) {
531 (Some((true, ..)), Some((true, ..))) => span,
532 (Some((true, _, sp)), _) => sp,
533 (_, Some((true, _, sp))) => sp,
534 _ => span_bug!(span, "emit_err_pat_range: no side failed or exists but still error?"),
536 let mut err = struct_span_err!(
540 "only `char` and numeric types are allowed in range patterns"
543 let ty = self.resolve_vars_if_possible(ty);
544 format!("this is of type `{}` but it should be `char` or numeric", ty)
546 let mut one_side_err = |first_span, first_ty, second: Option<(bool, Ty<'tcx>, Span)>| {
547 err.span_label(first_span, &msg(first_ty));
548 if let Some((_, ty, sp)) = second {
549 let ty = self.resolve_vars_if_possible(ty);
550 self.endpoint_has_type(&mut err, sp, ty);
554 (Some((true, lhs_ty, lhs_sp)), Some((true, rhs_ty, rhs_sp))) => {
555 err.span_label(lhs_sp, &msg(lhs_ty));
556 err.span_label(rhs_sp, &msg(rhs_ty));
558 (Some((true, lhs_ty, lhs_sp)), rhs) => one_side_err(lhs_sp, lhs_ty, rhs),
559 (lhs, Some((true, rhs_ty, rhs_sp))) => one_side_err(rhs_sp, rhs_ty, lhs),
560 _ => span_bug!(span, "Impossible, verified above."),
562 if self.tcx.sess.teach(&err.get_code().unwrap()) {
564 "In a match expression, only numbers and characters can be matched \
565 against a range. This is because the compiler checks that the range \
566 is non-empty at compile-time, and is unable to evaluate arbitrary \
567 comparison functions. If you want to capture values of an orderable \
568 type between two end-points, you can use a guard.",
576 pat: &'tcx Pat<'tcx>,
577 ba: hir::BindingAnnotation,
579 sub: Option<&'tcx Pat<'tcx>>,
584 // Determine the binding mode...
586 hir::BindingAnnotation::Unannotated => def_bm,
587 _ => BindingMode::convert(ba),
589 // ...and store it in a side table:
590 self.inh.typeck_results.borrow_mut().pat_binding_modes_mut().insert(pat.hir_id, bm);
592 debug!("check_pat_ident: pat.hir_id={:?} bm={:?}", pat.hir_id, bm);
594 let local_ty = self.local_ty(pat.span, pat.hir_id).decl_ty;
595 let eq_ty = match bm {
596 ty::BindByReference(mutbl) => {
597 // If the binding is like `ref x | ref mut x`,
598 // then `x` is assigned a value of type `&M T` where M is the
599 // mutability and T is the expected type.
601 // `x` is assigned a value of type `&M T`, hence `&M T <: typeof(x)`
602 // is required. However, we use equality, which is stronger.
603 // See (note_1) for an explanation.
604 self.new_ref_ty(pat.span, mutbl, expected)
606 // Otherwise, the type of x is the expected type `T`.
607 ty::BindByValue(_) => {
608 // As above, `T <: typeof(x)` is required, but we use equality, see (note_1).
612 self.demand_eqtype_pat(pat.span, eq_ty, local_ty, ti);
614 // If there are multiple arms, make sure they all agree on
615 // what the type of the binding `x` ought to be.
616 if var_id != pat.hir_id {
617 self.check_binding_alt_eq_ty(pat.span, var_id, local_ty, ti);
620 if let Some(p) = sub {
621 self.check_pat(p, expected, def_bm, TopInfo { parent_pat: Some(pat), ..ti });
627 fn check_binding_alt_eq_ty(&self, span: Span, var_id: HirId, ty: Ty<'tcx>, ti: TopInfo<'tcx>) {
628 let var_ty = self.local_ty(span, var_id).decl_ty;
629 if let Some(mut err) = self.demand_eqtype_pat_diag(span, var_ty, ty, ti) {
630 let hir = self.tcx.hir();
631 let var_ty = self.resolve_vars_with_obligations(var_ty);
632 let msg = format!("first introduced with type `{}` here", var_ty);
633 err.span_label(hir.span(var_id), msg);
634 let in_match = hir.parent_iter(var_id).any(|(_, n)| {
637 hir::Node::Expr(hir::Expr {
638 kind: hir::ExprKind::Match(.., hir::MatchSource::Normal),
643 let pre = if in_match { "in the same arm, " } else { "" };
644 err.note(&format!("{}a binding must have the same type in all alternatives", pre));
649 fn borrow_pat_suggestion(
651 err: &mut Diagnostic,
657 if let PatKind::Binding(..) = inner.kind {
658 let binding_parent_id = tcx.hir().get_parent_node(pat.hir_id);
659 let binding_parent = tcx.hir().get(binding_parent_id);
660 debug!("inner {:?} pat {:?} parent {:?}", inner, pat, binding_parent);
661 match binding_parent {
662 hir::Node::Param(hir::Param { span, .. })
663 if let Ok(snippet) = tcx.sess.source_map().span_to_snippet(inner.span) =>
667 &format!("did you mean `{}`", snippet),
668 format!(" &{}", expected),
669 Applicability::MachineApplicable,
672 hir::Node::Arm(_) | hir::Node::Pat(_) => {
673 // rely on match ergonomics or it might be nested `&&pat`
674 if let Ok(snippet) = tcx.sess.source_map().span_to_snippet(inner.span) {
677 "you can probably remove the explicit borrow",
679 Applicability::MaybeIncorrect,
683 _ => {} // don't provide suggestions in other cases #55175
688 pub fn check_dereferenceable(&self, span: Span, expected: Ty<'tcx>, inner: &Pat<'_>) -> bool {
689 if let PatKind::Binding(..) = inner.kind
690 && let Some(mt) = self.shallow_resolve(expected).builtin_deref(true)
691 && let ty::Dynamic(..) = mt.ty.kind()
693 // This is "x = SomeTrait" being reduced from
694 // "let &x = &SomeTrait" or "let box x = Box<SomeTrait>", an error.
