1 use crate::{FnCtxt, RawTy};
3 use rustc_data_structures::fx::FxHashMap;
5 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, TypeVisitable};
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, DUMMY_SP};
22 use rustc_trait_selection::traits::{ObligationCause, Pattern};
26 use std::collections::hash_map::Entry::{Occupied, Vacant};
28 use super::report_unexpected_variant_res;
30 const CANNOT_IMPLICITLY_DEREF_POINTER_TRAIT_OBJ: &str = "\
31 This error indicates that a pointer to a trait type cannot be implicitly dereferenced by a \
32 pattern. Every trait defines a type, but because the size of trait implementors isn't fixed, \
33 this type has no compile-time size. Therefore, all accesses to trait types must be through \
34 pointers. If you encounter this error you should try to avoid dereferencing the pointer.
36 You can read more about trait objects in the Trait Objects section of the Reference: \
37 https://doc.rust-lang.org/reference/types.html#trait-objects";
39 /// Information about the expected type at the top level of type checking a pattern.
41 /// **NOTE:** This is only for use by diagnostics. Do NOT use for type checking logic!
42 #[derive(Copy, Clone)]
43 struct TopInfo<'tcx> {
44 /// The `expected` type at the top level of type checking a pattern.
46 /// Was the origin of the `span` from a scrutinee expression?
48 /// Otherwise there is no scrutinee and it could be e.g. from the type of a formal parameter.
50 /// The span giving rise to the `expected` type, if one could be provided.
52 /// If `origin_expr` is `true`, then this is the span of the scrutinee as in:
54 /// - `match scrutinee { ... }`
55 /// - `let _ = scrutinee;`
57 /// This is used to point to add context in type errors.
58 /// In the following example, `span` corresponds to the `a + b` expression:
61 /// error[E0308]: mismatched types
62 /// --> src/main.rs:L:C
64 /// L | let temp: usize = match a + b {
65 /// | ----- this expression has type `usize`
66 /// L | Ok(num) => num,
67 /// | ^^^^^^^ expected `usize`, found enum `std::result::Result`
69 /// = note: expected type `usize`
70 /// found type `std::result::Result<_, _>`
75 impl<'tcx> FnCtxt<'_, 'tcx> {
76 fn pattern_cause(&self, ti: TopInfo<'tcx>, cause_span: Span) -> ObligationCause<'tcx> {
77 let code = Pattern { span: ti.span, root_ty: ti.expected, origin_expr: ti.origin_expr };
78 self.cause(cause_span, code)
81 fn demand_eqtype_pat_diag(
87 ) -> Option<DiagnosticBuilder<'tcx, ErrorGuaranteed>> {
88 self.demand_eqtype_with_origin(&self.pattern_cause(ti, cause_span), expected, actual)
98 if let Some(mut err) = self.demand_eqtype_pat_diag(cause_span, expected, actual, ti) {
104 const INITIAL_BM: BindingMode = BindingMode::BindByValue(hir::Mutability::Not);
106 /// Mode for adjusting the expected type and binding mode.
108 /// Peel off all immediate reference types.
110 /// Reset binding mode to the initial mode.
112 /// Pass on the input binding mode and expected type.
116 impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
117 /// Type check the given top level pattern against the `expected` type.
119 /// If a `Some(span)` is provided and `origin_expr` holds,
120 /// then the `span` represents the scrutinee's span.
121 /// The scrutinee is found in e.g. `match scrutinee { ... }` and `let pat = scrutinee;`.
123 /// Otherwise, `Some(span)` represents the span of a type expression
124 /// which originated the `expected` type.
125 pub fn check_pat_top(
127 pat: &'tcx Pat<'tcx>,
132 let info = TopInfo { expected, origin_expr, span };
133 self.check_pat(pat, expected, INITIAL_BM, info);
136 /// Type check the given `pat` against the `expected` type
137 /// with the provided `def_bm` (default binding mode).
139 /// Outside of this module, `check_pat_top` should always be used.
140 /// Conversely, inside this module, `check_pat_top` should never be used.
141 #[instrument(level = "debug", skip(self, ti))]
144 pat: &'tcx Pat<'tcx>,
149 let path_res = match &pat.kind {
150 PatKind::Path(qpath) => {
151 Some(self.resolve_ty_and_res_fully_qualified_call(qpath, pat.hir_id, pat.span))
155 let adjust_mode = self.calc_adjust_mode(pat, path_res.map(|(res, ..)| res));
156 let (expected, def_bm) = self.calc_default_binding_mode(pat, expected, def_bm, adjust_mode);
158 let ty = match pat.kind {
159 PatKind::Wild => expected,
160 PatKind::Lit(lt) => self.check_pat_lit(pat.span, lt, expected, ti),
161 PatKind::Range(lhs, rhs, _) => self.check_pat_range(pat.span, lhs, rhs, expected, ti),
162 PatKind::Binding(ba, var_id, _, sub) => {
163 self.check_pat_ident(pat, ba, var_id, sub, expected, def_bm, ti)
165 PatKind::TupleStruct(ref qpath, subpats, ddpos) => {
166 self.check_pat_tuple_struct(pat, qpath, subpats, ddpos, expected, def_bm, ti)
168 PatKind::Path(ref qpath) => {
169 self.check_pat_path(pat, qpath, path_res.unwrap(), expected, ti)
171 PatKind::Struct(ref qpath, fields, has_rest_pat) => {
172 self.check_pat_struct(pat, qpath, fields, has_rest_pat, expected, def_bm, ti)
174 PatKind::Or(pats) => {
176 self.check_pat(pat, expected, def_bm, ti);
180 PatKind::Tuple(elements, ddpos) => {
181 self.check_pat_tuple(pat.span, elements, ddpos, expected, def_bm, ti)
183 PatKind::Box(inner) => self.check_pat_box(pat.span, inner, expected, def_bm, ti),
184 PatKind::Ref(inner, mutbl) => {
185 self.check_pat_ref(pat, inner, mutbl, expected, def_bm, ti)
187 PatKind::Slice(before, slice, after) => {
188 self.check_pat_slice(pat.span, before, slice, after, expected, def_bm, ti)
192 self.write_ty(pat.hir_id, ty);
194 // (note_1): In most of the cases where (note_1) is referenced
195 // (literals and constants being the exception), we relate types
196 // using strict equality, even though subtyping would be sufficient.
197 // There are a few reasons for this, some of which are fairly subtle
198 // and which cost me (nmatsakis) an hour or two debugging to remember,
199 // so I thought I'd write them down this time.
201 // 1. There is no loss of expressiveness here, though it does
202 // cause some inconvenience. What we are saying is that the type
203 // of `x` becomes *exactly* what is expected. This can cause unnecessary
204 // errors in some cases, such as this one:
207 // fn foo<'x>(x: &'x i32) {
214 // The reason we might get an error is that `z` might be
215 // assigned a type like `&'x i32`, and then we would have
216 // a problem when we try to assign `&a` to `z`, because
217 // the lifetime of `&a` (i.e., the enclosing block) is
218 // shorter than `'x`.
220 // HOWEVER, this code works fine. The reason is that the
221 // expected type here is whatever type the user wrote, not
222 // the initializer's type. In this case the user wrote
223 // nothing, so we are going to create a type variable `Z`.
224 // Then we will assign the type of the initializer (`&'x i32`)
225 // as a subtype of `Z`: `&'x i32 <: Z`. And hence we
226 // will instantiate `Z` as a type `&'0 i32` where `'0` is
227 // a fresh region variable, with the constraint that `'x : '0`.
228 // So basically we're all set.
230 // Note that there are two tests to check that this remains true
231 // (`regions-reassign-{match,let}-bound-pointer.rs`).
233 // 2. Things go horribly wrong if we use subtype. The reason for
234 // THIS is a fairly subtle case involving bound regions. See the
235 // `givens` field in `region_constraints`, as well as the test
236 // `regions-relate-bound-regions-on-closures-to-inference-variables.rs`,
237 // for details. Short version is that we must sometimes detect
238 // relationships between specific region variables and regions
239 // bound in a closure signature, and that detection gets thrown
240 // off when we substitute fresh region variables here to enable
244 /// Compute the new expected type and default binding mode from the old ones
245 /// as well as the pattern form we are currently checking.
246 fn calc_default_binding_mode(
248 pat: &'tcx Pat<'tcx>,
251 adjust_mode: AdjustMode,
252 ) -> (Ty<'tcx>, BindingMode) {
254 AdjustMode::Pass => (expected, def_bm),
255 AdjustMode::Reset => (expected, INITIAL_BM),
256 AdjustMode::Peel => self.peel_off_references(pat, expected, def_bm),
260 /// How should the binding mode and expected type be adjusted?
262 /// When the pattern is a path pattern, `opt_path_res` must be `Some(res)`.
