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 pub use self::Constructor::*;
12 use self::Usefulness::*;
13 use self::WitnessPreference::*;
15 use dep_graph::DepNode;
16 use middle::const_eval::{compare_const_vals, ConstVal};
17 use middle::const_eval::{eval_const_expr, eval_const_expr_partial};
18 use middle::const_eval::{const_expr_to_pat, lookup_const_by_id};
19 use middle::const_eval::EvalHint::ExprTypeChecked;
21 use middle::def_id::{DefId};
22 use middle::expr_use_visitor::{ConsumeMode, Delegate, ExprUseVisitor};
23 use middle::expr_use_visitor::{LoanCause, MutateMode};
24 use middle::expr_use_visitor as euv;
26 use middle::mem_categorization::{cmt};
27 use middle::pat_util::*;
30 use std::cmp::Ordering;
32 use std::iter::{FromIterator, IntoIterator, repeat};
35 use rustc_front::hir::Pat;
36 use rustc_front::intravisit::{self, Visitor, FnKind};
37 use rustc_front::util as front_util;
38 use rustc_back::slice;
40 use syntax::ast::{self, DUMMY_NODE_ID, NodeId};
42 use syntax::codemap::{Span, Spanned, DUMMY_SP};
43 use rustc_front::fold::{Folder, noop_fold_pat};
44 use rustc_front::print::pprust::pat_to_string;
46 use util::nodemap::FnvHashMap;
48 pub const DUMMY_WILD_PAT: &'static Pat = &Pat {
54 struct Matrix<'a>(Vec<Vec<&'a Pat>>);
56 /// Pretty-printer for matrices of patterns, example:
57 /// ++++++++++++++++++++++++++
59 /// ++++++++++++++++++++++++++
60 /// + true + [First] +
61 /// ++++++++++++++++++++++++++
62 /// + true + [Second(true)] +
63 /// ++++++++++++++++++++++++++
65 /// ++++++++++++++++++++++++++
66 /// + _ + [_, _, ..tail] +
67 /// ++++++++++++++++++++++++++
68 impl<'a> fmt::Debug for Matrix<'a> {
69 fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
70 try!(write!(f, "\n"));
72 let &Matrix(ref m) = self;
73 let pretty_printed_matrix: Vec<Vec<String>> = m.iter().map(|row| {
75 .map(|&pat| pat_to_string(&*pat))
76 .collect::<Vec<String>>()
79 let column_count = m.iter().map(|row| row.len()).max().unwrap_or(0);
80 assert!(m.iter().all(|row| row.len() == column_count));
81 let column_widths: Vec<usize> = (0..column_count).map(|col| {
82 pretty_printed_matrix.iter().map(|row| row[col].len()).max().unwrap_or(0)
85 let total_width = column_widths.iter().cloned().sum::<usize>() + column_count * 3 + 1;
86 let br = repeat('+').take(total_width).collect::<String>();
87 try!(write!(f, "{}\n", br));
88 for row in pretty_printed_matrix {
90 for (column, pat_str) in row.into_iter().enumerate() {
92 try!(write!(f, "{:1$}", pat_str, column_widths[column]));
93 try!(write!(f, " +"));
95 try!(write!(f, "\n"));
96 try!(write!(f, "{}\n", br));
102 impl<'a> FromIterator<Vec<&'a Pat>> for Matrix<'a> {
103 fn from_iter<T: IntoIterator<Item=Vec<&'a Pat>>>(iter: T) -> Matrix<'a> {
104 Matrix(iter.into_iter().collect())
108 //NOTE: appears to be the only place other then InferCtxt to contain a ParamEnv
109 pub struct MatchCheckCtxt<'a, 'tcx: 'a> {
110 pub tcx: &'a ty::ctxt<'tcx>,
111 pub param_env: ParameterEnvironment<'a, 'tcx>,
114 #[derive(Clone, PartialEq)]
115 pub enum Constructor {
116 /// The constructor of all patterns that don't vary by constructor,
117 /// e.g. struct patterns and fixed-length arrays.
122 ConstantValue(ConstVal),
123 /// Ranges of literal values (2..5).
124 ConstantRange(ConstVal, ConstVal),
125 /// Array patterns of length n.
127 /// Array patterns with a subslice.
128 SliceWithSubslice(usize, usize)
131 #[derive(Clone, PartialEq)]
134 UsefulWithWitness(Vec<P<Pat>>),
138 #[derive(Copy, Clone)]
139 enum WitnessPreference {
144 impl<'a, 'tcx, 'v> Visitor<'v> for MatchCheckCtxt<'a, 'tcx> {
145 fn visit_expr(&mut self, ex: &hir::Expr) {
146 check_expr(self, ex);
148 fn visit_local(&mut self, l: &hir::Local) {
149 check_local(self, l);
151 fn visit_fn(&mut self, fk: FnKind<'v>, fd: &'v hir::FnDecl,
152 b: &'v hir::Block, s: Span, n: NodeId) {
153 check_fn(self, fk, fd, b, s, n);
157 pub fn check_crate(tcx: &ty::ctxt) {
158 tcx.visit_all_items_in_krate(DepNode::MatchCheck, &mut MatchCheckCtxt {
160 param_env: tcx.empty_parameter_environment(),
162 tcx.sess.abort_if_errors();
165 fn check_expr(cx: &mut MatchCheckCtxt, ex: &hir::Expr) {
166 intravisit::walk_expr(cx, ex);
168 hir::ExprMatch(ref scrut, ref arms, source) => {
170 // First, check legality of move bindings.
