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 struct_span_err!(cx.tcx.sess, span, E0162,
320 "irrefutable if-let pattern")
321 .span_label(span, &format!("irrefutable pattern"))
323 printed_if_let_err = true;
327 hir::MatchSource::WhileLetDesugar => {
328 // find the first arm pattern so we can use its span
329 let &(ref first_arm_pats, _) = &arms[0];
330 let first_pat = &first_arm_pats[0];
331 let span = first_pat.span;
332 span_err!(cx.tcx.sess, span, E0165, "irrefutable while-let pattern");
335 hir::MatchSource::ForLoopDesugar => {
336 // this is a bug, because on `match iter.next()` we cover
337 // `Some(<head>)` and `None`. It's impossible to have an unreachable
339 // (see libsyntax/ext/expand.rs for the full expansion of a for loop)
340 span_bug!(pat.span, "unreachable for-loop pattern")
343 hir::MatchSource::Normal => {
344 let mut err = struct_span_err!(cx.tcx.sess, pat.span, E0001,
345 "unreachable pattern");
346 err.span_label(pat.span, &format!("this is an unreachable pattern"));
347 // if we had a catchall pattern, hint at that
349 if pat_is_catchall(&cx.tcx.def_map.borrow(), row[0].0) {
350 span_note!(err, row[0].0.span,
351 "this pattern matches any value");
357 hir::MatchSource::TryDesugar => {
358 span_bug!(pat.span, "unreachable try pattern")
363 UsefulWithWitness(_) => bug!()
366 let Matrix(mut rows) = seen;
374 /// Checks for common cases of "catchall" patterns that may not be intended as such.
375 fn pat_is_catchall(dm: &DefMap, p: &Pat) -> bool {
377 PatKind::Binding(_, _, None) => true,
378 PatKind::Binding(_, _, Some(ref s)) => pat_is_catchall(dm, &s),
379 PatKind::Ref(ref s, _) => pat_is_catchall(dm, &s),
380 PatKind::Tuple(ref v, _) => v.iter().all(|p| pat_is_catchall(dm, &p)),
385 fn raw_pat(p: &Pat) -> &Pat {
387 PatKind::Binding(_, _, Some(ref s)) => raw_pat(&s),
392 fn check_exhaustive<'a, 'tcx>(cx: &MatchCheckCtxt<'a, 'tcx>,
394 matrix: &Matrix<'a, 'tcx>,
395 source: hir::MatchSource) {
396 match is_useful(cx, matrix, &[(DUMMY_WILD_PAT, None)], ConstructWitness) {
397 UsefulWithWitness(pats) => {
398 let witnesses = if pats.is_empty() {
401 pats.iter().map(|w| &**w).collect()
404 hir::MatchSource::ForLoopDesugar => {
405 // `witnesses[0]` has the form `Some(<head>)`, peel off the `Some`
406 let witness = match witnesses[0].node {
407 PatKind::TupleStruct(_, ref pats, _) => match &pats[..] {
408 &[ref pat] => &**pat,
413 span_err!(cx.tcx.sess, sp, E0297,
414 "refutable pattern in `for` loop binding: \
416 pat_to_string(witness));
419 let pattern_strings: Vec<_> = witnesses.iter().map(|w| {
422 const LIMIT: usize = 3;
423 let joined_patterns = match pattern_strings.len() {
425 1 => format!("`{}`", pattern_strings[0]),
427 let (tail, head) = pattern_strings.split_last().unwrap();
428 format!("`{}`", head.join("`, `") + "` and `" + tail)