263 fn calc_adjust_mode(&self, pat: &'tcx Pat<'tcx>, opt_path_res: Option<Res>) -> AdjustMode {
264 // When we perform destructuring assignment, we disable default match bindings, which are
265 // unintuitive in this context.
266 if !pat.default_binding_modes {
267 return AdjustMode::Reset;
270 // Type checking these product-like types successfully always require
271 // that the expected type be of those types and not reference types.
273 | PatKind::TupleStruct(..)
277 | PatKind::Slice(..) => AdjustMode::Peel,
278 // String and byte-string literals result in types `&str` and `&[u8]` respectively.
279 // All other literals result in non-reference types.
280 // As a result, we allow `if let 0 = &&0 {}` but not `if let "foo" = &&"foo {}`.
282 // Call `resolve_vars_if_possible` here for inline const blocks.
283 PatKind::Lit(lt) => match self.resolve_vars_if_possible(self.check_expr(lt)).kind() {
284 ty::Ref(..) => AdjustMode::Pass,
285 _ => AdjustMode::Peel,
287 PatKind::Path(_) => match opt_path_res.unwrap() {
288 // These constants can be of a reference type, e.g. `const X: &u8 = &0;`.
289 // Peeling the reference types too early will cause type checking failures.
290 // Although it would be possible to *also* peel the types of the constants too.
291 Res::Def(DefKind::Const | DefKind::AssocConst, _) => AdjustMode::Pass,
292 // In the `ValueNS`, we have `SelfCtor(..) | Ctor(_, Const), _)` remaining which
293 // could successfully compile. The former being `Self` requires a unit struct.
294 // In either case, and unlike constants, the pattern itself cannot be
295 // a reference type wherefore peeling doesn't give up any expressiveness.
296 _ => AdjustMode::Peel,
298 // When encountering a `& mut? pat` pattern, reset to "by value".
299 // This is so that `x` and `y` here are by value, as they appear to be:
302 // match &(&22, &44) {
308 PatKind::Ref(..) => AdjustMode::Reset,
309 // A `_` pattern works with any expected type, so there's no need to do anything.
311 // Bindings also work with whatever the expected type is,
312 // and moreover if we peel references off, that will give us the wrong binding type.
313 // Also, we can have a subpattern `binding @ pat`.
314 // Each side of the `@` should be treated independently (like with OR-patterns).
315 | PatKind::Binding(..)
316 // An OR-pattern just propagates to each individual alternative.
317 // This is maximally flexible, allowing e.g., `Some(mut x) | &Some(mut x)`.
318 // In that example, `Some(mut x)` results in `Peel` whereas `&Some(mut x)` in `Reset`.
319 | PatKind::Or(_) => AdjustMode::Pass,
323 /// Peel off as many immediately nested `& mut?` from the expected type as possible
324 /// and return the new expected type and binding default binding mode.
325 /// The adjustments vector, if non-empty is stored in a table.
326 fn peel_off_references(
328 pat: &'tcx Pat<'tcx>,
330 mut def_bm: BindingMode,
331 ) -> (Ty<'tcx>, BindingMode) {
332 let mut expected = self.resolve_vars_with_obligations(expected);
334 // Peel off as many `&` or `&mut` from the scrutinee type as possible. For example,
335 // for `match &&&mut Some(5)` the loop runs three times, aborting when it reaches
336 // the `Some(5)` which is not of type Ref.
338 // For each ampersand peeled off, update the binding mode and push the original
339 // type into the adjustments vector.
341 // See the examples in `ui/match-defbm*.rs`.
342 let mut pat_adjustments = vec![];
343 while let ty::Ref(_, inner_ty, inner_mutability) = *expected.kind() {
344 debug!("inspecting {:?}", expected);
346 debug!("current discriminant is Ref, inserting implicit deref");
347 // Preserve the reference type. We'll need it later during THIR lowering.
348 pat_adjustments.push(expected);
351 def_bm = ty::BindByReference(match def_bm {
352 // If default binding mode is by value, make it `ref` or `ref mut`
353 // (depending on whether we observe `&` or `&mut`).
355 // When `ref mut`, stay a `ref mut` (on `&mut`) or downgrade to `ref` (on `&`).
356 ty::BindByReference(hir::Mutability::Mut) => inner_mutability,
357 // Once a `ref`, always a `ref`.
358 // This is because a `& &mut` cannot mutate the underlying value.
359 ty::BindByReference(m @ hir::Mutability::Not) => m,
363 if !pat_adjustments.is_empty() {
364 debug!("default binding mode is now {:?}", def_bm);
368 .pat_adjustments_mut()
369 .insert(pat.hir_id, pat_adjustments);
378 lt: &hir::Expr<'tcx>,
382 // We've already computed the type above (when checking for a non-ref pat),
383 // so avoid computing it again.
384 let ty = self.node_ty(lt.hir_id);
386 // Byte string patterns behave the same way as array patterns
387 // They can denote both statically and dynamically-sized byte arrays.
389 if let hir::ExprKind::Lit(Spanned { node: ast::LitKind::ByteStr(..), .. }) = lt.kind {
390 let expected = self.structurally_resolved_type(span, expected);
391 if let ty::Ref(_, inner_ty, _) = expected.kind()
392 && matches!(inner_ty.kind(), ty::Slice(_))
395 trace!(?lt.hir_id.local_id, "polymorphic byte string lit");
398 .treat_byte_string_as_slice
399 .insert(lt.hir_id.local_id);
400 pat_ty = tcx.mk_imm_ref(tcx.lifetimes.re_static, tcx.mk_slice(tcx.types.u8));
404 if self.tcx.features().string_deref_patterns && let hir::ExprKind::Lit(Spanned { node: ast::LitKind::Str(..), .. }) = lt.kind {
406 let expected = self.resolve_vars_if_possible(expected);
407 pat_ty = match expected.kind() {
408 ty::Adt(def, _) if Some(def.did()) == tcx.lang_items().string() => expected,
409 ty::Str => tcx.mk_static_str(),
414 // Somewhat surprising: in this case, the subtyping relation goes the
415 // opposite way as the other cases. Actually what we really want is not
416 // a subtyping relation at all but rather that there exists a LUB
417 // (so that they can be compared). However, in practice, constants are
418 // always scalars or strings. For scalars subtyping is irrelevant,
419 // and for strings `ty` is type is `&'static str`, so if we say that
421 // &'static str <: expected
423 // then that's equivalent to there existing a LUB.
424 let cause = self.pattern_cause(ti, span);
425 if let Some(mut err) = self.demand_suptype_with_origin(&cause, expected, pat_ty) {
429 // In the case of `if`- and `while`-expressions we've already checked
430 // that `scrutinee: bool`. We know that the pattern is `true`,
431 // so an error here would be a duplicate and from the wrong POV.
432 s.is_desugaring(DesugaringKind::CondTemporary)
444 lhs: Option<&'tcx hir::Expr<'tcx>>,
445 rhs: Option<&'tcx hir::Expr<'tcx>>,
449 let calc_side = |opt_expr: Option<&'tcx hir::Expr<'tcx>>| match opt_expr {
452 let ty = self.check_expr(expr);
453 // Check that the end-point is possibly of numeric or char type.
454 // The early check here is not for correctness, but rather better
455 // diagnostics (e.g. when `&str` is being matched, `expected` will
456 // be peeled to `str` while ty here is still `&str`, if we don't
457 // err early here, a rather confusing unification error will be
460 !(ty.is_numeric() || ty.is_char() || ty.is_ty_var() || ty.references_error());
461 Some((fail, ty, expr.span))
464 let mut lhs = calc_side(lhs);
465 let mut rhs = calc_side(rhs);
467 if let (Some((true, ..)), _) | (_, Some((true, ..))) = (lhs, rhs) {
468 // There exists a side that didn't meet our criteria that the end-point
469 // be of a numeric or char type, as checked in `calc_side` above.
470 self.emit_err_pat_range(span, lhs, rhs);
471 return self.tcx.ty_error();
474 // Unify each side with `expected`.
475 // Subtyping doesn't matter here, as the value is some kind of scalar.
476 let demand_eqtype = |x: &mut _, y| {
477 if let Some((ref mut fail, x_ty, x_span)) = *x
478 && let Some(mut err) = self.demand_eqtype_pat_diag(x_span, expected, x_ty, ti)
480 if let Some((_, y_ty, y_span)) = y {
481 self.endpoint_has_type(&mut err, y_span, y_ty);
487 demand_eqtype(&mut lhs, rhs);
488 demand_eqtype(&mut rhs, lhs);
490 if let (Some((true, ..)), _) | (_, Some((true, ..))) = (lhs, rhs) {
491 return self.tcx.ty_error();
494 // Find the unified type and check if it's of numeric or char type again.
495 // This check is needed if both sides are inference variables.
496 // We require types to be resolved here so that we emit inference failure
497 // rather than "_ is not a char or numeric".
