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(_) => self.check_pat_path(pat, path_res.unwrap(), expected, ti),
187 PatKind::Struct(ref qpath, fields, has_rest_pat) => {
188 self.check_pat_struct(pat, qpath, fields, has_rest_pat, expected, def_bm, ti)
190 PatKind::Or(pats) => {
191 let parent_pat = Some(pat);
193 self.check_pat(pat, expected, def_bm, TopInfo { parent_pat, ..ti });
197 PatKind::Tuple(elements, ddpos) => {
198 self.check_pat_tuple(pat.span, elements, ddpos, expected, def_bm, ti)
200 PatKind::Box(inner) => self.check_pat_box(pat.span, inner, expected, def_bm, ti),
201 PatKind::Ref(inner, mutbl) => {
202 self.check_pat_ref(pat, inner, mutbl, expected, def_bm, ti)
204 PatKind::Slice(before, slice, after) => {
205 self.check_pat_slice(pat.span, before, slice, after, expected, def_bm, ti)
209 self.write_ty(pat.hir_id, ty);
211 // (note_1): In most of the cases where (note_1) is referenced
212 // (literals and constants being the exception), we relate types
213 // using strict equality, even though subtyping would be sufficient.
214 // There are a few reasons for this, some of which are fairly subtle
215 // and which cost me (nmatsakis) an hour or two debugging to remember,
216 // so I thought I'd write them down this time.
218 // 1. There is no loss of expressiveness here, though it does
219 // cause some inconvenience. What we are saying is that the type
220 // of `x` becomes *exactly* what is expected. This can cause unnecessary
221 // errors in some cases, such as this one:
224 // fn foo<'x>(x: &'x i32) {
231 // The reason we might get an error is that `z` might be
232 // assigned a type like `&'x i32`, and then we would have
233 // a problem when we try to assign `&a` to `z`, because
234 // the lifetime of `&a` (i.e., the enclosing block) is
235 // shorter than `'x`.
237 // HOWEVER, this code works fine. The reason is that the
238 // expected type here is whatever type the user wrote, not
239 // the initializer's type. In this case the user wrote
240 // nothing, so we are going to create a type variable `Z`.
241 // Then we will assign the type of the initializer (`&'x i32`)
242 // as a subtype of `Z`: `&'x i32 <: Z`. And hence we
243 // will instantiate `Z` as a type `&'0 i32` where `'0` is
244 // a fresh region variable, with the constraint that `'x : '0`.
245 // So basically we're all set.
247 // Note that there are two tests to check that this remains true
248 // (`regions-reassign-{match,let}-bound-pointer.rs`).
250 // 2. Things go horribly wrong if we use subtype. The reason for
251 // THIS is a fairly subtle case involving bound regions. See the
252 // `givens` field in `region_constraints`, as well as the test
253 // `regions-relate-bound-regions-on-closures-to-inference-variables.rs`,
254 // for details. Short version is that we must sometimes detect
255 // relationships between specific region variables and regions
256 // bound in a closure signature, and that detection gets thrown
257 // off when we substitute fresh region variables here to enable
261 /// Compute the new expected type and default binding mode from the old ones
262 /// as well as the pattern form we are currently checking.
263 fn calc_default_binding_mode(
265 pat: &'tcx Pat<'tcx>,
268 adjust_mode: AdjustMode,
269 ) -> (Ty<'tcx>, BindingMode) {
271 AdjustMode::Pass => (expected, def_bm),
272 AdjustMode::Reset => (expected, INITIAL_BM),
273 AdjustMode::Peel => self.peel_off_references(pat, expected, def_bm),
277 /// How should the binding mode and expected type be adjusted?
279 /// When the pattern is a path pattern, `opt_path_res` must be `Some(res)`.
280 fn calc_adjust_mode(&self, pat: &'tcx Pat<'tcx>, opt_path_res: Option<Res>) -> AdjustMode {
281 // When we perform destructuring assignment, we disable default match bindings, which are
282 // unintuitive in this context.
283 if !pat.default_binding_modes {
284 return AdjustMode::Reset;
287 // Type checking these product-like types successfully always require
288 // that the expected type be of those types and not reference types.
290 | PatKind::TupleStruct(..)
294 | PatKind::Slice(..) => AdjustMode::Peel,
295 // String and byte-string literals result in types `&str` and `&[u8]` respectively.
296 // All other literals result in non-reference types.
297 // As a result, we allow `if let 0 = &&0 {}` but not `if let "foo" = &&"foo {}`.
299 // Call `resolve_vars_if_possible` here for inline const blocks.
300 PatKind::Lit(lt) => match self.resolve_vars_if_possible(self.check_expr(lt)).kind() {
301 ty::Ref(..) => AdjustMode::Pass,
302 _ => AdjustMode::Peel,
304 PatKind::Path(_) => match opt_path_res.unwrap() {
305 // These constants can be of a reference type, e.g. `const X: &u8 = &0;`.
306 // Peeling the reference types too early will cause type checking failures.
307 // Although it would be possible to *also* peel the types of the constants too.
308 Res::Def(DefKind::Const | DefKind::AssocConst, _) => AdjustMode::Pass,
309 // In the `ValueNS`, we have `SelfCtor(..) | Ctor(_, Const), _)` remaining which
310 // could successfully compile. The former being `Self` requires a unit struct.
311 // In either case, and unlike constants, the pattern itself cannot be
312 // a reference type wherefore peeling doesn't give up any expressiveness.
313 _ => AdjustMode::Peel,
315 // When encountering a `& mut? pat` pattern, reset to "by value".
316 // This is so that `x` and `y` here are by value, as they appear to be:
319 // match &(&22, &44) {
325 PatKind::Ref(..) => AdjustMode::Reset,
326 // A `_` pattern works with any expected type, so there's no need to do anything.
328 // Bindings also work with whatever the expected type is,
329 // and moreover if we peel references off, that will give us the wrong binding type.
330 // Also, we can have a subpattern `binding @ pat`.
331 // Each side of the `@` should be treated independently (like with OR-patterns).
332 | PatKind::Binding(..)
333 // An OR-pattern just propagates to each individual alternative.
334 // This is maximally flexible, allowing e.g., `Some(mut x) | &Some(mut x)`.
335 // In that example, `Some(mut x)` results in `Peel` whereas `&Some(mut x)` in `Reset`.
336 | PatKind::Or(_) => AdjustMode::Pass,
340 /// Peel off as many immediately nested `& mut?` from the expected type as possible
341 /// and return the new expected type and binding default binding mode.
342 /// The adjustments vector, if non-empty is stored in a table.
343 fn peel_off_references(
345 pat: &'tcx Pat<'tcx>,
347 mut def_bm: BindingMode,
348 ) -> (Ty<'tcx>, BindingMode) {
349 let mut expected = self.resolve_vars_with_obligations(expected);
351 // Peel off as many `&` or `&mut` from the scrutinee type as possible. For example,
352 // for `match &&&mut Some(5)` the loop runs three times, aborting when it reaches
353 // the `Some(5)` which is not of type Ref.
355 // For each ampersand peeled off, update the binding mode and push the original
356 // type into the adjustments vector.
358 // See the examples in `ui/match-defbm*.rs`.
359 let mut pat_adjustments = vec![];
360 while let ty::Ref(_, inner_ty, inner_mutability) = *expected.kind() {
361 debug!("inspecting {:?}", expected);
363 debug!("current discriminant is Ref, inserting implicit deref");
364 // Preserve the reference type. We'll need it later during THIR lowering.
365 pat_adjustments.push(expected);
368 def_bm = ty::BindByReference(match def_bm {
369 // If default binding mode is by value, make it `ref` or `ref mut`
370 // (depending on whether we observe `&` or `&mut`).
372 // When `ref mut`, stay a `ref mut` (on `&mut`) or downgrade to `ref` (on `&`).
373 ty::BindByReference(hir::Mutability::Mut) => inner_mutability,
374 // Once a `ref`, always a `ref`.
375 // This is because a `& &mut` cannot mutate the underlying value.