431 let (head, tail) = pattern_strings.split_at(LIMIT);
432 format!("`{}` and {} more", head.join("`, `"), tail.len())
436 let label_text = match pattern_strings.len(){
437 1 => format!("pattern {} not covered", joined_patterns),
438 _ => format!("patterns {} not covered", joined_patterns)
440 struct_span_err!(cx.tcx.sess, sp, E0004,
441 "non-exhaustive patterns: {} not covered",
443 ).span_label(sp, &label_text).emit();
448 // This is good, wildcard pattern isn't reachable
454 fn const_val_to_expr(value: &ConstVal) -> P<hir::Expr> {
455 let node = match value {
456 &ConstVal::Bool(b) => ast::LitKind::Bool(b),
461 node: hir::ExprLit(P(Spanned { node: node, span: DUMMY_SP })),
463 attrs: ast::ThinVec::new(),
467 pub struct StaticInliner<'a, 'tcx: 'a> {
468 pub tcx: TyCtxt<'a, 'tcx, 'tcx>,
470 pub renaming_map: Option<&'a mut FnvHashMap<(NodeId, Span), NodeId>>,
473 impl<'a, 'tcx> StaticInliner<'a, 'tcx> {
474 pub fn new<'b>(tcx: TyCtxt<'b, 'tcx, 'tcx>,
475 renaming_map: Option<&'b mut FnvHashMap<(NodeId, Span), NodeId>>)
476 -> StaticInliner<'b, 'tcx> {
480 renaming_map: renaming_map
485 struct RenamingRecorder<'map> {
486 substituted_node_id: NodeId,
488 renaming_map: &'map mut FnvHashMap<(NodeId, Span), NodeId>
491 impl<'v, 'map> Visitor<'v> for RenamingRecorder<'map> {
492 fn visit_id(&mut self, node_id: NodeId) {
493 let key = (node_id, self.origin_span);
494 self.renaming_map.insert(key, self.substituted_node_id);
498 impl<'a, 'tcx> Folder for StaticInliner<'a, 'tcx> {
499 fn fold_pat(&mut self, pat: P<Pat>) -> P<Pat> {
500 return match pat.node {
501 PatKind::Path(..) => {
502 match self.tcx.expect_def(pat.id) {
503 Def::AssociatedConst(did) | Def::Const(did) => {
504 let substs = Some(self.tcx.node_id_item_substs(pat.id).substs);
505 if let Some((const_expr, _)) = lookup_const_by_id(self.tcx, did, substs) {
506 match const_expr_to_pat(self.tcx, const_expr, pat.id, pat.span) {
508 if let Some(ref mut map) = self.renaming_map {
509 // Record any renamings we do here
510 record_renamings(const_expr, &pat, map);
516 self.tcx.sess.span_err(
518 &format!("constants of the type `{}` \
519 cannot be used in patterns",
520 self.tcx.item_path_str(def_id)));
526 span_err!(self.tcx.sess, pat.span, E0158,
527 "statics cannot be referenced in patterns");
531 _ => noop_fold_pat(pat, self)
534 _ => noop_fold_pat(pat, self)
537 fn record_renamings(const_expr: &hir::Expr,
538 substituted_pat: &hir::Pat,
539 renaming_map: &mut FnvHashMap<(NodeId, Span), NodeId>) {
540 let mut renaming_recorder = RenamingRecorder {
541 substituted_node_id: substituted_pat.id,
542 origin_span: substituted_pat.span,
543 renaming_map: renaming_map,
546 renaming_recorder.visit_expr(const_expr);
551 /// Constructs a partial witness for a pattern given a list of
552 /// patterns expanded by the specialization step.
