1 use crate::check::FnCtxt;
4 use rustc_data_structures::fx::FxHashMap;
5 use rustc_errors::{pluralize, struct_span_err, Applicability, Diagnostic, DiagnosticBuilder};
7 use rustc_hir::def::{CtorKind, DefKind, Res};
8 use rustc_hir::pat_util::EnumerateAndAdjustIterator;
9 use rustc_hir::{HirId, Pat, PatKind};
10 use rustc_infer::infer;
11 use rustc_infer::infer::type_variable::{TypeVariableOrigin, TypeVariableOriginKind};
12 use rustc_middle::ty::{self, Adt, BindingMode, Ty, TypeFoldable};
13 use rustc_session::lint::builtin::NON_EXHAUSTIVE_OMITTED_PATTERNS;
14 use rustc_span::hygiene::DesugaringKind;
15 use rustc_span::lev_distance::find_best_match_for_name;
16 use rustc_span::source_map::{Span, Spanned};
17 use rustc_span::symbol::{sym, Ident};
18 use rustc_span::{BytePos, MultiSpan, DUMMY_SP};
19 use rustc_trait_selection::autoderef::Autoderef;
20 use rustc_trait_selection::traits::{ObligationCause, Pattern};
24 use std::collections::hash_map::Entry::{Occupied, Vacant};
26 use super::report_unexpected_variant_res;
28 const CANNOT_IMPLICITLY_DEREF_POINTER_TRAIT_OBJ: &str = "\
29 This error indicates that a pointer to a trait type cannot be implicitly dereferenced by a \
30 pattern. Every trait defines a type, but because the size of trait implementors isn't fixed, \
31 this type has no compile-time size. Therefore, all accesses to trait types must be through \
32 pointers. If you encounter this error you should try to avoid dereferencing the pointer.
34 You can read more about trait objects in the Trait Objects section of the Reference: \
35 https://doc.rust-lang.org/reference/types.html#trait-objects";
37 /// Information about the expected type at the top level of type checking a pattern.
39 /// **NOTE:** This is only for use by diagnostics. Do NOT use for type checking logic!
40 #[derive(Copy, Clone)]
41 struct TopInfo<'tcx> {
42 /// The `expected` type at the top level of type checking a pattern.
44 /// Was the origin of the `span` from a scrutinee expression?
46 /// Otherwise there is no scrutinee and it could be e.g. from the type of a formal parameter.
48 /// The span giving rise to the `expected` type, if one could be provided.
50 /// If `origin_expr` is `true`, then this is the span of the scrutinee as in:
52 /// - `match scrutinee { ... }`
53 /// - `let _ = scrutinee;`
55 /// This is used to point to add context in type errors.
56 /// In the following example, `span` corresponds to the `a + b` expression:
59 /// error[E0308]: mismatched types
60 /// --> src/main.rs:L:C
62 /// L | let temp: usize = match a + b {
63 /// | ----- this expression has type `usize`
64 /// L | Ok(num) => num,
65 /// | ^^^^^^^ expected `usize`, found enum `std::result::Result`
67 /// = note: expected type `usize`
68 /// found type `std::result::Result<_, _>`
71 /// This refers to the parent pattern. Used to provide extra diagnostic information on errors.
73 /// error[E0308]: mismatched types
74 /// --> $DIR/const-in-struct-pat.rs:8:17
77 /// | --------- unit struct defined here
79 /// L | let Thing { f } = t;
82 /// | expected struct `std::string::String`, found struct `f`
83 /// | `f` is interpreted as a unit struct, not a new binding
84 /// | help: bind the struct field to a different name instead: `f: other_f`
86 parent_pat: Option<&'tcx Pat<'tcx>>,
89 impl<'tcx> FnCtxt<'_, 'tcx> {
90 fn pattern_cause(&self, ti: TopInfo<'tcx>, cause_span: Span) -> ObligationCause<'tcx> {
91 let code = Pattern { span: ti.span, root_ty: ti.expected, origin_expr: ti.origin_expr };
92 self.cause(cause_span, code)
95 fn demand_eqtype_pat_diag(
101 ) -> Option<DiagnosticBuilder<'tcx>> {
102 self.demand_eqtype_with_origin(&self.pattern_cause(ti, cause_span), expected, actual)
105 fn demand_eqtype_pat(
112 if let Some(mut err) = self.demand_eqtype_pat_diag(cause_span, expected, actual, ti) {
118 const INITIAL_BM: BindingMode = BindingMode::BindByValue(hir::Mutability::Not);
120 /// Mode for adjusting the expected type and binding mode.
122 /// Peel off all immediate reference types.
124 /// Reset binding mode to the initial mode.
126 /// Pass on the input binding mode and expected type.
130 impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
131 /// Type check the given top level pattern against the `expected` type.
133 /// If a `Some(span)` is provided and `origin_expr` holds,
134 /// then the `span` represents the scrutinee's span.
135 /// The scrutinee is found in e.g. `match scrutinee { ... }` and `let pat = scrutinee;`.
137 /// Otherwise, `Some(span)` represents the span of a type expression
138 /// which originated the `expected` type.
139 pub fn check_pat_top(
141 pat: &'tcx Pat<'tcx>,
146 let info = TopInfo { expected, origin_expr, span, parent_pat: None };
147 self.check_pat(pat, expected, INITIAL_BM, info);
150 /// Type check the given `pat` against the `expected` type
151 /// with the provided `def_bm` (default binding mode).
153 /// Outside of this module, `check_pat_top` should always be used.
154 /// Conversely, inside this module, `check_pat_top` should never be used.
155 #[instrument(level = "debug", skip(self, ti))]
158 pat: &'tcx Pat<'tcx>,
163 let path_res = match &pat.kind {
164 PatKind::Path(qpath) => {
165 Some(self.resolve_ty_and_res_fully_qualified_call(qpath, pat.hir_id, pat.span))
169 let adjust_mode = self.calc_adjust_mode(pat, path_res.map(|(res, ..)| res));
170 let (expected, def_bm) = self.calc_default_binding_mode(pat, expected, def_bm, adjust_mode);
172 let ty = match pat.kind {
173 PatKind::Wild => expected,
174 PatKind::Lit(lt) => self.check_pat_lit(pat.span, lt, expected, ti),
175 PatKind::Range(lhs, rhs, _) => self.check_pat_range(pat.span, lhs, rhs, expected, ti),
176 PatKind::Binding(ba, var_id, _, sub) => {
177 self.check_pat_ident(pat, ba, var_id, sub, expected, def_bm, ti)
179 PatKind::TupleStruct(ref qpath, subpats, ddpos) => {
180 self.check_pat_tuple_struct(pat, qpath, subpats, ddpos, expected, def_bm, ti)
182 PatKind::Path(_) => self.check_pat_path(pat, path_res.unwrap(), expected, ti),
183 PatKind::Struct(ref qpath, fields, has_rest_pat) => {
184 self.check_pat_struct(pat, qpath, fields, has_rest_pat, expected, def_bm, ti)
186 PatKind::Or(pats) => {
187 let parent_pat = Some(pat);
189 self.check_pat(pat, expected, def_bm, TopInfo { parent_pat, ..ti });
193 PatKind::Tuple(elements, ddpos) => {
194 self.check_pat_tuple(pat.span, elements, ddpos, expected, def_bm, ti)
196 PatKind::Box(inner) => self.check_pat_box(pat.span, inner, expected, def_bm, ti),
197 PatKind::Ref(inner, mutbl) => {
198 self.check_pat_ref(pat, inner, mutbl, expected, def_bm, ti)
200 PatKind::Slice(before, slice, after) => {
201 self.check_pat_slice(pat.span, before, slice, after, expected, def_bm, ti)
205 self.write_ty(pat.hir_id, ty);
207 // (note_1): In most of the cases where (note_1) is referenced
208 // (literals and constants being the exception), we relate types
209 // using strict equality, even though subtyping would be sufficient.
210 // There are a few reasons for this, some of which are fairly subtle
211 // and which cost me (nmatsakis) an hour or two debugging to remember,
212 // so I thought I'd write them down this time.
214 // 1. There is no loss of expressiveness here, though it does
215 // cause some inconvenience. What we are saying is that the type
216 // of `x` becomes *exactly* what is expected. This can cause unnecessary
217 // errors in some cases, such as this one:
220 // fn foo<'x>(x: &'x i32) {
227 // The reason we might get an error is that `z` might be
228 // assigned a type like `&'x i32`, and then we would have
229 // a problem when we try to assign `&a` to `z`, because
230 // the lifetime of `&a` (i.e., the enclosing block) is
231 // shorter than `'x`.
