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::Reveal;
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 check_exhaustive(cx, scrut.span, &matrix, source);
244 fn check_for_bindings_named_the_same_as_variants(cx: &MatchCheckCtxt, pat: &Pat) {
246 if let PatKind::Binding(hir::BindByValue(hir::MutImmutable), name, None) = p.node {
247 let pat_ty = cx.tcx.pat_ty(p);
248 if let ty::TyEnum(edef, _) = pat_ty.sty {
249 if let Def::Local(..) = cx.tcx.expect_def(p.id) {
250 if edef.variants.iter().any(|variant| {
251 variant.name == name.node && variant.kind == VariantKind::Unit
253 let ty_path = cx.tcx.item_path_str(edef.did);
254 let mut err = struct_span_warn!(cx.tcx.sess, p.span, E0170,
255 "pattern binding `{}` is named the same as one \
256 of the variants of the type `{}`",
259 "if you meant to match on a variant, \
260 consider making the path in the pattern qualified: `{}::{}`",
271 // Check that we do not match against a static NaN (#6804)
272 fn check_for_static_nan(cx: &MatchCheckCtxt, pat: &Pat) {
274 if let PatKind::Lit(ref expr) = p.node {
275 match eval_const_expr_partial(cx.tcx, &expr, ExprTypeChecked, None) {
276 Ok(ConstVal::Float(f)) if f.is_nan() => {
277 span_warn!(cx.tcx.sess, p.span, E0003,
278 "unmatchable NaN in pattern, \
279 use the is_nan method in a guard instead");
284 report_const_eval_err(cx.tcx, &err, p.span, "pattern").emit();
292 // Check for unreachable patterns
293 fn check_arms(cx: &MatchCheckCtxt,
294 arms: &[(Vec<P<Pat>>, Option<&hir::Expr>)],
295 source: hir::MatchSource) {
296 let mut seen = Matrix(vec![]);
297 let mut printed_if_let_err = false;
298 for &(ref pats, guard) in arms {
300 let v = vec![wrap_pat(cx, &pat)];
302 match is_useful(cx, &seen, &v[..], LeaveOutWitness) {
305 hir::MatchSource::IfLetDesugar { .. } => {
306 if printed_if_let_err {
307 // we already printed an irrefutable if-let pattern error.
308 // We don't want two, that's just confusing.
310 // find the first arm pattern so we can use its span
311 let &(ref first_arm_pats, _) = &arms[0];
312 let first_pat = &first_arm_pats[0];
313 let span = first_pat.span;
314 struct_span_err!(cx.tcx.sess, span, E0162,
315 "irrefutable if-let pattern")
316 .span_label(span, &format!("irrefutable pattern"))
318 printed_if_let_err = true;
322 hir::MatchSource::WhileLetDesugar => {
323 // find the first arm pattern so we can use its span
324 let &(ref first_arm_pats, _) = &arms[0];
325 let first_pat = &first_arm_pats[0];
326 let span = first_pat.span;
327 span_err!(cx.tcx.sess, span, E0165, "irrefutable while-let pattern");
330 hir::MatchSource::ForLoopDesugar => {
331 // this is a bug, because on `match iter.next()` we cover
332 // `Some(<head>)` and `None`. It's impossible to have an unreachable
334 // (see libsyntax/ext/expand.rs for the full expansion of a for loop)
335 span_bug!(pat.span, "unreachable for-loop pattern")
338 hir::MatchSource::Normal => {
339 let mut err = struct_span_err!(cx.tcx.sess, pat.span, E0001,
340 "unreachable pattern");
341 err.span_label(pat.span, &format!("this is an unreachable pattern"));
342 // if we had a catchall pattern, hint at that
344 if pat_is_catchall(&cx.tcx.def_map.borrow(), row[0].0) {
345 span_note!(err, row[0].0.span,
346 "this pattern matches any value");
352 hir::MatchSource::TryDesugar => {
353 span_bug!(pat.span, "unreachable try pattern")
358 UsefulWithWitness(_) => bug!()
361 let Matrix(mut rows) = seen;
369 /// Checks for common cases of "catchall" patterns that may not be intended as such.
