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;
29 use rustc::ty::{self, Ty, TyCtxt};
30 use std::cmp::Ordering;
32 use std::iter::{FromIterator, IntoIterator, repeat};
35 use rustc::hir::{Pat, PatKind};
36 use rustc::hir::intravisit::{self, Visitor, FnKind};
37 use rustc_back::slice;
39 use syntax::ast::{self, DUMMY_NODE_ID, NodeId};
40 use syntax::codemap::Spanned;
41 use syntax_pos::{Span, DUMMY_SP};
42 use rustc::hir::print::pat_to_string;
44 use syntax::util::move_map::MoveMap;
45 use rustc::util::common::ErrorReported;
47 pub const DUMMY_WILD_PAT: &'static Pat = &Pat {
53 struct Matrix<'a, 'tcx>(Vec<Vec<(&'a Pat, Option<Ty<'tcx>>)>>);
55 /// Pretty-printer for matrices of patterns, example:
56 /// ++++++++++++++++++++++++++
58 /// ++++++++++++++++++++++++++
59 /// + true + [First] +
60 /// ++++++++++++++++++++++++++
61 /// + true + [Second(true)] +
62 /// ++++++++++++++++++++++++++
64 /// ++++++++++++++++++++++++++
65 /// + _ + [_, _, ..tail] +
66 /// ++++++++++++++++++++++++++
67 impl<'a, 'tcx> fmt::Debug for Matrix<'a, 'tcx> {
68 fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
71 let &Matrix(ref m) = self;
72 let pretty_printed_matrix: Vec<Vec<String>> = m.iter().map(|row| {
74 .map(|&(pat,ty)| format!("{}: {:?}", pat_to_string(&pat), ty))
75 .collect::<Vec<String>>()
78 let column_count = m.iter().map(|row| row.len()).max().unwrap_or(0);
79 assert!(m.iter().all(|row| row.len() == column_count));
80 let column_widths: Vec<usize> = (0..column_count).map(|col| {
81 pretty_printed_matrix.iter().map(|row| row[col].len()).max().unwrap_or(0)
84 let total_width = column_widths.iter().cloned().sum::<usize>() + column_count * 3 + 1;
85 let br = repeat('+').take(total_width).collect::<String>();
86 write!(f, "{}\n", br)?;
87 for row in pretty_printed_matrix {
89 for (column, pat_str) in row.into_iter().enumerate() {
91 write!(f, "{:1$}", pat_str, column_widths[column])?;
95 write!(f, "{}\n", br)?;
101 impl<'a, 'tcx> FromIterator<Vec<(&'a Pat, Option<Ty<'tcx>>)>> for Matrix<'a, 'tcx> {
102 fn from_iter<T: IntoIterator<Item=Vec<(&'a Pat, Option<Ty<'tcx>>)>>>(iter: T)
105 Matrix(iter.into_iter().collect())
109 //NOTE: appears to be the only place other then InferCtxt to contain a ParamEnv
110 pub struct MatchCheckCtxt<'a, 'tcx: 'a> {
111 pub tcx: TyCtxt<'a, 'tcx, 'tcx>,
112 pub param_env: ty::ParameterEnvironment<'tcx>,
115 #[derive(Clone, Debug, PartialEq)]
116 pub enum Constructor {
117 /// The constructor of all patterns that don't vary by constructor,
118 /// e.g. struct patterns and fixed-length arrays.
123 ConstantValue(ConstVal),
124 /// Ranges of literal values (2..5).
125 ConstantRange(ConstVal, ConstVal),
126 /// Array patterns of length n.
128 /// Array patterns with a subslice.
129 SliceWithSubslice(usize, usize)
132 #[derive(Clone, PartialEq)]
135 UsefulWithWitness(Vec<P<Pat>>),
139 #[derive(Copy, Clone)]
140 enum WitnessPreference {
145 impl<'a, 'tcx, 'v> Visitor<'v> for MatchCheckCtxt<'a, 'tcx> {
146 fn visit_expr(&mut self, ex: &hir::Expr) {
147 check_expr(self, ex);
149 fn visit_local(&mut self, l: &hir::Local) {
150 check_local(self, l);
152 fn visit_fn(&mut self, fk: FnKind<'v>, fd: &'v hir::FnDecl,
153 b: &'v hir::Block, s: Span, n: NodeId) {
154 check_fn(self, fk, fd, b, s, n);
158 pub fn check_crate<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>) {
159 tcx.visit_all_items_in_krate(DepNode::MatchCheck, &mut MatchCheckCtxt {
161 param_env: tcx.empty_parameter_environment(),
163 tcx.sess.abort_if_errors();
166 fn check_expr(cx: &mut MatchCheckCtxt, ex: &hir::Expr) {
167 intravisit::walk_expr(cx, ex);
169 hir::ExprMatch(ref scrut, ref arms, source) => {
171 // First, check legality of move bindings.