695 let type_str = self.ty_to_string(expected);
696 let mut err = struct_span_err!(
700 "type `{}` cannot be dereferenced",
703 err.span_label(span, format!("type `{}` cannot be dereferenced", type_str));
704 if self.tcx.sess.teach(&err.get_code().unwrap()) {
705 err.note(CANNOT_IMPLICITLY_DEREF_POINTER_TRAIT_OBJ);
715 pat: &'tcx Pat<'tcx>,
716 qpath: &hir::QPath<'_>,
717 fields: &'tcx [hir::PatField<'tcx>],
723 // Resolve the path and check the definition for errors.
724 let Some((variant, pat_ty)) = self.check_struct_path(qpath, pat.hir_id) else {
725 let err = self.tcx.ty_error();
726 for field in fields {
727 let ti = TopInfo { parent_pat: Some(pat), ..ti };
728 self.check_pat(field.pat, err, def_bm, ti);
733 // Type-check the path.
734 self.demand_eqtype_pat(pat.span, expected, pat_ty, ti);
736 // Type-check subpatterns.
737 if self.check_struct_pat_fields(pat_ty, &pat, variant, fields, has_rest_pat, def_bm, ti) {
744 fn check_pat_path<'b>(
747 path_resolution: (Res, Option<Ty<'tcx>>, &'b [hir::PathSegment<'b>]),
753 // We have already resolved the path.
754 let (res, opt_ty, segments) = path_resolution;
757 self.set_tainted_by_errors();
758 return tcx.ty_error();
760 Res::Def(DefKind::AssocFn | DefKind::Ctor(_, CtorKind::Fictive | CtorKind::Fn), _) => {
761 report_unexpected_variant_res(tcx, res, pat.span);
762 return tcx.ty_error();
766 DefKind::Ctor(_, CtorKind::Const)
768 | DefKind::AssocConst
769 | DefKind::ConstParam,
772 _ => bug!("unexpected pattern resolution: {:?}", res),
775 // Type-check the path.
776 let (pat_ty, pat_res) =
777 self.instantiate_value_path(segments, opt_ty, res, pat.span, pat.hir_id);
779 self.demand_suptype_with_origin(&self.pattern_cause(ti, pat.span), expected, pat_ty)
781 self.emit_bad_pat_path(err, pat.span, res, pat_res, pat_ty, segments, ti.parent_pat);
786 fn maybe_suggest_range_literal(
789 opt_def_id: Option<hir::def_id::DefId>,
793 Some(def_id) => match self.tcx.hir().get_if_local(def_id) {
794 Some(hir::Node::Item(hir::Item {
795 kind: hir::ItemKind::Const(_, body_id), ..
796 })) => match self.tcx.hir().get(body_id.hir_id) {
797 hir::Node::Expr(expr) => {
798 if hir::is_range_literal(expr) {
799 let span = self.tcx.hir().span(body_id.hir_id);
800 if let Ok(snip) = self.tcx.sess.source_map().span_to_snippet(span) {
801 e.span_suggestion_verbose(
803 "you may want to move the range into the match block",
805 Applicability::MachineApplicable,
820 fn emit_bad_pat_path<'b>(
822 mut e: DiagnosticBuilder<'_, ErrorGuaranteed>,
827 segments: &'b [hir::PathSegment<'b>],
828 parent_pat: Option<&Pat<'_>>,
830 if let Some(span) = self.tcx.hir().res_span(pat_res) {
831 e.span_label(span, &format!("{} defined here", res.descr()));
832 if let [hir::PathSegment { ident, .. }] = &*segments {
836 "`{}` is interpreted as {} {}, not a new binding",
843 Some(Pat { kind: hir::PatKind::Struct(..), .. }) => {
844 e.span_suggestion_verbose(
845 ident.span.shrink_to_hi(),
846 "bind the struct field to a different name instead",
847 format!(": other_{}", ident.as_str().to_lowercase()),
848 Applicability::HasPlaceholders,
852 let (type_def_id, item_def_id) = match pat_ty.kind() {
853 Adt(def, _) => match res {
854 Res::Def(DefKind::Const, def_id) => (Some(def.did()), Some(def_id)),
861 self.tcx.lang_items().range_struct(),
862 self.tcx.lang_items().range_from_struct(),
863 self.tcx.lang_items().range_to_struct(),
864 self.tcx.lang_items().range_full_struct(),
865 self.tcx.lang_items().range_inclusive_struct(),
866 self.tcx.lang_items().range_to_inclusive_struct(),
868 if type_def_id != None && ranges.contains(&type_def_id) {
869 if !self.maybe_suggest_range_literal(&mut e, item_def_id, *ident) {
870 let msg = "constants only support matching by type, \
871 if you meant to match against a range of values, \
872 consider using a range pattern like `min ..= max` in the match block";
876 let msg = "introduce a new binding instead";
877 let sugg = format!("other_{}", ident.as_str().to_lowercase());
882 Applicability::HasPlaceholders,
892 fn check_pat_tuple_struct(
894 pat: &'tcx Pat<'tcx>,
895 qpath: &'tcx hir::QPath<'tcx>,
896 subpats: &'tcx [Pat<'tcx>],
897 ddpos: Option<usize>,
904 let parent_pat = Some(pat);
906 self.check_pat(pat, tcx.ty_error(), def_bm, TopInfo { parent_pat, ..ti });
909 let report_unexpected_res = |res: Res| {
910 let sm = tcx.sess.source_map();
912 .span_to_snippet(sm.span_until_char(pat.span, '('))
913 .map_or_else(|_| String::new(), |s| format!(" `{}`", s.trim_end()));
915 "expected tuple struct or tuple variant, found {}{}",
920 let mut err = struct_span_err!(tcx.sess, pat.span, E0164, "{}", msg);
922 Res::Def(DefKind::Fn | DefKind::AssocFn, _) => {
923 err.span_label(pat.span, "`fn` calls are not allowed in patterns");
925 "for more information, visit \
926 https://doc.rust-lang.org/book/ch18-00-patterns.html",
930 err.span_label(pat.span, "not a tuple variant or struct");
937 // Resolve the path and check the definition for errors.
