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<_, _>`
75 /// This refers to the parent pattern. Used to provide extra diagnostic information on errors.
77 /// error[E0308]: mismatched types
78 /// --> $DIR/const-in-struct-pat.rs:8:17
81 /// | --------- unit struct defined here
83 /// L | let Thing { f } = t;
86 /// | expected struct `std::string::String`, found struct `f`
87 /// | `f` is interpreted as a unit struct, not a new binding
88 /// | help: bind the struct field to a different name instead: `f: other_f`
90 parent_pat: Option<&'tcx Pat<'tcx>>,
93 impl<'tcx> FnCtxt<'_, 'tcx> {
94 fn pattern_cause(&self, ti: TopInfo<'tcx>, cause_span: Span) -> ObligationCause<'tcx> {
95 let code = Pattern { span: ti.span, root_ty: ti.expected, origin_expr: ti.origin_expr };
96 self.cause(cause_span, code)
99 fn demand_eqtype_pat_diag(
105 ) -> Option<DiagnosticBuilder<'tcx, ErrorGuaranteed>> {
106 self.demand_eqtype_with_origin(&self.pattern_cause(ti, cause_span), expected, actual)
109 fn demand_eqtype_pat(
116 if let Some(mut err) = self.demand_eqtype_pat_diag(cause_span, expected, actual, ti) {
122 const INITIAL_BM: BindingMode = BindingMode::BindByValue(hir::Mutability::Not);
124 /// Mode for adjusting the expected type and binding mode.
126 /// Peel off all immediate reference types.
128 /// Reset binding mode to the initial mode.
130 /// Pass on the input binding mode and expected type.
134 impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
135 /// Type check the given top level pattern against the `expected` type.
137 /// If a `Some(span)` is provided and `origin_expr` holds,
138 /// then the `span` represents the scrutinee's span.
139 /// The scrutinee is found in e.g. `match scrutinee { ... }` and `let pat = scrutinee;`.
141 /// Otherwise, `Some(span)` represents the span of a type expression
142 /// which originated the `expected` type.
143 pub fn check_pat_top(
145 pat: &'tcx Pat<'tcx>,
150 let info = TopInfo { expected, origin_expr, span, parent_pat: None };
151 self.check_pat(pat, expected, INITIAL_BM, info);
154 /// Type check the given `pat` against the `expected` type
155 /// with the provided `def_bm` (default binding mode).
157 /// Outside of this module, `check_pat_top` should always be used.
158 /// Conversely, inside this module, `check_pat_top` should never be used.
159 #[instrument(level = "debug", skip(self, ti))]
162 pat: &'tcx Pat<'tcx>,
167 let path_res = match &pat.kind {
168 PatKind::Path(qpath) => {
169 Some(self.resolve_ty_and_res_fully_qualified_call(qpath, pat.hir_id, pat.span))
173 let adjust_mode = self.calc_adjust_mode(pat, path_res.map(|(res, ..)| res));
174 let (expected, def_bm) = self.calc_default_binding_mode(pat, expected, def_bm, adjust_mode);
176 let ty = match pat.kind {
177 PatKind::Wild => expected,
178 PatKind::Lit(lt) => self.check_pat_lit(pat.span, lt, expected, ti),
179 PatKind::Range(lhs, rhs, _) => self.check_pat_range(pat.span, lhs, rhs, expected, ti),
180 PatKind::Binding(ba, var_id, _, sub) => {
181 self.check_pat_ident(pat, ba, var_id, sub, expected, def_bm, ti)
183 PatKind::TupleStruct(ref qpath, subpats, ddpos) => {
184 self.check_pat_tuple_struct(pat, qpath, subpats, ddpos, expected, def_bm, ti)
186 PatKind::Path(ref qpath) => {
187 self.check_pat_path(pat, qpath, path_res.unwrap(), expected, ti)
189 PatKind::Struct(ref qpath, fields, has_rest_pat) => {
190 self.check_pat_struct(pat, qpath, fields, has_rest_pat, expected, def_bm, ti)
192 PatKind::Or(pats) => {
193 let parent_pat = Some(pat);
195 self.check_pat(pat, expected, def_bm, TopInfo { parent_pat, ..ti });
199 PatKind::Tuple(elements, ddpos) => {
200 self.check_pat_tuple(pat.span, elements, ddpos, expected, def_bm, ti)
202 PatKind::Box(inner) => self.check_pat_box(pat.span, inner, expected, def_bm, ti),
203 PatKind::Ref(inner, mutbl) => {
204 self.check_pat_ref(pat, inner, mutbl, expected, def_bm, ti)
206 PatKind::Slice(before, slice, after) => {
207 self.check_pat_slice(pat.span, before, slice, after, expected, def_bm, ti)
211 self.write_ty(pat.hir_id, ty);
213 // (note_1): In most of the cases where (note_1) is referenced
214 // (literals and constants being the exception), we relate types
215 // using strict equality, even though subtyping would be sufficient.
216 // There are a few reasons for this, some of which are fairly subtle
217 // and which cost me (nmatsakis) an hour or two debugging to remember,
218 // so I thought I'd write them down this time.
220 // 1. There is no loss of expressiveness here, though it does
221 // cause some inconvenience. What we are saying is that the type
222 // of `x` becomes *exactly* what is expected. This can cause unnecessary
223 // errors in some cases, such as this one:
226 // fn foo<'x>(x: &'x i32) {
233 // The reason we might get an error is that `z` might be
234 // assigned a type like `&'x i32`, and then we would have
235 // a problem when we try to assign `&a` to `z`, because
236 // the lifetime of `&a` (i.e., the enclosing block) is
237 // shorter than `'x`.
239 // HOWEVER, this code works fine. The reason is that the
240 // expected type here is whatever type the user wrote, not
241 // the initializer's type. In this case the user wrote
242 // nothing, so we are going to create a type variable `Z`.
243 // Then we will assign the type of the initializer (`&'x i32`)
244 // as a subtype of `Z`: `&'x i32 <: Z`. And hence we
245 // will instantiate `Z` as a type `&'0 i32` where `'0` is
246 // a fresh region variable, with the constraint that `'x : '0`.
247 // So basically we're all set.
249 // Note that there are two tests to check that this remains true
250 // (`regions-reassign-{match,let}-bound-pointer.rs`).
252 // 2. Things go horribly wrong if we use subtype. The reason for
253 // THIS is a fairly subtle case involving bound regions. See the
254 // `givens` field in `region_constraints`, as well as the test
255 // `regions-relate-bound-regions-on-closures-to-inference-variables.rs`,
256 // for details. Short version is that we must sometimes detect
257 // relationships between specific region variables and regions
258 // bound in a closure signature, and that detection gets thrown
259 // off when we substitute fresh region variables here to enable
263 /// Compute the new expected type and default binding mode from the old ones
264 /// as well as the pattern form we are currently checking.
265 fn calc_default_binding_mode(
267 pat: &'tcx Pat<'tcx>,
270 adjust_mode: AdjustMode,
271 ) -> (Ty<'tcx>, BindingMode) {
273 AdjustMode::Pass => (expected, def_bm),
274 AdjustMode::Reset => (expected, INITIAL_BM),
275 AdjustMode::Peel => self.peel_off_references(pat, expected, def_bm),
279 /// How should the binding mode and expected type be adjusted?
281 /// When the pattern is a path pattern, `opt_path_res` must be `Some(res)`.
282 fn calc_adjust_mode(&self, pat: &'tcx Pat<'tcx>, opt_path_res: Option<Res>) -> AdjustMode {
283 // When we perform destructuring assignment, we disable default match bindings, which are
284 // unintuitive in this context.
285 if !pat.default_binding_modes {
286 return AdjustMode::Reset;
289 // Type checking these product-like types successfully always require
290 // that the expected type be of those types and not reference types.
292 | PatKind::TupleStruct(..)
296 | PatKind::Slice(..) => AdjustMode::Peel,
297 // String and byte-string literals result in types `&str` and `&[u8]` respectively.
298 // All other literals result in non-reference types.
299 // As a result, we allow `if let 0 = &&0 {}` but not `if let "foo" = &&"foo {}`.
301 // Call `resolve_vars_if_possible` here for inline const blocks.
302 PatKind::Lit(lt) => match self.resolve_vars_if_possible(self.check_expr(lt)).kind() {
303 ty::Ref(..) => AdjustMode::Pass,
304 _ => AdjustMode::Peel,
306 PatKind::Path(_) => match opt_path_res.unwrap() {
307 // These constants can be of a reference type, e.g. `const X: &u8 = &0;`.