376 ty::BindByReference(m @ hir::Mutability::Not) => m,
380 if !pat_adjustments.is_empty() {
381 debug!("default binding mode is now {:?}", def_bm);
385 .pat_adjustments_mut()
386 .insert(pat.hir_id, pat_adjustments);
395 lt: &hir::Expr<'tcx>,
399 // We've already computed the type above (when checking for a non-ref pat),
400 // so avoid computing it again.
401 let ty = self.node_ty(lt.hir_id);
403 // Byte string patterns behave the same way as array patterns
404 // They can denote both statically and dynamically-sized byte arrays.
406 if let hir::ExprKind::Lit(Spanned { node: ast::LitKind::ByteStr(_), .. }) = lt.kind {
407 let expected = self.structurally_resolved_type(span, expected);
408 if let ty::Ref(_, inner_ty, _) = expected.kind()
409 && matches!(inner_ty.kind(), ty::Slice(_))
412 trace!(?lt.hir_id.local_id, "polymorphic byte string lit");
415 .treat_byte_string_as_slice
416 .insert(lt.hir_id.local_id);
417 pat_ty = tcx.mk_imm_ref(tcx.lifetimes.re_static, tcx.mk_slice(tcx.types.u8));
421 // Somewhat surprising: in this case, the subtyping relation goes the
422 // opposite way as the other cases. Actually what we really want is not
423 // a subtyping relation at all but rather that there exists a LUB
424 // (so that they can be compared). However, in practice, constants are
425 // always scalars or strings. For scalars subtyping is irrelevant,
426 // and for strings `ty` is type is `&'static str`, so if we say that
428 // &'static str <: expected
430 // then that's equivalent to there existing a LUB.
431 let cause = self.pattern_cause(ti, span);
432 if let Some(mut err) = self.demand_suptype_with_origin(&cause, expected, pat_ty) {
436 // In the case of `if`- and `while`-expressions we've already checked
437 // that `scrutinee: bool`. We know that the pattern is `true`,
438 // so an error here would be a duplicate and from the wrong POV.
439 s.is_desugaring(DesugaringKind::CondTemporary)
451 lhs: Option<&'tcx hir::Expr<'tcx>>,
452 rhs: Option<&'tcx hir::Expr<'tcx>>,
456 let calc_side = |opt_expr: Option<&'tcx hir::Expr<'tcx>>| match opt_expr {
459 let ty = self.check_expr(expr);
460 // Check that the end-point is possibly of numeric or char type.
461 // The early check here is not for correctness, but rather better
462 // diagnostics (e.g. when `&str` is being matched, `expected` will
463 // be peeled to `str` while ty here is still `&str`, if we don't
464 // err early here, a rather confusing unification error will be
467 !(ty.is_numeric() || ty.is_char() || ty.is_ty_var() || ty.references_error());
468 Some((fail, ty, expr.span))
471 let mut lhs = calc_side(lhs);
472 let mut rhs = calc_side(rhs);
474 if let (Some((true, ..)), _) | (_, Some((true, ..))) = (lhs, rhs) {
475 // There exists a side that didn't meet our criteria that the end-point
476 // be of a numeric or char type, as checked in `calc_side` above.
477 self.emit_err_pat_range(span, lhs, rhs);
478 return self.tcx.ty_error();
481 // Unify each side with `expected`.
482 // Subtyping doesn't matter here, as the value is some kind of scalar.
483 let demand_eqtype = |x: &mut _, y| {
484 if let Some((ref mut fail, x_ty, x_span)) = *x
485 && let Some(mut err) = self.demand_eqtype_pat_diag(x_span, expected, x_ty, ti)
487 if let Some((_, y_ty, y_span)) = y {
488 self.endpoint_has_type(&mut err, y_span, y_ty);
494 demand_eqtype(&mut lhs, rhs);
495 demand_eqtype(&mut rhs, lhs);
497 if let (Some((true, ..)), _) | (_, Some((true, ..))) = (lhs, rhs) {
498 return self.tcx.ty_error();
501 // Find the unified type and check if it's of numeric or char type again.
502 // This check is needed if both sides are inference variables.
503 // We require types to be resolved here so that we emit inference failure
504 // rather than "_ is not a char or numeric".
505 let ty = self.structurally_resolved_type(span, expected);
506 if !(ty.is_numeric() || ty.is_char() || ty.references_error()) {
507 if let Some((ref mut fail, _, _)) = lhs {
510 if let Some((ref mut fail, _, _)) = rhs {
513 self.emit_err_pat_range(span, lhs, rhs);
514 return self.tcx.ty_error();
519 fn endpoint_has_type(&self, err: &mut Diagnostic, span: Span, ty: Ty<'_>) {
520 if !ty.references_error() {
521 err.span_label(span, &format!("this is of type `{}`", ty));
525 fn emit_err_pat_range(
528 lhs: Option<(bool, Ty<'tcx>, Span)>,
529 rhs: Option<(bool, Ty<'tcx>, Span)>,
531 let span = match (lhs, rhs) {
532 (Some((true, ..)), Some((true, ..))) => span,
533 (Some((true, _, sp)), _) => sp,
534 (_, Some((true, _, sp))) => sp,
535 _ => span_bug!(span, "emit_err_pat_range: no side failed or exists but still error?"),
537 let mut err = struct_span_err!(
541 "only `char` and numeric types are allowed in range patterns"
544 let ty = self.resolve_vars_if_possible(ty);
545 format!("this is of type `{}` but it should be `char` or numeric", ty)
547 let mut one_side_err = |first_span, first_ty, second: Option<(bool, Ty<'tcx>, Span)>| {
548 err.span_label(first_span, &msg(first_ty));
549 if let Some((_, ty, sp)) = second {
550 let ty = self.resolve_vars_if_possible(ty);
551 self.endpoint_has_type(&mut err, sp, ty);
555 (Some((true, lhs_ty, lhs_sp)), Some((true, rhs_ty, rhs_sp))) => {
556 err.span_label(lhs_sp, &msg(lhs_ty));
557 err.span_label(rhs_sp, &msg(rhs_ty));
559 (Some((true, lhs_ty, lhs_sp)), rhs) => one_side_err(lhs_sp, lhs_ty, rhs),
560 (lhs, Some((true, rhs_ty, rhs_sp))) => one_side_err(rhs_sp, rhs_ty, lhs),
561 _ => span_bug!(span, "Impossible, verified above."),
563 if self.tcx.sess.teach(&err.get_code().unwrap()) {
565 "In a match expression, only numbers and characters can be matched \
566 against a range. This is because the compiler checks that the range \
567 is non-empty at compile-time, and is unable to evaluate arbitrary \
568 comparison functions. If you want to capture values of an orderable \
569 type between two end-points, you can use a guard.",
577 pat: &'tcx Pat<'tcx>,
578 ba: hir::BindingAnnotation,
580 sub: Option<&'tcx Pat<'tcx>>,
585 // Determine the binding mode...
587 hir::BindingAnnotation::Unannotated => def_bm,
588 _ => BindingMode::convert(ba),
590 // ...and store it in a side table:
591 self.inh.typeck_results.borrow_mut().pat_binding_modes_mut().insert(pat.hir_id, bm);
593 debug!("check_pat_ident: pat.hir_id={:?} bm={:?}", pat.hir_id, bm);
595 let local_ty = self.local_ty(pat.span, pat.hir_id).decl_ty;
596 let eq_ty = match bm {
597 ty::BindByReference(mutbl) => {
598 // If the binding is like `ref x | ref mut x`,
599 // then `x` is assigned a value of type `&M T` where M is the
600 // mutability and T is the expected type.
602 // `x` is assigned a value of type `&M T`, hence `&M T <: typeof(x)`
603 // is required. However, we use equality, which is stronger.
604 // See (note_1) for an explanation.
605 self.new_ref_ty(pat.span, mutbl, expected)
607 // Otherwise, the type of x is the expected type `T`.
608 ty::BindByValue(_) => {
609 // As above, `T <: typeof(x)` is required, but we use equality, see (note_1).