554 /// When a pattern P is discovered to be useful, this function is used bottom-up
555 /// to reconstruct a complete witness, e.g. a pattern P' that covers a subset
556 /// of values, V, where each value in that set is not covered by any previously
557 /// used patterns and is covered by the pattern P'. Examples:
559 /// left_ty: tuple of 3 elements
560 /// pats: [10, 20, _] => (10, 20, _)
562 /// left_ty: struct X { a: (bool, &'static str), b: usize}
563 /// pats: [(false, "foo"), 42] => X { a: (false, "foo"), b: 42 }
564 fn construct_witness<'a,'tcx>(cx: &MatchCheckCtxt<'a,'tcx>, ctor: &Constructor,
565 pats: Vec<&Pat>, left_ty: Ty<'tcx>) -> P<Pat> {
566 let pats_len = pats.len();
567 let mut pats = pats.into_iter().map(|p| P((*p).clone()));
568 let pat = match left_ty.sty {
569 ty::TyTuple(..) => PatKind::Tuple(pats.collect(), None),
571 ty::TyEnum(adt, _) | ty::TyStruct(adt, _) => {
572 let v = ctor.variant_for_adt(adt);
574 VariantKind::Struct => {
575 let field_pats: hir::HirVec<_> = v.fields.iter()
577 .filter(|&(_, ref pat)| pat.node != PatKind::Wild)
578 .map(|(field, pat)| Spanned {
580 node: hir::FieldPat {
586 let has_more_fields = field_pats.len() < pats_len;
587 PatKind::Struct(def_to_path(cx.tcx, v.did), field_pats, has_more_fields)
589 VariantKind::Tuple => {
590 PatKind::TupleStruct(def_to_path(cx.tcx, v.did), pats.collect(), None)
592 VariantKind::Unit => {
593 PatKind::Path(None, def_to_path(cx.tcx, v.did))
598 ty::TyRef(_, ty::TypeAndMut { mutbl, .. }) => {
599 assert_eq!(pats_len, 1);
600 PatKind::Ref(pats.nth(0).unwrap(), mutbl)
603 ty::TySlice(_) => match ctor {
605 assert_eq!(pats_len, n);
606 PatKind::Vec(pats.collect(), None, hir::HirVec::new())
611 ty::TyArray(_, len) => {
612 assert_eq!(pats_len, len);
613 PatKind::Vec(pats.collect(), None, hir::HirVec::new())
618 ConstantValue(ref v) => PatKind::Lit(const_val_to_expr(v)),
632 fn variant_for_adt<'tcx, 'container, 'a>(&self,
633 adt: &'a ty::AdtDefData<'tcx, 'container>)
634 -> &'a VariantDefData<'tcx, 'container> {
636 &Variant(vid) => adt.variant_with_id(vid),
637 _ => adt.struct_variant()
642 fn missing_constructors(cx: &MatchCheckCtxt, &Matrix(ref rows): &Matrix,
643 left_ty: Ty, max_slice_length: usize) -> Vec<Constructor> {
644 let used_constructors: Vec<Constructor> = rows.iter()
645 .flat_map(|row| pat_constructors(cx, row[0].0, left_ty, max_slice_length))
647 all_constructors(cx, left_ty, max_slice_length)
649 .filter(|c| !used_constructors.contains(c))
653 /// This determines the set of all possible constructors of a pattern matching
654 /// values of type `left_ty`. For vectors, this would normally be an infinite set
655 /// but is instead bounded by the maximum fixed length of slice patterns in
656 /// the column of patterns being analyzed.
657 fn all_constructors(_cx: &MatchCheckCtxt, left_ty: Ty,
658 max_slice_length: usize) -> Vec<Constructor> {
661 [true, false].iter().map(|b| ConstantValue(ConstVal::Bool(*b))).collect(),
663 (0..max_slice_length+1).map(|length| Slice(length)).collect(),
664 ty::TyEnum(def, _) => def.variants.iter().map(|v| Variant(v.did)).collect(),
669 // Algorithm from http://moscova.inria.fr/~maranget/papers/warn/index.html
671 // Whether a vector `v` of patterns is 'useful' in relation to a set of such
672 // vectors `m` is defined as there being a set of inputs that will match `v`
673 // but not any of the sets in `m`.
675 // This is used both for reachability checking (if a pattern isn't useful in
676 // relation to preceding patterns, it is not reachable) and exhaustiveness
677 // checking (if a wildcard pattern is useful in relation to a matrix, the
678 // matrix isn't exhaustive).
680 // Note: is_useful doesn't work on empty types, as the paper notes.
681 // So it assumes that v is non-empty.