171 check_legality_of_move_bindings(cx,
175 // Second, if there is a guard on each arm, make sure it isn't
176 // assigning or borrowing anything mutably.
178 Some(ref guard) => check_for_mutation_in_guard(cx, &**guard),
183 let mut static_inliner = StaticInliner::new(cx.tcx, None);
184 let inlined_arms = arms.iter().map(|arm| {
185 (arm.pats.iter().map(|pat| {
186 static_inliner.fold_pat((*pat).clone())
187 }).collect(), arm.guard.as_ref().map(|e| &**e))
188 }).collect::<Vec<(Vec<P<Pat>>, Option<&hir::Expr>)>>();
190 // Bail out early if inlining failed.
191 if static_inliner.failed {
195 for pat in inlined_arms
197 .flat_map(|&(ref pats, _)| pats) {
198 // Third, check legality of move bindings.
199 check_legality_of_bindings_in_at_patterns(cx, &**pat);
201 // Fourth, check if there are any references to NaN that we should warn about.
202 check_for_static_nan(cx, &**pat);
204 // Fifth, check if for any of the patterns that match an enumerated type
205 // are bindings with the same name as one of the variants of said type.
206 check_for_bindings_named_the_same_as_variants(cx, &**pat);
209 // Fourth, check for unreachable arms.
210 check_arms(cx, &inlined_arms[..], source);
212 // Finally, check if the whole match expression is exhaustive.
213 // Check for empty enum, because is_useful only works on inhabited types.
214 let pat_ty = cx.tcx.node_id_to_type(scrut.id);
215 if inlined_arms.is_empty() {
216 if !pat_ty.is_empty(cx.tcx) {
217 // We know the type is inhabited, so this must be wrong
218 let mut err = struct_span_err!(cx.tcx.sess, ex.span, E0002,
219 "non-exhaustive patterns: type {} is non-empty",
221 span_help!(&mut err, ex.span,
222 "Please ensure that all possible cases are being handled; \
223 possibly adding wildcards or more match arms.");
226 // If the type *is* empty, it's vacuously exhaustive
230 let matrix: Matrix = inlined_arms
232 .filter(|&&(_, guard)| guard.is_none())
233 .flat_map(|arm| &arm.0)
234 .map(|pat| vec![&**pat])
236 check_exhaustive(cx, ex.span, &matrix, source);
242 fn check_for_bindings_named_the_same_as_variants(cx: &MatchCheckCtxt, pat: &Pat) {
243 front_util::walk_pat(pat, |p| {
245 hir::PatIdent(hir::BindByValue(hir::MutImmutable), ident, None) => {
246 let pat_ty = cx.tcx.pat_ty(p);
247 if let ty::TyEnum(edef, _) = pat_ty.sty {
248 let def = cx.tcx.def_map.borrow().get(&p.id).map(|d| d.full_def());
249 if let Some(DefLocal(..)) = def {
250 if edef.variants.iter().any(|variant|
251 variant.name == ident.node.unhygienic_name
252 && variant.kind() == VariantKind::Unit
254 let ty_path = cx.tcx.item_path_str(edef.did);
255 let mut err = struct_span_warn!(cx.tcx.sess, p.span, E0170,
256 "pattern binding `{}` is named the same as one \
257 of the variants of the type `{}`",
258 ident.node, ty_path);
259 fileline_help!(err, p.span,
260 "if you meant to match on a variant, \
261 consider making the path in the pattern qualified: `{}::{}`",
262 ty_path, ident.node);
274 // Check that we do not match against a static NaN (#6804)
275 fn check_for_static_nan(cx: &MatchCheckCtxt, pat: &Pat) {
276 front_util::walk_pat(pat, |p| {
277 if let hir::PatLit(ref expr) = p.node {
278 match eval_const_expr_partial(cx.tcx, &**expr, ExprTypeChecked, None) {
279 Ok(ConstVal::Float(f)) if f.is_nan() => {
280 span_warn!(cx.tcx.sess, p.span, E0003,
281 "unmatchable NaN in pattern, \
282 use the is_nan method in a guard instead");
287 let mut diag = struct_span_err!(cx.tcx.sess, err.span, E0471,
288 "constant evaluation error: {}",
290 if !p.span.contains(err.span) {
291 diag.span_note(p.span, "in pattern here");
301 // Check for unreachable patterns
302 fn check_arms(cx: &MatchCheckCtxt,
303 arms: &[(Vec<P<Pat>>, Option<&hir::Expr>)],
304 source: hir::MatchSource) {
305 let mut seen = Matrix(vec![]);
306 let mut printed_if_let_err = false;
307 for &(ref pats, guard) in arms {
309 let v = vec![&**pat];
311 match is_useful(cx, &seen, &v[..], LeaveOutWitness) {
314 hir::MatchSource::IfLetDesugar { .. } => {
315 if printed_if_let_err {
316 // we already printed an irrefutable if-let pattern error.