613 self.demand_eqtype_pat(pat.span, eq_ty, local_ty, ti);
615 // If there are multiple arms, make sure they all agree on
616 // what the type of the binding `x` ought to be.
617 if var_id != pat.hir_id {
618 self.check_binding_alt_eq_ty(pat.span, var_id, local_ty, ti);
621 if let Some(p) = sub {
622 self.check_pat(p, expected, def_bm, TopInfo { parent_pat: Some(pat), ..ti });
628 fn check_binding_alt_eq_ty(&self, span: Span, var_id: HirId, ty: Ty<'tcx>, ti: TopInfo<'tcx>) {
629 let var_ty = self.local_ty(span, var_id).decl_ty;
630 if let Some(mut err) = self.demand_eqtype_pat_diag(span, var_ty, ty, ti) {
631 let hir = self.tcx.hir();
632 let var_ty = self.resolve_vars_with_obligations(var_ty);
633 let msg = format!("first introduced with type `{var_ty}` here");
634 err.span_label(hir.span(var_id), msg);
635 let in_match = hir.parent_iter(var_id).any(|(_, n)| {
638 hir::Node::Expr(hir::Expr {
639 kind: hir::ExprKind::Match(.., hir::MatchSource::Normal),
644 let pre = if in_match { "in the same arm, " } else { "" };
645 err.note(&format!("{}a binding must have the same type in all alternatives", pre));
646 // FIXME: check if `var_ty` and `ty` can be made the same type by adding or removing
647 // `ref` or `&` to the pattern.
652 // Precondition: pat is a Ref(_) pattern
653 fn borrow_pat_suggestion(&self, err: &mut Diagnostic, pat: &Pat<'_>) {
655 if let PatKind::Ref(inner, mutbl) = pat.kind
656 && let PatKind::Binding(_, _, binding, ..) = inner.kind {
657 let binding_parent_id = tcx.hir().get_parent_node(pat.hir_id);
658 let binding_parent = tcx.hir().get(binding_parent_id);
659 debug!(?inner, ?pat, ?binding_parent);
661 let mutability = match mutbl {
662 ast::Mutability::Mut => "mut",
663 ast::Mutability::Not => "",
666 let mut_var_suggestion = 'block: {
667 if !matches!(mutbl, ast::Mutability::Mut) {
671 let ident_kind = match binding_parent {
672 hir::Node::Param(_) => "parameter",
673 hir::Node::Local(_) => "variable",
674 hir::Node::Arm(_) => "binding",
676 // Provide diagnostics only if the parent pattern is struct-like,
677 // i.e. where `mut binding` makes sense
678 hir::Node::Pat(Pat { kind, .. }) => match kind {
680 | PatKind::TupleStruct(..)
683 | PatKind::Slice(..) => "binding",
686 | PatKind::Binding(..)
691 | PatKind::Range(..) => break 'block None,
694 // Don't provide suggestions in other cases
695 _ => break 'block None,
700 format!("to declare a mutable {ident_kind} use"),
701 format!("mut {binding}"),
706 match binding_parent {
707 // Check that there is explicit type (ie this is not a closure param with inferred type)
708 // so we don't suggest moving something to the type that does not exist
709 hir::Node::Param(hir::Param { ty_span, .. }) if binding.span != *ty_span => {
710 err.multipart_suggestion_verbose(
711 format!("to take parameter `{binding}` by reference, move `&{mutability}` to the type"),
713 (pat.span.until(inner.span), "".to_owned()),
714 (ty_span.shrink_to_lo(), format!("&{}", mutbl.prefix_str())),
716 Applicability::MachineApplicable
719 if let Some((sp, msg, sugg)) = mut_var_suggestion {
720 err.span_note(sp, format!("{msg}: `{sugg}`"));
723 hir::Node::Param(_) | hir::Node::Arm(_) | hir::Node::Pat(_) => {
724 // rely on match ergonomics or it might be nested `&&pat`
725 err.span_suggestion_verbose(
726 pat.span.until(inner.span),
727 format!("consider removing `&{mutability}` from the pattern"),
729 Applicability::MaybeIncorrect,
732 if let Some((sp, msg, sugg)) = mut_var_suggestion {
733 err.span_note(sp, format!("{msg}: `{sugg}`"));
736 _ if let Some((sp, msg, sugg)) = mut_var_suggestion => {
737 err.span_suggestion(sp, msg, sugg, Applicability::MachineApplicable);
739 _ => {} // don't provide suggestions in other cases #55175
744 pub fn check_dereferenceable(&self, span: Span, expected: Ty<'tcx>, inner: &Pat<'_>) -> bool {
745 if let PatKind::Binding(..) = inner.kind
746 && let Some(mt) = self.shallow_resolve(expected).builtin_deref(true)
747 && let ty::Dynamic(..) = mt.ty.kind()
749 // This is "x = SomeTrait" being reduced from
750 // "let &x = &SomeTrait" or "let box x = Box<SomeTrait>", an error.
751 let type_str = self.ty_to_string(expected);
752 let mut err = struct_span_err!(
756 "type `{}` cannot be dereferenced",
759 err.span_label(span, format!("type `{type_str}` cannot be dereferenced"));
760 if self.tcx.sess.teach(&err.get_code().unwrap()) {
761 err.note(CANNOT_IMPLICITLY_DEREF_POINTER_TRAIT_OBJ);
771 pat: &'tcx Pat<'tcx>,
772 qpath: &hir::QPath<'_>,
773 fields: &'tcx [hir::PatField<'tcx>],
779 // Resolve the path and check the definition for errors.
780 let Some((variant, pat_ty)) = self.check_struct_path(qpath, pat.hir_id) else {
781 let err = self.tcx.ty_error();
782 for field in fields {
783 let ti = TopInfo { parent_pat: Some(pat), ..ti };
784 self.check_pat(field.pat, err, def_bm, ti);
789 // Type-check the path.
790 self.demand_eqtype_pat(pat.span, expected, pat_ty, ti);
792 // Type-check subpatterns.
793 if self.check_struct_pat_fields(pat_ty, &pat, variant, fields, has_rest_pat, def_bm, ti) {
800 fn check_pat_path<'b>(
803 path_resolution: (Res, Option<Ty<'tcx>>, &'b [hir::PathSegment<'b>]),
809 // We have already resolved the path.
810 let (res, opt_ty, segments) = path_resolution;
813 self.set_tainted_by_errors();
814 return tcx.ty_error();
816 Res::Def(DefKind::AssocFn | DefKind::Ctor(_, CtorKind::Fictive | CtorKind::Fn), _) => {
817 report_unexpected_variant_res(tcx, res, pat.span);
818 return tcx.ty_error();
822 DefKind::Ctor(_, CtorKind::Const)
824 | DefKind::AssocConst
825 | DefKind::ConstParam,
828 _ => bug!("unexpected pattern resolution: {:?}", res),
831 // Type-check the path.
832 let (pat_ty, pat_res) =
833 self.instantiate_value_path(segments, opt_ty, res, pat.span, pat.hir_id);
835 self.demand_suptype_with_origin(&self.pattern_cause(ti, pat.span), expected, pat_ty)
837 self.emit_bad_pat_path(err, pat.span, res, pat_res, pat_ty, segments, ti.parent_pat);
842 fn maybe_suggest_range_literal(
845 opt_def_id: Option<hir::def_id::DefId>,
849 Some(def_id) => match self.tcx.hir().get_if_local(def_id) {
850 Some(hir::Node::Item(hir::Item {
851 kind: hir::ItemKind::Const(_, body_id), ..