172 check_legality_of_move_bindings(cx,
176 // Second, if there is a guard on each arm, make sure it isn't
177 // assigning or borrowing anything mutably.
178 if let Some(ref guard) = arm.guard {
179 check_for_mutation_in_guard(cx, &guard);
183 let mut static_inliner = StaticInliner::new(cx.tcx);
184 let inlined_arms = arms.iter().map(|arm| {
185 (arm.pats.iter().map(|pat| {
186 static_inliner.fold_pat((*pat).clone())
187 }).collect(), arm.guard.as_ref().map(|e| &**e))
188 }).collect::<Vec<(Vec<P<Pat>>, Option<&hir::Expr>)>>();
190 // Bail out early if inlining failed.
191 if static_inliner.failed {
195 for pat in inlined_arms
197 .flat_map(|&(ref pats, _)| pats) {
198 // Third, check legality of move bindings.
199 check_legality_of_bindings_in_at_patterns(cx, &pat);
201 // Fourth, check if there are any references to NaN that we should warn about.
202 check_for_static_nan(cx, &pat);
204 // Fifth, check if for any of the patterns that match an enumerated type
205 // are bindings with the same name as one of the variants of said type.
206 check_for_bindings_named_the_same_as_variants(cx, &pat);
209 // Fourth, check for unreachable arms.
210 check_arms(cx, &inlined_arms[..], source);
212 // Finally, check if the whole match expression is exhaustive.
213 // Check for empty enum, because is_useful only works on inhabited types.
214 let pat_ty = cx.tcx.node_id_to_type(scrut.id);
215 if inlined_arms.is_empty() {
216 if !pat_ty.is_uninhabited(cx.tcx) {
217 // We know the type is inhabited, so this must be wrong
218 let mut err = struct_span_err!(cx.tcx.sess, ex.span, E0002,
219 "non-exhaustive patterns: type {} is non-empty",
221 span_help!(&mut err, ex.span,
222 "Please ensure that all possible cases are being handled; \
223 possibly adding wildcards or more match arms.");
226 // If the type *is* uninhabited, it's vacuously exhaustive
230 let matrix: Matrix = inlined_arms
232 .filter(|&&(_, guard)| guard.is_none())
233 .flat_map(|arm| &arm.0)
234 .map(|pat| vec![wrap_pat(cx, &pat)])
236 check_exhaustive(cx, scrut.span, &matrix, source);
242 fn check_for_bindings_named_the_same_as_variants(cx: &MatchCheckCtxt, pat: &Pat) {
244 if let PatKind::Binding(hir::BindByValue(hir::MutImmutable), name, None) = p.node {
245 let pat_ty = cx.tcx.pat_ty(p);
246 if let ty::TyAdt(edef, _) = pat_ty.sty {
248 if let Def::Local(..) = cx.tcx.expect_def(p.id) {
249 if edef.variants.iter().any(|variant| {
250 variant.name == name.node && variant.kind == ty::VariantKind::Unit
252 let ty_path = cx.tcx.item_path_str(edef.did);
253 let mut err = struct_span_warn!(cx.tcx.sess, p.span, E0170,
254 "pattern binding `{}` is named the same as one \
255 of the variants of the type `{}`",
258 "if you meant to match on a variant, \
259 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 struct_span_err!(cx.tcx.sess, span, E0165,
328 "irrefutable while-let pattern")
329 .span_label(span, &format!("irrefutable pattern"))
333 hir::MatchSource::ForLoopDesugar => {
334 // this is a bug, because on `match iter.next()` we cover
335 // `Some(<head>)` and `None`. It's impossible to have an unreachable
337 // (see libsyntax/ext/expand.rs for the full expansion of a for loop)
338 span_bug!(pat.span, "unreachable for-loop pattern")
341 hir::MatchSource::Normal => {
342 let mut err = struct_span_err!(cx.tcx.sess, pat.span, E0001,
343 "unreachable pattern");
344 err.span_label(pat.span, &format!("this is an unreachable pattern"));
345 // if we had a catchall pattern, hint at that
347 if pat_is_catchall(&cx.tcx.def_map.borrow(), row[0].0) {
348 span_note!(err, row[0].0.span,
349 "this pattern matches any value");
355 hir::MatchSource::TryDesugar => {
356 span_bug!(pat.span, "unreachable try pattern")
361 UsefulWithWitness(_) => bug!()
364 let Matrix(mut rows) = seen;
372 /// Checks for common cases of "catchall" patterns that may not be intended as such.
