1 use crate::check::FnCtxt;
4 use rustc_data_structures::fx::FxHashMap;
5 use rustc_errors::{pluralize, struct_span_err, Applicability, 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::subst::GenericArg;
13 use rustc_middle::ty::{self, Adt, BindingMode, Ty, TypeFoldable};
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::Ident;
18 use rustc_span::{BytePos, DUMMY_SP};
19 use rustc_trait_selection::traits::{ObligationCause, Pattern};
23 use std::collections::hash_map::Entry::{Occupied, Vacant};
25 use super::report_unexpected_variant_res;
27 const CANNOT_IMPLICITLY_DEREF_POINTER_TRAIT_OBJ: &str = "\
28 This error indicates that a pointer to a trait type cannot be implicitly dereferenced by a \
29 pattern. Every trait defines a type, but because the size of trait implementors isn't fixed, \
30 this type has no compile-time size. Therefore, all accesses to trait types must be through \
31 pointers. If you encounter this error you should try to avoid dereferencing the pointer.
33 You can read more about trait objects in the Trait Objects section of the Reference: \
34 https://doc.rust-lang.org/reference/types.html#trait-objects";
36 /// Information about the expected type at the top level of type checking a pattern.
38 /// **NOTE:** This is only for use by diagnostics. Do NOT use for type checking logic!
39 #[derive(Copy, Clone)]
40 struct TopInfo<'tcx> {
41 /// The `expected` type at the top level of type checking a pattern.
43 /// Was the origin of the `span` from a scrutinee expression?
45 /// Otherwise there is no scrutinee and it could be e.g. from the type of a formal parameter.
47 /// The span giving rise to the `expected` type, if one could be provided.
49 /// If `origin_expr` is `true`, then this is the span of the scrutinee as in:
51 /// - `match scrutinee { ... }`
52 /// - `let _ = scrutinee;`
54 /// This is used to point to add context in type errors.
55 /// In the following example, `span` corresponds to the `a + b` expression:
58 /// error[E0308]: mismatched types
59 /// --> src/main.rs:L:C
61 /// L | let temp: usize = match a + b {
62 /// | ----- this expression has type `usize`
63 /// L | Ok(num) => num,
64 /// | ^^^^^^^ expected `usize`, found enum `std::result::Result`
66 /// = note: expected type `usize`
67 /// found type `std::result::Result<_, _>`
70 /// This refers to the parent pattern. Used to provide extra diagnostic information on errors.
72 /// error[E0308]: mismatched types
73 /// --> $DIR/const-in-struct-pat.rs:8:17
76 /// | --------- unit struct defined here
78 /// L | let Thing { f } = t;
81 /// | expected struct `std::string::String`, found struct `f`
82 /// | `f` is interpreted as a unit struct, not a new binding
83 /// | help: bind the struct field to a different name instead: `f: other_f`
85 parent_pat: Option<&'tcx Pat<'tcx>>,
88 impl<'tcx> FnCtxt<'_, 'tcx> {
89 fn pattern_cause(&self, ti: TopInfo<'tcx>, cause_span: Span) -> ObligationCause<'tcx> {
90 let code = Pattern { span: ti.span, root_ty: ti.expected, origin_expr: ti.origin_expr };
91 self.cause(cause_span, code)
94 fn demand_eqtype_pat_diag(
100 ) -> Option<DiagnosticBuilder<'tcx>> {
101 self.demand_eqtype_with_origin(&self.pattern_cause(ti, cause_span), expected, actual)
104 fn demand_eqtype_pat(
111 if let Some(mut err) = self.demand_eqtype_pat_diag(cause_span, expected, actual, ti) {
117 const INITIAL_BM: BindingMode = BindingMode::BindByValue(hir::Mutability::Not);
119 /// Mode for adjusting the expected type and binding mode.
121 /// Peel off all immediate reference types.
123 /// Reset binding mode to the initial mode.
125 /// Pass on the input binding mode and expected type.
129 impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
130 /// Type check the given top level pattern against the `expected` type.
132 /// If a `Some(span)` is provided and `origin_expr` holds,
133 /// then the `span` represents the scrutinee's span.
134 /// The scrutinee is found in e.g. `match scrutinee { ... }` and `let pat = scrutinee;`.
136 /// Otherwise, `Some(span)` represents the span of a type expression
137 /// which originated the `expected` type.
138 pub fn check_pat_top(
140 pat: &'tcx Pat<'tcx>,
145 let info = TopInfo { expected, origin_expr, span, parent_pat: None };
146 self.check_pat(pat, expected, INITIAL_BM, info);
149 /// Type check the given `pat` against the `expected` type
150 /// with the provided `def_bm` (default binding mode).
152 /// Outside of this module, `check_pat_top` should always be used.
153 /// Conversely, inside this module, `check_pat_top` should never be used.
154 #[instrument(level = "debug", skip(self, ti))]
157 pat: &'tcx Pat<'tcx>,
162 let path_res = match &pat.kind {
163 PatKind::Path(qpath) => Some(self.resolve_ty_and_res_ufcs(qpath, pat.hir_id, pat.span)),
166 let adjust_mode = self.calc_adjust_mode(pat, path_res.map(|(res, ..)| res));
167 let (expected, def_bm) = self.calc_default_binding_mode(pat, expected, def_bm, adjust_mode);
169 let ty = match pat.kind {
170 PatKind::Wild => expected,
171 PatKind::Lit(lt) => self.check_pat_lit(pat.span, lt, expected, ti),
172 PatKind::Range(lhs, rhs, _) => self.check_pat_range(pat.span, lhs, rhs, expected, ti),
173 PatKind::Binding(ba, var_id, _, sub) => {
174 self.check_pat_ident(pat, ba, var_id, sub, expected, def_bm, ti)
176 PatKind::TupleStruct(ref qpath, subpats, ddpos) => {
177 self.check_pat_tuple_struct(pat, qpath, subpats, ddpos, expected, def_bm, ti)
179 PatKind::Path(_) => self.check_pat_path(pat, path_res.unwrap(), expected, ti),
180 PatKind::Struct(ref qpath, fields, etc) => {
181 self.check_pat_struct(pat, qpath, fields, etc, expected, def_bm, ti)
183 PatKind::Or(pats) => {
184 let parent_pat = Some(pat);
186 self.check_pat(pat, expected, def_bm, TopInfo { parent_pat, ..ti });
190 PatKind::Tuple(elements, ddpos) => {
191 self.check_pat_tuple(pat.span, elements, ddpos, expected, def_bm, ti)
193 PatKind::Box(inner) => self.check_pat_box(pat.span, inner, expected, def_bm, ti),
194 PatKind::Ref(inner, mutbl) => {
195 self.check_pat_ref(pat, inner, mutbl, expected, def_bm, ti)
197 PatKind::Slice(before, slice, after) => {
198 self.check_pat_slice(pat.span, before, slice, after, expected, def_bm, ti)
202 self.write_ty(pat.hir_id, ty);
204 // (note_1): In most of the cases where (note_1) is referenced
205 // (literals and constants being the exception), we relate types
206 // using strict equality, even though subtyping would be sufficient.
207 // There are a few reasons for this, some of which are fairly subtle
208 // and which cost me (nmatsakis) an hour or two debugging to remember,
209 // so I thought I'd write them down this time.
211 // 1. There is no loss of expressiveness here, though it does
212 // cause some inconvenience. What we are saying is that the type
213 // of `x` becomes *exactly* what is expected. This can cause unnecessary
214 // errors in some cases, such as this one:
217 // fn foo<'x>(x: &'x i32) {
224 // The reason we might get an error is that `z` might be
225 // assigned a type like `&'x i32`, and then we would have
226 // a problem when we try to assign `&a` to `z`, because
227 // the lifetime of `&a` (i.e., the enclosing block) is
228 // shorter than `'x`.