317 // We don't want two, that's just confusing.
319 // find the first arm pattern so we can use its span
320 let &(ref first_arm_pats, _) = &arms[0];
321 let first_pat = &first_arm_pats[0];
322 let span = first_pat.span;
323 span_err!(cx.tcx.sess, span, E0162, "irrefutable if-let pattern");
324 printed_if_let_err = true;
328 hir::MatchSource::WhileLetDesugar => {
329 // find the first arm pattern so we can use its span
330 let &(ref first_arm_pats, _) = &arms[0];
331 let first_pat = &first_arm_pats[0];
332 let span = first_pat.span;
333 span_err!(cx.tcx.sess, span, E0165, "irrefutable while-let pattern");
336 hir::MatchSource::ForLoopDesugar => {
337 // this is a bug, because on `match iter.next()` we cover
338 // `Some(<head>)` and `None`. It's impossible to have an unreachable
340 // (see libsyntax/ext/expand.rs for the full expansion of a for loop)
341 cx.tcx.sess.span_bug(pat.span, "unreachable for-loop pattern")
344 hir::MatchSource::Normal => {
345 span_err!(cx.tcx.sess, pat.span, E0001, "unreachable pattern")
350 UsefulWithWitness(_) => unreachable!()
353 let Matrix(mut rows) = seen;
361 fn raw_pat<'a>(p: &'a Pat) -> &'a Pat {
363 hir::PatIdent(_, _, Some(ref s)) => raw_pat(&**s),
368 fn check_exhaustive(cx: &MatchCheckCtxt, sp: Span, matrix: &Matrix, source: hir::MatchSource) {
369 match is_useful(cx, matrix, &[DUMMY_WILD_PAT], ConstructWitness) {
370 UsefulWithWitness(pats) => {
371 let witnesses = if pats.is_empty() {
374 pats.iter().map(|w| &**w ).collect()
377 hir::MatchSource::ForLoopDesugar => {
378 // `witnesses[0]` has the form `Some(<head>)`, peel off the `Some`
379 let witness = match witnesses[0].node {
380 hir::PatEnum(_, Some(ref pats)) => match &pats[..] {
386 span_err!(cx.tcx.sess, sp, E0297,
387 "refutable pattern in `for` loop binding: \
389 pat_to_string(witness));
392 let pattern_strings: Vec<_> = witnesses.iter().map(|w| {
395 const LIMIT: usize = 3;
396 let joined_patterns = match pattern_strings.len() {
398 1 => format!("`{}`", pattern_strings[0]),
400 let (tail, head) = pattern_strings.split_last().unwrap();
401 format!("`{}`", head.join("`, `") + "` and `" + tail)
404 let (head, tail) = pattern_strings.split_at(LIMIT);
405 format!("`{}` and {} more", head.join("`, `"), tail.len())
408 span_err!(cx.tcx.sess, sp, E0004,
409 "non-exhaustive patterns: {} not covered",
416 // This is good, wildcard pattern isn't reachable
422 fn const_val_to_expr(value: &ConstVal) -> P<hir::Expr> {
423 let node = match value {
424 &ConstVal::Bool(b) => ast::LitBool(b),
429 node: hir::ExprLit(P(Spanned { node: node, span: DUMMY_SP })),
435 pub struct StaticInliner<'a, 'tcx: 'a> {
436 pub tcx: &'a ty::ctxt<'tcx>,
438 pub renaming_map: Option<&'a mut FnvHashMap<(NodeId, Span), NodeId>>,
441 impl<'a, 'tcx> StaticInliner<'a, 'tcx> {
442 pub fn new<'b>(tcx: &'b ty::ctxt<'tcx>,
443 renaming_map: Option<&'b mut FnvHashMap<(NodeId, Span), NodeId>>)
444 -> StaticInliner<'b, 'tcx> {
448 renaming_map: renaming_map
453 struct RenamingRecorder<'map> {
454 substituted_node_id: NodeId,
456 renaming_map: &'map mut FnvHashMap<(NodeId, Span), NodeId>
459 impl<'map> ast_util::IdVisitingOperation for RenamingRecorder<'map> {
460 fn visit_id(&mut self, node_id: NodeId) {
461 let key = (node_id, self.origin_span);
462 self.renaming_map.insert(key, self.substituted_node_id);
466 impl<'a, 'tcx> Folder for StaticInliner<'a, 'tcx> {
467 fn fold_pat(&mut self, pat: P<Pat>) -> P<Pat> {
468 return match pat.node {
469 hir::PatIdent(..) | hir::PatEnum(..) | hir::PatQPath(..) => {
470 let def = self.tcx.def_map.borrow().get(&pat.id).map(|d| d.full_def());
472 Some(DefAssociatedConst(did)) |
473 Some(DefConst(did)) => match lookup_const_by_id(self.tcx, did,
474 Some(pat.id), None) {
475 Some(const_expr) => {
476 const_expr_to_pat(self.tcx, const_expr, pat.span).map(|new_pat| {
478 if let Some(ref mut renaming_map) = self.renaming_map {
479 // Record any renamings we do here
480 record_renamings(const_expr, &pat, renaming_map);
488 span_err!(self.tcx.sess, pat.span, E0158,
489 "statics cannot be referenced in patterns");
493 _ => noop_fold_pat(pat, self)
496 _ => noop_fold_pat(pat, self)
499 fn record_renamings(const_expr: &hir::Expr,
500 substituted_pat: &hir::Pat,
501 renaming_map: &mut FnvHashMap<(NodeId, Span), NodeId>) {
502 let mut renaming_recorder = RenamingRecorder {
503 substituted_node_id: substituted_pat.id,
504 origin_span: substituted_pat.span,
505 renaming_map: renaming_map,
508 let mut id_visitor = front_util::IdVisitor::new(&mut renaming_recorder);
510 id_visitor.visit_expr(const_expr);
515 /// Constructs a partial witness for a pattern given a list of
516 /// patterns expanded by the specialization step.