938 let (res, opt_ty, segments) =
939 self.resolve_ty_and_res_fully_qualified_call(qpath, pat.hir_id, pat.span);
941 self.set_tainted_by_errors();
943 return self.tcx.ty_error();
946 // Type-check the path.
948 self.instantiate_value_path(segments, opt_ty, res, pat.span, pat.hir_id);
950 report_unexpected_res(res);
951 return tcx.ty_error();
954 let variant = match res {
956 self.set_tainted_by_errors();
958 return tcx.ty_error();
960 Res::Def(DefKind::AssocConst | DefKind::AssocFn, _) => {
961 report_unexpected_res(res);
962 return tcx.ty_error();
964 Res::Def(DefKind::Ctor(_, CtorKind::Fn), _) => tcx.expect_variant_res(res),
965 _ => bug!("unexpected pattern resolution: {:?}", res),
968 // Replace constructor type with constructed type for tuple struct patterns.
969 let pat_ty = pat_ty.fn_sig(tcx).output();
970 let pat_ty = pat_ty.no_bound_vars().expect("expected fn type");
972 // Type-check the tuple struct pattern against the expected type.
973 let diag = self.demand_eqtype_pat_diag(pat.span, expected, pat_ty, ti);
974 let had_err = if let Some(mut err) = diag {
981 // Type-check subpatterns.
982 if subpats.len() == variant.fields.len()
983 || subpats.len() < variant.fields.len() && ddpos.is_some()
985 let ty::Adt(_, substs) = pat_ty.kind() else {
986 bug!("unexpected pattern type {:?}", pat_ty);
988 for (i, subpat) in subpats.iter().enumerate_and_adjust(variant.fields.len(), ddpos) {
989 let field_ty = self.field_ty(subpat.span, &variant.fields[i], substs);
990 self.check_pat(subpat, field_ty, def_bm, TopInfo { parent_pat: Some(pat), ..ti });
992 self.tcx.check_stability(
993 variant.fields[i].did,
1000 // Pattern has wrong number of fields.
1001 self.e0023(pat.span, res, qpath, subpats, &variant.fields, expected, had_err);
1003 return tcx.ty_error();
1012 qpath: &hir::QPath<'_>,
1013 subpats: &'tcx [Pat<'tcx>],
1014 fields: &'tcx [ty::FieldDef],
1018 let subpats_ending = pluralize!(subpats.len());
1019 let fields_ending = pluralize!(fields.len());
1021 let subpat_spans = if subpats.is_empty() {
1024 subpats.iter().map(|p| p.span).collect()
1026 let last_subpat_span = *subpat_spans.last().unwrap();
1027 let res_span = self.tcx.def_span(res.def_id());
1028 let def_ident_span = self.tcx.def_ident_span(res.def_id()).unwrap_or(res_span);
1029 let field_def_spans = if fields.is_empty() {
1032 fields.iter().map(|f| f.ident(self.tcx).span).collect()
1034 let last_field_def_span = *field_def_spans.last().unwrap();
1036 let mut err = struct_span_err!(
1038 MultiSpan::from_spans(subpat_spans),
1040 "this pattern has {} field{}, but the corresponding {} has {} field{}",
1049 &format!("expected {} field{}, found {}", fields.len(), fields_ending, subpats.len()),
1051 if self.tcx.sess.source_map().is_multiline(qpath.span().between(last_subpat_span)) {
1052 err.span_label(qpath.span(), "");
1054 if self.tcx.sess.source_map().is_multiline(def_ident_span.between(last_field_def_span)) {
1055 err.span_label(def_ident_span, format!("{} defined here", res.descr()));
1057 for span in &field_def_spans[..field_def_spans.len() - 1] {
1058 err.span_label(*span, "");
1061 last_field_def_span,
1062 &format!("{} has {} field{}", res.descr(), fields.len(), fields_ending),
1065 // Identify the case `Some(x, y)` where the expected type is e.g. `Option<(T, U)>`.
1066 // More generally, the expected type wants a tuple variant with one field of an
1067 // N-arity-tuple, e.g., `V_i((p_0, .., p_N))`. Meanwhile, the user supplied a pattern
1068 // with the subpatterns directly in the tuple variant pattern, e.g., `V_i(p_0, .., p_N)`.
1069 let missing_parentheses = match (&expected.kind(), fields, had_err) {
1070 // #67037: only do this if we could successfully type-check the expected type against
1071 // the tuple struct pattern. Otherwise the substs could get out of range on e.g.,
1072 // `let P() = U;` where `P != U` with `struct P<T>(T);`.
1073 (ty::Adt(_, substs), [field], false) => {
1074 let field_ty = self.field_ty(pat_span, field, substs);
1075 match field_ty.kind() {
1076 ty::Tuple(fields) => fields.len() == subpats.len(),
1082 if missing_parentheses {
1083 let (left, right) = match subpats {
1084 // This is the zero case; we aim to get the "hi" part of the `QPath`'s
1085 // span as the "lo" and then the "hi" part of the pattern's span as the "hi".
1088 // help: missing parentheses
1090 // L | let A(()) = A(());
1092 [] => (qpath.span().shrink_to_hi(), pat_span),
1093 // Easy case. Just take the "lo" of the first sub-pattern and the "hi" of the
1094 // last sub-pattern. In the case of `A(x)` the first and last may coincide.
1097 // help: missing parentheses
1099 // L | let A((x, y)) = A((1, 2));
1101 [first, ..] => (first.span.shrink_to_lo(), subpats.last().unwrap().span),
1103 err.multipart_suggestion(
1104 "missing parentheses",
1105 vec![(left, "(".to_string()), (right.shrink_to_hi(), ")".to_string())],
1106 Applicability::MachineApplicable,
1108 } else if fields.len() > subpats.len() && pat_span != DUMMY_SP {
1109 let after_fields_span = pat_span.with_hi(pat_span.hi() - BytePos(1)).shrink_to_hi();
1110 let all_fields_span = match subpats {
1111 [] => after_fields_span,
1112 [field] => field.span,
1113 [first, .., last] => first.span.to(last.span),
1116 // Check if all the fields in the pattern are wildcards.
