1 use crate::check::FnCtxt;
4 use rustc_data_structures::fx::FxHashMap;
6 pluralize, struct_span_err, Applicability, Diagnostic, DiagnosticBuilder, ErrorGuaranteed,
10 use rustc_hir::def::{CtorKind, DefKind, Res};
11 use rustc_hir::pat_util::EnumerateAndAdjustIterator;
12 use rustc_hir::{HirId, Pat, PatKind};
13 use rustc_infer::infer;
14 use rustc_infer::infer::type_variable::{TypeVariableOrigin, TypeVariableOriginKind};
15 use rustc_middle::middle::stability::EvalResult;
16 use rustc_middle::ty::{self, Adt, BindingMode, Ty, TypeVisitable};
17 use rustc_session::lint::builtin::NON_EXHAUSTIVE_OMITTED_PATTERNS;
18 use rustc_span::hygiene::DesugaringKind;
19 use rustc_span::lev_distance::find_best_match_for_name;
20 use rustc_span::source_map::{Span, Spanned};
21 use rustc_span::symbol::{kw, sym, Ident};
22 use rustc_span::{BytePos, DUMMY_SP};
23 use rustc_trait_selection::autoderef::Autoderef;
24 use rustc_trait_selection::traits::{ObligationCause, Pattern};
28 use std::collections::hash_map::Entry::{Occupied, Vacant};
30 use super::report_unexpected_variant_res;
32 const CANNOT_IMPLICITLY_DEREF_POINTER_TRAIT_OBJ: &str = "\
33 This error indicates that a pointer to a trait type cannot be implicitly dereferenced by a \
34 pattern. Every trait defines a type, but because the size of trait implementors isn't fixed, \
35 this type has no compile-time size. Therefore, all accesses to trait types must be through \
36 pointers. If you encounter this error you should try to avoid dereferencing the pointer.
38 You can read more about trait objects in the Trait Objects section of the Reference: \
39 https://doc.rust-lang.org/reference/types.html#trait-objects";
41 /// Information about the expected type at the top level of type checking a pattern.
43 /// **NOTE:** This is only for use by diagnostics. Do NOT use for type checking logic!
44 #[derive(Copy, Clone)]
45 struct TopInfo<'tcx> {
46 /// The `expected` type at the top level of type checking a pattern.
48 /// Was the origin of the `span` from a scrutinee expression?
50 /// Otherwise there is no scrutinee and it could be e.g. from the type of a formal parameter.
52 /// The span giving rise to the `expected` type, if one could be provided.
54 /// If `origin_expr` is `true`, then this is the span of the scrutinee as in:
56 /// - `match scrutinee { ... }`
57 /// - `let _ = scrutinee;`
59 /// This is used to point to add context in type errors.
60 /// In the following example, `span` corresponds to the `a + b` expression:
63 /// error[E0308]: mismatched types
64 /// --> src/main.rs:L:C
66 /// L | let temp: usize = match a + b {
67 /// | ----- this expression has type `usize`
68 /// L | Ok(num) => num,
69 /// | ^^^^^^^ expected `usize`, found enum `std::result::Result`
71 /// = note: expected type `usize`
72 /// found type `std::result::Result<_, _>`
77 impl<'tcx> FnCtxt<'_, 'tcx> {
78 fn pattern_cause(&self, ti: TopInfo<'tcx>, cause_span: Span) -> ObligationCause<'tcx> {
79 let code = Pattern { span: ti.span, root_ty: ti.expected, origin_expr: ti.origin_expr };
80 self.cause(cause_span, code)
83 fn demand_eqtype_pat_diag(
89 ) -> Option<DiagnosticBuilder<'tcx, ErrorGuaranteed>> {
90 self.demand_eqtype_with_origin(&self.pattern_cause(ti, cause_span), expected, actual)
100 if let Some(mut err) = self.demand_eqtype_pat_diag(cause_span, expected, actual, ti) {
106 const INITIAL_BM: BindingMode = BindingMode::BindByValue(hir::Mutability::Not);
108 /// Mode for adjusting the expected type and binding mode.
110 /// Peel off all immediate reference types.
112 /// Reset binding mode to the initial mode.
114 /// Pass on the input binding mode and expected type.
118 impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
119 /// Type check the given top level pattern against the `expected` type.
121 /// If a `Some(span)` is provided and `origin_expr` holds,
122 /// then the `span` represents the scrutinee's span.
123 /// The scrutinee is found in e.g. `match scrutinee { ... }` and `let pat = scrutinee;`.
125 /// Otherwise, `Some(span)` represents the span of a type expression
126 /// which originated the `expected` type.
127 pub fn check_pat_top(
129 pat: &'tcx Pat<'tcx>,
134 let info = TopInfo { expected, origin_expr, span };
135 self.check_pat(pat, expected, INITIAL_BM, info);
138 /// Type check the given `pat` against the `expected` type
139 /// with the provided `def_bm` (default binding mode).
141 /// Outside of this module, `check_pat_top` should always be used.
142 /// Conversely, inside this module, `check_pat_top` should never be used.
143 #[instrument(level = "debug", skip(self, ti))]
146 pat: &'tcx Pat<'tcx>,
151 let path_res = match &pat.kind {
152 PatKind::Path(qpath) => {
153 Some(self.resolve_ty_and_res_fully_qualified_call(qpath, pat.hir_id, pat.span))
157 let adjust_mode = self.calc_adjust_mode(pat, path_res.map(|(res, ..)| res));
158 let (expected, def_bm) = self.calc_default_binding_mode(pat, expected, def_bm, adjust_mode);
160 let ty = match pat.kind {
161 PatKind::Wild => expected,
162 PatKind::Lit(lt) => self.check_pat_lit(pat.span, lt, expected, ti),
163 PatKind::Range(lhs, rhs, _) => self.check_pat_range(pat.span, lhs, rhs, expected, ti),
164 PatKind::Binding(ba, var_id, _, sub) => {
165 self.check_pat_ident(pat, ba, var_id, sub, expected, def_bm, ti)
167 PatKind::TupleStruct(ref qpath, subpats, ddpos) => {
168 self.check_pat_tuple_struct(pat, qpath, subpats, ddpos, expected, def_bm, ti)
170 PatKind::Path(ref qpath) => {
171 self.check_pat_path(pat, qpath, path_res.unwrap(), expected, ti)
173 PatKind::Struct(ref qpath, fields, has_rest_pat) => {
174 self.check_pat_struct(pat, qpath, fields, has_rest_pat, expected, def_bm, ti)
176 PatKind::Or(pats) => {
178 self.check_pat(pat, expected, def_bm, ti);
182 PatKind::Tuple(elements, ddpos) => {
183 self.check_pat_tuple(pat.span, elements, ddpos, expected, def_bm, ti)
185 PatKind::Box(inner) => self.check_pat_box(pat.span, inner, expected, def_bm, ti),
186 PatKind::Ref(inner, mutbl) => {
187 self.check_pat_ref(pat, inner, mutbl, expected, def_bm, ti)
189 PatKind::Slice(before, slice, after) => {
190 self.check_pat_slice(pat.span, before, slice, after, expected, def_bm, ti)
194 self.write_ty(pat.hir_id, ty);
196 // (note_1): In most of the cases where (note_1) is referenced
197 // (literals and constants being the exception), we relate types
198 // using strict equality, even though subtyping would be sufficient.
199 // There are a few reasons for this, some of which are fairly subtle
200 // and which cost me (nmatsakis) an hour or two debugging to remember,
201 // so I thought I'd write them down this time.
203 // 1. There is no loss of expressiveness here, though it does
204 // cause some inconvenience. What we are saying is that the type
205 // of `x` becomes *exactly* what is expected. This can cause unnecessary
206 // errors in some cases, such as this one:
209 // fn foo<'x>(x: &'x i32) {
216 // The reason we might get an error is that `z` might be
217 // assigned a type like `&'x i32`, and then we would have
218 // a problem when we try to assign `&a` to `z`, because
219 // the lifetime of `&a` (i.e., the enclosing block) is
220 // shorter than `'x`.
222 // HOWEVER, this code works fine. The reason is that the
223 // expected type here is whatever type the user wrote, not
224 // the initializer's type. In this case the user wrote
225 // nothing, so we are going to create a type variable `Z`.
226 // Then we will assign the type of the initializer (`&'x i32`)
227 // as a subtype of `Z`: `&'x i32 <: Z`. And hence we
228 // will instantiate `Z` as a type `&'0 i32` where `'0` is
229 // a fresh region variable, with the constraint that `'x : '0`.
230 // So basically we're all set.
232 // Note that there are two tests to check that this remains true
233 // (`regions-reassign-{match,let}-bound-pointer.rs`).