682 fn is_useful<'a, 'tcx>(cx: &MatchCheckCtxt<'a, 'tcx>,
683 matrix: &Matrix<'a, 'tcx>,
684 v: &[(&Pat, Option<Ty<'tcx>>)],
685 witness: WitnessPreference)
687 let &Matrix(ref rows) = matrix;
688 debug!("is_useful({:?}, {:?})", matrix, v);
690 return match witness {
691 ConstructWitness => UsefulWithWitness(vec!()),
692 LeaveOutWitness => Useful
695 if rows[0].is_empty() {
698 assert!(rows.iter().all(|r| r.len() == v.len()));
699 let left_ty = match rows.iter().filter_map(|r| r[0].1).next().or_else(|| v[0].1) {
702 // all patterns are wildcards - we can pick any type we want
707 let max_slice_length = rows.iter().filter_map(|row| match row[0].0.node {
708 PatKind::Vec(ref before, _, ref after) => Some(before.len() + after.len()),
710 }).max().map_or(0, |v| v + 1);
712 let constructors = pat_constructors(cx, v[0].0, left_ty, max_slice_length);
713 debug!("is_useful - pat_constructors = {:?} left_ty = {:?}", constructors,
715 if constructors.is_empty() {
716 let constructors = missing_constructors(cx, matrix, left_ty, max_slice_length);
717 debug!("is_useful - missing_constructors = {:?}", constructors);
718 if constructors.is_empty() {
719 all_constructors(cx, left_ty, max_slice_length).into_iter().map(|c| {
720 match is_useful_specialized(cx, matrix, v, c.clone(), left_ty, witness) {
721 UsefulWithWitness(pats) => UsefulWithWitness({
722 let arity = constructor_arity(cx, &c, left_ty);
724 let pat_slice = &pats[..];
725 let subpats: Vec<_> = (0..arity).map(|i| {
726 pat_slice.get(i).map_or(DUMMY_WILD_PAT, |p| &**p)
728 vec![construct_witness(cx, &c, subpats, left_ty)]
730 result.extend(pats.into_iter().skip(arity));
735 }).find(|result| result != &NotUseful).unwrap_or(NotUseful)
737 let matrix = rows.iter().filter_map(|r| {
738 match raw_pat(r[0].0).node {
739 PatKind::Binding(..) | PatKind::Wild => Some(r[1..].to_vec()),
743 match is_useful(cx, &matrix, &v[1..], witness) {
744 UsefulWithWitness(pats) => {
745 let mut new_pats: Vec<_> = constructors.into_iter().map(|constructor| {
746 let arity = constructor_arity(cx, &constructor, left_ty);
747 let wild_pats = vec![DUMMY_WILD_PAT; arity];
748 construct_witness(cx, &constructor, wild_pats, left_ty)
750 new_pats.extend(pats);
751 UsefulWithWitness(new_pats)
757 constructors.into_iter().map(|c|
758 is_useful_specialized(cx, matrix, v, c.clone(), left_ty, witness)
759 ).find(|result| result != &NotUseful).unwrap_or(NotUseful)
763 fn is_useful_specialized<'a, 'tcx>(
764 cx: &MatchCheckCtxt<'a, 'tcx>,
765 &Matrix(ref m): &Matrix<'a, 'tcx>,
766 v: &[(&Pat, Option<Ty<'tcx>>)],
769 witness: WitnessPreference) -> Usefulness
771 let arity = constructor_arity(cx, &ctor, lty);
772 let matrix = Matrix(m.iter().filter_map(|r| {
773 specialize(cx, &r[..], &ctor, 0, arity)
775 match specialize(cx, v, &ctor, 0, arity) {
776 Some(v) => is_useful(cx, &matrix, &v[..], witness),
781 /// Determines the constructors that the given pattern can be specialized to.
783 /// In most cases, there's only one constructor that a specific pattern
784 /// represents, such as a specific enum variant or a specific literal value.
785 /// Slice patterns, however, can match slices of different lengths. For instance,
786 /// `[a, b, ..tail]` can match a slice of length 2, 3, 4 and so on.
788 /// On the other hand, a wild pattern and an identifier pattern cannot be
789 /// specialized in any way.