370 fn pat_is_catchall(dm: &DefMap, p: &Pat) -> bool {
372 PatKind::Binding(_, _, None) => true,
373 PatKind::Binding(_, _, Some(ref s)) => pat_is_catchall(dm, &s),
374 PatKind::Ref(ref s, _) => pat_is_catchall(dm, &s),
375 PatKind::Tuple(ref v, _) => v.iter().all(|p| pat_is_catchall(dm, &p)),
380 fn raw_pat(p: &Pat) -> &Pat {
382 PatKind::Binding(_, _, Some(ref s)) => raw_pat(&s),
387 fn check_exhaustive<'a, 'tcx>(cx: &MatchCheckCtxt<'a, 'tcx>,
389 matrix: &Matrix<'a, 'tcx>,
390 source: hir::MatchSource) {
391 match is_useful(cx, matrix, &[(DUMMY_WILD_PAT, None)], ConstructWitness) {
392 UsefulWithWitness(pats) => {
393 let witnesses = if pats.is_empty() {
396 pats.iter().map(|w| &**w).collect()
399 hir::MatchSource::ForLoopDesugar => {
400 // `witnesses[0]` has the form `Some(<head>)`, peel off the `Some`
401 let witness = match witnesses[0].node {
402 PatKind::TupleStruct(_, ref pats, _) => match &pats[..] {
403 &[ref pat] => &**pat,
408 span_err!(cx.tcx.sess, sp, E0297,
409 "refutable pattern in `for` loop binding: \
411 pat_to_string(witness));
414 let pattern_strings: Vec<_> = witnesses.iter().map(|w| {
417 const LIMIT: usize = 3;
418 let joined_patterns = match pattern_strings.len() {
420 1 => format!("`{}`", pattern_strings[0]),
422 let (tail, head) = pattern_strings.split_last().unwrap();
423 format!("`{}`", head.join("`, `") + "` and `" + tail)
426 let (head, tail) = pattern_strings.split_at(LIMIT);
427 format!("`{}` and {} more", head.join("`, `"), tail.len())
431 let label_text = match pattern_strings.len(){
432 1 => format!("pattern {} not covered", joined_patterns),
433 _ => format!("patterns {} not covered", joined_patterns)
435 struct_span_err!(cx.tcx.sess, sp, E0004,
436 "non-exhaustive patterns: {} not covered",
438 ).span_label(sp, &label_text).emit();
443 // This is good, wildcard pattern isn't reachable
449 fn const_val_to_expr(value: &ConstVal) -> P<hir::Expr> {
450 let node = match value {
451 &ConstVal::Bool(b) => ast::LitKind::Bool(b),
456 node: hir::ExprLit(P(Spanned { node: node, span: DUMMY_SP })),
458 attrs: ast::ThinVec::new(),
462 pub struct StaticInliner<'a, 'tcx: 'a> {
463 pub tcx: TyCtxt<'a, 'tcx, 'tcx>,
465 pub renaming_map: Option<&'a mut FnvHashMap<(NodeId, Span), NodeId>>,
468 impl<'a, 'tcx> StaticInliner<'a, 'tcx> {
469 pub fn new<'b>(tcx: TyCtxt<'b, 'tcx, 'tcx>,
470 renaming_map: Option<&'b mut FnvHashMap<(NodeId, Span), NodeId>>)
471 -> StaticInliner<'b, 'tcx> {
475 renaming_map: renaming_map
480 struct RenamingRecorder<'map> {
481 substituted_node_id: NodeId,
483 renaming_map: &'map mut FnvHashMap<(NodeId, Span), NodeId>
486 impl<'v, 'map> Visitor<'v> for RenamingRecorder<'map> {
487 fn visit_id(&mut self, node_id: NodeId) {
488 let key = (node_id, self.origin_span);
489 self.renaming_map.insert(key, self.substituted_node_id);
493 impl<'a, 'tcx> Folder for StaticInliner<'a, 'tcx> {
494 fn fold_pat(&mut self, pat: P<Pat>) -> P<Pat> {
495 return match pat.node {
496 PatKind::Path(..) => {
497 match self.tcx.expect_def(pat.id) {
498 Def::AssociatedConst(did) | Def::Const(did) => {
499 let substs = Some(self.tcx.node_id_item_substs(pat.id).substs);
500 if let Some((const_expr, _)) = lookup_const_by_id(self.tcx, did, substs) {
501 match const_expr_to_pat(self.tcx, const_expr, pat.id, pat.span) {
503 if let Some(ref mut map) = self.renaming_map {
504 // Record any renamings we do here
505 record_renamings(const_expr, &pat, map);
511 self.tcx.sess.span_err(
513 &format!("constants of the type `{}` \
514 cannot be used in patterns",
515 self.tcx.item_path_str(def_id)));
521 span_err!(self.tcx.sess, pat.span, E0158,
522 "statics cannot be referenced in patterns");
526 _ => noop_fold_pat(pat, self)
529 _ => noop_fold_pat(pat, self)
532 fn record_renamings(const_expr: &hir::Expr,
533 substituted_pat: &hir::Pat,
534 renaming_map: &mut FnvHashMap<(NodeId, Span), NodeId>) {
535 let mut renaming_recorder = RenamingRecorder {
536 substituted_node_id: substituted_pat.id,
537 origin_span: substituted_pat.span,
538 renaming_map: renaming_map,
541 renaming_recorder.visit_expr(const_expr);
546 /// Constructs a partial witness for a pattern given a list of
547 /// patterns expanded by the specialization step.
