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 self.tcx.sess.teach(&err.get_code().unwrap()) {
558 "In a match expression, only numbers and characters can be matched \
559 against a range. This is because the compiler checks that the range \
560 is non-empty at compile-time, and is unable to evaluate arbitrary \
561 comparison functions. If you want to capture values of an orderable \
562 type between two end-points, you can use a guard.",
570 pat: &'tcx Pat<'tcx>,
571 ba: hir::BindingAnnotation,
573 sub: Option<&'tcx Pat<'tcx>>,
578 // Determine the binding mode...
580 hir::BindingAnnotation::NONE => def_bm,
581 _ => BindingMode::convert(ba),
583 // ...and store it in a side table:
584 self.inh.typeck_results.borrow_mut().pat_binding_modes_mut().insert(pat.hir_id, bm);
586 debug!("check_pat_ident: pat.hir_id={:?} bm={:?}", pat.hir_id, bm);
588 let local_ty = self.local_ty(pat.span, pat.hir_id).decl_ty;
589 let eq_ty = match bm {
590 ty::BindByReference(mutbl) => {
591 // If the binding is like `ref x | ref mut x`,
592 // then `x` is assigned a value of type `&M T` where M is the
593 // mutability and T is the expected type.
595 // `x` is assigned a value of type `&M T`, hence `&M T <: typeof(x)`
596 // is required. However, we use equality, which is stronger.
597 // See (note_1) for an explanation.
598 self.new_ref_ty(pat.span, mutbl, expected)
600 // Otherwise, the type of x is the expected type `T`.
601 ty::BindByValue(_) => {
602 // As above, `T <: typeof(x)` is required, but we use equality, see (note_1).
606 self.demand_eqtype_pat(pat.span, eq_ty, local_ty, ti);
608 // If there are multiple arms, make sure they all agree on
609 // what the type of the binding `x` ought to be.
610 if var_id != pat.hir_id {
611 self.check_binding_alt_eq_ty(ba, pat.span, var_id, local_ty, ti);
614 if let Some(p) = sub {
615 self.check_pat(p, expected, def_bm, ti);
621 fn check_binding_alt_eq_ty(
623 ba: hir::BindingAnnotation,
629 let var_ty = self.local_ty(span, var_id).decl_ty;
630 if let Some(mut err) = self.demand_eqtype_pat_diag(span, var_ty, ty, ti) {
631 let hir = self.tcx.hir();
632 let var_ty = self.resolve_vars_with_obligations(var_ty);
633 let msg = format!("first introduced with type `{var_ty}` here");
634 err.span_label(hir.span(var_id), msg);
635 let in_match = hir.parent_iter(var_id).any(|(_, n)| {
638 hir::Node::Expr(hir::Expr {
639 kind: hir::ExprKind::Match(.., hir::MatchSource::Normal),
644 let pre = if in_match { "in the same arm, " } else { "" };
645 err.note(&format!("{}a binding must have the same type in all alternatives", pre));
646 self.suggest_adding_missing_ref_or_removing_ref(
650 self.resolve_vars_with_obligations(ty),
657 fn suggest_adding_missing_ref_or_removing_ref(
659 err: &mut Diagnostic,
663 ba: hir::BindingAnnotation,
665 match (expected.kind(), actual.kind(), ba) {
666 (ty::Ref(_, inner_ty, _), _, hir::BindingAnnotation::NONE)
667 if self.can_eq(self.param_env, *inner_ty, actual).is_ok() =>
669 err.span_suggestion_verbose(
671 "consider adding `ref`",
673 Applicability::MaybeIncorrect,
676 (_, ty::Ref(_, inner_ty, _), hir::BindingAnnotation::REF)
677 if self.can_eq(self.param_env, expected, *inner_ty).is_ok() =>
679 err.span_suggestion_verbose(
680 span.with_hi(span.lo() + BytePos(4)),
681 "consider removing `ref`",
683 Applicability::MaybeIncorrect,
690 // Precondition: pat is a Ref(_) pattern
691 fn borrow_pat_suggestion(&self, err: &mut Diagnostic, pat: &Pat<'_>) {
693 if let PatKind::Ref(inner, mutbl) = pat.kind
694 && let PatKind::Binding(_, _, binding, ..) = inner.kind {
695 let binding_parent_id = tcx.hir().get_parent_node(pat.hir_id);
696 let binding_parent = tcx.hir().get(binding_parent_id);
697 debug!(?inner, ?pat, ?binding_parent);
699 let mutability = match mutbl {
700 ast::Mutability::Mut => "mut",
701 ast::Mutability::Not => "",
704 let mut_var_suggestion = 'block: {
709 let ident_kind = match binding_parent {
710 hir::Node::Param(_) => "parameter",
711 hir::Node::Local(_) => "variable",
712 hir::Node::Arm(_) => "binding",
714 // Provide diagnostics only if the parent pattern is struct-like,
715 // i.e. where `mut binding` makes sense
716 hir::Node::Pat(Pat { kind, .. }) => match kind {
718 | PatKind::TupleStruct(..)
721 | PatKind::Slice(..) => "binding",
724 | PatKind::Binding(..)
729 | PatKind::Range(..) => break 'block None,
732 // Don't provide suggestions in other cases
733 _ => break 'block None,
738 format!("to declare a mutable {ident_kind} use"),
739 format!("mut {binding}"),
744 match binding_parent {
745 // Check that there is explicit type (ie this is not a closure param with inferred type)
746 // so we don't suggest moving something to the type that does not exist
747 hir::Node::Param(hir::Param { ty_span, .. }) if binding.span != *ty_span => {
748 err.multipart_suggestion_verbose(
749 format!("to take parameter `{binding}` by reference, move `&{mutability}` to the type"),
751 (pat.span.until(inner.span), "".to_owned()),
752 (ty_span.shrink_to_lo(), mutbl.ref_prefix_str().to_owned()),
754 Applicability::MachineApplicable
757 if let Some((sp, msg, sugg)) = mut_var_suggestion {
758 err.span_note(sp, format!("{msg}: `{sugg}`"));
761 hir::Node::Param(_) | hir::Node::Arm(_) | hir::Node::Pat(_) => {
762 // rely on match ergonomics or it might be nested `&&pat`
763 err.span_suggestion_verbose(
764 pat.span.until(inner.span),
765 format!("consider removing `&{mutability}` from the pattern"),
767 Applicability::MaybeIncorrect,
770 if let Some((sp, msg, sugg)) = mut_var_suggestion {
771 err.span_note(sp, format!("{msg}: `{sugg}`"));
774 _ if let Some((sp, msg, sugg)) = mut_var_suggestion => {
775 err.span_suggestion(sp, msg, sugg, Applicability::MachineApplicable);
777 _ => {} // don't provide suggestions in other cases #55175
782 pub fn check_dereferenceable(&self, span: Span, expected: Ty<'tcx>, inner: &Pat<'_>) -> bool {
783 if let PatKind::Binding(..) = inner.kind
784 && let Some(mt) = self.shallow_resolve(expected).builtin_deref(true)
785 && let ty::Dynamic(..) = mt.ty.kind()
787 // This is "x = SomeTrait" being reduced from
788 // "let &x = &SomeTrait" or "let box x = Box<SomeTrait>", an error.