308 // Peeling the reference types too early will cause type checking failures.
309 // Although it would be possible to *also* peel the types of the constants too.
310 Res::Def(DefKind::Const | DefKind::AssocConst, _) => AdjustMode::Pass,
311 // In the `ValueNS`, we have `SelfCtor(..) | Ctor(_, Const), _)` remaining which
312 // could successfully compile. The former being `Self` requires a unit struct.
313 // In either case, and unlike constants, the pattern itself cannot be
314 // a reference type wherefore peeling doesn't give up any expressiveness.
315 _ => AdjustMode::Peel,
317 // When encountering a `& mut? pat` pattern, reset to "by value".
318 // This is so that `x` and `y` here are by value, as they appear to be:
321 // match &(&22, &44) {
327 PatKind::Ref(..) => AdjustMode::Reset,
328 // A `_` pattern works with any expected type, so there's no need to do anything.
330 // Bindings also work with whatever the expected type is,
331 // and moreover if we peel references off, that will give us the wrong binding type.
332 // Also, we can have a subpattern `binding @ pat`.
333 // Each side of the `@` should be treated independently (like with OR-patterns).
334 | PatKind::Binding(..)
335 // An OR-pattern just propagates to each individual alternative.
336 // This is maximally flexible, allowing e.g., `Some(mut x) | &Some(mut x)`.
337 // In that example, `Some(mut x)` results in `Peel` whereas `&Some(mut x)` in `Reset`.
338 | PatKind::Or(_) => AdjustMode::Pass,
342 /// Peel off as many immediately nested `& mut?` from the expected type as possible
343 /// and return the new expected type and binding default binding mode.
344 /// The adjustments vector, if non-empty is stored in a table.
345 fn peel_off_references(
347 pat: &'tcx Pat<'tcx>,
349 mut def_bm: BindingMode,
350 ) -> (Ty<'tcx>, BindingMode) {
351 let mut expected = self.resolve_vars_with_obligations(expected);
353 // Peel off as many `&` or `&mut` from the scrutinee type as possible. For example,
354 // for `match &&&mut Some(5)` the loop runs three times, aborting when it reaches
355 // the `Some(5)` which is not of type Ref.
357 // For each ampersand peeled off, update the binding mode and push the original
358 // type into the adjustments vector.
360 // See the examples in `ui/match-defbm*.rs`.
361 let mut pat_adjustments = vec![];
362 while let ty::Ref(_, inner_ty, inner_mutability) = *expected.kind() {
363 debug!("inspecting {:?}", expected);
365 debug!("current discriminant is Ref, inserting implicit deref");
366 // Preserve the reference type. We'll need it later during THIR lowering.
367 pat_adjustments.push(expected);
370 def_bm = ty::BindByReference(match def_bm {
371 // If default binding mode is by value, make it `ref` or `ref mut`
372 // (depending on whether we observe `&` or `&mut`).
374 // When `ref mut`, stay a `ref mut` (on `&mut`) or downgrade to `ref` (on `&`).
375 ty::BindByReference(hir::Mutability::Mut) => inner_mutability,
376 // Once a `ref`, always a `ref`.
377 // This is because a `& &mut` cannot mutate the underlying value.
378 ty::BindByReference(m @ hir::Mutability::Not) => m,
382 if !pat_adjustments.is_empty() {
383 debug!("default binding mode is now {:?}", def_bm);
387 .pat_adjustments_mut()
388 .insert(pat.hir_id, pat_adjustments);
397 lt: &hir::Expr<'tcx>,
401 // We've already computed the type above (when checking for a non-ref pat),
402 // so avoid computing it again.
403 let ty = self.node_ty(lt.hir_id);
405 // Byte string patterns behave the same way as array patterns
406 // They can denote both statically and dynamically-sized byte arrays.
408 if let hir::ExprKind::Lit(Spanned { node: ast::LitKind::ByteStr(_), .. }) = lt.kind {
409 let expected = self.structurally_resolved_type(span, expected);
410 if let ty::Ref(_, inner_ty, _) = expected.kind()
411 && matches!(inner_ty.kind(), ty::Slice(_))
414 trace!(?lt.hir_id.local_id, "polymorphic byte string lit");
417 .treat_byte_string_as_slice
418 .insert(lt.hir_id.local_id);
419 pat_ty = tcx.mk_imm_ref(tcx.lifetimes.re_static, tcx.mk_slice(tcx.types.u8));
423 // Somewhat surprising: in this case, the subtyping relation goes the
424 // opposite way as the other cases. Actually what we really want is not
425 // a subtyping relation at all but rather that there exists a LUB
426 // (so that they can be compared). However, in practice, constants are
427 // always scalars or strings. For scalars subtyping is irrelevant,
428 // and for strings `ty` is type is `&'static str`, so if we say that
430 // &'static str <: expected
432 // then that's equivalent to there existing a LUB.
433 let cause = self.pattern_cause(ti, span);
434 if let Some(mut err) = self.demand_suptype_with_origin(&cause, expected, pat_ty) {
438 // In the case of `if`- and `while`-expressions we've already checked
439 // that `scrutinee: bool`. We know that the pattern is `true`,
440 // so an error here would be a duplicate and from the wrong POV.
441 s.is_desugaring(DesugaringKind::CondTemporary)
453 lhs: Option<&'tcx hir::Expr<'tcx>>,
454 rhs: Option<&'tcx hir::Expr<'tcx>>,
458 let calc_side = |opt_expr: Option<&'tcx hir::Expr<'tcx>>| match opt_expr {
461 let ty = self.check_expr(expr);
462 // Check that the end-point is possibly of numeric or char type.
463 // The early check here is not for correctness, but rather better
464 // diagnostics (e.g. when `&str` is being matched, `expected` will
465 // be peeled to `str` while ty here is still `&str`, if we don't
466 // err early here, a rather confusing unification error will be
469 !(ty.is_numeric() || ty.is_char() || ty.is_ty_var() || ty.references_error());
470 Some((fail, ty, expr.span))
473 let mut lhs = calc_side(lhs);
474 let mut rhs = calc_side(rhs);
476 if let (Some((true, ..)), _) | (_, Some((true, ..))) = (lhs, rhs) {
477 // There exists a side that didn't meet our criteria that the end-point
478 // be of a numeric or char type, as checked in `calc_side` above.
479 self.emit_err_pat_range(span, lhs, rhs);
480 return self.tcx.ty_error();
483 // Unify each side with `expected`.
484 // Subtyping doesn't matter here, as the value is some kind of scalar.
485 let demand_eqtype = |x: &mut _, y| {
486 if let Some((ref mut fail, x_ty, x_span)) = *x
487 && let Some(mut err) = self.demand_eqtype_pat_diag(x_span, expected, x_ty, ti)
489 if let Some((_, y_ty, y_span)) = y {
490 self.endpoint_has_type(&mut err, y_span, y_ty);
496 demand_eqtype(&mut lhs, rhs);
497 demand_eqtype(&mut rhs, lhs);
499 if let (Some((true, ..)), _) | (_, Some((true, ..))) = (lhs, rhs) {
500 return self.tcx.ty_error();
503 // Find the unified type and check if it's of numeric or char type again.
504 // This check is needed if both sides are inference variables.
505 // We require types to be resolved here so that we emit inference failure
506 // rather than "_ is not a char or numeric".