230 // HOWEVER, this code works fine. The reason is that the
231 // expected type here is whatever type the user wrote, not
232 // the initializer's type. In this case the user wrote
233 // nothing, so we are going to create a type variable `Z`.
234 // Then we will assign the type of the initializer (`&'x i32`)
235 // as a subtype of `Z`: `&'x i32 <: Z`. And hence we
236 // will instantiate `Z` as a type `&'0 i32` where `'0` is
237 // a fresh region variable, with the constraint that `'x : '0`.
238 // So basically we're all set.
240 // Note that there are two tests to check that this remains true
241 // (`regions-reassign-{match,let}-bound-pointer.rs`).
243 // 2. Things go horribly wrong if we use subtype. The reason for
244 // THIS is a fairly subtle case involving bound regions. See the
245 // `givens` field in `region_constraints`, as well as the test
246 // `regions-relate-bound-regions-on-closures-to-inference-variables.rs`,
247 // for details. Short version is that we must sometimes detect
248 // relationships between specific region variables and regions
249 // bound in a closure signature, and that detection gets thrown
250 // off when we substitute fresh region variables here to enable
254 /// Compute the new expected type and default binding mode from the old ones
255 /// as well as the pattern form we are currently checking.
256 fn calc_default_binding_mode(
258 pat: &'tcx Pat<'tcx>,
261 adjust_mode: AdjustMode,
262 ) -> (Ty<'tcx>, BindingMode) {
264 AdjustMode::Pass => (expected, def_bm),
265 AdjustMode::Reset => (expected, INITIAL_BM),
266 AdjustMode::Peel => self.peel_off_references(pat, expected, def_bm),
270 /// How should the binding mode and expected type be adjusted?
272 /// When the pattern is a path pattern, `opt_path_res` must be `Some(res)`.
273 fn calc_adjust_mode(&self, pat: &'tcx Pat<'tcx>, opt_path_res: Option<Res>) -> AdjustMode {
274 // When we perform destructuring assignment, we disable default match bindings, which are
275 // unintuitive in this context.
276 if !pat.default_binding_modes {
277 return AdjustMode::Reset;
280 // Type checking these product-like types successfully always require
281 // that the expected type be of those types and not reference types.
283 | PatKind::TupleStruct(..)
287 | PatKind::Slice(..) => AdjustMode::Peel,
288 // String and byte-string literals result in types `&str` and `&[u8]` respectively.
289 // All other literals result in non-reference types.
290 // As a result, we allow `if let 0 = &&0 {}` but not `if let "foo" = &&"foo {}`.
291 PatKind::Lit(lt) => match self.check_expr(lt).kind() {
292 ty::Ref(..) => AdjustMode::Pass,
293 _ => AdjustMode::Peel,
295 PatKind::Path(_) => match opt_path_res.unwrap() {
296 // These constants can be of a reference type, e.g. `const X: &u8 = &0;`.
297 // Peeling the reference types too early will cause type checking failures.
298 // Although it would be possible to *also* peel the types of the constants too.
299 Res::Def(DefKind::Const | DefKind::AssocConst, _) => AdjustMode::Pass,
300 // In the `ValueNS`, we have `SelfCtor(..) | Ctor(_, Const), _)` remaining which
301 // could successfully compile. The former being `Self` requires a unit struct.
302 // In either case, and unlike constants, the pattern itself cannot be
303 // a reference type wherefore peeling doesn't give up any expressivity.
304 _ => AdjustMode::Peel,
306 // When encountering a `& mut? pat` pattern, reset to "by value".
307 // This is so that `x` and `y` here are by value, as they appear to be:
310 // match &(&22, &44) {
316 PatKind::Ref(..) => AdjustMode::Reset,
317 // A `_` pattern works with any expected type, so there's no need to do anything.
319 // Bindings also work with whatever the expected type is,
320 // and moreover if we peel references off, that will give us the wrong binding type.
321 // Also, we can have a subpattern `binding @ pat`.
322 // Each side of the `@` should be treated independently (like with OR-patterns).
323 | PatKind::Binding(..)
324 // An OR-pattern just propagates to each individual alternative.
325 // This is maximally flexible, allowing e.g., `Some(mut x) | &Some(mut x)`.
326 // In that example, `Some(mut x)` results in `Peel` whereas `&Some(mut x)` in `Reset`.
327 | PatKind::Or(_) => AdjustMode::Pass,
331 /// Peel off as many immediately nested `& mut?` from the expected type as possible
332 /// and return the new expected type and binding default binding mode.
333 /// The adjustments vector, if non-empty is stored in a table.
334 fn peel_off_references(
336 pat: &'tcx Pat<'tcx>,
338 mut def_bm: BindingMode,
339 ) -> (Ty<'tcx>, BindingMode) {
340 let mut expected = self.resolve_vars_with_obligations(&expected);
342 // Peel off as many `&` or `&mut` from the scrutinee type as possible. For example,
343 // for `match &&&mut Some(5)` the loop runs three times, aborting when it reaches
344 // the `Some(5)` which is not of type Ref.
346 // For each ampersand peeled off, update the binding mode and push the original
347 // type into the adjustments vector.
349 // See the examples in `ui/match-defbm*.rs`.
350 let mut pat_adjustments = vec![];
351 while let ty::Ref(_, inner_ty, inner_mutability) = *expected.kind() {
352 debug!("inspecting {:?}", expected);
354 debug!("current discriminant is Ref, inserting implicit deref");
355 // Preserve the reference type. We'll need it later during THIR lowering.
356 pat_adjustments.push(expected);
359 def_bm = ty::BindByReference(match def_bm {
360 // If default binding mode is by value, make it `ref` or `ref mut`
361 // (depending on whether we observe `&` or `&mut`).
363 // When `ref mut`, stay a `ref mut` (on `&mut`) or downgrade to `ref` (on `&`).
364 ty::BindByReference(hir::Mutability::Mut) => inner_mutability,
365 // Once a `ref`, always a `ref`.
366 // This is because a `& &mut` cannot mutate the underlying value.
367 ty::BindByReference(m @ hir::Mutability::Not) => m,
371 if !pat_adjustments.is_empty() {
372 debug!("default binding mode is now {:?}", def_bm);
376 .pat_adjustments_mut()
377 .insert(pat.hir_id, pat_adjustments);
386 lt: &hir::Expr<'tcx>,
390 // We've already computed the type above (when checking for a non-ref pat),
391 // so avoid computing it again.
392 let ty = self.node_ty(lt.hir_id);
394 // Byte string patterns behave the same way as array patterns
395 // They can denote both statically and dynamically-sized byte arrays.
397 if let hir::ExprKind::Lit(Spanned { node: ast::LitKind::ByteStr(_), .. }) = lt.kind {
398 let expected = self.structurally_resolved_type(span, expected);
399 if let ty::Ref(_, inner_ty, _) = expected.kind() {
400 if matches!(inner_ty.kind(), ty::Slice(_)) {
402 trace!(?lt.hir_id.local_id, "polymorphic byte string lit");
405 .treat_byte_string_as_slice
406 .insert(lt.hir_id.local_id);
407 pat_ty = tcx.mk_imm_ref(tcx.lifetimes.re_static, tcx.mk_slice(tcx.types.u8));
412 // Somewhat surprising: in this case, the subtyping relation goes the
413 // opposite way as the other cases. Actually what we really want is not
414 // a subtyping relation at all but rather that there exists a LUB
415 // (so that they can be compared). However, in practice, constants are
416 // always scalars or strings. For scalars subtyping is irrelevant,
417 // and for strings `ty` is type is `&'static str`, so if we say that
419 // &'static str <: expected
421 // then that's equivalent to there existing a LUB.