233 // HOWEVER, this code works fine. The reason is that the
234 // expected type here is whatever type the user wrote, not
235 // the initializer's type. In this case the user wrote
236 // nothing, so we are going to create a type variable `Z`.
237 // Then we will assign the type of the initializer (`&'x i32`)
238 // as a subtype of `Z`: `&'x i32 <: Z`. And hence we
239 // will instantiate `Z` as a type `&'0 i32` where `'0` is
240 // a fresh region variable, with the constraint that `'x : '0`.
241 // So basically we're all set.
243 // Note that there are two tests to check that this remains true
244 // (`regions-reassign-{match,let}-bound-pointer.rs`).
246 // 2. Things go horribly wrong if we use subtype. The reason for
247 // THIS is a fairly subtle case involving bound regions. See the
248 // `givens` field in `region_constraints`, as well as the test
249 // `regions-relate-bound-regions-on-closures-to-inference-variables.rs`,
250 // for details. Short version is that we must sometimes detect
251 // relationships between specific region variables and regions
252 // bound in a closure signature, and that detection gets thrown
253 // off when we substitute fresh region variables here to enable
257 /// Compute the new expected type and default binding mode from the old ones
258 /// as well as the pattern form we are currently checking.
259 fn calc_default_binding_mode(
261 pat: &'tcx Pat<'tcx>,
264 adjust_mode: AdjustMode,
265 ) -> (Ty<'tcx>, BindingMode) {
267 AdjustMode::Pass => (expected, def_bm),
268 AdjustMode::Reset => (expected, INITIAL_BM),
269 AdjustMode::Peel => self.peel_off_references(pat, expected, def_bm),
273 /// How should the binding mode and expected type be adjusted?
275 /// When the pattern is a path pattern, `opt_path_res` must be `Some(res)`.
276 fn calc_adjust_mode(&self, pat: &'tcx Pat<'tcx>, opt_path_res: Option<Res>) -> AdjustMode {
277 // When we perform destructuring assignment, we disable default match bindings, which are
278 // unintuitive in this context.
279 if !pat.default_binding_modes {
280 return AdjustMode::Reset;
283 // Type checking these product-like types successfully always require
284 // that the expected type be of those types and not reference types.
286 | PatKind::TupleStruct(..)
290 | PatKind::Slice(..) => AdjustMode::Peel,
291 // String and byte-string literals result in types `&str` and `&[u8]` respectively.
292 // All other literals result in non-reference types.
293 // As a result, we allow `if let 0 = &&0 {}` but not `if let "foo" = &&"foo {}`.
295 // Call `resolve_vars_if_possible` here for inline const blocks.
296 PatKind::Lit(lt) => match self.resolve_vars_if_possible(self.check_expr(lt)).kind() {
297 ty::Ref(..) => AdjustMode::Pass,
298 _ => AdjustMode::Peel,
300 PatKind::Path(_) => match opt_path_res.unwrap() {
301 // These constants can be of a reference type, e.g. `const X: &u8 = &0;`.
302 // Peeling the reference types too early will cause type checking failures.
303 // Although it would be possible to *also* peel the types of the constants too.
304 Res::Def(DefKind::Const | DefKind::AssocConst, _) => AdjustMode::Pass,
305 // In the `ValueNS`, we have `SelfCtor(..) | Ctor(_, Const), _)` remaining which
306 // could successfully compile. The former being `Self` requires a unit struct.
307 // In either case, and unlike constants, the pattern itself cannot be
308 // a reference type wherefore peeling doesn't give up any expressivity.
309 _ => AdjustMode::Peel,
311 // When encountering a `& mut? pat` pattern, reset to "by value".
312 // This is so that `x` and `y` here are by value, as they appear to be:
315 // match &(&22, &44) {
321 PatKind::Ref(..) => AdjustMode::Reset,
322 // A `_` pattern works with any expected type, so there's no need to do anything.
324 // Bindings also work with whatever the expected type is,
325 // and moreover if we peel references off, that will give us the wrong binding type.
326 // Also, we can have a subpattern `binding @ pat`.
327 // Each side of the `@` should be treated independently (like with OR-patterns).
328 | PatKind::Binding(..)
329 // An OR-pattern just propagates to each individual alternative.
330 // This is maximally flexible, allowing e.g., `Some(mut x) | &Some(mut x)`.
331 // In that example, `Some(mut x)` results in `Peel` whereas `&Some(mut x)` in `Reset`.
332 | PatKind::Or(_) => AdjustMode::Pass,
336 /// Peel off as many immediately nested `& mut?` from the expected type as possible
337 /// and return the new expected type and binding default binding mode.
338 /// The adjustments vector, if non-empty is stored in a table.
339 fn peel_off_references(
341 pat: &'tcx Pat<'tcx>,
343 mut def_bm: BindingMode,
344 ) -> (Ty<'tcx>, BindingMode) {
345 let mut expected = self.resolve_vars_with_obligations(expected);
347 // Peel off as many `&` or `&mut` from the scrutinee type as possible. For example,
348 // for `match &&&mut Some(5)` the loop runs three times, aborting when it reaches
349 // the `Some(5)` which is not of type Ref.
351 // For each ampersand peeled off, update the binding mode and push the original
352 // type into the adjustments vector.
354 // See the examples in `ui/match-defbm*.rs`.
355 let mut pat_adjustments = vec![];
356 while let ty::Ref(_, inner_ty, inner_mutability) = *expected.kind() {
357 debug!("inspecting {:?}", expected);
359 debug!("current discriminant is Ref, inserting implicit deref");
360 // Preserve the reference type. We'll need it later during THIR lowering.
361 pat_adjustments.push(expected);
364 def_bm = ty::BindByReference(match def_bm {
365 // If default binding mode is by value, make it `ref` or `ref mut`
366 // (depending on whether we observe `&` or `&mut`).
368 // When `ref mut`, stay a `ref mut` (on `&mut`) or downgrade to `ref` (on `&`).
369 ty::BindByReference(hir::Mutability::Mut) => inner_mutability,
370 // Once a `ref`, always a `ref`.
371 // This is because a `& &mut` cannot mutate the underlying value.
372 ty::BindByReference(m @ hir::Mutability::Not) => m,
376 if !pat_adjustments.is_empty() {
377 debug!("default binding mode is now {:?}", def_bm);
381 .pat_adjustments_mut()
382 .insert(pat.hir_id, pat_adjustments);
391 lt: &hir::Expr<'tcx>,
395 // We've already computed the type above (when checking for a non-ref pat),
396 // so avoid computing it again.
397 let ty = self.node_ty(lt.hir_id);
399 // Byte string patterns behave the same way as array patterns
400 // They can denote both statically and dynamically-sized byte arrays.
402 if let hir::ExprKind::Lit(Spanned { node: ast::LitKind::ByteStr(_), .. }) = lt.kind {
403 let expected = self.structurally_resolved_type(span, expected);
404 if let ty::Ref(_, inner_ty, _) = expected.kind() {
405 if matches!(inner_ty.kind(), ty::Slice(_)) {
407 trace!(?lt.hir_id.local_id, "polymorphic byte string lit");
410 .treat_byte_string_as_slice
411 .insert(lt.hir_id.local_id);
412 pat_ty = tcx.mk_imm_ref(tcx.lifetimes.re_static, tcx.mk_slice(tcx.types.u8));
417 // Somewhat surprising: in this case, the subtyping relation goes the
418 // opposite way as the other cases. Actually what we really want is not
419 // a subtyping relation at all but rather that there exists a LUB
420 // (so that they can be compared). However, in practice, constants are
421 // always scalars or strings. For scalars subtyping is irrelevant,
422 // and for strings `ty` is type is `&'static str`, so if we say that
424 // &'static str <: expected
426 // then that's equivalent to there existing a LUB.
427 let cause = self.pattern_cause(ti, span);
428 if let Some(mut err) = self.demand_suptype_with_origin(&cause, expected, pat_ty) {
432 // In the case of `if`- and `while`-expressions we've already checked
433 // that `scrutinee: bool`. We know that the pattern is `true`,
434 // so an error here would be a duplicate and from the wrong POV.