1117 let all_wildcards = subpats.iter().all(|pat| matches!(pat.kind, PatKind::Wild));
1118 let first_tail_wildcard =
1119 subpats.iter().enumerate().fold(None, |acc, (pos, pat)| match (acc, &pat.kind) {
1120 (None, PatKind::Wild) => Some(pos),
1121 (Some(_), PatKind::Wild) => acc,
1124 let tail_span = match first_tail_wildcard {
1125 None => after_fields_span,
1126 Some(0) => subpats[0].span.to(after_fields_span),
1127 Some(pos) => subpats[pos - 1].span.shrink_to_hi().to(after_fields_span),
1130 // FIXME: heuristic-based suggestion to check current types for where to add `_`.
1131 let mut wildcard_sugg = vec!["_"; fields.len() - subpats.len()].join(", ");
1132 if !subpats.is_empty() {
1133 wildcard_sugg = String::from(", ") + &wildcard_sugg;
1136 err.span_suggestion_verbose(
1138 "use `_` to explicitly ignore each field",
1140 Applicability::MaybeIncorrect,
1143 // Only suggest `..` if more than one field is missing
1144 // or the pattern consists of all wildcards.
1145 if fields.len() - subpats.len() > 1 || all_wildcards {
1146 if subpats.is_empty() || all_wildcards {
1147 err.span_suggestion_verbose(
1149 "use `..` to ignore all fields",
1151 Applicability::MaybeIncorrect,
1154 err.span_suggestion_verbose(
1156 "use `..` to ignore the rest of the fields",
1157 String::from(", .."),
1158 Applicability::MaybeIncorrect,
1170 elements: &'tcx [Pat<'tcx>],
1171 ddpos: Option<usize>,
1173 def_bm: BindingMode,
1177 let mut expected_len = elements.len();
1178 if ddpos.is_some() {
1179 // Require known type only when `..` is present.
1180 if let ty::Tuple(tys) = self.structurally_resolved_type(span, expected).kind() {
1181 expected_len = tys.len();
1184 let max_len = cmp::max(expected_len, elements.len());
1186 let element_tys_iter = (0..max_len).map(|_| {
1188 // FIXME: `MiscVariable` for now -- obtaining the span and name information
1189 // from all tuple elements isn't trivial.
1190 TypeVariableOrigin { kind: TypeVariableOriginKind::TypeInference, span },
1193 let element_tys = tcx.mk_type_list(element_tys_iter);
1194 let pat_ty = tcx.mk_ty(ty::Tuple(element_tys));
1195 if let Some(mut err) = self.demand_eqtype_pat_diag(span, expected, pat_ty, ti) {
1197 // Walk subpatterns with an expected type of `err` in this case to silence
1198 // further errors being emitted when using the bindings. #50333
1199 let element_tys_iter = (0..max_len).map(|_| tcx.ty_error());
1200 for (_, elem) in elements.iter().enumerate_and_adjust(max_len, ddpos) {
1201 self.check_pat(elem, tcx.ty_error(), def_bm, ti);
1203 tcx.mk_tup(element_tys_iter)
1205 for (i, elem) in elements.iter().enumerate_and_adjust(max_len, ddpos) {
1206 self.check_pat(elem, element_tys[i], def_bm, ti);
1212 fn check_struct_pat_fields(
1215 pat: &'tcx Pat<'tcx>,
1216 variant: &'tcx ty::VariantDef,
1217 fields: &'tcx [hir::PatField<'tcx>],
1219 def_bm: BindingMode,
1224 let ty::Adt(adt, substs) = adt_ty.kind() else {
1225 span_bug!(pat.span, "struct pattern is not an ADT");
1228 // Index the struct fields' types.
1229 let field_map = variant
1233 .map(|(i, field)| (field.ident(self.tcx).normalize_to_macros_2_0(), (i, field)))
1234 .collect::<FxHashMap<_, _>>();
1236 // Keep track of which fields have already appeared in the pattern.
1237 let mut used_fields = FxHashMap::default();
1238 let mut no_field_errors = true;
1240 let mut inexistent_fields = vec![];
1241 // Typecheck each field.
1242 for field in fields {
1243 let span = field.span;
1244 let ident = tcx.adjust_ident(field.ident, variant.def_id);
1245 let field_ty = match used_fields.entry(ident) {
1246 Occupied(occupied) => {
1247 self.error_field_already_bound(span, field.ident, *occupied.get());
1248 no_field_errors = false;
1252 vacant.insert(span);
1256 self.write_field_index(field.hir_id, *i);
1257 self.tcx.check_stability(f.did, Some(pat.hir_id), span, None);
1258 self.field_ty(span, f, substs)
1260 .unwrap_or_else(|| {
1261 inexistent_fields.push(field);
1262 no_field_errors = false;
1268 self.check_pat(field.pat, field_ty, def_bm, TopInfo { parent_pat: Some(pat), ..ti });
1271 let mut unmentioned_fields = variant
1274 .map(|field| (field, field.ident(self.tcx).normalize_to_macros_2_0()))
1275 .filter(|(_, ident)| !used_fields.contains_key(ident))
1276 .collect::<Vec<_>>();
1278 let inexistent_fields_err = if !(inexistent_fields.is_empty() || variant.is_recovered())
1279 && !inexistent_fields.iter().any(|field| field.ident.name == kw::Underscore)
1281 Some(self.error_inexistent_fields(
1282 adt.variant_descr(),
1284 &mut unmentioned_fields,
1292 // Require `..` if struct has non_exhaustive attribute.
1293 let non_exhaustive = variant.is_field_list_non_exhaustive() && !adt.did().is_local();
1294 if non_exhaustive && !has_rest_pat {
1295 self.error_foreign_non_exhaustive_spat(pat, adt.variant_descr(), fields.is_empty());
1298 let mut unmentioned_err = None;
1299 // Report an error if an incorrect number of fields was specified.