789 let type_str = self.ty_to_string(expected);
790 let mut err = struct_span_err!(
794 "type `{}` cannot be dereferenced",
797 err.span_label(span, format!("type `{type_str}` cannot be dereferenced"));
798 if self.tcx.sess.teach(&err.get_code().unwrap()) {
799 err.note(CANNOT_IMPLICITLY_DEREF_POINTER_TRAIT_OBJ);
809 pat: &'tcx Pat<'tcx>,
810 qpath: &hir::QPath<'_>,
811 fields: &'tcx [hir::PatField<'tcx>],
817 // Resolve the path and check the definition for errors.
818 let Some((variant, pat_ty)) = self.check_struct_path(qpath, pat.hir_id) else {
819 let err = self.tcx.ty_error();
820 for field in fields {
822 self.check_pat(field.pat, err, def_bm, ti);
827 // Type-check the path.
828 self.demand_eqtype_pat(pat.span, expected, pat_ty, ti);
830 // Type-check subpatterns.
831 if self.check_struct_pat_fields(pat_ty, &pat, variant, fields, has_rest_pat, def_bm, ti) {
841 qpath: &hir::QPath<'_>,
842 path_resolution: (Res, Option<Ty<'tcx>>, &'tcx [hir::PathSegment<'tcx>]),
848 // We have already resolved the path.
849 let (res, opt_ty, segments) = path_resolution;
852 let e = tcx.sess.delay_span_bug(qpath.span(), "`Res::Err` but no error emitted");
853 self.set_tainted_by_errors(e);
854 return tcx.ty_error_with_guaranteed(e);
856 Res::Def(DefKind::AssocFn | DefKind::Ctor(_, CtorKind::Fn) | DefKind::Variant, _) => {
857 let expected = "unit struct, unit variant or constant";
858 let e = report_unexpected_variant_res(tcx, res, qpath, pat.span, "E0533", expected);
859 return tcx.ty_error_with_guaranteed(e);
863 DefKind::Ctor(_, CtorKind::Const)
865 | DefKind::AssocConst
866 | DefKind::ConstParam,
869 _ => bug!("unexpected pattern resolution: {:?}", res),
872 // Type-check the path.
873 let (pat_ty, pat_res) =
874 self.instantiate_value_path(segments, opt_ty, res, pat.span, pat.hir_id);
876 self.demand_suptype_with_origin(&self.pattern_cause(ti, pat.span), expected, pat_ty)
878 self.emit_bad_pat_path(err, pat, res, pat_res, pat_ty, segments);
883 fn maybe_suggest_range_literal(
886 opt_def_id: Option<hir::def_id::DefId>,
890 Some(def_id) => match self.tcx.hir().get_if_local(def_id) {
891 Some(hir::Node::Item(hir::Item {
892 kind: hir::ItemKind::Const(_, body_id), ..
893 })) => match self.tcx.hir().get(body_id.hir_id) {
894 hir::Node::Expr(expr) => {
895 if hir::is_range_literal(expr) {
896 let span = self.tcx.hir().span(body_id.hir_id);
897 if let Ok(snip) = self.tcx.sess.source_map().span_to_snippet(span) {
898 e.span_suggestion_verbose(
900 "you may want to move the range into the match block",
902 Applicability::MachineApplicable,
917 fn emit_bad_pat_path(
919 mut e: DiagnosticBuilder<'_, ErrorGuaranteed>,
920 pat: &hir::Pat<'tcx>,
924 segments: &'tcx [hir::PathSegment<'tcx>],
926 let pat_span = pat.span;
927 if let Some(span) = self.tcx.hir().res_span(pat_res) {
928 e.span_label(span, &format!("{} defined here", res.descr()));
929 if let [hir::PathSegment { ident, .. }] = &*segments {
933 "`{}` is interpreted as {} {}, not a new binding",
939 match self.tcx.hir().get(self.tcx.hir().get_parent_node(pat.hir_id)) {
940 hir::Node::PatField(..) => {
941 e.span_suggestion_verbose(
942 ident.span.shrink_to_hi(),
943 "bind the struct field to a different name instead",
944 format!(": other_{}", ident.as_str().to_lowercase()),
945 Applicability::HasPlaceholders,
949 let (type_def_id, item_def_id) = match pat_ty.kind() {
950 Adt(def, _) => match res {
951 Res::Def(DefKind::Const, def_id) => (Some(def.did()), Some(def_id)),
958 self.tcx.lang_items().range_struct(),
959 self.tcx.lang_items().range_from_struct(),
960 self.tcx.lang_items().range_to_struct(),
961 self.tcx.lang_items().range_full_struct(),
962 self.tcx.lang_items().range_inclusive_struct(),
963 self.tcx.lang_items().range_to_inclusive_struct(),
965 if type_def_id != None && ranges.contains(&type_def_id) {
966 if !self.maybe_suggest_range_literal(&mut e, item_def_id, *ident) {
967 let msg = "constants only support matching by type, \
968 if you meant to match against a range of values, \
969 consider using a range pattern like `min ..= max` in the match block";
973 let msg = "introduce a new binding instead";
974 let sugg = format!("other_{}", ident.as_str().to_lowercase());
979 Applicability::HasPlaceholders,
989 fn check_pat_tuple_struct(
991 pat: &'tcx Pat<'tcx>,
992 qpath: &'tcx hir::QPath<'tcx>,
993 subpats: &'tcx [Pat<'tcx>],
994 ddpos: hir::DotDotPos,
1000 let on_error = |e| {
1001 for pat in subpats {
1002 self.check_pat(pat, tcx.ty_error_with_guaranteed(e), def_bm, ti);
1005 let report_unexpected_res = |res: Res| {
1006 let expected = "tuple struct or tuple variant";
1007 let e = report_unexpected_variant_res(tcx, res, qpath, pat.span, "E0164", expected);
1012 // Resolve the path and check the definition for errors.