435 s.is_desugaring(DesugaringKind::CondTemporary)
447 lhs: Option<&'tcx hir::Expr<'tcx>>,
448 rhs: Option<&'tcx hir::Expr<'tcx>>,
452 let calc_side = |opt_expr: Option<&'tcx hir::Expr<'tcx>>| match opt_expr {
455 let ty = self.check_expr(expr);
456 // Check that the end-point is possibly of numeric or char type.
457 // The early check here is not for correctness, but rather better
458 // diagnostics (e.g. when `&str` is being matched, `expected` will
459 // be peeled to `str` while ty here is still `&str`, if we don't
460 // err ealy here, a rather confusing unification error will be
463 !(ty.is_numeric() || ty.is_char() || ty.is_ty_var() || ty.references_error());
464 Some((fail, ty, expr.span))
467 let mut lhs = calc_side(lhs);
468 let mut rhs = calc_side(rhs);
470 if let (Some((true, ..)), _) | (_, Some((true, ..))) = (lhs, rhs) {
471 // There exists a side that didn't meet our criteria that the end-point
472 // be of a numeric or char type, as checked in `calc_side` above.
473 self.emit_err_pat_range(span, lhs, rhs);
474 return self.tcx.ty_error();
477 // Unify each side with `expected`.
478 // Subtyping doesn't matter here, as the value is some kind of scalar.
479 let demand_eqtype = |x: &mut _, y| {
480 if let Some((ref mut fail, x_ty, x_span)) = *x {
481 if let Some(mut err) = self.demand_eqtype_pat_diag(x_span, expected, x_ty, ti) {
482 if let Some((_, y_ty, y_span)) = y {
483 self.endpoint_has_type(&mut err, y_span, y_ty);
490 demand_eqtype(&mut lhs, rhs);
491 demand_eqtype(&mut rhs, lhs);
493 if let (Some((true, ..)), _) | (_, Some((true, ..))) = (lhs, rhs) {
494 return self.tcx.ty_error();
497 // Find the unified type and check if it's of numeric or char type again.
498 // This check is needed if both sides are inference variables.
499 // We require types to be resolved here so that we emit inference failure
500 // rather than "_ is not a char or numeric".
501 let ty = self.structurally_resolved_type(span, expected);
502 if !(ty.is_numeric() || ty.is_char() || ty.references_error()) {
503 if let Some((ref mut fail, _, _)) = lhs {
506 if let Some((ref mut fail, _, _)) = rhs {
509 self.emit_err_pat_range(span, lhs, rhs);
510 return self.tcx.ty_error();
515 fn endpoint_has_type(&self, err: &mut Diagnostic, span: Span, ty: Ty<'_>) {
516 if !ty.references_error() {
517 err.span_label(span, &format!("this is of type `{}`", ty));
521 fn emit_err_pat_range(
524 lhs: Option<(bool, Ty<'tcx>, Span)>,
525 rhs: Option<(bool, Ty<'tcx>, Span)>,
527 let span = match (lhs, rhs) {
528 (Some((true, ..)), Some((true, ..))) => span,
529 (Some((true, _, sp)), _) => sp,
530 (_, Some((true, _, sp))) => sp,
531 _ => span_bug!(span, "emit_err_pat_range: no side failed or exists but still error?"),
533 let mut err = struct_span_err!(
537 "only `char` and numeric types are allowed in range patterns"
540 let ty = self.resolve_vars_if_possible(ty);
541 format!("this is of type `{}` but it should be `char` or numeric", ty)
543 let mut one_side_err = |first_span, first_ty, second: Option<(bool, Ty<'tcx>, Span)>| {
544 err.span_label(first_span, &msg(first_ty));
545 if let Some((_, ty, sp)) = second {
546 let ty = self.resolve_vars_if_possible(ty);
547 self.endpoint_has_type(&mut err, sp, ty);
551 (Some((true, lhs_ty, lhs_sp)), Some((true, rhs_ty, rhs_sp))) => {
552 err.span_label(lhs_sp, &msg(lhs_ty));
553 err.span_label(rhs_sp, &msg(rhs_ty));
555 (Some((true, lhs_ty, lhs_sp)), rhs) => one_side_err(lhs_sp, lhs_ty, rhs),
556 (lhs, Some((true, rhs_ty, rhs_sp))) => one_side_err(rhs_sp, rhs_ty, lhs),
557 _ => span_bug!(span, "Impossible, verified above."),
559 if self.tcx.sess.teach(&err.get_code().unwrap()) {
561 "In a match expression, only numbers and characters can be matched \
562 against a range. This is because the compiler checks that the range \
563 is non-empty at compile-time, and is unable to evaluate arbitrary \
564 comparison functions. If you want to capture values of an orderable \
565 type between two end-points, you can use a guard.",
573 pat: &'tcx Pat<'tcx>,
574 ba: hir::BindingAnnotation,
576 sub: Option<&'tcx Pat<'tcx>>,
581 // Determine the binding mode...
583 hir::BindingAnnotation::Unannotated => def_bm,
584 _ => BindingMode::convert(ba),
586 // ...and store it in a side table:
587 self.inh.typeck_results.borrow_mut().pat_binding_modes_mut().insert(pat.hir_id, bm);
589 debug!("check_pat_ident: pat.hir_id={:?} bm={:?}", pat.hir_id, bm);
591 let local_ty = self.local_ty(pat.span, pat.hir_id).decl_ty;
592 let eq_ty = match bm {
593 ty::BindByReference(mutbl) => {
594 // If the binding is like `ref x | ref mut x`,
595 // then `x` is assigned a value of type `&M T` where M is the
596 // mutability and T is the expected type.
598 // `x` is assigned a value of type `&M T`, hence `&M T <: typeof(x)`
599 // is required. However, we use equality, which is stronger.
600 // See (note_1) for an explanation.
601 self.new_ref_ty(pat.span, mutbl, expected)
603 // Otherwise, the type of x is the expected type `T`.
604 ty::BindByValue(_) => {
605 // As above, `T <: typeof(x)` is required, but we use equality, see (note_1).
609 self.demand_eqtype_pat(pat.span, eq_ty, local_ty, ti);
611 // If there are multiple arms, make sure they all agree on
612 // what the type of the binding `x` ought to be.
613 if var_id != pat.hir_id {
614 self.check_binding_alt_eq_ty(pat.span, var_id, local_ty, ti);
617 if let Some(p) = sub {
618 self.check_pat(p, expected, def_bm, TopInfo { parent_pat: Some(pat), ..ti });
624 fn check_binding_alt_eq_ty(&self, span: Span, var_id: HirId, ty: Ty<'tcx>, ti: TopInfo<'tcx>) {
625 let var_ty = self.local_ty(span, var_id).decl_ty;
626 if let Some(mut err) = self.demand_eqtype_pat_diag(span, var_ty, ty, ti) {
627 let hir = self.tcx.hir();
628 let var_ty = self.resolve_vars_with_obligations(var_ty);
629 let msg = format!("first introduced with type `{}` here", var_ty);
630 err.span_label(hir.span(var_id), msg);
631 let in_match = hir.parent_iter(var_id).any(|(_, n)| {
634 hir::Node::Expr(hir::Expr {
635 kind: hir::ExprKind::Match(.., hir::MatchSource::Normal),
640 let pre = if in_match { "in the same arm, " } else { "" };
641 err.note(&format!("{}a binding must have the same type in all alternatives", pre));
646 fn borrow_pat_suggestion(
648 err: &mut Diagnostic,
654 if let PatKind::Binding(..) = inner.kind {
655 let binding_parent_id = tcx.hir().get_parent_node(pat.hir_id);
656 let binding_parent = tcx.hir().get(binding_parent_id);
657 debug!("inner {:?} pat {:?} parent {:?}", inner, pat, binding_parent);
658 match binding_parent {
659 hir::Node::Param(hir::Param { span, .. })
660 if let Ok(snippet) = tcx.sess.source_map().span_to_snippet(inner.span) =>
664 &format!("did you mean `{}`", snippet),
665 format!(" &{}", expected),
666 Applicability::MachineApplicable,
669 hir::Node::Arm(_) | hir::Node::Pat(_) => {
670 // rely on match ergonomics or it might be nested `&&pat`
671 if let Ok(snippet) = tcx.sess.source_map().span_to_snippet(inner.span) {
674 "you can probably remove the explicit borrow",
676 Applicability::MaybeIncorrect,
680 _ => {} // don't provide suggestions in other cases #55175
685 pub fn check_dereferenceable(&self, span: Span, expected: Ty<'tcx>, inner: &Pat<'_>) -> bool {
686 if let PatKind::Binding(..) = inner.kind {
687 if let Some(mt) = self.shallow_resolve(expected).builtin_deref(true) {
688 if let ty::Dynamic(..) = mt.ty.kind() {
689 // This is "x = SomeTrait" being reduced from
690 // "let &x = &SomeTrait" or "let box x = Box<SomeTrait>", an error.
