1 // Copyright 2012-2016 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 self::Constructor::*;
12 use self::Usefulness::*;
13 use self::WitnessPreference::*;
15 use rustc::dep_graph::DepNode;
16 use rustc::middle::const_val::ConstVal;
17 use ::{eval_const_expr, eval_const_expr_partial, compare_const_vals};
18 use ::{const_expr_to_pat, lookup_const_by_id};
19 use ::EvalHint::ExprTypeChecked;
20 use eval::report_const_eval_err;
21 use rustc::hir::def::*;
22 use rustc::hir::def_id::{DefId};
23 use rustc::middle::expr_use_visitor::{ConsumeMode, Delegate, ExprUseVisitor};
24 use rustc::middle::expr_use_visitor::{LoanCause, MutateMode};
25 use rustc::middle::expr_use_visitor as euv;
26 use rustc::middle::mem_categorization::{cmt};
27 use rustc::hir::pat_util::*;
28 use rustc::traits::ProjectionMode;
31 use std::cmp::Ordering;
33 use std::iter::{FromIterator, IntoIterator, repeat};
36 use rustc::hir::{Pat, PatKind};
37 use rustc::hir::intravisit::{self, Visitor, FnKind};
38 use rustc_back::slice;
40 use syntax::ast::{self, DUMMY_NODE_ID, NodeId};
41 use syntax::codemap::Spanned;
42 use syntax_pos::{Span, DUMMY_SP};
43 use rustc::hir::fold::{Folder, noop_fold_pat};
44 use rustc::hir::print::pat_to_string;
46 use rustc::util::common::ErrorReported;
47 use rustc::util::nodemap::FnvHashMap;
49 pub const DUMMY_WILD_PAT: &'static Pat = &Pat {
55 struct Matrix<'a, 'tcx>(Vec<Vec<(&'a Pat, Option<Ty<'tcx>>)>>);
57 /// Pretty-printer for matrices of patterns, example:
58 /// ++++++++++++++++++++++++++
60 /// ++++++++++++++++++++++++++
61 /// + true + [First] +
62 /// ++++++++++++++++++++++++++
63 /// + true + [Second(true)] +
64 /// ++++++++++++++++++++++++++
66 /// ++++++++++++++++++++++++++
67 /// + _ + [_, _, ..tail] +
68 /// ++++++++++++++++++++++++++
69 impl<'a, 'tcx> fmt::Debug for Matrix<'a, 'tcx> {
70 fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
73 let &Matrix(ref m) = self;
74 let pretty_printed_matrix: Vec<Vec<String>> = m.iter().map(|row| {
76 .map(|&(pat,ty)| format!("{}: {:?}", pat_to_string(&pat), ty))
77 .collect::<Vec<String>>()
80 let column_count = m.iter().map(|row| row.len()).max().unwrap_or(0);
81 assert!(m.iter().all(|row| row.len() == column_count));
82 let column_widths: Vec<usize> = (0..column_count).map(|col| {
83 pretty_printed_matrix.iter().map(|row| row[col].len()).max().unwrap_or(0)
86 let total_width = column_widths.iter().cloned().sum::<usize>() + column_count * 3 + 1;
87 let br = repeat('+').take(total_width).collect::<String>();
88 write!(f, "{}\n", br)?;
89 for row in pretty_printed_matrix {
91 for (column, pat_str) in row.into_iter().enumerate() {
93 write!(f, "{:1$}", pat_str, column_widths[column])?;
97 write!(f, "{}\n", br)?;
103 impl<'a, 'tcx> FromIterator<Vec<(&'a Pat, Option<Ty<'tcx>>)>> for Matrix<'a, 'tcx> {
104 fn from_iter<T: IntoIterator<Item=Vec<(&'a Pat, Option<Ty<'tcx>>)>>>(iter: T)
107 Matrix(iter.into_iter().collect())
111 //NOTE: appears to be the only place other then InferCtxt to contain a ParamEnv
112 pub struct MatchCheckCtxt<'a, 'tcx: 'a> {
113 pub tcx: TyCtxt<'a, 'tcx, 'tcx>,
114 pub param_env: ParameterEnvironment<'tcx>,
117 #[derive(Clone, Debug, PartialEq)]
118 pub enum Constructor {
119 /// The constructor of all patterns that don't vary by constructor,
120 /// e.g. struct patterns and fixed-length arrays.
125 ConstantValue(ConstVal),
126 /// Ranges of literal values (2..5).
127 ConstantRange(ConstVal, ConstVal),
128 /// Array patterns of length n.
130 /// Array patterns with a subslice.
131 SliceWithSubslice(usize, usize)
134 #[derive(Clone, PartialEq)]
137 UsefulWithWitness(Vec<P<Pat>>),
141 #[derive(Copy, Clone)]
142 enum WitnessPreference {
147 impl<'a, 'tcx, 'v> Visitor<'v> for MatchCheckCtxt<'a, 'tcx> {
148 fn visit_expr(&mut self, ex: &hir::Expr) {
149 check_expr(self, ex);
151 fn visit_local(&mut self, l: &hir::Local) {
152 check_local(self, l);
154 fn visit_fn(&mut self, fk: FnKind<'v>, fd: &'v hir::FnDecl,
155 b: &'v hir::Block, s: Span, n: NodeId) {
156 check_fn(self, fk, fd, b, s, n);
160 pub fn check_crate<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>) {
161 tcx.visit_all_items_in_krate(DepNode::MatchCheck, &mut MatchCheckCtxt {
163 param_env: tcx.empty_parameter_environment(),
165 tcx.sess.abort_if_errors();
168 fn check_expr(cx: &mut MatchCheckCtxt, ex: &hir::Expr) {
169 intravisit::walk_expr(cx, ex);
171 hir::ExprMatch(ref scrut, ref arms, source) => {
173 // First, check legality of move bindings.
