| use check::{FnCtxt, Expectation, Diverges, Needs}; |
| use check::coercion::CoerceMany; |
| use rustc::hir::{self, PatKind}; |
| use rustc::hir::def::{Def, CtorKind}; |
| use rustc::hir::pat_util::EnumerateAndAdjustIterator; |
| use rustc::infer; |
| use rustc::infer::type_variable::TypeVariableOrigin; |
| use rustc::traits::ObligationCauseCode; |
| use rustc::ty::{self, Ty, TypeFoldable}; |
| use syntax::ast; |
| use syntax::source_map::Spanned; |
| use syntax::ptr::P; |
| use syntax::util::lev_distance::find_best_match_for_name; |
| use syntax_pos::Span; |
| use util::nodemap::FxHashMap; |
| |
| use std::collections::hash_map::Entry::{Occupied, Vacant}; |
| use std::cmp; |
| |
| use super::report_unexpected_variant_def; |
| |
| impl<'a, 'gcx, 'tcx> FnCtxt<'a, 'gcx, 'tcx> { |
| /// `match_discrim_span` argument having a `Span` indicates that this pattern is part of |
| /// a match expression arm guard, and it points to the match discriminant to add context |
| /// in type errors. In the folloowing example, `match_discrim_span` corresponds to the |
| /// `a + b` expression: |
| /// |
| /// ```text |
| /// error[E0308]: mismatched types |
| /// --> src/main.rs:5:9 |
| /// | |
| /// 4 | let temp: usize = match a + b { |
| /// | ----- this expression has type `usize` |
| /// 5 | Ok(num) => num, |
| /// | ^^^^^^^ expected usize, found enum `std::result::Result` |
| /// | |
| /// = note: expected type `usize` |
| /// found type `std::result::Result<_, _>` |
| /// ``` |
| pub fn check_pat_walk( |
| &self, |
| pat: &'gcx hir::Pat, |
| mut expected: Ty<'tcx>, |
| mut def_bm: ty::BindingMode, |
| match_discrim_span: Option<Span>, |
| ) { |
| let tcx = self.tcx; |
| |
| debug!("check_pat_walk(pat={:?},expected={:?},def_bm={:?})", pat, expected, def_bm); |
| |
| let is_non_ref_pat = match pat.node { |
| PatKind::Struct(..) | |
| PatKind::TupleStruct(..) | |
| PatKind::Tuple(..) | |
| PatKind::Box(_) | |
| PatKind::Range(..) | |
| PatKind::Slice(..) => true, |
| PatKind::Lit(ref lt) => { |
| let ty = self.check_expr(lt); |
| match ty.sty { |
| ty::Ref(..) => false, |
| _ => true, |
| } |
| } |
| PatKind::Path(ref qpath) => { |
| let (def, _, _) = self.resolve_ty_and_def_ufcs(qpath, pat.id, pat.span); |
| match def { |
| Def::Const(..) | Def::AssociatedConst(..) => false, |
| _ => true, |
| } |
| } |
| PatKind::Wild | |
| PatKind::Binding(..) | |
| PatKind::Ref(..) => false, |
| }; |
| if is_non_ref_pat { |
| debug!("pattern is non reference pattern"); |
| let mut exp_ty = self.resolve_type_vars_with_obligations(&expected); |
| |
| // Peel off as many `&` or `&mut` from the discriminant as possible. For example, |
| // for `match &&&mut Some(5)` the loop runs three times, aborting when it reaches |
| // the `Some(5)` which is not of type Ref. |
| // |
| // For each ampersand peeled off, update the binding mode and push the original |
| // type into the adjustments vector. |
| // |
| // See the examples in `run-pass/match-defbm*.rs`. |
| let mut pat_adjustments = vec![]; |
| while let ty::Ref(_, inner_ty, inner_mutability) = exp_ty.sty { |
| debug!("inspecting {:?} with type {:?}", exp_ty, exp_ty.sty); |
| |
| debug!("current discriminant is Ref, inserting implicit deref"); |
| // Preserve the reference type. We'll need it later during HAIR lowering. |
| pat_adjustments.push(exp_ty); |
| |
| exp_ty = inner_ty; |
| def_bm = match def_bm { |
| // If default binding mode is by value, make it `ref` or `ref mut` |
| // (depending on whether we observe `&` or `&mut`). |
| ty::BindByValue(_) => |
| ty::BindByReference(inner_mutability), |
| |
| // Once a `ref`, always a `ref`. This is because a `& &mut` can't mutate |
| // the underlying value. |
| ty::BindByReference(hir::Mutability::MutImmutable) => |
| ty::BindByReference(hir::Mutability::MutImmutable), |
| |
| // When `ref mut`, stay a `ref mut` (on `&mut`) or downgrade to `ref` |
| // (on `&`). |
| ty::BindByReference(hir::Mutability::MutMutable) => |
| ty::BindByReference(inner_mutability), |
| }; |
| } |
| expected = exp_ty; |
| |
| if pat_adjustments.len() > 0 { |
| debug!("default binding mode is now {:?}", def_bm); |
| self.inh.tables.borrow_mut() |
| .pat_adjustments_mut() |
| .insert(pat.hir_id, pat_adjustments); |
| } |
| } else if let PatKind::Ref(..) = pat.node { |
| // When you encounter a `&pat` pattern, reset to "by |
| // value". This is so that `x` and `y` here are by value, |
| // as they appear to be: |
| // |
| // ``` |
| // match &(&22, &44) { |
| // (&x, &y) => ... |
| // } |
| // ``` |
| // |
| // cc #46688 |
| def_bm = ty::BindByValue(hir::MutImmutable); |
| } |