691 let type_str = self.ty_to_string(expected);
692 let mut err = struct_span_err!(
696 "type `{}` cannot be dereferenced",
699 err.span_label(span, format!("type `{}` cannot be dereferenced", type_str));
700 if self.tcx.sess.teach(&err.get_code().unwrap()) {
701 err.note(CANNOT_IMPLICITLY_DEREF_POINTER_TRAIT_OBJ);
713 pat: &'tcx Pat<'tcx>,
714 qpath: &hir::QPath<'_>,
715 fields: &'tcx [hir::PatField<'tcx>],
721 // Resolve the path and check the definition for errors.
722 let Some((variant, pat_ty)) = self.check_struct_path(qpath, pat.hir_id) else {
723 let err = self.tcx.ty_error();
724 for field in fields {
725 let ti = TopInfo { parent_pat: Some(pat), ..ti };
726 self.check_pat(field.pat, err, def_bm, ti);
731 // Type-check the path.
732 self.demand_eqtype_pat(pat.span, expected, pat_ty, ti);
734 // Type-check subpatterns.
735 if self.check_struct_pat_fields(pat_ty, &pat, variant, fields, has_rest_pat, def_bm, ti) {
742 fn check_pat_path<'b>(
745 path_resolution: (Res, Option<Ty<'tcx>>, &'b [hir::PathSegment<'b>]),
751 // We have already resolved the path.
752 let (res, opt_ty, segments) = path_resolution;
755 self.set_tainted_by_errors();
756 return tcx.ty_error();
758 Res::Def(DefKind::AssocFn | DefKind::Ctor(_, CtorKind::Fictive | CtorKind::Fn), _) => {
759 report_unexpected_variant_res(tcx, res, pat.span);
760 return tcx.ty_error();
764 DefKind::Ctor(_, CtorKind::Const)
766 | DefKind::AssocConst
767 | DefKind::ConstParam,
770 _ => bug!("unexpected pattern resolution: {:?}", res),
773 // Type-check the path.
774 let (pat_ty, pat_res) =
775 self.instantiate_value_path(segments, opt_ty, res, pat.span, pat.hir_id);
777 self.demand_suptype_with_origin(&self.pattern_cause(ti, pat.span), expected, pat_ty)
779 self.emit_bad_pat_path(err, pat.span, res, pat_res, pat_ty, segments, ti.parent_pat);
784 fn maybe_suggest_range_literal(
787 opt_def_id: Option<hir::def_id::DefId>,
791 Some(def_id) => match self.tcx.hir().get_if_local(def_id) {
792 Some(hir::Node::Item(hir::Item {
793 kind: hir::ItemKind::Const(_, body_id), ..
794 })) => match self.tcx.hir().get(body_id.hir_id) {
795 hir::Node::Expr(expr) => {
796 if hir::is_range_literal(expr) {
797 let span = self.tcx.hir().span(body_id.hir_id);
798 if let Ok(snip) = self.tcx.sess.source_map().span_to_snippet(span) {
799 e.span_suggestion_verbose(
801 "you may want to move the range into the match block",
803 Applicability::MachineApplicable,
818 fn emit_bad_pat_path<'b>(
820 mut e: DiagnosticBuilder<'_>,
825 segments: &'b [hir::PathSegment<'b>],
826 parent_pat: Option<&Pat<'_>>,
828 if let Some(span) = self.tcx.hir().res_span(pat_res) {
829 e.span_label(span, &format!("{} defined here", res.descr()));
830 if let [hir::PathSegment { ident, .. }] = &*segments {
834 "`{}` is interpreted as {} {}, not a new binding",
841 Some(Pat { kind: hir::PatKind::Struct(..), .. }) => {
842 e.span_suggestion_verbose(
843 ident.span.shrink_to_hi(),
844 "bind the struct field to a different name instead",
845 format!(": other_{}", ident.as_str().to_lowercase()),
846 Applicability::HasPlaceholders,
850 let (type_def_id, item_def_id) = match pat_ty.kind() {
851 Adt(def, _) => match res {
852 Res::Def(DefKind::Const, def_id) => (Some(def.did), Some(def_id)),
859 self.tcx.lang_items().range_struct(),
860 self.tcx.lang_items().range_from_struct(),
861 self.tcx.lang_items().range_to_struct(),
862 self.tcx.lang_items().range_full_struct(),
863 self.tcx.lang_items().range_inclusive_struct(),
864 self.tcx.lang_items().range_to_inclusive_struct(),
866 if type_def_id != None && ranges.contains(&type_def_id) {
867 if !self.maybe_suggest_range_literal(&mut e, item_def_id, *ident) {
868 let msg = "constants only support matching by type, \
869 if you meant to match against a range of values, \
870 consider using a range pattern like `min ..= max` in the match block";
874 let msg = "introduce a new binding instead";
875 let sugg = format!("other_{}", ident.as_str().to_lowercase());
880 Applicability::HasPlaceholders,
890 fn check_pat_tuple_struct(
892 pat: &'tcx Pat<'tcx>,
893 qpath: &'tcx hir::QPath<'tcx>,
894 subpats: &'tcx [Pat<'tcx>],
895 ddpos: Option<usize>,
902 let parent_pat = Some(pat);
904 self.check_pat(pat, tcx.ty_error(), def_bm, TopInfo { parent_pat, ..ti });
907 let report_unexpected_res = |res: Res| {
908 let sm = tcx.sess.source_map();
910 .span_to_snippet(sm.span_until_char(pat.span, '('))
911 .map_or_else(|_| String::new(), |s| format!(" `{}`", s.trim_end()));
913 "expected tuple struct or tuple variant, found {}{}",
918 let mut err = struct_span_err!(tcx.sess, pat.span, E0164, "{}", msg);
920 Res::Def(DefKind::Fn | DefKind::AssocFn, _) => {
921 err.span_label(pat.span, "`fn` calls are not allowed in patterns");
923 "for more information, visit \
924 https://doc.rust-lang.org/book/ch18-00-patterns.html",
928 err.span_label(pat.span, "not a tuple variant or struct");
935 // Resolve the path and check the definition for errors.
936 let (res, opt_ty, segments) =
937 self.resolve_ty_and_res_fully_qualified_call(qpath, pat.hir_id, pat.span);
939 self.set_tainted_by_errors();
941 return self.tcx.ty_error();
944 // Type-check the path.
946 self.instantiate_value_path(segments, opt_ty, res, pat.span, pat.hir_id);
948 report_unexpected_res(res);
949 return tcx.ty_error();
952 let variant = match res {
954 self.set_tainted_by_errors();
956 return tcx.ty_error();
958 Res::Def(DefKind::AssocConst | DefKind::AssocFn, _) => {
959 report_unexpected_res(res);
960 return tcx.ty_error();
962 Res::Def(DefKind::Ctor(_, CtorKind::Fn), _) => tcx.expect_variant_res(res),
963 _ => bug!("unexpected pattern resolution: {:?}", res),
966 // Replace constructor type with constructed type for tuple struct patterns.
967 let pat_ty = pat_ty.fn_sig(tcx).output();
968 let pat_ty = pat_ty.no_bound_vars().expect("expected fn type");
970 // Type-check the tuple struct pattern against the expected type.
971 let diag = self.demand_eqtype_pat_diag(pat.span, expected, pat_ty, ti);
972 let had_err = if let Some(mut err) = diag {
979 // Type-check subpatterns.
980 if subpats.len() == variant.fields.len()
981 || subpats.len() < variant.fields.len() && ddpos.is_some()
983 let ty::Adt(_, substs) = pat_ty.kind() else {
984 bug!("unexpected pattern type {:?}", pat_ty);
986 for (i, subpat) in subpats.iter().enumerate_and_adjust(variant.fields.len(), ddpos) {
987 let field_ty = self.field_ty(subpat.span, &variant.fields[i], substs);
988 self.check_pat(subpat, field_ty, def_bm, TopInfo { parent_pat: Some(pat), ..ti });
990 self.tcx.check_stability(
991 variant.fields[i].did,
998 // Pattern has wrong number of fields.