174 check_legality_of_move_bindings(cx,
178 // Second, if there is a guard on each arm, make sure it isn't
179 // assigning or borrowing anything mutably.
180 if let Some(ref guard) = arm.guard {
181 check_for_mutation_in_guard(cx, &guard);
185 let mut static_inliner = StaticInliner::new(cx.tcx, None);
186 let inlined_arms = arms.iter().map(|arm| {
187 (arm.pats.iter().map(|pat| {
188 static_inliner.fold_pat((*pat).clone())
189 }).collect(), arm.guard.as_ref().map(|e| &**e))
190 }).collect::<Vec<(Vec<P<Pat>>, Option<&hir::Expr>)>>();
192 // Bail out early if inlining failed.
193 if static_inliner.failed {
197 for pat in inlined_arms
199 .flat_map(|&(ref pats, _)| pats) {
200 // Third, check legality of move bindings.
201 check_legality_of_bindings_in_at_patterns(cx, &pat);
203 // Fourth, check if there are any references to NaN that we should warn about.
204 check_for_static_nan(cx, &pat);
206 // Fifth, check if for any of the patterns that match an enumerated type
207 // are bindings with the same name as one of the variants of said type.
208 check_for_bindings_named_the_same_as_variants(cx, &pat);
211 // Fourth, check for unreachable arms.
212 check_arms(cx, &inlined_arms[..], source);
214 // Finally, check if the whole match expression is exhaustive.
215 // Check for empty enum, because is_useful only works on inhabited types.
216 let pat_ty = cx.tcx.node_id_to_type(scrut.id);
217 if inlined_arms.is_empty() {
218 if !pat_ty.is_empty(cx.tcx) {
219 // We know the type is inhabited, so this must be wrong
220 let mut err = struct_span_err!(cx.tcx.sess, ex.span, E0002,
221 "non-exhaustive patterns: type {} is non-empty",
223 span_help!(&mut err, ex.span,
224 "Please ensure that all possible cases are being handled; \
225 possibly adding wildcards or more match arms.");
228 // If the type *is* empty, it's vacuously exhaustive
232 let matrix: Matrix = inlined_arms
234 .filter(|&&(_, guard)| guard.is_none())
235 .flat_map(|arm| &arm.0)
236 .map(|pat| vec![wrap_pat(cx, &pat)])
238 let match_span = Span {
241 expn_id: ex.span.expn_id
243 check_exhaustive(cx, match_span, &matrix, source);
249 fn check_for_bindings_named_the_same_as_variants(cx: &MatchCheckCtxt, pat: &Pat) {
251 if let PatKind::Binding(hir::BindByValue(hir::MutImmutable), name, None) = p.node {
252 let pat_ty = cx.tcx.pat_ty(p);
253 if let ty::TyEnum(edef, _) = pat_ty.sty {
254 if let Def::Local(..) = cx.tcx.expect_def(p.id) {
255 if edef.variants.iter().any(|variant| {
256 variant.name == name.node && variant.kind == VariantKind::Unit
258 let ty_path = cx.tcx.item_path_str(edef.did);
259 let mut err = struct_span_warn!(cx.tcx.sess, p.span, E0170,
260 "pattern binding `{}` is named the same as one \
261 of the variants of the type `{}`",
264 "if you meant to match on a variant, \
265 consider making the path in the pattern qualified: `{}::{}`",
276 // Check that we do not match against a static NaN (#6804)
277 fn check_for_static_nan(cx: &MatchCheckCtxt, pat: &Pat) {
279 if let PatKind::Lit(ref expr) = p.node {
280 match eval_const_expr_partial(cx.tcx, &expr, ExprTypeChecked, None) {
281 Ok(ConstVal::Float(f)) if f.is_nan() => {
282 span_warn!(cx.tcx.sess, p.span, E0003,
283 "unmatchable NaN in pattern, \
284 use the is_nan method in a guard instead");
289 report_const_eval_err(cx.tcx, &err, p.span, "pattern").emit();
297 // Check for unreachable patterns
298 fn check_arms(cx: &MatchCheckCtxt,
299 arms: &[(Vec<P<Pat>>, Option<&hir::Expr>)],
300 source: hir::MatchSource) {
301 let mut seen = Matrix(vec![]);
302 let mut printed_if_let_err = false;
303 for &(ref pats, guard) in arms {
305 let v = vec![wrap_pat(cx, &pat)];
307 match is_useful(cx, &seen, &v[..], LeaveOutWitness) {
310 hir::MatchSource::IfLetDesugar { .. } => {
311 if printed_if_let_err {
312 // we already printed an irrefutable if-let pattern error.
313 // We don't want two, that's just confusing.