518 /// When a pattern P is discovered to be useful, this function is used bottom-up
519 /// to reconstruct a complete witness, e.g. a pattern P' that covers a subset
520 /// of values, V, where each value in that set is not covered by any previously
521 /// used patterns and is covered by the pattern P'. Examples:
523 /// left_ty: tuple of 3 elements
524 /// pats: [10, 20, _] => (10, 20, _)
526 /// left_ty: struct X { a: (bool, &'static str), b: usize}
527 /// pats: [(false, "foo"), 42] => X { a: (false, "foo"), b: 42 }
528 fn construct_witness<'a,'tcx>(cx: &MatchCheckCtxt<'a,'tcx>, ctor: &Constructor,
529 pats: Vec<&Pat>, left_ty: Ty<'tcx>) -> P<Pat> {
530 let pats_len = pats.len();
531 let mut pats = pats.into_iter().map(|p| P((*p).clone()));
532 let pat = match left_ty.sty {
533 ty::TyTuple(_) => hir::PatTup(pats.collect()),
535 ty::TyEnum(adt, _) | ty::TyStruct(adt, _) => {
536 let v = adt.variant_of_ctor(ctor);
537 if let VariantKind::Struct = v.kind() {
538 let field_pats: hir::HirVec<_> = v.fields.iter()
540 .filter(|&(_, ref pat)| pat.node != hir::PatWild)
541 .map(|(field, pat)| Spanned {
543 node: hir::FieldPat {
549 let has_more_fields = field_pats.len() < pats_len;
550 hir::PatStruct(def_to_path(cx.tcx, v.did), field_pats, has_more_fields)
552 hir::PatEnum(def_to_path(cx.tcx, v.did), Some(pats.collect()))
556 ty::TyRef(_, ty::TypeAndMut { ty, mutbl }) => {
558 ty::TyArray(_, n) => match ctor {
560 assert_eq!(pats_len, n);
561 hir::PatVec(pats.collect(), None, hir::HirVec::new())
565 ty::TySlice(_) => match ctor {
567 assert_eq!(pats_len, n);
568 hir::PatVec(pats.collect(), None, hir::HirVec::new())
572 ty::TyStr => hir::PatWild,
575 assert_eq!(pats_len, 1);
576 hir::PatRegion(pats.nth(0).unwrap(), mutbl)
581 ty::TyArray(_, len) => {
582 assert_eq!(pats_len, len);
583 hir::PatVec(pats.collect(), None, hir::HirVec::new())
588 ConstantValue(ref v) => hir::PatLit(const_val_to_expr(v)),
601 impl<'tcx, 'container> ty::AdtDefData<'tcx, 'container> {
602 fn variant_of_ctor(&self,
604 -> &VariantDefData<'tcx, 'container> {
606 &Variant(vid) => self.variant_with_id(vid),
607 _ => self.struct_variant()
612 fn missing_constructors(cx: &MatchCheckCtxt, &Matrix(ref rows): &Matrix,
613 left_ty: Ty, max_slice_length: usize) -> Vec<Constructor> {
614 let used_constructors: Vec<Constructor> = rows.iter()
615 .flat_map(|row| pat_constructors(cx, row[0], left_ty, max_slice_length))
617 all_constructors(cx, left_ty, max_slice_length)
619 .filter(|c| !used_constructors.contains(c)).collect()
622 /// This determines the set of all possible constructors of a pattern matching
623 /// values of type `left_ty`. For vectors, this would normally be an infinite set
624 /// but is instead bounded by the maximum fixed length of slice patterns in
625 /// the column of patterns being analyzed.
626 fn all_constructors(_cx: &MatchCheckCtxt, left_ty: Ty,
627 max_slice_length: usize) -> Vec<Constructor> {
630 [true, false].iter().map(|b| ConstantValue(ConstVal::Bool(*b))).collect(),
632 ty::TyRef(_, ty::TypeAndMut { ty, .. }) => match ty.sty {
634 (0..max_slice_length+1).map(|length| Slice(length)).collect(),
638 ty::TyEnum(def, _) => def.variants.iter().map(|v| Variant(v.did)).collect(),
643 // Algorithm from http://moscova.inria.fr/~maranget/papers/warn/index.html
645 // Whether a vector `v` of patterns is 'useful' in relation to a set of such
646 // vectors `m` is defined as there being a set of inputs that will match `v`
647 // but not any of the sets in `m`.