422 let cause = self.pattern_cause(ti, span);
423 if let Some(mut err) = self.demand_suptype_with_origin(&cause, expected, pat_ty) {
427 // In the case of `if`- and `while`-expressions we've already checked
428 // that `scrutinee: bool`. We know that the pattern is `true`,
429 // so an error here would be a duplicate and from the wrong POV.
430 s.is_desugaring(DesugaringKind::CondTemporary)
442 lhs: Option<&'tcx hir::Expr<'tcx>>,
443 rhs: Option<&'tcx hir::Expr<'tcx>>,
447 let calc_side = |opt_expr: Option<&'tcx hir::Expr<'tcx>>| match opt_expr {
448 None => (None, None),
450 let ty = self.check_expr(expr);
451 // Check that the end-point is of numeric or char type.
452 let fail = !(ty.is_numeric() || ty.is_char() || ty.references_error());
453 (Some(ty), Some((fail, ty, expr.span)))
456 let (lhs_ty, lhs) = calc_side(lhs);
457 let (rhs_ty, rhs) = calc_side(rhs);
459 if let (Some((true, ..)), _) | (_, Some((true, ..))) = (lhs, rhs) {
460 // There exists a side that didn't meet our criteria that the end-point
461 // be of a numeric or char type, as checked in `calc_side` above.
462 self.emit_err_pat_range(span, lhs, rhs);
463 return self.tcx.ty_error();
466 // Now that we know the types can be unified we find the unified type
467 // and use it to type the entire expression.
468 let common_type = self.resolve_vars_if_possible(lhs_ty.or(rhs_ty).unwrap_or(expected));
470 // Subtyping doesn't matter here, as the value is some kind of scalar.
471 let demand_eqtype = |x, y| {
472 if let Some((_, x_ty, x_span)) = x {
473 if let Some(mut err) = self.demand_eqtype_pat_diag(x_span, expected, x_ty, ti) {
474 if let Some((_, y_ty, y_span)) = y {
475 self.endpoint_has_type(&mut err, y_span, y_ty);
481 demand_eqtype(lhs, rhs);
482 demand_eqtype(rhs, lhs);
487 fn endpoint_has_type(&self, err: &mut DiagnosticBuilder<'_>, span: Span, ty: Ty<'_>) {
488 if !ty.references_error() {
489 err.span_label(span, &format!("this is of type `{}`", ty));
493 fn emit_err_pat_range(
496 lhs: Option<(bool, Ty<'tcx>, Span)>,
497 rhs: Option<(bool, Ty<'tcx>, Span)>,
499 let span = match (lhs, rhs) {
500 (Some((true, ..)), Some((true, ..))) => span,
501 (Some((true, _, sp)), _) => sp,
502 (_, Some((true, _, sp))) => sp,
503 _ => span_bug!(span, "emit_err_pat_range: no side failed or exists but still error?"),
505 let mut err = struct_span_err!(
509 "only `char` and numeric types are allowed in range patterns"
511 let msg = |ty| format!("this is of type `{}` but it should be `char` or numeric", ty);
512 let mut one_side_err = |first_span, first_ty, second: Option<(bool, Ty<'tcx>, Span)>| {
513 err.span_label(first_span, &msg(first_ty));
514 if let Some((_, ty, sp)) = second {
515 self.endpoint_has_type(&mut err, sp, ty);
519 (Some((true, lhs_ty, lhs_sp)), Some((true, rhs_ty, rhs_sp))) => {
520 err.span_label(lhs_sp, &msg(lhs_ty));
521 err.span_label(rhs_sp, &msg(rhs_ty));
523 (Some((true, lhs_ty, lhs_sp)), rhs) => one_side_err(lhs_sp, lhs_ty, rhs),
524 (lhs, Some((true, rhs_ty, rhs_sp))) => one_side_err(rhs_sp, rhs_ty, lhs),
525 _ => span_bug!(span, "Impossible, verified above."),
527 if self.tcx.sess.teach(&err.get_code().unwrap()) {
529 "In a match expression, only numbers and characters can be matched \
530 against a range. This is because the compiler checks that the range \
531 is non-empty at compile-time, and is unable to evaluate arbitrary \
532 comparison functions. If you want to capture values of an orderable \
533 type between two end-points, you can use a guard.",
541 pat: &'tcx Pat<'tcx>,
542 ba: hir::BindingAnnotation,
544 sub: Option<&'tcx Pat<'tcx>>,
549 // Determine the binding mode...
551 hir::BindingAnnotation::Unannotated => def_bm,
552 _ => BindingMode::convert(ba),
554 // ...and store it in a side table:
555 self.inh.typeck_results.borrow_mut().pat_binding_modes_mut().insert(pat.hir_id, bm);
557 debug!("check_pat_ident: pat.hir_id={:?} bm={:?}", pat.hir_id, bm);
559 let local_ty = self.local_ty(pat.span, pat.hir_id).decl_ty;
560 let eq_ty = match bm {
561 ty::BindByReference(mutbl) => {
562 // If the binding is like `ref x | ref mut x`,
563 // then `x` is assigned a value of type `&M T` where M is the
564 // mutability and T is the expected type.
566 // `x` is assigned a value of type `&M T`, hence `&M T <: typeof(x)`
567 // is required. However, we use equality, which is stronger.
568 // See (note_1) for an explanation.
569 self.new_ref_ty(pat.span, mutbl, expected)
571 // Otherwise, the type of x is the expected type `T`.
572 ty::BindByValue(_) => {
573 // As above, `T <: typeof(x)` is required, but we use equality, see (note_1).
577 self.demand_eqtype_pat(pat.span, eq_ty, local_ty, ti);
579 // If there are multiple arms, make sure they all agree on
580 // what the type of the binding `x` ought to be.
581 if var_id != pat.hir_id {
582 self.check_binding_alt_eq_ty(pat.span, var_id, local_ty, ti);
585 if let Some(p) = sub {
586 self.check_pat(&p, expected, def_bm, TopInfo { parent_pat: Some(&pat), ..ti });
592 fn check_binding_alt_eq_ty(&self, span: Span, var_id: HirId, ty: Ty<'tcx>, ti: TopInfo<'tcx>) {
593 let var_ty = self.local_ty(span, var_id).decl_ty;
594 if let Some(mut err) = self.demand_eqtype_pat_diag(span, var_ty, ty, ti) {
595 let hir = self.tcx.hir();
596 let var_ty = self.resolve_vars_with_obligations(var_ty);
597 let msg = format!("first introduced with type `{}` here", var_ty);
598 err.span_label(hir.span(var_id), msg);
599 let in_match = hir.parent_iter(var_id).any(|(_, n)| {
602 hir::Node::Expr(hir::Expr {
603 kind: hir::ExprKind::Match(.., hir::MatchSource::Normal),
608 let pre = if in_match { "in the same arm, " } else { "" };
609 err.note(&format!("{}a binding must have the same type in all alternatives", pre));
614 fn borrow_pat_suggestion(
616 err: &mut DiagnosticBuilder<'_>,
622 if let PatKind::Binding(..) = inner.kind {
623 let binding_parent_id = tcx.hir().get_parent_node(pat.hir_id);
624 let binding_parent = tcx.hir().get(binding_parent_id);
625 debug!("inner {:?} pat {:?} parent {:?}", inner, pat, binding_parent);
626 match binding_parent {
627 hir::Node::Param(hir::Param { span, .. }) => {
628 if let Ok(snippet) = tcx.sess.source_map().span_to_snippet(inner.span) {
631 &format!("did you mean `{}`", snippet),
632 format!(" &{}", expected),
633 Applicability::MachineApplicable,
637 hir::Node::Arm(_) | hir::Node::Pat(_) => {
638 // rely on match ergonomics or it might be nested `&&pat`
639 if let Ok(snippet) = tcx.sess.source_map().span_to_snippet(inner.span) {
642 "you can probably remove the explicit borrow",
644 Applicability::MaybeIncorrect,
648 _ => {} // don't provide suggestions in other cases #55175
653 pub fn check_dereferenceable(&self, span: Span, expected: Ty<'tcx>, inner: &Pat<'_>) -> bool {
654 if let PatKind::Binding(..) = inner.kind {
655 if let Some(mt) = self.shallow_resolve(expected).builtin_deref(true) {
656 if let ty::Dynamic(..) = mt.ty.kind() {
657 // This is "x = SomeTrait" being reduced from
658 // "let &x = &SomeTrait" or "let box x = Box<SomeTrait>", an error.