852 })) => match self.tcx.hir().get(body_id.hir_id) {
853 hir::Node::Expr(expr) => {
854 if hir::is_range_literal(expr) {
855 let span = self.tcx.hir().span(body_id.hir_id);
856 if let Ok(snip) = self.tcx.sess.source_map().span_to_snippet(span) {
857 e.span_suggestion_verbose(
859 "you may want to move the range into the match block",
861 Applicability::MachineApplicable,
876 fn emit_bad_pat_path<'b>(
878 mut e: DiagnosticBuilder<'_, ErrorGuaranteed>,
883 segments: &'b [hir::PathSegment<'b>],
884 parent_pat: Option<&Pat<'_>>,
886 if let Some(span) = self.tcx.hir().res_span(pat_res) {
887 e.span_label(span, &format!("{} defined here", res.descr()));
888 if let [hir::PathSegment { ident, .. }] = &*segments {
892 "`{}` is interpreted as {} {}, not a new binding",
899 Some(Pat { kind: hir::PatKind::Struct(..), .. }) => {
900 e.span_suggestion_verbose(
901 ident.span.shrink_to_hi(),
902 "bind the struct field to a different name instead",
903 format!(": other_{}", ident.as_str().to_lowercase()),
904 Applicability::HasPlaceholders,
908 let (type_def_id, item_def_id) = match pat_ty.kind() {
909 Adt(def, _) => match res {
910 Res::Def(DefKind::Const, def_id) => (Some(def.did()), Some(def_id)),
917 self.tcx.lang_items().range_struct(),
918 self.tcx.lang_items().range_from_struct(),
919 self.tcx.lang_items().range_to_struct(),
920 self.tcx.lang_items().range_full_struct(),
921 self.tcx.lang_items().range_inclusive_struct(),
922 self.tcx.lang_items().range_to_inclusive_struct(),
924 if type_def_id != None && ranges.contains(&type_def_id) {
925 if !self.maybe_suggest_range_literal(&mut e, item_def_id, *ident) {
926 let msg = "constants only support matching by type, \
927 if you meant to match against a range of values, \
928 consider using a range pattern like `min ..= max` in the match block";
932 let msg = "introduce a new binding instead";
933 let sugg = format!("other_{}", ident.as_str().to_lowercase());
938 Applicability::HasPlaceholders,
948 fn check_pat_tuple_struct(
950 pat: &'tcx Pat<'tcx>,
951 qpath: &'tcx hir::QPath<'tcx>,
952 subpats: &'tcx [Pat<'tcx>],
953 ddpos: Option<usize>,
960 let parent_pat = Some(pat);
962 self.check_pat(pat, tcx.ty_error(), def_bm, TopInfo { parent_pat, ..ti });
965 let report_unexpected_res = |res: Res| {
966 let sm = tcx.sess.source_map();
968 .span_to_snippet(sm.span_until_char(pat.span, '('))
969 .map_or_else(|_| String::new(), |s| format!(" `{}`", s.trim_end()));
971 "expected tuple struct or tuple variant, found {}{}",
976 let mut err = struct_span_err!(tcx.sess, pat.span, E0164, "{msg}");
978 Res::Def(DefKind::Fn | DefKind::AssocFn, _) => {
979 err.span_label(pat.span, "`fn` calls are not allowed in patterns");
981 "for more information, visit \
982 https://doc.rust-lang.org/book/ch18-00-patterns.html",
986 err.span_label(pat.span, "not a tuple variant or struct");
993 // Resolve the path and check the definition for errors.
994 let (res, opt_ty, segments) =
995 self.resolve_ty_and_res_fully_qualified_call(qpath, pat.hir_id, pat.span);
997 self.set_tainted_by_errors();
999 return self.tcx.ty_error();
1002 // Type-check the path.
1004 self.instantiate_value_path(segments, opt_ty, res, pat.span, pat.hir_id);
1005 if !pat_ty.is_fn() {
1006 report_unexpected_res(res);
1007 return tcx.ty_error();
1010 let variant = match res {
1012 self.set_tainted_by_errors();
1014 return tcx.ty_error();
1016 Res::Def(DefKind::AssocConst | DefKind::AssocFn, _) => {
1017 report_unexpected_res(res);
1018 return tcx.ty_error();
1020 Res::Def(DefKind::Ctor(_, CtorKind::Fn), _) => tcx.expect_variant_res(res),
1021 _ => bug!("unexpected pattern resolution: {:?}", res),
1024 // Replace constructor type with constructed type for tuple struct patterns.
1025 let pat_ty = pat_ty.fn_sig(tcx).output();
1026 let pat_ty = pat_ty.no_bound_vars().expect("expected fn type");
1028 // Type-check the tuple struct pattern against the expected type.
1029 let diag = self.demand_eqtype_pat_diag(pat.span, expected, pat_ty, ti);
1030 let had_err = if let Some(mut err) = diag {
1037 // Type-check subpatterns.
1038 if subpats.len() == variant.fields.len()
1039 || subpats.len() < variant.fields.len() && ddpos.is_some()
1041 let ty::Adt(_, substs) = pat_ty.kind() else {
1042 bug!("unexpected pattern type {:?}", pat_ty);
1044 for (i, subpat) in subpats.iter().enumerate_and_adjust(variant.fields.len(), ddpos) {
1045 let field_ty = self.field_ty(subpat.span, &variant.fields[i], substs);
1046 self.check_pat(subpat, field_ty, def_bm, TopInfo { parent_pat: Some(pat), ..ti });
1048 self.tcx.check_stability(
1049 variant.fields[i].did,
1056 // Pattern has wrong number of fields.
1057 self.e0023(pat.span, res, qpath, subpats, &variant.fields, expected, had_err);
1059 return tcx.ty_error();
1068 qpath: &hir::QPath<'_>,
1069 subpats: &'tcx [Pat<'tcx>],
1070 fields: &'tcx [ty::FieldDef],
1074 let subpats_ending = pluralize!(subpats.len());
1075 let fields_ending = pluralize!(fields.len());
1077 let subpat_spans = if subpats.is_empty() {
1080 subpats.iter().map(|p| p.span).collect()
1082 let last_subpat_span = *subpat_spans.last().unwrap();
1083 let res_span = self.tcx.def_span(res.def_id());
1084 let def_ident_span = self.tcx.def_ident_span(res.def_id()).unwrap_or(res_span);
1085 let field_def_spans = if fields.is_empty() {
1088 fields.iter().map(|f| f.ident(self.tcx).span).collect()
1090 let last_field_def_span = *field_def_spans.last().unwrap();
1092 let mut err = struct_span_err!(
1094 MultiSpan::from_spans(subpat_spans),
1096 "this pattern has {} field{}, but the corresponding {} has {} field{}",
1105 &format!("expected {} field{}, found {}", fields.len(), fields_ending, subpats.len()),
1107 if self.tcx.sess.source_map().is_multiline(qpath.span().between(last_subpat_span)) {
1108 err.span_label(qpath.span(), "");
1110 if self.tcx.sess.source_map().is_multiline(def_ident_span.between(last_field_def_span)) {
1111 err.span_label(def_ident_span, format!("{} defined here", res.descr()));
1113 for span in &field_def_spans[..field_def_spans.len() - 1] {
1114 err.span_label(*span, "");
1117 last_field_def_span,
1118 &format!("{} has {} field{}", res.descr(), fields.len(), fields_ending),
1121 // Identify the case `Some(x, y)` where the expected type is e.g. `Option<(T, U)>`.
1122 // More generally, the expected type wants a tuple variant with one field of an
1123 // N-arity-tuple, e.g., `V_i((p_0, .., p_N))`. Meanwhile, the user supplied a pattern
1124 // with the subpatterns directly in the tuple variant pattern, e.g., `V_i(p_0, .., p_N)`.
1125 let missing_parentheses = match (&expected.kind(), fields, had_err) {
1126 // #67037: only do this if we could successfully type-check the expected type against
1127 // the tuple struct pattern. Otherwise the substs could get out of range on e.g.,
1128 // `let P() = U;` where `P != U` with `struct P<T>(T);`.
1129 (ty::Adt(_, substs), [field], false) => {
1130 let field_ty = self.field_ty(pat_span, field, substs);
1131 match field_ty.kind() {
1132 ty::Tuple(fields) => fields.len() == subpats.len(),
1138 if missing_parentheses {
1139 let (left, right) = match subpats {
1140 // This is the zero case; we aim to get the "hi" part of the `QPath`'s
1141 // span as the "lo" and then the "hi" part of the pattern's span as the "hi".