315 // find the first arm pattern so we can use its span
316 let &(ref first_arm_pats, _) = &arms[0];
317 let first_pat = &first_arm_pats[0];
318 let span = first_pat.span;
319 span_err!(cx.tcx.sess, span, E0162, "irrefutable if-let pattern");
320 printed_if_let_err = true;
324 hir::MatchSource::WhileLetDesugar => {
325 // find the first arm pattern so we can use its span
326 let &(ref first_arm_pats, _) = &arms[0];
327 let first_pat = &first_arm_pats[0];
328 let span = first_pat.span;
329 span_err!(cx.tcx.sess, span, E0165, "irrefutable while-let pattern");
332 hir::MatchSource::ForLoopDesugar => {
333 // this is a bug, because on `match iter.next()` we cover
334 // `Some(<head>)` and `None`. It's impossible to have an unreachable
336 // (see libsyntax/ext/expand.rs for the full expansion of a for loop)
337 span_bug!(pat.span, "unreachable for-loop pattern")
340 hir::MatchSource::Normal => {
341 let mut err = struct_span_err!(cx.tcx.sess, pat.span, E0001,
342 "unreachable pattern");
343 err.span_label(pat.span, &format!("this is an unreachable pattern"));
344 // if we had a catchall pattern, hint at that
346 if pat_is_catchall(&cx.tcx.def_map.borrow(), row[0].0) {
347 span_note!(err, row[0].0.span,
348 "this pattern matches any value");
354 hir::MatchSource::TryDesugar => {
355 span_bug!(pat.span, "unreachable try pattern")
360 UsefulWithWitness(_) => bug!()
363 let Matrix(mut rows) = seen;
371 /// Checks for common cases of "catchall" patterns that may not be intended as such.
372 fn pat_is_catchall(dm: &DefMap, p: &Pat) -> bool {
374 PatKind::Binding(_, _, None) => true,
375 PatKind::Binding(_, _, Some(ref s)) => pat_is_catchall(dm, &s),
376 PatKind::Ref(ref s, _) => pat_is_catchall(dm, &s),
377 PatKind::Tuple(ref v, _) => v.iter().all(|p| pat_is_catchall(dm, &p)),
382 fn raw_pat(p: &Pat) -> &Pat {
384 PatKind::Binding(_, _, Some(ref s)) => raw_pat(&s),
389 fn check_exhaustive<'a, 'tcx>(cx: &MatchCheckCtxt<'a, 'tcx>,
391 matrix: &Matrix<'a, 'tcx>,
392 source: hir::MatchSource) {
393 match is_useful(cx, matrix, &[(DUMMY_WILD_PAT, None)], ConstructWitness) {
394 UsefulWithWitness(pats) => {
395 let witnesses = if pats.is_empty() {
398 pats.iter().map(|w| &**w).collect()
401 hir::MatchSource::ForLoopDesugar => {
402 // `witnesses[0]` has the form `Some(<head>)`, peel off the `Some`
403 let witness = match witnesses[0].node {
404 PatKind::TupleStruct(_, ref pats, _) => match &pats[..] {
405 &[ref pat] => &**pat,
410 span_err!(cx.tcx.sess, sp, E0297,
411 "refutable pattern in `for` loop binding: \
413 pat_to_string(witness));
416 let pattern_strings: Vec<_> = witnesses.iter().map(|w| {
419 const LIMIT: usize = 3;
420 let joined_patterns = match pattern_strings.len() {
422 1 => format!("`{}`", pattern_strings[0]),
424 let (tail, head) = pattern_strings.split_last().unwrap();
425 format!("`{}`", head.join("`, `") + "` and `" + tail)
428 let (head, tail) = pattern_strings.split_at(LIMIT);
429 format!("`{}` and {} more", head.join("`, `"), tail.len())
433 let label_text = match pattern_strings.len(){
434 1 => format!("pattern {} not covered", joined_patterns),
435 _ => format!("patterns {} not covered", joined_patterns)
437 struct_span_err!(cx.tcx.sess, sp, E0004,
438 "non-exhaustive patterns: {} not covered",
440 ).span_label(sp, &label_text).emit();
445 // This is good, wildcard pattern isn't reachable
451 fn const_val_to_expr(value: &ConstVal) -> P<hir::Expr> {
452 let node = match value {
453 &ConstVal::Bool(b) => ast::LitKind::Bool(b),
458 node: hir::ExprLit(P(Spanned { node: node, span: DUMMY_SP })),
460 attrs: ast::ThinVec::new(),
464 pub struct StaticInliner<'a, 'tcx: 'a> {
465 pub tcx: TyCtxt<'a, 'tcx, 'tcx>,
467 pub renaming_map: Option<&'a mut FnvHashMap<(NodeId, Span), NodeId>>,
470 impl<'a, 'tcx> StaticInliner<'a, 'tcx> {
471 pub fn new<'b>(tcx: TyCtxt<'b, 'tcx, 'tcx>,
472 renaming_map: Option<&'b mut FnvHashMap<(NodeId, Span), NodeId>>)
473 -> StaticInliner<'b, 'tcx> {
477 renaming_map: renaming_map
482 struct RenamingRecorder<'map> {
483 substituted_node_id: NodeId,
485 renaming_map: &'map mut FnvHashMap<(NodeId, Span), NodeId>
488 impl<'v, 'map> Visitor<'v> for RenamingRecorder<'map> {
489 fn visit_id(&mut self, node_id: NodeId) {
490 let key = (node_id, self.origin_span);
491 self.renaming_map.insert(key, self.substituted_node_id);
495 impl<'a, 'tcx> Folder for StaticInliner<'a, 'tcx> {
496 fn fold_pat(&mut self, pat: P<Pat>) -> P<Pat> {
497 return match pat.node {
498 PatKind::Path(..) => {
499 match self.tcx.expect_def(pat.id) {
500 Def::AssociatedConst(did) | Def::Const(did) => {
501 let substs = Some(self.tcx.node_id_item_substs(pat.id).substs);
502 if let Some((const_expr, _)) = lookup_const_by_id(self.tcx, did, substs) {
503 match const_expr_to_pat(self.tcx, const_expr, pat.id, pat.span) {
505 if let Some(ref mut map) = self.renaming_map {
506 // Record any renamings we do here
507 record_renamings(const_expr, &pat, map);
513 self.tcx.sess.span_err(
515 &format!("constants of the type `{}` \
516 cannot be used in patterns",
517 self.tcx.item_path_str(def_id)));
523 span_err!(self.tcx.sess, pat.span, E0158,
524 "statics cannot be referenced in patterns");
528 _ => noop_fold_pat(pat, self)
531 _ => noop_fold_pat(pat, self)
534 fn record_renamings(const_expr: &hir::Expr,
535 substituted_pat: &hir::Pat,
536 renaming_map: &mut FnvHashMap<(NodeId, Span), NodeId>) {
537 let mut renaming_recorder = RenamingRecorder {
538 substituted_node_id: substituted_pat.id,
539 origin_span: substituted_pat.span,
540 renaming_map: renaming_map,
543 renaming_recorder.visit_expr(const_expr);
548 /// Constructs a partial witness for a pattern given a list of
549 /// patterns expanded by the specialization step.