235 // 2. Things go horribly wrong if we use subtype. The reason for
236 // THIS is a fairly subtle case involving bound regions. See the
237 // `givens` field in `region_constraints`, as well as the test
238 // `regions-relate-bound-regions-on-closures-to-inference-variables.rs`,
239 // for details. Short version is that we must sometimes detect
240 // relationships between specific region variables and regions
241 // bound in a closure signature, and that detection gets thrown
242 // off when we substitute fresh region variables here to enable
246 /// Compute the new expected type and default binding mode from the old ones
247 /// as well as the pattern form we are currently checking.
248 fn calc_default_binding_mode(
250 pat: &'tcx Pat<'tcx>,
253 adjust_mode: AdjustMode,
254 ) -> (Ty<'tcx>, BindingMode) {
256 AdjustMode::Pass => (expected, def_bm),
257 AdjustMode::Reset => (expected, INITIAL_BM),
258 AdjustMode::Peel => self.peel_off_references(pat, expected, def_bm),
262 /// How should the binding mode and expected type be adjusted?
264 /// When the pattern is a path pattern, `opt_path_res` must be `Some(res)`.
265 fn calc_adjust_mode(&self, pat: &'tcx Pat<'tcx>, opt_path_res: Option<Res>) -> AdjustMode {
266 // When we perform destructuring assignment, we disable default match bindings, which are
267 // unintuitive in this context.
268 if !pat.default_binding_modes {
269 return AdjustMode::Reset;
272 // Type checking these product-like types successfully always require
273 // that the expected type be of those types and not reference types.
275 | PatKind::TupleStruct(..)
279 | PatKind::Slice(..) => AdjustMode::Peel,
280 // String and byte-string literals result in types `&str` and `&[u8]` respectively.
281 // All other literals result in non-reference types.
282 // As a result, we allow `if let 0 = &&0 {}` but not `if let "foo" = &&"foo {}`.
284 // Call `resolve_vars_if_possible` here for inline const blocks.
285 PatKind::Lit(lt) => match self.resolve_vars_if_possible(self.check_expr(lt)).kind() {
286 ty::Ref(..) => AdjustMode::Pass,
287 _ => AdjustMode::Peel,
289 PatKind::Path(_) => match opt_path_res.unwrap() {
290 // These constants can be of a reference type, e.g. `const X: &u8 = &0;`.
291 // Peeling the reference types too early will cause type checking failures.
292 // Although it would be possible to *also* peel the types of the constants too.
293 Res::Def(DefKind::Const | DefKind::AssocConst, _) => AdjustMode::Pass,
294 // In the `ValueNS`, we have `SelfCtor(..) | Ctor(_, Const), _)` remaining which
295 // could successfully compile. The former being `Self` requires a unit struct.
296 // In either case, and unlike constants, the pattern itself cannot be
297 // a reference type wherefore peeling doesn't give up any expressiveness.
298 _ => AdjustMode::Peel,
300 // When encountering a `& mut? pat` pattern, reset to "by value".
301 // This is so that `x` and `y` here are by value, as they appear to be:
304 // match &(&22, &44) {
310 PatKind::Ref(..) => AdjustMode::Reset,
311 // A `_` pattern works with any expected type, so there's no need to do anything.
313 // Bindings also work with whatever the expected type is,
314 // and moreover if we peel references off, that will give us the wrong binding type.
315 // Also, we can have a subpattern `binding @ pat`.
316 // Each side of the `@` should be treated independently (like with OR-patterns).
317 | PatKind::Binding(..)
318 // An OR-pattern just propagates to each individual alternative.
319 // This is maximally flexible, allowing e.g., `Some(mut x) | &Some(mut x)`.
320 // In that example, `Some(mut x)` results in `Peel` whereas `&Some(mut x)` in `Reset`.
321 | PatKind::Or(_) => AdjustMode::Pass,
325 /// Peel off as many immediately nested `& mut?` from the expected type as possible
326 /// and return the new expected type and binding default binding mode.
327 /// The adjustments vector, if non-empty is stored in a table.
328 fn peel_off_references(
330 pat: &'tcx Pat<'tcx>,
332 mut def_bm: BindingMode,
333 ) -> (Ty<'tcx>, BindingMode) {
334 let mut expected = self.resolve_vars_with_obligations(expected);
336 // Peel off as many `&` or `&mut` from the scrutinee type as possible. For example,
337 // for `match &&&mut Some(5)` the loop runs three times, aborting when it reaches
338 // the `Some(5)` which is not of type Ref.
340 // For each ampersand peeled off, update the binding mode and push the original
341 // type into the adjustments vector.
343 // See the examples in `ui/match-defbm*.rs`.
344 let mut pat_adjustments = vec![];
345 while let ty::Ref(_, inner_ty, inner_mutability) = *expected.kind() {
346 debug!("inspecting {:?}", expected);
348 debug!("current discriminant is Ref, inserting implicit deref");
349 // Preserve the reference type. We'll need it later during THIR lowering.
350 pat_adjustments.push(expected);
353 def_bm = ty::BindByReference(match def_bm {
354 // If default binding mode is by value, make it `ref` or `ref mut`
355 // (depending on whether we observe `&` or `&mut`).
357 // When `ref mut`, stay a `ref mut` (on `&mut`) or downgrade to `ref` (on `&`).
358 ty::BindByReference(hir::Mutability::Mut) => inner_mutability,
359 // Once a `ref`, always a `ref`.
360 // This is because a `& &mut` cannot mutate the underlying value.
361 ty::BindByReference(m @ hir::Mutability::Not) => m,
365 if !pat_adjustments.is_empty() {
366 debug!("default binding mode is now {:?}", def_bm);
370 .pat_adjustments_mut()
371 .insert(pat.hir_id, pat_adjustments);
380 lt: &hir::Expr<'tcx>,
384 // We've already computed the type above (when checking for a non-ref pat),
385 // so avoid computing it again.
386 let ty = self.node_ty(lt.hir_id);
388 // Byte string patterns behave the same way as array patterns
389 // They can denote both statically and dynamically-sized byte arrays.
391 if let hir::ExprKind::Lit(Spanned { node: ast::LitKind::ByteStr(_), .. }) = lt.kind {
392 let expected = self.structurally_resolved_type(span, expected);
393 if let ty::Ref(_, inner_ty, _) = expected.kind()
394 && matches!(inner_ty.kind(), ty::Slice(_))
397 trace!(?lt.hir_id.local_id, "polymorphic byte string lit");
400 .treat_byte_string_as_slice
401 .insert(lt.hir_id.local_id);
402 pat_ty = tcx.mk_imm_ref(tcx.lifetimes.re_static, tcx.mk_slice(tcx.types.u8));
406 // Somewhat surprising: in this case, the subtyping relation goes the
407 // opposite way as the other cases. Actually what we really want is not
408 // a subtyping relation at all but rather that there exists a LUB
409 // (so that they can be compared). However, in practice, constants are
410 // always scalars or strings. For scalars subtyping is irrelevant,
411 // and for strings `ty` is type is `&'static str`, so if we say that
413 // &'static str <: expected
415 // then that's equivalent to there existing a LUB.
416 let cause = self.pattern_cause(ti, span);
417 if let Some(mut err) = self.demand_suptype_with_origin(&cause, expected, pat_ty) {
421 // In the case of `if`- and `while`-expressions we've already checked
422 // that `scrutinee: bool`. We know that the pattern is `true`,
423 // so an error here would be a duplicate and from the wrong POV.
424 s.is_desugaring(DesugaringKind::CondTemporary)
436 lhs: Option<&'tcx hir::Expr<'tcx>>,
437 rhs: Option<&'tcx hir::Expr<'tcx>>,
441 let calc_side = |opt_expr: Option<&'tcx hir::Expr<'tcx>>| match opt_expr {
444 let ty = self.check_expr(expr);
445 // Check that the end-point is possibly of numeric or char type.
446 // The early check here is not for correctness, but rather better
447 // diagnostics (e.g. when `&str` is being matched, `expected` will
448 // be peeled to `str` while ty here is still `&str`, if we don't
449 // err early here, a rather confusing unification error will be
452 !(ty.is_numeric() || ty.is_char() || ty.is_ty_var() || ty.references_error());
453 Some((fail, ty, expr.span))
456 let mut lhs = calc_side(lhs);
457 let mut rhs = calc_side(rhs);
459 if let (Some((true, ..)), _) | (_, Some((true, ..))) = (lhs, rhs) {
460 // There exists a side that didn't meet our criteria that the end-point
461 // be of a numeric or char type, as checked in `calc_side` above.
462 self.emit_err_pat_range(span, lhs, rhs);
463 return self.tcx.ty_error();
466 // Unify each side with `expected`.
467 // Subtyping doesn't matter here, as the value is some kind of scalar.