498 let ty = self.structurally_resolved_type(span, expected);
499 if !(ty.is_numeric() || ty.is_char() || ty.references_error()) {
500 if let Some((ref mut fail, _, _)) = lhs {
503 if let Some((ref mut fail, _, _)) = rhs {
506 self.emit_err_pat_range(span, lhs, rhs);
507 return self.tcx.ty_error();
512 fn endpoint_has_type(&self, err: &mut Diagnostic, span: Span, ty: Ty<'_>) {
513 if !ty.references_error() {
514 err.span_label(span, &format!("this is of type `{}`", ty));
518 fn emit_err_pat_range(
521 lhs: Option<(bool, Ty<'tcx>, Span)>,
522 rhs: Option<(bool, Ty<'tcx>, Span)>,
524 let span = match (lhs, rhs) {
525 (Some((true, ..)), Some((true, ..))) => span,
526 (Some((true, _, sp)), _) => sp,
527 (_, Some((true, _, sp))) => sp,
528 _ => span_bug!(span, "emit_err_pat_range: no side failed or exists but still error?"),
530 let mut err = struct_span_err!(
534 "only `char` and numeric types are allowed in range patterns"
537 let ty = self.resolve_vars_if_possible(ty);
538 format!("this is of type `{}` but it should be `char` or numeric", ty)
540 let mut one_side_err = |first_span, first_ty, second: Option<(bool, Ty<'tcx>, Span)>| {
541 err.span_label(first_span, &msg(first_ty));
542 if let Some((_, ty, sp)) = second {
543 let ty = self.resolve_vars_if_possible(ty);
544 self.endpoint_has_type(&mut err, sp, ty);
548 (Some((true, lhs_ty, lhs_sp)), Some((true, rhs_ty, rhs_sp))) => {
549 err.span_label(lhs_sp, &msg(lhs_ty));
550 err.span_label(rhs_sp, &msg(rhs_ty));
552 (Some((true, lhs_ty, lhs_sp)), rhs) => one_side_err(lhs_sp, lhs_ty, rhs),
553 (lhs, Some((true, rhs_ty, rhs_sp))) => one_side_err(rhs_sp, rhs_ty, lhs),
554 _ => span_bug!(span, "Impossible, verified above."),
556 if (lhs, rhs).references_error() {
557 err.downgrade_to_delayed_bug();
559 if self.tcx.sess.teach(&err.get_code().unwrap()) {
561 "In a match expression, only numbers and characters can be matched \
562 against a range. This is because the compiler checks that the range \
563 is non-empty at compile-time, and is unable to evaluate arbitrary \
564 comparison functions. If you want to capture values of an orderable \
565 type between two end-points, you can use a guard.",
573 pat: &'tcx Pat<'tcx>,
574 ba: hir::BindingAnnotation,
576 sub: Option<&'tcx Pat<'tcx>>,
581 // Determine the binding mode...
583 hir::BindingAnnotation::NONE => def_bm,
584 _ => BindingMode::convert(ba),
586 // ...and store it in a side table:
587 self.inh.typeck_results.borrow_mut().pat_binding_modes_mut().insert(pat.hir_id, bm);
589 debug!("check_pat_ident: pat.hir_id={:?} bm={:?}", pat.hir_id, bm);
591 let local_ty = self.local_ty(pat.span, pat.hir_id).decl_ty;
592 let eq_ty = match bm {
593 ty::BindByReference(mutbl) => {
594 // If the binding is like `ref x | ref mut x`,
595 // then `x` is assigned a value of type `&M T` where M is the
596 // mutability and T is the expected type.
598 // `x` is assigned a value of type `&M T`, hence `&M T <: typeof(x)`
599 // is required. However, we use equality, which is stronger.
600 // See (note_1) for an explanation.
601 self.new_ref_ty(pat.span, mutbl, expected)
603 // Otherwise, the type of x is the expected type `T`.
604 ty::BindByValue(_) => {
605 // As above, `T <: typeof(x)` is required, but we use equality, see (note_1).
609 self.demand_eqtype_pat(pat.span, eq_ty, local_ty, ti);
611 // If there are multiple arms, make sure they all agree on
612 // what the type of the binding `x` ought to be.
613 if var_id != pat.hir_id {
614 self.check_binding_alt_eq_ty(ba, pat.span, var_id, local_ty, ti);
617 if let Some(p) = sub {
618 self.check_pat(p, expected, def_bm, ti);
624 fn check_binding_alt_eq_ty(
626 ba: hir::BindingAnnotation,
632 let var_ty = self.local_ty(span, var_id).decl_ty;
633 if let Some(mut err) = self.demand_eqtype_pat_diag(span, var_ty, ty, ti) {
634 let hir = self.tcx.hir();
635 let var_ty = self.resolve_vars_with_obligations(var_ty);
636 let msg = format!("first introduced with type `{var_ty}` here");
637 err.span_label(hir.span(var_id), msg);
638 let in_match = hir.parent_iter(var_id).any(|(_, n)| {
641 hir::Node::Expr(hir::Expr {
642 kind: hir::ExprKind::Match(.., hir::MatchSource::Normal),
647 let pre = if in_match { "in the same arm, " } else { "" };
648 err.note(&format!("{}a binding must have the same type in all alternatives", pre));
649 self.suggest_adding_missing_ref_or_removing_ref(
653 self.resolve_vars_with_obligations(ty),
660 fn suggest_adding_missing_ref_or_removing_ref(
662 err: &mut Diagnostic,
666 ba: hir::BindingAnnotation,
668 match (expected.kind(), actual.kind(), ba) {
669 (ty::Ref(_, inner_ty, _), _, hir::BindingAnnotation::NONE)
670 if self.can_eq(self.param_env, *inner_ty, actual).is_ok() =>
672 err.span_suggestion_verbose(
674 "consider adding `ref`",
676 Applicability::MaybeIncorrect,
679 (_, ty::Ref(_, inner_ty, _), hir::BindingAnnotation::REF)
680 if self.can_eq(self.param_env, expected, *inner_ty).is_ok() =>
682 err.span_suggestion_verbose(
683 span.with_hi(span.lo() + BytePos(4)),
684 "consider removing `ref`",
686 Applicability::MaybeIncorrect,
693 // Precondition: pat is a Ref(_) pattern
694 fn borrow_pat_suggestion(&self, err: &mut Diagnostic, pat: &Pat<'_>) {
696 if let PatKind::Ref(inner, mutbl) = pat.kind
697 && let PatKind::Binding(_, _, binding, ..) = inner.kind {
698 let binding_parent_id = tcx.hir().parent_id(pat.hir_id);
699 let binding_parent = tcx.hir().get(binding_parent_id);
700 debug!(?inner, ?pat, ?binding_parent);
702 let mutability = match mutbl {
703 ast::Mutability::Mut => "mut",
704 ast::Mutability::Not => "",
707 let mut_var_suggestion = 'block: {
712 let ident_kind = match binding_parent {
713 hir::Node::Param(_) => "parameter",
714 hir::Node::Local(_) => "variable",
715 hir::Node::Arm(_) => "binding",
717 // Provide diagnostics only if the parent pattern is struct-like,
718 // i.e. where `mut binding` makes sense
719 hir::Node::Pat(Pat { kind, .. }) => match kind {
721 | PatKind::TupleStruct(..)
724 | PatKind::Slice(..) => "binding",
727 | PatKind::Binding(..)
732 | PatKind::Range(..) => break 'block None,
735 // Don't provide suggestions in other cases
736 _ => break 'block None,
741 format!("to declare a mutable {ident_kind} use"),
742 format!("mut {binding}"),
747 match binding_parent {
748 // Check that there is explicit type (ie this is not a closure param with inferred type)
749 // so we don't suggest moving something to the type that does not exist
750 hir::Node::Param(hir::Param { ty_span, .. }) if binding.span != *ty_span => {
751 err.multipart_suggestion_verbose(
752 format!("to take parameter `{binding}` by reference, move `&{mutability}` to the type"),
754 (pat.span.until(inner.span), "".to_owned()),
755 (ty_span.shrink_to_lo(), mutbl.ref_prefix_str().to_owned()),
757 Applicability::MachineApplicable
760 if let Some((sp, msg, sugg)) = mut_var_suggestion {
761 err.span_note(sp, format!("{msg}: `{sugg}`"));
764 hir::Node::Pat(pt) if let PatKind::TupleStruct(_, pat_arr, _) = pt.kind => {
765 for i in pat_arr.iter() {
766 if let PatKind::Ref(the_ref, _) = i.kind
767 && let PatKind::Binding(mt, _, ident, _) = the_ref.kind {
768 let hir::BindingAnnotation(_, mtblty) = mt;
769 err.span_suggestion_verbose(
771 format!("consider removing `&{mutability}` from the pattern"),
772 mtblty.prefix_str().to_string() + &ident.name.to_string(),
773 Applicability::MaybeIncorrect,
777 if let Some((sp, msg, sugg)) = mut_var_suggestion {
778 err.span_note(sp, format!("{msg}: `{sugg}`"));
781 hir::Node::Param(_) | hir::Node::Arm(_) | hir::Node::Pat(_) => {
782 // rely on match ergonomics or it might be nested `&&pat`
783 err.span_suggestion_verbose(
784 pat.span.until(inner.span),
785 format!("consider removing `&{mutability}` from the pattern"),
787 Applicability::MaybeIncorrect,
790 if let Some((sp, msg, sugg)) = mut_var_suggestion {
791 err.span_note(sp, format!("{msg}: `{sugg}`"));
794 _ if let Some((sp, msg, sugg)) = mut_var_suggestion => {
795 err.span_suggestion(sp, msg, sugg, Applicability::MachineApplicable);
797 _ => {} // don't provide suggestions in other cases #55175
802 pub fn check_dereferenceable(&self, span: Span, expected: Ty<'tcx>, inner: &Pat<'_>) -> bool {
803 if let PatKind::Binding(..) = inner.kind
804 && let Some(mt) = self.shallow_resolve(expected).builtin_deref(true)
805 && let ty::Dynamic(..) = mt.ty.kind()
807 // This is "x = SomeTrait" being reduced from
808 // "let &x = &SomeTrait" or "let box x = Box<SomeTrait>", an error.
