use syntax::ptr::P;
pub fn check_pat<'a, 'tcx>(pcx: &pat_ctxt<'a, 'tcx>,
- pat: &ast::Pat, expected: Ty<'tcx>) {
+ pat: &ast::Pat,
+ expected: Ty<'tcx>)
+{
let fcx = pcx.fcx;
let tcx = pcx.fcx.ccx.tcx;
check_expr(fcx, &**lt);
let expr_ty = fcx.expr_ty(&**lt);
fcx.write_ty(pat.id, expr_ty);
+
+ // 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 `expr_ty` is
+ // type is `&'static str`, so if we say that
+ //
+ // &'static str <: expected
+ //
+ // that's equivalent to there existing a LUB.
demand::suptype(fcx, pat.span, expected, expr_ty);
}
ast::PatRange(ref begin, ref end) => {
let lhs_ty = fcx.expr_ty(&**begin);
let rhs_ty = fcx.expr_ty(&**end);
- if require_same_types(
- tcx, Some(fcx.infcx()), false, pat.span, lhs_ty, rhs_ty,
- || "mismatched types in range".to_string())
- && (ty::type_is_numeric(lhs_ty) || ty::type_is_char(rhs_ty)) {
+
+ let lhs_eq_rhs =
+ require_same_types(
+ tcx, Some(fcx.infcx()), false, pat.span, lhs_ty, rhs_ty,
+ || "mismatched types in range".to_string());
+
+ let numeric_or_char =
+ lhs_eq_rhs && (ty::type_is_numeric(lhs_ty) || ty::type_is_char(lhs_ty));
+
+ if numeric_or_char {
match valid_range_bounds(fcx.ccx, &**begin, &**end) {
Some(false) => {
span_err!(tcx.sess, begin.span, E0030,
}
} else {
span_err!(tcx.sess, begin.span, E0029,
- "only char and numeric types are allowed in range");
+ "only char and numeric types are allowed in range");
}
fcx.write_ty(pat.id, lhs_ty);
+
+ // subtyping doesn't matter here, as the value is some kind of scalar
demand::eqtype(fcx, pat.span, expected, lhs_ty);
}
ast::PatEnum(..) | ast::PatIdent(..) if pat_is_const(&tcx.def_map, pat) => {
let const_did = tcx.def_map.borrow()[pat.id].clone().def_id();
let const_scheme = ty::lookup_item_type(tcx, const_did);
- fcx.write_ty(pat.id, const_scheme.ty);
- demand::suptype(fcx, pat.span, expected, const_scheme.ty);
+ assert!(const_scheme.generics.is_empty());
+ let const_ty = pcx.fcx.instantiate_type_scheme(pat.span,
+ &Substs::empty(),
+ &const_scheme.ty);
+ fcx.write_ty(pat.id, const_ty);
+
+ // FIXME(#20489) -- we should limit the types here to scalars or something!
+
+ // As with PatLit, what we really want here is that there
+ // exist a LUB, but for the cases that can occur, subtype
+ // is good enough.
+ demand::suptype(fcx, pat.span, expected, const_ty);
}
ast::PatIdent(bm, ref path, ref sub) if pat_is_binding(&tcx.def_map, pat) => {
let typ = fcx.local_ty(pat.span, pat.id);
ast::BindByRef(mutbl) => {
// if the binding is like
// ref x | ref const x | ref mut x
- // then the type of x is &M T where M is the mutability
- // and T is the expected type
+ // then `x` is assigned a value of type `&M T` where M is the mutability
+ // and T is the expected type.
let region_var = fcx.infcx().next_region_var(infer::PatternRegion(pat.span));
let mt = ty::mt { ty: expected, mutbl: mutbl };
let region_ty = ty::mk_rptr(tcx, tcx.mk_region(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.
demand::eqtype(fcx, pat.span, region_ty, typ);
}
// otherwise the type of x is the expected type T
ast::BindByValue(_) => {
+ // As above, `T <: typeof(x)` is required but we
+ // use equality, see (*) below.