551 /// When a pattern P is discovered to be useful, this function is used bottom-up
552 /// to reconstruct a complete witness, e.g. a pattern P' that covers a subset
553 /// of values, V, where each value in that set is not covered by any previously
554 /// used patterns and is covered by the pattern P'. Examples:
556 /// left_ty: tuple of 3 elements
557 /// pats: [10, 20, _] => (10, 20, _)
559 /// left_ty: struct X { a: (bool, &'static str), b: usize}
560 /// pats: [(false, "foo"), 42] => X { a: (false, "foo"), b: 42 }
561 fn construct_witness<'a,'tcx>(cx: &MatchCheckCtxt<'a,'tcx>, ctor: &Constructor,
562 pats: Vec<&Pat>, left_ty: Ty<'tcx>) -> P<Pat> {
563 let pats_len = pats.len();
564 let mut pats = pats.into_iter().map(|p| P((*p).clone()));
565 let pat = match left_ty.sty {
566 ty::TyTuple(..) => PatKind::Tuple(pats.collect(), None),
568 ty::TyEnum(adt, _) | ty::TyStruct(adt, _) => {
569 let v = ctor.variant_for_adt(adt);
571 VariantKind::Struct => {
572 let field_pats: hir::HirVec<_> = v.fields.iter()
574 .filter(|&(_, ref pat)| pat.node != PatKind::Wild)
575 .map(|(field, pat)| Spanned {
577 node: hir::FieldPat {
583 let has_more_fields = field_pats.len() < pats_len;
584 PatKind::Struct(def_to_path(cx.tcx, v.did), field_pats, has_more_fields)
586 VariantKind::Tuple => {
587 PatKind::TupleStruct(def_to_path(cx.tcx, v.did), pats.collect(), None)
589 VariantKind::Unit => {
590 PatKind::Path(None, def_to_path(cx.tcx, v.did))
595 ty::TyRef(_, ty::TypeAndMut { mutbl, .. }) => {
596 assert_eq!(pats_len, 1);
597 PatKind::Ref(pats.nth(0).unwrap(), mutbl)
600 ty::TySlice(_) => match ctor {
602 assert_eq!(pats_len, n);
603 PatKind::Vec(pats.collect(), None, hir::HirVec::new())
608 ty::TyArray(_, len) => {
609 assert_eq!(pats_len, len);
610 PatKind::Vec(pats.collect(), None, hir::HirVec::new())
615 ConstantValue(ref v) => PatKind::Lit(const_val_to_expr(v)),
629 fn variant_for_adt<'tcx, 'container, 'a>(&self,
630 adt: &'a ty::AdtDefData<'tcx, 'container>)
631 -> &'a VariantDefData<'tcx, 'container> {
633 &Variant(vid) => adt.variant_with_id(vid),
634 _ => adt.struct_variant()
639 fn missing_constructors(cx: &MatchCheckCtxt, &Matrix(ref rows): &Matrix,
640 left_ty: Ty, max_slice_length: usize) -> Vec<Constructor> {
641 let used_constructors: Vec<Constructor> = rows.iter()
642 .flat_map(|row| pat_constructors(cx, row[0].0, left_ty, max_slice_length))
644 all_constructors(cx, left_ty, max_slice_length)
646 .filter(|c| !used_constructors.contains(c))
650 /// This determines the set of all possible constructors of a pattern matching
651 /// values of type `left_ty`. For vectors, this would normally be an infinite set
652 /// but is instead bounded by the maximum fixed length of slice patterns in
653 /// the column of patterns being analyzed.