999 self.e0023(pat.span, res, qpath, subpats, &variant.fields, expected, had_err);
1001 return tcx.ty_error();
1010 qpath: &hir::QPath<'_>,
1011 subpats: &'tcx [Pat<'tcx>],
1012 fields: &'tcx [ty::FieldDef],
1016 let subpats_ending = pluralize!(subpats.len());
1017 let fields_ending = pluralize!(fields.len());
1019 let subpat_spans = if subpats.is_empty() {
1022 subpats.iter().map(|p| p.span).collect()
1024 let last_subpat_span = *subpat_spans.last().unwrap();
1025 let res_span = self.tcx.def_span(res.def_id());
1026 let def_ident_span = self.tcx.def_ident_span(res.def_id()).unwrap_or(res_span);
1027 let field_def_spans = if fields.is_empty() {
1030 fields.iter().map(|f| f.ident(self.tcx).span).collect()
1032 let last_field_def_span = *field_def_spans.last().unwrap();
1034 let mut err = struct_span_err!(
1036 MultiSpan::from_spans(subpat_spans),
1038 "this pattern has {} field{}, but the corresponding {} has {} field{}",
1047 &format!("expected {} field{}, found {}", fields.len(), fields_ending, subpats.len()),
1049 if self.tcx.sess.source_map().is_multiline(qpath.span().between(last_subpat_span)) {
1050 err.span_label(qpath.span(), "");
1052 if self.tcx.sess.source_map().is_multiline(def_ident_span.between(last_field_def_span)) {
1053 err.span_label(def_ident_span, format!("{} defined here", res.descr()));
1055 for span in &field_def_spans[..field_def_spans.len() - 1] {
1056 err.span_label(*span, "");
1059 last_field_def_span,
1060 &format!("{} has {} field{}", res.descr(), fields.len(), fields_ending),
1063 // Identify the case `Some(x, y)` where the expected type is e.g. `Option<(T, U)>`.
1064 // More generally, the expected type wants a tuple variant with one field of an
1065 // N-arity-tuple, e.g., `V_i((p_0, .., p_N))`. Meanwhile, the user supplied a pattern
1066 // with the subpatterns directly in the tuple variant pattern, e.g., `V_i(p_0, .., p_N)`.
1067 let missing_parentheses = match (&expected.kind(), fields, had_err) {
1068 // #67037: only do this if we could successfully type-check the expected type against
1069 // the tuple struct pattern. Otherwise the substs could get out of range on e.g.,
1070 // `let P() = U;` where `P != U` with `struct P<T>(T);`.
1071 (ty::Adt(_, substs), [field], false) => {
1072 let field_ty = self.field_ty(pat_span, field, substs);
1073 match field_ty.kind() {
1074 ty::Tuple(fields) => fields.len() == subpats.len(),
1080 if missing_parentheses {
1081 let (left, right) = match subpats {
1082 // This is the zero case; we aim to get the "hi" part of the `QPath`'s
1083 // span as the "lo" and then the "hi" part of the pattern's span as the "hi".
1086 // help: missing parentheses
1088 // L | let A(()) = A(());
1090 [] => (qpath.span().shrink_to_hi(), pat_span),
1091 // Easy case. Just take the "lo" of the first sub-pattern and the "hi" of the
1092 // last sub-pattern. In the case of `A(x)` the first and last may coincide.
1095 // help: missing parentheses
1097 // L | let A((x, y)) = A((1, 2));
1099 [first, ..] => (first.span.shrink_to_lo(), subpats.last().unwrap().span),
1101 err.multipart_suggestion(
1102 "missing parentheses",
1103 vec![(left, "(".to_string()), (right.shrink_to_hi(), ")".to_string())],
1104 Applicability::MachineApplicable,
1106 } else if fields.len() > subpats.len() && pat_span != DUMMY_SP {
1107 let after_fields_span = pat_span.with_hi(pat_span.hi() - BytePos(1)).shrink_to_hi();
1108 let all_fields_span = match subpats {
1109 [] => after_fields_span,
1110 [field] => field.span,
1111 [first, .., last] => first.span.to(last.span),
1114 // Check if all the fields in the pattern are wildcards.
1115 let all_wildcards = subpats.iter().all(|pat| matches!(pat.kind, PatKind::Wild));
1116 let first_tail_wildcard =
1117 subpats.iter().enumerate().fold(None, |acc, (pos, pat)| match (acc, &pat.kind) {
1118 (None, PatKind::Wild) => Some(pos),
1119 (Some(_), PatKind::Wild) => acc,
1122 let tail_span = match first_tail_wildcard {
1123 None => after_fields_span,
1124 Some(0) => subpats[0].span.to(after_fields_span),
1125 Some(pos) => subpats[pos - 1].span.shrink_to_hi().to(after_fields_span),
1128 // FIXME: heuristic-based suggestion to check current types for where to add `_`.
1129 let mut wildcard_sugg = vec!["_"; fields.len() - subpats.len()].join(", ");
1130 if !subpats.is_empty() {
1131 wildcard_sugg = String::from(", ") + &wildcard_sugg;
1134 err.span_suggestion_verbose(
1136 "use `_` to explicitly ignore each field",
1138 Applicability::MaybeIncorrect,
1141 // Only suggest `..` if more than one field is missing
1142 // or the pattern consists of all wildcards.
1143 if fields.len() - subpats.len() > 1 || all_wildcards {
1144 if subpats.is_empty() || all_wildcards {
1145 err.span_suggestion_verbose(
1147 "use `..` to ignore all fields",
1149 Applicability::MaybeIncorrect,
1152 err.span_suggestion_verbose(
1154 "use `..` to ignore the rest of the fields",
1155 String::from(", .."),
1156 Applicability::MaybeIncorrect,
1168 elements: &'tcx [Pat<'tcx>],
1169 ddpos: Option<usize>,
1171 def_bm: BindingMode,
1175 let mut expected_len = elements.len();
1176 if ddpos.is_some() {
1177 // Require known type only when `..` is present.
1178 if let ty::Tuple(tys) = self.structurally_resolved_type(span, expected).kind() {
1179 expected_len = tys.len();
1182 let max_len = cmp::max(expected_len, elements.len());
1184 let element_tys_iter = (0..max_len).map(|_| {
1186 // FIXME: `MiscVariable` for now -- obtaining the span and name information
1187 // from all tuple elements isn't trivial.
1188 TypeVariableOrigin { kind: TypeVariableOriginKind::TypeInference, span },
1191 let element_tys = tcx.mk_type_list(element_tys_iter);
1192 let pat_ty = tcx.mk_ty(ty::Tuple(element_tys));
1193 if let Some(mut err) = self.demand_eqtype_pat_diag(span, expected, pat_ty, ti) {
1195 // Walk subpatterns with an expected type of `err` in this case to silence
1196 // further errors being emitted when using the bindings. #50333
1197 let element_tys_iter = (0..max_len).map(|_| tcx.ty_error());
1198 for (_, elem) in elements.iter().enumerate_and_adjust(max_len, ddpos) {
1199 self.check_pat(elem, tcx.ty_error(), def_bm, ti);
1201 tcx.mk_tup(element_tys_iter)
1203 for (i, elem) in elements.iter().enumerate_and_adjust(max_len, ddpos) {
1204 self.check_pat(elem, element_tys[i], def_bm, ti);
1210 fn check_struct_pat_fields(
1213 pat: &'tcx Pat<'tcx>,
1214 variant: &'tcx ty::VariantDef,
1215 fields: &'tcx [hir::PatField<'tcx>],
1217 def_bm: BindingMode,
1222 let ty::Adt(adt, substs) = adt_ty.kind() else {
1223 span_bug!(pat.span, "struct pattern is not an ADT");
1226 // Index the struct fields' types.
1227 let field_map = variant
1231 .map(|(i, field)| (field.ident(self.tcx).normalize_to_macros_2_0(), (i, field)))
1232 .collect::<FxHashMap<_, _>>();
1234 // Keep track of which fields have already appeared in the pattern.
1235 let mut used_fields = FxHashMap::default();
1236 let mut no_field_errors = true;
1238 let mut inexistent_fields = vec![];
1239 // Typecheck each field.