1144 // help: missing parentheses
1146 // L | let A(()) = A(());
1148 [] => (qpath.span().shrink_to_hi(), pat_span),
1149 // Easy case. Just take the "lo" of the first sub-pattern and the "hi" of the
1150 // last sub-pattern. In the case of `A(x)` the first and last may coincide.
1153 // help: missing parentheses
1155 // L | let A((x, y)) = A((1, 2));
1157 [first, ..] => (first.span.shrink_to_lo(), subpats.last().unwrap().span),
1159 err.multipart_suggestion(
1160 "missing parentheses",
1161 vec![(left, "(".to_string()), (right.shrink_to_hi(), ")".to_string())],
1162 Applicability::MachineApplicable,
1164 } else if fields.len() > subpats.len() && pat_span != DUMMY_SP {
1165 let after_fields_span = pat_span.with_hi(pat_span.hi() - BytePos(1)).shrink_to_hi();
1166 let all_fields_span = match subpats {
1167 [] => after_fields_span,
1168 [field] => field.span,
1169 [first, .., last] => first.span.to(last.span),
1172 // Check if all the fields in the pattern are wildcards.
1173 let all_wildcards = subpats.iter().all(|pat| matches!(pat.kind, PatKind::Wild));
1174 let first_tail_wildcard =
1175 subpats.iter().enumerate().fold(None, |acc, (pos, pat)| match (acc, &pat.kind) {
1176 (None, PatKind::Wild) => Some(pos),
1177 (Some(_), PatKind::Wild) => acc,
1180 let tail_span = match first_tail_wildcard {
1181 None => after_fields_span,
1182 Some(0) => subpats[0].span.to(after_fields_span),
1183 Some(pos) => subpats[pos - 1].span.shrink_to_hi().to(after_fields_span),
1186 // FIXME: heuristic-based suggestion to check current types for where to add `_`.
1187 let mut wildcard_sugg = vec!["_"; fields.len() - subpats.len()].join(", ");
1188 if !subpats.is_empty() {
1189 wildcard_sugg = String::from(", ") + &wildcard_sugg;
1192 err.span_suggestion_verbose(
1194 "use `_` to explicitly ignore each field",
1196 Applicability::MaybeIncorrect,
1199 // Only suggest `..` if more than one field is missing
1200 // or the pattern consists of all wildcards.
1201 if fields.len() - subpats.len() > 1 || all_wildcards {
1202 if subpats.is_empty() || all_wildcards {
1203 err.span_suggestion_verbose(
1205 "use `..` to ignore all fields",
1207 Applicability::MaybeIncorrect,
1210 err.span_suggestion_verbose(
1212 "use `..` to ignore the rest of the fields",
1214 Applicability::MaybeIncorrect,
1226 elements: &'tcx [Pat<'tcx>],
1227 ddpos: Option<usize>,
1229 def_bm: BindingMode,
1233 let mut expected_len = elements.len();
1234 if ddpos.is_some() {
1235 // Require known type only when `..` is present.
1236 if let ty::Tuple(tys) = self.structurally_resolved_type(span, expected).kind() {
1237 expected_len = tys.len();
1240 let max_len = cmp::max(expected_len, elements.len());
1242 let element_tys_iter = (0..max_len).map(|_| {
1244 // FIXME: `MiscVariable` for now -- obtaining the span and name information
1245 // from all tuple elements isn't trivial.
1246 TypeVariableOrigin { kind: TypeVariableOriginKind::TypeInference, span },
1249 let element_tys = tcx.mk_type_list(element_tys_iter);
1250 let pat_ty = tcx.mk_ty(ty::Tuple(element_tys));
1251 if let Some(mut err) = self.demand_eqtype_pat_diag(span, expected, pat_ty, ti) {
1253 // Walk subpatterns with an expected type of `err` in this case to silence
1254 // further errors being emitted when using the bindings. #50333
1255 let element_tys_iter = (0..max_len).map(|_| tcx.ty_error());
1256 for (_, elem) in elements.iter().enumerate_and_adjust(max_len, ddpos) {
1257 self.check_pat(elem, tcx.ty_error(), def_bm, ti);
1259 tcx.mk_tup(element_tys_iter)
1261 for (i, elem) in elements.iter().enumerate_and_adjust(max_len, ddpos) {
1262 self.check_pat(elem, element_tys[i], def_bm, ti);
1268 fn check_struct_pat_fields(
1271 pat: &'tcx Pat<'tcx>,
1272 variant: &'tcx ty::VariantDef,
1273 fields: &'tcx [hir::PatField<'tcx>],
1275 def_bm: BindingMode,
1280 let ty::Adt(adt, substs) = adt_ty.kind() else {
1281 span_bug!(pat.span, "struct pattern is not an ADT");
1284 // Index the struct fields' types.
1285 let field_map = variant
1289 .map(|(i, field)| (field.ident(self.tcx).normalize_to_macros_2_0(), (i, field)))
1290 .collect::<FxHashMap<_, _>>();
1292 // Keep track of which fields have already appeared in the pattern.
1293 let mut used_fields = FxHashMap::default();
1294 let mut no_field_errors = true;
1296 let mut inexistent_fields = vec![];
1297 // Typecheck each field.
1298 for field in fields {
1299 let span = field.span;
1300 let ident = tcx.adjust_ident(field.ident, variant.def_id);
1301 let field_ty = match used_fields.entry(ident) {
1302 Occupied(occupied) => {
1303 self.error_field_already_bound(span, field.ident, *occupied.get());
1304 no_field_errors = false;
1308 vacant.insert(span);
1312 self.write_field_index(field.hir_id, *i);
1313 self.tcx.check_stability(f.did, Some(pat.hir_id), span, None);
1314 self.field_ty(span, f, substs)
1316 .unwrap_or_else(|| {
1317 inexistent_fields.push(field);
1318 no_field_errors = false;
1324 self.check_pat(field.pat, field_ty, def_bm, TopInfo { parent_pat: Some(pat), ..ti });
1327 let mut unmentioned_fields = variant
1330 .map(|field| (field, field.ident(self.tcx).normalize_to_macros_2_0()))
1331 .filter(|(_, ident)| !used_fields.contains_key(ident))
1332 .collect::<Vec<_>>();
1334 let inexistent_fields_err = if !(inexistent_fields.is_empty() || variant.is_recovered())
1335 && !inexistent_fields.iter().any(|field| field.ident.name == kw::Underscore)
1337 Some(self.error_inexistent_fields(
1338 adt.variant_descr(),
1340 &mut unmentioned_fields,
1348 // Require `..` if struct has non_exhaustive attribute.
1349 let non_exhaustive = variant.is_field_list_non_exhaustive() && !adt.did().is_local();
1350 if non_exhaustive && !has_rest_pat {
1351 self.error_foreign_non_exhaustive_spat(pat, adt.variant_descr(), fields.is_empty());
1354 let mut unmentioned_err = None;
1355 // Report an error if an incorrect number of fields was specified.
1357 if fields.len() != 1 {
1359 .struct_span_err(pat.span, "union patterns should have exactly one field")
1363 tcx.sess.struct_span_err(pat.span, "`..` cannot be used in union patterns").emit();
1365 } else if !unmentioned_fields.is_empty() {
1366 let accessible_unmentioned_fields: Vec<_> = unmentioned_fields
1369 .filter(|(field, _)| {
1370 field.vis.is_accessible_from(tcx.parent_module(pat.hir_id).to_def_id(), tcx)
1372 tcx.eval_stability(field.did, None, DUMMY_SP, None),
1373 EvalResult::Deny { .. }
1375 // We only want to report the error if it is hidden and not local
1376 && !(tcx.is_doc_hidden(field.did) && !field.did.is_local())
1381 if accessible_unmentioned_fields.is_empty() {
1382 unmentioned_err = Some(self.error_no_accessible_fields(pat, fields));
1384 unmentioned_err = Some(self.error_unmentioned_fields(
1386 &accessible_unmentioned_fields,
1387 accessible_unmentioned_fields.len() != unmentioned_fields.len(),
1391 } else if non_exhaustive && !accessible_unmentioned_fields.is_empty() {
1392 self.lint_non_exhaustive_omitted_patterns(
1394 &accessible_unmentioned_fields,
1399 match (inexistent_fields_err, unmentioned_err) {
1400 (Some(mut i), Some(mut u)) => {
1401 if let Some(mut e) = self.error_tuple_variant_as_struct_pat(pat, fields, variant) {
1402 // We don't want to show the nonexistent fields error when this was
1403 // `Foo { a, b }` when it should have been `Foo(a, b)`.