1013 let (res, opt_ty, segments) =
1014 self.resolve_ty_and_res_fully_qualified_call(qpath, pat.hir_id, pat.span);
1015 if res == Res::Err {
1016 let e = tcx.sess.delay_span_bug(pat.span, "`Res:Err` but no error emitted");
1017 self.set_tainted_by_errors(e);
1019 return tcx.ty_error_with_guaranteed(e);
1022 // Type-check the path.
1024 self.instantiate_value_path(segments, opt_ty, res, pat.span, pat.hir_id);
1025 if !pat_ty.is_fn() {
1026 let e = report_unexpected_res(res);
1027 return tcx.ty_error_with_guaranteed(e);
1030 let variant = match res {
1032 let e = tcx.sess.delay_span_bug(pat.span, "`Res::Err` but no error emitted");
1033 self.set_tainted_by_errors(e);
1035 return tcx.ty_error_with_guaranteed(e);
1037 Res::Def(DefKind::AssocConst | DefKind::AssocFn, _) => {
1038 let e = report_unexpected_res(res);
1039 return tcx.ty_error_with_guaranteed(e);
1041 Res::Def(DefKind::Ctor(_, CtorKind::Fn), _) => tcx.expect_variant_res(res),
1042 _ => bug!("unexpected pattern resolution: {:?}", res),
1045 // Replace constructor type with constructed type for tuple struct patterns.
1046 let pat_ty = pat_ty.fn_sig(tcx).output();
1047 let pat_ty = pat_ty.no_bound_vars().expect("expected fn type");
1049 // Type-check the tuple struct pattern against the expected type.
1050 let diag = self.demand_eqtype_pat_diag(pat.span, expected, pat_ty, ti);
1051 let had_err = if let Some(mut err) = diag {
1058 // Type-check subpatterns.
1059 if subpats.len() == variant.fields.len()
1060 || subpats.len() < variant.fields.len() && ddpos.as_opt_usize().is_some()
1062 let ty::Adt(_, substs) = pat_ty.kind() else {
1063 bug!("unexpected pattern type {:?}", pat_ty);
1065 for (i, subpat) in subpats.iter().enumerate_and_adjust(variant.fields.len(), ddpos) {
1066 let field_ty = self.field_ty(subpat.span, &variant.fields[i], substs);
1067 self.check_pat(subpat, field_ty, def_bm, ti);
1069 self.tcx.check_stability(
1070 variant.fields[i].did,
1077 // Pattern has wrong number of fields.
1078 let e = self.e0023(pat.span, res, qpath, subpats, &variant.fields, expected, had_err);
1080 return tcx.ty_error_with_guaranteed(e);
1089 qpath: &hir::QPath<'_>,
1090 subpats: &'tcx [Pat<'tcx>],
1091 fields: &'tcx [ty::FieldDef],
1094 ) -> ErrorGuaranteed {
1095 let subpats_ending = pluralize!(subpats.len());
1096 let fields_ending = pluralize!(fields.len());
1098 let subpat_spans = if subpats.is_empty() {
1101 subpats.iter().map(|p| p.span).collect()
1103 let last_subpat_span = *subpat_spans.last().unwrap();
1104 let res_span = self.tcx.def_span(res.def_id());
1105 let def_ident_span = self.tcx.def_ident_span(res.def_id()).unwrap_or(res_span);
1106 let field_def_spans = if fields.is_empty() {
1109 fields.iter().map(|f| f.ident(self.tcx).span).collect()
1111 let last_field_def_span = *field_def_spans.last().unwrap();
1113 let mut err = struct_span_err!(
1115 MultiSpan::from_spans(subpat_spans),
1117 "this pattern has {} field{}, but the corresponding {} has {} field{}",
1126 &format!("expected {} field{}, found {}", fields.len(), fields_ending, subpats.len()),
1128 if self.tcx.sess.source_map().is_multiline(qpath.span().between(last_subpat_span)) {
1129 err.span_label(qpath.span(), "");
1131 if self.tcx.sess.source_map().is_multiline(def_ident_span.between(last_field_def_span)) {
1132 err.span_label(def_ident_span, format!("{} defined here", res.descr()));
1134 for span in &field_def_spans[..field_def_spans.len() - 1] {
1135 err.span_label(*span, "");
1138 last_field_def_span,
1139 &format!("{} has {} field{}", res.descr(), fields.len(), fields_ending),
1142 // Identify the case `Some(x, y)` where the expected type is e.g. `Option<(T, U)>`.
1143 // More generally, the expected type wants a tuple variant with one field of an
1144 // N-arity-tuple, e.g., `V_i((p_0, .., p_N))`. Meanwhile, the user supplied a pattern
1145 // with the subpatterns directly in the tuple variant pattern, e.g., `V_i(p_0, .., p_N)`.
1146 let missing_parentheses = match (&expected.kind(), fields, had_err) {
1147 // #67037: only do this if we could successfully type-check the expected type against
1148 // the tuple struct pattern. Otherwise the substs could get out of range on e.g.,
1149 // `let P() = U;` where `P != U` with `struct P<T>(T);`.
1150 (ty::Adt(_, substs), [field], false) => {
1151 let field_ty = self.field_ty(pat_span, field, substs);
1152 match field_ty.kind() {
1153 ty::Tuple(fields) => fields.len() == subpats.len(),
1159 if missing_parentheses {
1160 let (left, right) = match subpats {
1161 // This is the zero case; we aim to get the "hi" part of the `QPath`'s
1162 // span as the "lo" and then the "hi" part of the pattern's span as the "hi".
1165 // help: missing parentheses
1167 // L | let A(()) = A(());
1169 [] => (qpath.span().shrink_to_hi(), pat_span),
1170 // Easy case. Just take the "lo" of the first sub-pattern and the "hi" of the
1171 // last sub-pattern. In the case of `A(x)` the first and last may coincide.