507 let ty = self.structurally_resolved_type(span, expected);
508 if !(ty.is_numeric() || ty.is_char() || ty.references_error()) {
509 if let Some((ref mut fail, _, _)) = lhs {
512 if let Some((ref mut fail, _, _)) = rhs {
515 self.emit_err_pat_range(span, lhs, rhs);
516 return self.tcx.ty_error();
521 fn endpoint_has_type(&self, err: &mut Diagnostic, span: Span, ty: Ty<'_>) {
522 if !ty.references_error() {
523 err.span_label(span, &format!("this is of type `{}`", ty));
527 fn emit_err_pat_range(
530 lhs: Option<(bool, Ty<'tcx>, Span)>,
531 rhs: Option<(bool, Ty<'tcx>, Span)>,
533 let span = match (lhs, rhs) {
534 (Some((true, ..)), Some((true, ..))) => span,
535 (Some((true, _, sp)), _) => sp,
536 (_, Some((true, _, sp))) => sp,
537 _ => span_bug!(span, "emit_err_pat_range: no side failed or exists but still error?"),
539 let mut err = struct_span_err!(
543 "only `char` and numeric types are allowed in range patterns"
546 let ty = self.resolve_vars_if_possible(ty);
547 format!("this is of type `{}` but it should be `char` or numeric", ty)
549 let mut one_side_err = |first_span, first_ty, second: Option<(bool, Ty<'tcx>, Span)>| {
550 err.span_label(first_span, &msg(first_ty));
551 if let Some((_, ty, sp)) = second {
552 let ty = self.resolve_vars_if_possible(ty);
553 self.endpoint_has_type(&mut err, sp, ty);
557 (Some((true, lhs_ty, lhs_sp)), Some((true, rhs_ty, rhs_sp))) => {
558 err.span_label(lhs_sp, &msg(lhs_ty));
559 err.span_label(rhs_sp, &msg(rhs_ty));
561 (Some((true, lhs_ty, lhs_sp)), rhs) => one_side_err(lhs_sp, lhs_ty, rhs),
562 (lhs, Some((true, rhs_ty, rhs_sp))) => one_side_err(rhs_sp, rhs_ty, lhs),
563 _ => span_bug!(span, "Impossible, verified above."),
565 if self.tcx.sess.teach(&err.get_code().unwrap()) {
567 "In a match expression, only numbers and characters can be matched \
568 against a range. This is because the compiler checks that the range \
569 is non-empty at compile-time, and is unable to evaluate arbitrary \
570 comparison functions. If you want to capture values of an orderable \
571 type between two end-points, you can use a guard.",
579 pat: &'tcx Pat<'tcx>,
580 ba: hir::BindingAnnotation,
582 sub: Option<&'tcx Pat<'tcx>>,
587 // Determine the binding mode...
589 hir::BindingAnnotation::Unannotated => def_bm,
590 _ => BindingMode::convert(ba),
592 // ...and store it in a side table:
593 self.inh.typeck_results.borrow_mut().pat_binding_modes_mut().insert(pat.hir_id, bm);
595 debug!("check_pat_ident: pat.hir_id={:?} bm={:?}", pat.hir_id, bm);
597 let local_ty = self.local_ty(pat.span, pat.hir_id).decl_ty;
598 let eq_ty = match bm {
599 ty::BindByReference(mutbl) => {
600 // If the binding is like `ref x | ref mut x`,
601 // then `x` is assigned a value of type `&M T` where M is the
602 // mutability and T is the expected type.
604 // `x` is assigned a value of type `&M T`, hence `&M T <: typeof(x)`
605 // is required. However, we use equality, which is stronger.
606 // See (note_1) for an explanation.
607 self.new_ref_ty(pat.span, mutbl, expected)
609 // Otherwise, the type of x is the expected type `T`.
610 ty::BindByValue(_) => {
611 // As above, `T <: typeof(x)` is required, but we use equality, see (note_1).
615 self.demand_eqtype_pat(pat.span, eq_ty, local_ty, ti);
617 // If there are multiple arms, make sure they all agree on
618 // what the type of the binding `x` ought to be.
619 if var_id != pat.hir_id {
620 self.check_binding_alt_eq_ty(pat.span, var_id, local_ty, ti);
623 if let Some(p) = sub {
624 self.check_pat(p, expected, def_bm, TopInfo { parent_pat: Some(pat), ..ti });
630 fn check_binding_alt_eq_ty(&self, span: Span, var_id: HirId, ty: Ty<'tcx>, ti: TopInfo<'tcx>) {
631 let var_ty = self.local_ty(span, var_id).decl_ty;
632 if let Some(mut err) = self.demand_eqtype_pat_diag(span, var_ty, ty, ti) {
633 let hir = self.tcx.hir();
634 let var_ty = self.resolve_vars_with_obligations(var_ty);
635 let msg = format!("first introduced with type `{var_ty}` here");
636 err.span_label(hir.span(var_id), msg);
637 let in_match = hir.parent_iter(var_id).any(|(_, n)| {
640 hir::Node::Expr(hir::Expr {
641 kind: hir::ExprKind::Match(.., hir::MatchSource::Normal),
646 let pre = if in_match { "in the same arm, " } else { "" };
647 err.note(&format!("{}a binding must have the same type in all alternatives", pre));
648 // FIXME: check if `var_ty` and `ty` can be made the same type by adding or removing
649 // `ref` or `&` to the pattern.
654 // Precondition: pat is a Ref(_) pattern
655 fn borrow_pat_suggestion(&self, err: &mut Diagnostic, pat: &Pat<'_>) {
657 if let PatKind::Ref(inner, mutbl) = pat.kind
658 && let PatKind::Binding(_, _, binding, ..) = inner.kind {
659 let binding_parent_id = tcx.hir().get_parent_node(pat.hir_id);
660 let binding_parent = tcx.hir().get(binding_parent_id);
661 debug!(?inner, ?pat, ?binding_parent);
663 let mutability = match mutbl {
664 ast::Mutability::Mut => "mut",
665 ast::Mutability::Not => "",
668 let mut_var_suggestion = 'block: {
669 if !matches!(mutbl, ast::Mutability::Mut) {
673 let ident_kind = match binding_parent {
674 hir::Node::Param(_) => "parameter",
675 hir::Node::Local(_) => "variable",
676 hir::Node::Arm(_) => "binding",
678 // Provide diagnostics only if the parent pattern is struct-like,
679 // i.e. where `mut binding` makes sense
680 hir::Node::Pat(Pat { kind, .. }) => match kind {
682 | PatKind::TupleStruct(..)
685 | PatKind::Slice(..) => "binding",
688 | PatKind::Binding(..)
693 | PatKind::Range(..) => break 'block None,
696 // Don't provide suggestions in other cases
697 _ => break 'block None,
702 format!("to declare a mutable {ident_kind} use"),
703 format!("mut {binding}"),
708 match binding_parent {
709 // Check that there is explicit type (ie this is not a closure param with inferred type)
710 // so we don't suggest moving something to the type that does not exist
711 hir::Node::Param(hir::Param { ty_span, .. }) if binding.span != *ty_span => {
712 err.multipart_suggestion_verbose(
713 format!("to take parameter `{binding}` by reference, move `&{mutability}` to the type"),
715 (pat.span.until(inner.span), "".to_owned()),
716 (ty_span.shrink_to_lo(), format!("&{}", mutbl.prefix_str())),
718 Applicability::MachineApplicable
721 if let Some((sp, msg, sugg)) = mut_var_suggestion {
722 err.span_note(sp, format!("{msg}: `{sugg}`"));
725 hir::Node::Param(_) | hir::Node::Arm(_) | hir::Node::Pat(_) => {
726 // rely on match ergonomics or it might be nested `&&pat`
727 err.span_suggestion_verbose(
728 pat.span.until(inner.span),
729 format!("consider removing `&{mutability}` from the pattern"),
731 Applicability::MaybeIncorrect,
734 if let Some((sp, msg, sugg)) = mut_var_suggestion {
735 err.span_note(sp, format!("{msg}: `{sugg}`"));
738 _ if let Some((sp, msg, sugg)) = mut_var_suggestion => {
739 err.span_suggestion(sp, msg, sugg, Applicability::MachineApplicable);
741 _ => {} // don't provide suggestions in other cases #55175
746 pub fn check_dereferenceable(&self, span: Span, expected: Ty<'tcx>, inner: &Pat<'_>) -> bool {
747 if let PatKind::Binding(..) = inner.kind
748 && let Some(mt) = self.shallow_resolve(expected).builtin_deref(true)
749 && let ty::Dynamic(..) = mt.ty.kind()
751 // This is "x = SomeTrait" being reduced from
752 // "let &x = &SomeTrait" or "let box x = Box<SomeTrait>", an error.
753 let type_str = self.ty_to_string(expected);
754 let mut err = struct_span_err!(
758 "type `{}` cannot be dereferenced",
761 err.span_label(span, format!("type `{type_str}` cannot be dereferenced"));
762 if self.tcx.sess.teach(&err.get_code().unwrap()) {
763 err.note(CANNOT_IMPLICITLY_DEREF_POINTER_TRAIT_OBJ);
773 pat: &'tcx Pat<'tcx>,
774 qpath: &hir::QPath<'_>,
775 fields: &'tcx [hir::PatField<'tcx>],
781 // Resolve the path and check the definition for errors.
782 let Some((variant, pat_ty)) = self.check_struct_path(qpath, pat.hir_id) else {
783 let err = self.tcx.ty_error();
784 for field in fields {
785 let ti = TopInfo { parent_pat: Some(pat), ..ti };
786 self.check_pat(field.pat, err, def_bm, ti);
791 // Type-check the path.