654 fn all_constructors(_cx: &MatchCheckCtxt, left_ty: Ty,
655 max_slice_length: usize) -> Vec<Constructor> {
658 [true, false].iter().map(|b| ConstantValue(ConstVal::Bool(*b))).collect(),
660 (0..max_slice_length+1).map(|length| Slice(length)).collect(),
661 ty::TyEnum(def, _) => def.variants.iter().map(|v| Variant(v.did)).collect(),
666 // Algorithm from http://moscova.inria.fr/~maranget/papers/warn/index.html
668 // Whether a vector `v` of patterns is 'useful' in relation to a set of such
669 // vectors `m` is defined as there being a set of inputs that will match `v`
670 // but not any of the sets in `m`.
672 // This is used both for reachability checking (if a pattern isn't useful in
673 // relation to preceding patterns, it is not reachable) and exhaustiveness
674 // checking (if a wildcard pattern is useful in relation to a matrix, the
675 // matrix isn't exhaustive).
677 // Note: is_useful doesn't work on empty types, as the paper notes.
678 // So it assumes that v is non-empty.
679 fn is_useful<'a, 'tcx>(cx: &MatchCheckCtxt<'a, 'tcx>,
680 matrix: &Matrix<'a, 'tcx>,
681 v: &[(&Pat, Option<Ty<'tcx>>)],
682 witness: WitnessPreference)
684 let &Matrix(ref rows) = matrix;
685 debug!("is_useful({:?}, {:?})", matrix, v);
687 return match witness {
688 ConstructWitness => UsefulWithWitness(vec!()),
689 LeaveOutWitness => Useful
692 if rows[0].is_empty() {
695 assert!(rows.iter().all(|r| r.len() == v.len()));
696 let left_ty = match rows.iter().filter_map(|r| r[0].1).next().or_else(|| v[0].1) {
699 // all patterns are wildcards - we can pick any type we want
704 let max_slice_length = rows.iter().filter_map(|row| match row[0].0.node {
705 PatKind::Vec(ref before, _, ref after) => Some(before.len() + after.len()),
707 }).max().map_or(0, |v| v + 1);
709 let constructors = pat_constructors(cx, v[0].0, left_ty, max_slice_length);
710 debug!("is_useful - pat_constructors = {:?} left_ty = {:?}", constructors,
712 if constructors.is_empty() {
713 let constructors = missing_constructors(cx, matrix, left_ty, max_slice_length);
714 debug!("is_useful - missing_constructors = {:?}", constructors);
715 if constructors.is_empty() {
716 all_constructors(cx, left_ty, max_slice_length).into_iter().map(|c| {
717 match is_useful_specialized(cx, matrix, v, c.clone(), left_ty, witness) {
718 UsefulWithWitness(pats) => UsefulWithWitness({
719 let arity = constructor_arity(cx, &c, left_ty);
721 let pat_slice = &pats[..];
722 let subpats: Vec<_> = (0..arity).map(|i| {
723 pat_slice.get(i).map_or(DUMMY_WILD_PAT, |p| &**p)
725 vec![construct_witness(cx, &c, subpats, left_ty)]
727 result.extend(pats.into_iter().skip(arity));
732 }).find(|result| result != &NotUseful).unwrap_or(NotUseful)
734 let matrix = rows.iter().filter_map(|r| {
735 match raw_pat(r[0].0).node {
736 PatKind::Binding(..) | PatKind::Wild => Some(r[1..].to_vec()),
740 match is_useful(cx, &matrix, &v[1..], witness) {
741 UsefulWithWitness(pats) => {
742 let mut new_pats: Vec<_> = constructors.into_iter().map(|constructor| {
743 let arity = constructor_arity(cx, &constructor, left_ty);
744 let wild_pats = vec![DUMMY_WILD_PAT; arity];
745 construct_witness(cx, &constructor, wild_pats, left_ty)
747 new_pats.extend(pats);
748 UsefulWithWitness(new_pats)
754 constructors.into_iter().map(|c|
755 is_useful_specialized(cx, matrix, v, c.clone(), left_ty, witness)
756 ).find(|result| result != &NotUseful).unwrap_or(NotUseful)
760 fn is_useful_specialized<'a, 'tcx>(
761 cx: &MatchCheckCtxt<'a, 'tcx>,
762 &Matrix(ref m): &Matrix<'a, 'tcx>,
763 v: &[(&Pat, Option<Ty<'tcx>>)],
766 witness: WitnessPreference) -> Usefulness
768 let arity = constructor_arity(cx, &ctor, lty);
769 let matrix = Matrix(m.iter().filter_map(|r| {
770 specialize(cx, &r[..], &ctor, 0, arity)
772 match specialize(cx, v, &ctor, 0, arity) {
773 Some(v) => is_useful(cx, &matrix, &v[..], witness),
778 /// Determines the constructors that the given pattern can be specialized to.
780 /// In most cases, there's only one constructor that a specific pattern
781 /// represents, such as a specific enum variant or a specific literal value.
782 /// Slice patterns, however, can match slices of different lengths. For instance,
783 /// `[a, b, ..tail]` can match a slice of length 2, 3, 4 and so on.
785 /// On the other hand, a wild pattern and an identifier pattern cannot be
786 /// specialized in any way.