809 let type_str = self.ty_to_string(expected);
810 let mut err = struct_span_err!(
814 "type `{}` cannot be dereferenced",
817 err.span_label(span, format!("type `{type_str}` cannot be dereferenced"));
818 if self.tcx.sess.teach(&err.get_code().unwrap()) {
819 err.note(CANNOT_IMPLICITLY_DEREF_POINTER_TRAIT_OBJ);
829 pat: &'tcx Pat<'tcx>,
830 qpath: &hir::QPath<'_>,
831 fields: &'tcx [hir::PatField<'tcx>],
837 // Resolve the path and check the definition for errors.
838 let Some((variant, pat_ty)) = self.check_struct_path(qpath, pat.hir_id) else {
839 let err = self.tcx.ty_error();
840 for field in fields {
842 self.check_pat(field.pat, err, def_bm, ti);
847 // Type-check the path.
848 self.demand_eqtype_pat(pat.span, expected, pat_ty, ti);
850 // Type-check subpatterns.
851 if self.check_struct_pat_fields(pat_ty, &pat, variant, fields, has_rest_pat, def_bm, ti) {
861 qpath: &hir::QPath<'_>,
862 path_resolution: (Res, Option<RawTy<'tcx>>, &'tcx [hir::PathSegment<'tcx>]),
868 // We have already resolved the path.
869 let (res, opt_ty, segments) = path_resolution;
872 let e = tcx.sess.delay_span_bug(qpath.span(), "`Res::Err` but no error emitted");
873 self.set_tainted_by_errors(e);
874 return tcx.ty_error_with_guaranteed(e);
876 Res::Def(DefKind::AssocFn | DefKind::Ctor(_, CtorKind::Fn) | DefKind::Variant, _) => {
877 let expected = "unit struct, unit variant or constant";
878 let e = report_unexpected_variant_res(tcx, res, qpath, pat.span, "E0533", expected);
879 return tcx.ty_error_with_guaranteed(e);
883 DefKind::Ctor(_, CtorKind::Const)
885 | DefKind::AssocConst
886 | DefKind::ConstParam,
889 _ => bug!("unexpected pattern resolution: {:?}", res),
892 // Type-check the path.
893 let (pat_ty, pat_res) =
894 self.instantiate_value_path(segments, opt_ty, res, pat.span, pat.hir_id);
896 self.demand_suptype_with_origin(&self.pattern_cause(ti, pat.span), expected, pat_ty)
898 self.emit_bad_pat_path(err, pat, res, pat_res, pat_ty, segments);
903 fn maybe_suggest_range_literal(
906 opt_def_id: Option<hir::def_id::DefId>,
910 Some(def_id) => match self.tcx.hir().get_if_local(def_id) {
911 Some(hir::Node::Item(hir::Item {
912 kind: hir::ItemKind::Const(_, body_id), ..
913 })) => match self.tcx.hir().get(body_id.hir_id) {
914 hir::Node::Expr(expr) => {
915 if hir::is_range_literal(expr) {
916 let span = self.tcx.hir().span(body_id.hir_id);
917 if let Ok(snip) = self.tcx.sess.source_map().span_to_snippet(span) {
918 e.span_suggestion_verbose(
920 "you may want to move the range into the match block",
922 Applicability::MachineApplicable,
937 fn emit_bad_pat_path(
939 mut e: DiagnosticBuilder<'_, ErrorGuaranteed>,
940 pat: &hir::Pat<'tcx>,
944 segments: &'tcx [hir::PathSegment<'tcx>],
946 let pat_span = pat.span;
947 if let Some(span) = self.tcx.hir().res_span(pat_res) {
948 e.span_label(span, &format!("{} defined here", res.descr()));
949 if let [hir::PathSegment { ident, .. }] = &*segments {
953 "`{}` is interpreted as {} {}, not a new binding",
959 match self.tcx.hir().get_parent(pat.hir_id) {
960 hir::Node::PatField(..) => {
961 e.span_suggestion_verbose(
962 ident.span.shrink_to_hi(),
963 "bind the struct field to a different name instead",
964 format!(": other_{}", ident.as_str().to_lowercase()),
965 Applicability::HasPlaceholders,
969 let (type_def_id, item_def_id) = match pat_ty.kind() {
970 Adt(def, _) => match res {
971 Res::Def(DefKind::Const, def_id) => (Some(def.did()), Some(def_id)),
978 self.tcx.lang_items().range_struct(),
979 self.tcx.lang_items().range_from_struct(),
980 self.tcx.lang_items().range_to_struct(),
981 self.tcx.lang_items().range_full_struct(),
982 self.tcx.lang_items().range_inclusive_struct(),
983 self.tcx.lang_items().range_to_inclusive_struct(),
985 if type_def_id != None && ranges.contains(&type_def_id) {
986 if !self.maybe_suggest_range_literal(&mut e, item_def_id, *ident) {
987 let msg = "constants only support matching by type, \
988 if you meant to match against a range of values, \
989 consider using a range pattern like `min ..= max` in the match block";
993 let msg = "introduce a new binding instead";
994 let sugg = format!("other_{}", ident.as_str().to_lowercase());
999 Applicability::HasPlaceholders,
1009 fn check_pat_tuple_struct(
1011 pat: &'tcx Pat<'tcx>,
1012 qpath: &'tcx hir::QPath<'tcx>,
1013 subpats: &'tcx [Pat<'tcx>],
1014 ddpos: hir::DotDotPos,
1016 def_bm: BindingMode,
1020 let on_error = |e| {
1021 for pat in subpats {
1022 self.check_pat(pat, tcx.ty_error_with_guaranteed(e), def_bm, ti);
1025 let report_unexpected_res = |res: Res| {
1026 let expected = "tuple struct or tuple variant";
1027 let e = report_unexpected_variant_res(tcx, res, qpath, pat.span, "E0164", expected);
1032 // Resolve the path and check the definition for errors.
1033 let (res, opt_ty, segments) =
1034 self.resolve_ty_and_res_fully_qualified_call(qpath, pat.hir_id, pat.span);
1035 if res == Res::Err {
1036 let e = tcx.sess.delay_span_bug(pat.span, "`Res::Err` but no error emitted");
1037 self.set_tainted_by_errors(e);
1039 return tcx.ty_error_with_guaranteed(e);
1042 // Type-check the path.
1044 self.instantiate_value_path(segments, opt_ty, res, pat.span, pat.hir_id);
1045 if !pat_ty.is_fn() {
1046 let e = report_unexpected_res(res);
1047 return tcx.ty_error_with_guaranteed(e);
1050 let variant = match res {
1052 let e = tcx.sess.delay_span_bug(pat.span, "`Res::Err` but no error emitted");
1053 self.set_tainted_by_errors(e);
1055 return tcx.ty_error_with_guaranteed(e);
1057 Res::Def(DefKind::AssocConst | DefKind::AssocFn, _) => {
1058 let e = report_unexpected_res(res);
1059 return tcx.ty_error_with_guaranteed(e);
1061 Res::Def(DefKind::Ctor(_, CtorKind::Fn), _) => tcx.expect_variant_res(res),
1062 _ => bug!("unexpected pattern resolution: {:?}", res),
1065 // Replace constructor type with constructed type for tuple struct patterns.
1066 let pat_ty = pat_ty.fn_sig(tcx).output();
1067 let pat_ty = pat_ty.no_bound_vars().expect("expected fn type");
1069 // Type-check the tuple struct pattern against the expected type.
1070 let diag = self.demand_eqtype_pat_diag(pat.span, expected, pat_ty, ti);
1071 let had_err = if let Some(mut err) = diag {
1078 // Type-check subpatterns.
