1 use crate::check::FnCtxt;
3 use rustc_ast::util::lev_distance::find_best_match_for_name;
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, BindingMode, Ty, TypeFoldable};
14 use rustc_span::hygiene::DesugaringKind;
15 use rustc_span::source_map::{Span, Spanned};
16 use rustc_span::symbol::Ident;
17 use rustc_trait_selection::traits::{ObligationCause, Pattern};
20 use std::collections::hash_map::Entry::{Occupied, Vacant};
22 use super::report_unexpected_variant_res;
24 const CANNOT_IMPLICITLY_DEREF_POINTER_TRAIT_OBJ: &str = "\
25 This error indicates that a pointer to a trait type cannot be implicitly dereferenced by a \
26 pattern. Every trait defines a type, but because the size of trait implementors isn't fixed, \
27 this type has no compile-time size. Therefore, all accesses to trait types must be through \
28 pointers. If you encounter this error you should try to avoid dereferencing the pointer.
30 You can read more about trait objects in the Trait Objects section of the Reference: \
31 https://doc.rust-lang.org/reference/types.html#trait-objects";
33 /// Information about the expected type at the top level of type checking a pattern.
35 /// **NOTE:** This is only for use by diagnostics. Do NOT use for type checking logic!
36 #[derive(Copy, Clone)]
37 struct TopInfo<'tcx> {
38 /// The `expected` type at the top level of type checking a pattern.
40 /// Was the origin of the `span` from a scrutinee expression?
42 /// Otherwise there is no scrutinee and it could be e.g. from the type of a formal parameter.
44 /// The span giving rise to the `expected` type, if one could be provided.
46 /// If `origin_expr` is `true`, then this is the span of the scrutinee as in:
48 /// - `match scrutinee { ... }`
49 /// - `let _ = scrutinee;`
51 /// This is used to point to add context in type errors.
52 /// In the following example, `span` corresponds to the `a + b` expression:
55 /// error[E0308]: mismatched types
56 /// --> src/main.rs:L:C
58 /// L | let temp: usize = match a + b {
59 /// | ----- this expression has type `usize`
60 /// L | Ok(num) => num,
61 /// | ^^^^^^^ expected `usize`, found enum `std::result::Result`
63 /// = note: expected type `usize`
64 /// found type `std::result::Result<_, _>`
67 /// This refers to the parent pattern. Used to provide extra diagnostic information on errors.
69 /// error[E0308]: mismatched types
70 /// --> $DIR/const-in-struct-pat.rs:8:17
73 /// | --------- unit struct defined here
75 /// L | let Thing { f } = t;
78 /// | expected struct `std::string::String`, found struct `f`
79 /// | `f` is interpreted as a unit struct, not a new binding
80 /// | help: bind the struct field to a different name instead: `f: other_f`
82 parent_pat: Option<&'tcx Pat<'tcx>>,
85 impl<'tcx> FnCtxt<'_, 'tcx> {
86 fn pattern_cause(&self, ti: TopInfo<'tcx>, cause_span: Span) -> ObligationCause<'tcx> {
87 let code = Pattern { span: ti.span, root_ty: ti.expected, origin_expr: ti.origin_expr };
88 self.cause(cause_span, code)
91 fn demand_eqtype_pat_diag(
97 ) -> Option<DiagnosticBuilder<'tcx>> {
98 self.demand_eqtype_with_origin(&self.pattern_cause(ti, cause_span), expected, actual)
101 fn demand_eqtype_pat(
108 if let Some(mut err) = self.demand_eqtype_pat_diag(cause_span, expected, actual, ti) {
114 const INITIAL_BM: BindingMode = BindingMode::BindByValue(hir::Mutability::Not);
116 /// Mode for adjusting the expected type and binding mode.
118 /// Peel off all immediate reference types.
120 /// Reset binding mode to the initial mode.
122 /// Pass on the input binding mode and expected type.
126 impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
127 /// Type check the given top level pattern against the `expected` type.
129 /// If a `Some(span)` is provided and `origin_expr` holds,
130 /// then the `span` represents the scrutinee's span.
131 /// The scrutinee is found in e.g. `match scrutinee { ... }` and `let pat = scrutinee;`.
133 /// Otherwise, `Some(span)` represents the span of a type expression
134 /// which originated the `expected` type.
135 pub fn check_pat_top(
137 pat: &'tcx Pat<'tcx>,
142 let info = TopInfo { expected, origin_expr, span, parent_pat: None };
143 self.check_pat(pat, expected, INITIAL_BM, info);
146 /// Type check the given `pat` against the `expected` type
147 /// with the provided `def_bm` (default binding mode).
149 /// Outside of this module, `check_pat_top` should always be used.
150 /// Conversely, inside this module, `check_pat_top` should never be used.
153 pat: &'tcx Pat<'tcx>,
158 debug!("check_pat(pat={:?},expected={:?},def_bm={:?})", pat, expected, def_bm);
160 let path_res = match &pat.kind {
161 PatKind::Path(qpath) => Some(self.resolve_ty_and_res_ufcs(qpath, pat.hir_id, pat.span)),
164 let adjust_mode = self.calc_adjust_mode(pat, path_res.map(|(res, ..)| res));
165 let (expected, def_bm) = self.calc_default_binding_mode(pat, expected, def_bm, adjust_mode);
167 let ty = match pat.kind {
168 PatKind::Wild => expected,
169 PatKind::Lit(lt) => self.check_pat_lit(pat.span, lt, expected, ti),
170 PatKind::Range(lhs, rhs, _) => self.check_pat_range(pat.span, lhs, rhs, expected, ti),
171 PatKind::Binding(ba, var_id, _, sub) => {
172 self.check_pat_ident(pat, ba, var_id, sub, expected, def_bm, ti)
174 PatKind::TupleStruct(ref qpath, subpats, ddpos) => {
175 self.check_pat_tuple_struct(pat, qpath, subpats, ddpos, expected, def_bm, ti)
177 PatKind::Path(_) => self.check_pat_path(pat, path_res.unwrap(), expected, ti),
178 PatKind::Struct(ref qpath, fields, etc) => {
179 self.check_pat_struct(pat, qpath, fields, etc, expected, def_bm, ti)
181 PatKind::Or(pats) => {
182 let parent_pat = Some(pat);
184 self.check_pat(pat, expected, def_bm, TopInfo { parent_pat, ..ti });
188 PatKind::Tuple(elements, ddpos) => {
189 self.check_pat_tuple(pat.span, elements, ddpos, expected, def_bm, ti)
191 PatKind::Box(inner) => self.check_pat_box(pat.span, inner, expected, def_bm, ti),
192 PatKind::Ref(inner, mutbl) => {
193 self.check_pat_ref(pat, inner, mutbl, expected, def_bm, ti)
195 PatKind::Slice(before, slice, after) => {
196 self.check_pat_slice(pat.span, before, slice, after, expected, def_bm, ti)
200 self.write_ty(pat.hir_id, ty);
202 // (note_1): In most of the cases where (note_1) is referenced
203 // (literals and constants being the exception), we relate types
204 // using strict equality, even though subtyping would be sufficient.
