1 // Copyright 2012-2014 The Rust Project Developers. See the COPYRIGHT
2 // file at the top-level directory of this distribution and at
3 // http://rust-lang.org/COPYRIGHT.
5 // Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
6 // http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
7 // <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
8 // option. This file may not be copied, modified, or distributed
9 // except according to those terms.
11 use middle::const_eval;
14 use middle::pat_util::{PatIdMap, pat_id_map, pat_is_binding, pat_is_const};
15 use middle::subst::{Substs};
16 use middle::ty::{self, Ty};
17 use check::{check_expr, check_expr_has_type, check_expr_with_expectation};
18 use check::{check_expr_coercable_to_type, demand, FnCtxt, Expectation};
19 use check::{instantiate_path, structurally_resolved_type};
20 use require_same_types;
21 use util::nodemap::FnvHashMap;
22 use util::ppaux::Repr;
24 use std::cmp::{self, Ordering};
25 use std::collections::hash_map::Entry::{Occupied, Vacant};
28 use syntax::codemap::{Span, Spanned};
29 use syntax::parse::token;
30 use syntax::print::pprust;
33 pub fn check_pat<'a, 'tcx>(pcx: &pat_ctxt<'a, 'tcx>,
38 let tcx = pcx.fcx.ccx.tcx;
40 debug!("check_pat(pat={},expected={})",
46 fcx.write_ty(pat.id, expected);
48 ast::PatLit(ref lt) => {
49 check_expr(fcx, &**lt);
50 let expr_ty = fcx.expr_ty(&**lt);
51 fcx.write_ty(pat.id, expr_ty);
53 // somewhat surprising: in this case, the subtyping
54 // relation goes the opposite way as the other
55 // cases. Actually what we really want is not a subtyping
56 // relation at all but rather that there exists a LUB (so
57 // that they can be compared). However, in practice,
58 // constants are always scalars or strings. For scalars
59 // subtyping is irrelevant, and for strings `expr_ty` is
60 // type is `&'static str`, so if we say that
62 // &'static str <: expected
64 // that's equivalent to there existing a LUB.
65 demand::suptype(fcx, pat.span, expected, expr_ty);
67 ast::PatRange(ref begin, ref end) => {
68 check_expr(fcx, &**begin);
69 check_expr(fcx, &**end);
71 let lhs_ty = fcx.expr_ty(&**begin);
72 let rhs_ty = fcx.expr_ty(&**end);
76 tcx, Some(fcx.infcx()), false, pat.span, lhs_ty, rhs_ty,
77 || "mismatched types in range".to_string());
80 lhs_eq_rhs && (ty::type_is_numeric(lhs_ty) || ty::type_is_char(lhs_ty));
83 match const_eval::compare_lit_exprs(tcx, &**begin, &**end, Some(lhs_ty)) {
84 Some(Ordering::Less) |
85 Some(Ordering::Equal) => {}
86 Some(Ordering::Greater) => {
87 span_err!(tcx.sess, begin.span, E0030,
88 "lower range bound must be less than upper");
91 span_err!(tcx.sess, begin.span, E0031,
92 "mismatched types in range");
96 span_err!(tcx.sess, begin.span, E0029,
97 "only char and numeric types are allowed in range");
100 fcx.write_ty(pat.id, lhs_ty);
102 // subtyping doesn't matter here, as the value is some kind of scalar
103 demand::eqtype(fcx, pat.span, expected, lhs_ty);
105 ast::PatEnum(..) | ast::PatIdent(..) if pat_is_const(&tcx.def_map, pat) => {
106 let const_did = tcx.def_map.borrow()[pat.id].clone().def_id();
107 let const_scheme = ty::lookup_item_type(tcx, const_did);
108 assert!(const_scheme.generics.is_empty());
109 let const_ty = pcx.fcx.instantiate_type_scheme(pat.span,
112 fcx.write_ty(pat.id, const_ty);
114 // FIXME(#20489) -- we should limit the types here to scalars or something!
116 // As with PatLit, what we really want here is that there
117 // exist a LUB, but for the cases that can occur, subtype
119 demand::suptype(fcx, pat.span, expected, const_ty);
121 ast::PatIdent(bm, ref path, ref sub) if pat_is_binding(&tcx.def_map, pat) => {
122 let typ = fcx.local_ty(pat.span, pat.id);
124 ast::BindByRef(mutbl) => {
125 // if the binding is like
126 // ref x | ref const x | ref mut x
127 // then `x` is assigned a value of type `&M T` where M is the mutability
128 // and T is the expected type.