| |
| // Lose mutability now that we know binding mode and discriminant type. |
| let def_bm = def_bm; |
| let expected = expected; |
| |
| let ty = match pat.node { |
| PatKind::Wild => { |
| expected |
| } |
| PatKind::Lit(ref lt) => { |
| // We've already computed the type above (when checking for a non-ref pat), so |
| // avoid computing it again. |
| let ty = self.node_ty(lt.hir_id); |
| |
| // Byte string patterns behave the same way as array patterns |
| // They can denote both statically and dynamically sized byte arrays |
| let mut pat_ty = ty; |
| if let hir::ExprKind::Lit(ref lt) = lt.node { |
| if let ast::LitKind::ByteStr(_) = lt.node { |
| let expected_ty = self.structurally_resolved_type(pat.span, expected); |
| if let ty::Ref(_, r_ty, _) = expected_ty.sty { |
| if let ty::Slice(_) = r_ty.sty { |
| pat_ty = tcx.mk_imm_ref(tcx.types.re_static, |
| tcx.mk_slice(tcx.types.u8)) |
| } |
| } |
| } |
| } |
| |
| // somewhat surprising: in this case, the subtyping |
| // relation goes the opposite way as the other |
| // cases. Actually what we really want is not a subtyping |
| // relation at all but rather that there exists a LUB (so |
| // that they can be compared). However, in practice, |
| // constants are always scalars or strings. For scalars |
| // subtyping is irrelevant, and for strings `ty` is |
| // type is `&'static str`, so if we say that |
| // |
| // &'static str <: expected |
| // |
| // that's equivalent to there existing a LUB. |
| self.demand_suptype(pat.span, expected, pat_ty); |
| pat_ty |
| } |
| PatKind::Range(ref begin, ref end, _) => { |
| let lhs_ty = self.check_expr(begin); |
| let rhs_ty = self.check_expr(end); |
| |
| // Check that both end-points are of numeric or char type. |
| let numeric_or_char = |ty: Ty| ty.is_numeric() || ty.is_char(); |
| let lhs_compat = numeric_or_char(lhs_ty); |
| let rhs_compat = numeric_or_char(rhs_ty); |
| |
| if !lhs_compat || !rhs_compat { |
| let span = if !lhs_compat && !rhs_compat { |
| pat.span |
| } else if !lhs_compat { |
| begin.span |
| } else { |
| end.span |
| }; |
| |
| let mut err = struct_span_err!( |
| tcx.sess, |
| span, |
| E0029, |
| "only char and numeric types are allowed in range patterns" |
| ); |
| err.span_label(span, "ranges require char or numeric types"); |
| err.note(&format!("start type: {}", self.ty_to_string(lhs_ty))); |
| err.note(&format!("end type: {}", self.ty_to_string(rhs_ty))); |
| if tcx.sess.teach(&err.get_code().unwrap()) { |
| err.note( |
| "In a match expression, only numbers and characters can be matched \ |
| against a range. This is because the compiler checks that the range \ |
| is non-empty at compile-time, and is unable to evaluate arbitrary \ |
| comparison functions. If you want to capture values of an orderable \ |
| type between two end-points, you can use a guard." |
| ); |
| } |
| err.emit(); |
| return; |
| } |
| |
| // Now that we know the types can be unified we find the unified type and use |
| // it to type the entire expression. |
| let common_type = self.resolve_type_vars_if_possible(&lhs_ty); |
| |
| // subtyping doesn't matter here, as the value is some kind of scalar |
| self.demand_eqtype_pat(pat.span, expected, lhs_ty, match_discrim_span); |
| self.demand_eqtype_pat(pat.span, expected, rhs_ty, match_discrim_span); |
| common_type |
| } |
| PatKind::Binding(ba, var_id, _, ref sub) => { |
| let bm = if ba == hir::BindingAnnotation::Unannotated { |
| def_bm |
| } else { |
| ty::BindingMode::convert(ba) |
| }; |
| self.inh |
| .tables |
| .borrow_mut() |
| .pat_binding_modes_mut() |
| .insert(pat.hir_id, bm); |
| debug!("check_pat_walk: pat.hir_id={:?} bm={:?}", pat.hir_id, bm); |
| let local_ty = self.local_ty(pat.span, pat.id).decl_ty; |
| match bm { |
| ty::BindByReference(mutbl) => { |
| // if the binding is like |
| // ref x | ref const x | ref mut x |
| // then `x` is assigned a value of type `&M T` where M is the mutability |
| // and T is the expected type. |
| let region_var = self.next_region_var(infer::PatternRegion(pat.span)); |
| let mt = ty::TypeAndMut { ty: expected, mutbl: mutbl }; |
| let region_ty = tcx.mk_ref(region_var, mt); |
| |
| // `x` is assigned a value of type `&M T`, hence `&M T <: typeof(x)` is |
| // required. However, we use equality, which is stronger. See (*) for |
| // an explanation. |
| self.demand_eqtype_pat(pat.span, region_ty, local_ty, match_discrim_span); |
| } |
| // otherwise the type of x is the expected type T |
| ty::BindByValue(_) => { |
| // As above, `T <: typeof(x)` is required but we |
| // use equality, see (*) below. |