659 let type_str = self.ty_to_string(expected);
660 let mut err = struct_span_err!(
664 "type `{}` cannot be dereferenced",
667 err.span_label(span, format!("type `{}` cannot be dereferenced", type_str));
668 if self.tcx.sess.teach(&err.get_code().unwrap()) {
669 err.note(CANNOT_IMPLICITLY_DEREF_POINTER_TRAIT_OBJ);
681 pat: &'tcx Pat<'tcx>,
682 qpath: &hir::QPath<'_>,
683 fields: &'tcx [hir::PatField<'tcx>],
689 // Resolve the path and check the definition for errors.
690 let (variant, pat_ty) = if let Some(variant_ty) = self.check_struct_path(qpath, pat.hir_id)
694 let err = self.tcx.ty_error();
695 for field in fields {
696 let ti = TopInfo { parent_pat: Some(&pat), ..ti };
697 self.check_pat(&field.pat, err, def_bm, ti);
702 // Type-check the path.
703 self.demand_eqtype_pat(pat.span, expected, pat_ty, ti);
705 // Type-check subpatterns.
706 if self.check_struct_pat_fields(pat_ty, &pat, variant, fields, etc, def_bm, ti) {
716 path_resolution: (Res, Option<Ty<'tcx>>, &'b [hir::PathSegment<'b>]),
722 // We have already resolved the path.
723 let (res, opt_ty, segments) = path_resolution;
726 self.set_tainted_by_errors();
727 return tcx.ty_error();
729 Res::Def(DefKind::AssocFn | DefKind::Ctor(_, CtorKind::Fictive | CtorKind::Fn), _) => {
730 report_unexpected_variant_res(tcx, res, pat.span);
731 return tcx.ty_error();
735 DefKind::Ctor(_, CtorKind::Const)
737 | DefKind::AssocConst
738 | DefKind::ConstParam,
741 _ => bug!("unexpected pattern resolution: {:?}", res),
744 // Type-check the path.
745 let (pat_ty, pat_res) =
746 self.instantiate_value_path(segments, opt_ty, res, pat.span, pat.hir_id);
748 self.demand_suptype_with_origin(&self.pattern_cause(ti, pat.span), expected, pat_ty)
750 self.emit_bad_pat_path(err, pat.span, res, pat_res, pat_ty, segments, ti.parent_pat);
755 fn maybe_suggest_range_literal(
757 e: &mut DiagnosticBuilder<'_>,
758 opt_def_id: Option<hir::def_id::DefId>,
762 Some(def_id) => match self.tcx.hir().get_if_local(def_id) {
763 Some(hir::Node::Item(hir::Item {
764 kind: hir::ItemKind::Const(_, body_id), ..
765 })) => match self.tcx.hir().get(body_id.hir_id) {
766 hir::Node::Expr(expr) => {
767 if hir::is_range_literal(expr) {
768 let span = self.tcx.hir().span(body_id.hir_id);
769 if let Ok(snip) = self.tcx.sess.source_map().span_to_snippet(span) {
770 e.span_suggestion_verbose(
772 "you may want to move the range into the match block",
774 Applicability::MachineApplicable,
789 fn emit_bad_pat_path(
791 mut e: DiagnosticBuilder<'_>,
796 segments: &'b [hir::PathSegment<'b>],
797 parent_pat: Option<&Pat<'_>>,
799 if let Some(span) = self.tcx.hir().res_span(pat_res) {
800 e.span_label(span, &format!("{} defined here", res.descr()));
801 if let [hir::PathSegment { ident, .. }] = &*segments {
805 "`{}` is interpreted as {} {}, not a new binding",
812 Some(Pat { kind: hir::PatKind::Struct(..), .. }) => {
813 e.span_suggestion_verbose(
814 ident.span.shrink_to_hi(),
815 "bind the struct field to a different name instead",
816 format!(": other_{}", ident.as_str().to_lowercase()),
817 Applicability::HasPlaceholders,
821 let (type_def_id, item_def_id) = match pat_ty.kind() {
822 Adt(def, _) => match res {
823 Res::Def(DefKind::Const, def_id) => (Some(def.did), Some(def_id)),
830 self.tcx.lang_items().range_struct(),
831 self.tcx.lang_items().range_from_struct(),
832 self.tcx.lang_items().range_to_struct(),
833 self.tcx.lang_items().range_full_struct(),
834 self.tcx.lang_items().range_inclusive_struct(),
835 self.tcx.lang_items().range_to_inclusive_struct(),
837 if type_def_id != None && ranges.contains(&type_def_id) {
838 if !self.maybe_suggest_range_literal(&mut e, item_def_id, *ident) {
839 let msg = "constants only support matching by type, \
840 if you meant to match against a range of values, \
841 consider using a range pattern like `min ..= max` in the match block";
845 let msg = "introduce a new binding instead";
846 let sugg = format!("other_{}", ident.as_str().to_lowercase());
851 Applicability::HasPlaceholders,
861 fn check_pat_tuple_struct(
863 pat: &'tcx Pat<'tcx>,
864 qpath: &hir::QPath<'_>,
865 subpats: &'tcx [&'tcx Pat<'tcx>],
866 ddpos: Option<usize>,
873 let parent_pat = Some(pat);
875 self.check_pat(&pat, tcx.ty_error(), def_bm, TopInfo { parent_pat, ..ti });
878 let report_unexpected_res = |res: Res| {
879 let sm = tcx.sess.source_map();
881 .span_to_snippet(sm.span_until_char(pat.span, '('))
882 .map_or_else(|_| String::new(), |s| format!(" `{}`", s.trim_end()));
884 "expected tuple struct or tuple variant, found {}{}",
889 let mut err = struct_span_err!(tcx.sess, pat.span, E0164, "{}", msg);
891 Res::Def(DefKind::Fn | DefKind::AssocFn, _) => {
892 err.span_label(pat.span, "`fn` calls are not allowed in patterns");
894 "for more information, visit \
895 https://doc.rust-lang.org/book/ch18-00-patterns.html",
899 err.span_label(pat.span, "not a tuple variant or struct");
906 // Resolve the path and check the definition for errors.
907 let (res, opt_ty, segments) = self.resolve_ty_and_res_ufcs(qpath, pat.hir_id, pat.span);
909 self.set_tainted_by_errors();
911 return self.tcx.ty_error();
914 // Type-check the path.