1301 if fields.len() != 1 {
1303 .struct_span_err(pat.span, "union patterns should have exactly one field")
1307 tcx.sess.struct_span_err(pat.span, "`..` cannot be used in union patterns").emit();
1309 } else if !unmentioned_fields.is_empty() {
1310 let accessible_unmentioned_fields: Vec<_> = unmentioned_fields
1313 .filter(|(field, _)| {
1314 field.vis.is_accessible_from(tcx.parent_module(pat.hir_id).to_def_id(), tcx)
1316 tcx.eval_stability(field.did, None, DUMMY_SP, None),
1317 EvalResult::Deny { .. }
1319 // We only want to report the error if it is hidden and not local
1320 && !(tcx.is_doc_hidden(field.did) && !field.did.is_local())
1325 if accessible_unmentioned_fields.is_empty() {
1326 unmentioned_err = Some(self.error_no_accessible_fields(pat, fields));
1328 unmentioned_err = Some(self.error_unmentioned_fields(
1330 &accessible_unmentioned_fields,
1331 accessible_unmentioned_fields.len() != unmentioned_fields.len(),
1335 } else if non_exhaustive && !accessible_unmentioned_fields.is_empty() {
1336 self.lint_non_exhaustive_omitted_patterns(
1338 &accessible_unmentioned_fields,
1343 match (inexistent_fields_err, unmentioned_err) {
1344 (Some(mut i), Some(mut u)) => {
1345 if let Some(mut e) = self.error_tuple_variant_as_struct_pat(pat, fields, variant) {
1346 // We don't want to show the inexistent fields error when this was
1347 // `Foo { a, b }` when it should have been `Foo(a, b)`.
1356 (None, Some(mut u)) => {
1357 if let Some(mut e) = self.error_tuple_variant_as_struct_pat(pat, fields, variant) {
1364 (Some(mut err), None) => {
1367 (None, None) if let Some(mut err) =
1368 self.error_tuple_variant_index_shorthand(variant, pat, fields) =>
1377 fn error_tuple_variant_index_shorthand(
1379 variant: &VariantDef,
1381 fields: &[hir::PatField<'_>],
1382 ) -> Option<DiagnosticBuilder<'_, ErrorGuaranteed>> {
1383 // if this is a tuple struct, then all field names will be numbers
1384 // so if any fields in a struct pattern use shorthand syntax, they will
1385 // be invalid identifiers (for example, Foo { 0, 1 }).
1386 if let (CtorKind::Fn, PatKind::Struct(qpath, field_patterns, ..)) =
1387 (variant.ctor_kind, &pat.kind)
1389 let has_shorthand_field_name = field_patterns.iter().any(|field| field.is_shorthand);
1390 if has_shorthand_field_name {
1391 let path = rustc_hir_pretty::to_string(rustc_hir_pretty::NO_ANN, |s| {
1392 s.print_qpath(qpath, false)
1394 let mut err = struct_span_err!(
1398 "tuple variant `{}` written as struct variant",
1401 err.span_suggestion_verbose(
1402 qpath.span().shrink_to_hi().to(pat.span.shrink_to_hi()),
1403 "use the tuple variant pattern syntax instead",
1404 format!("({})", self.get_suggested_tuple_struct_pattern(fields, variant)),
1405 Applicability::MaybeIncorrect,
1413 fn error_foreign_non_exhaustive_spat(&self, pat: &Pat<'_>, descr: &str, no_fields: bool) {
1414 let sess = self.tcx.sess;
1415 let sm = sess.source_map();
1416 let sp_brace = sm.end_point(pat.span);
1417 let sp_comma = sm.end_point(pat.span.with_hi(sp_brace.hi()));
1418 let sugg = if no_fields || sp_brace != sp_comma { ".. }" } else { ", .. }" };
1420 let mut err = struct_span_err!(
1424 "`..` required with {} marked as non-exhaustive",
1427 err.span_suggestion_verbose(
1429 "add `..` at the end of the field list to ignore all other fields",
1431 Applicability::MachineApplicable,
1436 fn error_field_already_bound(&self, span: Span, ident: Ident, other_field: Span) {
1441 "field `{}` bound multiple times in the pattern",
1444 .span_label(span, format!("multiple uses of `{}` in pattern", ident))
1445 .span_label(other_field, format!("first use of `{}`", ident))
1449 fn error_inexistent_fields(
1452 inexistent_fields: &[&hir::PatField<'tcx>],
1453 unmentioned_fields: &mut Vec<(&'tcx ty::FieldDef, Ident)>,
1454 variant: &ty::VariantDef,
1455 substs: &'tcx ty::List<ty::subst::GenericArg<'tcx>>,
1456 ) -> DiagnosticBuilder<'tcx, ErrorGuaranteed> {
1458 let (field_names, t, plural) = if inexistent_fields.len() == 1 {
1459 (format!("a field named `{}`", inexistent_fields[0].ident), "this", "")
1466 .map(|field| format!("`{}`", field.ident))
1467 .collect::<Vec<String>>()
1474 let spans = inexistent_fields.iter().map(|field| field.ident.span).collect::<Vec<_>>();
1475 let mut err = struct_span_err!(
1479 "{} `{}` does not have {}",
1481 tcx.def_path_str(variant.def_id),
1484 if let Some(pat_field) = inexistent_fields.last() {
1486 pat_field.ident.span,
1488 "{} `{}` does not have {} field{}",
1490 tcx.def_path_str(variant.def_id),
1496 if unmentioned_fields.len() == 1 {
1498 unmentioned_fields.iter().map(|(_, field)| field.name).collect::<Vec<_>>();
1499 let suggested_name = find_best_match_for_name(&input, pat_field.ident.name, None);
1500 if let Some(suggested_name) = suggested_name {
1501 err.span_suggestion(
1502 pat_field.ident.span,
1503 "a field with a similar name exists",
1504 suggested_name.to_string(),
1505 Applicability::MaybeIncorrect,
1508 // When we have a tuple struct used with struct we don't want to suggest using
1509 // the (valid) struct syntax with numeric field names. Instead we want to
1510 // suggest the expected syntax. We infer that this is the case by parsing the
1511 // `Ident` into an unsized integer. The suggestion will be emitted elsewhere in
1512 // `smart_resolve_context_dependent_help`.
1513 if suggested_name.to_ident_string().parse::<usize>().is_err() {
1514 // We don't want to throw `E0027` in case we have thrown `E0026` for them.