| self.demand_eqtype_pat(pat.span, expected, local_ty, match_discrim_span); |
| } |
| } |
| |
| // if there are multiple arms, make sure they all agree on |
| // what the type of the binding `x` ought to be |
| if var_id != pat.id { |
| let vt = self.local_ty(pat.span, var_id).decl_ty; |
| self.demand_eqtype_pat(pat.span, vt, local_ty, match_discrim_span); |
| } |
| |
| if let Some(ref p) = *sub { |
| self.check_pat_walk(&p, expected, def_bm, match_discrim_span); |
| } |
| |
| local_ty |
| } |
| PatKind::TupleStruct(ref qpath, ref subpats, ddpos) => { |
| self.check_pat_tuple_struct( |
| pat, |
| qpath, |
| &subpats, |
| ddpos, |
| expected, |
| def_bm, |
| match_discrim_span, |
| ) |
| } |
| PatKind::Path(ref qpath) => { |
| self.check_pat_path(pat, qpath, expected) |
| } |
| PatKind::Struct(ref qpath, ref fields, etc) => { |
| self.check_pat_struct(pat, qpath, fields, etc, expected, def_bm, match_discrim_span) |
| } |
| PatKind::Tuple(ref elements, ddpos) => { |
| let mut expected_len = elements.len(); |
| if ddpos.is_some() { |
| // Require known type only when `..` is present. |
| if let ty::Tuple(ref tys) = |
| self.structurally_resolved_type(pat.span, expected).sty { |
| expected_len = tys.len(); |
| } |
| } |
| let max_len = cmp::max(expected_len, elements.len()); |
| |
| let element_tys_iter = (0..max_len).map(|_| self.next_ty_var( |
| // FIXME: `MiscVariable` for now -- obtaining the span and name information |
| // from all tuple elements isn't trivial. |
| TypeVariableOrigin::TypeInference(pat.span))); |
| let element_tys = tcx.mk_type_list(element_tys_iter); |
| let pat_ty = tcx.mk_ty(ty::Tuple(element_tys)); |
| if let Some(mut err) = self.demand_eqtype_diag(pat.span, expected, pat_ty) { |
| err.emit(); |
| // Walk subpatterns with an expected type of `err` in this case to silence |
| // further errors being emitted when using the bindings. #50333 |
| let element_tys_iter = (0..max_len).map(|_| tcx.types.err); |
| for (_, elem) in elements.iter().enumerate_and_adjust(max_len, ddpos) { |
| self.check_pat_walk(elem, &tcx.types.err, def_bm, match_discrim_span); |
| } |
| tcx.mk_tup(element_tys_iter) |
| } else { |
| for (i, elem) in elements.iter().enumerate_and_adjust(max_len, ddpos) { |
| self.check_pat_walk(elem, &element_tys[i], def_bm, match_discrim_span); |
| } |
| pat_ty |
| } |
| } |
| PatKind::Box(ref inner) => { |
| let inner_ty = self.next_ty_var(TypeVariableOrigin::TypeInference(inner.span)); |
| let uniq_ty = tcx.mk_box(inner_ty); |
| |
| if self.check_dereferencable(pat.span, expected, &inner) { |
| // Here, `demand::subtype` is good enough, but I don't |
| // think any errors can be introduced by using |
| // `demand::eqtype`. |
| self.demand_eqtype_pat(pat.span, expected, uniq_ty, match_discrim_span); |
| self.check_pat_walk(&inner, inner_ty, def_bm, match_discrim_span); |
| uniq_ty |
| } else { |
| self.check_pat_walk(&inner, tcx.types.err, def_bm, match_discrim_span); |
| tcx.types.err |
| } |
| } |
| PatKind::Ref(ref inner, mutbl) => { |
| let expected = self.shallow_resolve(expected); |
| if self.check_dereferencable(pat.span, expected, &inner) { |
| // `demand::subtype` would be good enough, but using |
| // `eqtype` turns out to be equally general. See (*) |
| // below for details. |
| |
| // Take region, inner-type from expected type if we |
| // can, to avoid creating needless variables. This |
| // also helps with the bad interactions of the given |
| // hack detailed in (*) below. |
| debug!("check_pat_walk: expected={:?}", expected); |
| let (rptr_ty, inner_ty) = match expected.sty { |
| ty::Ref(_, r_ty, r_mutbl) if r_mutbl == mutbl => { |
| (expected, r_ty) |
| } |
| _ => { |
| let inner_ty = self.next_ty_var( |
| TypeVariableOrigin::TypeInference(inner.span)); |
| let mt = ty::TypeAndMut { ty: inner_ty, mutbl: mutbl }; |
| let region = self.next_region_var(infer::PatternRegion(pat.span)); |
| let rptr_ty = tcx.mk_ref(region, mt); |
| debug!("check_pat_walk: demanding {:?} = {:?}", expected, rptr_ty); |
| let err = self.demand_eqtype_diag(pat.span, expected, rptr_ty); |
| |
| // Look for a case like `fn foo(&foo: u32)` and suggest |
| // `fn foo(foo: &u32)` |
| if let Some(mut err) = err { |
| if let PatKind::Binding(..) = inner.node { |
| if let Ok(snippet) = tcx.sess.source_map() |
| .span_to_snippet(pat.span) |
| { |
| err.help(&format!("did you mean `{}: &{}`?", |
| &snippet[1..], |
| expected)); |
| } |
| } |
| err.emit(); |
| } |
| (rptr_ty, inner_ty) |
| } |
| }; |
| |
| self.check_pat_walk(&inner, inner_ty, def_bm, match_discrim_span); |
| rptr_ty |
| } else { |