205 // There are a few reasons for this, some of which are fairly subtle
206 // and which cost me (nmatsakis) an hour or two debugging to remember,
207 // so I thought I'd write them down this time.
209 // 1. There is no loss of expressiveness here, though it does
210 // cause some inconvenience. What we are saying is that the type
211 // of `x` becomes *exactly* what is expected. This can cause unnecessary
212 // errors in some cases, such as this one:
215 // fn foo<'x>(x: &'x i32) {
222 // The reason we might get an error is that `z` might be
223 // assigned a type like `&'x i32`, and then we would have
224 // a problem when we try to assign `&a` to `z`, because
225 // the lifetime of `&a` (i.e., the enclosing block) is
226 // shorter than `'x`.
228 // HOWEVER, this code works fine. The reason is that the
229 // expected type here is whatever type the user wrote, not
230 // the initializer's type. In this case the user wrote
231 // nothing, so we are going to create a type variable `Z`.
232 // Then we will assign the type of the initializer (`&'x i32`)
233 // as a subtype of `Z`: `&'x i32 <: Z`. And hence we
234 // will instantiate `Z` as a type `&'0 i32` where `'0` is
235 // a fresh region variable, with the constraint that `'x : '0`.
236 // So basically we're all set.
238 // Note that there are two tests to check that this remains true
239 // (`regions-reassign-{match,let}-bound-pointer.rs`).
241 // 2. Things go horribly wrong if we use subtype. The reason for
242 // THIS is a fairly subtle case involving bound regions. See the
243 // `givens` field in `region_constraints`, as well as the test
244 // `regions-relate-bound-regions-on-closures-to-inference-variables.rs`,
245 // for details. Short version is that we must sometimes detect
246 // relationships between specific region variables and regions
247 // bound in a closure signature, and that detection gets thrown
248 // off when we substitute fresh region variables here to enable
252 /// Compute the new expected type and default binding mode from the old ones
253 /// as well as the pattern form we are currently checking.
254 fn calc_default_binding_mode(
256 pat: &'tcx Pat<'tcx>,
259 adjust_mode: AdjustMode,
260 ) -> (Ty<'tcx>, BindingMode) {
262 AdjustMode::Pass => (expected, def_bm),
263 AdjustMode::Reset => (expected, INITIAL_BM),
264 AdjustMode::Peel => self.peel_off_references(pat, expected, def_bm),
268 /// How should the binding mode and expected type be adjusted?
270 /// When the pattern is a path pattern, `opt_path_res` must be `Some(res)`.
271 fn calc_adjust_mode(&self, pat: &'tcx Pat<'tcx>, opt_path_res: Option<Res>) -> AdjustMode {
273 // Type checking these product-like types successfully always require
274 // that the expected type be of those types and not reference types.
276 | PatKind::TupleStruct(..)
280 | PatKind::Slice(..) => AdjustMode::Peel,
281 // String and byte-string literals result in types `&str` and `&[u8]` respectively.
282 // All other literals result in non-reference types.
283 // As a result, we allow `if let 0 = &&0 {}` but not `if let "foo" = &&"foo {}`.
284 PatKind::Lit(lt) => match self.check_expr(lt).kind {
285 ty::Ref(..) => AdjustMode::Pass,
286 _ => AdjustMode::Peel,
288 PatKind::Path(_) => match opt_path_res.unwrap() {
289 // These constants can be of a reference type, e.g. `const X: &u8 = &0;`.
290 // Peeling the reference types too early will cause type checking failures.
291 // Although it would be possible to *also* peel the types of the constants too.
292 Res::Def(DefKind::Const | DefKind::AssocConst, _) => AdjustMode::Pass,
293 // In the `ValueNS`, we have `SelfCtor(..) | Ctor(_, Const), _)` remaining which
294 // could successfully compile. The former being `Self` requires a unit struct.
295 // In either case, and unlike constants, the pattern itself cannot be
296 // a reference type wherefore peeling doesn't give up any expressivity.
297 _ => AdjustMode::Peel,
299 // When encountering a `& mut? pat` pattern, reset to "by value".
300 // This is so that `x` and `y` here are by value, as they appear to be:
303 // match &(&22, &44) {
309 PatKind::Ref(..) => AdjustMode::Reset,
310 // A `_` pattern works with any expected type, so there's no need to do anything.
312 // Bindings also work with whatever the expected type is,
313 // and moreover if we peel references off, that will give us the wrong binding type.
314 // Also, we can have a subpattern `binding @ pat`.
315 // Each side of the `@` should be treated independently (like with OR-patterns).
316 | PatKind::Binding(..)
317 // An OR-pattern just propagates to each individual alternative.
318 // This is maximally flexible, allowing e.g., `Some(mut x) | &Some(mut x)`.
319 // In that example, `Some(mut x)` results in `Peel` whereas `&Some(mut x)` in `Reset`.
320 | PatKind::Or(_) => AdjustMode::Pass,
324 /// Peel off as many immediately nested `& mut?` from the expected type as possible
325 /// and return the new expected type and binding default binding mode.
326 /// The adjustments vector, if non-empty is stored in a table.