549 /// When a pattern P is discovered to be useful, this function is used bottom-up
550 /// to reconstruct a complete witness, e.g. a pattern P' that covers a subset
551 /// of values, V, where each value in that set is not covered by any previously
552 /// used patterns and is covered by the pattern P'. Examples:
554 /// left_ty: tuple of 3 elements
555 /// pats: [10, 20, _] => (10, 20, _)
557 /// left_ty: struct X { a: (bool, &'static str), b: usize}
558 /// pats: [(false, "foo"), 42] => X { a: (false, "foo"), b: 42 }
559 fn construct_witness<'a,'tcx>(cx: &MatchCheckCtxt<'a,'tcx>, ctor: &Constructor,
560 pats: Vec<&Pat>, left_ty: Ty<'tcx>) -> P<Pat> {
561 let pats_len = pats.len();
562 let mut pats = pats.into_iter().map(|p| P((*p).clone()));
563 let pat = match left_ty.sty {
564 ty::TyTuple(..) => PatKind::Tuple(pats.collect(), None),
566 ty::TyEnum(adt, _) | ty::TyStruct(adt, _) => {
567 let v = ctor.variant_for_adt(adt);
569 VariantKind::Struct => {
570 let field_pats: hir::HirVec<_> = v.fields.iter()
572 .filter(|&(_, ref pat)| pat.node != PatKind::Wild)
573 .map(|(field, pat)| Spanned {
575 node: hir::FieldPat {
581 let has_more_fields = field_pats.len() < pats_len;
582 PatKind::Struct(def_to_path(cx.tcx, v.did), field_pats, has_more_fields)
584 VariantKind::Tuple => {
585 PatKind::TupleStruct(def_to_path(cx.tcx, v.did), pats.collect(), None)
587 VariantKind::Unit => {
588 PatKind::Path(None, def_to_path(cx.tcx, v.did))
593 ty::TyRef(_, ty::TypeAndMut { mutbl, .. }) => {
594 assert_eq!(pats_len, 1);
595 PatKind::Ref(pats.nth(0).unwrap(), mutbl)
598 ty::TySlice(_) => match ctor {
600 assert_eq!(pats_len, n);
601 PatKind::Vec(pats.collect(), None, hir::HirVec::new())
606 ty::TyArray(_, len) => {
607 assert_eq!(pats_len, len);
608 PatKind::Vec(pats.collect(), None, hir::HirVec::new())
613 ConstantValue(ref v) => PatKind::Lit(const_val_to_expr(v)),
627 fn variant_for_adt<'tcx, 'container, 'a>(&self,
628 adt: &'a ty::AdtDefData<'tcx, 'container>)
629 -> &'a VariantDefData<'tcx, 'container> {
631 &Variant(vid) => adt.variant_with_id(vid),
632 _ => adt.struct_variant()
637 fn missing_constructors(cx: &MatchCheckCtxt, &Matrix(ref rows): &Matrix,
638 left_ty: Ty, max_slice_length: usize) -> Vec<Constructor> {
639 let used_constructors: Vec<Constructor> = rows.iter()
640 .flat_map(|row| pat_constructors(cx, row[0].0, left_ty, max_slice_length))
642 all_constructors(cx, left_ty, max_slice_length)
644 .filter(|c| !used_constructors.contains(c))
648 /// This determines the set of all possible constructors of a pattern matching
649 /// values of type `left_ty`. For vectors, this would normally be an infinite set
650 /// but is instead bounded by the maximum fixed length of slice patterns in
651 /// the column of patterns being analyzed.