1174 // help: missing parentheses
1176 // L | let A((x, y)) = A((1, 2));
1178 [first, ..] => (first.span.shrink_to_lo(), subpats.last().unwrap().span),
1180 err.multipart_suggestion(
1181 "missing parentheses",
1182 vec![(left, "(".to_string()), (right.shrink_to_hi(), ")".to_string())],
1183 Applicability::MachineApplicable,
1185 } else if fields.len() > subpats.len() && pat_span != DUMMY_SP {
1186 let after_fields_span = pat_span.with_hi(pat_span.hi() - BytePos(1)).shrink_to_hi();
1187 let all_fields_span = match subpats {
1188 [] => after_fields_span,
1189 [field] => field.span,
1190 [first, .., last] => first.span.to(last.span),
1193 // Check if all the fields in the pattern are wildcards.
1194 let all_wildcards = subpats.iter().all(|pat| matches!(pat.kind, PatKind::Wild));
1195 let first_tail_wildcard =
1196 subpats.iter().enumerate().fold(None, |acc, (pos, pat)| match (acc, &pat.kind) {
1197 (None, PatKind::Wild) => Some(pos),
1198 (Some(_), PatKind::Wild) => acc,
1201 let tail_span = match first_tail_wildcard {
1202 None => after_fields_span,
1203 Some(0) => subpats[0].span.to(after_fields_span),
1204 Some(pos) => subpats[pos - 1].span.shrink_to_hi().to(after_fields_span),
1207 // FIXME: heuristic-based suggestion to check current types for where to add `_`.
1208 let mut wildcard_sugg = vec!["_"; fields.len() - subpats.len()].join(", ");
1209 if !subpats.is_empty() {
1210 wildcard_sugg = String::from(", ") + &wildcard_sugg;
1213 err.span_suggestion_verbose(
1215 "use `_` to explicitly ignore each field",
1217 Applicability::MaybeIncorrect,
1220 // Only suggest `..` if more than one field is missing
1221 // or the pattern consists of all wildcards.
1222 if fields.len() - subpats.len() > 1 || all_wildcards {
1223 if subpats.is_empty() || all_wildcards {
1224 err.span_suggestion_verbose(
1226 "use `..` to ignore all fields",
1228 Applicability::MaybeIncorrect,
1231 err.span_suggestion_verbose(
1233 "use `..` to ignore the rest of the fields",
1235 Applicability::MaybeIncorrect,
1247 elements: &'tcx [Pat<'tcx>],
1248 ddpos: hir::DotDotPos,
1250 def_bm: BindingMode,
1254 let mut expected_len = elements.len();
1255 if ddpos.as_opt_usize().is_some() {
1256 // Require known type only when `..` is present.
1257 if let ty::Tuple(tys) = self.structurally_resolved_type(span, expected).kind() {
1258 expected_len = tys.len();
1261 let max_len = cmp::max(expected_len, elements.len());
1263 let element_tys_iter = (0..max_len).map(|_| {
1265 // FIXME: `MiscVariable` for now -- obtaining the span and name information
1266 // from all tuple elements isn't trivial.
1267 TypeVariableOrigin { kind: TypeVariableOriginKind::TypeInference, span },
1270 let element_tys = tcx.mk_type_list(element_tys_iter);
1271 let pat_ty = tcx.mk_ty(ty::Tuple(element_tys));
1272 if let Some(mut err) = self.demand_eqtype_pat_diag(span, expected, pat_ty, ti) {
1273 let reported = err.emit();
1274 // Walk subpatterns with an expected type of `err` in this case to silence
1275 // further errors being emitted when using the bindings. #50333
1276 let element_tys_iter = (0..max_len).map(|_| tcx.ty_error_with_guaranteed(reported));
1277 for (_, elem) in elements.iter().enumerate_and_adjust(max_len, ddpos) {
1278 self.check_pat(elem, tcx.ty_error_with_guaranteed(reported), def_bm, ti);
1280 tcx.mk_tup(element_tys_iter)
1282 for (i, elem) in elements.iter().enumerate_and_adjust(max_len, ddpos) {
1283 self.check_pat(elem, element_tys[i], def_bm, ti);
1289 fn check_struct_pat_fields(
1292 pat: &'tcx Pat<'tcx>,
1293 variant: &'tcx ty::VariantDef,
1294 fields: &'tcx [hir::PatField<'tcx>],
1296 def_bm: BindingMode,
1301 let ty::Adt(adt, substs) = adt_ty.kind() else {
1302 span_bug!(pat.span, "struct pattern is not an ADT");
1305 // Index the struct fields' types.
1306 let field_map = variant
1310 .map(|(i, field)| (field.ident(self.tcx).normalize_to_macros_2_0(), (i, field)))
1311 .collect::<FxHashMap<_, _>>();
1313 // Keep track of which fields have already appeared in the pattern.
1314 let mut used_fields = FxHashMap::default();
1315 let mut no_field_errors = true;
1317 let mut inexistent_fields = vec![];
1318 // Typecheck each field.
1319 for field in fields {
1320 let span = field.span;
1321 let ident = tcx.adjust_ident(field.ident, variant.def_id);
1322 let field_ty = match used_fields.entry(ident) {
1323 Occupied(occupied) => {
1324 self.error_field_already_bound(span, field.ident, *occupied.get());
1325 no_field_errors = false;
1329 vacant.insert(span);
1333 self.write_field_index(field.hir_id, *i);
1334 self.tcx.check_stability(f.did, Some(pat.hir_id), span, None);
1335 self.field_ty(span, f, substs)
1337 .unwrap_or_else(|| {
1338 inexistent_fields.push(field);
1339 no_field_errors = false;
1345 self.check_pat(field.pat, field_ty, def_bm, ti);
1348 let mut unmentioned_fields = variant
1351 .map(|field| (field, field.ident(self.tcx).normalize_to_macros_2_0()))
1352 .filter(|(_, ident)| !used_fields.contains_key(ident))
1353 .collect::<Vec<_>>();
1355 let inexistent_fields_err = if !(inexistent_fields.is_empty() || variant.is_recovered())
1356 && !inexistent_fields.iter().any(|field| field.ident.name == kw::Underscore)
1358 Some(self.error_inexistent_fields(
1359 adt.variant_descr(),
1361 &mut unmentioned_fields,
1369 // Require `..` if struct has non_exhaustive attribute.