1515 unmentioned_fields.retain(|&(_, x)| x.name != suggested_name);
1517 } else if inexistent_fields.len() == 1 {
1518 match pat_field.pat.kind {
1520 if !self.can_coerce(
1521 self.typeck_results.borrow().expr_ty(expr),
1523 unmentioned_fields[0].1.span,
1524 unmentioned_fields[0].0,
1529 let unmentioned_field = unmentioned_fields[0].1.name;
1530 err.span_suggestion_short(
1531 pat_field.ident.span,
1533 "`{}` has a field named `{}`",
1534 tcx.def_path_str(variant.def_id),
1537 unmentioned_field.to_string(),
1538 Applicability::MaybeIncorrect,
1545 if tcx.sess.teach(&err.get_code().unwrap()) {
1547 "This error indicates that a struct pattern attempted to \
1548 extract a non-existent field from a struct. Struct fields \
1549 are identified by the name used before the colon : so struct \
1550 patterns should resemble the declaration of the struct type \
1552 If you are using shorthand field patterns but want to refer \
1553 to the struct field by a different name, you should rename \
1560 fn error_tuple_variant_as_struct_pat(
1563 fields: &'tcx [hir::PatField<'tcx>],
1564 variant: &ty::VariantDef,
1565 ) -> Option<DiagnosticBuilder<'tcx, ErrorGuaranteed>> {
1566 if let (CtorKind::Fn, PatKind::Struct(qpath, ..)) = (variant.ctor_kind, &pat.kind) {
1567 let path = rustc_hir_pretty::to_string(rustc_hir_pretty::NO_ANN, |s| {
1568 s.print_qpath(qpath, false)
1570 let mut err = struct_span_err!(
1574 "tuple variant `{}` written as struct variant",
1577 let (sugg, appl) = if fields.len() == variant.fields.len() {
1579 self.get_suggested_tuple_struct_pattern(fields, variant),
1580 Applicability::MachineApplicable,
1584 variant.fields.iter().map(|_| "_").collect::<Vec<&str>>().join(", "),
1585 Applicability::MaybeIncorrect,
1588 err.span_suggestion_verbose(
1589 qpath.span().shrink_to_hi().to(pat.span.shrink_to_hi()),
1590 "use the tuple variant pattern syntax instead",
1591 format!("({})", sugg),
1599 fn get_suggested_tuple_struct_pattern(
1601 fields: &[hir::PatField<'_>],
1602 variant: &VariantDef,
1604 let variant_field_idents =
1605 variant.fields.iter().map(|f| f.ident(self.tcx)).collect::<Vec<Ident>>();
1609 match self.tcx.sess.source_map().span_to_snippet(field.pat.span) {
1611 // Field names are numbers, but numbers
1612 // are not valid identifiers
1613 if variant_field_idents.contains(&field.ident) {
1619 Err(_) => rustc_hir_pretty::to_string(rustc_hir_pretty::NO_ANN, |s| {
1620 s.print_pat(field.pat)
1624 .collect::<Vec<String>>()
1628 /// Returns a diagnostic reporting a struct pattern which is missing an `..` due to
1629 /// inaccessible fields.
1632 /// error: pattern requires `..` due to inaccessible fields
1633 /// --> src/main.rs:10:9
1635 /// LL | let foo::Foo {} = foo::Foo::default();
1638 /// help: add a `..`
1640 /// LL | let foo::Foo { .. } = foo::Foo::default();
1643 fn error_no_accessible_fields(
1646 fields: &'tcx [hir::PatField<'tcx>],
1647 ) -> DiagnosticBuilder<'tcx, ErrorGuaranteed> {
1651 .struct_span_err(pat.span, "pattern requires `..` due to inaccessible fields");
1653 if let Some(field) = fields.last() {
1654 err.span_suggestion_verbose(
1655 field.span.shrink_to_hi(),
1656 "ignore the inaccessible and unused fields",
1658 Applicability::MachineApplicable,
1661 let qpath_span = if let PatKind::Struct(qpath, ..) = &pat.kind {
1664 bug!("`error_no_accessible_fields` called on non-struct pattern");
1667 // Shrink the span to exclude the `foo:Foo` in `foo::Foo { }`.
1668 let span = pat.span.with_lo(qpath_span.shrink_to_hi().hi());
1669 err.span_suggestion_verbose(
1671 "ignore the inaccessible and unused fields",
1672 " { .. }".to_string(),
1673 Applicability::MachineApplicable,
1679 /// Report that a pattern for a `#[non_exhaustive]` struct marked with `non_exhaustive_omitted_patterns`
1680 /// is not exhaustive enough.
1682 /// Nb: the partner lint for enums lives in `compiler/rustc_mir_build/src/thir/pattern/usefulness.rs`.
1683 fn lint_non_exhaustive_omitted_patterns(
1686 unmentioned_fields: &[(&ty::FieldDef, Ident)],
1689 fn joined_uncovered_patterns(witnesses: &[&Ident]) -> String {
1690 const LIMIT: usize = 3;
1693 [witness] => format!("`{}`", witness),
1694 [head @ .., tail] if head.len() < LIMIT => {
1695 let head: Vec<_> = head.iter().map(<_>::to_string).collect();
1696 format!("`{}` and `{}`", head.join("`, `"), tail)
1699 let (head, tail) = witnesses.split_at(LIMIT);
1700 let head: Vec<_> = head.iter().map(<_>::to_string).collect();
1701 format!("`{}` and {} more", head.join("`, `"), tail.len())
1705 let joined_patterns = joined_uncovered_patterns(
1706 &unmentioned_fields.iter().map(|(_, i)| i).collect::<Vec<_>>(),
1709 self.tcx.struct_span_lint_hir(NON_EXHAUSTIVE_OMITTED_PATTERNS, pat.hir_id, pat.span, |build| {
1710 let mut lint = build.build("some fields are not explicitly listed");
1711 lint.span_label(pat.span, format!("field{} {} not listed", rustc_errors::pluralize!(unmentioned_fields.len()), joined_patterns));
1714 "ensure that all fields are mentioned explicitly by adding the suggested fields",
1717 "the pattern is of type `{}` and the `non_exhaustive_omitted_patterns` attribute was found",
1724 /// Returns a diagnostic reporting a struct pattern which does not mention some fields.