652 fn all_constructors(_cx: &MatchCheckCtxt, left_ty: Ty,
653 max_slice_length: usize) -> Vec<Constructor> {
656 [true, false].iter().map(|b| ConstantValue(ConstVal::Bool(*b))).collect(),
658 (0..max_slice_length+1).map(|length| Slice(length)).collect(),
659 ty::TyEnum(def, _) => def.variants.iter().map(|v| Variant(v.did)).collect(),
664 // Algorithm from http://moscova.inria.fr/~maranget/papers/warn/index.html
666 // Whether a vector `v` of patterns is 'useful' in relation to a set of such
667 // vectors `m` is defined as there being a set of inputs that will match `v`
668 // but not any of the sets in `m`.
670 // This is used both for reachability checking (if a pattern isn't useful in
671 // relation to preceding patterns, it is not reachable) and exhaustiveness
672 // checking (if a wildcard pattern is useful in relation to a matrix, the
673 // matrix isn't exhaustive).
675 // Note: is_useful doesn't work on empty types, as the paper notes.
676 // So it assumes that v is non-empty.
677 fn is_useful<'a, 'tcx>(cx: &MatchCheckCtxt<'a, 'tcx>,
678 matrix: &Matrix<'a, 'tcx>,
679 v: &[(&Pat, Option<Ty<'tcx>>)],
680 witness: WitnessPreference)
682 let &Matrix(ref rows) = matrix;
683 debug!("is_useful({:?}, {:?})", matrix, v);
685 return match witness {
686 ConstructWitness => UsefulWithWitness(vec!()),
687 LeaveOutWitness => Useful
690 if rows[0].is_empty() {
693 assert!(rows.iter().all(|r| r.len() == v.len()));
694 let left_ty = match rows.iter().filter_map(|r| r[0].1).next().or_else(|| v[0].1) {
697 // all patterns are wildcards - we can pick any type we want
702 let max_slice_length = rows.iter().filter_map(|row| match row[0].0.node {
703 PatKind::Vec(ref before, _, ref after) => Some(before.len() + after.len()),
705 }).max().map_or(0, |v| v + 1);
707 let constructors = pat_constructors(cx, v[0].0, left_ty, max_slice_length);
708 debug!("is_useful - pat_constructors = {:?} left_ty = {:?}", constructors,
710 if constructors.is_empty() {
711 let constructors = missing_constructors(cx, matrix, left_ty, max_slice_length);
712 debug!("is_useful - missing_constructors = {:?}", constructors);
713 if constructors.is_empty() {
714 all_constructors(cx, left_ty, max_slice_length).into_iter().map(|c| {
715 match is_useful_specialized(cx, matrix, v, c.clone(), left_ty, witness) {
716 UsefulWithWitness(pats) => UsefulWithWitness({
717 let arity = constructor_arity(cx, &c, left_ty);
719 let pat_slice = &pats[..];
720 let subpats: Vec<_> = (0..arity).map(|i| {
721 pat_slice.get(i).map_or(DUMMY_WILD_PAT, |p| &**p)
723 vec![construct_witness(cx, &c, subpats, left_ty)]
725 result.extend(pats.into_iter().skip(arity));
730 }).find(|result| result != &NotUseful).unwrap_or(NotUseful)
732 let matrix = rows.iter().filter_map(|r| {
733 match raw_pat(r[0].0).node {
734 PatKind::Binding(..) | PatKind::Wild => Some(r[1..].to_vec()),
738 match is_useful(cx, &matrix, &v[1..], witness) {
739 UsefulWithWitness(pats) => {
740 let mut new_pats: Vec<_> = constructors.into_iter().map(|constructor| {
741 let arity = constructor_arity(cx, &constructor, left_ty);
742 let wild_pats = vec![DUMMY_WILD_PAT; arity];
743 construct_witness(cx, &constructor, wild_pats, left_ty)
745 new_pats.extend(pats);
746 UsefulWithWitness(new_pats)
752 constructors.into_iter().map(|c|
753 is_useful_specialized(cx, matrix, v, c.clone(), left_ty, witness)
754 ).find(|result| result != &NotUseful).unwrap_or(NotUseful)
758 fn is_useful_specialized<'a, 'tcx>(
759 cx: &MatchCheckCtxt<'a, 'tcx>,
760 &Matrix(ref m): &Matrix<'a, 'tcx>,
761 v: &[(&Pat, Option<Ty<'tcx>>)],
764 witness: WitnessPreference) -> Usefulness
766 let arity = constructor_arity(cx, &ctor, lty);
767 let matrix = Matrix(m.iter().filter_map(|r| {
768 specialize(cx, &r[..], &ctor, 0, arity)
770 match specialize(cx, v, &ctor, 0, arity) {
771 Some(v) => is_useful(cx, &matrix, &v[..], witness),
776 /// Determines the constructors that the given pattern can be specialized to.