327 fn peel_off_references(
329 pat: &'tcx Pat<'tcx>,
331 mut def_bm: BindingMode,
332 ) -> (Ty<'tcx>, BindingMode) {
333 let mut expected = self.resolve_vars_with_obligations(&expected);
335 // Peel off as many `&` or `&mut` from the scrutinee type as possible. For example,
336 // for `match &&&mut Some(5)` the loop runs three times, aborting when it reaches
337 // the `Some(5)` which is not of type Ref.
339 // For each ampersand peeled off, update the binding mode and push the original
340 // type into the adjustments vector.
342 // See the examples in `ui/match-defbm*.rs`.
343 let mut pat_adjustments = vec![];
344 while let ty::Ref(_, inner_ty, inner_mutability) = expected.kind {
345 debug!("inspecting {:?}", expected);
347 debug!("current discriminant is Ref, inserting implicit deref");
348 // Preserve the reference type. We'll need it later during HAIR lowering.
349 pat_adjustments.push(expected);
352 def_bm = ty::BindByReference(match def_bm {
353 // If default binding mode is by value, make it `ref` or `ref mut`
354 // (depending on whether we observe `&` or `&mut`).
356 // When `ref mut`, stay a `ref mut` (on `&mut`) or downgrade to `ref` (on `&`).
357 ty::BindByReference(hir::Mutability::Mut) => inner_mutability,
358 // Once a `ref`, always a `ref`.
359 // This is because a `& &mut` cannot mutate the underlying value.
360 ty::BindByReference(m @ hir::Mutability::Not) => m,
364 if !pat_adjustments.is_empty() {
365 debug!("default binding mode is now {:?}", def_bm);
366 self.inh.tables.borrow_mut().pat_adjustments_mut().insert(pat.hir_id, pat_adjustments);
375 lt: &hir::Expr<'tcx>,
379 // We've already computed the type above (when checking for a non-ref pat),
380 // so avoid computing it again.
381 let ty = self.node_ty(lt.hir_id);
383 // Byte string patterns behave the same way as array patterns
384 // They can denote both statically and dynamically-sized byte arrays.
386 if let hir::ExprKind::Lit(Spanned { node: ast::LitKind::ByteStr(_), .. }) = lt.kind {
387 let expected = self.structurally_resolved_type(span, expected);
388 if let ty::Ref(_, ty::TyS { kind: ty::Slice(_), .. }, _) = expected.kind {
390 pat_ty = tcx.mk_imm_ref(tcx.lifetimes.re_static, tcx.mk_slice(tcx.types.u8));
394 // Somewhat surprising: in this case, the subtyping relation goes the
395 // opposite way as the other cases. Actually what we really want is not
396 // a subtyping relation at all but rather that there exists a LUB
397 // (so that they can be compared). However, in practice, constants are
398 // always scalars or strings. For scalars subtyping is irrelevant,
399 // and for strings `ty` is type is `&'static str`, so if we say that
401 // &'static str <: expected
403 // then that's equivalent to there existing a LUB.
404 let cause = self.pattern_cause(ti, span);
405 if let Some(mut err) = self.demand_suptype_with_origin(&cause, expected, pat_ty) {
409 // In the case of `if`- and `while`-expressions we've already checked
410 // that `scrutinee: bool`. We know that the pattern is `true`,
411 // so an error here would be a duplicate and from the wrong POV.
412 s.is_desugaring(DesugaringKind::CondTemporary)
424 lhs: Option<&'tcx hir::Expr<'tcx>>,
425 rhs: Option<&'tcx hir::Expr<'tcx>>,
429 let calc_side = |opt_expr: Option<&'tcx hir::Expr<'tcx>>| match opt_expr {
430 None => (None, None),
432 let ty = self.check_expr(expr);
433 // Check that the end-point is of numeric or char type.
434 let fail = !(ty.is_numeric() || ty.is_char() || ty.references_error());
435 (Some(ty), Some((fail, ty, expr.span)))
438 let (lhs_ty, lhs) = calc_side(lhs);
439 let (rhs_ty, rhs) = calc_side(rhs);
441 if let (Some((true, ..)), _) | (_, Some((true, ..))) = (lhs, rhs) {
442 // There exists a side that didn't meet our criteria that the end-point
443 // be of a numeric or char type, as checked in `calc_side` above.
444 self.emit_err_pat_range(span, lhs, rhs);
445 return self.tcx.ty_error();
448 // Now that we know the types can be unified we find the unified type
449 // and use it to type the entire expression.
450 let common_type = self.resolve_vars_if_possible(&lhs_ty.or(rhs_ty).unwrap_or(expected));
452 // Subtyping doesn't matter here, as the value is some kind of scalar.
453 let demand_eqtype = |x, y| {
454 if let Some((_, x_ty, x_span)) = x {
455 if let Some(mut err) = self.demand_eqtype_pat_diag(x_span, expected, x_ty, ti) {
456 if let Some((_, y_ty, y_span)) = y {
457 self.endpoint_has_type(&mut err, y_span, y_ty);
463 demand_eqtype(lhs, rhs);
464 demand_eqtype(rhs, lhs);
469 fn endpoint_has_type(&self, err: &mut DiagnosticBuilder<'_>, span: Span, ty: Ty<'_>) {
470 if !ty.references_error() {
471 err.span_label(span, &format!("this is of type `{}`", ty));
475 fn emit_err_pat_range(
478 lhs: Option<(bool, Ty<'tcx>, Span)>,
479 rhs: Option<(bool, Ty<'tcx>, Span)>,
481 let span = match (lhs, rhs) {
482 (Some((true, ..)), Some((true, ..))) => span,
483 (Some((true, _, sp)), _) => sp,
484 (_, Some((true, _, sp))) => sp,
485 _ => span_bug!(span, "emit_err_pat_range: no side failed or exists but still error?"),
487 let mut err = struct_span_err!(
491 "only char and numeric types are allowed in range patterns"
493 let msg = |ty| format!("this is of type `{}` but it should be `char` or numeric", ty);
494 let mut one_side_err = |first_span, first_ty, second: Option<(bool, Ty<'tcx>, Span)>| {
495 err.span_label(first_span, &msg(first_ty));
496 if let Some((_, ty, sp)) = second {
497 self.endpoint_has_type(&mut err, sp, ty);
501 (Some((true, lhs_ty, lhs_sp)), Some((true, rhs_ty, rhs_sp))) => {
502 err.span_label(lhs_sp, &msg(lhs_ty));
503 err.span_label(rhs_sp, &msg(rhs_ty));
505 (Some((true, lhs_ty, lhs_sp)), rhs) => one_side_err(lhs_sp, lhs_ty, rhs),
506 (lhs, Some((true, rhs_ty, rhs_sp))) => one_side_err(rhs_sp, rhs_ty, lhs),
507 _ => span_bug!(span, "Impossible, verified above."),
509 if self.tcx.sess.teach(&err.get_code().unwrap()) {
511 "In a match expression, only numbers and characters can be matched \
512 against a range. This is because the compiler checks that the range \
513 is non-empty at compile-time, and is unable to evaluate arbitrary \
514 comparison functions. If you want to capture values of an orderable \
515 type between two end-points, you can use a guard.",
523 pat: &'tcx Pat<'tcx>,
524 ba: hir::BindingAnnotation,
526 sub: Option<&'tcx Pat<'tcx>>,
531 // Determine the binding mode...