1370 let non_exhaustive = variant.is_field_list_non_exhaustive() && !adt.did().is_local();
1371 if non_exhaustive && !has_rest_pat {
1372 self.error_foreign_non_exhaustive_spat(pat, adt.variant_descr(), fields.is_empty());
1375 let mut unmentioned_err = None;
1376 // Report an error if an incorrect number of fields was specified.
1378 if fields.len() != 1 {
1380 .struct_span_err(pat.span, "union patterns should have exactly one field")
1384 tcx.sess.struct_span_err(pat.span, "`..` cannot be used in union patterns").emit();
1386 } else if !unmentioned_fields.is_empty() {
1387 let accessible_unmentioned_fields: Vec<_> = unmentioned_fields
1390 .filter(|(field, _)| {
1391 field.vis.is_accessible_from(tcx.parent_module(pat.hir_id), tcx)
1393 tcx.eval_stability(field.did, None, DUMMY_SP, None),
1394 EvalResult::Deny { .. }
1396 // We only want to report the error if it is hidden and not local
1397 && !(tcx.is_doc_hidden(field.did) && !field.did.is_local())
1402 if accessible_unmentioned_fields.is_empty() {
1403 unmentioned_err = Some(self.error_no_accessible_fields(pat, fields));
1405 unmentioned_err = Some(self.error_unmentioned_fields(
1407 &accessible_unmentioned_fields,
1408 accessible_unmentioned_fields.len() != unmentioned_fields.len(),
1412 } else if non_exhaustive && !accessible_unmentioned_fields.is_empty() {
1413 self.lint_non_exhaustive_omitted_patterns(
1415 &accessible_unmentioned_fields,
1420 match (inexistent_fields_err, unmentioned_err) {
1421 (Some(mut i), Some(mut u)) => {
1422 if let Some(mut e) = self.error_tuple_variant_as_struct_pat(pat, fields, variant) {
1423 // We don't want to show the nonexistent fields error when this was
1424 // `Foo { a, b }` when it should have been `Foo(a, b)`.
1433 (None, Some(mut u)) => {
1434 if let Some(mut e) = self.error_tuple_variant_as_struct_pat(pat, fields, variant) {
1441 (Some(mut err), None) => {
1444 (None, None) if let Some(mut err) =
1445 self.error_tuple_variant_index_shorthand(variant, pat, fields) =>
1454 fn error_tuple_variant_index_shorthand(
1456 variant: &VariantDef,
1458 fields: &[hir::PatField<'_>],
1459 ) -> Option<DiagnosticBuilder<'_, ErrorGuaranteed>> {
1460 // if this is a tuple struct, then all field names will be numbers
1461 // so if any fields in a struct pattern use shorthand syntax, they will
1462 // be invalid identifiers (for example, Foo { 0, 1 }).
1463 if let (Some(CtorKind::Fn), PatKind::Struct(qpath, field_patterns, ..)) =
1464 (variant.ctor_kind(), &pat.kind)
1466 let has_shorthand_field_name = field_patterns.iter().any(|field| field.is_shorthand);
1467 if has_shorthand_field_name {
1468 let path = rustc_hir_pretty::to_string(rustc_hir_pretty::NO_ANN, |s| {
1469 s.print_qpath(qpath, false)
1471 let mut err = struct_span_err!(
1475 "tuple variant `{path}` written as struct variant",
1477 err.span_suggestion_verbose(
1478 qpath.span().shrink_to_hi().to(pat.span.shrink_to_hi()),
1479 "use the tuple variant pattern syntax instead",
1480 format!("({})", self.get_suggested_tuple_struct_pattern(fields, variant)),
1481 Applicability::MaybeIncorrect,
1489 fn error_foreign_non_exhaustive_spat(&self, pat: &Pat<'_>, descr: &str, no_fields: bool) {
1490 let sess = self.tcx.sess;
1491 let sm = sess.source_map();
1492 let sp_brace = sm.end_point(pat.span);
1493 let sp_comma = sm.end_point(pat.span.with_hi(sp_brace.hi()));
1494 let sugg = if no_fields || sp_brace != sp_comma { ".. }" } else { ", .. }" };
1496 let mut err = struct_span_err!(
1500 "`..` required with {descr} marked as non-exhaustive",
1502 err.span_suggestion_verbose(
1504 "add `..` at the end of the field list to ignore all other fields",
1506 Applicability::MachineApplicable,
1511 fn error_field_already_bound(&self, span: Span, ident: Ident, other_field: Span) {
1516 "field `{}` bound multiple times in the pattern",
1519 .span_label(span, format!("multiple uses of `{ident}` in pattern"))
1520 .span_label(other_field, format!("first use of `{ident}`"))
1524 fn error_inexistent_fields(
1527 inexistent_fields: &[&hir::PatField<'tcx>],
1528 unmentioned_fields: &mut Vec<(&'tcx ty::FieldDef, Ident)>,
1529 variant: &ty::VariantDef,
1530 substs: &'tcx ty::List<ty::subst::GenericArg<'tcx>>,
1531 ) -> DiagnosticBuilder<'tcx, ErrorGuaranteed> {
1533 let (field_names, t, plural) = if inexistent_fields.len() == 1 {
1534 (format!("a field named `{}`", inexistent_fields[0].ident), "this", "")
1541 .map(|field| format!("`{}`", field.ident))
1542 .collect::<Vec<String>>()
1549 let spans = inexistent_fields.iter().map(|field| field.ident.span).collect::<Vec<_>>();
1550 let mut err = struct_span_err!(
1554 "{} `{}` does not have {}",
1556 tcx.def_path_str(variant.def_id),
1559 if let Some(pat_field) = inexistent_fields.last() {
1561 pat_field.ident.span,
1563 "{} `{}` does not have {} field{}",
1565 tcx.def_path_str(variant.def_id),
1571 if unmentioned_fields.len() == 1 {
1573 unmentioned_fields.iter().map(|(_, field)| field.name).collect::<Vec<_>>();
1574 let suggested_name = find_best_match_for_name(&input, pat_field.ident.name, None);
1575 if let Some(suggested_name) = suggested_name {
1576 err.span_suggestion(
1577 pat_field.ident.span,
1578 "a field with a similar name exists",
1580 Applicability::MaybeIncorrect,
1583 // When we have a tuple struct used with struct we don't want to suggest using
1584 // the (valid) struct syntax with numeric field names. Instead we want to
1585 // suggest the expected syntax. We infer that this is the case by parsing the
1586 // `Ident` into an unsized integer. The suggestion will be emitted elsewhere in
1587 // `smart_resolve_context_dependent_help`.