778 /// In most cases, there's only one constructor that a specific pattern
779 /// represents, such as a specific enum variant or a specific literal value.
780 /// Slice patterns, however, can match slices of different lengths. For instance,
781 /// `[a, b, ..tail]` can match a slice of length 2, 3, 4 and so on.
783 /// On the other hand, a wild pattern and an identifier pattern cannot be
784 /// specialized in any way.
785 fn pat_constructors(cx: &MatchCheckCtxt, p: &Pat,
786 left_ty: Ty, max_slice_length: usize) -> Vec<Constructor> {
787 let pat = raw_pat(p);
789 PatKind::Struct(..) | PatKind::TupleStruct(..) | PatKind::Path(..) =>
790 match cx.tcx.expect_def(pat.id) {
791 Def::Variant(_, id) => vec![Variant(id)],
792 Def::Struct(..) | Def::TyAlias(..) | Def::AssociatedTy(..) => vec![Single],
793 Def::Const(..) | Def::AssociatedConst(..) =>
794 span_bug!(pat.span, "const pattern should've been rewritten"),
795 def => span_bug!(pat.span, "pat_constructors: unexpected definition {:?}", def),
797 PatKind::Lit(ref expr) =>
798 vec![ConstantValue(eval_const_expr(cx.tcx, &expr))],
799 PatKind::Range(ref lo, ref hi) =>
800 vec![ConstantRange(eval_const_expr(cx.tcx, &lo), eval_const_expr(cx.tcx, &hi))],
801 PatKind::Vec(ref before, ref slice, ref after) =>
803 ty::TyArray(_, _) => vec![Single],
804 ty::TySlice(_) if slice.is_some() => {
805 (before.len() + after.len()..max_slice_length+1)
806 .map(|length| Slice(length))
809 ty::TySlice(_) => vec!(Slice(before.len() + after.len())),
810 _ => span_bug!(pat.span, "pat_constructors: unexpected \
811 slice pattern type {:?}", left_ty)
813 PatKind::Box(..) | PatKind::Tuple(..) | PatKind::Ref(..) =>
815 PatKind::Binding(..) | PatKind::Wild =>
820 /// This computes the arity of a constructor. The arity of a constructor
821 /// is how many subpattern patterns of that constructor should be expanded to.
823 /// For instance, a tuple pattern (_, 42, Some([])) has the arity of 3.
824 /// A struct pattern's arity is the number of fields it contains, etc.
825 pub fn constructor_arity(_cx: &MatchCheckCtxt, ctor: &Constructor, ty: Ty) -> usize {
826 debug!("constructor_arity({:?}, {:?})", ctor, ty);
828 ty::TyTuple(ref fs) => fs.len(),
830 ty::TySlice(_) => match *ctor {
831 Slice(length) => length,
832 ConstantValue(_) => 0,
836 ty::TyEnum(adt, _) | ty::TyStruct(adt, _) => {
837 ctor.variant_for_adt(adt).fields.len()
839 ty::TyArray(_, n) => n,
844 fn range_covered_by_constructor(tcx: TyCtxt, span: Span,
846 from: &ConstVal, to: &ConstVal)
847 -> Result<bool, ErrorReported> {
848 let (c_from, c_to) = match *ctor {
849 ConstantValue(ref value) => (value, value),
850 ConstantRange(ref from, ref to) => (from, to),
851 Single => return Ok(true),
854 let cmp_from = compare_const_vals(tcx, span, c_from, from)?;
855 let cmp_to = compare_const_vals(tcx, span, c_to, to)?;
856 Ok(cmp_from != Ordering::Less && cmp_to != Ordering::Greater)
859 fn wrap_pat<'a, 'b, 'tcx>(cx: &MatchCheckCtxt<'b, 'tcx>,
861 -> (&'a Pat, Option<Ty<'tcx>>)
863 let pat_ty = cx.tcx.pat_ty(pat);
864 (pat, Some(match pat.node {
865 PatKind::Binding(hir::BindByRef(..), _, _) => {
866 pat_ty.builtin_deref(false, NoPreference).unwrap().ty
872 /// This is the main specialization step. It expands the first pattern in the given row
873 /// into `arity` patterns based on the constructor. For most patterns, the step is trivial,
874 /// for instance tuple patterns are flattened and box patterns expand into their inner pattern.