468 let demand_eqtype = |x: &mut _, y| {
469 if let Some((ref mut fail, x_ty, x_span)) = *x
470 && let Some(mut err) = self.demand_eqtype_pat_diag(x_span, expected, x_ty, ti)
472 if let Some((_, y_ty, y_span)) = y {
473 self.endpoint_has_type(&mut err, y_span, y_ty);
479 demand_eqtype(&mut lhs, rhs);
480 demand_eqtype(&mut rhs, lhs);
482 if let (Some((true, ..)), _) | (_, Some((true, ..))) = (lhs, rhs) {
483 return self.tcx.ty_error();
486 // Find the unified type and check if it's of numeric or char type again.
487 // This check is needed if both sides are inference variables.
488 // We require types to be resolved here so that we emit inference failure
489 // rather than "_ is not a char or numeric".
490 let ty = self.structurally_resolved_type(span, expected);
491 if !(ty.is_numeric() || ty.is_char() || ty.references_error()) {
492 if let Some((ref mut fail, _, _)) = lhs {
495 if let Some((ref mut fail, _, _)) = rhs {
498 self.emit_err_pat_range(span, lhs, rhs);
499 return self.tcx.ty_error();
504 fn endpoint_has_type(&self, err: &mut Diagnostic, span: Span, ty: Ty<'_>) {
505 if !ty.references_error() {
506 err.span_label(span, &format!("this is of type `{}`", ty));
510 fn emit_err_pat_range(
513 lhs: Option<(bool, Ty<'tcx>, Span)>,
514 rhs: Option<(bool, Ty<'tcx>, Span)>,
516 let span = match (lhs, rhs) {
517 (Some((true, ..)), Some((true, ..))) => span,
518 (Some((true, _, sp)), _) => sp,
519 (_, Some((true, _, sp))) => sp,
520 _ => span_bug!(span, "emit_err_pat_range: no side failed or exists but still error?"),
522 let mut err = struct_span_err!(
526 "only `char` and numeric types are allowed in range patterns"
529 let ty = self.resolve_vars_if_possible(ty);
530 format!("this is of type `{}` but it should be `char` or numeric", ty)
532 let mut one_side_err = |first_span, first_ty, second: Option<(bool, Ty<'tcx>, Span)>| {
533 err.span_label(first_span, &msg(first_ty));
534 if let Some((_, ty, sp)) = second {
535 let ty = self.resolve_vars_if_possible(ty);
536 self.endpoint_has_type(&mut err, sp, ty);
540 (Some((true, lhs_ty, lhs_sp)), Some((true, rhs_ty, rhs_sp))) => {
541 err.span_label(lhs_sp, &msg(lhs_ty));
542 err.span_label(rhs_sp, &msg(rhs_ty));
544 (Some((true, lhs_ty, lhs_sp)), rhs) => one_side_err(lhs_sp, lhs_ty, rhs),
545 (lhs, Some((true, rhs_ty, rhs_sp))) => one_side_err(rhs_sp, rhs_ty, lhs),
546 _ => span_bug!(span, "Impossible, verified above."),
548 if self.tcx.sess.teach(&err.get_code().unwrap()) {
550 "In a match expression, only numbers and characters can be matched \
551 against a range. This is because the compiler checks that the range \
552 is non-empty at compile-time, and is unable to evaluate arbitrary \
553 comparison functions. If you want to capture values of an orderable \
554 type between two end-points, you can use a guard.",
562 pat: &'tcx Pat<'tcx>,
563 ba: hir::BindingAnnotation,
565 sub: Option<&'tcx Pat<'tcx>>,
570 // Determine the binding mode...
572 hir::BindingAnnotation::Unannotated => def_bm,
573 _ => BindingMode::convert(ba),
575 // ...and store it in a side table:
576 self.inh.typeck_results.borrow_mut().pat_binding_modes_mut().insert(pat.hir_id, bm);
578 debug!("check_pat_ident: pat.hir_id={:?} bm={:?}", pat.hir_id, bm);
580 let local_ty = self.local_ty(pat.span, pat.hir_id).decl_ty;
581 let eq_ty = match bm {
582 ty::BindByReference(mutbl) => {
583 // If the binding is like `ref x | ref mut x`,
584 // then `x` is assigned a value of type `&M T` where M is the
585 // mutability and T is the expected type.
587 // `x` is assigned a value of type `&M T`, hence `&M T <: typeof(x)`
588 // is required. However, we use equality, which is stronger.
589 // See (note_1) for an explanation.
590 self.new_ref_ty(pat.span, mutbl, expected)
592 // Otherwise, the type of x is the expected type `T`.
593 ty::BindByValue(_) => {
594 // As above, `T <: typeof(x)` is required, but we use equality, see (note_1).
598 self.demand_eqtype_pat(pat.span, eq_ty, local_ty, ti);
600 // If there are multiple arms, make sure they all agree on
601 // what the type of the binding `x` ought to be.
602 if var_id != pat.hir_id {
603 self.check_binding_alt_eq_ty(ba, pat.span, var_id, local_ty, ti);
606 if let Some(p) = sub {
607 self.check_pat(p, expected, def_bm, ti);
613 fn check_binding_alt_eq_ty(
615 ba: hir::BindingAnnotation,
621 let var_ty = self.local_ty(span, var_id).decl_ty;
622 if let Some(mut err) = self.demand_eqtype_pat_diag(span, var_ty, ty, ti) {
623 let hir = self.tcx.hir();
624 let var_ty = self.resolve_vars_with_obligations(var_ty);
625 let msg = format!("first introduced with type `{var_ty}` here");
626 err.span_label(hir.span(var_id), msg);
627 let in_match = hir.parent_iter(var_id).any(|(_, n)| {
630 hir::Node::Expr(hir::Expr {
631 kind: hir::ExprKind::Match(.., hir::MatchSource::Normal),
636 let pre = if in_match { "in the same arm, " } else { "" };
637 err.note(&format!("{}a binding must have the same type in all alternatives", pre));
638 self.suggest_adding_missing_ref_or_removing_ref(
642 self.resolve_vars_with_obligations(ty),
649 fn suggest_adding_missing_ref_or_removing_ref(
651 err: &mut Diagnostic,
655 ba: hir::BindingAnnotation,
657 match (expected.kind(), actual.kind(), ba) {
658 (ty::Ref(_, inner_ty, _), _, hir::BindingAnnotation::Unannotated)
659 if self.can_eq(self.param_env, *inner_ty, actual).is_ok() =>
661 err.span_suggestion_verbose(
663 "consider adding `ref`",
665 Applicability::MaybeIncorrect,
668 (_, ty::Ref(_, inner_ty, _), hir::BindingAnnotation::Ref)
669 if self.can_eq(self.param_env, expected, *inner_ty).is_ok() =>
671 err.span_suggestion_verbose(
672 span.with_hi(span.lo() + BytePos(4)),
673 "consider removing `ref`",
675 Applicability::MaybeIncorrect,
682 // Precondition: pat is a Ref(_) pattern
683 fn borrow_pat_suggestion(&self, err: &mut Diagnostic, pat: &Pat<'_>) {
685 if let PatKind::Ref(inner, mutbl) = pat.kind
686 && let PatKind::Binding(_, _, binding, ..) = inner.kind {
687 let binding_parent_id = tcx.hir().get_parent_node(pat.hir_id);
688 let binding_parent = tcx.hir().get(binding_parent_id);
689 debug!(?inner, ?pat, ?binding_parent);
691 let mutability = match mutbl {
692 ast::Mutability::Mut => "mut",
693 ast::Mutability::Not => "",
696 let mut_var_suggestion = 'block: {
697 if !matches!(mutbl, ast::Mutability::Mut) {
701 let ident_kind = match binding_parent {
702 hir::Node::Param(_) => "parameter",
703 hir::Node::Local(_) => "variable",
704 hir::Node::Arm(_) => "binding",
706 // Provide diagnostics only if the parent pattern is struct-like,
707 // i.e. where `mut binding` makes sense
708 hir::Node::Pat(Pat { kind, .. }) => match kind {
710 | PatKind::TupleStruct(..)
713 | PatKind::Slice(..) => "binding",
716 | PatKind::Binding(..)