1588 if suggested_name.to_ident_string().parse::<usize>().is_err() {
1589 // We don't want to throw `E0027` in case we have thrown `E0026` for them.
1590 unmentioned_fields.retain(|&(_, x)| x.name != suggested_name);
1592 } else if inexistent_fields.len() == 1 {
1593 match pat_field.pat.kind {
1595 if !self.can_coerce(
1596 self.typeck_results.borrow().expr_ty(expr),
1598 unmentioned_fields[0].1.span,
1599 unmentioned_fields[0].0,
1604 let unmentioned_field = unmentioned_fields[0].1.name;
1605 err.span_suggestion_short(
1606 pat_field.ident.span,
1608 "`{}` has a field named `{}`",
1609 tcx.def_path_str(variant.def_id),
1612 unmentioned_field.to_string(),
1613 Applicability::MaybeIncorrect,
1620 if tcx.sess.teach(&err.get_code().unwrap()) {
1622 "This error indicates that a struct pattern attempted to \
1623 extract a non-existent field from a struct. Struct fields \
1624 are identified by the name used before the colon : so struct \
1625 patterns should resemble the declaration of the struct type \
1627 If you are using shorthand field patterns but want to refer \
1628 to the struct field by a different name, you should rename \
1635 fn error_tuple_variant_as_struct_pat(
1638 fields: &'tcx [hir::PatField<'tcx>],
1639 variant: &ty::VariantDef,
1640 ) -> Option<DiagnosticBuilder<'tcx, ErrorGuaranteed>> {
1641 if let (Some(CtorKind::Fn), PatKind::Struct(qpath, ..)) = (variant.ctor_kind(), &pat.kind) {
1642 let path = rustc_hir_pretty::to_string(rustc_hir_pretty::NO_ANN, |s| {
1643 s.print_qpath(qpath, false)
1645 let mut err = struct_span_err!(
1649 "tuple variant `{}` written as struct variant",
1652 let (sugg, appl) = if fields.len() == variant.fields.len() {
1654 self.get_suggested_tuple_struct_pattern(fields, variant),
1655 Applicability::MachineApplicable,
1659 variant.fields.iter().map(|_| "_").collect::<Vec<&str>>().join(", "),
1660 Applicability::MaybeIncorrect,
1663 err.span_suggestion_verbose(
1664 qpath.span().shrink_to_hi().to(pat.span.shrink_to_hi()),
1665 "use the tuple variant pattern syntax instead",
1666 format!("({})", sugg),
1674 fn get_suggested_tuple_struct_pattern(
1676 fields: &[hir::PatField<'_>],
1677 variant: &VariantDef,
1679 let variant_field_idents =
1680 variant.fields.iter().map(|f| f.ident(self.tcx)).collect::<Vec<Ident>>();
1684 match self.tcx.sess.source_map().span_to_snippet(field.pat.span) {
1686 // Field names are numbers, but numbers
1687 // are not valid identifiers
1688 if variant_field_idents.contains(&field.ident) {
1694 Err(_) => rustc_hir_pretty::to_string(rustc_hir_pretty::NO_ANN, |s| {
1695 s.print_pat(field.pat)
1699 .collect::<Vec<String>>()
1703 /// Returns a diagnostic reporting a struct pattern which is missing an `..` due to
1704 /// inaccessible fields.
1707 /// error: pattern requires `..` due to inaccessible fields
1708 /// --> src/main.rs:10:9
1710 /// LL | let foo::Foo {} = foo::Foo::default();
1713 /// help: add a `..`
1715 /// LL | let foo::Foo { .. } = foo::Foo::default();
1718 fn error_no_accessible_fields(
1721 fields: &'tcx [hir::PatField<'tcx>],
1722 ) -> DiagnosticBuilder<'tcx, ErrorGuaranteed> {
1726 .struct_span_err(pat.span, "pattern requires `..` due to inaccessible fields");
1728 if let Some(field) = fields.last() {
1729 err.span_suggestion_verbose(
1730 field.span.shrink_to_hi(),
1731 "ignore the inaccessible and unused fields",
1733 Applicability::MachineApplicable,
1736 let qpath_span = if let PatKind::Struct(qpath, ..) = &pat.kind {
1739 bug!("`error_no_accessible_fields` called on non-struct pattern");
1742 // Shrink the span to exclude the `foo:Foo` in `foo::Foo { }`.
1743 let span = pat.span.with_lo(qpath_span.shrink_to_hi().hi());
1744 err.span_suggestion_verbose(
1746 "ignore the inaccessible and unused fields",
1748 Applicability::MachineApplicable,
1754 /// Report that a pattern for a `#[non_exhaustive]` struct marked with `non_exhaustive_omitted_patterns`
1755 /// is not exhaustive enough.
1757 /// Nb: the partner lint for enums lives in `compiler/rustc_mir_build/src/thir/pattern/usefulness.rs`.
1758 fn lint_non_exhaustive_omitted_patterns(
1761 unmentioned_fields: &[(&ty::FieldDef, Ident)],
1764 fn joined_uncovered_patterns(witnesses: &[&Ident]) -> String {
1765 const LIMIT: usize = 3;
1768 [witness] => format!("`{}`", witness),
1769 [head @ .., tail] if head.len() < LIMIT => {
1770 let head: Vec<_> = head.iter().map(<_>::to_string).collect();
1771 format!("`{}` and `{}`", head.join("`, `"), tail)
1774 let (head, tail) = witnesses.split_at(LIMIT);
1775 let head: Vec<_> = head.iter().map(<_>::to_string).collect();
1776 format!("`{}` and {} more", head.join("`, `"), tail.len())
1780 let joined_patterns = joined_uncovered_patterns(
1781 &unmentioned_fields.iter().map(|(_, i)| i).collect::<Vec<_>>(),
1784 self.tcx.struct_span_lint_hir(NON_EXHAUSTIVE_OMITTED_PATTERNS, pat.hir_id, pat.span, "some fields are not explicitly listed", |lint| {
1785 lint.span_label(pat.span, format!("field{} {} not listed", rustc_errors::pluralize!(unmentioned_fields.len()), joined_patterns));
1787 "ensure that all fields are mentioned explicitly by adding the suggested fields",
1790 "the pattern is of type `{}` and the `non_exhaustive_omitted_patterns` attribute was found",
1798 /// Returns a diagnostic reporting a struct pattern which does not mention some fields.