792 self.demand_eqtype_pat(pat.span, expected, pat_ty, ti);
794 // Type-check subpatterns.
795 if self.check_struct_pat_fields(pat_ty, &pat, variant, fields, has_rest_pat, def_bm, ti) {
802 fn check_pat_path<'b>(
805 qpath: &hir::QPath<'_>,
806 path_resolution: (Res, Option<Ty<'tcx>>, &'b [hir::PathSegment<'b>]),
812 // We have already resolved the path.
813 let (res, opt_ty, segments) = path_resolution;
816 self.set_tainted_by_errors();
817 return tcx.ty_error();
819 Res::Def(DefKind::AssocFn | DefKind::Ctor(_, CtorKind::Fictive | CtorKind::Fn), _) => {
820 report_unexpected_variant_res(tcx, res, qpath, pat.span);
821 return tcx.ty_error();
825 DefKind::Ctor(_, CtorKind::Const)
827 | DefKind::AssocConst
828 | DefKind::ConstParam,
831 _ => bug!("unexpected pattern resolution: {:?}", res),
834 // Type-check the path.
835 let (pat_ty, pat_res) =
836 self.instantiate_value_path(segments, opt_ty, res, pat.span, pat.hir_id);
838 self.demand_suptype_with_origin(&self.pattern_cause(ti, pat.span), expected, pat_ty)
840 self.emit_bad_pat_path(err, pat.span, res, pat_res, pat_ty, segments, ti.parent_pat);
845 fn maybe_suggest_range_literal(
848 opt_def_id: Option<hir::def_id::DefId>,
852 Some(def_id) => match self.tcx.hir().get_if_local(def_id) {
853 Some(hir::Node::Item(hir::Item {
854 kind: hir::ItemKind::Const(_, body_id), ..
855 })) => match self.tcx.hir().get(body_id.hir_id) {
856 hir::Node::Expr(expr) => {
857 if hir::is_range_literal(expr) {
858 let span = self.tcx.hir().span(body_id.hir_id);
859 if let Ok(snip) = self.tcx.sess.source_map().span_to_snippet(span) {
860 e.span_suggestion_verbose(
862 "you may want to move the range into the match block",
864 Applicability::MachineApplicable,
879 fn emit_bad_pat_path<'b>(
881 mut e: DiagnosticBuilder<'_, ErrorGuaranteed>,
886 segments: &'b [hir::PathSegment<'b>],
887 parent_pat: Option<&Pat<'_>>,
889 if let Some(span) = self.tcx.hir().res_span(pat_res) {
890 e.span_label(span, &format!("{} defined here", res.descr()));
891 if let [hir::PathSegment { ident, .. }] = &*segments {
895 "`{}` is interpreted as {} {}, not a new binding",
902 Some(Pat { kind: hir::PatKind::Struct(..), .. }) => {
903 e.span_suggestion_verbose(
904 ident.span.shrink_to_hi(),
905 "bind the struct field to a different name instead",
906 format!(": other_{}", ident.as_str().to_lowercase()),
907 Applicability::HasPlaceholders,
911 let (type_def_id, item_def_id) = match pat_ty.kind() {
912 Adt(def, _) => match res {
913 Res::Def(DefKind::Const, def_id) => (Some(def.did()), Some(def_id)),
920 self.tcx.lang_items().range_struct(),
921 self.tcx.lang_items().range_from_struct(),
922 self.tcx.lang_items().range_to_struct(),
923 self.tcx.lang_items().range_full_struct(),
924 self.tcx.lang_items().range_inclusive_struct(),
925 self.tcx.lang_items().range_to_inclusive_struct(),
927 if type_def_id != None && ranges.contains(&type_def_id) {
928 if !self.maybe_suggest_range_literal(&mut e, item_def_id, *ident) {
929 let msg = "constants only support matching by type, \
930 if you meant to match against a range of values, \
931 consider using a range pattern like `min ..= max` in the match block";
935 let msg = "introduce a new binding instead";
936 let sugg = format!("other_{}", ident.as_str().to_lowercase());
941 Applicability::HasPlaceholders,
951 fn check_pat_tuple_struct(
953 pat: &'tcx Pat<'tcx>,
954 qpath: &'tcx hir::QPath<'tcx>,
955 subpats: &'tcx [Pat<'tcx>],
956 ddpos: Option<usize>,
963 let parent_pat = Some(pat);
965 self.check_pat(pat, tcx.ty_error(), def_bm, TopInfo { parent_pat, ..ti });
968 let report_unexpected_res = |res: Res| {
969 let sm = tcx.sess.source_map();
971 .span_to_snippet(sm.span_until_char(pat.span, '('))
972 .map_or_else(|_| String::new(), |s| format!(" `{}`", s.trim_end()));
974 "expected tuple struct or tuple variant, found {}{}",
979 let mut err = struct_span_err!(tcx.sess, pat.span, E0164, "{msg}");
981 Res::Def(DefKind::Fn | DefKind::AssocFn, _) => {
982 err.span_label(pat.span, "`fn` calls are not allowed in patterns");
984 "for more information, visit \
985 https://doc.rust-lang.org/book/ch18-00-patterns.html",
989 err.span_label(pat.span, "not a tuple variant or struct");
996 // Resolve the path and check the definition for errors.
997 let (res, opt_ty, segments) =
998 self.resolve_ty_and_res_fully_qualified_call(qpath, pat.hir_id, pat.span);
1000 self.set_tainted_by_errors();
1002 return self.tcx.ty_error();
1005 // Type-check the path.
1007 self.instantiate_value_path(segments, opt_ty, res, pat.span, pat.hir_id);
1008 if !pat_ty.is_fn() {
1009 report_unexpected_res(res);
1010 return tcx.ty_error();
1013 let variant = match res {
1015 self.set_tainted_by_errors();
1017 return tcx.ty_error();
1019 Res::Def(DefKind::AssocConst | DefKind::AssocFn, _) => {
1020 report_unexpected_res(res);
1021 return tcx.ty_error();
1023 Res::Def(DefKind::Ctor(_, CtorKind::Fn), _) => tcx.expect_variant_res(res),
1024 _ => bug!("unexpected pattern resolution: {:?}", res),
1027 // Replace constructor type with constructed type for tuple struct patterns.
1028 let pat_ty = pat_ty.fn_sig(tcx).output();
1029 let pat_ty = pat_ty.no_bound_vars().expect("expected fn type");
1031 // Type-check the tuple struct pattern against the expected type.
1032 let diag = self.demand_eqtype_pat_diag(pat.span, expected, pat_ty, ti);
1033 let had_err = if let Some(mut err) = diag {
1040 // Type-check subpatterns.
1041 if subpats.len() == variant.fields.len()
1042 || subpats.len() < variant.fields.len() && ddpos.is_some()
1044 let ty::Adt(_, substs) = pat_ty.kind() else {
1045 bug!("unexpected pattern type {:?}", pat_ty);
1047 for (i, subpat) in subpats.iter().enumerate_and_adjust(variant.fields.len(), ddpos) {
1048 let field_ty = self.field_ty(subpat.span, &variant.fields[i], substs);
1049 self.check_pat(subpat, field_ty, def_bm, TopInfo { parent_pat: Some(pat), ..ti });
1051 self.tcx.check_stability(
1052 variant.fields[i].did,
1059 // Pattern has wrong number of fields.
1060 self.e0023(pat.span, res, qpath, subpats, &variant.fields, expected, had_err);
1062 return tcx.ty_error();
1071 qpath: &hir::QPath<'_>,
1072 subpats: &'tcx [Pat<'tcx>],
1073 fields: &'tcx [ty::FieldDef],
1077 let subpats_ending = pluralize!(subpats.len());
1078 let fields_ending = pluralize!(fields.len());
1080 let subpat_spans = if subpats.is_empty() {
1083 subpats.iter().map(|p| p.span).collect()
1085 let last_subpat_span = *subpat_spans.last().unwrap();
1086 let res_span = self.tcx.def_span(res.def_id());
1087 let def_ident_span = self.tcx.def_ident_span(res.def_id()).unwrap_or(res_span);
1088 let field_def_spans = if fields.is_empty() {
1091 fields.iter().map(|f| f.ident(self.tcx).span).collect()
1093 let last_field_def_span = *field_def_spans.last().unwrap();
1095 let mut err = struct_span_err!(
1097 MultiSpan::from_spans(subpat_spans),
1099 "this pattern has {} field{}, but the corresponding {} has {} field{}",
1108 &format!("expected {} field{}, found {}", fields.len(), fields_ending, subpats.len()),
1110 if self.tcx.sess.source_map().is_multiline(qpath.span().between(last_subpat_span)) {
1111 err.span_label(qpath.span(), "");
1113 if self.tcx.sess.source_map().is_multiline(def_ident_span.between(last_field_def_span)) {
1114 err.span_label(def_ident_span, format!("{} defined here", res.descr()));
1116 for span in &field_def_spans[..field_def_spans.len() - 1] {
1117 err.span_label(*span, "");
1120 last_field_def_span,
1121 &format!("{} has {} field{}", res.descr(), fields.len(), fields_ending),
1124 // Identify the case `Some(x, y)` where the expected type is e.g. `Option<(T, U)>`.