1079 if subpats.len() == variant.fields.len()
1080 || subpats.len() < variant.fields.len() && ddpos.as_opt_usize().is_some()
1082 let ty::Adt(_, substs) = pat_ty.kind() else {
1083 bug!("unexpected pattern type {:?}", pat_ty);
1085 for (i, subpat) in subpats.iter().enumerate_and_adjust(variant.fields.len(), ddpos) {
1086 let field_ty = self.field_ty(subpat.span, &variant.fields[i], substs);
1087 self.check_pat(subpat, field_ty, def_bm, ti);
1089 self.tcx.check_stability(
1090 variant.fields[i].did,
1097 // Pattern has wrong number of fields.
1098 let e = self.e0023(pat.span, res, qpath, subpats, &variant.fields, expected, had_err);
1100 return tcx.ty_error_with_guaranteed(e);
1109 qpath: &hir::QPath<'_>,
1110 subpats: &'tcx [Pat<'tcx>],
1111 fields: &'tcx [ty::FieldDef],
1114 ) -> ErrorGuaranteed {
1115 let subpats_ending = pluralize!(subpats.len());
1116 let fields_ending = pluralize!(fields.len());
1118 let subpat_spans = if subpats.is_empty() {
1121 subpats.iter().map(|p| p.span).collect()
1123 let last_subpat_span = *subpat_spans.last().unwrap();
1124 let res_span = self.tcx.def_span(res.def_id());
1125 let def_ident_span = self.tcx.def_ident_span(res.def_id()).unwrap_or(res_span);
1126 let field_def_spans = if fields.is_empty() {
1129 fields.iter().map(|f| f.ident(self.tcx).span).collect()
1131 let last_field_def_span = *field_def_spans.last().unwrap();
1133 let mut err = struct_span_err!(
1135 MultiSpan::from_spans(subpat_spans),
1137 "this pattern has {} field{}, but the corresponding {} has {} field{}",
1146 &format!("expected {} field{}, found {}", fields.len(), fields_ending, subpats.len()),
1148 if self.tcx.sess.source_map().is_multiline(qpath.span().between(last_subpat_span)) {
1149 err.span_label(qpath.span(), "");
1151 if self.tcx.sess.source_map().is_multiline(def_ident_span.between(last_field_def_span)) {
1152 err.span_label(def_ident_span, format!("{} defined here", res.descr()));
1154 for span in &field_def_spans[..field_def_spans.len() - 1] {
1155 err.span_label(*span, "");
1158 last_field_def_span,
1159 &format!("{} has {} field{}", res.descr(), fields.len(), fields_ending),
1162 // Identify the case `Some(x, y)` where the expected type is e.g. `Option<(T, U)>`.
1163 // More generally, the expected type wants a tuple variant with one field of an
1164 // N-arity-tuple, e.g., `V_i((p_0, .., p_N))`. Meanwhile, the user supplied a pattern
1165 // with the subpatterns directly in the tuple variant pattern, e.g., `V_i(p_0, .., p_N)`.
1166 let missing_parentheses = match (&expected.kind(), fields, had_err) {
1167 // #67037: only do this if we could successfully type-check the expected type against
1168 // the tuple struct pattern. Otherwise the substs could get out of range on e.g.,
1169 // `let P() = U;` where `P != U` with `struct P<T>(T);`.
1170 (ty::Adt(_, substs), [field], false) => {
1171 let field_ty = self.field_ty(pat_span, field, substs);
1172 match field_ty.kind() {
1173 ty::Tuple(fields) => fields.len() == subpats.len(),
1179 if missing_parentheses {
1180 let (left, right) = match subpats {
1181 // This is the zero case; we aim to get the "hi" part of the `QPath`'s
1182 // span as the "lo" and then the "hi" part of the pattern's span as the "hi".
1185 // help: missing parentheses
1187 // L | let A(()) = A(());
1189 [] => (qpath.span().shrink_to_hi(), pat_span),
1190 // Easy case. Just take the "lo" of the first sub-pattern and the "hi" of the
1191 // last sub-pattern. In the case of `A(x)` the first and last may coincide.
1194 // help: missing parentheses
1196 // L | let A((x, y)) = A((1, 2));
1198 [first, ..] => (first.span.shrink_to_lo(), subpats.last().unwrap().span),
1200 err.multipart_suggestion(
1201 "missing parentheses",
1202 vec![(left, "(".to_string()), (right.shrink_to_hi(), ")".to_string())],
1203 Applicability::MachineApplicable,
1205 } else if fields.len() > subpats.len() && pat_span != DUMMY_SP {
1206 let after_fields_span = pat_span.with_hi(pat_span.hi() - BytePos(1)).shrink_to_hi();
1207 let all_fields_span = match subpats {
1208 [] => after_fields_span,
1209 [field] => field.span,
1210 [first, .., last] => first.span.to(last.span),
1213 // Check if all the fields in the pattern are wildcards.
1214 let all_wildcards = subpats.iter().all(|pat| matches!(pat.kind, PatKind::Wild));
1215 let first_tail_wildcard =
1216 subpats.iter().enumerate().fold(None, |acc, (pos, pat)| match (acc, &pat.kind) {
1217 (None, PatKind::Wild) => Some(pos),
1218 (Some(_), PatKind::Wild) => acc,
1221 let tail_span = match first_tail_wildcard {
1222 None => after_fields_span,
1223 Some(0) => subpats[0].span.to(after_fields_span),
1224 Some(pos) => subpats[pos - 1].span.shrink_to_hi().to(after_fields_span),
1227 // FIXME: heuristic-based suggestion to check current types for where to add `_`.
1228 let mut wildcard_sugg = vec!["_"; fields.len() - subpats.len()].join(", ");
1229 if !subpats.is_empty() {
1230 wildcard_sugg = String::from(", ") + &wildcard_sugg;
1233 err.span_suggestion_verbose(
1235 "use `_` to explicitly ignore each field",
1237 Applicability::MaybeIncorrect,
1240 // Only suggest `..` if more than one field is missing
1241 // or the pattern consists of all wildcards.
1242 if fields.len() - subpats.len() > 1 || all_wildcards {
1243 if subpats.is_empty() || all_wildcards {
1244 err.span_suggestion_verbose(
1246 "use `..` to ignore all fields",
1248 Applicability::MaybeIncorrect,
1251 err.span_suggestion_verbose(
1253 "use `..` to ignore the rest of the fields",
1255 Applicability::MaybeIncorrect,
1267 elements: &'tcx [Pat<'tcx>],
1268 ddpos: hir::DotDotPos,
1270 def_bm: BindingMode,
1274 let mut expected_len = elements.len();
1275 if ddpos.as_opt_usize().is_some() {
1276 // Require known type only when `..` is present.
1277 if let ty::Tuple(tys) = self.structurally_resolved_type(span, expected).kind() {
1278 expected_len = tys.len();
1281 let max_len = cmp::max(expected_len, elements.len());
1283 let element_tys_iter = (0..max_len).map(|_| {
1285 // FIXME: `MiscVariable` for now -- obtaining the span and name information
1286 // from all tuple elements isn't trivial.
1287 TypeVariableOrigin { kind: TypeVariableOriginKind::TypeInference, span },
1290 let element_tys = tcx.mk_type_list(element_tys_iter);
1291 let pat_ty = tcx.mk_ty(ty::Tuple(element_tys));
1292 if let Some(mut err) = self.demand_eqtype_pat_diag(span, expected, pat_ty, ti) {
1293 let reported = err.emit();
1294 // Walk subpatterns with an expected type of `err` in this case to silence
1295 // further errors being emitted when using the bindings. #50333
1296 let element_tys_iter = (0..max_len).map(|_| tcx.ty_error_with_guaranteed(reported));
1297 for (_, elem) in elements.iter().enumerate_and_adjust(max_len, ddpos) {
1298 self.check_pat(elem, tcx.ty_error_with_guaranteed(reported), def_bm, ti);
1300 tcx.mk_tup(element_tys_iter)
1302 for (i, elem) in elements.iter().enumerate_and_adjust(max_len, ddpos) {
1303 self.check_pat(elem, element_tys[i], def_bm, ti);
1309 fn check_struct_pat_fields(
1312 pat: &'tcx Pat<'tcx>,
1313 variant: &'tcx ty::VariantDef,
1314 fields: &'tcx [hir::PatField<'tcx>],
1316 def_bm: BindingMode,
1321 let ty::Adt(adt, substs) = adt_ty.kind() else {
1322 span_bug!(pat.span, "struct pattern is not an ADT");
1325 // Index the struct fields' types.
1326 let field_map = variant
1330 .map(|(i, field)| (field.ident(self.tcx).normalize_to_macros_2_0(), (i, field)))
1331 .collect::<FxHashMap<_, _>>();
1333 // Keep track of which fields have already appeared in the pattern.