1727 /// error[E0027]: pattern does not mention field `bar`
1728 /// --> src/main.rs:15:9
1730 /// LL | let foo::Foo {} = foo::Foo::new();
1731 /// | ^^^^^^^^^^^ missing field `bar`
1733 fn error_unmentioned_fields(
1736 unmentioned_fields: &[(&ty::FieldDef, Ident)],
1737 have_inaccessible_fields: bool,
1738 fields: &'tcx [hir::PatField<'tcx>],
1739 ) -> DiagnosticBuilder<'tcx, ErrorGuaranteed> {
1740 let inaccessible = if have_inaccessible_fields { " and inaccessible fields" } else { "" };
1741 let field_names = if unmentioned_fields.len() == 1 {
1742 format!("field `{}`{}", unmentioned_fields[0].1, inaccessible)
1744 let fields = unmentioned_fields
1746 .map(|(_, name)| format!("`{}`", name))
1747 .collect::<Vec<String>>()
1749 format!("fields {}{}", fields, inaccessible)
1751 let mut err = struct_span_err!(
1755 "pattern does not mention {}",
1758 err.span_label(pat.span, format!("missing {}", field_names));
1759 let len = unmentioned_fields.len();
1760 let (prefix, postfix, sp) = match fields {
1761 [] => match &pat.kind {
1762 PatKind::Struct(path, [], false) => {
1763 (" { ", " }", path.span().shrink_to_hi().until(pat.span.shrink_to_hi()))
1768 // Account for last field having a trailing comma or parse recovery at the tail of
1769 // the pattern to avoid invalid suggestion (#78511).
1770 let tail = field.span.shrink_to_hi().with_hi(pat.span.hi());
1772 PatKind::Struct(..) => (", ", " }", tail),
1777 err.span_suggestion(
1780 "include the missing field{} in the pattern{}",
1782 if have_inaccessible_fields { " and ignore the inaccessible fields" } else { "" }
1789 .map(|(_, name)| name.to_string())
1790 .collect::<Vec<_>>()
1792 if have_inaccessible_fields { ", .." } else { "" },
1795 Applicability::MachineApplicable,
1797 err.span_suggestion(
1800 "if you don't care about {these} missing field{s}, you can explicitly ignore {them}",
1801 these = pluralize!("this", len),
1802 s = pluralize!(len),
1803 them = if len == 1 { "it" } else { "them" },
1805 format!("{}..{}", prefix, postfix),
1806 Applicability::MachineApplicable,
1814 inner: &'tcx Pat<'tcx>,
1816 def_bm: BindingMode,
1820 let (box_ty, inner_ty) = if self.check_dereferenceable(span, expected, inner) {
1821 // Here, `demand::subtype` is good enough, but I don't
1822 // think any errors can be introduced by using `demand::eqtype`.
1823 let inner_ty = self.next_ty_var(TypeVariableOrigin {
1824 kind: TypeVariableOriginKind::TypeInference,
1827 let box_ty = tcx.mk_box(inner_ty);
1828 self.demand_eqtype_pat(span, expected, box_ty, ti);
1831 let err = tcx.ty_error();
1834 self.check_pat(inner, inner_ty, def_bm, ti);
1840 pat: &'tcx Pat<'tcx>,
1841 inner: &'tcx Pat<'tcx>,
1842 mutbl: hir::Mutability,
1844 def_bm: BindingMode,
1848 let expected = self.shallow_resolve(expected);
1849 let (rptr_ty, inner_ty) = if self.check_dereferenceable(pat.span, expected, inner) {
1850 // `demand::subtype` would be good enough, but using `eqtype` turns
1851 // out to be equally general. See (note_1) for details.
1853 // Take region, inner-type from expected type if we can,
1854 // to avoid creating needless variables. This also helps with
1855 // the bad interactions of the given hack detailed in (note_1).
1856 debug!("check_pat_ref: expected={:?}", expected);
1857 match *expected.kind() {
1858 ty::Ref(_, r_ty, r_mutbl) if r_mutbl == mutbl => (expected, r_ty),
1860 let inner_ty = self.next_ty_var(TypeVariableOrigin {
1861 kind: TypeVariableOriginKind::TypeInference,
1864 let rptr_ty = self.new_ref_ty(pat.span, mutbl, inner_ty);
1865 debug!("check_pat_ref: demanding {:?} = {:?}", expected, rptr_ty);
1866 let err = self.demand_eqtype_pat_diag(pat.span, expected, rptr_ty, ti);
1868 // Look for a case like `fn foo(&foo: u32)` and suggest
1869 // `fn foo(foo: &u32)`
1870 if let Some(mut err) = err {
1871 self.borrow_pat_suggestion(&mut err, pat, inner, expected);
1878 let err = tcx.ty_error();
1881 self.check_pat(inner, inner_ty, def_bm, TopInfo { parent_pat: Some(pat), ..ti });
1885 /// Create a reference type with a fresh region variable.
1886 fn new_ref_ty(&self, span: Span, mutbl: hir::Mutability, ty: Ty<'tcx>) -> Ty<'tcx> {
1887 let region = self.next_region_var(infer::PatternRegion(span));
1888 let mt = ty::TypeAndMut { ty, mutbl };
1889 self.tcx.mk_ref(region, mt)
1892 /// Type check a slice pattern.
1894 /// Syntactically, these look like `[pat_0, ..., pat_n]`.
1895 /// Semantically, we are type checking a pattern with structure:
1897 /// [before_0, ..., before_n, (slice, after_0, ... after_n)?]
1899 /// The type of `slice`, if it is present, depends on the `expected` type.
1900 /// If `slice` is missing, then so is `after_i`.
1901 /// If `slice` is present, it can still represent 0 elements.