1125 // More generally, the expected type wants a tuple variant with one field of an
1126 // N-arity-tuple, e.g., `V_i((p_0, .., p_N))`. Meanwhile, the user supplied a pattern
1127 // with the subpatterns directly in the tuple variant pattern, e.g., `V_i(p_0, .., p_N)`.
1128 let missing_parentheses = match (&expected.kind(), fields, had_err) {
1129 // #67037: only do this if we could successfully type-check the expected type against
1130 // the tuple struct pattern. Otherwise the substs could get out of range on e.g.,
1131 // `let P() = U;` where `P != U` with `struct P<T>(T);`.
1132 (ty::Adt(_, substs), [field], false) => {
1133 let field_ty = self.field_ty(pat_span, field, substs);
1134 match field_ty.kind() {
1135 ty::Tuple(fields) => fields.len() == subpats.len(),
1141 if missing_parentheses {
1142 let (left, right) = match subpats {
1143 // This is the zero case; we aim to get the "hi" part of the `QPath`'s
1144 // span as the "lo" and then the "hi" part of the pattern's span as the "hi".
1147 // help: missing parentheses
1149 // L | let A(()) = A(());
1151 [] => (qpath.span().shrink_to_hi(), pat_span),
1152 // Easy case. Just take the "lo" of the first sub-pattern and the "hi" of the
1153 // last sub-pattern. In the case of `A(x)` the first and last may coincide.
1156 // help: missing parentheses
1158 // L | let A((x, y)) = A((1, 2));
1160 [first, ..] => (first.span.shrink_to_lo(), subpats.last().unwrap().span),
1162 err.multipart_suggestion(
1163 "missing parentheses",
1164 vec![(left, "(".to_string()), (right.shrink_to_hi(), ")".to_string())],
1165 Applicability::MachineApplicable,
1167 } else if fields.len() > subpats.len() && pat_span != DUMMY_SP {
1168 let after_fields_span = pat_span.with_hi(pat_span.hi() - BytePos(1)).shrink_to_hi();
1169 let all_fields_span = match subpats {
1170 [] => after_fields_span,
1171 [field] => field.span,
1172 [first, .., last] => first.span.to(last.span),
1175 // Check if all the fields in the pattern are wildcards.
1176 let all_wildcards = subpats.iter().all(|pat| matches!(pat.kind, PatKind::Wild));
1177 let first_tail_wildcard =
1178 subpats.iter().enumerate().fold(None, |acc, (pos, pat)| match (acc, &pat.kind) {
1179 (None, PatKind::Wild) => Some(pos),
1180 (Some(_), PatKind::Wild) => acc,
1183 let tail_span = match first_tail_wildcard {
1184 None => after_fields_span,
1185 Some(0) => subpats[0].span.to(after_fields_span),
1186 Some(pos) => subpats[pos - 1].span.shrink_to_hi().to(after_fields_span),
1189 // FIXME: heuristic-based suggestion to check current types for where to add `_`.
1190 let mut wildcard_sugg = vec!["_"; fields.len() - subpats.len()].join(", ");
1191 if !subpats.is_empty() {
1192 wildcard_sugg = String::from(", ") + &wildcard_sugg;
1195 err.span_suggestion_verbose(
1197 "use `_` to explicitly ignore each field",
1199 Applicability::MaybeIncorrect,
1202 // Only suggest `..` if more than one field is missing
1203 // or the pattern consists of all wildcards.
1204 if fields.len() - subpats.len() > 1 || all_wildcards {
1205 if subpats.is_empty() || all_wildcards {
1206 err.span_suggestion_verbose(
1208 "use `..` to ignore all fields",
1210 Applicability::MaybeIncorrect,
1213 err.span_suggestion_verbose(
1215 "use `..` to ignore the rest of the fields",
1217 Applicability::MaybeIncorrect,
1229 elements: &'tcx [Pat<'tcx>],
1230 ddpos: Option<usize>,
1232 def_bm: BindingMode,
1236 let mut expected_len = elements.len();
1237 if ddpos.is_some() {
1238 // Require known type only when `..` is present.
1239 if let ty::Tuple(tys) = self.structurally_resolved_type(span, expected).kind() {
1240 expected_len = tys.len();
1243 let max_len = cmp::max(expected_len, elements.len());
1245 let element_tys_iter = (0..max_len).map(|_| {
1247 // FIXME: `MiscVariable` for now -- obtaining the span and name information
1248 // from all tuple elements isn't trivial.
1249 TypeVariableOrigin { kind: TypeVariableOriginKind::TypeInference, span },
1252 let element_tys = tcx.mk_type_list(element_tys_iter);
1253 let pat_ty = tcx.mk_ty(ty::Tuple(element_tys));
1254 if let Some(mut err) = self.demand_eqtype_pat_diag(span, expected, pat_ty, ti) {
1256 // Walk subpatterns with an expected type of `err` in this case to silence
1257 // further errors being emitted when using the bindings. #50333
1258 let element_tys_iter = (0..max_len).map(|_| tcx.ty_error());
1259 for (_, elem) in elements.iter().enumerate_and_adjust(max_len, ddpos) {
1260 self.check_pat(elem, tcx.ty_error(), def_bm, ti);
1262 tcx.mk_tup(element_tys_iter)
1264 for (i, elem) in elements.iter().enumerate_and_adjust(max_len, ddpos) {
1265 self.check_pat(elem, element_tys[i], def_bm, ti);
1271 fn check_struct_pat_fields(
1274 pat: &'tcx Pat<'tcx>,
1275 variant: &'tcx ty::VariantDef,
1276 fields: &'tcx [hir::PatField<'tcx>],
1278 def_bm: BindingMode,
1283 let ty::Adt(adt, substs) = adt_ty.kind() else {
1284 span_bug!(pat.span, "struct pattern is not an ADT");
1287 // Index the struct fields' types.
1288 let field_map = variant
1292 .map(|(i, field)| (field.ident(self.tcx).normalize_to_macros_2_0(), (i, field)))
1293 .collect::<FxHashMap<_, _>>();
1295 // Keep track of which fields have already appeared in the pattern.
1296 let mut used_fields = FxHashMap::default();
1297 let mut no_field_errors = true;
1299 let mut inexistent_fields = vec![];
1300 // Typecheck each field.
1301 for field in fields {
1302 let span = field.span;
1303 let ident = tcx.adjust_ident(field.ident, variant.def_id);
1304 let field_ty = match used_fields.entry(ident) {
1305 Occupied(occupied) => {
1306 self.error_field_already_bound(span, field.ident, *occupied.get());
1307 no_field_errors = false;
1311 vacant.insert(span);
1315 self.write_field_index(field.hir_id, *i);
1316 self.tcx.check_stability(f.did, Some(pat.hir_id), span, None);
1317 self.field_ty(span, f, substs)
1319 .unwrap_or_else(|| {
1320 inexistent_fields.push(field);
1321 no_field_errors = false;
1327 self.check_pat(field.pat, field_ty, def_bm, TopInfo { parent_pat: Some(pat), ..ti });
1330 let mut unmentioned_fields = variant
1333 .map(|field| (field, field.ident(self.tcx).normalize_to_macros_2_0()))
1334 .filter(|(_, ident)| !used_fields.contains_key(ident))
1335 .collect::<Vec<_>>();
1337 let inexistent_fields_err = if !(inexistent_fields.is_empty() || variant.is_recovered())
1338 && !inexistent_fields.iter().any(|field| field.ident.name == kw::Underscore)
1340 Some(self.error_inexistent_fields(
1341 adt.variant_descr(),
1343 &mut unmentioned_fields,
1351 // Require `..` if struct has non_exhaustive attribute.