129 let region_var = fcx.infcx().next_region_var(infer::PatternRegion(pat.span));
130 let mt = ty::mt { ty: expected, mutbl: mutbl };
131 let region_ty = ty::mk_rptr(tcx, tcx.mk_region(region_var), mt);
133 // `x` is assigned a value of type `&M T`, hence `&M T <: typeof(x)` is
134 // required. However, we use equality, which is stronger. See (*) for
136 demand::eqtype(fcx, pat.span, region_ty, typ);
138 // otherwise the type of x is the expected type T
139 ast::BindByValue(_) => {
140 // As above, `T <: typeof(x)` is required but we
141 // use equality, see (*) below.
142 demand::eqtype(fcx, pat.span, expected, typ);
146 fcx.write_ty(pat.id, typ);
148 // if there are multiple arms, make sure they all agree on
149 // what the type of the binding `x` ought to be
150 let canon_id = pcx.map[path.node];
151 if canon_id != pat.id {
152 let ct = fcx.local_ty(pat.span, canon_id);
153 demand::eqtype(fcx, pat.span, ct, typ);
156 if let Some(ref p) = *sub {
157 check_pat(pcx, &**p, expected);
160 ast::PatIdent(_, ref path, _) => {
161 let path = ast_util::ident_to_path(path.span, path.node);
162 check_pat_enum(pcx, pat, &path, Some(&[]), expected);
164 ast::PatEnum(ref path, ref subpats) => {
165 let subpats = subpats.as_ref().map(|v| &v[..]);
166 check_pat_enum(pcx, pat, path, subpats, expected);
168 ast::PatStruct(ref path, ref fields, etc) => {
169 check_pat_struct(pcx, pat, path, fields, etc, expected);
171 ast::PatTup(ref elements) => {
172 let element_tys: Vec<_> =
173 (0..elements.len()).map(|_| fcx.infcx().next_ty_var())
175 let pat_ty = ty::mk_tup(tcx, element_tys.clone());
176 fcx.write_ty(pat.id, pat_ty);
177 demand::eqtype(fcx, pat.span, expected, pat_ty);
178 for (element_pat, element_ty) in elements.iter().zip(element_tys.into_iter()) {
179 check_pat(pcx, &**element_pat, element_ty);
182 ast::PatBox(ref inner) => {
183 let inner_ty = fcx.infcx().next_ty_var();
184 let uniq_ty = ty::mk_uniq(tcx, inner_ty);
186 if check_dereferencable(pcx, pat.span, expected, &**inner) {
187 // Here, `demand::subtype` is good enough, but I don't
188 // think any errors can be introduced by using
190 demand::eqtype(fcx, pat.span, expected, uniq_ty);
191 fcx.write_ty(pat.id, uniq_ty);
192 check_pat(pcx, &**inner, inner_ty);
194 fcx.write_error(pat.id);
195 check_pat(pcx, &**inner, tcx.types.err);
198 ast::PatRegion(ref inner, mutbl) => {
199 let inner_ty = fcx.infcx().next_ty_var();
201 let mt = ty::mt { ty: inner_ty, mutbl: mutbl };
202 let region = fcx.infcx().next_region_var(infer::PatternRegion(pat.span));
203 let rptr_ty = ty::mk_rptr(tcx, tcx.mk_region(region), mt);
205 if check_dereferencable(pcx, pat.span, expected, &**inner) {
206 // `demand::subtype` would be good enough, but using
207 // `eqtype` turns out to be equally general. See (*)
208 // below for details.
209 demand::eqtype(fcx, pat.span, expected, rptr_ty);
210 fcx.write_ty(pat.id, rptr_ty);
211 check_pat(pcx, &**inner, inner_ty);
213 fcx.write_error(pat.id);
214 check_pat(pcx, &**inner, tcx.types.err);
217 ast::PatVec(ref before, ref slice, ref after) => {
218 let expected_ty = structurally_resolved_type(fcx, pat.span, expected);
219 let inner_ty = fcx.infcx().next_ty_var();
220 let pat_ty = match expected_ty.sty {
221 ty::ty_vec(_, Some(size)) => ty::mk_vec(tcx, inner_ty, Some({
222 let min_len = before.len() + after.len();
224 Some(_) => cmp::max(min_len, size),
229 let region = fcx.infcx().next_region_var(infer::PatternRegion(pat.span));
230 ty::mk_slice(tcx, tcx.mk_region(region), ty::mt {
232 mutbl: ty::deref(expected_ty, true).map(|mt| mt.mutbl)
233 .unwrap_or(ast::MutImmutable)
238 fcx.write_ty(pat.id, pat_ty);
240 // `demand::subtype` would be good enough, but using
241 // `eqtype` turns out to be equally general. See (*)
242 // below for details.