790 fn pat_constructors(cx: &MatchCheckCtxt, p: &Pat,
791 left_ty: Ty, max_slice_length: usize) -> Vec<Constructor> {
792 let pat = raw_pat(p);
794 PatKind::Struct(..) | PatKind::TupleStruct(..) | PatKind::Path(..) =>
795 match cx.tcx.expect_def(pat.id) {
796 Def::Variant(_, id) => vec![Variant(id)],
797 Def::Struct(..) | Def::TyAlias(..) | Def::AssociatedTy(..) => vec![Single],
798 Def::Const(..) | Def::AssociatedConst(..) =>
799 span_bug!(pat.span, "const pattern should've been rewritten"),
800 def => span_bug!(pat.span, "pat_constructors: unexpected definition {:?}", def),
802 PatKind::Lit(ref expr) =>
803 vec![ConstantValue(eval_const_expr(cx.tcx, &expr))],
804 PatKind::Range(ref lo, ref hi) =>
805 vec![ConstantRange(eval_const_expr(cx.tcx, &lo), eval_const_expr(cx.tcx, &hi))],
806 PatKind::Vec(ref before, ref slice, ref after) =>
808 ty::TyArray(_, _) => vec![Single],
809 ty::TySlice(_) if slice.is_some() => {
810 (before.len() + after.len()..max_slice_length+1)
811 .map(|length| Slice(length))
814 ty::TySlice(_) => vec!(Slice(before.len() + after.len())),
815 _ => span_bug!(pat.span, "pat_constructors: unexpected \
816 slice pattern type {:?}", left_ty)
818 PatKind::Box(..) | PatKind::Tuple(..) | PatKind::Ref(..) =>
820 PatKind::Binding(..) | PatKind::Wild =>
825 /// This computes the arity of a constructor. The arity of a constructor
826 /// is how many subpattern patterns of that constructor should be expanded to.
828 /// For instance, a tuple pattern (_, 42, Some([])) has the arity of 3.
829 /// A struct pattern's arity is the number of fields it contains, etc.
830 pub fn constructor_arity(_cx: &MatchCheckCtxt, ctor: &Constructor, ty: Ty) -> usize {
831 debug!("constructor_arity({:?}, {:?})", ctor, ty);
833 ty::TyTuple(ref fs) => fs.len(),
835 ty::TySlice(_) => match *ctor {
836 Slice(length) => length,
837 ConstantValue(_) => 0,
841 ty::TyEnum(adt, _) | ty::TyStruct(adt, _) => {
842 ctor.variant_for_adt(adt).fields.len()
844 ty::TyArray(_, n) => n,
849 fn range_covered_by_constructor(tcx: TyCtxt, span: Span,
851 from: &ConstVal, to: &ConstVal)
852 -> Result<bool, ErrorReported> {
853 let (c_from, c_to) = match *ctor {
854 ConstantValue(ref value) => (value, value),
855 ConstantRange(ref from, ref to) => (from, to),
856 Single => return Ok(true),
859 let cmp_from = compare_const_vals(tcx, span, c_from, from)?;
860 let cmp_to = compare_const_vals(tcx, span, c_to, to)?;
861 Ok(cmp_from != Ordering::Less && cmp_to != Ordering::Greater)
864 fn wrap_pat<'a, 'b, 'tcx>(cx: &MatchCheckCtxt<'b, 'tcx>,
866 -> (&'a Pat, Option<Ty<'tcx>>)
868 let pat_ty = cx.tcx.pat_ty(pat);
869 (pat, Some(match pat.node {
870 PatKind::Binding(hir::BindByRef(..), _, _) => {
871 pat_ty.builtin_deref(false, NoPreference).unwrap().ty
877 /// This is the main specialization step. It expands the first pattern in the given row
878 /// into `arity` patterns based on the constructor. For most patterns, the step is trivial,
879 /// for instance tuple patterns are flattened and box patterns expand into their inner pattern.
881 /// OTOH, slice patterns with a subslice pattern (..tail) can be expanded into multiple
882 /// different patterns.
883 /// Structure patterns with a partial wild pattern (Foo { a: 42, .. }) have their missing
884 /// fields filled with wild patterns.