demand::eqtype(fcx, pat.span, expected, typ);
}
}
+
fcx.write_ty(pat.id, typ);
+ // if there are multiple arms, make sure they all agree on
+ // what the type of the binding `x` ought to be
let canon_id = pcx.map[path.node];
if canon_id != pat.id {
let ct = fcx.local_ty(pat.span, canon_id);
check_pat_struct(pcx, pat, path, fields.as_slice(), etc, expected);
}
ast::PatTup(ref elements) => {
- let element_tys: Vec<_> = range(0, elements.len()).map(|_| fcx.infcx()
- .next_ty_var()).collect();
+ let element_tys: Vec<_> =
+ range(0, elements.len()).map(|_| fcx.infcx().next_ty_var())
+ .collect();
let pat_ty = ty::mk_tup(tcx, element_tys.clone());
fcx.write_ty(pat.id, pat_ty);
demand::eqtype(fcx, pat.span, expected, pat_ty);
let uniq_ty = ty::mk_uniq(tcx, inner_ty);
if check_dereferencable(pcx, pat.span, expected, &**inner) {
- demand::suptype(fcx, pat.span, expected, uniq_ty);
+ // Here, `demand::subtype` is good enough, but I don't
+ // think any errors can be introduced by using
+ // `demand::eqtype`.
+ demand::eqtype(fcx, pat.span, expected, uniq_ty);
fcx.write_ty(pat.id, uniq_ty);
check_pat(pcx, &**inner, inner_ty);
} else {
check_pat(pcx, &**inner, tcx.types.err);
}
}
- ast::PatRegion(ref inner) => {
+ ast::PatRegion(ref inner, mutbl) => {
let inner_ty = fcx.infcx().next_ty_var();
- let mutbl =
+ // SNAP 340ac04 remove this `if`-`else` entirely after next snapshot
+ let mutbl = if mutbl == ast::MutImmutable {
ty::deref(fcx.infcx().shallow_resolve(expected), true)
- .map_or(ast::MutImmutable, |mt| mt.mutbl);
+ .map(|mt| mt.mutbl).unwrap_or(ast::MutImmutable)
+ } else {
+ mutbl
+ };
let mt = ty::mt { ty: inner_ty, mutbl: mutbl };
let region = fcx.infcx().next_region_var(infer::PatternRegion(pat.span));
let rptr_ty = ty::mk_rptr(tcx, tcx.mk_region(region), mt);
if check_dereferencable(pcx, pat.span, expected, &**inner) {
- demand::suptype(fcx, pat.span, expected, rptr_ty);
+ // `demand::subtype` would be good enough, but using
+ // `eqtype` turns out to be equally general. See (*)
+ // below for details.
+ demand::eqtype(fcx, pat.span, expected, rptr_ty);
fcx.write_ty(pat.id, rptr_ty);
check_pat(pcx, &**inner, inner_ty);
} else {
let region = fcx.infcx().next_region_var(infer::PatternRegion(pat.span));
ty::mk_slice(tcx, tcx.mk_region(region), ty::mt {
ty: inner_ty,
- mutbl: ty::deref(expected_ty, true)
- .map_or(ast::MutImmutable, |mt| mt.mutbl)
+ mutbl: ty::deref(expected_ty, true).map(|mt| mt.mutbl)
+ .unwrap_or(ast::MutImmutable)
})
}
};
fcx.write_ty(pat.id, pat_ty);
- demand::suptype(fcx, pat.span, expected, pat_ty);
+
+ // `demand::subtype` would be good enough, but using
+ // `eqtype` turns out to be equally general. See (*)
+ // below for details.
+ demand::eqtype(fcx, pat.span, expected, pat_ty);
for elt in before.iter() {
check_pat(pcx, &**elt, inner_ty);
}
ast::PatMac(_) => tcx.sess.bug("unexpanded macro")
}
+
+
+ // (*) In most of the cases above (literals and constants being
+ // the exception), we relate types using strict equality, evewn
+ // 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. Most importantly, there is no loss of expressiveness
+ // here. What we are saying is that the type of `x`
+ // becomes *exactly* what is expected. This might seem
+ // like it will cause errors in a case like this:
+ //
+ // ```
+ // 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_inference`, 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<'a, 'tcx>(pcx: &pat_ctxt<'a, 'tcx>,
let ctor_scheme = ty::lookup_item_type(tcx, enum_def);
let path_scheme = if ty::is_fn_ty(ctor_scheme.ty) {
+ let fn_ret = ty::assert_no_late_bound_regions(tcx, &ty::ty_fn_ret(ctor_scheme.ty));
ty::TypeScheme {
- ty: ty::ty_fn_ret(ctor_scheme.ty).unwrap(),
- ..ctor_scheme
+ ty: fn_ret.unwrap(),
+ generics: ctor_scheme.generics,
}
} else {
ctor_scheme
tcx.types.err
}
Vacant(vacant) => {
- vacant.set(span);
+ vacant.insert(span);
field_type_map.get(&field.ident.name).cloned()
.unwrap_or_else(|| {
span_err!(tcx.sess, span, E0026,
projects / rust.git / blobdiff