| self.check_pat_walk(&inner, tcx.types.err, def_bm, match_discrim_span); |
| tcx.types.err |
| } |
| } |
| PatKind::Slice(ref before, ref slice, ref after) => { |
| let expected_ty = self.structurally_resolved_type(pat.span, expected); |
| let (inner_ty, slice_ty) = match expected_ty.sty { |
| ty::Array(inner_ty, size) => { |
| let size = size.unwrap_usize(tcx); |
| let min_len = before.len() as u64 + after.len() as u64; |
| if slice.is_none() { |
| if min_len != size { |
| struct_span_err!( |
| tcx.sess, pat.span, E0527, |
| "pattern requires {} elements but array has {}", |
| min_len, size) |
| .span_label(pat.span, format!("expected {} elements", size)) |
| .emit(); |
| } |
| (inner_ty, tcx.types.err) |
| } else if let Some(rest) = size.checked_sub(min_len) { |
| (inner_ty, tcx.mk_array(inner_ty, rest)) |
| } else { |
| struct_span_err!(tcx.sess, pat.span, E0528, |
| "pattern requires at least {} elements but array has {}", |
| min_len, size) |
| .span_label(pat.span, |
| format!("pattern cannot match array of {} elements", size)) |
| .emit(); |
| (inner_ty, tcx.types.err) |
| } |
| } |
| ty::Slice(inner_ty) => (inner_ty, expected_ty), |
| _ => { |
| if !expected_ty.references_error() { |
| let mut err = struct_span_err!( |
| tcx.sess, pat.span, E0529, |
| "expected an array or slice, found `{}`", |
| expected_ty); |
| if let ty::Ref(_, ty, _) = expected_ty.sty { |
| match ty.sty { |
| ty::Array(..) | ty::Slice(..) => { |
| err.help("the semantics of slice patterns changed \ |
| recently; see issue #23121"); |
| } |
| _ => {} |
| } |
| } |
| |
| err.span_label( pat.span, |
| format!("pattern cannot match with input type `{}`", expected_ty) |
| ).emit(); |
| } |
| (tcx.types.err, tcx.types.err) |
| } |
| }; |
| |
| for elt in before { |
| self.check_pat_walk(&elt, inner_ty, def_bm, match_discrim_span); |
| } |
| if let Some(ref slice) = *slice { |
| self.check_pat_walk(&slice, slice_ty, def_bm, match_discrim_span); |
| } |
| for elt in after { |
| self.check_pat_walk(&elt, inner_ty, def_bm, match_discrim_span); |
| } |
| expected_ty |
| } |
| }; |
| |
| self.write_ty(pat.hir_id, ty); |
| |
| // (*) In most of the cases above (literals and constants being |
| // the exception), we relate types using strict equality, even |
| // though subtyping would be sufficient. There are a few reasons |
| // for this, some of which are fairly subtle and which cost me |
| // (nmatsakis) an hour or two debugging to remember, so I thought |
| // I'd write them down this time. |
| // |
| // 1. There is no loss of expressiveness here, though it does |
| // cause some inconvenience. What we are saying is that the type |
| // of `x` becomes *exactly* what is expected. This can cause unnecessary |
| // errors in some cases, such as this one: |
| // |
| // ``` |
| // fn foo<'x>(x: &'x int) { |
| // let a = 1; |
| // let mut z = x; |
| // z = &a; |
| // } |
| // ``` |
| // |
| // The reason we might get an error is that `z` might be |
| // assigned a type like `&'x int`, and then we would have |
| // a problem when we try to assign `&a` to `z`, because |
| // the lifetime of `&a` (i.e., the enclosing block) is |
| // shorter than `'x`. |
| // |
| // HOWEVER, this code works fine. The reason is that the |
| // expected type here is whatever type the user wrote, not |
| // the initializer's type. In this case the user wrote |
| // nothing, so we are going to create a type variable `Z`. |
| // Then we will assign the type of the initializer (`&'x |
| // int`) as a subtype of `Z`: `&'x int <: Z`. And hence we |
| // will instantiate `Z` as a type `&'0 int` where `'0` is |
| // a fresh region variable, with the constraint that `'x : |
| // '0`. So basically we're all set. |
| // |
| // Note that there are two tests to check that this remains true |
| // (`regions-reassign-{match,let}-bound-pointer.rs`). |
| // |
| // 2. Things go horribly wrong if we use subtype. The reason for |
| // THIS is a fairly subtle case involving bound regions. See the |
| // `givens` field in `region_constraints`, as well as the test |
| // `regions-relate-bound-regions-on-closures-to-inference-variables.rs`, |
| // for details. Short version is that we must sometimes detect |
| // relationships between specific region variables and regions |
| // bound in a closure signature, and that detection gets thrown |
| // off when we substitute fresh region variables here to enable |
| // subtyping. |
| } |
| |
| pub fn check_dereferencable(&self, span: Span, expected: Ty<'tcx>, inner: &hir::Pat) -> bool { |
| if let PatKind::Binding(..) = inner.node { |
| if let Some(mt) = self.shallow_resolve(expected).builtin_deref(true) { |