533 hir::BindingAnnotation::Unannotated => def_bm,
534 _ => BindingMode::convert(ba),
536 // ...and store it in a side table:
537 self.inh.tables.borrow_mut().pat_binding_modes_mut().insert(pat.hir_id, bm);
539 debug!("check_pat_ident: pat.hir_id={:?} bm={:?}", pat.hir_id, bm);
541 let local_ty = self.local_ty(pat.span, pat.hir_id).decl_ty;
542 let eq_ty = match bm {
543 ty::BindByReference(mutbl) => {
544 // If the binding is like `ref x | ref mut x`,
545 // then `x` is assigned a value of type `&M T` where M is the
546 // mutability and T is the expected type.
548 // `x` is assigned a value of type `&M T`, hence `&M T <: typeof(x)`
549 // is required. However, we use equality, which is stronger.
550 // See (note_1) for an explanation.
551 self.new_ref_ty(pat.span, mutbl, expected)
553 // Otherwise, the type of x is the expected type `T`.
554 ty::BindByValue(_) => {
555 // As above, `T <: typeof(x)` is required, but we use equality, see (note_1).
559 self.demand_eqtype_pat(pat.span, eq_ty, local_ty, ti);
561 // If there are multiple arms, make sure they all agree on
562 // what the type of the binding `x` ought to be.
563 if var_id != pat.hir_id {
564 self.check_binding_alt_eq_ty(pat.span, var_id, local_ty, ti);
567 if let Some(p) = sub {
568 self.check_pat(&p, expected, def_bm, TopInfo { parent_pat: Some(&pat), ..ti });
574 fn check_binding_alt_eq_ty(&self, span: Span, var_id: HirId, ty: Ty<'tcx>, ti: TopInfo<'tcx>) {
575 let var_ty = self.local_ty(span, var_id).decl_ty;
576 if let Some(mut err) = self.demand_eqtype_pat_diag(span, var_ty, ty, ti) {
577 let hir = self.tcx.hir();
578 let var_ty = self.resolve_vars_with_obligations(var_ty);
579 let msg = format!("first introduced with type `{}` here", var_ty);
580 err.span_label(hir.span(var_id), msg);
581 let in_match = hir.parent_iter(var_id).any(|(_, n)| {
584 hir::Node::Expr(hir::Expr {
585 kind: hir::ExprKind::Match(.., hir::MatchSource::Normal),
590 let pre = if in_match { "in the same arm, " } else { "" };
591 err.note(&format!("{}a binding must have the same type in all alternatives", pre));
596 fn borrow_pat_suggestion(
598 err: &mut DiagnosticBuilder<'_>,
604 if let PatKind::Binding(..) = inner.kind {
605 let binding_parent_id = tcx.hir().get_parent_node(pat.hir_id);
606 let binding_parent = tcx.hir().get(binding_parent_id);
607 debug!("inner {:?} pat {:?} parent {:?}", inner, pat, binding_parent);
608 match binding_parent {
609 hir::Node::Param(hir::Param { span, .. }) => {
610 if let Ok(snippet) = tcx.sess.source_map().span_to_snippet(inner.span) {
613 &format!("did you mean `{}`", snippet),
614 format!(" &{}", expected),
615 Applicability::MachineApplicable,
619 hir::Node::Arm(_) | hir::Node::Pat(_) => {
620 // rely on match ergonomics or it might be nested `&&pat`
621 if let Ok(snippet) = tcx.sess.source_map().span_to_snippet(inner.span) {
624 "you can probably remove the explicit borrow",
626 Applicability::MaybeIncorrect,
630 _ => {} // don't provide suggestions in other cases #55175
635 pub fn check_dereferenceable(&self, span: Span, expected: Ty<'tcx>, inner: &Pat<'_>) -> bool {
636 if let PatKind::Binding(..) = inner.kind {
637 if let Some(mt) = self.shallow_resolve(expected).builtin_deref(true) {
638 if let ty::Dynamic(..) = mt.ty.kind {
639 // This is "x = SomeTrait" being reduced from
640 // "let &x = &SomeTrait" or "let box x = Box<SomeTrait>", an error.
641 let type_str = self.ty_to_string(expected);
642 let mut err = struct_span_err!(
646 "type `{}` cannot be dereferenced",
649 err.span_label(span, format!("type `{}` cannot be dereferenced", type_str));
650 if self.tcx.sess.teach(&err.get_code().unwrap()) {
651 err.note(CANNOT_IMPLICITLY_DEREF_POINTER_TRAIT_OBJ);
663 pat: &'tcx Pat<'tcx>,
664 qpath: &hir::QPath<'_>,
665 fields: &'tcx [hir::FieldPat<'tcx>],
671 // Resolve the path and check the definition for errors.
672 let (variant, pat_ty) = if let Some(variant_ty) = self.check_struct_path(qpath, pat.hir_id)
676 let err = self.tcx.ty_error();
677 for field in fields {
678 let ti = TopInfo { parent_pat: Some(&pat), ..ti };
679 self.check_pat(&field.pat, err, def_bm, ti);
684 // Type-check the path.
685 self.demand_eqtype_pat(pat.span, expected, pat_ty, ti);
687 // Type-check subpatterns.