1240 for field in fields {
1241 let span = field.span;
1242 let ident = tcx.adjust_ident(field.ident, variant.def_id);
1243 let field_ty = match used_fields.entry(ident) {
1244 Occupied(occupied) => {
1245 self.error_field_already_bound(span, field.ident, *occupied.get());
1246 no_field_errors = false;
1250 vacant.insert(span);
1254 self.write_field_index(field.hir_id, *i);
1255 self.tcx.check_stability(f.did, Some(pat.hir_id), span, None);
1256 self.field_ty(span, f, substs)
1258 .unwrap_or_else(|| {
1259 inexistent_fields.push(field.ident);
1260 no_field_errors = false;
1266 self.check_pat(field.pat, field_ty, def_bm, TopInfo { parent_pat: Some(pat), ..ti });
1269 let mut unmentioned_fields = variant
1272 .map(|field| (field, field.ident(self.tcx).normalize_to_macros_2_0()))
1273 .filter(|(_, ident)| !used_fields.contains_key(ident))
1274 .collect::<Vec<_>>();
1276 let inexistent_fields_err = if !(inexistent_fields.is_empty() || variant.is_recovered()) {
1277 Some(self.error_inexistent_fields(
1278 adt.variant_descr(),
1280 &mut unmentioned_fields,
1287 // Require `..` if struct has non_exhaustive attribute.
1288 let non_exhaustive = variant.is_field_list_non_exhaustive() && !adt.did.is_local();
1289 if non_exhaustive && !has_rest_pat {
1290 self.error_foreign_non_exhaustive_spat(pat, adt.variant_descr(), fields.is_empty());
1293 let mut unmentioned_err = None;
1294 // Report an error if an incorrect number of fields was specified.
1296 if fields.len() != 1 {
1298 .struct_span_err(pat.span, "union patterns should have exactly one field")
1302 tcx.sess.struct_span_err(pat.span, "`..` cannot be used in union patterns").emit();
1304 } else if !unmentioned_fields.is_empty() {
1305 let accessible_unmentioned_fields: Vec<_> = unmentioned_fields
1308 .filter(|(field, _)| {
1309 field.vis.is_accessible_from(tcx.parent_module(pat.hir_id).to_def_id(), tcx)
1314 if accessible_unmentioned_fields.is_empty() {
1315 unmentioned_err = Some(self.error_no_accessible_fields(pat, fields));
1317 unmentioned_err = Some(self.error_unmentioned_fields(
1319 &accessible_unmentioned_fields,
1320 accessible_unmentioned_fields.len() != unmentioned_fields.len(),
1324 } else if non_exhaustive && !accessible_unmentioned_fields.is_empty() {
1325 self.lint_non_exhaustive_omitted_patterns(
1327 &accessible_unmentioned_fields,
1332 match (inexistent_fields_err, unmentioned_err) {
1333 (Some(mut i), Some(mut u)) => {
1334 if let Some(mut e) = self.error_tuple_variant_as_struct_pat(pat, fields, variant) {
1335 // We don't want to show the inexistent fields error when this was
1336 // `Foo { a, b }` when it should have been `Foo(a, b)`.
1345 (None, Some(mut u)) => {
1346 if let Some(mut e) = self.error_tuple_variant_as_struct_pat(pat, fields, variant) {
1353 (Some(mut err), None) => {
1356 (None, None) if let Some(mut err) =
1357 self.error_tuple_variant_index_shorthand(variant, pat, fields) =>
1366 fn error_tuple_variant_index_shorthand(
1368 variant: &VariantDef,
1370 fields: &[hir::PatField<'_>],
1371 ) -> Option<DiagnosticBuilder<'_>> {
1372 // if this is a tuple struct, then all field names will be numbers
1373 // so if any fields in a struct pattern use shorthand syntax, they will
1374 // be invalid identifiers (for example, Foo { 0, 1 }).
1375 if let (CtorKind::Fn, PatKind::Struct(qpath, field_patterns, ..)) =
1376 (variant.ctor_kind, &pat.kind)
1378 let has_shorthand_field_name = field_patterns.iter().any(|field| field.is_shorthand);
1379 if has_shorthand_field_name {
1380 let path = rustc_hir_pretty::to_string(rustc_hir_pretty::NO_ANN, |s| {
1381 s.print_qpath(qpath, false)
1383 let mut err = struct_span_err!(
1387 "tuple variant `{}` written as struct variant",
1390 err.span_suggestion_verbose(
1391 qpath.span().shrink_to_hi().to(pat.span.shrink_to_hi()),
1392 "use the tuple variant pattern syntax instead",
1393 format!("({})", self.get_suggested_tuple_struct_pattern(fields, variant)),
1394 Applicability::MaybeIncorrect,
1402 fn error_foreign_non_exhaustive_spat(&self, pat: &Pat<'_>, descr: &str, no_fields: bool) {
1403 let sess = self.tcx.sess;
1404 let sm = sess.source_map();
1405 let sp_brace = sm.end_point(pat.span);
1406 let sp_comma = sm.end_point(pat.span.with_hi(sp_brace.hi()));
1407 let sugg = if no_fields || sp_brace != sp_comma { ".. }" } else { ", .. }" };
1409 let mut err = struct_span_err!(
1413 "`..` required with {} marked as non-exhaustive",
1416 err.span_suggestion_verbose(
1418 "add `..` at the end of the field list to ignore all other fields",
1420 Applicability::MachineApplicable,
1425 fn error_field_already_bound(&self, span: Span, ident: Ident, other_field: Span) {
1430 "field `{}` bound multiple times in the pattern",
1433 .span_label(span, format!("multiple uses of `{}` in pattern", ident))
1434 .span_label(other_field, format!("first use of `{}`", ident))
1438 fn error_inexistent_fields(
1441 inexistent_fields: &[Ident],
1442 unmentioned_fields: &mut Vec<(&ty::FieldDef, Ident)>,
1443 variant: &ty::VariantDef,
1444 ) -> DiagnosticBuilder<'tcx> {
1446 let (field_names, t, plural) = if inexistent_fields.len() == 1 {
1447 (format!("a field named `{}`", inexistent_fields[0]), "this", "")
1454 .map(|ident| format!("`{}`", ident))
1455 .collect::<Vec<String>>()
1462 let spans = inexistent_fields.iter().map(|ident| ident.span).collect::<Vec<_>>();
1463 let mut err = struct_span_err!(
1467 "{} `{}` does not have {}",
1469 tcx.def_path_str(variant.def_id),
1472 if let Some(ident) = inexistent_fields.last() {
1476 "{} `{}` does not have {} field{}",
1478 tcx.def_path_str(variant.def_id),
1484 if unmentioned_fields.len() == 1 {
1486 unmentioned_fields.iter().map(|(_, field)| field.name).collect::<Vec<_>>();
1487 let suggested_name = find_best_match_for_name(&input, ident.name, None);
1488 if let Some(suggested_name) = suggested_name {
1489 err.span_suggestion(
1491 "a field with a similar name exists",
1492 suggested_name.to_string(),
1493 Applicability::MaybeIncorrect,
1496 // When we have a tuple struct used with struct we don't want to suggest using
1497 // the (valid) struct syntax with numeric field names. Instead we want to
1498 // suggest the expected syntax. We infer that this is the case by parsing the
1499 // `Ident` into an unsized integer. The suggestion will be emitted elsewhere in
1500 // `smart_resolve_context_dependent_help`.
1501 if suggested_name.to_ident_string().parse::<usize>().is_err() {
1502 // We don't want to throw `E0027` in case we have thrown `E0026` for them.