| if let ty::Dynamic(..) = mt.ty.sty { |
| // This is "x = SomeTrait" being reduced from |
| // "let &x = &SomeTrait" or "let box x = Box<SomeTrait>", an error. |
| let type_str = self.ty_to_string(expected); |
| let mut err = struct_span_err!( |
| self.tcx.sess, |
| span, |
| E0033, |
| "type `{}` cannot be dereferenced", |
| type_str |
| ); |
| err.span_label(span, format!("type `{}` cannot be dereferenced", type_str)); |
| if self.tcx.sess.teach(&err.get_code().unwrap()) { |
| err.note("\ |
| This error indicates that a pointer to a trait type cannot be implicitly dereferenced by a \ |
| pattern. Every trait defines a type, but because the size of trait implementors isn't fixed, \ |
| this type has no compile-time size. Therefore, all accesses to trait types must be through \ |
| pointers. If you encounter this error you should try to avoid dereferencing the pointer. |
| |
| You can read more about trait objects in the Trait Objects section of the Reference: \ |
| https://doc.rust-lang.org/reference/types.html#trait-objects"); |
| } |
| err.emit(); |
| return false |
| } |
| } |
| } |
| true |
| } |
| |
| pub fn check_match( |
| &self, |
| expr: &'gcx hir::Expr, |
| discrim: &'gcx hir::Expr, |
| arms: &'gcx [hir::Arm], |
| expected: Expectation<'tcx>, |
| match_src: hir::MatchSource, |
| ) -> Ty<'tcx> { |
| let tcx = self.tcx; |
| |
| // Not entirely obvious: if matches may create ref bindings, we want to |
| // use the *precise* type of the discriminant, *not* some supertype, as |
| // the "discriminant type" (issue #23116). |
| // |
| // arielb1 [writes here in this comment thread][c] that there |
| // is certainly *some* potential danger, e.g., for an example |
| // like: |
| // |
| // [c]: https://github.com/rust-lang/rust/pull/43399#discussion_r130223956 |
| // |
| // ``` |
| // let Foo(x) = f()[0]; |
| // ``` |
| // |
| // Then if the pattern matches by reference, we want to match |
| // `f()[0]` as a lexpr, so we can't allow it to be |
| // coerced. But if the pattern matches by value, `f()[0]` is |
| // still syntactically a lexpr, but we *do* want to allow |
| // coercions. |
| // |
| // However, *likely* we are ok with allowing coercions to |
| // happen if there are no explicit ref mut patterns - all |
| // implicit ref mut patterns must occur behind a reference, so |
| // they will have the "correct" variance and lifetime. |
| // |
| // This does mean that the following pattern would be legal: |
| // |
| // ``` |
| // struct Foo(Bar); |
| // struct Bar(u32); |
| // impl Deref for Foo { |
| // type Target = Bar; |
| // fn deref(&self) -> &Bar { &self.0 } |
| // } |
| // impl DerefMut for Foo { |
| // fn deref_mut(&mut self) -> &mut Bar { &mut self.0 } |
| // } |
| // fn foo(x: &mut Foo) { |
| // { |
| // let Bar(z): &mut Bar = x; |
| // *z = 42; |
| // } |
| // assert_eq!(foo.0.0, 42); |
| // } |
| // ``` |
| // |
| // FIXME(tschottdorf): don't call contains_explicit_ref_binding, which |
| // is problematic as the HIR is being scraped, but ref bindings may be |
| // implicit after #42640. We need to make sure that pat_adjustments |
| // (once introduced) is populated by the time we get here. |
| // |
| // See #44848. |
| let contains_ref_bindings = arms.iter() |
| .filter_map(|a| a.contains_explicit_ref_binding()) |
| .max_by_key(|m| match *m { |
| hir::MutMutable => 1, |
| hir::MutImmutable => 0, |
| }); |
| let discrim_ty; |
| if let Some(m) = contains_ref_bindings { |
| discrim_ty = self.check_expr_with_needs(discrim, Needs::maybe_mut_place(m)); |
| } else { |
| // ...but otherwise we want to use any supertype of the |
| // discriminant. This is sort of a workaround, see note (*) in |
| // `check_pat` for some details. |
| discrim_ty = self.next_ty_var(TypeVariableOrigin::TypeInference(discrim.span)); |
| self.check_expr_has_type_or_error(discrim, discrim_ty); |
| }; |
| |
| // If there are no arms, that is a diverging match; a special case. |
| if arms.is_empty() { |
| self.diverges.set(self.diverges.get() | Diverges::Always); |
| return tcx.types.never; |
| } |
| |
| if self.diverges.get().always() { |
| for arm in arms { |
| self.warn_if_unreachable(arm.body.id, arm.body.span, "arm"); |
| } |
| } |
| |
| // Otherwise, we have to union together the types that the |
| // arms produce and so forth. |
| let discrim_diverges = self.diverges.get(); |
| self.diverges.set(Diverges::Maybe); |
| |
| // rust-lang/rust#55810: Typecheck patterns first (via eager |
| // collection into `Vec`), so we get types for all bindings. |
| let all_arm_pats_diverge: Vec<_> = arms.iter().map(|arm| { |