649 // This is used both for reachability checking (if a pattern isn't useful in
650 // relation to preceding patterns, it is not reachable) and exhaustiveness
651 // checking (if a wildcard pattern is useful in relation to a matrix, the
652 // matrix isn't exhaustive).
654 // Note: is_useful doesn't work on empty types, as the paper notes.
655 // So it assumes that v is non-empty.
656 fn is_useful(cx: &MatchCheckCtxt,
659 witness: WitnessPreference)
661 let &Matrix(ref rows) = matrix;
662 debug!("{:?}", matrix);
664 return match witness {
665 ConstructWitness => UsefulWithWitness(vec!()),
666 LeaveOutWitness => Useful
669 if rows[0].is_empty() {
672 assert!(rows.iter().all(|r| r.len() == v.len()));
673 let real_pat = match rows.iter().find(|r| (*r)[0].id != DUMMY_NODE_ID) {
674 Some(r) => raw_pat(r[0]),
675 None if v.is_empty() => return NotUseful,
678 let left_ty = if real_pat.id == DUMMY_NODE_ID {
681 let left_ty = cx.tcx.pat_ty(&*real_pat);
683 match real_pat.node {
684 hir::PatIdent(hir::BindByRef(..), _, _) => {
685 left_ty.builtin_deref(false, NoPreference).unwrap().ty
691 let max_slice_length = rows.iter().filter_map(|row| match row[0].node {
692 hir::PatVec(ref before, _, ref after) => Some(before.len() + after.len()),
694 }).max().map_or(0, |v| v + 1);
696 let constructors = pat_constructors(cx, v[0], left_ty, max_slice_length);
697 if constructors.is_empty() {
698 match &missing_constructors(cx, matrix, left_ty, max_slice_length)[..] {
700 all_constructors(cx, left_ty, max_slice_length).into_iter().map(|c| {
701 match is_useful_specialized(cx, matrix, v, c.clone(), left_ty, witness) {
702 UsefulWithWitness(pats) => UsefulWithWitness({
703 let arity = constructor_arity(cx, &c, left_ty);
705 let pat_slice = &pats[..];
706 let subpats: Vec<_> = (0..arity).map(|i| {
707 pat_slice.get(i).map_or(DUMMY_WILD_PAT, |p| &**p)
709 vec![construct_witness(cx, &c, subpats, left_ty)]
711 result.extend(pats.into_iter().skip(arity));
716 }).find(|result| result != &NotUseful).unwrap_or(NotUseful)
719 [constructors..] => {
720 let matrix = rows.iter().filter_map(|r| {
721 if pat_is_binding_or_wild(&cx.tcx.def_map.borrow(), raw_pat(r[0])) {
722 Some(r[1..].to_vec())
727 match is_useful(cx, &matrix, &v[1..], witness) {
728 UsefulWithWitness(pats) => {
729 let mut new_pats: Vec<_> = constructors.into_iter().map(|constructor| {
730 let arity = constructor_arity(cx, &constructor, left_ty);
731 let wild_pats = vec![DUMMY_WILD_PAT; arity];
732 construct_witness(cx, &constructor, wild_pats, left_ty)
734 new_pats.extend(pats);
735 UsefulWithWitness(new_pats)
742 constructors.into_iter().map(|c|
743 is_useful_specialized(cx, matrix, v, c.clone(), left_ty, witness)
744 ).find(|result| result != &NotUseful).unwrap_or(NotUseful)
748 fn is_useful_specialized(cx: &MatchCheckCtxt, &Matrix(ref m): &Matrix,
749 v: &[&Pat], ctor: Constructor, lty: Ty,
750 witness: WitnessPreference) -> Usefulness {
751 let arity = constructor_arity(cx, &ctor, lty);
752 let matrix = Matrix(m.iter().filter_map(|r| {
753 specialize(cx, &r[..], &ctor, 0, arity)
755 match specialize(cx, v, &ctor, 0, arity) {
756 Some(v) => is_useful(cx, &matrix, &v[..], witness),
761 /// Determines the constructors that the given pattern can be specialized to.
763 /// In most cases, there's only one constructor that a specific pattern
764 /// represents, such as a specific enum variant or a specific literal value.
765 /// Slice patterns, however, can match slices of different lengths. For instance,
766 /// `[a, b, ..tail]` can match a slice of length 2, 3, 4 and so on.
768 /// On the other hand, a wild pattern and an identifier pattern cannot be
769 /// specialized in any way.