1352 let non_exhaustive = variant.is_field_list_non_exhaustive() && !adt.did().is_local();
1353 if non_exhaustive && !has_rest_pat {
1354 self.error_foreign_non_exhaustive_spat(pat, adt.variant_descr(), fields.is_empty());
1357 let mut unmentioned_err = None;
1358 // Report an error if an incorrect number of fields was specified.
1360 if fields.len() != 1 {
1362 .struct_span_err(pat.span, "union patterns should have exactly one field")
1366 tcx.sess.struct_span_err(pat.span, "`..` cannot be used in union patterns").emit();
1368 } else if !unmentioned_fields.is_empty() {
1369 let accessible_unmentioned_fields: Vec<_> = unmentioned_fields
1372 .filter(|(field, _)| {
1373 field.vis.is_accessible_from(tcx.parent_module(pat.hir_id).to_def_id(), tcx)
1375 tcx.eval_stability(field.did, None, DUMMY_SP, None),
1376 EvalResult::Deny { .. }
1378 // We only want to report the error if it is hidden and not local
1379 && !(tcx.is_doc_hidden(field.did) && !field.did.is_local())
1384 if accessible_unmentioned_fields.is_empty() {
1385 unmentioned_err = Some(self.error_no_accessible_fields(pat, fields));
1387 unmentioned_err = Some(self.error_unmentioned_fields(
1389 &accessible_unmentioned_fields,
1390 accessible_unmentioned_fields.len() != unmentioned_fields.len(),
1394 } else if non_exhaustive && !accessible_unmentioned_fields.is_empty() {
1395 self.lint_non_exhaustive_omitted_patterns(
1397 &accessible_unmentioned_fields,
1402 match (inexistent_fields_err, unmentioned_err) {
1403 (Some(mut i), Some(mut u)) => {
1404 if let Some(mut e) = self.error_tuple_variant_as_struct_pat(pat, fields, variant) {
1405 // We don't want to show the nonexistent fields error when this was
1406 // `Foo { a, b }` when it should have been `Foo(a, b)`.
1415 (None, Some(mut u)) => {
1416 if let Some(mut e) = self.error_tuple_variant_as_struct_pat(pat, fields, variant) {
1423 (Some(mut err), None) => {
1426 (None, None) if let Some(mut err) =
1427 self.error_tuple_variant_index_shorthand(variant, pat, fields) =>
1436 fn error_tuple_variant_index_shorthand(
1438 variant: &VariantDef,
1440 fields: &[hir::PatField<'_>],
1441 ) -> Option<DiagnosticBuilder<'_, ErrorGuaranteed>> {
1442 // if this is a tuple struct, then all field names will be numbers
1443 // so if any fields in a struct pattern use shorthand syntax, they will
1444 // be invalid identifiers (for example, Foo { 0, 1 }).
1445 if let (CtorKind::Fn, PatKind::Struct(qpath, field_patterns, ..)) =
1446 (variant.ctor_kind, &pat.kind)
1448 let has_shorthand_field_name = field_patterns.iter().any(|field| field.is_shorthand);
1449 if has_shorthand_field_name {
1450 let path = rustc_hir_pretty::to_string(rustc_hir_pretty::NO_ANN, |s| {
1451 s.print_qpath(qpath, false)
1453 let mut err = struct_span_err!(
1457 "tuple variant `{path}` written as struct variant",
1459 err.span_suggestion_verbose(
1460 qpath.span().shrink_to_hi().to(pat.span.shrink_to_hi()),
1461 "use the tuple variant pattern syntax instead",
1462 format!("({})", self.get_suggested_tuple_struct_pattern(fields, variant)),
1463 Applicability::MaybeIncorrect,
1471 fn error_foreign_non_exhaustive_spat(&self, pat: &Pat<'_>, descr: &str, no_fields: bool) {
1472 let sess = self.tcx.sess;
1473 let sm = sess.source_map();
1474 let sp_brace = sm.end_point(pat.span);
1475 let sp_comma = sm.end_point(pat.span.with_hi(sp_brace.hi()));
1476 let sugg = if no_fields || sp_brace != sp_comma { ".. }" } else { ", .. }" };
1478 let mut err = struct_span_err!(
1482 "`..` required with {descr} marked as non-exhaustive",
1484 err.span_suggestion_verbose(
1486 "add `..` at the end of the field list to ignore all other fields",
1488 Applicability::MachineApplicable,
1493 fn error_field_already_bound(&self, span: Span, ident: Ident, other_field: Span) {
1498 "field `{}` bound multiple times in the pattern",
1501 .span_label(span, format!("multiple uses of `{ident}` in pattern"))
1502 .span_label(other_field, format!("first use of `{ident}`"))
1506 fn error_inexistent_fields(
1509 inexistent_fields: &[&hir::PatField<'tcx>],
1510 unmentioned_fields: &mut Vec<(&'tcx ty::FieldDef, Ident)>,
1511 variant: &ty::VariantDef,
1512 substs: &'tcx ty::List<ty::subst::GenericArg<'tcx>>,
1513 ) -> DiagnosticBuilder<'tcx, ErrorGuaranteed> {
1515 let (field_names, t, plural) = if inexistent_fields.len() == 1 {
1516 (format!("a field named `{}`", inexistent_fields[0].ident), "this", "")
1523 .map(|field| format!("`{}`", field.ident))
1524 .collect::<Vec<String>>()
1531 let spans = inexistent_fields.iter().map(|field| field.ident.span).collect::<Vec<_>>();
1532 let mut err = struct_span_err!(
1536 "{} `{}` does not have {}",
1538 tcx.def_path_str(variant.def_id),
1541 if let Some(pat_field) = inexistent_fields.last() {
1543 pat_field.ident.span,
1545 "{} `{}` does not have {} field{}",
1547 tcx.def_path_str(variant.def_id),
1553 if unmentioned_fields.len() == 1 {
1555 unmentioned_fields.iter().map(|(_, field)| field.name).collect::<Vec<_>>();
1556 let suggested_name = find_best_match_for_name(&input, pat_field.ident.name, None);
1557 if let Some(suggested_name) = suggested_name {
1558 err.span_suggestion(
1559 pat_field.ident.span,
1560 "a field with a similar name exists",
1562 Applicability::MaybeIncorrect,
1565 // When we have a tuple struct used with struct we don't want to suggest using
1566 // the (valid) struct syntax with numeric field names. Instead we want to
1567 // suggest the expected syntax. We infer that this is the case by parsing the
1568 // `Ident` into an unsized integer. The suggestion will be emitted elsewhere in
1569 // `smart_resolve_context_dependent_help`.
1570 if suggested_name.to_ident_string().parse::<usize>().is_err() {
1571 // We don't want to throw `E0027` in case we have thrown `E0026` for them.
1572 unmentioned_fields.retain(|&(_, x)| x.name != suggested_name);
1574 } else if inexistent_fields.len() == 1 {
1575 match pat_field.pat.kind {
1577 if !self.can_coerce(
1578 self.typeck_results.borrow().expr_ty(expr),
1580 unmentioned_fields[0].1.span,
1581 unmentioned_fields[0].0,
1586 let unmentioned_field = unmentioned_fields[0].1.name;
1587 err.span_suggestion_short(
1588 pat_field.ident.span,
1590 "`{}` has a field named `{}`",
1591 tcx.def_path_str(variant.def_id),
1594 unmentioned_field.to_string(),
1595 Applicability::MaybeIncorrect,
1602 if tcx.sess.teach(&err.get_code().unwrap()) {
1604 "This error indicates that a struct pattern attempted to \
1605 extract a non-existent field from a struct. Struct fields \
1606 are identified by the name used before the colon : so struct \
1607 patterns should resemble the declaration of the struct type \
1609 If you are using shorthand field patterns but want to refer \
1610 to the struct field by a different name, you should rename \
1617 fn error_tuple_variant_as_struct_pat(
1620 fields: &'tcx [hir::PatField<'tcx>],
1621 variant: &ty::VariantDef,
1622 ) -> Option<DiagnosticBuilder<'tcx, ErrorGuaranteed>> {
1623 if let (CtorKind::Fn, PatKind::Struct(qpath, ..)) = (variant.ctor_kind, &pat.kind) {
1624 let path = rustc_hir_pretty::to_string(rustc_hir_pretty::NO_ANN, |s| {
1625 s.print_qpath(qpath, false)
1627 let mut err = struct_span_err!(
1631 "tuple variant `{}` written as struct variant",
1634 let (sugg, appl) = if fields.len() == variant.fields.len() {
1636 self.get_suggested_tuple_struct_pattern(fields, variant),
1637 Applicability::MachineApplicable,
1641 variant.fields.iter().map(|_| "_").collect::<Vec<&str>>().join(", "),
1642 Applicability::MaybeIncorrect,
1645 err.span_suggestion_verbose(
1646 qpath.span().shrink_to_hi().to(pat.span.shrink_to_hi()),
1647 "use the tuple variant pattern syntax instead",
1648 format!("({})", sugg),
1656 fn get_suggested_tuple_struct_pattern(
1658 fields: &[hir::PatField<'_>],
1659 variant: &VariantDef,
1661 let variant_field_idents =
1662 variant.fields.iter().map(|f| f.ident(self.tcx)).collect::<Vec<Ident>>();
1666 match self.tcx.sess.source_map().span_to_snippet(field.pat.span) {
1668 // Field names are numbers, but numbers
1669 // are not valid identifiers
1670 if variant_field_idents.contains(&field.ident) {
1676 Err(_) => rustc_hir_pretty::to_string(rustc_hir_pretty::NO_ANN, |s| {
1677 s.print_pat(field.pat)
1681 .collect::<Vec<String>>()
1685 /// Returns a diagnostic reporting a struct pattern which is missing an `..` due to
1686 /// inaccessible fields.