1801 /// error[E0027]: pattern does not mention field `bar`
1802 /// --> src/main.rs:15:9
1804 /// LL | let foo::Foo {} = foo::Foo::new();
1805 /// | ^^^^^^^^^^^ missing field `bar`
1807 fn error_unmentioned_fields(
1810 unmentioned_fields: &[(&ty::FieldDef, Ident)],
1811 have_inaccessible_fields: bool,
1812 fields: &'tcx [hir::PatField<'tcx>],
1813 ) -> DiagnosticBuilder<'tcx, ErrorGuaranteed> {
1814 let inaccessible = if have_inaccessible_fields { " and inaccessible fields" } else { "" };
1815 let field_names = if unmentioned_fields.len() == 1 {
1816 format!("field `{}`{}", unmentioned_fields[0].1, inaccessible)
1818 let fields = unmentioned_fields
1820 .map(|(_, name)| format!("`{}`", name))
1821 .collect::<Vec<String>>()
1823 format!("fields {}{}", fields, inaccessible)
1825 let mut err = struct_span_err!(
1829 "pattern does not mention {}",
1832 err.span_label(pat.span, format!("missing {}", field_names));
1833 let len = unmentioned_fields.len();
1834 let (prefix, postfix, sp) = match fields {
1835 [] => match &pat.kind {
1836 PatKind::Struct(path, [], false) => {
1837 (" { ", " }", path.span().shrink_to_hi().until(pat.span.shrink_to_hi()))
1842 // Account for last field having a trailing comma or parse recovery at the tail of
1843 // the pattern to avoid invalid suggestion (#78511).
1844 let tail = field.span.shrink_to_hi().with_hi(pat.span.hi());
1846 PatKind::Struct(..) => (", ", " }", tail),
1851 err.span_suggestion(
1854 "include the missing field{} in the pattern{}",
1856 if have_inaccessible_fields { " and ignore the inaccessible fields" } else { "" }
1863 .map(|(_, name)| name.to_string())
1864 .collect::<Vec<_>>()
1866 if have_inaccessible_fields { ", .." } else { "" },
1869 Applicability::MachineApplicable,
1871 err.span_suggestion(
1874 "if you don't care about {these} missing field{s}, you can explicitly ignore {them}",
1875 these = pluralize!("this", len),
1876 s = pluralize!(len),
1877 them = if len == 1 { "it" } else { "them" },
1879 format!("{}..{}", prefix, postfix),
1880 Applicability::MachineApplicable,
1888 inner: &'tcx Pat<'tcx>,
1890 def_bm: BindingMode,
1894 let (box_ty, inner_ty) = if self.check_dereferenceable(span, expected, inner) {
1895 // Here, `demand::subtype` is good enough, but I don't
1896 // think any errors can be introduced by using `demand::eqtype`.
1897 let inner_ty = self.next_ty_var(TypeVariableOrigin {
1898 kind: TypeVariableOriginKind::TypeInference,
1901 let box_ty = tcx.mk_box(inner_ty);
1902 self.demand_eqtype_pat(span, expected, box_ty, ti);
1905 let err = tcx.ty_error();
1908 self.check_pat(inner, inner_ty, def_bm, ti);
1912 // Precondition: Pat is Ref(inner)
1915 pat: &'tcx Pat<'tcx>,
1916 inner: &'tcx Pat<'tcx>,
1917 mutbl: hir::Mutability,
1919 def_bm: BindingMode,
1923 let expected = self.shallow_resolve(expected);
1924 let (rptr_ty, inner_ty) = if self.check_dereferenceable(pat.span, expected, inner) {
1925 // `demand::subtype` would be good enough, but using `eqtype` turns
1926 // out to be equally general. See (note_1) for details.
1928 // Take region, inner-type from expected type if we can,
1929 // to avoid creating needless variables. This also helps with
1930 // the bad interactions of the given hack detailed in (note_1).
1931 debug!("check_pat_ref: expected={:?}", expected);
1932 match *expected.kind() {
1933 ty::Ref(_, r_ty, r_mutbl) if r_mutbl == mutbl => (expected, r_ty),
1935 let inner_ty = self.next_ty_var(TypeVariableOrigin {
1936 kind: TypeVariableOriginKind::TypeInference,
1939 let rptr_ty = self.new_ref_ty(pat.span, mutbl, inner_ty);
1940 debug!("check_pat_ref: demanding {:?} = {:?}", expected, rptr_ty);
1941 let err = self.demand_eqtype_pat_diag(pat.span, expected, rptr_ty, ti);
1943 // Look for a case like `fn foo(&foo: u32)` and suggest
1944 // `fn foo(foo: &u32)`
1945 if let Some(mut err) = err {
1946 self.borrow_pat_suggestion(&mut err, pat);
1953 let err = tcx.ty_error();
1956 self.check_pat(inner, inner_ty, def_bm, ti);
1960 /// Create a reference type with a fresh region variable.
1961 fn new_ref_ty(&self, span: Span, mutbl: hir::Mutability, ty: Ty<'tcx>) -> Ty<'tcx> {
1962 let region = self.next_region_var(infer::PatternRegion(span));
1963 let mt = ty::TypeAndMut { ty, mutbl };
1964 self.tcx.mk_ref(region, mt)
1967 /// Type check a slice pattern.
1969 /// Syntactically, these look like `[pat_0, ..., pat_n]`.
1970 /// Semantically, we are type checking a pattern with structure:
1971 /// ```ignore (not-rust)
1972 /// [before_0, ..., before_n, (slice, after_0, ... after_n)?]
1974 /// The type of `slice`, if it is present, depends on the `expected` type.
1975 /// If `slice` is missing, then so is `after_i`.
1976 /// If `slice` is present, it can still represent 0 elements.
1980 before: &'tcx [Pat<'tcx>],
1981 slice: Option<&'tcx Pat<'tcx>>,
1982 after: &'tcx [Pat<'tcx>],
1984 def_bm: BindingMode,
1987 let expected = self.structurally_resolved_type(span, expected);
1988 let (element_ty, opt_slice_ty, inferred) = match *expected.kind() {
1989 // An array, so we might have something like `let [a, b, c] = [0, 1, 2];`.