| let mut all_pats_diverge = Diverges::WarnedAlways; |
| for p in &arm.pats { |
| self.diverges.set(Diverges::Maybe); |
| self.check_pat_walk( |
| &p, |
| discrim_ty, |
| ty::BindingMode::BindByValue(hir::Mutability::MutImmutable), |
| Some(discrim.span), |
| ); |
| all_pats_diverge &= self.diverges.get(); |
| } |
| |
| // As discussed with @eddyb, this is for disabling unreachable_code |
| // warnings on patterns (they're now subsumed by unreachable_patterns |
| // warnings). |
| match all_pats_diverge { |
| Diverges::Maybe => Diverges::Maybe, |
| Diverges::Always | Diverges::WarnedAlways => Diverges::WarnedAlways, |
| } |
| }).collect(); |
| |
| // Now typecheck the blocks. |
| // |
| // The result of the match is the common supertype of all the |
| // arms. Start out the value as bottom, since it's the, well, |
| // bottom the type lattice, and we'll be moving up the lattice as |
| // we process each arm. (Note that any match with 0 arms is matching |
| // on any empty type and is therefore unreachable; should the flow |
| // of execution reach it, we will panic, so bottom is an appropriate |
| // type in that case) |
| let mut all_arms_diverge = Diverges::WarnedAlways; |
| |
| let expected = expected.adjust_for_branches(self); |
| |
| let mut coercion = { |
| let coerce_first = match expected { |
| // We don't coerce to `()` so that if the match expression is a |
| // statement it's branches can have any consistent type. That allows |
| // us to give better error messages (pointing to a usually better |
| // arm for inconsistent arms or to the whole match when a `()` type |
| // is required). |
| Expectation::ExpectHasType(ety) if ety != self.tcx.mk_unit() => ety, |
| _ => self.next_ty_var(TypeVariableOrigin::MiscVariable(expr.span)), |
| }; |
| CoerceMany::with_coercion_sites(coerce_first, arms) |
| }; |
| |
| for (i, (arm, pats_diverge)) in arms.iter().zip(all_arm_pats_diverge).enumerate() { |
| if let Some(ref g) = arm.guard { |
| self.diverges.set(pats_diverge); |
| match g { |
| hir::Guard::If(e) => self.check_expr_has_type_or_error(e, tcx.types.bool), |
| }; |
| } |
| |
| self.diverges.set(pats_diverge); |
| let arm_ty = self.check_expr_with_expectation(&arm.body, expected); |
| all_arms_diverge &= self.diverges.get(); |
| |
| // Handle the fallback arm of a desugared if-let like a missing else. |
| let is_if_let_fallback = match match_src { |
| hir::MatchSource::IfLetDesugar { contains_else_clause: false } => { |
| i == arms.len() - 1 && arm_ty.is_unit() |
| } |
| _ => false |
| }; |
| |
| if is_if_let_fallback { |
| let cause = self.cause(expr.span, ObligationCauseCode::IfExpressionWithNoElse); |
| assert!(arm_ty.is_unit()); |
| coercion.coerce_forced_unit(self, &cause, &mut |_| (), true); |
| } else { |
| let cause = self.cause(expr.span, ObligationCauseCode::MatchExpressionArm { |
| arm_span: arm.body.span, |
| source: match_src |
| }); |
| coercion.coerce(self, &cause, &arm.body, arm_ty); |
| } |
| } |
| |
| // We won't diverge unless the discriminant or all arms diverge. |
| self.diverges.set(discrim_diverges | all_arms_diverge); |
| |
| coercion.complete(self) |
| } |
| |
| fn check_pat_struct( |
| &self, |
| pat: &'gcx hir::Pat, |
| qpath: &hir::QPath, |
| fields: &'gcx [Spanned<hir::FieldPat>], |
| etc: bool, |
| expected: Ty<'tcx>, |
| def_bm: ty::BindingMode, |
| match_discrim_span: Option<Span>, |
| ) -> Ty<'tcx> |
| { |
| // Resolve the path and check the definition for errors. |
| let (variant, pat_ty) = if let Some(variant_ty) = self.check_struct_path(qpath, pat.id) { |
| variant_ty |
| } else { |
| for field in fields { |
| self.check_pat_walk( |
| &field.node.pat, |
| self.tcx.types.err, |
| def_bm, |
| match_discrim_span, |
| ); |
| } |
| return self.tcx.types.err; |
| }; |
| |
| // Type-check the path. |
| self.demand_eqtype_pat(pat.span, expected, pat_ty, match_discrim_span); |
| |
| // Type-check subpatterns. |
| if self.check_struct_pat_fields(pat_ty, pat.id, pat.span, variant, fields, etc, def_bm) { |
| pat_ty |
| } else { |
| self.tcx.types.err |
| } |
| } |
| |
| fn check_pat_path( |
| &self, |
| pat: &hir::Pat, |
| qpath: &hir::QPath, |
| expected: Ty<'tcx>, |
| ) -> Ty<'tcx> { |
| let tcx = self.tcx; |
| |
| // Resolve the path and check the definition for errors. |
| let (def, opt_ty, segments) = self.resolve_ty_and_def_ufcs(qpath, pat.id, pat.span); |
| match def { |
| Def::Err => { |
| self.set_tainted_by_errors(); |
| return tcx.types.err; |
| } |
| Def::Method(..) => { |
| report_unexpected_variant_def(tcx, &def, pat.span, qpath); |
| return tcx.types.err; |
| } |