770 fn pat_constructors(cx: &MatchCheckCtxt, p: &Pat,
771 left_ty: Ty, max_slice_length: usize) -> Vec<Constructor> {
772 let pat = raw_pat(p);
775 match cx.tcx.def_map.borrow().get(&pat.id).map(|d| d.full_def()) {
776 Some(DefConst(..)) | Some(DefAssociatedConst(..)) =>
777 cx.tcx.sess.span_bug(pat.span, "const pattern should've \
779 Some(DefStruct(_)) => vec!(Single),
780 Some(DefVariant(_, id, _)) => vec!(Variant(id)),
784 match cx.tcx.def_map.borrow().get(&pat.id).map(|d| d.full_def()) {
785 Some(DefConst(..)) | Some(DefAssociatedConst(..)) =>
786 cx.tcx.sess.span_bug(pat.span, "const pattern should've \
788 Some(DefVariant(_, id, _)) => vec!(Variant(id)),
792 cx.tcx.sess.span_bug(pat.span, "const pattern should've \
794 hir::PatStruct(..) =>
795 match cx.tcx.def_map.borrow().get(&pat.id).map(|d| d.full_def()) {
796 Some(DefConst(..)) | Some(DefAssociatedConst(..)) =>
797 cx.tcx.sess.span_bug(pat.span, "const pattern should've \
799 Some(DefVariant(_, id, _)) => vec!(Variant(id)),
802 hir::PatLit(ref expr) =>
803 vec!(ConstantValue(eval_const_expr(cx.tcx, &**expr))),
804 hir::PatRange(ref lo, ref hi) =>
805 vec!(ConstantRange(eval_const_expr(cx.tcx, &**lo), eval_const_expr(cx.tcx, &**hi))),
806 hir::PatVec(ref before, ref slice, ref after) =>
808 ty::TyArray(_, _) => vec!(Single),
809 _ => if slice.is_some() {
810 (before.len() + after.len()..max_slice_length+1)
811 .map(|length| Slice(length))
814 vec!(Slice(before.len() + after.len()))
817 hir::PatBox(_) | hir::PatTup(_) | hir::PatRegion(..) =>
824 /// This computes the arity of a constructor. The arity of a constructor
825 /// is how many subpattern patterns of that constructor should be expanded to.
827 /// For instance, a tuple pattern (_, 42, Some([])) has the arity of 3.
828 /// A struct pattern's arity is the number of fields it contains, etc.
829 pub fn constructor_arity(_cx: &MatchCheckCtxt, ctor: &Constructor, ty: Ty) -> usize {
831 ty::TyTuple(ref fs) => fs.len(),
833 ty::TyRef(_, ty::TypeAndMut { ty, .. }) => match ty.sty {
834 ty::TySlice(_) => match *ctor {
835 Slice(length) => length,
836 ConstantValue(_) => 0,
842 ty::TyEnum(adt, _) | ty::TyStruct(adt, _) => {
843 adt.variant_of_ctor(ctor).fields.len()
845 ty::TyArray(_, n) => n,
850 fn range_covered_by_constructor(ctor: &Constructor,
851 from: &ConstVal, to: &ConstVal) -> Option<bool> {
852 let (c_from, c_to) = match *ctor {
853 ConstantValue(ref value) => (value, value),
854 ConstantRange(ref from, ref to) => (from, to),
855 Single => return Some(true),
858 let cmp_from = compare_const_vals(c_from, from);
859 let cmp_to = compare_const_vals(c_to, to);
860 match (cmp_from, cmp_to) {
861 (Some(cmp_from), Some(cmp_to)) => {
862 Some(cmp_from != Ordering::Less && cmp_to != Ordering::Greater)
868 /// This is the main specialization step. It expands the first pattern in the given row
869 /// into `arity` patterns based on the constructor. For most patterns, the step is trivial,
870 /// for instance tuple patterns are flattened and box patterns expand into their inner pattern.
872 /// OTOH, slice patterns with a subslice pattern (..tail) can be expanded into multiple
873 /// different patterns.
874 /// Structure patterns with a partial wild pattern (Foo { a: 42, .. }) have their missing
875 /// fields filled with wild patterns.