787 fn pat_constructors(cx: &MatchCheckCtxt, p: &Pat,
788 left_ty: Ty, max_slice_length: usize) -> Vec<Constructor> {
789 let pat = raw_pat(p);
791 PatKind::Struct(..) | PatKind::TupleStruct(..) | PatKind::Path(..) =>
792 match cx.tcx.expect_def(pat.id) {
793 Def::Variant(_, id) => vec![Variant(id)],
794 Def::Struct(..) | Def::TyAlias(..) | Def::AssociatedTy(..) => vec![Single],
795 Def::Const(..) | Def::AssociatedConst(..) =>
796 span_bug!(pat.span, "const pattern should've been rewritten"),
797 def => span_bug!(pat.span, "pat_constructors: unexpected definition {:?}", def),
799 PatKind::Lit(ref expr) =>
800 vec![ConstantValue(eval_const_expr(cx.tcx, &expr))],
801 PatKind::Range(ref lo, ref hi) =>
802 vec![ConstantRange(eval_const_expr(cx.tcx, &lo), eval_const_expr(cx.tcx, &hi))],
803 PatKind::Vec(ref before, ref slice, ref after) =>
805 ty::TyArray(_, _) => vec![Single],
806 ty::TySlice(_) if slice.is_some() => {
807 (before.len() + after.len()..max_slice_length+1)
808 .map(|length| Slice(length))
811 ty::TySlice(_) => vec!(Slice(before.len() + after.len())),
812 _ => span_bug!(pat.span, "pat_constructors: unexpected \
813 slice pattern type {:?}", left_ty)
815 PatKind::Box(..) | PatKind::Tuple(..) | PatKind::Ref(..) =>
817 PatKind::Binding(..) | PatKind::Wild =>
822 /// This computes the arity of a constructor. The arity of a constructor
823 /// is how many subpattern patterns of that constructor should be expanded to.
825 /// For instance, a tuple pattern (_, 42, Some([])) has the arity of 3.
826 /// A struct pattern's arity is the number of fields it contains, etc.
827 pub fn constructor_arity(_cx: &MatchCheckCtxt, ctor: &Constructor, ty: Ty) -> usize {
828 debug!("constructor_arity({:?}, {:?})", ctor, ty);
830 ty::TyTuple(ref fs) => fs.len(),
832 ty::TySlice(_) => match *ctor {
833 Slice(length) => length,
834 ConstantValue(_) => 0,
838 ty::TyEnum(adt, _) | ty::TyStruct(adt, _) => {
839 ctor.variant_for_adt(adt).fields.len()
841 ty::TyArray(_, n) => n,
846 fn range_covered_by_constructor(tcx: TyCtxt, span: Span,
848 from: &ConstVal, to: &ConstVal)
849 -> Result<bool, ErrorReported> {
850 let (c_from, c_to) = match *ctor {
851 ConstantValue(ref value) => (value, value),
852 ConstantRange(ref from, ref to) => (from, to),
853 Single => return Ok(true),
856 let cmp_from = compare_const_vals(tcx, span, c_from, from)?;
857 let cmp_to = compare_const_vals(tcx, span, c_to, to)?;
858 Ok(cmp_from != Ordering::Less && cmp_to != Ordering::Greater)
861 fn wrap_pat<'a, 'b, 'tcx>(cx: &MatchCheckCtxt<'b, 'tcx>,
863 -> (&'a Pat, Option<Ty<'tcx>>)
865 let pat_ty = cx.tcx.pat_ty(pat);
866 (pat, Some(match pat.node {
867 PatKind::Binding(hir::BindByRef(..), _, _) => {
868 pat_ty.builtin_deref(false, NoPreference).unwrap().ty
874 /// This is the main specialization step. It expands the first pattern in the given row
875 /// into `arity` patterns based on the constructor. For most patterns, the step is trivial,
876 /// for instance tuple patterns are flattened and box patterns expand into their inner pattern.
878 /// OTOH, slice patterns with a subslice pattern (..tail) can be expanded into multiple
879 /// different patterns.
880 /// Structure patterns with a partial wild pattern (Foo { a: 42, .. }) have their missing
881 /// fields filled with wild patterns.
882 pub fn specialize<'a, 'b, 'tcx>(
883 cx: &MatchCheckCtxt<'b, 'tcx>,
884 r: &[(&'a Pat, Option<Ty<'tcx>>)],
885 constructor: &Constructor, col: usize, arity: usize)
886 -> Option<Vec<(&'a Pat, Option<Ty<'tcx>>)>>
888 let pat = raw_pat(r[col].0);
890 id: pat_id, ref node, span: pat_span
892 let wpat = |pat: &'a Pat| wrap_pat(cx, pat);
893 let dummy_pat = (DUMMY_WILD_PAT, None);
895 let head: Option<Vec<(&Pat, Option<Ty>)>> = match *node {
896 PatKind::Binding(..) | PatKind::Wild =>
897 Some(vec![dummy_pat; arity]),
899 PatKind::Path(..) => {
900 match cx.tcx.expect_def(pat_id) {
901 Def::Const(..) | Def::AssociatedConst(..) =>
902 span_bug!(pat_span, "const pattern should've \
904 Def::Variant(_, id) if *constructor != Variant(id) => None,
905 Def::Variant(..) | Def::Struct(..) => Some(Vec::new()),
906 def => span_bug!(pat_span, "specialize: unexpected \
907 definition {:?}", def),
911 PatKind::TupleStruct(_, ref args, ddpos) => {
912 match cx.tcx.expect_def(pat_id) {
913 Def::Const(..) | Def::AssociatedConst(..) =>
914 span_bug!(pat_span, "const pattern should've \
916 Def::Variant(_, id) if *constructor != Variant(id) => None,
917 Def::Variant(..) | Def::Struct(..) => {
920 let mut pats: Vec<_> = args[..ddpos].iter().map(|p| {
923 pats.extend(repeat((DUMMY_WILD_PAT, None)).take(arity - args.len()));
924 pats.extend(args[ddpos..].iter().map(|p| wpat(p)));