916 self.instantiate_value_path(segments, opt_ty, res, pat.span, pat.hir_id);
918 report_unexpected_res(res);
919 return tcx.ty_error();
922 let variant = match res {
924 self.set_tainted_by_errors();
926 return tcx.ty_error();
928 Res::Def(DefKind::AssocConst | DefKind::AssocFn, _) => {
929 report_unexpected_res(res);
930 return tcx.ty_error();
932 Res::Def(DefKind::Ctor(_, CtorKind::Fn), _) => tcx.expect_variant_res(res),
933 _ => bug!("unexpected pattern resolution: {:?}", res),
936 // Replace constructor type with constructed type for tuple struct patterns.
937 let pat_ty = pat_ty.fn_sig(tcx).output();
938 let pat_ty = pat_ty.no_bound_vars().expect("expected fn type");
940 // Type-check the tuple struct pattern against the expected type.
941 let diag = self.demand_eqtype_pat_diag(pat.span, expected, pat_ty, ti);
942 let had_err = if let Some(mut err) = diag {
949 // Type-check subpatterns.
950 if subpats.len() == variant.fields.len()
951 || subpats.len() < variant.fields.len() && ddpos.is_some()
953 let substs = match pat_ty.kind() {
954 ty::Adt(_, substs) => substs,
955 _ => bug!("unexpected pattern type {:?}", pat_ty),
957 for (i, subpat) in subpats.iter().enumerate_and_adjust(variant.fields.len(), ddpos) {
958 let field_ty = self.field_ty(subpat.span, &variant.fields[i], substs);
959 self.check_pat(&subpat, field_ty, def_bm, TopInfo { parent_pat: Some(&pat), ..ti });
961 self.tcx.check_stability(variant.fields[i].did, Some(pat.hir_id), subpat.span);
964 // Pattern has wrong number of fields.
965 self.e0023(pat.span, res, qpath, subpats, &variant.fields, expected, had_err);
967 return tcx.ty_error();
976 qpath: &hir::QPath<'_>,
977 subpats: &'tcx [&'tcx Pat<'tcx>],
978 fields: &'tcx [ty::FieldDef],
982 let subpats_ending = pluralize!(subpats.len());
983 let fields_ending = pluralize!(fields.len());
984 let res_span = self.tcx.def_span(res.def_id());
985 let mut err = struct_span_err!(
989 "this pattern has {} field{}, but the corresponding {} has {} field{}",
998 format!("expected {} field{}, found {}", fields.len(), fields_ending, subpats.len(),),
1000 .span_label(res_span, format!("{} defined here", res.descr()));
1002 // Identify the case `Some(x, y)` where the expected type is e.g. `Option<(T, U)>`.
1003 // More generally, the expected type wants a tuple variant with one field of an
1004 // N-arity-tuple, e.g., `V_i((p_0, .., p_N))`. Meanwhile, the user supplied a pattern
1005 // with the subpatterns directly in the tuple variant pattern, e.g., `V_i(p_0, .., p_N)`.
1006 let missing_parentheses = match (&expected.kind(), fields, had_err) {
1007 // #67037: only do this if we could successfully type-check the expected type against
1008 // the tuple struct pattern. Otherwise the substs could get out of range on e.g.,
1009 // `let P() = U;` where `P != U` with `struct P<T>(T);`.
1010 (ty::Adt(_, substs), [field], false) => {
1011 let field_ty = self.field_ty(pat_span, field, substs);
1012 match field_ty.kind() {
1013 ty::Tuple(_) => field_ty.tuple_fields().count() == subpats.len(),
1019 if missing_parentheses {
1020 let (left, right) = match subpats {
1021 // This is the zero case; we aim to get the "hi" part of the `QPath`'s
1022 // span as the "lo" and then the "hi" part of the pattern's span as the "hi".
1025 // help: missing parentheses
1027 // L | let A(()) = A(());
1029 [] => (qpath.span().shrink_to_hi(), pat_span),
1030 // Easy case. Just take the "lo" of the first sub-pattern and the "hi" of the
1031 // last sub-pattern. In the case of `A(x)` the first and last may coincide.
1034 // help: missing parentheses
1036 // L | let A((x, y)) = A((1, 2));
1038 [first, ..] => (first.span.shrink_to_lo(), subpats.last().unwrap().span),
1040 err.multipart_suggestion(
1041 "missing parentheses",
1042 vec![(left, "(".to_string()), (right.shrink_to_hi(), ")".to_string())],
1043 Applicability::MachineApplicable,
1045 } else if fields.len() > subpats.len() && pat_span != DUMMY_SP {
1046 let after_fields_span = pat_span.with_hi(pat_span.hi() - BytePos(1)).shrink_to_hi();
1047 let all_fields_span = match subpats {
1048 [] => after_fields_span,
1049 [field] => field.span,
1050 [first, .., last] => first.span.to(last.span),
1053 // Check if all the fields in the pattern are wildcards.
1054 let all_wildcards = subpats.iter().all(|pat| matches!(pat.kind, PatKind::Wild));
1055 let first_tail_wildcard =
1056 subpats.iter().enumerate().fold(None, |acc, (pos, pat)| match (acc, &pat.kind) {
1057 (None, PatKind::Wild) => Some(pos),
1058 (Some(_), PatKind::Wild) => acc,
1061 let tail_span = match first_tail_wildcard {
1062 None => after_fields_span,
1063 Some(0) => subpats[0].span.to(after_fields_span),
1064 Some(pos) => subpats[pos - 1].span.shrink_to_hi().to(after_fields_span),
1067 // FIXME: heuristic-based suggestion to check current types for where to add `_`.
1068 let mut wildcard_sugg = vec!["_"; fields.len() - subpats.len()].join(", ");
1069 if !subpats.is_empty() {
1070 wildcard_sugg = String::from(", ") + &wildcard_sugg;
1073 err.span_suggestion_verbose(
1075 "use `_` to explicitly ignore each field",
1077 Applicability::MaybeIncorrect,
1080 // Only suggest `..` if more than one field is missing
1081 // or the pattern consists of all wildcards.
1082 if fields.len() - subpats.len() > 1 || all_wildcards {
1083 if subpats.is_empty() || all_wildcards {
1084 err.span_suggestion_verbose(
1086 "use `..` to ignore all fields",
1088 Applicability::MaybeIncorrect,
1091 err.span_suggestion_verbose(
1093 "use `..` to ignore the rest of the fields",
1094 String::from(", .."),
1095 Applicability::MaybeIncorrect,
1107 elements: &'tcx [&'tcx Pat<'tcx>],
1108 ddpos: Option<usize>,
1110 def_bm: BindingMode,
1114 let mut expected_len = elements.len();
1115 if ddpos.is_some() {
1116 // Require known type only when `..` is present.
1117 if let ty::Tuple(ref tys) = self.structurally_resolved_type(span, expected).kind() {
1118 expected_len = tys.len();
1121 let max_len = cmp::max(expected_len, elements.len());
1123 let element_tys_iter = (0..max_len).map(|_| {
1124 GenericArg::from(self.next_ty_var(
1125 // FIXME: `MiscVariable` for now -- obtaining the span and name information
1126 // from all tuple elements isn't trivial.