373 fn pat_is_catchall(dm: &DefMap, p: &Pat) -> bool {
375 PatKind::Binding(.., None) => true,
376 PatKind::Binding(.., Some(ref s)) => pat_is_catchall(dm, &s),
377 PatKind::Ref(ref s, _) => pat_is_catchall(dm, &s),
378 PatKind::Tuple(ref v, _) => v.iter().all(|p| pat_is_catchall(dm, &p)),
383 fn raw_pat(p: &Pat) -> &Pat {
385 PatKind::Binding(.., Some(ref s)) => raw_pat(&s),
390 fn check_exhaustive<'a, 'tcx>(cx: &MatchCheckCtxt<'a, 'tcx>,
392 matrix: &Matrix<'a, 'tcx>,
393 source: hir::MatchSource) {
394 match is_useful(cx, matrix, &[(DUMMY_WILD_PAT, None)], ConstructWitness) {
395 UsefulWithWitness(pats) => {
396 let witnesses = if pats.is_empty() {
399 pats.iter().map(|w| &**w).collect()
402 hir::MatchSource::ForLoopDesugar => {
403 // `witnesses[0]` has the form `Some(<head>)`, peel off the `Some`
404 let witness = match witnesses[0].node {
405 PatKind::TupleStruct(_, ref pats, _) => match &pats[..] {
406 &[ref pat] => &**pat,
411 let pattern_string = pat_to_string(witness);
412 struct_span_err!(cx.tcx.sess, sp, E0297,
413 "refutable pattern in `for` loop binding: \
416 .span_label(sp, &format!("pattern `{}` not covered", pattern_string))
420 let pattern_strings: Vec<_> = witnesses.iter().map(|w| {
423 const LIMIT: usize = 3;
424 let joined_patterns = match pattern_strings.len() {
426 1 => format!("`{}`", pattern_strings[0]),
428 let (tail, head) = pattern_strings.split_last().unwrap();
429 format!("`{}`", head.join("`, `") + "` and `" + tail)
432 let (head, tail) = pattern_strings.split_at(LIMIT);
433 format!("`{}` and {} more", head.join("`, `"), tail.len())
437 let label_text = match pattern_strings.len(){
438 1 => format!("pattern {} not covered", joined_patterns),
439 _ => format!("patterns {} not covered", joined_patterns)
441 struct_span_err!(cx.tcx.sess, sp, E0004,
442 "non-exhaustive patterns: {} not covered",
444 ).span_label(sp, &label_text).emit();
449 // This is good, wildcard pattern isn't reachable
455 fn const_val_to_expr(value: &ConstVal) -> P<hir::Expr> {
456 let node = match value {
457 &ConstVal::Bool(b) => ast::LitKind::Bool(b),
462 node: hir::ExprLit(P(Spanned { node: node, span: DUMMY_SP })),
464 attrs: ast::ThinVec::new(),
468 struct StaticInliner<'a, 'tcx: 'a> {
469 tcx: TyCtxt<'a, 'tcx, 'tcx>,
473 impl<'a, 'tcx> StaticInliner<'a, 'tcx> {
474 pub fn new<'b>(tcx: TyCtxt<'b, 'tcx, 'tcx>) -> StaticInliner<'b, 'tcx> {
482 impl<'a, 'tcx> StaticInliner<'a, 'tcx> {
483 fn fold_pat(&mut self, pat: P<Pat>) -> P<Pat> {
485 PatKind::Path(..) => {
486 match self.tcx.expect_def(pat.id) {
487 Def::AssociatedConst(did) | Def::Const(did) => {
488 let substs = Some(self.tcx.node_id_item_substs(pat.id).substs);
489 if let Some((const_expr, _)) = lookup_const_by_id(self.tcx, did, substs) {
490 match const_expr_to_pat(self.tcx, const_expr, pat.id, pat.span) {
491 Ok(new_pat) => return new_pat,
494 self.tcx.sess.span_err(
496 &format!("constants of the type `{}` \
497 cannot be used in patterns",
498 self.tcx.item_path_str(def_id)));
503 span_err!(self.tcx.sess, pat.span, E0158,
504 "statics cannot be referenced in patterns");