1503 unmentioned_fields.retain(|&(_, x)| x.name != suggested_name);
1505 } else if inexistent_fields.len() == 1 {
1506 let unmentioned_field = unmentioned_fields[0].1.name;
1507 err.span_suggestion_short(
1510 "`{}` has a field named `{}`",
1511 tcx.def_path_str(variant.def_id),
1514 unmentioned_field.to_string(),
1515 Applicability::MaybeIncorrect,
1520 if tcx.sess.teach(&err.get_code().unwrap()) {
1522 "This error indicates that a struct pattern attempted to \
1523 extract a non-existent field from a struct. Struct fields \
1524 are identified by the name used before the colon : so struct \
1525 patterns should resemble the declaration of the struct type \
1527 If you are using shorthand field patterns but want to refer \
1528 to the struct field by a different name, you should rename \
1535 fn error_tuple_variant_as_struct_pat(
1538 fields: &'tcx [hir::PatField<'tcx>],
1539 variant: &ty::VariantDef,
1540 ) -> Option<DiagnosticBuilder<'tcx>> {
1541 if let (CtorKind::Fn, PatKind::Struct(qpath, ..)) = (variant.ctor_kind, &pat.kind) {
1542 let path = rustc_hir_pretty::to_string(rustc_hir_pretty::NO_ANN, |s| {
1543 s.print_qpath(qpath, false)
1545 let mut err = struct_span_err!(
1549 "tuple variant `{}` written as struct variant",
1552 let (sugg, appl) = if fields.len() == variant.fields.len() {
1554 self.get_suggested_tuple_struct_pattern(fields, variant),
1555 Applicability::MachineApplicable,
1559 variant.fields.iter().map(|_| "_").collect::<Vec<&str>>().join(", "),
1560 Applicability::MaybeIncorrect,
1563 err.span_suggestion_verbose(
1564 qpath.span().shrink_to_hi().to(pat.span.shrink_to_hi()),
1565 "use the tuple variant pattern syntax instead",
1566 format!("({})", sugg),
1574 fn get_suggested_tuple_struct_pattern(
1576 fields: &[hir::PatField<'_>],
1577 variant: &VariantDef,
1579 let variant_field_idents =
1580 variant.fields.iter().map(|f| f.ident(self.tcx)).collect::<Vec<Ident>>();
1584 match self.tcx.sess.source_map().span_to_snippet(field.pat.span) {
1586 // Field names are numbers, but numbers
1587 // are not valid identifiers
1588 if variant_field_idents.contains(&field.ident) {
1594 Err(_) => rustc_hir_pretty::to_string(rustc_hir_pretty::NO_ANN, |s| {
1595 s.print_pat(field.pat)
1599 .collect::<Vec<String>>()
1603 /// Returns a diagnostic reporting a struct pattern which is missing an `..` due to
1604 /// inaccessible fields.
1607 /// error: pattern requires `..` due to inaccessible fields
1608 /// --> src/main.rs:10:9
1610 /// LL | let foo::Foo {} = foo::Foo::default();
1613 /// help: add a `..`
1615 /// LL | let foo::Foo { .. } = foo::Foo::default();
1618 fn error_no_accessible_fields(
1621 fields: &'tcx [hir::PatField<'tcx>],
1622 ) -> DiagnosticBuilder<'tcx> {
1626 .struct_span_err(pat.span, "pattern requires `..` due to inaccessible fields");
1628 if let Some(field) = fields.last() {
1629 err.span_suggestion_verbose(
1630 field.span.shrink_to_hi(),
1631 "ignore the inaccessible and unused fields",
1633 Applicability::MachineApplicable,
1636 let qpath_span = if let PatKind::Struct(qpath, ..) = &pat.kind {
1639 bug!("`error_no_accessible_fields` called on non-struct pattern");
1642 // Shrink the span to exclude the `foo:Foo` in `foo::Foo { }`.
1643 let span = pat.span.with_lo(qpath_span.shrink_to_hi().hi());
1644 err.span_suggestion_verbose(
1646 "ignore the inaccessible and unused fields",
1647 " { .. }".to_string(),
1648 Applicability::MachineApplicable,
1654 /// Report that a pattern for a `#[non_exhaustive]` struct marked with `non_exhaustive_omitted_patterns`
1655 /// is not exhaustive enough.
1657 /// Nb: the partner lint for enums lives in `compiler/rustc_mir_build/src/thir/pattern/usefulness.rs`.
1658 fn lint_non_exhaustive_omitted_patterns(
1661 unmentioned_fields: &[(&ty::FieldDef, Ident)],
1664 fn joined_uncovered_patterns(witnesses: &[&Ident]) -> String {
1665 const LIMIT: usize = 3;
1668 [witness] => format!("`{}`", witness),
1669 [head @ .., tail] if head.len() < LIMIT => {
1670 let head: Vec<_> = head.iter().map(<_>::to_string).collect();
1671 format!("`{}` and `{}`", head.join("`, `"), tail)
1674 let (head, tail) = witnesses.split_at(LIMIT);
1675 let head: Vec<_> = head.iter().map(<_>::to_string).collect();
1676 format!("`{}` and {} more", head.join("`, `"), tail.len())
1680 let joined_patterns = joined_uncovered_patterns(
1681 &unmentioned_fields.iter().map(|(_, i)| i).collect::<Vec<_>>(),
1684 self.tcx.struct_span_lint_hir(NON_EXHAUSTIVE_OMITTED_PATTERNS, pat.hir_id, pat.span, |build| {
1685 let mut lint = build.build("some fields are not explicitly listed");
1686 lint.span_label(pat.span, format!("field{} {} not listed", rustc_errors::pluralize!(unmentioned_fields.len()), joined_patterns));
1689 "ensure that all fields are mentioned explicitly by adding the suggested fields",
1692 "the pattern is of type `{}` and the `non_exhaustive_omitted_patterns` attribute was found",
1699 /// Returns a diagnostic reporting a struct pattern which does not mention some fields.
1702 /// error[E0027]: pattern does not mention field `bar`
1703 /// --> src/main.rs:15:9
1705 /// LL | let foo::Foo {} = foo::Foo::new();
1706 /// | ^^^^^^^^^^^ missing field `bar`
1708 fn error_unmentioned_fields(
1711 unmentioned_fields: &[(&ty::FieldDef, Ident)],
1712 have_inaccessible_fields: bool,
1713 fields: &'tcx [hir::PatField<'tcx>],
1714 ) -> DiagnosticBuilder<'tcx> {
1715 let inaccessible = if have_inaccessible_fields { " and inaccessible fields" } else { "" };
1716 let field_names = if unmentioned_fields.len() == 1 {
1717 format!("field `{}`{}", unmentioned_fields[0].1, inaccessible)
1719 let fields = unmentioned_fields
1721 .map(|(_, name)| format!("`{}`", name))
1722 .collect::<Vec<String>>()
1724 format!("fields {}{}", fields, inaccessible)
1726 let mut err = struct_span_err!(
1730 "pattern does not mention {}",
1733 err.span_label(pat.span, format!("missing {}", field_names));
1734 let len = unmentioned_fields.len();
1735 let (prefix, postfix, sp) = match fields {
1736 [] => match &pat.kind {
1737 PatKind::Struct(path, [], false) => {
1738 (" { ", " }", path.span().shrink_to_hi().until(pat.span.shrink_to_hi()))
1743 // Account for last field having a trailing comma or parse recovery at the tail of
1744 // the pattern to avoid invalid suggestion (#78511).
1745 let tail = field.span.shrink_to_hi().with_hi(pat.span.hi());
1747 PatKind::Struct(..) => (", ", " }", tail),
1752 err.span_suggestion(
1755 "include the missing field{} in the pattern{}",
1756 if len == 1 { "" } else { "s" },
1757 if have_inaccessible_fields { " and ignore the inaccessible fields" } else { "" }
1764 .map(|(_, name)| name.to_string())
1765 .collect::<Vec<_>>()
1767 if have_inaccessible_fields { ", .." } else { "" },
1770 Applicability::MachineApplicable,
1772 err.span_suggestion(
1775 "if you don't care about {} missing field{}, you can explicitly ignore {}",
1776 if len == 1 { "this" } else { "these" },
1777 if len == 1 { "" } else { "s" },
1778 if len == 1 { "it" } else { "them" },
1780 format!("{}..{}", prefix, postfix),
1781 Applicability::MachineApplicable,
1789 inner: &'tcx Pat<'tcx>,
1791 def_bm: BindingMode,
1795 let (box_ty, inner_ty) = if self.check_dereferenceable(span, expected, inner) {
1796 // Here, `demand::subtype` is good enough, but I don't
1797 // think any errors can be introduced by using `demand::eqtype`.
1798 let inner_ty = self.next_ty_var(TypeVariableOrigin {
1799 kind: TypeVariableOriginKind::TypeInference,
1802 let box_ty = tcx.mk_box(inner_ty);
1803 self.demand_eqtype_pat(span, expected, box_ty, ti);
1806 let err = tcx.ty_error();
1809 self.check_pat(inner, inner_ty, def_bm, ti);
1815 pat: &'tcx Pat<'tcx>,
1816 inner: &'tcx Pat<'tcx>,
1817 mutbl: hir::Mutability,
1819 def_bm: BindingMode,
1823 let expected = self.shallow_resolve(expected);
1824 let (rptr_ty, inner_ty) = if self.check_dereferenceable(pat.span, expected, inner) {
1825 // `demand::subtype` would be good enough, but using `eqtype` turns
1826 // out to be equally general. See (note_1) for details.