243 demand::eqtype(fcx, pat.span, expected, pat_ty);
246 check_pat(pcx, &**elt, inner_ty);
248 if let Some(ref slice) = *slice {
249 let region = fcx.infcx().next_region_var(infer::PatternRegion(pat.span));
250 let mutbl = ty::deref(expected_ty, true)
251 .map_or(ast::MutImmutable, |mt| mt.mutbl);
253 let slice_ty = ty::mk_slice(tcx, tcx.mk_region(region), ty::mt {
257 check_pat(pcx, &**slice, slice_ty);
260 check_pat(pcx, &**elt, inner_ty);
263 ast::PatMac(_) => tcx.sess.bug("unexpanded macro")
267 // (*) In most of the cases above (literals and constants being
268 // the exception), we relate types using strict equality, evewn
269 // though subtyping would be sufficient. There are a few reasons
270 // for this, some of which are fairly subtle and which cost me
271 // (nmatsakis) an hour or two debugging to remember, so I thought
272 // I'd write them down this time.
274 // 1. Most importantly, there is no loss of expressiveness
275 // here. What we are saying is that the type of `x`
276 // becomes *exactly* what is expected. This might seem
277 // like it will cause errors in a case like this:
280 // fn foo<'x>(x: &'x int) {
287 // The reason we might get an error is that `z` might be
288 // assigned a type like `&'x int`, and then we would have
289 // a problem when we try to assign `&a` to `z`, because
290 // the lifetime of `&a` (i.e., the enclosing block) is
291 // shorter than `'x`.
293 // HOWEVER, this code works fine. The reason is that the
294 // expected type here is whatever type the user wrote, not
295 // the initializer's type. In this case the user wrote
296 // nothing, so we are going to create a type variable `Z`.
297 // Then we will assign the type of the initializer (`&'x
298 // int`) as a subtype of `Z`: `&'x int <: Z`. And hence we
299 // will instantiate `Z` as a type `&'0 int` where `'0` is
300 // a fresh region variable, with the constraint that `'x :
301 // '0`. So basically we're all set.
303 // Note that there are two tests to check that this remains true
304 // (`regions-reassign-{match,let}-bound-pointer.rs`).
306 // 2. Things go horribly wrong if we use subtype. The reason for
307 // THIS is a fairly subtle case involving bound regions. See the
308 // `givens` field in `region_inference`, as well as the test
309 // `regions-relate-bound-regions-on-closures-to-inference-variables.rs`,
310 // for details. Short version is that we must sometimes detect
311 // relationships between specific region variables and regions
312 // bound in a closure signature, and that detection gets thrown
313 // off when we substitute fresh region variables here to enable
317 pub fn check_dereferencable<'a, 'tcx>(pcx: &pat_ctxt<'a, 'tcx>,
318 span: Span, expected: Ty<'tcx>,
319 inner: &ast::Pat) -> bool {
321 let tcx = pcx.fcx.ccx.tcx;
322 if pat_is_binding(&tcx.def_map, inner) {
323 let expected = fcx.infcx().shallow_resolve(expected);
324 ty::deref(expected, true).map_or(true, |mt| match mt.ty.sty {
326 // This is "x = SomeTrait" being reduced from
327 // "let &x = &SomeTrait" or "let box x = Box<SomeTrait>", an error.
328 span_err!(tcx.sess, span, E0033,
329 "type `{}` cannot be dereferenced",
330 fcx.infcx().ty_to_string(expected));
340 pub fn check_match<'a, 'tcx>(fcx: &FnCtxt<'a, 'tcx>,
341 expr: &'tcx ast::Expr,
342 discrim: &'tcx ast::Expr,
343 arms: &'tcx [ast::Arm],
344 expected: Expectation<'tcx>,
345 match_src: ast::MatchSource) {
346 let tcx = fcx.ccx.tcx;
348 let discrim_ty = fcx.infcx().next_ty_var();
349 check_expr_has_type(fcx, discrim, discrim_ty);
351 // Typecheck the patterns first, so that we get types for all the
354 let mut pcx = pat_ctxt {
356 map: pat_id_map(&tcx.def_map, &*arm.pats[0]),
359 check_pat(&mut pcx, &**p, discrim_ty);
363 // Now typecheck the blocks.