1127 TypeVariableOrigin { kind: TypeVariableOriginKind::TypeInference, span },
1130 let element_tys = tcx.mk_substs(element_tys_iter);
1131 let pat_ty = tcx.mk_ty(ty::Tuple(element_tys));
1132 if let Some(mut err) = self.demand_eqtype_pat_diag(span, expected, pat_ty, ti) {
1134 // Walk subpatterns with an expected type of `err` in this case to silence
1135 // further errors being emitted when using the bindings. #50333
1136 let element_tys_iter = (0..max_len).map(|_| tcx.ty_error());
1137 for (_, elem) in elements.iter().enumerate_and_adjust(max_len, ddpos) {
1138 self.check_pat(elem, &tcx.ty_error(), def_bm, ti);
1140 tcx.mk_tup(element_tys_iter)
1142 for (i, elem) in elements.iter().enumerate_and_adjust(max_len, ddpos) {
1143 self.check_pat(elem, &element_tys[i].expect_ty(), def_bm, ti);
1149 fn check_struct_pat_fields(
1152 pat: &'tcx Pat<'tcx>,
1153 variant: &'tcx ty::VariantDef,
1154 fields: &'tcx [hir::PatField<'tcx>],
1156 def_bm: BindingMode,
1161 let (substs, adt) = match adt_ty.kind() {
1162 ty::Adt(adt, substs) => (substs, adt),
1163 _ => span_bug!(pat.span, "struct pattern is not an ADT"),
1166 // Index the struct fields' types.
1167 let field_map = variant
1171 .map(|(i, field)| (field.ident.normalize_to_macros_2_0(), (i, field)))
1172 .collect::<FxHashMap<_, _>>();
1174 // Keep track of which fields have already appeared in the pattern.
1175 let mut used_fields = FxHashMap::default();
1176 let mut no_field_errors = true;
1178 let mut inexistent_fields = vec![];
1179 // Typecheck each field.
1180 for field in fields {
1181 let span = field.span;
1182 let ident = tcx.adjust_ident(field.ident, variant.def_id);
1183 let field_ty = match used_fields.entry(ident) {
1184 Occupied(occupied) => {
1185 self.error_field_already_bound(span, field.ident, *occupied.get());
1186 no_field_errors = false;
1190 vacant.insert(span);
1194 self.write_field_index(field.hir_id, *i);
1195 self.tcx.check_stability(f.did, Some(pat.hir_id), span);
1196 self.field_ty(span, f, substs)
1198 .unwrap_or_else(|| {
1199 inexistent_fields.push(field.ident);
1200 no_field_errors = false;
1206 self.check_pat(&field.pat, field_ty, def_bm, TopInfo { parent_pat: Some(&pat), ..ti });
1209 let mut unmentioned_fields = variant
1212 .map(|field| (field, field.ident.normalize_to_macros_2_0()))
1213 .filter(|(_, ident)| !used_fields.contains_key(&ident))
1214 .collect::<Vec<_>>();
1216 let inexistent_fields_err = if !(inexistent_fields.is_empty() || variant.is_recovered()) {
1217 Some(self.error_inexistent_fields(
1218 adt.variant_descr(),
1220 &mut unmentioned_fields,
1227 // Require `..` if struct has non_exhaustive attribute.
1228 if variant.is_field_list_non_exhaustive() && !adt.did.is_local() && !etc {
1229 self.error_foreign_non_exhaustive_spat(pat, adt.variant_descr(), fields.is_empty());
1232 let mut unmentioned_err = None;
1233 // Report an error if an incorrect number of fields was specified.
1235 if fields.len() != 1 {
1237 .struct_span_err(pat.span, "union patterns should have exactly one field")
1241 tcx.sess.struct_span_err(pat.span, "`..` cannot be used in union patterns").emit();
1243 } else if !etc && !unmentioned_fields.is_empty() {
1244 let no_accessible_unmentioned_fields = !unmentioned_fields.iter().any(|(field, _)| {
1245 field.vis.is_accessible_from(tcx.parent_module(pat.hir_id).to_def_id(), tcx)
1248 if no_accessible_unmentioned_fields {
1249 unmentioned_err = Some(self.error_no_accessible_fields(pat, &fields));
1252 Some(self.error_unmentioned_fields(pat, &unmentioned_fields, &fields));
1255 match (inexistent_fields_err, unmentioned_err) {
1256 (Some(mut i), Some(mut u)) => {
1257 if let Some(mut e) = self.error_tuple_variant_as_struct_pat(pat, fields, variant) {
1258 // We don't want to show the inexistent fields error when this was
1259 // `Foo { a, b }` when it should have been `Foo(a, b)`.
1268 (None, Some(mut u)) => {
1269 if let Some(mut e) = self.error_tuple_variant_as_struct_pat(pat, fields, variant) {
1276 (Some(mut err), None) => {
1280 if let Some(mut err) =
1281 self.error_tuple_variant_index_shorthand(variant, pat, fields)
1290 fn error_tuple_variant_index_shorthand(
1292 variant: &VariantDef,
1294 fields: &[hir::PatField<'_>],
1295 ) -> Option<DiagnosticBuilder<'_>> {
1296 // if this is a tuple struct, then all field names will be numbers
1297 // so if any fields in a struct pattern use shorthand syntax, they will
1298 // be invalid identifiers (for example, Foo { 0, 1 }).
1299 if let (CtorKind::Fn, PatKind::Struct(qpath, field_patterns, ..)) =
1300 (variant.ctor_kind, &pat.kind)
1302 let has_shorthand_field_name = field_patterns.iter().any(|field| field.is_shorthand);
1303 if has_shorthand_field_name {
1304 let path = rustc_hir_pretty::to_string(rustc_hir_pretty::NO_ANN, |s| {
1305 s.print_qpath(qpath, false)
1307 let mut err = struct_span_err!(
1311 "tuple variant `{}` written as struct variant",
1314 err.span_suggestion_verbose(
1315 qpath.span().shrink_to_hi().to(pat.span.shrink_to_hi()),
1316 "use the tuple variant pattern syntax instead",
1317 format!("({})", self.get_suggested_tuple_struct_pattern(fields, variant)),
1318 Applicability::MaybeIncorrect,
1326 fn error_foreign_non_exhaustive_spat(&self, pat: &Pat<'_>, descr: &str, no_fields: bool) {
1327 let sess = self.tcx.sess;
1328 let sm = sess.source_map();
1329 let sp_brace = sm.end_point(pat.span);
1330 let sp_comma = sm.end_point(pat.span.with_hi(sp_brace.hi()));
1331 let sugg = if no_fields || sp_brace != sp_comma { ".. }" } else { ", .. }" };
1333 let mut err = struct_span_err!(
1337 "`..` required with {} marked as non-exhaustive",
1340 err.span_suggestion_verbose(
1342 "add `..` at the end of the field list to ignore all other fields",
1344 Applicability::MachineApplicable,
1349 fn error_field_already_bound(&self, span: Span, ident: Ident, other_field: Span) {
1354 "field `{}` bound multiple times in the pattern",
1357 .span_label(span, format!("multiple uses of `{}` in pattern", ident))
1358 .span_label(other_field, format!("first use of `{}`", ident))
1362 fn error_inexistent_fields(
1365 inexistent_fields: &[Ident],
1366 unmentioned_fields: &mut Vec<(&ty::FieldDef, Ident)>,
1367 variant: &ty::VariantDef,
1368 ) -> DiagnosticBuilder<'tcx> {
1370 let (field_names, t, plural) = if inexistent_fields.len() == 1 {
1371 (format!("a field named `{}`", inexistent_fields[0]), "this", "")
1378 .map(|ident| format!("`{}`", ident))
1379 .collect::<Vec<String>>()
1386 let spans = inexistent_fields.iter().map(|ident| ident.span).collect::<Vec<_>>();
1387 let mut err = struct_span_err!(
1391 "{} `{}` does not have {}",
1393 tcx.def_path_str(variant.def_id),
1396 if let Some(ident) = inexistent_fields.last() {
1400 "{} `{}` does not have {} field{}",
1402 tcx.def_path_str(variant.def_id),
1409 unmentioned_fields.iter().map(|(_, field)| field.name).collect::<Vec<_>>();
1410 let suggested_name = find_best_match_for_name(&input, ident.name, None);
1411 if let Some(suggested_name) = suggested_name {
1412 err.span_suggestion(
1414 "a field with a similar name exists",
1415 suggested_name.to_string(),
1416 Applicability::MaybeIncorrect,
1419 // When we have a tuple struct used with struct we don't want to suggest using
1420 // the (valid) struct syntax with numeric field names. Instead we want to
1421 // suggest the expected syntax. We infer that this is the case by parsing the
1422 // `Ident` into an unsized integer. The suggestion will be emitted elsewhere in
1423 // `smart_resolve_context_dependent_help`.