| Def::VariantCtor(_, CtorKind::Fictive) => { |
| report_unexpected_variant_def(tcx, &def, pat.span, qpath); |
| return tcx.types.err; |
| } |
| Def::VariantCtor(_, CtorKind::Const) | |
| Def::StructCtor(_, CtorKind::Const) | |
| Def::SelfCtor(..) | |
| Def::Const(..) | Def::AssociatedConst(..) => {} // OK |
| _ => bug!("unexpected pattern definition: {:?}", def) |
| } |
| |
| // Type-check the path. |
| let pat_ty = self.instantiate_value_path(segments, opt_ty, def, pat.span, pat.id).0; |
| self.demand_suptype(pat.span, expected, pat_ty); |
| pat_ty |
| } |
| |
| fn check_pat_tuple_struct( |
| &self, |
| pat: &hir::Pat, |
| qpath: &hir::QPath, |
| subpats: &'gcx [P<hir::Pat>], |
| ddpos: Option<usize>, |
| expected: Ty<'tcx>, |
| def_bm: ty::BindingMode, |
| match_arm_pat_span: Option<Span>, |
| ) -> Ty<'tcx> { |
| let tcx = self.tcx; |
| let on_error = || { |
| for pat in subpats { |
| self.check_pat_walk(&pat, tcx.types.err, def_bm, match_arm_pat_span); |
| } |
| }; |
| let report_unexpected_def = |def: Def| { |
| let msg = format!("expected tuple struct/variant, found {} `{}`", |
| def.kind_name(), |
| hir::print::to_string(tcx.hir(), |s| s.print_qpath(qpath, false))); |
| struct_span_err!(tcx.sess, pat.span, E0164, "{}", msg) |
| .span_label(pat.span, "not a tuple variant or struct").emit(); |
| on_error(); |
| }; |
| |
| // Resolve the path and check the definition for errors. |
| let (def, opt_ty, segments) = self.resolve_ty_and_def_ufcs(qpath, pat.id, pat.span); |
| if def == Def::Err { |
| self.set_tainted_by_errors(); |
| on_error(); |
| return self.tcx.types.err; |
| } |
| |
| // Type-check the path. |
| let (pat_ty, def) = self.instantiate_value_path(segments, opt_ty, def, pat.span, pat.id); |
| if !pat_ty.is_fn() { |
| report_unexpected_def(def); |
| return self.tcx.types.err; |
| } |
| |
| let variant = match def { |
| Def::Err => { |
| self.set_tainted_by_errors(); |
| on_error(); |
| return tcx.types.err; |
| } |
| Def::AssociatedConst(..) | Def::Method(..) => { |
| report_unexpected_def(def); |
| return tcx.types.err; |
| } |
| Def::VariantCtor(_, CtorKind::Fn) | |
| Def::StructCtor(_, CtorKind::Fn) => { |
| tcx.expect_variant_def(def) |
| } |
| _ => bug!("unexpected pattern definition: {:?}", def) |
| }; |
| |
| // Replace constructor type with constructed type for tuple struct patterns. |
| let pat_ty = pat_ty.fn_sig(tcx).output(); |
| let pat_ty = pat_ty.no_bound_vars().expect("expected fn type"); |
| |
| self.demand_eqtype_pat(pat.span, expected, pat_ty, match_arm_pat_span); |
| |
| // Type-check subpatterns. |
| if subpats.len() == variant.fields.len() || |
| subpats.len() < variant.fields.len() && ddpos.is_some() { |
| let substs = match pat_ty.sty { |
| ty::Adt(_, substs) => substs, |
| ref ty => bug!("unexpected pattern type {:?}", ty), |
| }; |
| for (i, subpat) in subpats.iter().enumerate_and_adjust(variant.fields.len(), ddpos) { |
| let field_ty = self.field_ty(subpat.span, &variant.fields[i], substs); |
| self.check_pat_walk(&subpat, field_ty, def_bm, match_arm_pat_span); |
| |
| self.tcx.check_stability(variant.fields[i].did, Some(pat.id), subpat.span); |
| } |
| } else { |
| let subpats_ending = if subpats.len() == 1 { "" } else { "s" }; |
| let fields_ending = if variant.fields.len() == 1 { "" } else { "s" }; |
| struct_span_err!(tcx.sess, pat.span, E0023, |
| "this pattern has {} field{}, but the corresponding {} has {} field{}", |
| subpats.len(), subpats_ending, def.kind_name(), |
| variant.fields.len(), fields_ending) |
| .span_label(pat.span, format!("expected {} field{}, found {}", |
| variant.fields.len(), fields_ending, subpats.len())) |
| .emit(); |
| on_error(); |
| return tcx.types.err; |
| } |
| pat_ty |
| } |
| |
| fn check_struct_pat_fields(&self, |
| adt_ty: Ty<'tcx>, |
| pat_id: ast::NodeId, |
| span: Span, |
| variant: &'tcx ty::VariantDef, |
| fields: &'gcx [Spanned<hir::FieldPat>], |
| etc: bool, |
| def_bm: ty::BindingMode) -> bool { |
| let tcx = self.tcx; |
| |
| let (substs, adt) = match adt_ty.sty { |
| ty::Adt(adt, substs) => (substs, adt), |
| _ => span_bug!(span, "struct pattern is not an ADT") |
| }; |
| let kind_name = adt.variant_descr(); |
| |
| // Index the struct fields' types. |
| let field_map = variant.fields |
| .iter() |
| .enumerate() |
| .map(|(i, field)| (field.ident.modern(), (i, field))) |
| .collect::<FxHashMap<_, _>>(); |
| |
| // Keep track of which fields have already appeared in the pattern. |
| let mut used_fields = FxHashMap::default(); |
| let mut no_field_errors = true; |
| |
| let mut inexistent_fields = vec![]; |
| // Typecheck each field. |