927 None => Some(args.iter().map(|p| wpat(p)).collect())
934 PatKind::Struct(_, ref pattern_fields, _) => {
935 let adt = cx.tcx.node_id_to_type(pat_id).ty_adt_def().unwrap();
936 let variant = constructor.variant_for_adt(adt);
937 let def_variant = adt.variant_of_def(cx.tcx.expect_def(pat_id));
938 if variant.did == def_variant.did {
939 Some(variant.fields.iter().map(|sf| {
940 match pattern_fields.iter().find(|f| f.node.name == sf.name) {
941 Some(ref f) => wpat(&f.node.pat),
950 PatKind::Tuple(ref args, Some(ddpos)) => {
951 let mut pats: Vec<_> = args[..ddpos].iter().map(|p| wpat(p)).collect();
952 pats.extend(repeat(dummy_pat).take(arity - args.len()));
953 pats.extend(args[ddpos..].iter().map(|p| wpat(p)));
956 PatKind::Tuple(ref args, None) =>
957 Some(args.iter().map(|p| wpat(&**p)).collect()),
959 PatKind::Box(ref inner) | PatKind::Ref(ref inner, _) =>
960 Some(vec![wpat(&**inner)]),
962 PatKind::Lit(ref expr) => {
963 if let Some(&ty::TyS { sty: ty::TyRef(_, mt), .. }) = r[col].1 {
964 // HACK: handle string literals. A string literal pattern
965 // serves both as an unary reference pattern and as a
966 // nullary value pattern, depending on the type.
967 Some(vec![(pat, Some(mt.ty))])
969 let expr_value = eval_const_expr(cx.tcx, &expr);
970 match range_covered_by_constructor(
971 cx.tcx, expr.span, constructor, &expr_value, &expr_value
973 Ok(true) => Some(vec![]),
975 Err(ErrorReported) => None,
980 PatKind::Range(ref from, ref to) => {
981 let from_value = eval_const_expr(cx.tcx, &from);
982 let to_value = eval_const_expr(cx.tcx, &to);
983 match range_covered_by_constructor(
984 cx.tcx, pat_span, constructor, &from_value, &to_value
986 Ok(true) => Some(vec![]),
988 Err(ErrorReported) => None,
992 PatKind::Vec(ref before, ref slice, ref after) => {
993 let pat_len = before.len() + after.len();
996 // Fixed-length vectors.
998 before.iter().map(|p| wpat(p)).chain(
999 repeat(dummy_pat).take(arity - pat_len).chain(
1000 after.iter().map(|p| wpat(p))
1003 Slice(length) if pat_len <= length && slice.is_some() => {
1005 before.iter().map(|p| wpat(p)).chain(
1006 repeat(dummy_pat).take(arity - pat_len).chain(
1007 after.iter().map(|p| wpat(p))
1010 Slice(length) if pat_len == length => {
1012 before.iter().map(|p| wpat(p)).chain(
1013 after.iter().map(|p| wpat(p))
1016 SliceWithSubslice(prefix, suffix)
1017 if before.len() == prefix
1018 && after.len() == suffix
1019 && slice.is_some() => {
1020 // this is used by trans::_match only
1021 let mut pats: Vec<_> = before.iter()
1022 .map(|p| (&**p, None)).collect();
1023 pats.extend(after.iter().map(|p| (&**p, None)));
1030 debug!("specialize({:?}, {:?}) = {:?}", r[col], arity, head);
1032 head.map(|mut head| {
1033 head.extend_from_slice(&r[..col]);
1034 head.extend_from_slice(&r[col + 1..]);
1039 fn check_local(cx: &mut MatchCheckCtxt, loc: &hir::Local) {
1040 intravisit::walk_local(cx, loc);
1042 let pat = StaticInliner::new(cx.tcx, None).fold_pat(loc.pat.clone());
1043 check_irrefutable(cx, &pat, false);
1045 // Check legality of move bindings and `@` patterns.
1046 check_legality_of_move_bindings(cx, false, slice::ref_slice(&loc.pat));
1047 check_legality_of_bindings_in_at_patterns(cx, &loc.pat);
1050 fn check_fn(cx: &mut MatchCheckCtxt,
1057 FnKind::Closure(_) => {}
1058 _ => cx.param_env = ParameterEnvironment::for_item(cx.tcx, fn_id),
1061 intravisit::walk_fn(cx, kind, decl, body, sp, fn_id);
1063 for input in &decl.inputs {
1064 check_irrefutable(cx, &input.pat, true);
1065 check_legality_of_move_bindings(cx, false, slice::ref_slice(&input.pat));
1066 check_legality_of_bindings_in_at_patterns(cx, &input.pat);
1070 fn check_irrefutable(cx: &MatchCheckCtxt, pat: &Pat, is_fn_arg: bool) {
1071 let origin = if is_fn_arg {
1077 is_refutable(cx, pat, |uncovered_pat| {
1078 span_err!(cx.tcx.sess, pat.span, E0005,
1079 "refutable pattern in {}: `{}` not covered",
1081 pat_to_string(uncovered_pat),
1086 fn is_refutable<A, F>(cx: &MatchCheckCtxt, pat: &Pat, refutable: F) -> Option<A> where
1087 F: FnOnce(&Pat) -> A,
1089 let pats = Matrix(vec!(vec!(wrap_pat(cx, pat))));
1090 match is_useful(cx, &pats, &[(DUMMY_WILD_PAT, None)], ConstructWitness) {
1091 UsefulWithWitness(pats) => Some(refutable(&pats[0])),
1097 // Legality of move bindings checking
1098 fn check_legality_of_move_bindings(cx: &MatchCheckCtxt,
1101 let mut by_ref_span = None;
1103 pat_bindings(&pat, |bm, _, span, _path| {
1104 if let hir::BindByRef(..) = bm {
1105 by_ref_span = Some(span);
1110 let check_move = |p: &Pat, sub: Option<&Pat>| {
1111 // check legality of moving out of the enum
1113 // x @ Foo(..) is legal, but x @ Foo(y) isn't.