721 | PatKind::Range(..) => break 'block None,
724 // Don't provide suggestions in other cases
725 _ => break 'block None,
730 format!("to declare a mutable {ident_kind} use"),
731 format!("mut {binding}"),
736 match binding_parent {
737 // Check that there is explicit type (ie this is not a closure param with inferred type)
738 // so we don't suggest moving something to the type that does not exist
739 hir::Node::Param(hir::Param { ty_span, .. }) if binding.span != *ty_span => {
740 err.multipart_suggestion_verbose(
741 format!("to take parameter `{binding}` by reference, move `&{mutability}` to the type"),
743 (pat.span.until(inner.span), "".to_owned()),
744 (ty_span.shrink_to_lo(), format!("&{}", mutbl.prefix_str())),
746 Applicability::MachineApplicable
749 if let Some((sp, msg, sugg)) = mut_var_suggestion {
750 err.span_note(sp, format!("{msg}: `{sugg}`"));
753 hir::Node::Param(_) | hir::Node::Arm(_) | hir::Node::Pat(_) => {
754 // rely on match ergonomics or it might be nested `&&pat`
755 err.span_suggestion_verbose(
756 pat.span.until(inner.span),
757 format!("consider removing `&{mutability}` from the pattern"),
759 Applicability::MaybeIncorrect,
762 if let Some((sp, msg, sugg)) = mut_var_suggestion {
763 err.span_note(sp, format!("{msg}: `{sugg}`"));
766 _ if let Some((sp, msg, sugg)) = mut_var_suggestion => {
767 err.span_suggestion(sp, msg, sugg, Applicability::MachineApplicable);
769 _ => {} // don't provide suggestions in other cases #55175
774 pub fn check_dereferenceable(&self, span: Span, expected: Ty<'tcx>, inner: &Pat<'_>) -> bool {
775 if let PatKind::Binding(..) = inner.kind
776 && let Some(mt) = self.shallow_resolve(expected).builtin_deref(true)
777 && let ty::Dynamic(..) = mt.ty.kind()
779 // This is "x = SomeTrait" being reduced from
780 // "let &x = &SomeTrait" or "let box x = Box<SomeTrait>", an error.
781 let type_str = self.ty_to_string(expected);
782 let mut err = struct_span_err!(
786 "type `{}` cannot be dereferenced",
789 err.span_label(span, format!("type `{type_str}` cannot be dereferenced"));
790 if self.tcx.sess.teach(&err.get_code().unwrap()) {
791 err.note(CANNOT_IMPLICITLY_DEREF_POINTER_TRAIT_OBJ);
801 pat: &'tcx Pat<'tcx>,
802 qpath: &hir::QPath<'_>,
803 fields: &'tcx [hir::PatField<'tcx>],
809 // Resolve the path and check the definition for errors.
810 let Some((variant, pat_ty)) = self.check_struct_path(qpath, pat.hir_id) else {
811 let err = self.tcx.ty_error();
812 for field in fields {
814 self.check_pat(field.pat, err, def_bm, ti);
819 // Type-check the path.
820 self.demand_eqtype_pat(pat.span, expected, pat_ty, ti);
822 // Type-check subpatterns.
823 if self.check_struct_pat_fields(pat_ty, &pat, variant, fields, has_rest_pat, def_bm, ti) {
833 qpath: &hir::QPath<'_>,
834 path_resolution: (Res, Option<Ty<'tcx>>, &'tcx [hir::PathSegment<'tcx>]),
840 // We have already resolved the path.
841 let (res, opt_ty, segments) = path_resolution;
844 self.set_tainted_by_errors();
845 return tcx.ty_error();
847 Res::Def(DefKind::AssocFn | DefKind::Ctor(_, CtorKind::Fictive | CtorKind::Fn), _) => {
848 report_unexpected_variant_res(tcx, res, qpath, pat.span);
849 return tcx.ty_error();
853 DefKind::Ctor(_, CtorKind::Const)
855 | DefKind::AssocConst
856 | DefKind::ConstParam,
859 _ => bug!("unexpected pattern resolution: {:?}", res),
862 // Type-check the path.
863 let (pat_ty, pat_res) =
864 self.instantiate_value_path(segments, opt_ty, res, pat.span, pat.hir_id);
866 self.demand_suptype_with_origin(&self.pattern_cause(ti, pat.span), expected, pat_ty)
868 self.emit_bad_pat_path(err, pat, res, pat_res, pat_ty, segments);
873 fn maybe_suggest_range_literal(
876 opt_def_id: Option<hir::def_id::DefId>,
880 Some(def_id) => match self.tcx.hir().get_if_local(def_id) {
881 Some(hir::Node::Item(hir::Item {
882 kind: hir::ItemKind::Const(_, body_id), ..
883 })) => match self.tcx.hir().get(body_id.hir_id) {
884 hir::Node::Expr(expr) => {
885 if hir::is_range_literal(expr) {
886 let span = self.tcx.hir().span(body_id.hir_id);
887 if let Ok(snip) = self.tcx.sess.source_map().span_to_snippet(span) {
888 e.span_suggestion_verbose(
890 "you may want to move the range into the match block",
892 Applicability::MachineApplicable,
907 fn emit_bad_pat_path(
909 mut e: DiagnosticBuilder<'_, ErrorGuaranteed>,
910 pat: &hir::Pat<'tcx>,
914 segments: &'tcx [hir::PathSegment<'tcx>],
916 let pat_span = pat.span;
917 if let Some(span) = self.tcx.hir().res_span(pat_res) {
918 e.span_label(span, &format!("{} defined here", res.descr()));
919 if let [hir::PathSegment { ident, .. }] = &*segments {
923 "`{}` is interpreted as {} {}, not a new binding",
929 match self.tcx.hir().get(self.tcx.hir().get_parent_node(pat.hir_id)) {
930 hir::Node::Pat(Pat { kind: hir::PatKind::Struct(..), .. }) => {
931 e.span_suggestion_verbose(
932 ident.span.shrink_to_hi(),
933 "bind the struct field to a different name instead",
934 format!(": other_{}", ident.as_str().to_lowercase()),
935 Applicability::HasPlaceholders,
939 let (type_def_id, item_def_id) = match pat_ty.kind() {
940 Adt(def, _) => match res {
941 Res::Def(DefKind::Const, def_id) => (Some(def.did()), Some(def_id)),
948 self.tcx.lang_items().range_struct(),
949 self.tcx.lang_items().range_from_struct(),
950 self.tcx.lang_items().range_to_struct(),
951 self.tcx.lang_items().range_full_struct(),
952 self.tcx.lang_items().range_inclusive_struct(),
953 self.tcx.lang_items().range_to_inclusive_struct(),
955 if type_def_id != None && ranges.contains(&type_def_id) {
956 if !self.maybe_suggest_range_literal(&mut e, item_def_id, *ident) {
957 let msg = "constants only support matching by type, \
958 if you meant to match against a range of values, \
959 consider using a range pattern like `min ..= max` in the match block";
963 let msg = "introduce a new binding instead";
964 let sugg = format!("other_{}", ident.as_str().to_lowercase());
969 Applicability::HasPlaceholders,
979 fn check_pat_tuple_struct(
981 pat: &'tcx Pat<'tcx>,
982 qpath: &'tcx hir::QPath<'tcx>,
983 subpats: &'tcx [Pat<'tcx>],
984 ddpos: Option<usize>,
992 self.check_pat(pat, tcx.ty_error(), def_bm, ti);
995 let report_unexpected_res = |res: Res| {
996 let sm = tcx.sess.source_map();
998 .span_to_snippet(sm.span_until_char(pat.span, '('))
999 .map_or_else(|_| String::new(), |s| format!(" `{}`", s.trim_end()));
1001 "expected tuple struct or tuple variant, found {}{}",
1006 let mut err = struct_span_err!(tcx.sess, pat.span, E0164, "{msg}");
1008 Res::Def(DefKind::Fn | DefKind::AssocFn, _) => {
1009 err.span_label(pat.span, "`fn` calls are not allowed in patterns");
1011 "for more information, visit \
1012 https://doc.rust-lang.org/book/ch18-00-patterns.html",
1016 err.span_label(pat.span, "not a tuple variant or struct");
1023 // Resolve the path and check the definition for errors.
1024 let (res, opt_ty, segments) =
1025 self.resolve_ty_and_res_fully_qualified_call(qpath, pat.hir_id, pat.span);
1026 if res == Res::Err {
1027 self.set_tainted_by_errors();
1029 return self.tcx.ty_error();
1032 // Type-check the path.
1034 self.instantiate_value_path(segments, opt_ty, res, pat.span, pat.hir_id);
1035 if !pat_ty.is_fn() {
1036 report_unexpected_res(res);
1037 return tcx.ty_error();
1040 let variant = match res {
1042 self.set_tainted_by_errors();
1044 return tcx.ty_error();
1046 Res::Def(DefKind::AssocConst | DefKind::AssocFn, _) => {
1047 report_unexpected_res(res);
1048 return tcx.ty_error();
1050 Res::Def(DefKind::Ctor(_, CtorKind::Fn), _) => tcx.expect_variant_res(res),
1051 _ => bug!("unexpected pattern resolution: {:?}", res),
1054 // Replace constructor type with constructed type for tuple struct patterns.
1055 let pat_ty = pat_ty.fn_sig(tcx).output();
1056 let pat_ty = pat_ty.no_bound_vars().expect("expected fn type");
1058 // Type-check the tuple struct pattern against the expected type.
1059 let diag = self.demand_eqtype_pat_diag(pat.span, expected, pat_ty, ti);
1060 let had_err = if let Some(mut err) = diag {
1067 // Type-check subpatterns.