1424 if suggested_name.to_ident_string().parse::<usize>().is_err() {
1425 // We don't want to throw `E0027` in case we have thrown `E0026` for them.
1426 unmentioned_fields.retain(|&(_, x)| x.name != suggested_name);
1431 if tcx.sess.teach(&err.get_code().unwrap()) {
1433 "This error indicates that a struct pattern attempted to \
1434 extract a non-existent field from a struct. Struct fields \
1435 are identified by the name used before the colon : so struct \
1436 patterns should resemble the declaration of the struct type \
1438 If you are using shorthand field patterns but want to refer \
1439 to the struct field by a different name, you should rename \
1446 fn error_tuple_variant_as_struct_pat(
1449 fields: &'tcx [hir::PatField<'tcx>],
1450 variant: &ty::VariantDef,
1451 ) -> Option<DiagnosticBuilder<'tcx>> {
1452 if let (CtorKind::Fn, PatKind::Struct(qpath, ..)) = (variant.ctor_kind, &pat.kind) {
1453 let path = rustc_hir_pretty::to_string(rustc_hir_pretty::NO_ANN, |s| {
1454 s.print_qpath(qpath, false)
1456 let mut err = struct_span_err!(
1460 "tuple variant `{}` written as struct variant",
1463 let (sugg, appl) = if fields.len() == variant.fields.len() {
1465 self.get_suggested_tuple_struct_pattern(fields, variant),
1466 Applicability::MachineApplicable,
1470 variant.fields.iter().map(|_| "_").collect::<Vec<&str>>().join(", "),
1471 Applicability::MaybeIncorrect,
1474 err.span_suggestion_verbose(
1475 qpath.span().shrink_to_hi().to(pat.span.shrink_to_hi()),
1476 "use the tuple variant pattern syntax instead",
1477 format!("({})", sugg),
1485 fn get_suggested_tuple_struct_pattern(
1487 fields: &[hir::PatField<'_>],
1488 variant: &VariantDef,
1490 let variant_field_idents = variant.fields.iter().map(|f| f.ident).collect::<Vec<Ident>>();
1494 match self.tcx.sess.source_map().span_to_snippet(field.pat.span) {
1496 // Field names are numbers, but numbers
1497 // are not valid identifiers
1498 if variant_field_idents.contains(&field.ident) {
1504 Err(_) => rustc_hir_pretty::to_string(rustc_hir_pretty::NO_ANN, |s| {
1505 s.print_pat(field.pat)
1509 .collect::<Vec<String>>()
1513 /// Returns a diagnostic reporting a struct pattern which is missing an `..` due to
1514 /// inaccessible fields.
1517 /// error: pattern requires `..` due to inaccessible fields
1518 /// --> src/main.rs:10:9
1520 /// LL | let foo::Foo {} = foo::Foo::default();
1523 /// help: add a `..`
1525 /// LL | let foo::Foo { .. } = foo::Foo::default();
1528 fn error_no_accessible_fields(
1531 fields: &'tcx [hir::PatField<'tcx>],
1532 ) -> DiagnosticBuilder<'tcx> {
1536 .struct_span_err(pat.span, "pattern requires `..` due to inaccessible fields");
1538 if let Some(field) = fields.last() {
1539 err.span_suggestion_verbose(
1540 field.span.shrink_to_hi(),
1541 "ignore the inaccessible and unused fields",
1543 Applicability::MachineApplicable,
1546 let qpath_span = if let PatKind::Struct(qpath, ..) = &pat.kind {
1549 bug!("`error_no_accessible_fields` called on non-struct pattern");
1552 // Shrink the span to exclude the `foo:Foo` in `foo::Foo { }`.
1553 let span = pat.span.with_lo(qpath_span.shrink_to_hi().hi());
1554 err.span_suggestion_verbose(
1556 "ignore the inaccessible and unused fields",
1557 " { .. }".to_string(),
1558 Applicability::MachineApplicable,
1564 /// Returns a diagnostic reporting a struct pattern which does not mention some fields.
1567 /// error[E0027]: pattern does not mention field `bar`
1568 /// --> src/main.rs:15:9
1570 /// LL | let foo::Foo {} = foo::Foo::new();
1571 /// | ^^^^^^^^^^^ missing field `bar`
1573 fn error_unmentioned_fields(
1576 unmentioned_fields: &[(&ty::FieldDef, Ident)],
1577 fields: &'tcx [hir::PatField<'tcx>],
1578 ) -> DiagnosticBuilder<'tcx> {
1579 let field_names = if unmentioned_fields.len() == 1 {
1580 format!("field `{}`", unmentioned_fields[0].1)
1582 let fields = unmentioned_fields
1584 .map(|(_, name)| format!("`{}`", name))
1585 .collect::<Vec<String>>()
1587 format!("fields {}", fields)
1589 let mut err = struct_span_err!(
1593 "pattern does not mention {}",
1596 err.span_label(pat.span, format!("missing {}", field_names));
1597 let len = unmentioned_fields.len();
1598 let (prefix, postfix, sp) = match fields {
1599 [] => match &pat.kind {
1600 PatKind::Struct(path, [], false) => {
1601 (" { ", " }", path.span().shrink_to_hi().until(pat.span.shrink_to_hi()))
1606 // Account for last field having a trailing comma or parse recovery at the tail of
1607 // the pattern to avoid invalid suggestion (#78511).
1608 let tail = field.span.shrink_to_hi().with_hi(pat.span.hi());
1610 PatKind::Struct(..) => (", ", " }", tail),
1615 err.span_suggestion(
1618 "include the missing field{} in the pattern",
1619 if len == 1 { "" } else { "s" },
1626 .map(|(_, name)| name.to_string())
1627 .collect::<Vec<_>>()
1631 Applicability::MachineApplicable,
1633 err.span_suggestion(
1636 "if you don't care about {} missing field{}, you can explicitly ignore {}",
1637 if len == 1 { "this" } else { "these" },
1638 if len == 1 { "" } else { "s" },
1639 if len == 1 { "it" } else { "them" },
1641 format!("{}..{}", prefix, postfix),
1642 Applicability::MachineApplicable,
1650 inner: &'tcx Pat<'tcx>,
1652 def_bm: BindingMode,
1656 let (box_ty, inner_ty) = if self.check_dereferenceable(span, expected, &inner) {
1657 // Here, `demand::subtype` is good enough, but I don't
1658 // think any errors can be introduced by using `demand::eqtype`.