885 pub fn specialize<'a, 'b, 'tcx>(
886 cx: &MatchCheckCtxt<'b, 'tcx>,
887 r: &[(&'a Pat, Option<Ty<'tcx>>)],
888 constructor: &Constructor, col: usize, arity: usize)
889 -> Option<Vec<(&'a Pat, Option<Ty<'tcx>>)>>
891 let pat = raw_pat(r[col].0);
893 id: pat_id, ref node, span: pat_span
895 let wpat = |pat: &'a Pat| wrap_pat(cx, pat);
896 let dummy_pat = (DUMMY_WILD_PAT, None);
898 let head: Option<Vec<(&Pat, Option<Ty>)>> = match *node {
899 PatKind::Binding(..) | PatKind::Wild =>
900 Some(vec![dummy_pat; arity]),
902 PatKind::Path(..) => {
903 match cx.tcx.expect_def(pat_id) {
904 Def::Const(..) | Def::AssociatedConst(..) =>
905 span_bug!(pat_span, "const pattern should've \
907 Def::Variant(_, id) if *constructor != Variant(id) => None,
908 Def::Variant(..) | Def::Struct(..) => Some(Vec::new()),
909 def => span_bug!(pat_span, "specialize: unexpected \
910 definition {:?}", def),
914 PatKind::TupleStruct(_, ref args, ddpos) => {
915 match cx.tcx.expect_def(pat_id) {
916 Def::Const(..) | Def::AssociatedConst(..) =>
917 span_bug!(pat_span, "const pattern should've \
919 Def::Variant(_, id) if *constructor != Variant(id) => None,
920 Def::Variant(..) | Def::Struct(..) => {
923 let mut pats: Vec<_> = args[..ddpos].iter().map(|p| {
926 pats.extend(repeat((DUMMY_WILD_PAT, None)).take(arity - args.len()));
927 pats.extend(args[ddpos..].iter().map(|p| wpat(p)));
930 None => Some(args.iter().map(|p| wpat(p)).collect())
937 PatKind::Struct(_, ref pattern_fields, _) => {
938 let adt = cx.tcx.node_id_to_type(pat_id).ty_adt_def().unwrap();
939 let variant = constructor.variant_for_adt(adt);
940 let def_variant = adt.variant_of_def(cx.tcx.expect_def(pat_id));
941 if variant.did == def_variant.did {
942 Some(variant.fields.iter().map(|sf| {
943 match pattern_fields.iter().find(|f| f.node.name == sf.name) {
944 Some(ref f) => wpat(&f.node.pat),
953 PatKind::Tuple(ref args, Some(ddpos)) => {
954 let mut pats: Vec<_> = args[..ddpos].iter().map(|p| wpat(p)).collect();
955 pats.extend(repeat(dummy_pat).take(arity - args.len()));
956 pats.extend(args[ddpos..].iter().map(|p| wpat(p)));
959 PatKind::Tuple(ref args, None) =>
960 Some(args.iter().map(|p| wpat(&**p)).collect()),
962 PatKind::Box(ref inner) | PatKind::Ref(ref inner, _) =>
963 Some(vec![wpat(&**inner)]),
965 PatKind::Lit(ref expr) => {
966 if let Some(&ty::TyS { sty: ty::TyRef(_, mt), .. }) = r[col].1 {
967 // HACK: handle string literals. A string literal pattern
968 // serves both as an unary reference pattern and as a
969 // nullary value pattern, depending on the type.
970 Some(vec![(pat, Some(mt.ty))])
972 let expr_value = eval_const_expr(cx.tcx, &expr);
973 match range_covered_by_constructor(
974 cx.tcx, expr.span, constructor, &expr_value, &expr_value
976 Ok(true) => Some(vec![]),
978 Err(ErrorReported) => None,
983 PatKind::Range(ref from, ref to) => {
984 let from_value = eval_const_expr(cx.tcx, &from);
985 let to_value = eval_const_expr(cx.tcx, &to);
986 match range_covered_by_constructor(
987 cx.tcx, pat_span, constructor, &from_value, &to_value
989 Ok(true) => Some(vec![]),
991 Err(ErrorReported) => None,
995 PatKind::Vec(ref before, ref slice, ref after) => {
996 let pat_len = before.len() + after.len();
999 // Fixed-length vectors.