1068 if subpats.len() == variant.fields.len()
1069 || subpats.len() < variant.fields.len() && ddpos.is_some()
1071 let ty::Adt(_, substs) = pat_ty.kind() else {
1072 bug!("unexpected pattern type {:?}", pat_ty);
1074 for (i, subpat) in subpats.iter().enumerate_and_adjust(variant.fields.len(), ddpos) {
1075 let field_ty = self.field_ty(subpat.span, &variant.fields[i], substs);
1076 self.check_pat(subpat, field_ty, def_bm, ti);
1078 self.tcx.check_stability(
1079 variant.fields[i].did,
1086 // Pattern has wrong number of fields.
1087 self.e0023(pat.span, res, qpath, subpats, &variant.fields, expected, had_err);
1089 return tcx.ty_error();
1098 qpath: &hir::QPath<'_>,
1099 subpats: &'tcx [Pat<'tcx>],
1100 fields: &'tcx [ty::FieldDef],
1104 let subpats_ending = pluralize!(subpats.len());
1105 let fields_ending = pluralize!(fields.len());
1107 let subpat_spans = if subpats.is_empty() {
1110 subpats.iter().map(|p| p.span).collect()
1112 let last_subpat_span = *subpat_spans.last().unwrap();
1113 let res_span = self.tcx.def_span(res.def_id());
1114 let def_ident_span = self.tcx.def_ident_span(res.def_id()).unwrap_or(res_span);
1115 let field_def_spans = if fields.is_empty() {
1118 fields.iter().map(|f| f.ident(self.tcx).span).collect()
1120 let last_field_def_span = *field_def_spans.last().unwrap();
1122 let mut err = struct_span_err!(
1124 MultiSpan::from_spans(subpat_spans),
1126 "this pattern has {} field{}, but the corresponding {} has {} field{}",
1135 &format!("expected {} field{}, found {}", fields.len(), fields_ending, subpats.len()),
1137 if self.tcx.sess.source_map().is_multiline(qpath.span().between(last_subpat_span)) {
1138 err.span_label(qpath.span(), "");
1140 if self.tcx.sess.source_map().is_multiline(def_ident_span.between(last_field_def_span)) {
1141 err.span_label(def_ident_span, format!("{} defined here", res.descr()));
1143 for span in &field_def_spans[..field_def_spans.len() - 1] {
1144 err.span_label(*span, "");
1147 last_field_def_span,
1148 &format!("{} has {} field{}", res.descr(), fields.len(), fields_ending),
1151 // Identify the case `Some(x, y)` where the expected type is e.g. `Option<(T, U)>`.
1152 // More generally, the expected type wants a tuple variant with one field of an
1153 // N-arity-tuple, e.g., `V_i((p_0, .., p_N))`. Meanwhile, the user supplied a pattern
1154 // with the subpatterns directly in the tuple variant pattern, e.g., `V_i(p_0, .., p_N)`.
1155 let missing_parentheses = match (&expected.kind(), fields, had_err) {
1156 // #67037: only do this if we could successfully type-check the expected type against
1157 // the tuple struct pattern. Otherwise the substs could get out of range on e.g.,
1158 // `let P() = U;` where `P != U` with `struct P<T>(T);`.
1159 (ty::Adt(_, substs), [field], false) => {
1160 let field_ty = self.field_ty(pat_span, field, substs);
1161 match field_ty.kind() {
1162 ty::Tuple(fields) => fields.len() == subpats.len(),
1168 if missing_parentheses {
1169 let (left, right) = match subpats {
1170 // This is the zero case; we aim to get the "hi" part of the `QPath`'s
1171 // span as the "lo" and then the "hi" part of the pattern's span as the "hi".
1174 // help: missing parentheses
1176 // L | let A(()) = A(());
1178 [] => (qpath.span().shrink_to_hi(), pat_span),
1179 // Easy case. Just take the "lo" of the first sub-pattern and the "hi" of the
1180 // last sub-pattern. In the case of `A(x)` the first and last may coincide.
1183 // help: missing parentheses
1185 // L | let A((x, y)) = A((1, 2));
1187 [first, ..] => (first.span.shrink_to_lo(), subpats.last().unwrap().span),
1189 err.multipart_suggestion(
1190 "missing parentheses",
1191 vec![(left, "(".to_string()), (right.shrink_to_hi(), ")".to_string())],
1192 Applicability::MachineApplicable,
1194 } else if fields.len() > subpats.len() && pat_span != DUMMY_SP {
1195 let after_fields_span = pat_span.with_hi(pat_span.hi() - BytePos(1)).shrink_to_hi();
1196 let all_fields_span = match subpats {
1197 [] => after_fields_span,
1198 [field] => field.span,
1199 [first, .., last] => first.span.to(last.span),
1202 // Check if all the fields in the pattern are wildcards.
1203 let all_wildcards = subpats.iter().all(|pat| matches!(pat.kind, PatKind::Wild));
1204 let first_tail_wildcard =
1205 subpats.iter().enumerate().fold(None, |acc, (pos, pat)| match (acc, &pat.kind) {
1206 (None, PatKind::Wild) => Some(pos),
1207 (Some(_), PatKind::Wild) => acc,
1210 let tail_span = match first_tail_wildcard {
1211 None => after_fields_span,
1212 Some(0) => subpats[0].span.to(after_fields_span),
1213 Some(pos) => subpats[pos - 1].span.shrink_to_hi().to(after_fields_span),
1216 // FIXME: heuristic-based suggestion to check current types for where to add `_`.
1217 let mut wildcard_sugg = vec!["_"; fields.len() - subpats.len()].join(", ");
1218 if !subpats.is_empty() {
1219 wildcard_sugg = String::from(", ") + &wildcard_sugg;
1222 err.span_suggestion_verbose(
1224 "use `_` to explicitly ignore each field",
1226 Applicability::MaybeIncorrect,
1229 // Only suggest `..` if more than one field is missing
1230 // or the pattern consists of all wildcards.
1231 if fields.len() - subpats.len() > 1 || all_wildcards {
1232 if subpats.is_empty() || all_wildcards {
1233 err.span_suggestion_verbose(
1235 "use `..` to ignore all fields",
1237 Applicability::MaybeIncorrect,
1240 err.span_suggestion_verbose(
1242 "use `..` to ignore the rest of the fields",
1244 Applicability::MaybeIncorrect,
1256 elements: &'tcx [Pat<'tcx>],
1257 ddpos: Option<usize>,
1259 def_bm: BindingMode,
1263 let mut expected_len = elements.len();
1264 if ddpos.is_some() {
1265 // Require known type only when `..` is present.
1266 if let ty::Tuple(tys) = self.structurally_resolved_type(span, expected).kind() {
1267 expected_len = tys.len();
1270 let max_len = cmp::max(expected_len, elements.len());
1272 let element_tys_iter = (0..max_len).map(|_| {
1274 // FIXME: `MiscVariable` for now -- obtaining the span and name information
1275 // from all tuple elements isn't trivial.
1276 TypeVariableOrigin { kind: TypeVariableOriginKind::TypeInference, span },
1279 let element_tys = tcx.mk_type_list(element_tys_iter);
1280 let pat_ty = tcx.mk_ty(ty::Tuple(element_tys));
1281 if let Some(mut err) = self.demand_eqtype_pat_diag(span, expected, pat_ty, ti) {
1283 // Walk subpatterns with an expected type of `err` in this case to silence
1284 // further errors being emitted when using the bindings. #50333
1285 let element_tys_iter = (0..max_len).map(|_| tcx.ty_error());
1286 for (_, elem) in elements.iter().enumerate_and_adjust(max_len, ddpos) {
1287 self.check_pat(elem, tcx.ty_error(), def_bm, ti);
1289 tcx.mk_tup(element_tys_iter)
1291 for (i, elem) in elements.iter().enumerate_and_adjust(max_len, ddpos) {
1292 self.check_pat(elem, element_tys[i], def_bm, ti);
1298 fn check_struct_pat_fields(
1301 pat: &'tcx Pat<'tcx>,
1302 variant: &'tcx ty::VariantDef,
1303 fields: &'tcx [hir::PatField<'tcx>],
1305 def_bm: BindingMode,
1310 let ty::Adt(adt, substs) = adt_ty.kind() else {
1311 span_bug!(pat.span, "struct pattern is not an ADT");
1314 // Index the struct fields' types.
1315 let field_map = variant
1319 .map(|(i, field)| (field.ident(self.tcx).normalize_to_macros_2_0(), (i, field)))
1320 .collect::<FxHashMap<_, _>>();
1322 // Keep track of which fields have already appeared in the pattern.
1323 let mut used_fields = FxHashMap::default();
1324 let mut no_field_errors = true;
1326 let mut inexistent_fields = vec![];
1327 // Typecheck each field.