1412 (None, Some(mut u)) => {
1413 if let Some(mut e) = self.error_tuple_variant_as_struct_pat(pat, fields, variant) {
1420 (Some(mut err), None) => {
1423 (None, None) if let Some(mut err) =
1424 self.error_tuple_variant_index_shorthand(variant, pat, fields) =>
1433 fn error_tuple_variant_index_shorthand(
1435 variant: &VariantDef,
1437 fields: &[hir::PatField<'_>],
1438 ) -> Option<DiagnosticBuilder<'_, ErrorGuaranteed>> {
1439 // if this is a tuple struct, then all field names will be numbers
1440 // so if any fields in a struct pattern use shorthand syntax, they will
1441 // be invalid identifiers (for example, Foo { 0, 1 }).
1442 if let (CtorKind::Fn, PatKind::Struct(qpath, field_patterns, ..)) =
1443 (variant.ctor_kind, &pat.kind)
1445 let has_shorthand_field_name = field_patterns.iter().any(|field| field.is_shorthand);
1446 if has_shorthand_field_name {
1447 let path = rustc_hir_pretty::to_string(rustc_hir_pretty::NO_ANN, |s| {
1448 s.print_qpath(qpath, false)
1450 let mut err = struct_span_err!(
1454 "tuple variant `{path}` written as struct variant",
1456 err.span_suggestion_verbose(
1457 qpath.span().shrink_to_hi().to(pat.span.shrink_to_hi()),
1458 "use the tuple variant pattern syntax instead",
1459 format!("({})", self.get_suggested_tuple_struct_pattern(fields, variant)),
1460 Applicability::MaybeIncorrect,
1468 fn error_foreign_non_exhaustive_spat(&self, pat: &Pat<'_>, descr: &str, no_fields: bool) {
1469 let sess = self.tcx.sess;
1470 let sm = sess.source_map();
1471 let sp_brace = sm.end_point(pat.span);
1472 let sp_comma = sm.end_point(pat.span.with_hi(sp_brace.hi()));
1473 let sugg = if no_fields || sp_brace != sp_comma { ".. }" } else { ", .. }" };
1475 let mut err = struct_span_err!(
1479 "`..` required with {descr} marked as non-exhaustive",
1481 err.span_suggestion_verbose(
1483 "add `..` at the end of the field list to ignore all other fields",
1485 Applicability::MachineApplicable,
1490 fn error_field_already_bound(&self, span: Span, ident: Ident, other_field: Span) {
1495 "field `{}` bound multiple times in the pattern",
1498 .span_label(span, format!("multiple uses of `{ident}` in pattern"))
1499 .span_label(other_field, format!("first use of `{ident}`"))
1503 fn error_inexistent_fields(
1506 inexistent_fields: &[&hir::PatField<'tcx>],
1507 unmentioned_fields: &mut Vec<(&'tcx ty::FieldDef, Ident)>,
1508 variant: &ty::VariantDef,
1509 substs: &'tcx ty::List<ty::subst::GenericArg<'tcx>>,
1510 ) -> DiagnosticBuilder<'tcx, ErrorGuaranteed> {
1512 let (field_names, t, plural) = if inexistent_fields.len() == 1 {
1513 (format!("a field named `{}`", inexistent_fields[0].ident), "this", "")
1520 .map(|field| format!("`{}`", field.ident))
1521 .collect::<Vec<String>>()
1528 let spans = inexistent_fields.iter().map(|field| field.ident.span).collect::<Vec<_>>();
1529 let mut err = struct_span_err!(
1533 "{} `{}` does not have {}",
1535 tcx.def_path_str(variant.def_id),
1538 if let Some(pat_field) = inexistent_fields.last() {
1540 pat_field.ident.span,
1542 "{} `{}` does not have {} field{}",
1544 tcx.def_path_str(variant.def_id),
1550 if unmentioned_fields.len() == 1 {
1552 unmentioned_fields.iter().map(|(_, field)| field.name).collect::<Vec<_>>();
1553 let suggested_name = find_best_match_for_name(&input, pat_field.ident.name, None);
1554 if let Some(suggested_name) = suggested_name {
1555 err.span_suggestion(
1556 pat_field.ident.span,
1557 "a field with a similar name exists",
1559 Applicability::MaybeIncorrect,
1562 // When we have a tuple struct used with struct we don't want to suggest using
1563 // the (valid) struct syntax with numeric field names. Instead we want to
1564 // suggest the expected syntax. We infer that this is the case by parsing the
1565 // `Ident` into an unsized integer. The suggestion will be emitted elsewhere in
1566 // `smart_resolve_context_dependent_help`.
1567 if suggested_name.to_ident_string().parse::<usize>().is_err() {
1568 // We don't want to throw `E0027` in case we have thrown `E0026` for them.
1569 unmentioned_fields.retain(|&(_, x)| x.name != suggested_name);
1571 } else if inexistent_fields.len() == 1 {
1572 match pat_field.pat.kind {
1574 if !self.can_coerce(
1575 self.typeck_results.borrow().expr_ty(expr),
1577 unmentioned_fields[0].1.span,
1578 unmentioned_fields[0].0,
1583 let unmentioned_field = unmentioned_fields[0].1.name;
1584 err.span_suggestion_short(
1585 pat_field.ident.span,
1587 "`{}` has a field named `{}`",
1588 tcx.def_path_str(variant.def_id),
1591 unmentioned_field.to_string(),
1592 Applicability::MaybeIncorrect,
1599 if tcx.sess.teach(&err.get_code().unwrap()) {
1601 "This error indicates that a struct pattern attempted to \
1602 extract a non-existent field from a struct. Struct fields \
1603 are identified by the name used before the colon : so struct \
1604 patterns should resemble the declaration of the struct type \
1606 If you are using shorthand field patterns but want to refer \
1607 to the struct field by a different name, you should rename \
1614 fn error_tuple_variant_as_struct_pat(
1617 fields: &'tcx [hir::PatField<'tcx>],
1618 variant: &ty::VariantDef,
1619 ) -> Option<DiagnosticBuilder<'tcx, ErrorGuaranteed>> {
1620 if let (CtorKind::Fn, PatKind::Struct(qpath, ..)) = (variant.ctor_kind, &pat.kind) {
1621 let path = rustc_hir_pretty::to_string(rustc_hir_pretty::NO_ANN, |s| {
1622 s.print_qpath(qpath, false)
1624 let mut err = struct_span_err!(
1628 "tuple variant `{}` written as struct variant",
1631 let (sugg, appl) = if fields.len() == variant.fields.len() {
1633 self.get_suggested_tuple_struct_pattern(fields, variant),
1634 Applicability::MachineApplicable,
1638 variant.fields.iter().map(|_| "_").collect::<Vec<&str>>().join(", "),
1639 Applicability::MaybeIncorrect,
1642 err.span_suggestion_verbose(
1643 qpath.span().shrink_to_hi().to(pat.span.shrink_to_hi()),
1644 "use the tuple variant pattern syntax instead",
1645 format!("({})", sugg),
1653 fn get_suggested_tuple_struct_pattern(
1655 fields: &[hir::PatField<'_>],
1656 variant: &VariantDef,
1658 let variant_field_idents =
1659 variant.fields.iter().map(|f| f.ident(self.tcx)).collect::<Vec<Ident>>();
1663 match self.tcx.sess.source_map().span_to_snippet(field.pat.span) {
1665 // Field names are numbers, but numbers
1666 // are not valid identifiers
1667 if variant_field_idents.contains(&field.ident) {
1673 Err(_) => rustc_hir_pretty::to_string(rustc_hir_pretty::NO_ANN, |s| {
1674 s.print_pat(field.pat)
1678 .collect::<Vec<String>>()
1682 /// Returns a diagnostic reporting a struct pattern which is missing an `..` due to
1683 /// inaccessible fields.