876 pub fn specialize<'a>(cx: &MatchCheckCtxt, r: &[&'a Pat],
877 constructor: &Constructor, col: usize, arity: usize) -> Option<Vec<&'a Pat>> {
879 id: pat_id, ref node, span: pat_span
881 let head: Option<Vec<&Pat>> = match *node {
883 Some(vec![DUMMY_WILD_PAT; arity]),
885 hir::PatIdent(_, _, _) => {
886 let opt_def = cx.tcx.def_map.borrow().get(&pat_id).map(|d| d.full_def());
888 Some(DefConst(..)) | Some(DefAssociatedConst(..)) =>
889 cx.tcx.sess.span_bug(pat_span, "const pattern should've \
891 Some(DefVariant(_, id, _)) => if *constructor == Variant(id) {
896 _ => Some(vec![DUMMY_WILD_PAT; arity])
900 hir::PatEnum(_, ref args) => {
901 let def = cx.tcx.def_map.borrow().get(&pat_id).unwrap().full_def();
903 DefConst(..) | DefAssociatedConst(..) =>
904 cx.tcx.sess.span_bug(pat_span, "const pattern should've \
906 DefVariant(_, id, _) if *constructor != Variant(id) => None,
907 DefVariant(..) | DefStruct(..) => {
909 &Some(ref args) => args.iter().map(|p| &**p).collect(),
910 &None => vec![DUMMY_WILD_PAT; arity],
917 hir::PatQPath(_, _) => {
918 cx.tcx.sess.span_bug(pat_span, "const pattern should've \
922 hir::PatStruct(_, ref pattern_fields, _) => {
923 let def = cx.tcx.def_map.borrow().get(&pat_id).unwrap().full_def();
924 let adt = cx.tcx.node_id_to_type(pat_id).ty_adt_def().unwrap();
925 let variant = adt.variant_of_ctor(constructor);
926 let def_variant = adt.variant_of_def(def);
927 if variant.did == def_variant.did {
928 Some(variant.fields.iter().map(|sf| {
929 match pattern_fields.iter().find(|f| f.node.name == sf.name) {
930 Some(ref f) => &*f.node.pat,
939 hir::PatTup(ref args) =>
940 Some(args.iter().map(|p| &**p).collect()),
942 hir::PatBox(ref inner) | hir::PatRegion(ref inner, _) =>
943 Some(vec![&**inner]),
945 hir::PatLit(ref expr) => {
946 let expr_value = eval_const_expr(cx.tcx, &**expr);
947 match range_covered_by_constructor(constructor, &expr_value, &expr_value) {
948 Some(true) => Some(vec![]),
951 span_err!(cx.tcx.sess, pat_span, E0298, "mismatched types between arms");
957 hir::PatRange(ref from, ref to) => {
958 let from_value = eval_const_expr(cx.tcx, &**from);
959 let to_value = eval_const_expr(cx.tcx, &**to);
960 match range_covered_by_constructor(constructor, &from_value, &to_value) {
961 Some(true) => Some(vec![]),
964 span_err!(cx.tcx.sess, pat_span, E0299, "mismatched types between arms");
970 hir::PatVec(ref before, ref slice, ref after) => {
972 // Fixed-length vectors.
974 let mut pats: Vec<&Pat> = before.iter().map(|p| &**p).collect();
975 pats.extend(repeat(DUMMY_WILD_PAT).take(arity - before.len() - after.len()));
976 pats.extend(after.iter().map(|p| &**p));
979 Slice(length) if before.len() + after.len() <= length && slice.is_some() => {
980 let mut pats: Vec<&Pat> = before.iter().map(|p| &**p).collect();
981 pats.extend(repeat(DUMMY_WILD_PAT).take(arity - before.len() - after.len()));
982 pats.extend(after.iter().map(|p| &**p));
985 Slice(length) if before.len() + after.len() == length => {
986 let mut pats: Vec<&Pat> = before.iter().map(|p| &**p).collect();
987 pats.extend(after.iter().map(|p| &**p));
990 SliceWithSubslice(prefix, suffix)
991 if before.len() == prefix
992 && after.len() == suffix
993 && slice.is_some() => {
994 let mut pats: Vec<&Pat> = before.iter().map(|p| &**p).collect();
995 pats.extend(after.iter().map(|p| &**p));
1002 head.map(|mut head| {
1003 head.extend_from_slice(&r[..col]);
1004 head.extend_from_slice(&r[col + 1..]);
1009 fn check_local(cx: &mut MatchCheckCtxt, loc: &hir::Local) {
1010 intravisit::walk_local(cx, loc);
1012 let pat = StaticInliner::new(cx.tcx, None).fold_pat(loc.pat.clone());
1013 check_irrefutable(cx, &pat, false);
1015 // Check legality of move bindings and `@` patterns.
1016 check_legality_of_move_bindings(cx, false, slice::ref_slice(&loc.pat));
1017 check_legality_of_bindings_in_at_patterns(cx, &*loc.pat);
1020 fn check_fn(cx: &mut MatchCheckCtxt,
1027 FnKind::Closure => {}
1028 _ => cx.param_env = ParameterEnvironment::for_item(cx.tcx, fn_id),
1031 intravisit::walk_fn(cx, kind, decl, body, sp);
1033 for input in &decl.inputs {
1034 check_irrefutable(cx, &input.pat, true);
1035 check_legality_of_move_bindings(cx, false, slice::ref_slice(&input.pat));
1036 check_legality_of_bindings_in_at_patterns(cx, &*input.pat);
1040 fn check_irrefutable(cx: &MatchCheckCtxt, pat: &Pat, is_fn_arg: bool) {
1041 let origin = if is_fn_arg {
1047 is_refutable(cx, pat, |uncovered_pat| {
1048 span_err!(cx.tcx.sess, pat.span, E0005,
1049 "refutable pattern in {}: `{}` not covered",
1051 pat_to_string(uncovered_pat),
1056 fn is_refutable<A, F>(cx: &MatchCheckCtxt, pat: &Pat, refutable: F) -> Option<A> where
1057 F: FnOnce(&Pat) -> A,
1059 let pats = Matrix(vec!(vec!(pat)));
1060 match is_useful(cx, &pats, &[DUMMY_WILD_PAT], ConstructWitness) {
1061 UsefulWithWitness(pats) => {
1062 assert_eq!(pats.len(), 1);
1063 Some(refutable(&*pats[0]))
1066 Useful => unreachable!()
1070 // Legality of move bindings checking
1071 fn check_legality_of_move_bindings(cx: &MatchCheckCtxt,
1075 let def_map = &tcx.def_map;
1076 let mut by_ref_span = None;
1078 pat_bindings(def_map, &**pat, |bm, _, span, _path| {
1080 hir::BindByRef(_) => {
1081 by_ref_span = Some(span);
1083 hir::BindByValue(_) => {
1089 let check_move = |p: &Pat, sub: Option<&Pat>| {
1090 // check legality of moving out of the enum
1092 // x @ Foo(..) is legal, but x @ Foo(y) isn't.