1328 for field in fields {
1329 let span = field.span;
1330 let ident = tcx.adjust_ident(field.ident, variant.def_id);
1331 let field_ty = match used_fields.entry(ident) {
1332 Occupied(occupied) => {
1333 self.error_field_already_bound(span, field.ident, *occupied.get());
1334 no_field_errors = false;
1338 vacant.insert(span);
1342 self.write_field_index(field.hir_id, *i);
1343 self.tcx.check_stability(f.did, Some(pat.hir_id), span, None);
1344 self.field_ty(span, f, substs)
1346 .unwrap_or_else(|| {
1347 inexistent_fields.push(field);
1348 no_field_errors = false;
1354 self.check_pat(field.pat, field_ty, def_bm, ti);
1357 let mut unmentioned_fields = variant
1360 .map(|field| (field, field.ident(self.tcx).normalize_to_macros_2_0()))
1361 .filter(|(_, ident)| !used_fields.contains_key(ident))
1362 .collect::<Vec<_>>();
1364 let inexistent_fields_err = if !(inexistent_fields.is_empty() || variant.is_recovered())
1365 && !inexistent_fields.iter().any(|field| field.ident.name == kw::Underscore)
1367 Some(self.error_inexistent_fields(
1368 adt.variant_descr(),
1370 &mut unmentioned_fields,
1378 // Require `..` if struct has non_exhaustive attribute.
1379 let non_exhaustive = variant.is_field_list_non_exhaustive() && !adt.did().is_local();
1380 if non_exhaustive && !has_rest_pat {
1381 self.error_foreign_non_exhaustive_spat(pat, adt.variant_descr(), fields.is_empty());
1384 let mut unmentioned_err = None;
1385 // Report an error if an incorrect number of fields was specified.
1387 if fields.len() != 1 {
1389 .struct_span_err(pat.span, "union patterns should have exactly one field")
1393 tcx.sess.struct_span_err(pat.span, "`..` cannot be used in union patterns").emit();
1395 } else if !unmentioned_fields.is_empty() {
1396 let accessible_unmentioned_fields: Vec<_> = unmentioned_fields
1399 .filter(|(field, _)| {
1400 field.vis.is_accessible_from(tcx.parent_module(pat.hir_id).to_def_id(), tcx)
1402 tcx.eval_stability(field.did, None, DUMMY_SP, None),
1403 EvalResult::Deny { .. }
1405 // We only want to report the error if it is hidden and not local
1406 && !(tcx.is_doc_hidden(field.did) && !field.did.is_local())
1411 if accessible_unmentioned_fields.is_empty() {
1412 unmentioned_err = Some(self.error_no_accessible_fields(pat, fields));
1414 unmentioned_err = Some(self.error_unmentioned_fields(
1416 &accessible_unmentioned_fields,
1417 accessible_unmentioned_fields.len() != unmentioned_fields.len(),
1421 } else if non_exhaustive && !accessible_unmentioned_fields.is_empty() {
1422 self.lint_non_exhaustive_omitted_patterns(
1424 &accessible_unmentioned_fields,
1429 match (inexistent_fields_err, unmentioned_err) {
1430 (Some(mut i), Some(mut u)) => {
1431 if let Some(mut e) = self.error_tuple_variant_as_struct_pat(pat, fields, variant) {
1432 // We don't want to show the nonexistent fields error when this was
1433 // `Foo { a, b }` when it should have been `Foo(a, b)`.
1442 (None, Some(mut u)) => {
1443 if let Some(mut e) = self.error_tuple_variant_as_struct_pat(pat, fields, variant) {
1450 (Some(mut err), None) => {
1453 (None, None) if let Some(mut err) =
1454 self.error_tuple_variant_index_shorthand(variant, pat, fields) =>
1463 fn error_tuple_variant_index_shorthand(
1465 variant: &VariantDef,
1467 fields: &[hir::PatField<'_>],
1468 ) -> Option<DiagnosticBuilder<'_, ErrorGuaranteed>> {
1469 // if this is a tuple struct, then all field names will be numbers
1470 // so if any fields in a struct pattern use shorthand syntax, they will
1471 // be invalid identifiers (for example, Foo { 0, 1 }).
1472 if let (CtorKind::Fn, PatKind::Struct(qpath, field_patterns, ..)) =
1473 (variant.ctor_kind, &pat.kind)
1475 let has_shorthand_field_name = field_patterns.iter().any(|field| field.is_shorthand);
1476 if has_shorthand_field_name {
1477 let path = rustc_hir_pretty::to_string(rustc_hir_pretty::NO_ANN, |s| {
1478 s.print_qpath(qpath, false)
1480 let mut err = struct_span_err!(
1484 "tuple variant `{path}` written as struct variant",
1486 err.span_suggestion_verbose(
1487 qpath.span().shrink_to_hi().to(pat.span.shrink_to_hi()),
1488 "use the tuple variant pattern syntax instead",
1489 format!("({})", self.get_suggested_tuple_struct_pattern(fields, variant)),
1490 Applicability::MaybeIncorrect,
1498 fn error_foreign_non_exhaustive_spat(&self, pat: &Pat<'_>, descr: &str, no_fields: bool) {
1499 let sess = self.tcx.sess;
1500 let sm = sess.source_map();
1501 let sp_brace = sm.end_point(pat.span);
1502 let sp_comma = sm.end_point(pat.span.with_hi(sp_brace.hi()));
1503 let sugg = if no_fields || sp_brace != sp_comma { ".. }" } else { ", .. }" };
1505 let mut err = struct_span_err!(
1509 "`..` required with {descr} marked as non-exhaustive",
1511 err.span_suggestion_verbose(
1513 "add `..` at the end of the field list to ignore all other fields",
1515 Applicability::MachineApplicable,
1520 fn error_field_already_bound(&self, span: Span, ident: Ident, other_field: Span) {
1525 "field `{}` bound multiple times in the pattern",
1528 .span_label(span, format!("multiple uses of `{ident}` in pattern"))
1529 .span_label(other_field, format!("first use of `{ident}`"))
1533 fn error_inexistent_fields(
1536 inexistent_fields: &[&hir::PatField<'tcx>],
1537 unmentioned_fields: &mut Vec<(&'tcx ty::FieldDef, Ident)>,
1538 variant: &ty::VariantDef,
1539 substs: &'tcx ty::List<ty::subst::GenericArg<'tcx>>,
1540 ) -> DiagnosticBuilder<'tcx, ErrorGuaranteed> {
1542 let (field_names, t, plural) = if inexistent_fields.len() == 1 {
1543 (format!("a field named `{}`", inexistent_fields[0].ident), "this", "")
1550 .map(|field| format!("`{}`", field.ident))
1551 .collect::<Vec<String>>()
1558 let spans = inexistent_fields.iter().map(|field| field.ident.span).collect::<Vec<_>>();
1559 let mut err = struct_span_err!(
1563 "{} `{}` does not have {}",
1565 tcx.def_path_str(variant.def_id),
1568 if let Some(pat_field) = inexistent_fields.last() {
1570 pat_field.ident.span,
1572 "{} `{}` does not have {} field{}",
1574 tcx.def_path_str(variant.def_id),
1580 if unmentioned_fields.len() == 1 {
1582 unmentioned_fields.iter().map(|(_, field)| field.name).collect::<Vec<_>>();
1583 let suggested_name = find_best_match_for_name(&input, pat_field.ident.name, None);
1584 if let Some(suggested_name) = suggested_name {
1585 err.span_suggestion(
1586 pat_field.ident.span,
1587 "a field with a similar name exists",
1589 Applicability::MaybeIncorrect,
1592 // When we have a tuple struct used with struct we don't want to suggest using
1593 // the (valid) struct syntax with numeric field names. Instead we want to
1594 // suggest the expected syntax. We infer that this is the case by parsing the
1595 // `Ident` into an unsized integer. The suggestion will be emitted elsewhere in
1596 // `smart_resolve_context_dependent_help`.
1597 if suggested_name.to_ident_string().parse::<usize>().is_err() {
1598 // We don't want to throw `E0027` in case we have thrown `E0026` for them.