1990 ty::Array(element_ty, len) => {
1991 let min = before.len() as u64 + after.len() as u64;
1992 let (opt_slice_ty, expected) =
1993 self.check_array_pat_len(span, element_ty, expected, slice, len, min);
1994 // `opt_slice_ty.is_none()` => `slice.is_none()`.
1995 // Note, though, that opt_slice_ty could be `Some(error_ty)`.
1996 assert!(opt_slice_ty.is_some() || slice.is_none());
1997 (element_ty, opt_slice_ty, expected)
1999 ty::Slice(element_ty) => (element_ty, Some(expected), expected),
2000 // The expected type must be an array or slice, but was neither, so error.
2002 if !expected.references_error() {
2003 self.error_expected_array_or_slice(span, expected, ti);
2005 let err = self.tcx.ty_error();
2006 (err, Some(err), err)
2010 // Type check all the patterns before `slice`.
2012 self.check_pat(elt, element_ty, def_bm, ti);
2014 // Type check the `slice`, if present, against its expected type.
2015 if let Some(slice) = slice {
2016 self.check_pat(slice, opt_slice_ty.unwrap(), def_bm, ti);
2018 // Type check the elements after `slice`, if present.
2020 self.check_pat(elt, element_ty, def_bm, ti);
2025 /// Type check the length of an array pattern.
2027 /// Returns both the type of the variable length pattern (or `None`), and the potentially
2028 /// inferred array type. We only return `None` for the slice type if `slice.is_none()`.
2029 fn check_array_pat_len(
2032 element_ty: Ty<'tcx>,
2034 slice: Option<&'tcx Pat<'tcx>>,
2035 len: ty::Const<'tcx>,
2037 ) -> (Option<Ty<'tcx>>, Ty<'tcx>) {
2038 if let Some(len) = len.try_eval_usize(self.tcx, self.param_env) {
2039 // Now we know the length...
2040 if slice.is_none() {
2041 // ...and since there is no variable-length pattern,
2042 // we require an exact match between the number of elements
2043 // in the array pattern and as provided by the matched type.
2045 return (None, arr_ty);
2048 self.error_scrutinee_inconsistent_length(span, min_len, len);
2049 } else if let Some(pat_len) = len.checked_sub(min_len) {
2050 // The variable-length pattern was there,
2051 // so it has an array type with the remaining elements left as its size...
2052 return (Some(self.tcx.mk_array(element_ty, pat_len)), arr_ty);
2054 // ...however, in this case, there were no remaining elements.
2055 // That is, the slice pattern requires more than the array type offers.
2056 self.error_scrutinee_with_rest_inconsistent_length(span, min_len, len);
2058 } else if slice.is_none() {
2059 // We have a pattern with a fixed length,
2060 // which we can use to infer the length of the array.
2061 let updated_arr_ty = self.tcx.mk_array(element_ty, min_len);
2062 self.demand_eqtype(span, updated_arr_ty, arr_ty);
2063 return (None, updated_arr_ty);
2065 // We have a variable-length pattern and don't know the array length.
2066 // This happens if we have e.g.,
2067 // `let [a, b, ..] = arr` where `arr: [T; N]` where `const N: usize`.
2068 self.error_scrutinee_unfixed_length(span);
2071 // If we get here, we must have emitted an error.
2072 (Some(self.tcx.ty_error()), arr_ty)
2075 fn error_scrutinee_inconsistent_length(&self, span: Span, min_len: u64, size: u64) {
2080 "pattern requires {} element{} but array has {}",
2082 pluralize!(min_len),
2085 .span_label(span, format!("expected {} element{}", size, pluralize!(size)))
2089 fn error_scrutinee_with_rest_inconsistent_length(&self, span: Span, min_len: u64, size: u64) {
2094 "pattern requires at least {} element{} but array has {}",
2096 pluralize!(min_len),
2101 format!("pattern cannot match array of {} element{}", size, pluralize!(size),),
2106 fn error_scrutinee_unfixed_length(&self, span: Span) {
2111 "cannot pattern-match on an array without a fixed length",
2116 fn error_expected_array_or_slice(&self, span: Span, expected_ty: Ty<'tcx>, ti: TopInfo<'tcx>) {
2117 let mut err = struct_span_err!(
2121 "expected an array or slice, found `{expected_ty}`"
2123 if let ty::Ref(_, ty, _) = expected_ty.kind()
2124 && let ty::Array(..) | ty::Slice(..) = ty.kind()
2126 err.help("the semantics of slice patterns changed recently; see issue #62254");
2127 } else if self.autoderef(span, expected_ty)
2128 .any(|(ty, _)| matches!(ty.kind(), ty::Slice(..) | ty::Array(..)))
2129 && let (Some(span), true) = (ti.span, ti.origin_expr)
2130 && let Ok(snippet) = self.tcx.sess.source_map().span_to_snippet(span)
2132 let ty = self.resolve_vars_if_possible(ti.expected);
2133 let is_slice_or_array_or_vector = self.is_slice_or_array_or_vector(&mut err, snippet.clone(), ty);
2134 match is_slice_or_array_or_vector.1.kind() {
2136 if self.tcx.is_diagnostic_item(sym::Option, adt_def.did())
2137 || self.tcx.is_diagnostic_item(sym::Result, adt_def.did()) =>
2139 // Slicing won't work here, but `.as_deref()` might (issue #91328).
2140 err.span_suggestion(
2142 "consider using `as_deref` here",
2143 format!("{snippet}.as_deref()"),
2144 Applicability::MaybeIncorrect,
2149 if is_slice_or_array_or_vector.0 {
2150 err.span_suggestion(
2152 "consider slicing here",
2153 format!("{snippet}[..]"),
2154 Applicability::MachineApplicable,
2158 err.span_label(span, format!("pattern cannot match with input type `{expected_ty}`"));
2162 fn is_slice_or_array_or_vector(
2164 err: &mut Diagnostic,
2167 ) -> (bool, Ty<'tcx>) {
2169 ty::Adt(adt_def, _) if self.tcx.is_diagnostic_item(sym::Vec, adt_def.did()) => {
2172 ty::Ref(_, ty, _) => self.is_slice_or_array_or_vector(err, snippet, *ty),
2173 ty::Slice(..) | ty::Array(..) => (true, ty),