1334 let mut used_fields = FxHashMap::default();
1335 let mut no_field_errors = true;
1337 let mut inexistent_fields = vec![];
1338 // Typecheck each field.
1339 for field in fields {
1340 let span = field.span;
1341 let ident = tcx.adjust_ident(field.ident, variant.def_id);
1342 let field_ty = match used_fields.entry(ident) {
1343 Occupied(occupied) => {
1344 self.error_field_already_bound(span, field.ident, *occupied.get());
1345 no_field_errors = false;
1349 vacant.insert(span);
1353 self.write_field_index(field.hir_id, *i);
1354 self.tcx.check_stability(f.did, Some(pat.hir_id), span, None);
1355 self.field_ty(span, f, substs)
1357 .unwrap_or_else(|| {
1358 inexistent_fields.push(field);
1359 no_field_errors = false;
1365 self.check_pat(field.pat, field_ty, def_bm, ti);
1368 let mut unmentioned_fields = variant
1371 .map(|field| (field, field.ident(self.tcx).normalize_to_macros_2_0()))
1372 .filter(|(_, ident)| !used_fields.contains_key(ident))
1373 .collect::<Vec<_>>();
1375 let inexistent_fields_err = if !(inexistent_fields.is_empty() || variant.is_recovered())
1376 && !inexistent_fields.iter().any(|field| field.ident.name == kw::Underscore)
1378 Some(self.error_inexistent_fields(
1379 adt.variant_descr(),
1381 &mut unmentioned_fields,
1389 // Require `..` if struct has non_exhaustive attribute.
1390 let non_exhaustive = variant.is_field_list_non_exhaustive() && !adt.did().is_local();
1391 if non_exhaustive && !has_rest_pat {
1392 self.error_foreign_non_exhaustive_spat(pat, adt.variant_descr(), fields.is_empty());
1395 let mut unmentioned_err = None;
1396 // Report an error if an incorrect number of fields was specified.
1398 if fields.len() != 1 {
1400 .struct_span_err(pat.span, "union patterns should have exactly one field")
1404 tcx.sess.struct_span_err(pat.span, "`..` cannot be used in union patterns").emit();
1406 } else if !unmentioned_fields.is_empty() {
1407 let accessible_unmentioned_fields: Vec<_> = unmentioned_fields
1410 .filter(|(field, _)| {
1411 field.vis.is_accessible_from(tcx.parent_module(pat.hir_id), tcx)
1413 tcx.eval_stability(field.did, None, DUMMY_SP, None),
1414 EvalResult::Deny { .. }
1416 // We only want to report the error if it is hidden and not local
1417 && !(tcx.is_doc_hidden(field.did) && !field.did.is_local())
1422 if accessible_unmentioned_fields.is_empty() {
1423 unmentioned_err = Some(self.error_no_accessible_fields(pat, fields));
1425 unmentioned_err = Some(self.error_unmentioned_fields(
1427 &accessible_unmentioned_fields,
1428 accessible_unmentioned_fields.len() != unmentioned_fields.len(),
1432 } else if non_exhaustive && !accessible_unmentioned_fields.is_empty() {
1433 self.lint_non_exhaustive_omitted_patterns(
1435 &accessible_unmentioned_fields,
1440 match (inexistent_fields_err, unmentioned_err) {
1441 (Some(mut i), Some(mut u)) => {
1442 if let Some(mut e) = self.error_tuple_variant_as_struct_pat(pat, fields, variant) {
1443 // We don't want to show the nonexistent fields error when this was
1444 // `Foo { a, b }` when it should have been `Foo(a, b)`.
1453 (None, Some(mut u)) => {
1454 if let Some(mut e) = self.error_tuple_variant_as_struct_pat(pat, fields, variant) {
1461 (Some(mut err), None) => {
1464 (None, None) if let Some(mut err) =
1465 self.error_tuple_variant_index_shorthand(variant, pat, fields) =>
1474 fn error_tuple_variant_index_shorthand(
1476 variant: &VariantDef,
1478 fields: &[hir::PatField<'_>],
1479 ) -> Option<DiagnosticBuilder<'_, ErrorGuaranteed>> {
1480 // if this is a tuple struct, then all field names will be numbers
1481 // so if any fields in a struct pattern use shorthand syntax, they will
1482 // be invalid identifiers (for example, Foo { 0, 1 }).
1483 if let (Some(CtorKind::Fn), PatKind::Struct(qpath, field_patterns, ..)) =
1484 (variant.ctor_kind(), &pat.kind)
1486 let has_shorthand_field_name = field_patterns.iter().any(|field| field.is_shorthand);
1487 if has_shorthand_field_name {
1488 let path = rustc_hir_pretty::to_string(rustc_hir_pretty::NO_ANN, |s| {
1489 s.print_qpath(qpath, false)
1491 let mut err = struct_span_err!(
1495 "tuple variant `{path}` written as struct variant",
1497 err.span_suggestion_verbose(
1498 qpath.span().shrink_to_hi().to(pat.span.shrink_to_hi()),
1499 "use the tuple variant pattern syntax instead",
1500 format!("({})", self.get_suggested_tuple_struct_pattern(fields, variant)),
1501 Applicability::MaybeIncorrect,
1509 fn error_foreign_non_exhaustive_spat(&self, pat: &Pat<'_>, descr: &str, no_fields: bool) {
1510 let sess = self.tcx.sess;
1511 let sm = sess.source_map();
1512 let sp_brace = sm.end_point(pat.span);
1513 let sp_comma = sm.end_point(pat.span.with_hi(sp_brace.hi()));
1514 let sugg = if no_fields || sp_brace != sp_comma { ".. }" } else { ", .. }" };
1516 let mut err = struct_span_err!(
1520 "`..` required with {descr} marked as non-exhaustive",
1522 err.span_suggestion_verbose(
1524 "add `..` at the end of the field list to ignore all other fields",
1526 Applicability::MachineApplicable,
1531 fn error_field_already_bound(&self, span: Span, ident: Ident, other_field: Span) {
1536 "field `{}` bound multiple times in the pattern",
1539 .span_label(span, format!("multiple uses of `{ident}` in pattern"))
1540 .span_label(other_field, format!("first use of `{ident}`"))
1544 fn error_inexistent_fields(
1547 inexistent_fields: &[&hir::PatField<'tcx>],
1548 unmentioned_fields: &mut Vec<(&'tcx ty::FieldDef, Ident)>,
1549 variant: &ty::VariantDef,
1550 substs: &'tcx ty::List<ty::subst::GenericArg<'tcx>>,
1551 ) -> DiagnosticBuilder<'tcx, ErrorGuaranteed> {
1553 let (field_names, t, plural) = if inexistent_fields.len() == 1 {
1554 (format!("a field named `{}`", inexistent_fields[0].ident), "this", "")
1561 .map(|field| format!("`{}`", field.ident))
1562 .collect::<Vec<String>>()
1569 let spans = inexistent_fields.iter().map(|field| field.ident.span).collect::<Vec<_>>();
1570 let mut err = struct_span_err!(
1574 "{} `{}` does not have {}",
1576 tcx.def_path_str(variant.def_id),
1579 if let Some(pat_field) = inexistent_fields.last() {
1581 pat_field.ident.span,
1583 "{} `{}` does not have {} field{}",
1585 tcx.def_path_str(variant.def_id),
1591 if unmentioned_fields.len() == 1 {
1593 unmentioned_fields.iter().map(|(_, field)| field.name).collect::<Vec<_>>();
1594 let suggested_name = find_best_match_for_name(&input, pat_field.ident.name, None);
1595 if let Some(suggested_name) = suggested_name {
1596 err.span_suggestion(
1597 pat_field.ident.span,
1598 "a field with a similar name exists",
1600 Applicability::MaybeIncorrect,
1603 // When we have a tuple struct used with struct we don't want to suggest using
1604 // the (valid) struct syntax with numeric field names. Instead we want to
1605 // suggest the expected syntax. We infer that this is the case by parsing the
1606 // `Ident` into an unsized integer. The suggestion will be emitted elsewhere in
1607 // `smart_resolve_context_dependent_help`.
1608 if suggested_name.to_ident_string().parse::<usize>().is_err() {
1609 // We don't want to throw `E0027` in case we have thrown `E0026` for them.