1599 unmentioned_fields.retain(|&(_, x)| x.name != suggested_name);
1601 } else if inexistent_fields.len() == 1 {
1602 match pat_field.pat.kind {
1604 if !self.can_coerce(
1605 self.typeck_results.borrow().expr_ty(expr),
1607 unmentioned_fields[0].1.span,
1608 unmentioned_fields[0].0,
1613 let unmentioned_field = unmentioned_fields[0].1.name;
1614 err.span_suggestion_short(
1615 pat_field.ident.span,
1617 "`{}` has a field named `{}`",
1618 tcx.def_path_str(variant.def_id),
1621 unmentioned_field.to_string(),
1622 Applicability::MaybeIncorrect,
1629 if tcx.sess.teach(&err.get_code().unwrap()) {
1631 "This error indicates that a struct pattern attempted to \
1632 extract a non-existent field from a struct. Struct fields \
1633 are identified by the name used before the colon : so struct \
1634 patterns should resemble the declaration of the struct type \
1636 If you are using shorthand field patterns but want to refer \
1637 to the struct field by a different name, you should rename \
1644 fn error_tuple_variant_as_struct_pat(
1647 fields: &'tcx [hir::PatField<'tcx>],
1648 variant: &ty::VariantDef,
1649 ) -> Option<DiagnosticBuilder<'tcx, ErrorGuaranteed>> {
1650 if let (CtorKind::Fn, PatKind::Struct(qpath, ..)) = (variant.ctor_kind, &pat.kind) {
1651 let path = rustc_hir_pretty::to_string(rustc_hir_pretty::NO_ANN, |s| {
1652 s.print_qpath(qpath, false)
1654 let mut err = struct_span_err!(
1658 "tuple variant `{}` written as struct variant",
1661 let (sugg, appl) = if fields.len() == variant.fields.len() {
1663 self.get_suggested_tuple_struct_pattern(fields, variant),
1664 Applicability::MachineApplicable,
1668 variant.fields.iter().map(|_| "_").collect::<Vec<&str>>().join(", "),
1669 Applicability::MaybeIncorrect,
1672 err.span_suggestion_verbose(
1673 qpath.span().shrink_to_hi().to(pat.span.shrink_to_hi()),
1674 "use the tuple variant pattern syntax instead",
1675 format!("({})", sugg),
1683 fn get_suggested_tuple_struct_pattern(
1685 fields: &[hir::PatField<'_>],
1686 variant: &VariantDef,
1688 let variant_field_idents =
1689 variant.fields.iter().map(|f| f.ident(self.tcx)).collect::<Vec<Ident>>();
1693 match self.tcx.sess.source_map().span_to_snippet(field.pat.span) {
1695 // Field names are numbers, but numbers
1696 // are not valid identifiers
1697 if variant_field_idents.contains(&field.ident) {
1703 Err(_) => rustc_hir_pretty::to_string(rustc_hir_pretty::NO_ANN, |s| {
1704 s.print_pat(field.pat)
1708 .collect::<Vec<String>>()
1712 /// Returns a diagnostic reporting a struct pattern which is missing an `..` due to
1713 /// inaccessible fields.
1716 /// error: pattern requires `..` due to inaccessible fields
1717 /// --> src/main.rs:10:9
1719 /// LL | let foo::Foo {} = foo::Foo::default();
1722 /// help: add a `..`
1724 /// LL | let foo::Foo { .. } = foo::Foo::default();
1727 fn error_no_accessible_fields(
1730 fields: &'tcx [hir::PatField<'tcx>],
1731 ) -> DiagnosticBuilder<'tcx, ErrorGuaranteed> {
1735 .struct_span_err(pat.span, "pattern requires `..` due to inaccessible fields");
1737 if let Some(field) = fields.last() {
1738 err.span_suggestion_verbose(
1739 field.span.shrink_to_hi(),
1740 "ignore the inaccessible and unused fields",
1742 Applicability::MachineApplicable,
1745 let qpath_span = if let PatKind::Struct(qpath, ..) = &pat.kind {
1748 bug!("`error_no_accessible_fields` called on non-struct pattern");
1751 // Shrink the span to exclude the `foo:Foo` in `foo::Foo { }`.
1752 let span = pat.span.with_lo(qpath_span.shrink_to_hi().hi());
1753 err.span_suggestion_verbose(
1755 "ignore the inaccessible and unused fields",
1757 Applicability::MachineApplicable,
1763 /// Report that a pattern for a `#[non_exhaustive]` struct marked with `non_exhaustive_omitted_patterns`
1764 /// is not exhaustive enough.
1766 /// Nb: the partner lint for enums lives in `compiler/rustc_mir_build/src/thir/pattern/usefulness.rs`.
1767 fn lint_non_exhaustive_omitted_patterns(
1770 unmentioned_fields: &[(&ty::FieldDef, Ident)],
1773 fn joined_uncovered_patterns(witnesses: &[&Ident]) -> String {
1774 const LIMIT: usize = 3;
1777 [witness] => format!("`{}`", witness),
1778 [head @ .., tail] if head.len() < LIMIT => {
1779 let head: Vec<_> = head.iter().map(<_>::to_string).collect();
1780 format!("`{}` and `{}`", head.join("`, `"), tail)
1783 let (head, tail) = witnesses.split_at(LIMIT);
1784 let head: Vec<_> = head.iter().map(<_>::to_string).collect();
1785 format!("`{}` and {} more", head.join("`, `"), tail.len())
1789 let joined_patterns = joined_uncovered_patterns(
1790 &unmentioned_fields.iter().map(|(_, i)| i).collect::<Vec<_>>(),
1793 self.tcx.struct_span_lint_hir(NON_EXHAUSTIVE_OMITTED_PATTERNS, pat.hir_id, pat.span, |build| {
1794 let mut lint = build.build("some fields are not explicitly listed");
1795 lint.span_label(pat.span, format!("field{} {} not listed", rustc_errors::pluralize!(unmentioned_fields.len()), joined_patterns));
1798 "ensure that all fields are mentioned explicitly by adding the suggested fields",
1801 "the pattern is of type `{}` and the `non_exhaustive_omitted_patterns` attribute was found",
1808 /// Returns a diagnostic reporting a struct pattern which does not mention some fields.
1811 /// error[E0027]: pattern does not mention field `bar`
1812 /// --> src/main.rs:15:9
1814 /// LL | let foo::Foo {} = foo::Foo::new();
1815 /// | ^^^^^^^^^^^ missing field `bar`
1817 fn error_unmentioned_fields(
1820 unmentioned_fields: &[(&ty::FieldDef, Ident)],
1821 have_inaccessible_fields: bool,
1822 fields: &'tcx [hir::PatField<'tcx>],
1823 ) -> DiagnosticBuilder<'tcx, ErrorGuaranteed> {
1824 let inaccessible = if have_inaccessible_fields { " and inaccessible fields" } else { "" };
1825 let field_names = if unmentioned_fields.len() == 1 {
1826 format!("field `{}`{}", unmentioned_fields[0].1, inaccessible)
1828 let fields = unmentioned_fields
1830 .map(|(_, name)| format!("`{}`", name))
1831 .collect::<Vec<String>>()
1833 format!("fields {}{}", fields, inaccessible)
1835 let mut err = struct_span_err!(
1839 "pattern does not mention {}",
1842 err.span_label(pat.span, format!("missing {}", field_names));
1843 let len = unmentioned_fields.len();
1844 let (prefix, postfix, sp) = match fields {
1845 [] => match &pat.kind {
1846 PatKind::Struct(path, [], false) => {
1847 (" { ", " }", path.span().shrink_to_hi().until(pat.span.shrink_to_hi()))
1852 // Account for last field having a trailing comma or parse recovery at the tail of
1853 // the pattern to avoid invalid suggestion (#78511).
1854 let tail = field.span.shrink_to_hi().with_hi(pat.span.hi());
1856 PatKind::Struct(..) => (", ", " }", tail),
1861 err.span_suggestion(
1864 "include the missing field{} in the pattern{}",
1866 if have_inaccessible_fields { " and ignore the inaccessible fields" } else { "" }
1873 .map(|(_, name)| name.to_string())
1874 .collect::<Vec<_>>()
1876 if have_inaccessible_fields { ", .." } else { "" },
1879 Applicability::MachineApplicable,
1881 err.span_suggestion(
1884 "if you don't care about {these} missing field{s}, you can explicitly ignore {them}",
1885 these = pluralize!("this", len),
1886 s = pluralize!(len),
1887 them = if len == 1 { "it" } else { "them" },
1889 format!("{}..{}", prefix, postfix),
1890 Applicability::MachineApplicable,
1898 inner: &'tcx Pat<'tcx>,
1900 def_bm: BindingMode,
1904 let (box_ty, inner_ty) = if self.check_dereferenceable(span, expected, inner) {
1905 // Here, `demand::subtype` is good enough, but I don't
1906 // think any errors can be introduced by using `demand::eqtype`.
1907 let inner_ty = self.next_ty_var(TypeVariableOrigin {
1908 kind: TypeVariableOriginKind::TypeInference,
1911 let box_ty = tcx.mk_box(inner_ty);
1912 self.demand_eqtype_pat(span, expected, box_ty, ti);
1915 let err = tcx.ty_error();
1918 self.check_pat(inner, inner_ty, def_bm, ti);
1922 // Precondition: Pat is Ref(inner)
1925 pat: &'tcx Pat<'tcx>,
1926 inner: &'tcx Pat<'tcx>,
1927 mutbl: hir::Mutability,
1929 def_bm: BindingMode,
1933 let expected = self.shallow_resolve(expected);
1934 let (rptr_ty, inner_ty) = if self.check_dereferenceable(pat.span, expected, inner) {
1935 // `demand::subtype` would be good enough, but using `eqtype` turns
1936 // out to be equally general. See (note_1) for details.