1093 if sub.map_or(false, |p| pat_contains_bindings(&def_map.borrow(), &*p)) {
1094 span_err!(cx.tcx.sess, p.span, E0007, "cannot bind by-move with sub-bindings");
1095 } else if has_guard {
1096 span_err!(cx.tcx.sess, p.span, E0008, "cannot bind by-move into a pattern guard");
1097 } else if by_ref_span.is_some() {
1098 let mut err = struct_span_err!(cx.tcx.sess, p.span, E0009,
1099 "cannot bind by-move and by-ref in the same pattern");
1100 span_note!(&mut err, by_ref_span.unwrap(), "by-ref binding occurs here");
1106 front_util::walk_pat(&**pat, |p| {
1107 if pat_is_binding(&def_map.borrow(), &*p) {
1109 hir::PatIdent(hir::BindByValue(_), _, ref sub) => {
1110 let pat_ty = tcx.node_id_to_type(p.id);
1111 //FIXME: (@jroesch) this code should be floated up as well
1112 let infcx = infer::new_infer_ctxt(cx.tcx,
1114 Some(cx.param_env.clone()));
1115 if infcx.type_moves_by_default(pat_ty, pat.span) {
1116 check_move(p, sub.as_ref().map(|p| &**p));
1119 hir::PatIdent(hir::BindByRef(_), _, _) => {
1122 cx.tcx.sess.span_bug(
1124 &format!("binding pattern {} is not an \
1136 /// Ensures that a pattern guard doesn't borrow by mutable reference or
1138 fn check_for_mutation_in_guard<'a, 'tcx>(cx: &'a MatchCheckCtxt<'a, 'tcx>,
1139 guard: &hir::Expr) {
1140 let mut checker = MutationChecker {
1144 let infcx = infer::new_infer_ctxt(cx.tcx,
1146 Some(checker.cx.param_env.clone()));
1148 let mut visitor = ExprUseVisitor::new(&mut checker, &infcx);
1149 visitor.walk_expr(guard);
1152 struct MutationChecker<'a, 'tcx: 'a> {
1153 cx: &'a MatchCheckCtxt<'a, 'tcx>,
1156 impl<'a, 'tcx> Delegate<'tcx> for MutationChecker<'a, 'tcx> {
1157 fn matched_pat(&mut self, _: &Pat, _: cmt, _: euv::MatchMode) {}
1158 fn consume(&mut self, _: NodeId, _: Span, _: cmt, _: ConsumeMode) {}
1159 fn consume_pat(&mut self, _: &Pat, _: cmt, _: ConsumeMode) {}
1160 fn borrow(&mut self,
1169 span_err!(self.cx.tcx.sess, span, E0301,
1170 "cannot mutably borrow in a pattern guard")
1172 ImmBorrow | UniqueImmBorrow => {}
1175 fn decl_without_init(&mut self, _: NodeId, _: Span) {}
1176 fn mutate(&mut self, _: NodeId, span: Span, _: cmt, mode: MutateMode) {
1178 MutateMode::JustWrite | MutateMode::WriteAndRead => {
1179 span_err!(self.cx.tcx.sess, span, E0302, "cannot assign in a pattern guard")
1181 MutateMode::Init => {}
1186 /// Forbids bindings in `@` patterns. This is necessary for memory safety,
1187 /// because of the way rvalues are handled in the borrow check. (See issue
1189 fn check_legality_of_bindings_in_at_patterns(cx: &MatchCheckCtxt, pat: &Pat) {
1190 AtBindingPatternVisitor { cx: cx, bindings_allowed: true }.visit_pat(pat);
1193 struct AtBindingPatternVisitor<'a, 'b:'a, 'tcx:'b> {
1194 cx: &'a MatchCheckCtxt<'b, 'tcx>,
1195 bindings_allowed: bool
1198 impl<'a, 'b, 'tcx, 'v> Visitor<'v> for AtBindingPatternVisitor<'a, 'b, 'tcx> {
1199 fn visit_pat(&mut self, pat: &Pat) {
1200 if !self.bindings_allowed && pat_is_binding(&self.cx.tcx.def_map.borrow(), pat) {
1201 span_err!(self.cx.tcx.sess, pat.span, E0303,
1202 "pattern bindings are not allowed \
1207 hir::PatIdent(_, _, Some(_)) => {
1208 let bindings_were_allowed = self.bindings_allowed;
1209 self.bindings_allowed = false;
1210 intravisit::walk_pat(self, pat);
1211 self.bindings_allowed = bindings_were_allowed;
1213 _ => intravisit::walk_pat(self, pat),