1686 /// error: pattern requires `..` due to inaccessible fields
1687 /// --> src/main.rs:10:9
1689 /// LL | let foo::Foo {} = foo::Foo::default();
1692 /// help: add a `..`
1694 /// LL | let foo::Foo { .. } = foo::Foo::default();
1697 fn error_no_accessible_fields(
1700 fields: &'tcx [hir::PatField<'tcx>],
1701 ) -> DiagnosticBuilder<'tcx, ErrorGuaranteed> {
1705 .struct_span_err(pat.span, "pattern requires `..` due to inaccessible fields");
1707 if let Some(field) = fields.last() {
1708 err.span_suggestion_verbose(
1709 field.span.shrink_to_hi(),
1710 "ignore the inaccessible and unused fields",
1712 Applicability::MachineApplicable,
1715 let qpath_span = if let PatKind::Struct(qpath, ..) = &pat.kind {
1718 bug!("`error_no_accessible_fields` called on non-struct pattern");
1721 // Shrink the span to exclude the `foo:Foo` in `foo::Foo { }`.
1722 let span = pat.span.with_lo(qpath_span.shrink_to_hi().hi());
1723 err.span_suggestion_verbose(
1725 "ignore the inaccessible and unused fields",
1727 Applicability::MachineApplicable,
1733 /// Report that a pattern for a `#[non_exhaustive]` struct marked with `non_exhaustive_omitted_patterns`
1734 /// is not exhaustive enough.
1736 /// Nb: the partner lint for enums lives in `compiler/rustc_mir_build/src/thir/pattern/usefulness.rs`.
1737 fn lint_non_exhaustive_omitted_patterns(
1740 unmentioned_fields: &[(&ty::FieldDef, Ident)],
1743 fn joined_uncovered_patterns(witnesses: &[&Ident]) -> String {
1744 const LIMIT: usize = 3;
1747 [witness] => format!("`{}`", witness),
1748 [head @ .., tail] if head.len() < LIMIT => {
1749 let head: Vec<_> = head.iter().map(<_>::to_string).collect();
1750 format!("`{}` and `{}`", head.join("`, `"), tail)
1753 let (head, tail) = witnesses.split_at(LIMIT);
1754 let head: Vec<_> = head.iter().map(<_>::to_string).collect();
1755 format!("`{}` and {} more", head.join("`, `"), tail.len())
1759 let joined_patterns = joined_uncovered_patterns(
1760 &unmentioned_fields.iter().map(|(_, i)| i).collect::<Vec<_>>(),
1763 self.tcx.struct_span_lint_hir(NON_EXHAUSTIVE_OMITTED_PATTERNS, pat.hir_id, pat.span, |build| {
1764 let mut lint = build.build("some fields are not explicitly listed");
1765 lint.span_label(pat.span, format!("field{} {} not listed", rustc_errors::pluralize!(unmentioned_fields.len()), joined_patterns));
1768 "ensure that all fields are mentioned explicitly by adding the suggested fields",
1771 "the pattern is of type `{}` and the `non_exhaustive_omitted_patterns` attribute was found",
1778 /// Returns a diagnostic reporting a struct pattern which does not mention some fields.
1781 /// error[E0027]: pattern does not mention field `bar`
1782 /// --> src/main.rs:15:9
1784 /// LL | let foo::Foo {} = foo::Foo::new();
1785 /// | ^^^^^^^^^^^ missing field `bar`
1787 fn error_unmentioned_fields(
1790 unmentioned_fields: &[(&ty::FieldDef, Ident)],
1791 have_inaccessible_fields: bool,
1792 fields: &'tcx [hir::PatField<'tcx>],
1793 ) -> DiagnosticBuilder<'tcx, ErrorGuaranteed> {
1794 let inaccessible = if have_inaccessible_fields { " and inaccessible fields" } else { "" };
1795 let field_names = if unmentioned_fields.len() == 1 {
1796 format!("field `{}`{}", unmentioned_fields[0].1, inaccessible)
1798 let fields = unmentioned_fields
1800 .map(|(_, name)| format!("`{}`", name))
1801 .collect::<Vec<String>>()
1803 format!("fields {}{}", fields, inaccessible)
1805 let mut err = struct_span_err!(
1809 "pattern does not mention {}",
1812 err.span_label(pat.span, format!("missing {}", field_names));
1813 let len = unmentioned_fields.len();
1814 let (prefix, postfix, sp) = match fields {
1815 [] => match &pat.kind {
1816 PatKind::Struct(path, [], false) => {
1817 (" { ", " }", path.span().shrink_to_hi().until(pat.span.shrink_to_hi()))
1822 // Account for last field having a trailing comma or parse recovery at the tail of
1823 // the pattern to avoid invalid suggestion (#78511).
1824 let tail = field.span.shrink_to_hi().with_hi(pat.span.hi());
1826 PatKind::Struct(..) => (", ", " }", tail),
1831 err.span_suggestion(
1834 "include the missing field{} in the pattern{}",
1836 if have_inaccessible_fields { " and ignore the inaccessible fields" } else { "" }
1843 .map(|(_, name)| name.to_string())
1844 .collect::<Vec<_>>()
1846 if have_inaccessible_fields { ", .." } else { "" },
1849 Applicability::MachineApplicable,
1851 err.span_suggestion(
1854 "if you don't care about {these} missing field{s}, you can explicitly ignore {them}",
1855 these = pluralize!("this", len),
1856 s = pluralize!(len),
1857 them = if len == 1 { "it" } else { "them" },
1859 format!("{}..{}", prefix, postfix),
1860 Applicability::MachineApplicable,
1868 inner: &'tcx Pat<'tcx>,
1870 def_bm: BindingMode,
1874 let (box_ty, inner_ty) = if self.check_dereferenceable(span, expected, inner) {
1875 // Here, `demand::subtype` is good enough, but I don't
1876 // think any errors can be introduced by using `demand::eqtype`.
1877 let inner_ty = self.next_ty_var(TypeVariableOrigin {
1878 kind: TypeVariableOriginKind::TypeInference,
1881 let box_ty = tcx.mk_box(inner_ty);
1882 self.demand_eqtype_pat(span, expected, box_ty, ti);
1885 let err = tcx.ty_error();
1888 self.check_pat(inner, inner_ty, def_bm, ti);
1892 // Precondition: Pat is Ref(inner)
1895 pat: &'tcx Pat<'tcx>,
1896 inner: &'tcx Pat<'tcx>,
1897 mutbl: hir::Mutability,
1899 def_bm: BindingMode,
1903 let expected = self.shallow_resolve(expected);
1904 let (rptr_ty, inner_ty) = if self.check_dereferenceable(pat.span, expected, inner) {
1905 // `demand::subtype` would be good enough, but using `eqtype` turns
1906 // out to be equally general. See (note_1) for details.
1908 // Take region, inner-type from expected type if we can,
1909 // to avoid creating needless variables. This also helps with
1910 // the bad interactions of the given hack detailed in (note_1).
1911 debug!("check_pat_ref: expected={:?}", expected);
1912 match *expected.kind() {
1913 ty::Ref(_, r_ty, r_mutbl) if r_mutbl == mutbl => (expected, r_ty),
1915 let inner_ty = self.next_ty_var(TypeVariableOrigin {
1916 kind: TypeVariableOriginKind::TypeInference,
1919 let rptr_ty = self.new_ref_ty(pat.span, mutbl, inner_ty);
1920 debug!("check_pat_ref: demanding {:?} = {:?}", expected, rptr_ty);
1921 let err = self.demand_eqtype_pat_diag(pat.span, expected, rptr_ty, ti);
1923 // Look for a case like `fn foo(&foo: u32)` and suggest
1924 // `fn foo(foo: &u32)`
1925 if let Some(mut err) = err {
1926 self.borrow_pat_suggestion(&mut err, pat);
1933 let err = tcx.ty_error();
1936 self.check_pat(inner, inner_ty, def_bm, TopInfo { parent_pat: Some(pat), ..ti });
1940 /// Create a reference type with a fresh region variable.