688 if self.check_struct_pat_fields(pat_ty, &pat, variant, fields, etc, def_bm, ti) {
698 path_resolution: (Res, Option<Ty<'tcx>>, &'b [hir::PathSegment<'b>]),
704 // We have already resolved the path.
705 let (res, opt_ty, segments) = path_resolution;
708 self.set_tainted_by_errors();
709 return tcx.ty_error();
711 Res::Def(DefKind::AssocFn | DefKind::Ctor(_, CtorKind::Fictive | CtorKind::Fn), _) => {
712 report_unexpected_variant_res(tcx, res, pat.span);
713 return tcx.ty_error();
717 DefKind::Ctor(_, CtorKind::Const)
719 | DefKind::AssocConst
720 | DefKind::ConstParam,
723 _ => bug!("unexpected pattern resolution: {:?}", res),
726 // Type-check the path.
727 let (pat_ty, pat_res) =
728 self.instantiate_value_path(segments, opt_ty, res, pat.span, pat.hir_id);
730 self.demand_suptype_with_origin(&self.pattern_cause(ti, pat.span), expected, pat_ty)
732 self.emit_bad_pat_path(err, pat.span, res, pat_res, segments, ti.parent_pat);
737 fn emit_bad_pat_path(
739 mut e: DiagnosticBuilder<'_>,
743 segments: &'b [hir::PathSegment<'b>],
744 parent_pat: Option<&Pat<'_>>,
746 if let Some(span) = self.tcx.hir().res_span(pat_res) {
747 e.span_label(span, &format!("{} defined here", res.descr()));
748 if let [hir::PathSegment { ident, .. }] = &*segments {
752 "`{}` is interpreted as {} {}, not a new binding",
759 Some(Pat { kind: hir::PatKind::Struct(..), .. }) => {
760 e.span_suggestion_verbose(
761 ident.span.shrink_to_hi(),
762 "bind the struct field to a different name instead",
763 format!(": other_{}", ident.as_str().to_lowercase()),
764 Applicability::HasPlaceholders,
768 let msg = "introduce a new binding instead";
769 let sugg = format!("other_{}", ident.as_str().to_lowercase());
770 e.span_suggestion(ident.span, msg, sugg, Applicability::HasPlaceholders);
778 fn check_pat_tuple_struct(
780 pat: &'tcx Pat<'tcx>,
781 qpath: &hir::QPath<'_>,
782 subpats: &'tcx [&'tcx Pat<'tcx>],
783 ddpos: Option<usize>,
790 let parent_pat = Some(pat);
792 self.check_pat(&pat, tcx.ty_error(), def_bm, TopInfo { parent_pat, ..ti });
795 let report_unexpected_res = |res: Res| {
796 let sm = tcx.sess.source_map();
798 .span_to_snippet(sm.span_until_char(pat.span, '('))
799 .map_or(String::new(), |s| format!(" `{}`", s.trim_end()));
801 "expected tuple struct or tuple variant, found {}{}",
806 let mut err = struct_span_err!(tcx.sess, pat.span, E0164, "{}", msg);
808 Res::Def(DefKind::Fn | DefKind::AssocFn, _) => {
809 err.span_label(pat.span, "`fn` calls are not allowed in patterns");
811 "for more information, visit \
812 https://doc.rust-lang.org/book/ch18-00-patterns.html",
816 err.span_label(pat.span, "not a tuple variant or struct");
823 // Resolve the path and check the definition for errors.
824 let (res, opt_ty, segments) = self.resolve_ty_and_res_ufcs(qpath, pat.hir_id, pat.span);
826 self.set_tainted_by_errors();
828 return self.tcx.ty_error();
831 // Type-check the path.
833 self.instantiate_value_path(segments, opt_ty, res, pat.span, pat.hir_id);
835 report_unexpected_res(res);
836 return tcx.ty_error();
839 let variant = match res {
841 self.set_tainted_by_errors();
843 return tcx.ty_error();
845 Res::Def(DefKind::AssocConst | DefKind::AssocFn, _) => {
846 report_unexpected_res(res);
847 return tcx.ty_error();
849 Res::Def(DefKind::Ctor(_, CtorKind::Fn), _) => tcx.expect_variant_res(res),
850 _ => bug!("unexpected pattern resolution: {:?}", res),
853 // Replace constructor type with constructed type for tuple struct patterns.
854 let pat_ty = pat_ty.fn_sig(tcx).output();
855 let pat_ty = pat_ty.no_bound_vars().expect("expected fn type");
857 // Type-check the tuple struct pattern against the expected type.
858 let diag = self.demand_eqtype_pat_diag(pat.span, expected, pat_ty, ti);
859 let had_err = if let Some(mut err) = diag {
866 // Type-check subpatterns.
867 if subpats.len() == variant.fields.len()
868 || subpats.len() < variant.fields.len() && ddpos.is_some()
870 let substs = match pat_ty.kind {
871 ty::Adt(_, substs) => substs,
872 _ => bug!("unexpected pattern type {:?}", pat_ty),
874 for (i, subpat) in subpats.iter().enumerate_and_adjust(variant.fields.len(), ddpos) {
875 let field_ty = self.field_ty(subpat.span, &variant.fields[i], substs);
876 self.check_pat(&subpat, field_ty, def_bm, TopInfo { parent_pat: Some(&pat), ..ti });
878 self.tcx.check_stability(variant.fields[i].did, Some(pat.hir_id), subpat.span);
881 // Pattern has wrong number of fields.
882 self.e0023(pat.span, res, qpath, subpats, &variant.fields, expected, had_err);
884 return tcx.ty_error();
893 qpath: &hir::QPath<'_>,
894 subpats: &'tcx [&'tcx Pat<'tcx>],
895 fields: &'tcx [ty::FieldDef],
899 let subpats_ending = pluralize!(subpats.len());
900 let fields_ending = pluralize!(fields.len());
901 let res_span = self.tcx.def_span(res.def_id());
902 let mut err = struct_span_err!(
906 "this pattern has {} field{}, but the corresponding {} has {} field{}",
915 format!("expected {} field{}, found {}", fields.len(), fields_ending, subpats.len(),),
917 .span_label(res_span, format!("{} defined here", res.descr()));
919 // Identify the case `Some(x, y)` where the expected type is e.g. `Option<(T, U)>`.