1828 // Take region, inner-type from expected type if we can,
1829 // to avoid creating needless variables. This also helps with
1830 // the bad interactions of the given hack detailed in (note_1).
1831 debug!("check_pat_ref: expected={:?}", expected);
1832 match *expected.kind() {
1833 ty::Ref(_, r_ty, r_mutbl) if r_mutbl == mutbl => (expected, r_ty),
1835 let inner_ty = self.next_ty_var(TypeVariableOrigin {
1836 kind: TypeVariableOriginKind::TypeInference,
1839 let rptr_ty = self.new_ref_ty(pat.span, mutbl, inner_ty);
1840 debug!("check_pat_ref: demanding {:?} = {:?}", expected, rptr_ty);
1841 let err = self.demand_eqtype_pat_diag(pat.span, expected, rptr_ty, ti);
1843 // Look for a case like `fn foo(&foo: u32)` and suggest
1844 // `fn foo(foo: &u32)`
1845 if let Some(mut err) = err {
1846 self.borrow_pat_suggestion(&mut err, pat, inner, expected);
1853 let err = tcx.ty_error();
1856 self.check_pat(inner, inner_ty, def_bm, TopInfo { parent_pat: Some(pat), ..ti });
1860 /// Create a reference type with a fresh region variable.
1861 fn new_ref_ty(&self, span: Span, mutbl: hir::Mutability, ty: Ty<'tcx>) -> Ty<'tcx> {
1862 let region = self.next_region_var(infer::PatternRegion(span));
1863 let mt = ty::TypeAndMut { ty, mutbl };
1864 self.tcx.mk_ref(region, mt)
1867 /// Type check a slice pattern.
1869 /// Syntactically, these look like `[pat_0, ..., pat_n]`.
1870 /// Semantically, we are type checking a pattern with structure:
1872 /// [before_0, ..., before_n, (slice, after_0, ... after_n)?]
1874 /// The type of `slice`, if it is present, depends on the `expected` type.
1875 /// If `slice` is missing, then so is `after_i`.
1876 /// If `slice` is present, it can still represent 0 elements.
1880 before: &'tcx [Pat<'tcx>],
1881 slice: Option<&'tcx Pat<'tcx>>,
1882 after: &'tcx [Pat<'tcx>],
1884 def_bm: BindingMode,
1887 let expected = self.structurally_resolved_type(span, expected);
1888 let (element_ty, opt_slice_ty, inferred) = match *expected.kind() {
1889 // An array, so we might have something like `let [a, b, c] = [0, 1, 2];`.
1890 ty::Array(element_ty, len) => {
1891 let min = before.len() as u64 + after.len() as u64;
1892 let (opt_slice_ty, expected) =
1893 self.check_array_pat_len(span, element_ty, expected, slice, len, min);
1894 // `opt_slice_ty.is_none()` => `slice.is_none()`.
1895 // Note, though, that opt_slice_ty could be `Some(error_ty)`.
1896 assert!(opt_slice_ty.is_some() || slice.is_none());
1897 (element_ty, opt_slice_ty, expected)
1899 ty::Slice(element_ty) => (element_ty, Some(expected), expected),
1900 // The expected type must be an array or slice, but was neither, so error.
1902 if !expected.references_error() {
1903 self.error_expected_array_or_slice(span, expected, ti);
1905 let err = self.tcx.ty_error();
1906 (err, Some(err), err)
1910 // Type check all the patterns before `slice`.
1912 self.check_pat(elt, element_ty, def_bm, ti);
1914 // Type check the `slice`, if present, against its expected type.
1915 if let Some(slice) = slice {
1916 self.check_pat(slice, opt_slice_ty.unwrap(), def_bm, ti);
1918 // Type check the elements after `slice`, if present.
1920 self.check_pat(elt, element_ty, def_bm, ti);
1925 /// Type check the length of an array pattern.
1927 /// Returns both the type of the variable length pattern (or `None`), and the potentially
1928 /// inferred array type. We only return `None` for the slice type if `slice.is_none()`.
1929 fn check_array_pat_len(
1932 element_ty: Ty<'tcx>,
1934 slice: Option<&'tcx Pat<'tcx>>,
1935 len: ty::Const<'tcx>,
1937 ) -> (Option<Ty<'tcx>>, Ty<'tcx>) {
1938 if let Some(len) = len.try_eval_usize(self.tcx, self.param_env) {
1939 // Now we know the length...
1940 if slice.is_none() {
1941 // ...and since there is no variable-length pattern,
1942 // we require an exact match between the number of elements
1943 // in the array pattern and as provided by the matched type.
1945 return (None, arr_ty);
1948 self.error_scrutinee_inconsistent_length(span, min_len, len);
1949 } else if let Some(pat_len) = len.checked_sub(min_len) {
1950 // The variable-length pattern was there,
1951 // so it has an array type with the remaining elements left as its size...
1952 return (Some(self.tcx.mk_array(element_ty, pat_len)), arr_ty);
1954 // ...however, in this case, there were no remaining elements.
1955 // That is, the slice pattern requires more than the array type offers.
1956 self.error_scrutinee_with_rest_inconsistent_length(span, min_len, len);
1958 } else if slice.is_none() {
1959 // We have a pattern with a fixed length,
1960 // which we can use to infer the length of the array.
1961 let updated_arr_ty = self.tcx.mk_array(element_ty, min_len);
1962 self.demand_eqtype(span, updated_arr_ty, arr_ty);
1963 return (None, updated_arr_ty);
1965 // We have a variable-length pattern and don't know the array length.
1966 // This happens if we have e.g.,
1967 // `let [a, b, ..] = arr` where `arr: [T; N]` where `const N: usize`.
1968 self.error_scrutinee_unfixed_length(span);
1971 // If we get here, we must have emitted an error.
1972 (Some(self.tcx.ty_error()), arr_ty)
1975 fn error_scrutinee_inconsistent_length(&self, span: Span, min_len: u64, size: u64) {
1980 "pattern requires {} element{} but array has {}",
1982 pluralize!(min_len),
1985 .span_label(span, format!("expected {} element{}", size, pluralize!(size)))
1989 fn error_scrutinee_with_rest_inconsistent_length(&self, span: Span, min_len: u64, size: u64) {
1994 "pattern requires at least {} element{} but array has {}",
1996 pluralize!(min_len),
2001 format!("pattern cannot match array of {} element{}", size, pluralize!(size),),
2006 fn error_scrutinee_unfixed_length(&self, span: Span) {
2011 "cannot pattern-match on an array without a fixed length",
2016 fn error_expected_array_or_slice(&self, span: Span, expected_ty: Ty<'tcx>, ti: TopInfo<'tcx>) {
2017 let mut err = struct_span_err!(
2021 "expected an array or slice, found `{}`",
2024 if let ty::Ref(_, ty, _) = expected_ty.kind() {
2025 if let ty::Array(..) | ty::Slice(..) = ty.kind() {
2026 err.help("the semantics of slice patterns changed recently; see issue #62254");
2028 } else if Autoderef::new(&self.infcx, self.param_env, self.body_id, span, expected_ty, span)
2029 .any(|(ty, _)| matches!(ty.kind(), ty::Slice(..) | ty::Array(..)))
2031 if let (Some(span), true) = (ti.span, ti.origin_expr) {
2032 if let Ok(snippet) = self.tcx.sess.source_map().span_to_snippet(span) {
2033 let applicability = Autoderef::new(
2038 self.resolve_vars_if_possible(ti.expected),
2041 .find_map(|(ty, _)| {
2044 if self.tcx.is_diagnostic_item(sym::Option, adt_def.did)
2045 || self.tcx.is_diagnostic_item(sym::Result, adt_def.did) =>
2047 // Slicing won't work here, but `.as_deref()` might (issue #91328).
2048 err.span_suggestion(
2050 "consider using `as_deref` here",
2051 format!("{}.as_deref()", snippet),
2052 Applicability::MaybeIncorrect,
2057 ty::Slice(..) | ty::Array(..) => {
2058 Some(Some(Applicability::MachineApplicable))
2064 .unwrap_or(Some(Applicability::MaybeIncorrect));
2066 if let Some(applicability) = applicability {
2067 err.span_suggestion(
2069 "consider slicing here",
2070 format!("{}[..]", snippet),
2077 err.span_label(span, format!("pattern cannot match with input type `{}`", expected_ty));