1610 unmentioned_fields.retain(|&(_, x)| x.name != suggested_name);
1612 } else if inexistent_fields.len() == 1 {
1613 match pat_field.pat.kind {
1615 if !self.can_coerce(
1616 self.typeck_results.borrow().expr_ty(expr),
1618 unmentioned_fields[0].1.span,
1619 unmentioned_fields[0].0,
1624 let unmentioned_field = unmentioned_fields[0].1.name;
1625 err.span_suggestion_short(
1626 pat_field.ident.span,
1628 "`{}` has a field named `{}`",
1629 tcx.def_path_str(variant.def_id),
1632 unmentioned_field.to_string(),
1633 Applicability::MaybeIncorrect,
1640 if tcx.sess.teach(&err.get_code().unwrap()) {
1642 "This error indicates that a struct pattern attempted to \
1643 extract a non-existent field from a struct. Struct fields \
1644 are identified by the name used before the colon : so struct \
1645 patterns should resemble the declaration of the struct type \
1647 If you are using shorthand field patterns but want to refer \
1648 to the struct field by a different name, you should rename \
1655 fn error_tuple_variant_as_struct_pat(
1658 fields: &'tcx [hir::PatField<'tcx>],
1659 variant: &ty::VariantDef,
1660 ) -> Option<DiagnosticBuilder<'tcx, ErrorGuaranteed>> {
1661 if let (Some(CtorKind::Fn), PatKind::Struct(qpath, ..)) = (variant.ctor_kind(), &pat.kind) {
1662 let path = rustc_hir_pretty::to_string(rustc_hir_pretty::NO_ANN, |s| {
1663 s.print_qpath(qpath, false)
1665 let mut err = struct_span_err!(
1669 "tuple variant `{}` written as struct variant",
1672 let (sugg, appl) = if fields.len() == variant.fields.len() {
1674 self.get_suggested_tuple_struct_pattern(fields, variant),
1675 Applicability::MachineApplicable,
1679 variant.fields.iter().map(|_| "_").collect::<Vec<&str>>().join(", "),
1680 Applicability::MaybeIncorrect,
1683 err.span_suggestion_verbose(
1684 qpath.span().shrink_to_hi().to(pat.span.shrink_to_hi()),
1685 "use the tuple variant pattern syntax instead",
1686 format!("({})", sugg),
1694 fn get_suggested_tuple_struct_pattern(
1696 fields: &[hir::PatField<'_>],
1697 variant: &VariantDef,
1699 let variant_field_idents =
1700 variant.fields.iter().map(|f| f.ident(self.tcx)).collect::<Vec<Ident>>();
1704 match self.tcx.sess.source_map().span_to_snippet(field.pat.span) {
1706 // Field names are numbers, but numbers
1707 // are not valid identifiers
1708 if variant_field_idents.contains(&field.ident) {
1714 Err(_) => rustc_hir_pretty::to_string(rustc_hir_pretty::NO_ANN, |s| {
1715 s.print_pat(field.pat)
1719 .collect::<Vec<String>>()
1723 /// Returns a diagnostic reporting a struct pattern which is missing an `..` due to
1724 /// inaccessible fields.
1727 /// error: pattern requires `..` due to inaccessible fields
1728 /// --> src/main.rs:10:9
1730 /// LL | let foo::Foo {} = foo::Foo::default();
1733 /// help: add a `..`
1735 /// LL | let foo::Foo { .. } = foo::Foo::default();
1738 fn error_no_accessible_fields(
1741 fields: &'tcx [hir::PatField<'tcx>],
1742 ) -> DiagnosticBuilder<'tcx, ErrorGuaranteed> {
1746 .struct_span_err(pat.span, "pattern requires `..` due to inaccessible fields");
1748 if let Some(field) = fields.last() {
1749 err.span_suggestion_verbose(
1750 field.span.shrink_to_hi(),
1751 "ignore the inaccessible and unused fields",
1753 Applicability::MachineApplicable,
1756 let qpath_span = if let PatKind::Struct(qpath, ..) = &pat.kind {
1759 bug!("`error_no_accessible_fields` called on non-struct pattern");
1762 // Shrink the span to exclude the `foo:Foo` in `foo::Foo { }`.
1763 let span = pat.span.with_lo(qpath_span.shrink_to_hi().hi());
1764 err.span_suggestion_verbose(
1766 "ignore the inaccessible and unused fields",
1768 Applicability::MachineApplicable,
1774 /// Report that a pattern for a `#[non_exhaustive]` struct marked with `non_exhaustive_omitted_patterns`
1775 /// is not exhaustive enough.
1777 /// Nb: the partner lint for enums lives in `compiler/rustc_mir_build/src/thir/pattern/usefulness.rs`.
1778 fn lint_non_exhaustive_omitted_patterns(
1781 unmentioned_fields: &[(&ty::FieldDef, Ident)],
1784 fn joined_uncovered_patterns(witnesses: &[&Ident]) -> String {
1785 const LIMIT: usize = 3;
1788 [witness] => format!("`{}`", witness),
1789 [head @ .., tail] if head.len() < LIMIT => {
1790 let head: Vec<_> = head.iter().map(<_>::to_string).collect();
1791 format!("`{}` and `{}`", head.join("`, `"), tail)
1794 let (head, tail) = witnesses.split_at(LIMIT);
1795 let head: Vec<_> = head.iter().map(<_>::to_string).collect();
1796 format!("`{}` and {} more", head.join("`, `"), tail.len())
1800 let joined_patterns = joined_uncovered_patterns(
1801 &unmentioned_fields.iter().map(|(_, i)| i).collect::<Vec<_>>(),
1804 self.tcx.struct_span_lint_hir(NON_EXHAUSTIVE_OMITTED_PATTERNS, pat.hir_id, pat.span, "some fields are not explicitly listed", |lint| {
1805 lint.span_label(pat.span, format!("field{} {} not listed", rustc_errors::pluralize!(unmentioned_fields.len()), joined_patterns));
1807 "ensure that all fields are mentioned explicitly by adding the suggested fields",
1810 "the pattern is of type `{}` and the `non_exhaustive_omitted_patterns` attribute was found",
1818 /// Returns a diagnostic reporting a struct pattern which does not mention some fields.
1821 /// error[E0027]: pattern does not mention field `bar`
1822 /// --> src/main.rs:15:9
1824 /// LL | let foo::Foo {} = foo::Foo::new();
1825 /// | ^^^^^^^^^^^ missing field `bar`
1827 fn error_unmentioned_fields(
1830 unmentioned_fields: &[(&ty::FieldDef, Ident)],
1831 have_inaccessible_fields: bool,
1832 fields: &'tcx [hir::PatField<'tcx>],
1833 ) -> DiagnosticBuilder<'tcx, ErrorGuaranteed> {
1834 let inaccessible = if have_inaccessible_fields { " and inaccessible fields" } else { "" };
1835 let field_names = if unmentioned_fields.len() == 1 {
1836 format!("field `{}`{}", unmentioned_fields[0].1, inaccessible)
1838 let fields = unmentioned_fields
1840 .map(|(_, name)| format!("`{}`", name))
1841 .collect::<Vec<String>>()
1843 format!("fields {}{}", fields, inaccessible)
1845 let mut err = struct_span_err!(
1849 "pattern does not mention {}",
1852 err.span_label(pat.span, format!("missing {}", field_names));
1853 let len = unmentioned_fields.len();
1854 let (prefix, postfix, sp) = match fields {
1855 [] => match &pat.kind {
1856 PatKind::Struct(path, [], false) => {
1857 (" { ", " }", path.span().shrink_to_hi().until(pat.span.shrink_to_hi()))
1862 // Account for last field having a trailing comma or parse recovery at the tail of
1863 // the pattern to avoid invalid suggestion (#78511).
1864 let tail = field.span.shrink_to_hi().with_hi(pat.span.hi());
1866 PatKind::Struct(..) => (", ", " }", tail),
1871 err.span_suggestion(
1874 "include the missing field{} in the pattern{}",
1876 if have_inaccessible_fields { " and ignore the inaccessible fields" } else { "" }
1883 .map(|(_, name)| name.to_string())
1884 .collect::<Vec<_>>()
1886 if have_inaccessible_fields { ", .." } else { "" },
1889 Applicability::MachineApplicable,
1891 err.span_suggestion(
1894 "if you don't care about {these} missing field{s}, you can explicitly ignore {them}",
1895 these = pluralize!("this", len),
1896 s = pluralize!(len),
1897 them = if len == 1 { "it" } else { "them" },
1899 format!("{}..{}", prefix, postfix),
1900 Applicability::MachineApplicable,
1908 inner: &'tcx Pat<'tcx>,
1910 def_bm: BindingMode,
1914 let (box_ty, inner_ty) = if self.check_dereferenceable(span, expected, inner) {
1915 // Here, `demand::subtype` is good enough, but I don't
1916 // think any errors can be introduced by using `demand::eqtype`.
1917 let inner_ty = self.next_ty_var(TypeVariableOrigin {
1918 kind: TypeVariableOriginKind::TypeInference,
1921 let box_ty = tcx.mk_box(inner_ty);
1922 self.demand_eqtype_pat(span, expected, box_ty, ti);
1925 let err = tcx.ty_error();
1928 self.check_pat(inner, inner_ty, def_bm, ti);
1932 // Precondition: Pat is Ref(inner)
1935 pat: &'tcx Pat<'tcx>,
1936 inner: &'tcx Pat<'tcx>,
1937 mutbl: hir::Mutability,
1939 def_bm: BindingMode,
1943 let expected = self.shallow_resolve(expected);
1944 let (ref_ty, inner_ty) = if self.check_dereferenceable(pat.span, expected, inner) {
1945 // `demand::subtype` would be good enough, but using `eqtype` turns
1946 // out to be equally general. See (note_1) for details.