876 /// OTOH, slice patterns with a subslice pattern (..tail) can be expanded into multiple
877 /// different patterns.
878 /// Structure patterns with a partial wild pattern (Foo { a: 42, .. }) have their missing
879 /// fields filled with wild patterns.
880 pub fn specialize<'a, 'b, 'tcx>(
881 cx: &MatchCheckCtxt<'b, 'tcx>,
882 r: &[(&'a Pat, Option<Ty<'tcx>>)],
883 constructor: &Constructor, col: usize, arity: usize)
884 -> Option<Vec<(&'a Pat, Option<Ty<'tcx>>)>>
886 let pat = raw_pat(r[col].0);
888 id: pat_id, ref node, span: pat_span
890 let wpat = |pat: &'a Pat| wrap_pat(cx, pat);
891 let dummy_pat = (DUMMY_WILD_PAT, None);
893 let head: Option<Vec<(&Pat, Option<Ty>)>> = match *node {
894 PatKind::Binding(..) | PatKind::Wild =>
895 Some(vec![dummy_pat; arity]),
897 PatKind::Path(..) => {
898 match cx.tcx.expect_def(pat_id) {
899 Def::Const(..) | Def::AssociatedConst(..) =>
900 span_bug!(pat_span, "const pattern should've \
902 Def::Variant(_, id) if *constructor != Variant(id) => None,
903 Def::Variant(..) | Def::Struct(..) => Some(Vec::new()),
904 def => span_bug!(pat_span, "specialize: unexpected \
905 definition {:?}", def),
909 PatKind::TupleStruct(_, ref args, ddpos) => {
910 match cx.tcx.expect_def(pat_id) {
911 Def::Const(..) | Def::AssociatedConst(..) =>
912 span_bug!(pat_span, "const pattern should've \
914 Def::Variant(_, id) if *constructor != Variant(id) => None,
915 Def::Variant(..) | Def::Struct(..) => {
918 let mut pats: Vec<_> = args[..ddpos].iter().map(|p| {
921 pats.extend(repeat((DUMMY_WILD_PAT, None)).take(arity - args.len()));
922 pats.extend(args[ddpos..].iter().map(|p| wpat(p)));
925 None => Some(args.iter().map(|p| wpat(p)).collect())
932 PatKind::Struct(_, ref pattern_fields, _) => {
933 let adt = cx.tcx.node_id_to_type(pat_id).ty_adt_def().unwrap();
934 let variant = constructor.variant_for_adt(adt);
935 let def_variant = adt.variant_of_def(cx.tcx.expect_def(pat_id));
936 if variant.did == def_variant.did {
937 Some(variant.fields.iter().map(|sf| {
938 match pattern_fields.iter().find(|f| f.node.name == sf.name) {
939 Some(ref f) => wpat(&f.node.pat),
948 PatKind::Tuple(ref args, Some(ddpos)) => {
949 let mut pats: Vec<_> = args[..ddpos].iter().map(|p| wpat(p)).collect();
950 pats.extend(repeat(dummy_pat).take(arity - args.len()));
951 pats.extend(args[ddpos..].iter().map(|p| wpat(p)));
954 PatKind::Tuple(ref args, None) =>
955 Some(args.iter().map(|p| wpat(&**p)).collect()),
957 PatKind::Box(ref inner) | PatKind::Ref(ref inner, _) =>
958 Some(vec![wpat(&**inner)]),
960 PatKind::Lit(ref expr) => {
961 if let Some(&ty::TyS { sty: ty::TyRef(_, mt), .. }) = r[col].1 {
962 // HACK: handle string literals. A string literal pattern
963 // serves both as an unary reference pattern and as a
964 // nullary value pattern, depending on the type.