| for &Spanned { node: ref field, span } in fields { |
| let ident = tcx.adjust_ident(field.ident, variant.did, self.body_id).0; |
| let field_ty = match used_fields.entry(ident) { |
| Occupied(occupied) => { |
| struct_span_err!(tcx.sess, span, E0025, |
| "field `{}` bound multiple times \ |
| in the pattern", |
| field.ident) |
| .span_label(span, |
| format!("multiple uses of `{}` in pattern", field.ident)) |
| .span_label(*occupied.get(), format!("first use of `{}`", field.ident)) |
| .emit(); |
| no_field_errors = false; |
| tcx.types.err |
| } |
| Vacant(vacant) => { |
| vacant.insert(span); |
| field_map.get(&ident) |
| .map(|(i, f)| { |
| self.write_field_index(field.id, *i); |
| self.tcx.check_stability(f.did, Some(pat_id), span); |
| self.field_ty(span, f, substs) |
| }) |
| .unwrap_or_else(|| { |
| inexistent_fields.push((span, field.ident)); |
| no_field_errors = false; |
| tcx.types.err |
| }) |
| } |
| }; |
| |
| self.check_pat_walk(&field.pat, field_ty, def_bm, None); |
| } |
| let mut unmentioned_fields = variant.fields |
| .iter() |
| .map(|field| field.ident.modern()) |
| .filter(|ident| !used_fields.contains_key(&ident)) |
| .collect::<Vec<_>>(); |
| if inexistent_fields.len() > 0 { |
| let (field_names, t, plural) = if inexistent_fields.len() == 1 { |
| (format!("a field named `{}`", inexistent_fields[0].1), "this", "") |
| } else { |
| (format!("fields named {}", |
| inexistent_fields.iter() |
| .map(|(_, name)| format!("`{}`", name)) |
| .collect::<Vec<String>>() |
| .join(", ")), "these", "s") |
| }; |
| let spans = inexistent_fields.iter().map(|(span, _)| *span).collect::<Vec<_>>(); |
| let mut err = struct_span_err!(tcx.sess, |
| spans, |
| E0026, |
| "{} `{}` does not have {}", |
| kind_name, |
| tcx.item_path_str(variant.did), |
| field_names); |
| if let Some((span, ident)) = inexistent_fields.last() { |
| err.span_label(*span, |
| format!("{} `{}` does not have {} field{}", |
| kind_name, |
| tcx.item_path_str(variant.did), |
| t, |
| plural)); |
| if plural == "" { |
| let input = unmentioned_fields.iter().map(|field| &field.name); |
| let suggested_name = |
| find_best_match_for_name(input, &ident.as_str(), None); |
| if let Some(suggested_name) = suggested_name { |
| err.span_suggestion(*span, "did you mean", suggested_name.to_string()); |
| // we don't want to throw `E0027` in case we have thrown `E0026` for them |
| unmentioned_fields.retain(|&x| x.as_str() != suggested_name.as_str()); |
| } |
| } |
| } |
| if tcx.sess.teach(&err.get_code().unwrap()) { |
| err.note( |
| "This error indicates that a struct pattern attempted to \ |
| extract a non-existent field from a struct. Struct fields \ |
| are identified by the name used before the colon : so struct \ |
| patterns should resemble the declaration of the struct type \ |
| being matched.\n\n\ |
| If you are using shorthand field patterns but want to refer \ |
| to the struct field by a different name, you should rename \ |
| it explicitly." |
| ); |
| } |
| err.emit(); |
| } |
| |
| // Require `..` if struct has non_exhaustive attribute. |
| if variant.is_field_list_non_exhaustive() && !adt.did.is_local() && !etc { |
| span_err!(tcx.sess, span, E0638, |
| "`..` required with {} marked as non-exhaustive", |
| kind_name); |
| } |
| |
| // Report an error if incorrect number of the fields were specified. |
| if kind_name == "union" { |
| if fields.len() != 1 { |
| tcx.sess.span_err(span, "union patterns should have exactly one field"); |
| } |
| if etc { |
| tcx.sess.span_err(span, "`..` cannot be used in union patterns"); |
| } |
| } else if !etc { |
| if unmentioned_fields.len() > 0 { |
| let field_names = if unmentioned_fields.len() == 1 { |
| format!("field `{}`", unmentioned_fields[0]) |
| } else { |
| format!("fields {}", |
| unmentioned_fields.iter() |
| .map(|name| format!("`{}`", name)) |
| .collect::<Vec<String>>() |
| .join(", ")) |
| }; |
| let mut diag = struct_span_err!(tcx.sess, span, E0027, |
| "pattern does not mention {}", |
| field_names); |
| diag.span_label(span, format!("missing {}", field_names)); |
| if variant.ctor_kind == CtorKind::Fn { |
| diag.note("trying to match a tuple variant with a struct variant pattern"); |
| } |
| if tcx.sess.teach(&diag.get_code().unwrap()) { |
| diag.note( |
| "This error indicates that a pattern for a struct fails to specify a \ |
| sub-pattern for every one of the struct's fields. Ensure that each field \ |
| from the struct's definition is mentioned in the pattern, or use `..` to \ |
| ignore unwanted fields." |
| ); |
| } |
| diag.emit(); |
| } |
| } |
| no_field_errors |
| } |
| } |