920 // More generally, the expected type wants a tuple variant with one field of an
921 // N-arity-tuple, e.g., `V_i((p_0, .., p_N))`. Meanwhile, the user supplied a pattern
922 // with the subpatterns directly in the tuple variant pattern, e.g., `V_i(p_0, .., p_N)`.
923 let missing_parenthesis = match (&expected.kind, fields, had_err) {
924 // #67037: only do this if we could successfully type-check the expected type against
925 // the tuple struct pattern. Otherwise the substs could get out of range on e.g.,
926 // `let P() = U;` where `P != U` with `struct P<T>(T);`.
927 (ty::Adt(_, substs), [field], false) => {
928 let field_ty = self.field_ty(pat_span, field, substs);
929 match field_ty.kind {
930 ty::Tuple(_) => field_ty.tuple_fields().count() == subpats.len(),
936 if missing_parenthesis {
937 let (left, right) = match subpats {
938 // This is the zero case; we aim to get the "hi" part of the `QPath`'s
939 // span as the "lo" and then the "hi" part of the pattern's span as the "hi".
942 // help: missing parenthesis
944 // L | let A(()) = A(());
947 let qpath_span = match qpath {
948 hir::QPath::Resolved(_, path) => path.span,
949 hir::QPath::TypeRelative(_, ps) => ps.ident.span,
951 (qpath_span.shrink_to_hi(), pat_span)
953 // Easy case. Just take the "lo" of the first sub-pattern and the "hi" of the
954 // last sub-pattern. In the case of `A(x)` the first and last may coincide.
957 // help: missing parenthesis
959 // L | let A((x, y)) = A((1, 2));
961 [first, ..] => (first.span.shrink_to_lo(), subpats.last().unwrap().span),
963 err.multipart_suggestion(
964 "missing parenthesis",
965 vec![(left, "(".to_string()), (right.shrink_to_hi(), ")".to_string())],
966 Applicability::MachineApplicable,
976 elements: &'tcx [&'tcx Pat<'tcx>],
977 ddpos: Option<usize>,
983 let mut expected_len = elements.len();
985 // Require known type only when `..` is present.
986 if let ty::Tuple(ref tys) = self.structurally_resolved_type(span, expected).kind {
987 expected_len = tys.len();
990 let max_len = cmp::max(expected_len, elements.len());
992 let element_tys_iter = (0..max_len).map(|_| {
993 GenericArg::from(self.next_ty_var(
994 // FIXME: `MiscVariable` for now -- obtaining the span and name information
995 // from all tuple elements isn't trivial.
996 TypeVariableOrigin { kind: TypeVariableOriginKind::TypeInference, span },
999 let element_tys = tcx.mk_substs(element_tys_iter);
1000 let pat_ty = tcx.mk_ty(ty::Tuple(element_tys));
1001 if let Some(mut err) = self.demand_eqtype_pat_diag(span, expected, pat_ty, ti) {
1003 // Walk subpatterns with an expected type of `err` in this case to silence
1004 // further errors being emitted when using the bindings. #50333
1005 let element_tys_iter = (0..max_len).map(|_| tcx.ty_error());
1006 for (_, elem) in elements.iter().enumerate_and_adjust(max_len, ddpos) {
1007 self.check_pat(elem, &tcx.ty_error(), def_bm, ti);
1009 tcx.mk_tup(element_tys_iter)
1011 for (i, elem) in elements.iter().enumerate_and_adjust(max_len, ddpos) {
1012 self.check_pat(elem, &element_tys[i].expect_ty(), def_bm, ti);
1018 fn check_struct_pat_fields(
1021 pat: &'tcx Pat<'tcx>,
1022 variant: &'tcx ty::VariantDef,
1023 fields: &'tcx [hir::FieldPat<'tcx>],
1025 def_bm: BindingMode,
1030 let (substs, adt) = match adt_ty.kind {
1031 ty::Adt(adt, substs) => (substs, adt),
1032 _ => span_bug!(pat.span, "struct pattern is not an ADT"),
1035 // Index the struct fields' types.
1036 let field_map = variant
1040 .map(|(i, field)| (field.ident.normalize_to_macros_2_0(), (i, field)))
1041 .collect::<FxHashMap<_, _>>();
1043 // Keep track of which fields have already appeared in the pattern.
1044 let mut used_fields = FxHashMap::default();
1045 let mut no_field_errors = true;
1047 let mut inexistent_fields = vec![];
1048 // Typecheck each field.
1049 for field in fields {
1050 let span = field.span;
1051 let ident = tcx.adjust_ident(field.ident, variant.def_id);
1052 let field_ty = match used_fields.entry(ident) {
1053 Occupied(occupied) => {
1054 self.error_field_already_bound(span, field.ident, *occupied.get());
1055 no_field_errors = false;
1059 vacant.insert(span);
1063 self.write_field_index(field.hir_id, *i);
1064 self.tcx.check_stability(f.did, Some(pat.hir_id), span);
1065 self.field_ty(span, f, substs)
1067 .unwrap_or_else(|| {
1068 inexistent_fields.push(field.ident);
1069 no_field_errors = false;
1075 self.check_pat(&field.pat, field_ty, def_bm, TopInfo { parent_pat: Some(&pat), ..ti });
1078 let mut unmentioned_fields = variant
1081 .map(|field| field.ident.normalize_to_macros_2_0())
1082 .filter(|ident| !used_fields.contains_key(&ident))
1083 .collect::<Vec<_>>();
1085 if !inexistent_fields.is_empty() && !variant.recovered {
1086 self.error_inexistent_fields(
1087 adt.variant_descr(),
1089 &mut unmentioned_fields,
1094 // Require `..` if struct has non_exhaustive attribute.
1095 if variant.is_field_list_non_exhaustive() && !adt.did.is_local() && !etc {
1096 self.error_foreign_non_exhaustive_spat(pat, adt.variant_descr(), fields.is_empty());
1099 // Report an error if incorrect number of the fields were specified.