965 Some(vec![(pat, Some(mt.ty))])
967 let expr_value = eval_const_expr(cx.tcx, &expr);
968 match range_covered_by_constructor(
969 cx.tcx, expr.span, constructor, &expr_value, &expr_value
971 Ok(true) => Some(vec![]),
973 Err(ErrorReported) => None,
978 PatKind::Range(ref from, ref to) => {
979 let from_value = eval_const_expr(cx.tcx, &from);
980 let to_value = eval_const_expr(cx.tcx, &to);
981 match range_covered_by_constructor(
982 cx.tcx, pat_span, constructor, &from_value, &to_value
984 Ok(true) => Some(vec![]),
986 Err(ErrorReported) => None,
990 PatKind::Vec(ref before, ref slice, ref after) => {
991 let pat_len = before.len() + after.len();
994 // Fixed-length vectors.
996 before.iter().map(|p| wpat(p)).chain(
997 repeat(dummy_pat).take(arity - pat_len).chain(
998 after.iter().map(|p| wpat(p))
1001 Slice(length) if pat_len <= length && slice.is_some() => {
1003 before.iter().map(|p| wpat(p)).chain(
1004 repeat(dummy_pat).take(arity - pat_len).chain(
1005 after.iter().map(|p| wpat(p))
1008 Slice(length) if pat_len == length => {
1010 before.iter().map(|p| wpat(p)).chain(
1011 after.iter().map(|p| wpat(p))
1014 SliceWithSubslice(prefix, suffix)
1015 if before.len() == prefix
1016 && after.len() == suffix
1017 && slice.is_some() => {
1018 // this is used by trans::_match only
1019 let mut pats: Vec<_> = before.iter()
1020 .map(|p| (&**p, None)).collect();
1021 pats.extend(after.iter().map(|p| (&**p, None)));
1028 debug!("specialize({:?}, {:?}) = {:?}", r[col], arity, head);
1030 head.map(|mut head| {
1031 head.extend_from_slice(&r[..col]);
1032 head.extend_from_slice(&r[col + 1..]);
1037 fn check_local(cx: &mut MatchCheckCtxt, loc: &hir::Local) {
1038 intravisit::walk_local(cx, loc);
1040 let pat = StaticInliner::new(cx.tcx, None).fold_pat(loc.pat.clone());
1041 check_irrefutable(cx, &pat, false);
1043 // Check legality of move bindings and `@` patterns.
1044 check_legality_of_move_bindings(cx, false, slice::ref_slice(&loc.pat));
1045 check_legality_of_bindings_in_at_patterns(cx, &loc.pat);
1048 fn check_fn(cx: &mut MatchCheckCtxt,
1055 FnKind::Closure(_) => {}
1056 _ => cx.param_env = ParameterEnvironment::for_item(cx.tcx, fn_id),
1059 intravisit::walk_fn(cx, kind, decl, body, sp, fn_id);
1061 for input in &decl.inputs {
1062 check_irrefutable(cx, &input.pat, true);
1063 check_legality_of_move_bindings(cx, false, slice::ref_slice(&input.pat));
1064 check_legality_of_bindings_in_at_patterns(cx, &input.pat);
1068 fn check_irrefutable(cx: &MatchCheckCtxt, pat: &Pat, is_fn_arg: bool) {
1069 let origin = if is_fn_arg {
1075 is_refutable(cx, pat, |uncovered_pat| {
1076 span_err!(cx.tcx.sess, pat.span, E0005,
1077 "refutable pattern in {}: `{}` not covered",
1079 pat_to_string(uncovered_pat),
1084 fn is_refutable<A, F>(cx: &MatchCheckCtxt, pat: &Pat, refutable: F) -> Option<A> where
1085 F: FnOnce(&Pat) -> A,
1087 let pats = Matrix(vec!(vec!(wrap_pat(cx, pat))));
1088 match is_useful(cx, &pats, &[(DUMMY_WILD_PAT, None)], ConstructWitness) {
1089 UsefulWithWitness(pats) => Some(refutable(&pats[0])),
1095 // Legality of move bindings checking
1096 fn check_legality_of_move_bindings(cx: &MatchCheckCtxt,
1099 let mut by_ref_span = None;
1101 pat_bindings(&pat, |bm, _, span, _path| {
1102 if let hir::BindByRef(..) = bm {
1103 by_ref_span = Some(span);
1108 let check_move = |p: &Pat, sub: Option<&Pat>| {
1109 // check legality of moving out of the enum
1111 // x @ Foo(..) is legal, but x @ Foo(y) isn't.