1659 let inner_ty = self.next_ty_var(TypeVariableOrigin {
1660 kind: TypeVariableOriginKind::TypeInference,
1663 let box_ty = tcx.mk_box(inner_ty);
1664 self.demand_eqtype_pat(span, expected, box_ty, ti);
1667 let err = tcx.ty_error();
1670 self.check_pat(&inner, inner_ty, def_bm, ti);
1676 pat: &'tcx Pat<'tcx>,
1677 inner: &'tcx Pat<'tcx>,
1678 mutbl: hir::Mutability,
1680 def_bm: BindingMode,
1684 let expected = self.shallow_resolve(expected);
1685 let (rptr_ty, inner_ty) = if self.check_dereferenceable(pat.span, expected, &inner) {
1686 // `demand::subtype` would be good enough, but using `eqtype` turns
1687 // out to be equally general. See (note_1) for details.
1689 // Take region, inner-type from expected type if we can,
1690 // to avoid creating needless variables. This also helps with
1691 // the bad interactions of the given hack detailed in (note_1).
1692 debug!("check_pat_ref: expected={:?}", expected);
1693 match *expected.kind() {
1694 ty::Ref(_, r_ty, r_mutbl) if r_mutbl == mutbl => (expected, r_ty),
1696 let inner_ty = self.next_ty_var(TypeVariableOrigin {
1697 kind: TypeVariableOriginKind::TypeInference,
1700 let rptr_ty = self.new_ref_ty(pat.span, mutbl, inner_ty);
1701 debug!("check_pat_ref: demanding {:?} = {:?}", expected, rptr_ty);
1702 let err = self.demand_eqtype_pat_diag(pat.span, expected, rptr_ty, ti);
1704 // Look for a case like `fn foo(&foo: u32)` and suggest
1705 // `fn foo(foo: &u32)`
1706 if let Some(mut err) = err {
1707 self.borrow_pat_suggestion(&mut err, &pat, &inner, &expected);
1714 let err = tcx.ty_error();
1717 self.check_pat(&inner, inner_ty, def_bm, TopInfo { parent_pat: Some(&pat), ..ti });
1721 /// Create a reference type with a fresh region variable.
1722 fn new_ref_ty(&self, span: Span, mutbl: hir::Mutability, ty: Ty<'tcx>) -> Ty<'tcx> {
1723 let region = self.next_region_var(infer::PatternRegion(span));
1724 let mt = ty::TypeAndMut { ty, mutbl };
1725 self.tcx.mk_ref(region, mt)
1728 /// Type check a slice pattern.
1730 /// Syntactically, these look like `[pat_0, ..., pat_n]`.
1731 /// Semantically, we are type checking a pattern with structure:
1733 /// [before_0, ..., before_n, (slice, after_0, ... after_n)?]
1735 /// The type of `slice`, if it is present, depends on the `expected` type.
1736 /// If `slice` is missing, then so is `after_i`.
1737 /// If `slice` is present, it can still represent 0 elements.
1741 before: &'tcx [&'tcx Pat<'tcx>],
1742 slice: Option<&'tcx Pat<'tcx>>,
1743 after: &'tcx [&'tcx Pat<'tcx>],
1745 def_bm: BindingMode,
1748 let expected = self.structurally_resolved_type(span, expected);
1749 let (element_ty, opt_slice_ty, inferred) = match *expected.kind() {
1750 // An array, so we might have something like `let [a, b, c] = [0, 1, 2];`.
1751 ty::Array(element_ty, len) => {
1752 let min = before.len() as u64 + after.len() as u64;
1753 let (opt_slice_ty, expected) =
1754 self.check_array_pat_len(span, element_ty, expected, slice, len, min);
1755 // `opt_slice_ty.is_none()` => `slice.is_none()`.
1756 // Note, though, that opt_slice_ty could be `Some(error_ty)`.
1757 assert!(opt_slice_ty.is_some() || slice.is_none());
1758 (element_ty, opt_slice_ty, expected)
1760 ty::Slice(element_ty) => (element_ty, Some(expected), expected),
1761 // The expected type must be an array or slice, but was neither, so error.
1763 if !expected.references_error() {
1764 self.error_expected_array_or_slice(span, expected);
1766 let err = self.tcx.ty_error();
1767 (err, Some(err), err)
1771 // Type check all the patterns before `slice`.
1773 self.check_pat(&elt, element_ty, def_bm, ti);
1775 // Type check the `slice`, if present, against its expected type.
1776 if let Some(slice) = slice {
1777 self.check_pat(&slice, opt_slice_ty.unwrap(), def_bm, ti);
1779 // Type check the elements after `slice`, if present.
1781 self.check_pat(&elt, element_ty, def_bm, ti);
1786 /// Type check the length of an array pattern.
1788 /// Returns both the type of the variable length pattern (or `None`), and the potentially
1789 /// inferred array type. We only return `None` for the slice type if `slice.is_none()`.
1790 fn check_array_pat_len(
1793 element_ty: Ty<'tcx>,
1795 slice: Option<&'tcx Pat<'tcx>>,
1796 len: &ty::Const<'tcx>,
1798 ) -> (Option<Ty<'tcx>>, Ty<'tcx>) {
1799 if let Some(len) = len.try_eval_usize(self.tcx, self.param_env) {
1800 // Now we know the length...
1801 if slice.is_none() {
1802 // ...and since there is no variable-length pattern,
1803 // we require an exact match between the number of elements
1804 // in the array pattern and as provided by the matched type.
1806 return (None, arr_ty);
1809 self.error_scrutinee_inconsistent_length(span, min_len, len);
1810 } else if let Some(pat_len) = len.checked_sub(min_len) {
1811 // The variable-length pattern was there,
1812 // so it has an array type with the remaining elements left as its size...
1813 return (Some(self.tcx.mk_array(element_ty, pat_len)), arr_ty);
1815 // ...however, in this case, there were no remaining elements.
1816 // That is, the slice pattern requires more than the array type offers.
1817 self.error_scrutinee_with_rest_inconsistent_length(span, min_len, len);
1819 } else if slice.is_none() {
1820 // We have a pattern with a fixed length,
1821 // which we can use to infer the length of the array.
1822 let updated_arr_ty = self.tcx.mk_array(element_ty, min_len);
1823 self.demand_eqtype(span, updated_arr_ty, arr_ty);
1824 return (None, updated_arr_ty);
1826 // We have a variable-length pattern and don't know the array length.
1827 // This happens if we have e.g.,
1828 // `let [a, b, ..] = arr` where `arr: [T; N]` where `const N: usize`.
1829 self.error_scrutinee_unfixed_length(span);
1832 // If we get here, we must have emitted an error.
1833 (Some(self.tcx.ty_error()), arr_ty)
1836 fn error_scrutinee_inconsistent_length(&self, span: Span, min_len: u64, size: u64) {
1841 "pattern requires {} element{} but array has {}",
1843 pluralize!(min_len),
1846 .span_label(span, format!("expected {} element{}", size, pluralize!(size)))
1850 fn error_scrutinee_with_rest_inconsistent_length(&self, span: Span, min_len: u64, size: u64) {
1855 "pattern requires at least {} element{} but array has {}",
1857 pluralize!(min_len),
1862 format!("pattern cannot match array of {} element{}", size, pluralize!(size),),
1867 fn error_scrutinee_unfixed_length(&self, span: Span) {
1872 "cannot pattern-match on an array without a fixed length",
1877 fn error_expected_array_or_slice(&self, span: Span, expected_ty: Ty<'tcx>) {
1878 let mut err = struct_span_err!(
1882 "expected an array or slice, found `{}`",
1885 if let ty::Ref(_, ty, _) = expected_ty.kind() {
1886 if let ty::Array(..) | ty::Slice(..) = ty.kind() {
1887 err.help("the semantics of slice patterns changed recently; see issue #62254");
1890 err.span_label(span, format!("pattern cannot match with input type `{}`", expected_ty));