1001 before.iter().map(|p| wpat(p)).chain(
1002 repeat(dummy_pat).take(arity - pat_len).chain(
1003 after.iter().map(|p| wpat(p))
1006 Slice(length) if pat_len <= length && slice.is_some() => {
1008 before.iter().map(|p| wpat(p)).chain(
1009 repeat(dummy_pat).take(arity - pat_len).chain(
1010 after.iter().map(|p| wpat(p))
1013 Slice(length) if pat_len == length => {
1015 before.iter().map(|p| wpat(p)).chain(
1016 after.iter().map(|p| wpat(p))
1019 SliceWithSubslice(prefix, suffix)
1020 if before.len() == prefix
1021 && after.len() == suffix
1022 && slice.is_some() => {
1023 // this is used by trans::_match only
1024 let mut pats: Vec<_> = before.iter()
1025 .map(|p| (&**p, None)).collect();
1026 pats.extend(after.iter().map(|p| (&**p, None)));
1033 debug!("specialize({:?}, {:?}) = {:?}", r[col], arity, head);
1035 head.map(|mut head| {
1036 head.extend_from_slice(&r[..col]);
1037 head.extend_from_slice(&r[col + 1..]);
1042 fn check_local(cx: &mut MatchCheckCtxt, loc: &hir::Local) {
1043 intravisit::walk_local(cx, loc);
1045 let pat = StaticInliner::new(cx.tcx, None).fold_pat(loc.pat.clone());
1046 check_irrefutable(cx, &pat, false);
1048 // Check legality of move bindings and `@` patterns.
1049 check_legality_of_move_bindings(cx, false, slice::ref_slice(&loc.pat));
1050 check_legality_of_bindings_in_at_patterns(cx, &loc.pat);
1053 fn check_fn(cx: &mut MatchCheckCtxt,
1060 FnKind::Closure(_) => {}
1061 _ => cx.param_env = ParameterEnvironment::for_item(cx.tcx, fn_id),
1064 intravisit::walk_fn(cx, kind, decl, body, sp, fn_id);
1066 for input in &decl.inputs {
1067 check_irrefutable(cx, &input.pat, true);
1068 check_legality_of_move_bindings(cx, false, slice::ref_slice(&input.pat));
1069 check_legality_of_bindings_in_at_patterns(cx, &input.pat);
1073 fn check_irrefutable(cx: &MatchCheckCtxt, pat: &Pat, is_fn_arg: bool) {
1074 let origin = if is_fn_arg {
1080 is_refutable(cx, pat, |uncovered_pat| {
1081 span_err!(cx.tcx.sess, pat.span, E0005,
1082 "refutable pattern in {}: `{}` not covered",
1084 pat_to_string(uncovered_pat),
1089 fn is_refutable<A, F>(cx: &MatchCheckCtxt, pat: &Pat, refutable: F) -> Option<A> where
1090 F: FnOnce(&Pat) -> A,
1092 let pats = Matrix(vec!(vec!(wrap_pat(cx, pat))));
1093 match is_useful(cx, &pats, &[(DUMMY_WILD_PAT, None)], ConstructWitness) {
1094 UsefulWithWitness(pats) => Some(refutable(&pats[0])),
1100 // Legality of move bindings checking
1101 fn check_legality_of_move_bindings(cx: &MatchCheckCtxt,
1104 let mut by_ref_span = None;
1106 pat_bindings(&pat, |bm, _, span, _path| {
1107 if let hir::BindByRef(..) = bm {
1108 by_ref_span = Some(span);
1113 let check_move = |p: &Pat, sub: Option<&Pat>| {
1114 // check legality of moving out of the enum
1116 // x @ Foo(..) is legal, but x @ Foo(y) isn't.