1112 if sub.map_or(false, |p| pat_contains_bindings(&p)) {
1113 struct_span_err!(cx.tcx.sess, p.span, E0007,
1114 "cannot bind by-move with sub-bindings")
1115 .span_label(p.span, &format!("binds an already bound by-move value by moving it"))
1117 } else if has_guard {
1118 struct_span_err!(cx.tcx.sess, p.span, E0008,
1119 "cannot bind by-move into a pattern guard")
1120 .span_label(p.span, &format!("moves value into pattern guard"))
1122 } else if by_ref_span.is_some() {
1123 let mut err = struct_span_err!(cx.tcx.sess, p.span, E0009,
1124 "cannot bind by-move and by-ref in the same pattern");
1125 span_note!(&mut err, by_ref_span.unwrap(), "by-ref binding occurs here");
1132 if let PatKind::Binding(hir::BindByValue(..), _, ref sub) = p.node {
1133 let pat_ty = cx.tcx.node_id_to_type(p.id);
1134 //FIXME: (@jroesch) this code should be floated up as well
1135 cx.tcx.infer_ctxt(None, Some(cx.param_env.clone()),
1136 Reveal::NotSpecializable).enter(|infcx| {
1137 if infcx.type_moves_by_default(pat_ty, pat.span) {
1138 check_move(p, sub.as_ref().map(|p| &**p));
1147 /// Ensures that a pattern guard doesn't borrow by mutable reference or
1149 fn check_for_mutation_in_guard<'a, 'tcx>(cx: &'a MatchCheckCtxt<'a, 'tcx>,
1150 guard: &hir::Expr) {
1151 cx.tcx.infer_ctxt(None, Some(cx.param_env.clone()),
1152 Reveal::NotSpecializable).enter(|infcx| {
1153 let mut checker = MutationChecker {
1156 let mut visitor = ExprUseVisitor::new(&mut checker, &infcx);
1157 visitor.walk_expr(guard);
1161 struct MutationChecker<'a, 'gcx: 'a> {
1162 cx: &'a MatchCheckCtxt<'a, 'gcx>,
1165 impl<'a, 'gcx, 'tcx> Delegate<'tcx> for MutationChecker<'a, 'gcx> {
1166 fn matched_pat(&mut self, _: &Pat, _: cmt, _: euv::MatchMode) {}
1167 fn consume(&mut self, _: NodeId, _: Span, _: cmt, _: ConsumeMode) {}
1168 fn consume_pat(&mut self, _: &Pat, _: cmt, _: ConsumeMode) {}
1169 fn borrow(&mut self,
1178 span_err!(self.cx.tcx.sess, span, E0301,
1179 "cannot mutably borrow in a pattern guard")
1181 ImmBorrow | UniqueImmBorrow => {}
1184 fn decl_without_init(&mut self, _: NodeId, _: Span) {}
1185 fn mutate(&mut self, _: NodeId, span: Span, _: cmt, mode: MutateMode) {
1187 MutateMode::JustWrite | MutateMode::WriteAndRead => {
1188 span_err!(self.cx.tcx.sess, span, E0302, "cannot assign in a pattern guard")
1190 MutateMode::Init => {}
1195 /// Forbids bindings in `@` patterns. This is necessary for memory safety,
1196 /// because of the way rvalues are handled in the borrow check. (See issue
1198 fn check_legality_of_bindings_in_at_patterns(cx: &MatchCheckCtxt, pat: &Pat) {
1199 AtBindingPatternVisitor { cx: cx, bindings_allowed: true }.visit_pat(pat);
1202 struct AtBindingPatternVisitor<'a, 'b:'a, 'tcx:'b> {
1203 cx: &'a MatchCheckCtxt<'b, 'tcx>,
1204 bindings_allowed: bool
1207 impl<'a, 'b, 'tcx, 'v> Visitor<'v> for AtBindingPatternVisitor<'a, 'b, 'tcx> {
1208 fn visit_pat(&mut self, pat: &Pat) {
1210 PatKind::Binding(_, _, ref subpat) => {
1211 if !self.bindings_allowed {
1212 span_err!(self.cx.tcx.sess, pat.span, E0303,
1213 "pattern bindings are not allowed after an `@`");
1216 if subpat.is_some() {
1217 let bindings_were_allowed = self.bindings_allowed;
1218 self.bindings_allowed = false;
1219 intravisit::walk_pat(self, pat);
1220 self.bindings_allowed = bindings_were_allowed;
1223 _ => intravisit::walk_pat(self, pat),