1941 fn new_ref_ty(&self, span: Span, mutbl: hir::Mutability, ty: Ty<'tcx>) -> Ty<'tcx> {
1942 let region = self.next_region_var(infer::PatternRegion(span));
1943 let mt = ty::TypeAndMut { ty, mutbl };
1944 self.tcx.mk_ref(region, mt)
1947 /// Type check a slice pattern.
1949 /// Syntactically, these look like `[pat_0, ..., pat_n]`.
1950 /// Semantically, we are type checking a pattern with structure:
1951 /// ```ignore (not-rust)
1952 /// [before_0, ..., before_n, (slice, after_0, ... after_n)?]
1954 /// The type of `slice`, if it is present, depends on the `expected` type.
1955 /// If `slice` is missing, then so is `after_i`.
1956 /// If `slice` is present, it can still represent 0 elements.
1960 before: &'tcx [Pat<'tcx>],
1961 slice: Option<&'tcx Pat<'tcx>>,
1962 after: &'tcx [Pat<'tcx>],
1964 def_bm: BindingMode,
1967 let expected = self.structurally_resolved_type(span, expected);
1968 let (element_ty, opt_slice_ty, inferred) = match *expected.kind() {
1969 // An array, so we might have something like `let [a, b, c] = [0, 1, 2];`.
1970 ty::Array(element_ty, len) => {
1971 let min = before.len() as u64 + after.len() as u64;
1972 let (opt_slice_ty, expected) =
1973 self.check_array_pat_len(span, element_ty, expected, slice, len, min);
1974 // `opt_slice_ty.is_none()` => `slice.is_none()`.
1975 // Note, though, that opt_slice_ty could be `Some(error_ty)`.
1976 assert!(opt_slice_ty.is_some() || slice.is_none());
1977 (element_ty, opt_slice_ty, expected)
1979 ty::Slice(element_ty) => (element_ty, Some(expected), expected),
1980 // The expected type must be an array or slice, but was neither, so error.
1982 if !expected.references_error() {
1983 self.error_expected_array_or_slice(span, expected, ti);
1985 let err = self.tcx.ty_error();
1986 (err, Some(err), err)
1990 // Type check all the patterns before `slice`.
1992 self.check_pat(elt, element_ty, def_bm, ti);
1994 // Type check the `slice`, if present, against its expected type.
1995 if let Some(slice) = slice {
1996 self.check_pat(slice, opt_slice_ty.unwrap(), def_bm, ti);
1998 // Type check the elements after `slice`, if present.
2000 self.check_pat(elt, element_ty, def_bm, ti);
2005 /// Type check the length of an array pattern.
2007 /// Returns both the type of the variable length pattern (or `None`), and the potentially
2008 /// inferred array type. We only return `None` for the slice type if `slice.is_none()`.
2009 fn check_array_pat_len(
2012 element_ty: Ty<'tcx>,
2014 slice: Option<&'tcx Pat<'tcx>>,
2015 len: ty::Const<'tcx>,
2017 ) -> (Option<Ty<'tcx>>, Ty<'tcx>) {
2018 if let Some(len) = len.try_eval_usize(self.tcx, self.param_env) {
2019 // Now we know the length...
2020 if slice.is_none() {
2021 // ...and since there is no variable-length pattern,
2022 // we require an exact match between the number of elements
2023 // in the array pattern and as provided by the matched type.
2025 return (None, arr_ty);
2028 self.error_scrutinee_inconsistent_length(span, min_len, len);
2029 } else if let Some(pat_len) = len.checked_sub(min_len) {
2030 // The variable-length pattern was there,
2031 // so it has an array type with the remaining elements left as its size...
2032 return (Some(self.tcx.mk_array(element_ty, pat_len)), arr_ty);
2034 // ...however, in this case, there were no remaining elements.
2035 // That is, the slice pattern requires more than the array type offers.
2036 self.error_scrutinee_with_rest_inconsistent_length(span, min_len, len);
2038 } else if slice.is_none() {
2039 // We have a pattern with a fixed length,
2040 // which we can use to infer the length of the array.
2041 let updated_arr_ty = self.tcx.mk_array(element_ty, min_len);
2042 self.demand_eqtype(span, updated_arr_ty, arr_ty);
2043 return (None, updated_arr_ty);
2045 // We have a variable-length pattern and don't know the array length.
2046 // This happens if we have e.g.,
2047 // `let [a, b, ..] = arr` where `arr: [T; N]` where `const N: usize`.
2048 self.error_scrutinee_unfixed_length(span);
2051 // If we get here, we must have emitted an error.
2052 (Some(self.tcx.ty_error()), arr_ty)
2055 fn error_scrutinee_inconsistent_length(&self, span: Span, min_len: u64, size: u64) {
2060 "pattern requires {} element{} but array has {}",
2062 pluralize!(min_len),
2065 .span_label(span, format!("expected {} element{}", size, pluralize!(size)))
2069 fn error_scrutinee_with_rest_inconsistent_length(&self, span: Span, min_len: u64, size: u64) {
2074 "pattern requires at least {} element{} but array has {}",
2076 pluralize!(min_len),
2081 format!("pattern cannot match array of {} element{}", size, pluralize!(size),),
2086 fn error_scrutinee_unfixed_length(&self, span: Span) {
2091 "cannot pattern-match on an array without a fixed length",
2096 fn error_expected_array_or_slice(&self, span: Span, expected_ty: Ty<'tcx>, ti: TopInfo<'tcx>) {
2097 let mut err = struct_span_err!(
2101 "expected an array or slice, found `{expected_ty}`"
2103 if let ty::Ref(_, ty, _) = expected_ty.kind()
2104 && let ty::Array(..) | ty::Slice(..) = ty.kind()
2106 err.help("the semantics of slice patterns changed recently; see issue #62254");
2107 } else if Autoderef::new(&self.infcx, self.param_env, self.body_id, span, expected_ty, span)
2108 .any(|(ty, _)| matches!(ty.kind(), ty::Slice(..) | ty::Array(..)))
2109 && let (Some(span), true) = (ti.span, ti.origin_expr)
2110 && let Ok(snippet) = self.tcx.sess.source_map().span_to_snippet(span)
2112 let ty = self.resolve_vars_if_possible(ti.expected);
2113 let is_slice_or_array_or_vector = self.is_slice_or_array_or_vector(&mut err, snippet.clone(), ty);
2114 match is_slice_or_array_or_vector.1.kind() {
2116 if self.tcx.is_diagnostic_item(sym::Option, adt_def.did())
2117 || self.tcx.is_diagnostic_item(sym::Result, adt_def.did()) =>
2119 // Slicing won't work here, but `.as_deref()` might (issue #91328).
2120 err.span_suggestion(
2122 "consider using `as_deref` here",
2123 format!("{snippet}.as_deref()"),
2124 Applicability::MaybeIncorrect,
2129 if is_slice_or_array_or_vector.0 {
2130 err.span_suggestion(
2132 "consider slicing here",
2133 format!("{snippet}[..]"),
2134 Applicability::MachineApplicable,
2138 err.span_label(span, format!("pattern cannot match with input type `{expected_ty}`"));
2142 fn is_slice_or_array_or_vector(
2144 err: &mut Diagnostic,
2147 ) -> (bool, Ty<'tcx>) {
2149 ty::Adt(adt_def, _) if self.tcx.is_diagnostic_item(sym::Vec, adt_def.did()) => {
2152 ty::Ref(_, ty, _) => self.is_slice_or_array_or_vector(err, snippet, *ty),
2153 ty::Slice(..) | ty::Array(..) => (true, ty),