1905 before: &'tcx [Pat<'tcx>],
1906 slice: Option<&'tcx Pat<'tcx>>,
1907 after: &'tcx [Pat<'tcx>],
1909 def_bm: BindingMode,
1912 let expected = self.structurally_resolved_type(span, expected);
1913 let (element_ty, opt_slice_ty, inferred) = match *expected.kind() {
1914 // An array, so we might have something like `let [a, b, c] = [0, 1, 2];`.
1915 ty::Array(element_ty, len) => {
1916 let min = before.len() as u64 + after.len() as u64;
1917 let (opt_slice_ty, expected) =
1918 self.check_array_pat_len(span, element_ty, expected, slice, len, min);
1919 // `opt_slice_ty.is_none()` => `slice.is_none()`.
1920 // Note, though, that opt_slice_ty could be `Some(error_ty)`.
1921 assert!(opt_slice_ty.is_some() || slice.is_none());
1922 (element_ty, opt_slice_ty, expected)
1924 ty::Slice(element_ty) => (element_ty, Some(expected), expected),
1925 // The expected type must be an array or slice, but was neither, so error.
1927 if !expected.references_error() {
1928 self.error_expected_array_or_slice(span, expected, ti);
1930 let err = self.tcx.ty_error();
1931 (err, Some(err), err)
1935 // Type check all the patterns before `slice`.
1937 self.check_pat(elt, element_ty, def_bm, ti);
1939 // Type check the `slice`, if present, against its expected type.
1940 if let Some(slice) = slice {
1941 self.check_pat(slice, opt_slice_ty.unwrap(), def_bm, ti);
1943 // Type check the elements after `slice`, if present.
1945 self.check_pat(elt, element_ty, def_bm, ti);
1950 /// Type check the length of an array pattern.
1952 /// Returns both the type of the variable length pattern (or `None`), and the potentially
1953 /// inferred array type. We only return `None` for the slice type if `slice.is_none()`.
1954 fn check_array_pat_len(
1957 element_ty: Ty<'tcx>,
1959 slice: Option<&'tcx Pat<'tcx>>,
1960 len: ty::Const<'tcx>,
1962 ) -> (Option<Ty<'tcx>>, Ty<'tcx>) {
1963 if let Some(len) = len.try_eval_usize(self.tcx, self.param_env) {
1964 // Now we know the length...
1965 if slice.is_none() {
1966 // ...and since there is no variable-length pattern,
1967 // we require an exact match between the number of elements
1968 // in the array pattern and as provided by the matched type.
1970 return (None, arr_ty);
1973 self.error_scrutinee_inconsistent_length(span, min_len, len);
1974 } else if let Some(pat_len) = len.checked_sub(min_len) {
1975 // The variable-length pattern was there,
1976 // so it has an array type with the remaining elements left as its size...
1977 return (Some(self.tcx.mk_array(element_ty, pat_len)), arr_ty);
1979 // ...however, in this case, there were no remaining elements.
1980 // That is, the slice pattern requires more than the array type offers.
1981 self.error_scrutinee_with_rest_inconsistent_length(span, min_len, len);
1983 } else if slice.is_none() {
1984 // We have a pattern with a fixed length,
1985 // which we can use to infer the length of the array.
1986 let updated_arr_ty = self.tcx.mk_array(element_ty, min_len);
1987 self.demand_eqtype(span, updated_arr_ty, arr_ty);
1988 return (None, updated_arr_ty);
1990 // We have a variable-length pattern and don't know the array length.
1991 // This happens if we have e.g.,
1992 // `let [a, b, ..] = arr` where `arr: [T; N]` where `const N: usize`.
1993 self.error_scrutinee_unfixed_length(span);
1996 // If we get here, we must have emitted an error.
1997 (Some(self.tcx.ty_error()), arr_ty)
2000 fn error_scrutinee_inconsistent_length(&self, span: Span, min_len: u64, size: u64) {
2005 "pattern requires {} element{} but array has {}",
2007 pluralize!(min_len),
2010 .span_label(span, format!("expected {} element{}", size, pluralize!(size)))
2014 fn error_scrutinee_with_rest_inconsistent_length(&self, span: Span, min_len: u64, size: u64) {
2019 "pattern requires at least {} element{} but array has {}",
2021 pluralize!(min_len),
2026 format!("pattern cannot match array of {} element{}", size, pluralize!(size),),
2031 fn error_scrutinee_unfixed_length(&self, span: Span) {
2036 "cannot pattern-match on an array without a fixed length",
2041 fn error_expected_array_or_slice(&self, span: Span, expected_ty: Ty<'tcx>, ti: TopInfo<'tcx>) {
2042 let mut err = struct_span_err!(
2046 "expected an array or slice, found `{}`",
2049 if let ty::Ref(_, ty, _) = expected_ty.kind() {
2050 if let ty::Array(..) | ty::Slice(..) = ty.kind() {
2051 err.help("the semantics of slice patterns changed recently; see issue #62254");
2053 } else if Autoderef::new(&self.infcx, self.param_env, self.body_id, span, expected_ty, span)
2054 .any(|(ty, _)| matches!(ty.kind(), ty::Slice(..) | ty::Array(..)))
2056 if let (Some(span), true) = (ti.span, ti.origin_expr) {
2057 if let Ok(snippet) = self.tcx.sess.source_map().span_to_snippet(span) {
2058 let applicability = Autoderef::new(
2063 self.resolve_vars_if_possible(ti.expected),
2066 .find_map(|(ty, _)| {
2069 if self.tcx.is_diagnostic_item(sym::Option, adt_def.did())
2070 || self.tcx.is_diagnostic_item(sym::Result, adt_def.did()) =>
2072 // Slicing won't work here, but `.as_deref()` might (issue #91328).
2073 err.span_suggestion(
2075 "consider using `as_deref` here",
2076 format!("{}.as_deref()", snippet),
2077 Applicability::MaybeIncorrect,
2082 ty::Slice(..) | ty::Array(..) => {
2083 Some(Some(Applicability::MachineApplicable))
2089 .unwrap_or(Some(Applicability::MaybeIncorrect));
2091 if let Some(applicability) = applicability {
2092 err.span_suggestion(
2094 "consider slicing here",
2095 format!("{}[..]", snippet),
2102 err.span_label(span, format!("pattern cannot match with input type `{}`", expected_ty));