1101 if fields.len() != 1 {
1103 .struct_span_err(pat.span, "union patterns should have exactly one field")
1107 tcx.sess.struct_span_err(pat.span, "`..` cannot be used in union patterns").emit();
1109 } else if !etc && !unmentioned_fields.is_empty() {
1110 self.error_unmentioned_fields(pat.span, &unmentioned_fields, variant);
1115 fn error_foreign_non_exhaustive_spat(&self, pat: &Pat<'_>, descr: &str, no_fields: bool) {
1116 let sess = self.tcx.sess;
1117 let sm = sess.source_map();
1118 let sp_brace = sm.end_point(pat.span);
1119 let sp_comma = sm.end_point(pat.span.with_hi(sp_brace.hi()));
1120 let sugg = if no_fields || sp_brace != sp_comma { ".. }" } else { ", .. }" };
1122 let mut err = struct_span_err!(
1126 "`..` required with {} marked as non-exhaustive",
1129 err.span_suggestion_verbose(
1131 "add `..` at the end of the field list to ignore all other fields",
1133 Applicability::MachineApplicable,
1138 fn error_field_already_bound(&self, span: Span, ident: Ident, other_field: Span) {
1143 "field `{}` bound multiple times in the pattern",
1146 .span_label(span, format!("multiple uses of `{}` in pattern", ident))
1147 .span_label(other_field, format!("first use of `{}`", ident))
1151 fn error_inexistent_fields(
1154 inexistent_fields: &[Ident],
1155 unmentioned_fields: &mut Vec<Ident>,
1156 variant: &ty::VariantDef,
1159 let (field_names, t, plural) = if inexistent_fields.len() == 1 {
1160 (format!("a field named `{}`", inexistent_fields[0]), "this", "")
1167 .map(|ident| format!("`{}`", ident))
1168 .collect::<Vec<String>>()
1175 let spans = inexistent_fields.iter().map(|ident| ident.span).collect::<Vec<_>>();
1176 let mut err = struct_span_err!(
1180 "{} `{}` does not have {}",
1182 tcx.def_path_str(variant.def_id),
1185 if let Some(ident) = inexistent_fields.last() {
1189 "{} `{}` does not have {} field{}",
1191 tcx.def_path_str(variant.def_id),
1197 let input = unmentioned_fields.iter().map(|field| &field.name);
1198 let suggested_name = find_best_match_for_name(input, &ident.as_str(), None);
1199 if let Some(suggested_name) = suggested_name {
1200 err.span_suggestion(
1202 "a field with a similar name exists",
1203 suggested_name.to_string(),
1204 Applicability::MaybeIncorrect,
1207 // we don't want to throw `E0027` in case we have thrown `E0026` for them
1208 unmentioned_fields.retain(|&x| x.name != suggested_name);
1212 if tcx.sess.teach(&err.get_code().unwrap()) {
1214 "This error indicates that a struct pattern attempted to \
1215 extract a non-existent field from a struct. Struct fields \
1216 are identified by the name used before the colon : so struct \
1217 patterns should resemble the declaration of the struct type \
1219 If you are using shorthand field patterns but want to refer \
1220 to the struct field by a different name, you should rename \
1227 fn error_unmentioned_fields(
1230 unmentioned_fields: &[Ident],
1231 variant: &ty::VariantDef,
1233 let field_names = if unmentioned_fields.len() == 1 {
1234 format!("field `{}`", unmentioned_fields[0])
1236 let fields = unmentioned_fields
1238 .map(|name| format!("`{}`", name))
1239 .collect::<Vec<String>>()
1241 format!("fields {}", fields)
1243 let mut diag = struct_span_err!(
1247 "pattern does not mention {}",
1250 diag.span_label(span, format!("missing {}", field_names));
1251 if variant.ctor_kind == CtorKind::Fn {
1252 diag.note("trying to match a tuple variant with a struct variant pattern");
1254 if self.tcx.sess.teach(&diag.get_code().unwrap()) {
1256 "This error indicates that a pattern for a struct fails to specify a \
1257 sub-pattern for every one of the struct's fields. Ensure that each field \
1258 from the struct's definition is mentioned in the pattern, or use `..` to \
1259 ignore unwanted fields.",
1268 inner: &'tcx Pat<'tcx>,
1270 def_bm: BindingMode,
1274 let (box_ty, inner_ty) = if self.check_dereferenceable(span, expected, &inner) {
1275 // Here, `demand::subtype` is good enough, but I don't
1276 // think any errors can be introduced by using `demand::eqtype`.
1277 let inner_ty = self.next_ty_var(TypeVariableOrigin {
1278 kind: TypeVariableOriginKind::TypeInference,
1281 let box_ty = tcx.mk_box(inner_ty);
1282 self.demand_eqtype_pat(span, expected, box_ty, ti);
1285 let err = tcx.ty_error();
1288 self.check_pat(&inner, inner_ty, def_bm, ti);
1294 pat: &'tcx Pat<'tcx>,
1295 inner: &'tcx Pat<'tcx>,
1296 mutbl: hir::Mutability,
1298 def_bm: BindingMode,
1302 let expected = self.shallow_resolve(expected);
1303 let (rptr_ty, inner_ty) = if self.check_dereferenceable(pat.span, expected, &inner) {
1304 // `demand::subtype` would be good enough, but using `eqtype` turns
1305 // out to be equally general. See (note_1) for details.
1307 // Take region, inner-type from expected type if we can,
1308 // to avoid creating needless variables. This also helps with
1309 // the bad interactions of the given hack detailed in (note_1).
1310 debug!("check_pat_ref: expected={:?}", expected);
1311 match expected.kind {
1312 ty::Ref(_, r_ty, r_mutbl) if r_mutbl == mutbl => (expected, r_ty),
1314 let inner_ty = self.next_ty_var(TypeVariableOrigin {
1315 kind: TypeVariableOriginKind::TypeInference,
1318 let rptr_ty = self.new_ref_ty(pat.span, mutbl, inner_ty);
1319 debug!("check_pat_ref: demanding {:?} = {:?}", expected, rptr_ty);
1320 let err = self.demand_eqtype_pat_diag(pat.span, expected, rptr_ty, ti);
1322 // Look for a case like `fn foo(&foo: u32)` and suggest
1323 // `fn foo(foo: &u32)`
1324 if let Some(mut err) = err {
1325 self.borrow_pat_suggestion(&mut err, &pat, &inner, &expected);
1332 let err = tcx.ty_error();
1335 self.check_pat(&inner, inner_ty, def_bm, TopInfo { parent_pat: Some(&pat), ..ti });
1339 /// Create a reference type with a fresh region variable.