365 // The result of the match is the common supertype of all the
366 // arms. Start out the value as bottom, since it's the, well,
367 // bottom the type lattice, and we'll be moving up the lattice as
368 // we process each arm. (Note that any match with 0 arms is matching
369 // on any empty type and is therefore unreachable; should the flow
370 // of execution reach it, we will panic, so bottom is an appropriate
371 // type in that case)
372 let expected = expected.adjust_for_branches(fcx);
373 let result_ty = arms.iter().fold(fcx.infcx().next_diverging_ty_var(), |result_ty, arm| {
374 let bty = match expected {
375 // We don't coerce to `()` so that if the match expression is a
376 // statement it's branches can have any consistent type. That allows
377 // us to give better error messages (pointing to a usually better
378 // arm for inconsistent arms or to the whole match when a `()` type
380 Expectation::ExpectHasType(ety) if ety != ty::mk_nil(fcx.tcx()) => {
381 check_expr_coercable_to_type(fcx, &*arm.body, ety);
385 check_expr_with_expectation(fcx, &*arm.body, expected);
386 fcx.node_ty(arm.body.id)
390 if let Some(ref e) = arm.guard {
391 check_expr_has_type(fcx, &**e, tcx.types.bool);
394 if ty::type_is_error(result_ty) || ty::type_is_error(bty) {
397 let (origin, expected, found) = match match_src {
398 /* if-let construct without an else block */
399 ast::MatchSource::IfLetDesugar { contains_else_clause }
400 if !contains_else_clause => (
401 infer::IfExpressionWithNoElse(expr.span),
406 infer::MatchExpressionArm(expr.span, arm.body.span),
412 infer::common_supertype(
422 fcx.write_ty(expr.id, result_ty);
425 pub struct pat_ctxt<'a, 'tcx: 'a> {
426 pub fcx: &'a FnCtxt<'a, 'tcx>,
430 pub fn check_pat_struct<'a, 'tcx>(pcx: &pat_ctxt<'a, 'tcx>, pat: &'tcx ast::Pat,
431 path: &ast::Path, fields: &'tcx [Spanned<ast::FieldPat>],
432 etc: bool, expected: Ty<'tcx>) {
434 let tcx = pcx.fcx.ccx.tcx;
436 let def = tcx.def_map.borrow()[pat.id].clone();
437 let (enum_def_id, variant_def_id) = match def {
438 def::DefTrait(_) => {
439 let name = pprust::path_to_string(path);
440 span_err!(tcx.sess, pat.span, E0168,
441 "use of trait `{}` in a struct pattern", name);
442 fcx.write_error(pat.id);
444 for field in fields {
445 check_pat(pcx, &*field.node.pat, tcx.types.err);
450 let def_type = ty::lookup_item_type(tcx, def.def_id());
451 match def_type.ty.sty {
452 ty::ty_struct(struct_def_id, _) =>
453 (struct_def_id, struct_def_id),
454 ty::ty_enum(enum_def_id, _)
455 if def == def::DefVariant(enum_def_id, def.def_id(), true) =>
456 (enum_def_id, def.def_id()),
458 let name = pprust::path_to_string(path);
459 span_err!(tcx.sess, pat.span, E0163,
460 "`{}` does not name a struct or a struct variant", name);
461 fcx.write_error(pat.id);
463 for field in fields {
464 check_pat(pcx, &*field.node.pat, tcx.types.err);
472 instantiate_path(pcx.fcx,
474 ty::lookup_item_type(tcx, enum_def_id),
475 &ty::lookup_predicates(tcx, enum_def_id),
481 let pat_ty = fcx.node_ty(pat.id);
482 demand::eqtype(fcx, pat.span, expected, pat_ty);
484 let item_substs = fcx
487 .map(|substs| substs.substs.clone())
488 .unwrap_or_else(|| Substs::empty());
490 let struct_fields = ty::struct_fields(tcx, variant_def_id, &item_substs);
491 check_struct_pat_fields(pcx, pat.span, fields, &struct_fields,
492 variant_def_id, etc);
495 pub fn check_pat_enum<'a, 'tcx>(pcx: &pat_ctxt<'a, 'tcx>,
498 subpats: Option<&'tcx [P<ast::Pat>]>,
501 // Typecheck the path.