1117 if sub.map_or(false, |p| pat_contains_bindings(&p)) {
1118 struct_span_err!(cx.tcx.sess, p.span, E0007,
1119 "cannot bind by-move with sub-bindings")
1120 .span_label(p.span, &format!("binds an already bound by-move value by moving it"))
1122 } else if has_guard {
1123 struct_span_err!(cx.tcx.sess, p.span, E0008,
1124 "cannot bind by-move into a pattern guard")
1125 .span_label(p.span, &format!("moves value into pattern guard"))
1127 } else if by_ref_span.is_some() {
1128 let mut err = struct_span_err!(cx.tcx.sess, p.span, E0009,
1129 "cannot bind by-move and by-ref in the same pattern");
1130 span_note!(&mut err, by_ref_span.unwrap(), "by-ref binding occurs here");
1137 if let PatKind::Binding(hir::BindByValue(..), _, ref sub) = p.node {
1138 let pat_ty = cx.tcx.node_id_to_type(p.id);
1139 //FIXME: (@jroesch) this code should be floated up as well
1140 cx.tcx.infer_ctxt(None, Some(cx.param_env.clone()),
1141 ProjectionMode::AnyFinal).enter(|infcx| {
1142 if infcx.type_moves_by_default(pat_ty, pat.span) {
1143 check_move(p, sub.as_ref().map(|p| &**p));
1152 /// Ensures that a pattern guard doesn't borrow by mutable reference or
1154 fn check_for_mutation_in_guard<'a, 'tcx>(cx: &'a MatchCheckCtxt<'a, 'tcx>,
1155 guard: &hir::Expr) {
1156 cx.tcx.infer_ctxt(None, Some(cx.param_env.clone()),
1157 ProjectionMode::AnyFinal).enter(|infcx| {
1158 let mut checker = MutationChecker {
1161 let mut visitor = ExprUseVisitor::new(&mut checker, &infcx);
1162 visitor.walk_expr(guard);
1166 struct MutationChecker<'a, 'gcx: 'a> {
1167 cx: &'a MatchCheckCtxt<'a, 'gcx>,
1170 impl<'a, 'gcx, 'tcx> Delegate<'tcx> for MutationChecker<'a, 'gcx> {
1171 fn matched_pat(&mut self, _: &Pat, _: cmt, _: euv::MatchMode) {}
1172 fn consume(&mut self, _: NodeId, _: Span, _: cmt, _: ConsumeMode) {}
1173 fn consume_pat(&mut self, _: &Pat, _: cmt, _: ConsumeMode) {}
1174 fn borrow(&mut self,
1183 span_err!(self.cx.tcx.sess, span, E0301,
1184 "cannot mutably borrow in a pattern guard")
1186 ImmBorrow | UniqueImmBorrow => {}
1189 fn decl_without_init(&mut self, _: NodeId, _: Span) {}
1190 fn mutate(&mut self, _: NodeId, span: Span, _: cmt, mode: MutateMode) {
1192 MutateMode::JustWrite | MutateMode::WriteAndRead => {
1193 span_err!(self.cx.tcx.sess, span, E0302, "cannot assign in a pattern guard")
1195 MutateMode::Init => {}
1200 /// Forbids bindings in `@` patterns. This is necessary for memory safety,
1201 /// because of the way rvalues are handled in the borrow check. (See issue
1203 fn check_legality_of_bindings_in_at_patterns(cx: &MatchCheckCtxt, pat: &Pat) {
1204 AtBindingPatternVisitor { cx: cx, bindings_allowed: true }.visit_pat(pat);
1207 struct AtBindingPatternVisitor<'a, 'b:'a, 'tcx:'b> {
1208 cx: &'a MatchCheckCtxt<'b, 'tcx>,
1209 bindings_allowed: bool
1212 impl<'a, 'b, 'tcx, 'v> Visitor<'v> for AtBindingPatternVisitor<'a, 'b, 'tcx> {
1213 fn visit_pat(&mut self, pat: &Pat) {
1215 PatKind::Binding(_, _, ref subpat) => {
1216 if !self.bindings_allowed {
1217 span_err!(self.cx.tcx.sess, pat.span, E0303,
1218 "pattern bindings are not allowed after an `@`");
1221 if subpat.is_some() {
1222 let bindings_were_allowed = self.bindings_allowed;
1223 self.bindings_allowed = false;
1224 intravisit::walk_pat(self, pat);
1225 self.bindings_allowed = bindings_were_allowed;
1228 _ => intravisit::walk_pat(self, pat),