1114 if sub.map_or(false, |p| pat_contains_bindings(&p)) {
1115 struct_span_err!(cx.tcx.sess, p.span, E0007,
1116 "cannot bind by-move with sub-bindings")
1117 .span_label(p.span, &format!("binds an already bound by-move value by moving it"))
1119 } else if has_guard {
1120 struct_span_err!(cx.tcx.sess, p.span, E0008,
1121 "cannot bind by-move into a pattern guard")
1122 .span_label(p.span, &format!("moves value into pattern guard"))
1124 } else if by_ref_span.is_some() {
1125 let mut err = struct_span_err!(cx.tcx.sess, p.span, E0009,
1126 "cannot bind by-move and by-ref in the same pattern");
1127 span_note!(&mut err, by_ref_span.unwrap(), "by-ref binding occurs here");
1134 if let PatKind::Binding(hir::BindByValue(..), _, ref sub) = p.node {
1135 let pat_ty = cx.tcx.node_id_to_type(p.id);
1136 //FIXME: (@jroesch) this code should be floated up as well
1137 cx.tcx.infer_ctxt(None, Some(cx.param_env.clone()),
1138 ProjectionMode::AnyFinal).enter(|infcx| {
1139 if infcx.type_moves_by_default(pat_ty, pat.span) {
1140 check_move(p, sub.as_ref().map(|p| &**p));
1149 /// Ensures that a pattern guard doesn't borrow by mutable reference or
1151 fn check_for_mutation_in_guard<'a, 'tcx>(cx: &'a MatchCheckCtxt<'a, 'tcx>,
1152 guard: &hir::Expr) {
1153 cx.tcx.infer_ctxt(None, Some(cx.param_env.clone()),
1154 ProjectionMode::AnyFinal).enter(|infcx| {
1155 let mut checker = MutationChecker {
1158 let mut visitor = ExprUseVisitor::new(&mut checker, &infcx);
1159 visitor.walk_expr(guard);
1163 struct MutationChecker<'a, 'gcx: 'a> {
1164 cx: &'a MatchCheckCtxt<'a, 'gcx>,
1167 impl<'a, 'gcx, 'tcx> Delegate<'tcx> for MutationChecker<'a, 'gcx> {
1168 fn matched_pat(&mut self, _: &Pat, _: cmt, _: euv::MatchMode) {}
1169 fn consume(&mut self, _: NodeId, _: Span, _: cmt, _: ConsumeMode) {}
1170 fn consume_pat(&mut self, _: &Pat, _: cmt, _: ConsumeMode) {}
1171 fn borrow(&mut self,
1180 span_err!(self.cx.tcx.sess, span, E0301,
1181 "cannot mutably borrow in a pattern guard")
1183 ImmBorrow | UniqueImmBorrow => {}
1186 fn decl_without_init(&mut self, _: NodeId, _: Span) {}
1187 fn mutate(&mut self, _: NodeId, span: Span, _: cmt, mode: MutateMode) {
1189 MutateMode::JustWrite | MutateMode::WriteAndRead => {
1190 span_err!(self.cx.tcx.sess, span, E0302, "cannot assign in a pattern guard")
1192 MutateMode::Init => {}
1197 /// Forbids bindings in `@` patterns. This is necessary for memory safety,
1198 /// because of the way rvalues are handled in the borrow check. (See issue
1200 fn check_legality_of_bindings_in_at_patterns(cx: &MatchCheckCtxt, pat: &Pat) {
1201 AtBindingPatternVisitor { cx: cx, bindings_allowed: true }.visit_pat(pat);
1204 struct AtBindingPatternVisitor<'a, 'b:'a, 'tcx:'b> {
1205 cx: &'a MatchCheckCtxt<'b, 'tcx>,
1206 bindings_allowed: bool
1209 impl<'a, 'b, 'tcx, 'v> Visitor<'v> for AtBindingPatternVisitor<'a, 'b, 'tcx> {
1210 fn visit_pat(&mut self, pat: &Pat) {
1212 PatKind::Binding(_, _, ref subpat) => {
1213 if !self.bindings_allowed {
1214 span_err!(self.cx.tcx.sess, pat.span, E0303,
1215 "pattern bindings are not allowed after an `@`");
1218 if subpat.is_some() {
1219 let bindings_were_allowed = self.bindings_allowed;
1220 self.bindings_allowed = false;
1221 intravisit::walk_pat(self, pat);
1222 self.bindings_allowed = bindings_were_allowed;
1225 _ => intravisit::walk_pat(self, pat),