1689 /// error: pattern requires `..` due to inaccessible fields
1690 /// --> src/main.rs:10:9
1692 /// LL | let foo::Foo {} = foo::Foo::default();
1695 /// help: add a `..`
1697 /// LL | let foo::Foo { .. } = foo::Foo::default();
1700 fn error_no_accessible_fields(
1703 fields: &'tcx [hir::PatField<'tcx>],
1704 ) -> DiagnosticBuilder<'tcx, ErrorGuaranteed> {
1708 .struct_span_err(pat.span, "pattern requires `..` due to inaccessible fields");
1710 if let Some(field) = fields.last() {
1711 err.span_suggestion_verbose(
1712 field.span.shrink_to_hi(),
1713 "ignore the inaccessible and unused fields",
1715 Applicability::MachineApplicable,
1718 let qpath_span = if let PatKind::Struct(qpath, ..) = &pat.kind {
1721 bug!("`error_no_accessible_fields` called on non-struct pattern");
1724 // Shrink the span to exclude the `foo:Foo` in `foo::Foo { }`.
1725 let span = pat.span.with_lo(qpath_span.shrink_to_hi().hi());
1726 err.span_suggestion_verbose(
1728 "ignore the inaccessible and unused fields",
1730 Applicability::MachineApplicable,
1736 /// Report that a pattern for a `#[non_exhaustive]` struct marked with `non_exhaustive_omitted_patterns`
1737 /// is not exhaustive enough.
1739 /// Nb: the partner lint for enums lives in `compiler/rustc_mir_build/src/thir/pattern/usefulness.rs`.
1740 fn lint_non_exhaustive_omitted_patterns(
1743 unmentioned_fields: &[(&ty::FieldDef, Ident)],
1746 fn joined_uncovered_patterns(witnesses: &[&Ident]) -> String {
1747 const LIMIT: usize = 3;
1750 [witness] => format!("`{}`", witness),
1751 [head @ .., tail] if head.len() < LIMIT => {
1752 let head: Vec<_> = head.iter().map(<_>::to_string).collect();
1753 format!("`{}` and `{}`", head.join("`, `"), tail)
1756 let (head, tail) = witnesses.split_at(LIMIT);
1757 let head: Vec<_> = head.iter().map(<_>::to_string).collect();
1758 format!("`{}` and {} more", head.join("`, `"), tail.len())
1762 let joined_patterns = joined_uncovered_patterns(
1763 &unmentioned_fields.iter().map(|(_, i)| i).collect::<Vec<_>>(),
1766 self.tcx.struct_span_lint_hir(NON_EXHAUSTIVE_OMITTED_PATTERNS, pat.hir_id, pat.span, |build| {
1767 let mut lint = build.build("some fields are not explicitly listed");
1768 lint.span_label(pat.span, format!("field{} {} not listed", rustc_errors::pluralize!(unmentioned_fields.len()), joined_patterns));
1771 "ensure that all fields are mentioned explicitly by adding the suggested fields",
1774 "the pattern is of type `{}` and the `non_exhaustive_omitted_patterns` attribute was found",
1781 /// Returns a diagnostic reporting a struct pattern which does not mention some fields.
1784 /// error[E0027]: pattern does not mention field `bar`
1785 /// --> src/main.rs:15:9
1787 /// LL | let foo::Foo {} = foo::Foo::new();
1788 /// | ^^^^^^^^^^^ missing field `bar`
1790 fn error_unmentioned_fields(
1793 unmentioned_fields: &[(&ty::FieldDef, Ident)],
1794 have_inaccessible_fields: bool,
1795 fields: &'tcx [hir::PatField<'tcx>],
1796 ) -> DiagnosticBuilder<'tcx, ErrorGuaranteed> {
1797 let inaccessible = if have_inaccessible_fields { " and inaccessible fields" } else { "" };
1798 let field_names = if unmentioned_fields.len() == 1 {
1799 format!("field `{}`{}", unmentioned_fields[0].1, inaccessible)
1801 let fields = unmentioned_fields
1803 .map(|(_, name)| format!("`{}`", name))
1804 .collect::<Vec<String>>()
1806 format!("fields {}{}", fields, inaccessible)
1808 let mut err = struct_span_err!(
1812 "pattern does not mention {}",
1815 err.span_label(pat.span, format!("missing {}", field_names));
1816 let len = unmentioned_fields.len();
1817 let (prefix, postfix, sp) = match fields {
1818 [] => match &pat.kind {
1819 PatKind::Struct(path, [], false) => {
1820 (" { ", " }", path.span().shrink_to_hi().until(pat.span.shrink_to_hi()))
1825 // Account for last field having a trailing comma or parse recovery at the tail of
1826 // the pattern to avoid invalid suggestion (#78511).
1827 let tail = field.span.shrink_to_hi().with_hi(pat.span.hi());
1829 PatKind::Struct(..) => (", ", " }", tail),
1834 err.span_suggestion(
1837 "include the missing field{} in the pattern{}",
1839 if have_inaccessible_fields { " and ignore the inaccessible fields" } else { "" }
1846 .map(|(_, name)| name.to_string())
1847 .collect::<Vec<_>>()
1849 if have_inaccessible_fields { ", .." } else { "" },
1852 Applicability::MachineApplicable,
1854 err.span_suggestion(
1857 "if you don't care about {these} missing field{s}, you can explicitly ignore {them}",
1858 these = pluralize!("this", len),
1859 s = pluralize!(len),
1860 them = if len == 1 { "it" } else { "them" },
1862 format!("{}..{}", prefix, postfix),
1863 Applicability::MachineApplicable,
1871 inner: &'tcx Pat<'tcx>,
1873 def_bm: BindingMode,
1877 let (box_ty, inner_ty) = if self.check_dereferenceable(span, expected, inner) {
1878 // Here, `demand::subtype` is good enough, but I don't
1879 // think any errors can be introduced by using `demand::eqtype`.
1880 let inner_ty = self.next_ty_var(TypeVariableOrigin {
1881 kind: TypeVariableOriginKind::TypeInference,
1884 let box_ty = tcx.mk_box(inner_ty);
1885 self.demand_eqtype_pat(span, expected, box_ty, ti);
1888 let err = tcx.ty_error();
1891 self.check_pat(inner, inner_ty, def_bm, ti);
1895 // Precondition: Pat is Ref(inner)
1898 pat: &'tcx Pat<'tcx>,
1899 inner: &'tcx Pat<'tcx>,
1900 mutbl: hir::Mutability,
1902 def_bm: BindingMode,
1906 let expected = self.shallow_resolve(expected);
1907 let (rptr_ty, inner_ty) = if self.check_dereferenceable(pat.span, expected, inner) {
1908 // `demand::subtype` would be good enough, but using `eqtype` turns
1909 // out to be equally general. See (note_1) for details.
1911 // Take region, inner-type from expected type if we can,
1912 // to avoid creating needless variables. This also helps with
1913 // the bad interactions of the given hack detailed in (note_1).