503 let tcx = pcx.fcx.ccx.tcx;
505 let def = tcx.def_map.borrow()[pat.id].clone();
506 let enum_def = def.variant_def_ids()
507 .map_or_else(|| def.def_id(), |(enum_def, _)| enum_def);
509 let ctor_scheme = ty::lookup_item_type(tcx, enum_def);
510 let ctor_predicates = ty::lookup_predicates(tcx, enum_def);
511 let path_scheme = if ty::is_fn_ty(ctor_scheme.ty) {
512 let fn_ret = ty::no_late_bound_regions(tcx, &ty::ty_fn_ret(ctor_scheme.ty)).unwrap();
515 generics: ctor_scheme.generics,
520 instantiate_path(pcx.fcx, path, path_scheme, &ctor_predicates, None, def, pat.span, pat.id);
522 let pat_ty = fcx.node_ty(pat.id);
523 demand::eqtype(fcx, pat.span, expected, pat_ty);
525 let real_path_ty = fcx.node_ty(pat.id);
526 let (arg_tys, kind_name): (Vec<_>, &'static str) = match real_path_ty.sty {
527 ty::ty_enum(enum_def_id, expected_substs)
528 if def == def::DefVariant(enum_def_id, def.def_id(), false) =>
530 let variant = ty::enum_variant_with_id(tcx, enum_def_id, def.def_id());
532 .map(|t| fcx.instantiate_type_scheme(pat.span, expected_substs, t))
536 ty::ty_struct(struct_def_id, expected_substs) => {
537 let struct_fields = ty::struct_fields(tcx, struct_def_id, expected_substs);
538 (struct_fields.iter()
539 .map(|field| fcx.instantiate_type_scheme(pat.span,
546 let name = pprust::path_to_string(path);
547 span_err!(tcx.sess, pat.span, E0164,
548 "`{}` does not name a non-struct variant or a tuple struct", name);
549 fcx.write_error(pat.id);
551 if let Some(subpats) = subpats {
553 check_pat(pcx, &**pat, tcx.types.err);
560 if let Some(subpats) = subpats {
561 if subpats.len() == arg_tys.len() {
562 for (subpat, arg_ty) in subpats.iter().zip(arg_tys.iter()) {
563 check_pat(pcx, &**subpat, *arg_ty);
565 } else if arg_tys.len() == 0 {
566 span_err!(tcx.sess, pat.span, E0024,
567 "this pattern has {} field{}, but the corresponding {} has no fields",
568 subpats.len(), if subpats.len() == 1 {""} else {"s"}, kind_name);
571 check_pat(pcx, &**pat, tcx.types.err);
574 span_err!(tcx.sess, pat.span, E0023,
575 "this pattern has {} field{}, but the corresponding {} has {} field{}",
576 subpats.len(), if subpats.len() == 1 {""} else {"s"},
578 arg_tys.len(), if arg_tys.len() == 1 {""} else {"s"});
581 check_pat(pcx, &**pat, tcx.types.err);
587 /// `path` is the AST path item naming the type of this struct.
588 /// `fields` is the field patterns of the struct pattern.
589 /// `struct_fields` describes the type of each field of the struct.
590 /// `struct_id` is the ID of the struct.
591 /// `etc` is true if the pattern said '...' and false otherwise.
592 pub fn check_struct_pat_fields<'a, 'tcx>(pcx: &pat_ctxt<'a, 'tcx>,
594 fields: &'tcx [Spanned<ast::FieldPat>],
595 struct_fields: &[ty::field<'tcx>],
596 struct_id: ast::DefId,
598 let tcx = pcx.fcx.ccx.tcx;
600 // Index the struct fields' types.
601 let field_type_map = struct_fields
603 .map(|field| (field.name, field.mt.ty))
604 .collect::<FnvHashMap<_, _>>();
606 // Keep track of which fields have already appeared in the pattern.
607 let mut used_fields = FnvHashMap();
609 // Typecheck each field.
610 for &Spanned { node: ref field, span } in fields {
611 let field_type = match used_fields.entry(field.ident.name) {
612 Occupied(occupied) => {
613 span_err!(tcx.sess, span, E0025,
614 "field `{}` bound multiple times in the pattern",
615 token::get_ident(field.ident));
616 span_note!(tcx.sess, *occupied.get(),
617 "field `{}` previously bound here",
618 token::get_ident(field.ident));
623 field_type_map.get(&field.ident.name).cloned()
625 span_err!(tcx.sess, span, E0026,
626 "struct `{}` does not have a field named `{}`",
627 ty::item_path_str(tcx, struct_id),
628 token::get_ident(field.ident));
634 let field_type = pcx.fcx.normalize_associated_types_in(span, &field_type);
636 check_pat(pcx, &*field.pat, field_type);
639 // Report an error if not all the fields were specified.
641 for field in struct_fields
643 .filter(|field| !used_fields.contains_key(&field.name)) {
644 span_err!(tcx.sess, span, E0027,
645 "pattern does not mention field `{}`",
646 token::get_name(field.name));