1340 fn new_ref_ty(&self, span: Span, mutbl: hir::Mutability, ty: Ty<'tcx>) -> Ty<'tcx> {
1341 let region = self.next_region_var(infer::PatternRegion(span));
1342 let mt = ty::TypeAndMut { ty, mutbl };
1343 self.tcx.mk_ref(region, mt)
1346 /// Type check a slice pattern.
1348 /// Syntactically, these look like `[pat_0, ..., pat_n]`.
1349 /// Semantically, we are type checking a pattern with structure:
1351 /// [before_0, ..., before_n, (slice, after_0, ... after_n)?]
1353 /// The type of `slice`, if it is present, depends on the `expected` type.
1354 /// If `slice` is missing, then so is `after_i`.
1355 /// If `slice` is present, it can still represent 0 elements.
1359 before: &'tcx [&'tcx Pat<'tcx>],
1360 slice: Option<&'tcx Pat<'tcx>>,
1361 after: &'tcx [&'tcx Pat<'tcx>],
1363 def_bm: BindingMode,
1366 let expected = self.structurally_resolved_type(span, expected);
1367 let (element_ty, opt_slice_ty, inferred) = match expected.kind {
1368 // An array, so we might have something like `let [a, b, c] = [0, 1, 2];`.
1369 ty::Array(element_ty, len) => {
1370 let min = before.len() as u64 + after.len() as u64;
1371 let (opt_slice_ty, expected) =
1372 self.check_array_pat_len(span, element_ty, expected, slice, len, min);
1373 // `opt_slice_ty.is_none()` => `slice.is_none()`.
1374 // Note, though, that opt_slice_ty could be `Some(error_ty)`.
1375 assert!(opt_slice_ty.is_some() || slice.is_none());
1376 (element_ty, opt_slice_ty, expected)
1378 ty::Slice(element_ty) => (element_ty, Some(expected), expected),
1379 // The expected type must be an array or slice, but was neither, so error.
1381 if !expected.references_error() {
1382 self.error_expected_array_or_slice(span, expected);
1384 let err = self.tcx.ty_error();
1385 (err, Some(err), err)
1389 // Type check all the patterns before `slice`.
1391 self.check_pat(&elt, element_ty, def_bm, ti);
1393 // Type check the `slice`, if present, against its expected type.
1394 if let Some(slice) = slice {
1395 self.check_pat(&slice, opt_slice_ty.unwrap(), def_bm, ti);
1397 // Type check the elements after `slice`, if present.
1399 self.check_pat(&elt, element_ty, def_bm, ti);
1404 /// Type check the length of an array pattern.
1406 /// Returns both the type of the variable length pattern (or `None`), and the potentially
1407 /// inferred array type. We only return `None` for the slice type if `slice.is_none()`.
1408 fn check_array_pat_len(
1411 element_ty: Ty<'tcx>,
1413 slice: Option<&'tcx Pat<'tcx>>,
1414 len: &ty::Const<'tcx>,
1416 ) -> (Option<Ty<'tcx>>, Ty<'tcx>) {
1417 if let Some(len) = len.try_eval_usize(self.tcx, self.param_env) {
1418 // Now we know the length...
1419 if slice.is_none() {
1420 // ...and since there is no variable-length pattern,
1421 // we require an exact match between the number of elements
1422 // in the array pattern and as provided by the matched type.
1424 return (None, arr_ty);
1427 self.error_scrutinee_inconsistent_length(span, min_len, len);
1428 } else if let Some(pat_len) = len.checked_sub(min_len) {
1429 // The variable-length pattern was there,
1430 // so it has an array type with the remaining elements left as its size...
1431 return (Some(self.tcx.mk_array(element_ty, pat_len)), arr_ty);
1433 // ...however, in this case, there were no remaining elements.
1434 // That is, the slice pattern requires more than the array type offers.
1435 self.error_scrutinee_with_rest_inconsistent_length(span, min_len, len);
1437 } else if slice.is_none() {
1438 // We have a pattern with a fixed length,
1439 // which we can use to infer the length of the array.
1440 let updated_arr_ty = self.tcx.mk_array(element_ty, min_len);
1441 self.demand_eqtype(span, updated_arr_ty, arr_ty);
1442 return (None, updated_arr_ty);
1444 // We have a variable-length pattern and don't know the array length.
1445 // This happens if we have e.g.,
1446 // `let [a, b, ..] = arr` where `arr: [T; N]` where `const N: usize`.
1447 self.error_scrutinee_unfixed_length(span);
1450 // If we get here, we must have emitted an error.
1451 (Some(self.tcx.ty_error()), arr_ty)
1454 fn error_scrutinee_inconsistent_length(&self, span: Span, min_len: u64, size: u64) {
1459 "pattern requires {} element{} but array has {}",
1461 pluralize!(min_len),
1464 .span_label(span, format!("expected {} element{}", size, pluralize!(size)))
1468 fn error_scrutinee_with_rest_inconsistent_length(&self, span: Span, min_len: u64, size: u64) {
1473 "pattern requires at least {} element{} but array has {}",
1475 pluralize!(min_len),
1480 format!("pattern cannot match array of {} element{}", size, pluralize!(size),),
1485 fn error_scrutinee_unfixed_length(&self, span: Span) {
1490 "cannot pattern-match on an array without a fixed length",
1495 fn error_expected_array_or_slice(&self, span: Span, expected_ty: Ty<'tcx>) {
1496 let mut err = struct_span_err!(
1500 "expected an array or slice, found `{}`",
1503 if let ty::Ref(_, ty, _) = expected_ty.kind {
1504 if let ty::Array(..) | ty::Slice(..) = ty.kind {
1505 err.help("the semantics of slice patterns changed recently; see issue #62254");
1508 err.span_label(span, format!("pattern cannot match with input type `{}`", expected_ty));