1948 // Take region, inner-type from expected type if we can,
1949 // to avoid creating needless variables. This also helps with
1950 // the bad interactions of the given hack detailed in (note_1).
1951 debug!("check_pat_ref: expected={:?}", expected);
1952 match *expected.kind() {
1953 ty::Ref(_, r_ty, r_mutbl) if r_mutbl == mutbl => (expected, r_ty),
1955 let inner_ty = self.next_ty_var(TypeVariableOrigin {
1956 kind: TypeVariableOriginKind::TypeInference,
1959 let ref_ty = self.new_ref_ty(pat.span, mutbl, inner_ty);
1960 debug!("check_pat_ref: demanding {:?} = {:?}", expected, ref_ty);
1961 let err = self.demand_eqtype_pat_diag(pat.span, expected, ref_ty, ti);
1963 // Look for a case like `fn foo(&foo: u32)` and suggest
1964 // `fn foo(foo: &u32)`
1965 if let Some(mut err) = err {
1966 self.borrow_pat_suggestion(&mut err, pat);
1973 let err = tcx.ty_error();
1976 self.check_pat(inner, inner_ty, def_bm, ti);
1980 /// Create a reference type with a fresh region variable.
1981 fn new_ref_ty(&self, span: Span, mutbl: hir::Mutability, ty: Ty<'tcx>) -> Ty<'tcx> {
1982 let region = self.next_region_var(infer::PatternRegion(span));
1983 let mt = ty::TypeAndMut { ty, mutbl };
1984 self.tcx.mk_ref(region, mt)
1987 /// Type check a slice pattern.
1989 /// Syntactically, these look like `[pat_0, ..., pat_n]`.
1990 /// Semantically, we are type checking a pattern with structure:
1991 /// ```ignore (not-rust)
1992 /// [before_0, ..., before_n, (slice, after_0, ... after_n)?]
1994 /// The type of `slice`, if it is present, depends on the `expected` type.
1995 /// If `slice` is missing, then so is `after_i`.
1996 /// If `slice` is present, it can still represent 0 elements.
2000 before: &'tcx [Pat<'tcx>],
2001 slice: Option<&'tcx Pat<'tcx>>,
2002 after: &'tcx [Pat<'tcx>],
2004 def_bm: BindingMode,
2007 let expected = self.structurally_resolved_type(span, expected);
2008 let (element_ty, opt_slice_ty, inferred) = match *expected.kind() {
2009 // An array, so we might have something like `let [a, b, c] = [0, 1, 2];`.
2010 ty::Array(element_ty, len) => {
2011 let min = before.len() as u64 + after.len() as u64;
2012 let (opt_slice_ty, expected) =
2013 self.check_array_pat_len(span, element_ty, expected, slice, len, min);
2014 // `opt_slice_ty.is_none()` => `slice.is_none()`.
2015 // Note, though, that opt_slice_ty could be `Some(error_ty)`.
2016 assert!(opt_slice_ty.is_some() || slice.is_none());
2017 (element_ty, opt_slice_ty, expected)
2019 ty::Slice(element_ty) => (element_ty, Some(expected), expected),
2020 // The expected type must be an array or slice, but was neither, so error.
2022 if !expected.references_error() {
2023 self.error_expected_array_or_slice(span, expected, ti);
2025 let err = self.tcx.ty_error();
2026 (err, Some(err), err)
2030 // Type check all the patterns before `slice`.
2032 self.check_pat(elt, element_ty, def_bm, ti);
2034 // Type check the `slice`, if present, against its expected type.
2035 if let Some(slice) = slice {
2036 self.check_pat(slice, opt_slice_ty.unwrap(), def_bm, ti);
2038 // Type check the elements after `slice`, if present.
2040 self.check_pat(elt, element_ty, def_bm, ti);
2045 /// Type check the length of an array pattern.
2047 /// Returns both the type of the variable length pattern (or `None`), and the potentially
2048 /// inferred array type. We only return `None` for the slice type if `slice.is_none()`.
2049 fn check_array_pat_len(
2052 element_ty: Ty<'tcx>,
2054 slice: Option<&'tcx Pat<'tcx>>,
2055 len: ty::Const<'tcx>,
2057 ) -> (Option<Ty<'tcx>>, Ty<'tcx>) {
2058 if let Some(len) = len.try_eval_usize(self.tcx, self.param_env) {
2059 // Now we know the length...
2060 if slice.is_none() {
2061 // ...and since there is no variable-length pattern,
2062 // we require an exact match between the number of elements
2063 // in the array pattern and as provided by the matched type.
2065 return (None, arr_ty);
2068 self.error_scrutinee_inconsistent_length(span, min_len, len);
2069 } else if let Some(pat_len) = len.checked_sub(min_len) {
2070 // The variable-length pattern was there,
2071 // so it has an array type with the remaining elements left as its size...
2072 return (Some(self.tcx.mk_array(element_ty, pat_len)), arr_ty);
2074 // ...however, in this case, there were no remaining elements.
2075 // That is, the slice pattern requires more than the array type offers.
2076 self.error_scrutinee_with_rest_inconsistent_length(span, min_len, len);
2078 } else if slice.is_none() {
2079 // We have a pattern with a fixed length,
2080 // which we can use to infer the length of the array.
2081 let updated_arr_ty = self.tcx.mk_array(element_ty, min_len);
2082 self.demand_eqtype(span, updated_arr_ty, arr_ty);
2083 return (None, updated_arr_ty);
2085 // We have a variable-length pattern and don't know the array length.
2086 // This happens if we have e.g.,
2087 // `let [a, b, ..] = arr` where `arr: [T; N]` where `const N: usize`.
2088 self.error_scrutinee_unfixed_length(span);
2091 // If we get here, we must have emitted an error.
2092 (Some(self.tcx.ty_error()), arr_ty)
2095 fn error_scrutinee_inconsistent_length(&self, span: Span, min_len: u64, size: u64) {
2100 "pattern requires {} element{} but array has {}",
2102 pluralize!(min_len),
2105 .span_label(span, format!("expected {} element{}", size, pluralize!(size)))
2109 fn error_scrutinee_with_rest_inconsistent_length(&self, span: Span, min_len: u64, size: u64) {
2114 "pattern requires at least {} element{} but array has {}",
2116 pluralize!(min_len),
2121 format!("pattern cannot match array of {} element{}", size, pluralize!(size),),
2126 fn error_scrutinee_unfixed_length(&self, span: Span) {
2131 "cannot pattern-match on an array without a fixed length",
2136 fn error_expected_array_or_slice(&self, span: Span, expected_ty: Ty<'tcx>, ti: TopInfo<'tcx>) {
2137 let mut err = struct_span_err!(
2141 "expected an array or slice, found `{expected_ty}`"
2143 if let ty::Ref(_, ty, _) = expected_ty.kind()
2144 && let ty::Array(..) | ty::Slice(..) = ty.kind()
2146 err.help("the semantics of slice patterns changed recently; see issue #62254");
2147 } else if self.autoderef(span, expected_ty)
2148 .any(|(ty, _)| matches!(ty.kind(), ty::Slice(..) | ty::Array(..)))
2149 && let (Some(span), true) = (ti.span, ti.origin_expr)
2150 && let Ok(snippet) = self.tcx.sess.source_map().span_to_snippet(span)
2152 let ty = self.resolve_vars_if_possible(ti.expected);
2153 let is_slice_or_array_or_vector = self.is_slice_or_array_or_vector(ty);
2154 match is_slice_or_array_or_vector.1.kind() {
2156 if self.tcx.is_diagnostic_item(sym::Option, adt_def.did())
2157 || self.tcx.is_diagnostic_item(sym::Result, adt_def.did()) =>
2159 // Slicing won't work here, but `.as_deref()` might (issue #91328).
2160 err.span_suggestion(
2162 "consider using `as_deref` here",
2163 format!("{snippet}.as_deref()"),
2164 Applicability::MaybeIncorrect,
2169 if is_slice_or_array_or_vector.0 {
2170 err.span_suggestion(
2172 "consider slicing here",
2173 format!("{snippet}[..]"),
2174 Applicability::MachineApplicable,
2178 err.span_label(span, format!("pattern cannot match with input type `{expected_ty}`"));
2182 fn is_slice_or_array_or_vector(&self, ty: Ty<'tcx>) -> (bool, Ty<'tcx>) {
2184 ty::Adt(adt_def, _) if self.tcx.is_diagnostic_item(sym::Vec, adt_def.did()) => {
2187 ty::Ref(_, ty, _) => self.is_slice_or_array_or_vector(*ty),
2188 ty::Slice(..) | ty::Array(..) => (true, ty),