1914 debug!("check_pat_ref: expected={:?}", expected);
1915 match *expected.kind() {
1916 ty::Ref(_, r_ty, r_mutbl) if r_mutbl == mutbl => (expected, r_ty),
1918 let inner_ty = self.next_ty_var(TypeVariableOrigin {
1919 kind: TypeVariableOriginKind::TypeInference,
1922 let rptr_ty = self.new_ref_ty(pat.span, mutbl, inner_ty);
1923 debug!("check_pat_ref: demanding {:?} = {:?}", expected, rptr_ty);
1924 let err = self.demand_eqtype_pat_diag(pat.span, expected, rptr_ty, ti);
1926 // Look for a case like `fn foo(&foo: u32)` and suggest
1927 // `fn foo(foo: &u32)`
1928 if let Some(mut err) = err {
1929 self.borrow_pat_suggestion(&mut err, pat);
1936 let err = tcx.ty_error();
1939 self.check_pat(inner, inner_ty, def_bm, TopInfo { parent_pat: Some(pat), ..ti });
1943 /// Create a reference type with a fresh region variable.
1944 fn new_ref_ty(&self, span: Span, mutbl: hir::Mutability, ty: Ty<'tcx>) -> Ty<'tcx> {
1945 let region = self.next_region_var(infer::PatternRegion(span));
1946 let mt = ty::TypeAndMut { ty, mutbl };
1947 self.tcx.mk_ref(region, mt)
1950 /// Type check a slice pattern.
1952 /// Syntactically, these look like `[pat_0, ..., pat_n]`.
1953 /// Semantically, we are type checking a pattern with structure:
1954 /// ```ignore (not-rust)
1955 /// [before_0, ..., before_n, (slice, after_0, ... after_n)?]
1957 /// The type of `slice`, if it is present, depends on the `expected` type.
1958 /// If `slice` is missing, then so is `after_i`.
1959 /// If `slice` is present, it can still represent 0 elements.
1963 before: &'tcx [Pat<'tcx>],
1964 slice: Option<&'tcx Pat<'tcx>>,
1965 after: &'tcx [Pat<'tcx>],
1967 def_bm: BindingMode,
1970 let expected = self.structurally_resolved_type(span, expected);
1971 let (element_ty, opt_slice_ty, inferred) = match *expected.kind() {
1972 // An array, so we might have something like `let [a, b, c] = [0, 1, 2];`.
1973 ty::Array(element_ty, len) => {
1974 let min = before.len() as u64 + after.len() as u64;
1975 let (opt_slice_ty, expected) =
1976 self.check_array_pat_len(span, element_ty, expected, slice, len, min);
1977 // `opt_slice_ty.is_none()` => `slice.is_none()`.
1978 // Note, though, that opt_slice_ty could be `Some(error_ty)`.
1979 assert!(opt_slice_ty.is_some() || slice.is_none());
1980 (element_ty, opt_slice_ty, expected)
1982 ty::Slice(element_ty) => (element_ty, Some(expected), expected),
1983 // The expected type must be an array or slice, but was neither, so error.
1985 if !expected.references_error() {
1986 self.error_expected_array_or_slice(span, expected, ti);
1988 let err = self.tcx.ty_error();
1989 (err, Some(err), err)
1993 // Type check all the patterns before `slice`.
1995 self.check_pat(elt, element_ty, def_bm, ti);
1997 // Type check the `slice`, if present, against its expected type.
1998 if let Some(slice) = slice {
1999 self.check_pat(slice, opt_slice_ty.unwrap(), def_bm, ti);
2001 // Type check the elements after `slice`, if present.
2003 self.check_pat(elt, element_ty, def_bm, ti);
2008 /// Type check the length of an array pattern.
2010 /// Returns both the type of the variable length pattern (or `None`), and the potentially
2011 /// inferred array type. We only return `None` for the slice type if `slice.is_none()`.
2012 fn check_array_pat_len(
2015 element_ty: Ty<'tcx>,
2017 slice: Option<&'tcx Pat<'tcx>>,
2018 len: ty::Const<'tcx>,
2020 ) -> (Option<Ty<'tcx>>, Ty<'tcx>) {
2021 if let Some(len) = len.try_eval_usize(self.tcx, self.param_env) {
2022 // Now we know the length...
2023 if slice.is_none() {
2024 // ...and since there is no variable-length pattern,
2025 // we require an exact match between the number of elements
2026 // in the array pattern and as provided by the matched type.
2028 return (None, arr_ty);
2031 self.error_scrutinee_inconsistent_length(span, min_len, len);
2032 } else if let Some(pat_len) = len.checked_sub(min_len) {
2033 // The variable-length pattern was there,
2034 // so it has an array type with the remaining elements left as its size...
2035 return (Some(self.tcx.mk_array(element_ty, pat_len)), arr_ty);
2037 // ...however, in this case, there were no remaining elements.
2038 // That is, the slice pattern requires more than the array type offers.
2039 self.error_scrutinee_with_rest_inconsistent_length(span, min_len, len);
2041 } else if slice.is_none() {
2042 // We have a pattern with a fixed length,
2043 // which we can use to infer the length of the array.
2044 let updated_arr_ty = self.tcx.mk_array(element_ty, min_len);
2045 self.demand_eqtype(span, updated_arr_ty, arr_ty);
2046 return (None, updated_arr_ty);
2048 // We have a variable-length pattern and don't know the array length.
2049 // This happens if we have e.g.,
2050 // `let [a, b, ..] = arr` where `arr: [T; N]` where `const N: usize`.
2051 self.error_scrutinee_unfixed_length(span);
2054 // If we get here, we must have emitted an error.
2055 (Some(self.tcx.ty_error()), arr_ty)
2058 fn error_scrutinee_inconsistent_length(&self, span: Span, min_len: u64, size: u64) {
2063 "pattern requires {} element{} but array has {}",
2065 pluralize!(min_len),
2068 .span_label(span, format!("expected {} element{}", size, pluralize!(size)))
2072 fn error_scrutinee_with_rest_inconsistent_length(&self, span: Span, min_len: u64, size: u64) {
2077 "pattern requires at least {} element{} but array has {}",
2079 pluralize!(min_len),
2084 format!("pattern cannot match array of {} element{}", size, pluralize!(size),),
2089 fn error_scrutinee_unfixed_length(&self, span: Span) {
2094 "cannot pattern-match on an array without a fixed length",
2099 fn error_expected_array_or_slice(&self, span: Span, expected_ty: Ty<'tcx>, ti: TopInfo<'tcx>) {
2100 let mut err = struct_span_err!(
2104 "expected an array or slice, found `{expected_ty}`"
2106 if let ty::Ref(_, ty, _) = expected_ty.kind()
2107 && let ty::Array(..) | ty::Slice(..) = ty.kind()
2109 err.help("the semantics of slice patterns changed recently; see issue #62254");
2110 } else if Autoderef::new(&self.infcx, self.param_env, self.body_id, span, expected_ty, span)
2111 .any(|(ty, _)| matches!(ty.kind(), ty::Slice(..) | ty::Array(..)))
2112 && let (Some(span), true) = (ti.span, ti.origin_expr)
2113 && let Ok(snippet) = self.tcx.sess.source_map().span_to_snippet(span)
2115 let ty = self.resolve_vars_if_possible(ti.expected);
2116 let is_slice_or_array_or_vector = self.is_slice_or_array_or_vector(&mut err, snippet.clone(), ty);
2117 match is_slice_or_array_or_vector.1.kind() {
2119 if self.tcx.is_diagnostic_item(sym::Option, adt_def.did())
2120 || self.tcx.is_diagnostic_item(sym::Result, adt_def.did()) =>
2122 // Slicing won't work here, but `.as_deref()` might (issue #91328).
2123 err.span_suggestion(
2125 "consider using `as_deref` here",
2126 format!("{snippet}.as_deref()"),
2127 Applicability::MaybeIncorrect,
2132 if is_slice_or_array_or_vector.0 {
2133 err.span_suggestion(
2135 "consider slicing here",
2136 format!("{snippet}[..]"),
2137 Applicability::MachineApplicable,
2141 err.span_label(span, format!("pattern cannot match with input type `{expected_ty}`"));
2145 fn is_slice_or_array_or_vector(
2147 err: &mut Diagnostic,
2150 ) -> (bool, Ty<'tcx>) {
2152 ty::Adt(adt_def, _) if self.tcx.is_diagnostic_item(sym::Vec, adt_def.did()) => {
2155 ty::Ref(_, ty, _) => self.is_slice_or_array_or_vector(err, snippet, *ty),
2156 ty::Slice(..) | ty::Array(..) => (true, ty),