1938 // Take region, inner-type from expected type if we can,
1939 // to avoid creating needless variables. This also helps with
1940 // the bad interactions of the given hack detailed in (note_1).
1941 debug!("check_pat_ref: expected={:?}", expected);
1942 match *expected.kind() {
1943 ty::Ref(_, r_ty, r_mutbl) if r_mutbl == mutbl => (expected, r_ty),
1945 let inner_ty = self.next_ty_var(TypeVariableOrigin {
1946 kind: TypeVariableOriginKind::TypeInference,
1949 let rptr_ty = self.new_ref_ty(pat.span, mutbl, inner_ty);
1950 debug!("check_pat_ref: demanding {:?} = {:?}", expected, rptr_ty);
1951 let err = self.demand_eqtype_pat_diag(pat.span, expected, rptr_ty, ti);
1953 // Look for a case like `fn foo(&foo: u32)` and suggest
1954 // `fn foo(foo: &u32)`
1955 if let Some(mut err) = err {
1956 self.borrow_pat_suggestion(&mut err, pat);
1963 let err = tcx.ty_error();
1966 self.check_pat(inner, inner_ty, def_bm, ti);
1970 /// Create a reference type with a fresh region variable.
1971 fn new_ref_ty(&self, span: Span, mutbl: hir::Mutability, ty: Ty<'tcx>) -> Ty<'tcx> {
1972 let region = self.next_region_var(infer::PatternRegion(span));
1973 let mt = ty::TypeAndMut { ty, mutbl };
1974 self.tcx.mk_ref(region, mt)
1977 /// Type check a slice pattern.
1979 /// Syntactically, these look like `[pat_0, ..., pat_n]`.
1980 /// Semantically, we are type checking a pattern with structure:
1981 /// ```ignore (not-rust)
1982 /// [before_0, ..., before_n, (slice, after_0, ... after_n)?]
1984 /// The type of `slice`, if it is present, depends on the `expected` type.
1985 /// If `slice` is missing, then so is `after_i`.
1986 /// If `slice` is present, it can still represent 0 elements.
1990 before: &'tcx [Pat<'tcx>],
1991 slice: Option<&'tcx Pat<'tcx>>,
1992 after: &'tcx [Pat<'tcx>],
1994 def_bm: BindingMode,
1997 let expected = self.structurally_resolved_type(span, expected);
1998 let (element_ty, opt_slice_ty, inferred) = match *expected.kind() {
1999 // An array, so we might have something like `let [a, b, c] = [0, 1, 2];`.
2000 ty::Array(element_ty, len) => {
2001 let min = before.len() as u64 + after.len() as u64;
2002 let (opt_slice_ty, expected) =
2003 self.check_array_pat_len(span, element_ty, expected, slice, len, min);
2004 // `opt_slice_ty.is_none()` => `slice.is_none()`.
2005 // Note, though, that opt_slice_ty could be `Some(error_ty)`.
2006 assert!(opt_slice_ty.is_some() || slice.is_none());
2007 (element_ty, opt_slice_ty, expected)
2009 ty::Slice(element_ty) => (element_ty, Some(expected), expected),
2010 // The expected type must be an array or slice, but was neither, so error.
2012 if !expected.references_error() {
2013 self.error_expected_array_or_slice(span, expected, ti);
2015 let err = self.tcx.ty_error();
2016 (err, Some(err), err)
2020 // Type check all the patterns before `slice`.
2022 self.check_pat(elt, element_ty, def_bm, ti);
2024 // Type check the `slice`, if present, against its expected type.
2025 if let Some(slice) = slice {
2026 self.check_pat(slice, opt_slice_ty.unwrap(), def_bm, ti);
2028 // Type check the elements after `slice`, if present.
2030 self.check_pat(elt, element_ty, def_bm, ti);
2035 /// Type check the length of an array pattern.
2037 /// Returns both the type of the variable length pattern (or `None`), and the potentially
2038 /// inferred array type. We only return `None` for the slice type if `slice.is_none()`.
2039 fn check_array_pat_len(
2042 element_ty: Ty<'tcx>,
2044 slice: Option<&'tcx Pat<'tcx>>,
2045 len: ty::Const<'tcx>,
2047 ) -> (Option<Ty<'tcx>>, Ty<'tcx>) {
2048 if let Some(len) = len.try_eval_usize(self.tcx, self.param_env) {
2049 // Now we know the length...
2050 if slice.is_none() {
2051 // ...and since there is no variable-length pattern,
2052 // we require an exact match between the number of elements
2053 // in the array pattern and as provided by the matched type.
2055 return (None, arr_ty);
2058 self.error_scrutinee_inconsistent_length(span, min_len, len);
2059 } else if let Some(pat_len) = len.checked_sub(min_len) {
2060 // The variable-length pattern was there,
2061 // so it has an array type with the remaining elements left as its size...
2062 return (Some(self.tcx.mk_array(element_ty, pat_len)), arr_ty);
2064 // ...however, in this case, there were no remaining elements.
2065 // That is, the slice pattern requires more than the array type offers.
2066 self.error_scrutinee_with_rest_inconsistent_length(span, min_len, len);
2068 } else if slice.is_none() {
2069 // We have a pattern with a fixed length,
2070 // which we can use to infer the length of the array.
2071 let updated_arr_ty = self.tcx.mk_array(element_ty, min_len);
2072 self.demand_eqtype(span, updated_arr_ty, arr_ty);
2073 return (None, updated_arr_ty);
2075 // We have a variable-length pattern and don't know the array length.
2076 // This happens if we have e.g.,
2077 // `let [a, b, ..] = arr` where `arr: [T; N]` where `const N: usize`.
2078 self.error_scrutinee_unfixed_length(span);
2081 // If we get here, we must have emitted an error.
2082 (Some(self.tcx.ty_error()), arr_ty)
2085 fn error_scrutinee_inconsistent_length(&self, span: Span, min_len: u64, size: u64) {
2090 "pattern requires {} element{} but array has {}",
2092 pluralize!(min_len),
2095 .span_label(span, format!("expected {} element{}", size, pluralize!(size)))
2099 fn error_scrutinee_with_rest_inconsistent_length(&self, span: Span, min_len: u64, size: u64) {
2104 "pattern requires at least {} element{} but array has {}",
2106 pluralize!(min_len),
2111 format!("pattern cannot match array of {} element{}", size, pluralize!(size),),
2116 fn error_scrutinee_unfixed_length(&self, span: Span) {
2121 "cannot pattern-match on an array without a fixed length",
2126 fn error_expected_array_or_slice(&self, span: Span, expected_ty: Ty<'tcx>, ti: TopInfo<'tcx>) {
2127 let mut err = struct_span_err!(
2131 "expected an array or slice, found `{expected_ty}`"
2133 if let ty::Ref(_, ty, _) = expected_ty.kind()
2134 && let ty::Array(..) | ty::Slice(..) = ty.kind()
2136 err.help("the semantics of slice patterns changed recently; see issue #62254");
2137 } else if Autoderef::new(&self.infcx, self.param_env, self.body_id, span, expected_ty, span)
2138 .any(|(ty, _)| matches!(ty.kind(), ty::Slice(..) | ty::Array(..)))
2139 && let (Some(span), true) = (ti.span, ti.origin_expr)
2140 && let Ok(snippet) = self.tcx.sess.source_map().span_to_snippet(span)
2142 let ty = self.resolve_vars_if_possible(ti.expected);
2143 let is_slice_or_array_or_vector = self.is_slice_or_array_or_vector(&mut err, snippet.clone(), ty);
2144 match is_slice_or_array_or_vector.1.kind() {
2146 if self.tcx.is_diagnostic_item(sym::Option, adt_def.did())
2147 || self.tcx.is_diagnostic_item(sym::Result, adt_def.did()) =>
2149 // Slicing won't work here, but `.as_deref()` might (issue #91328).
2150 err.span_suggestion(
2152 "consider using `as_deref` here",
2153 format!("{snippet}.as_deref()"),
2154 Applicability::MaybeIncorrect,
2159 if is_slice_or_array_or_vector.0 {
2160 err.span_suggestion(
2162 "consider slicing here",
2163 format!("{snippet}[..]"),
2164 Applicability::MachineApplicable,
2168 err.span_label(span, format!("pattern cannot match with input type `{expected_ty}`"));
2172 fn is_slice_or_array_or_vector(
2174 err: &mut Diagnostic,
2177 ) -> (bool, Ty<'tcx>) {
2179 ty::Adt(adt_def, _) if self.tcx.is_diagnostic_item(sym::Vec, adt_def.did()) => {
2182 ty::Ref(_, ty, _) => self.is_slice_or_array_or_vector(err, snippet, *ty),
2183 ty::Slice(..) | ty::Array(..) => (true, ty),