513 pat.map(|Pat { id, node, span }| {
514 let node = match node {
515 PatKind::Binding(binding_mode, pth1, sub) => {
516 PatKind::Binding(binding_mode, pth1, sub.map(|x| self.fold_pat(x)))
518 PatKind::TupleStruct(pth, pats, ddpos) => {
519 PatKind::TupleStruct(pth, pats.move_map(|x| self.fold_pat(x)), ddpos)
521 PatKind::Struct(pth, fields, etc) => {
522 let fs = fields.move_map(|f| {
525 node: hir::FieldPat {
527 pat: self.fold_pat(f.node.pat),
528 is_shorthand: f.node.is_shorthand,
532 PatKind::Struct(pth, fs, etc)
534 PatKind::Tuple(elts, ddpos) => {
535 PatKind::Tuple(elts.move_map(|x| self.fold_pat(x)), ddpos)
537 PatKind::Box(inner) => PatKind::Box(self.fold_pat(inner)),
538 PatKind::Ref(inner, mutbl) => PatKind::Ref(self.fold_pat(inner), mutbl),
539 PatKind::Vec(before, slice, after) => {
540 PatKind::Vec(before.move_map(|x| self.fold_pat(x)),
541 slice.map(|x| self.fold_pat(x)),
542 after.move_map(|x| self.fold_pat(x)))
547 PatKind::Path(..) => node
558 /// Constructs a partial witness for a pattern given a list of
559 /// patterns expanded by the specialization step.
561 /// When a pattern P is discovered to be useful, this function is used bottom-up
562 /// to reconstruct a complete witness, e.g. a pattern P' that covers a subset
563 /// of values, V, where each value in that set is not covered by any previously
564 /// used patterns and is covered by the pattern P'. Examples:
566 /// left_ty: tuple of 3 elements
567 /// pats: [10, 20, _] => (10, 20, _)
569 /// left_ty: struct X { a: (bool, &'static str), b: usize}
570 /// pats: [(false, "foo"), 42] => X { a: (false, "foo"), b: 42 }
571 fn construct_witness<'a,'tcx>(cx: &MatchCheckCtxt<'a,'tcx>, ctor: &Constructor,
572 pats: Vec<&Pat>, left_ty: Ty<'tcx>) -> P<Pat> {
573 let pats_len = pats.len();
574 let mut pats = pats.into_iter().map(|p| P((*p).clone()));
575 let pat = match left_ty.sty {
576 ty::TyTuple(..) => PatKind::Tuple(pats.collect(), None),
578 ty::TyAdt(adt, _) => {
579 let v = ctor.variant_for_adt(adt);
581 ty::VariantKind::Struct => {
582 let field_pats: hir::HirVec<_> = v.fields.iter()
584 .filter(|&(_, ref pat)| pat.node != PatKind::Wild)
585 .map(|(field, pat)| Spanned {
587 node: hir::FieldPat {
593 let has_more_fields = field_pats.len() < pats_len;
594 PatKind::Struct(def_to_path(cx.tcx, v.did), field_pats, has_more_fields)
596 ty::VariantKind::Tuple => {
597 PatKind::TupleStruct(def_to_path(cx.tcx, v.did), pats.collect(), None)
599 ty::VariantKind::Unit => {
600 PatKind::Path(None, def_to_path(cx.tcx, v.did))
605 ty::TyRef(_, ty::TypeAndMut { mutbl, .. }) => {
606 assert_eq!(pats_len, 1);
607 PatKind::Ref(pats.nth(0).unwrap(), mutbl)
610 ty::TySlice(_) => match ctor {
612 assert_eq!(pats_len, n);
613 PatKind::Slice(pats.collect(), None, hir::HirVec::new())
618 ty::TyArray(_, len) => {
619 assert_eq!(pats_len, len);
620 PatKind::Slice(pats.collect(), None, hir::HirVec::new())
625 ConstantValue(ref v) => PatKind::Lit(const_val_to_expr(v)),
639 fn variant_for_adt<'tcx, 'container, 'a>(&self,
640 adt: &'a ty::AdtDefData<'tcx, 'container>)
641 -> &'a ty::VariantDefData<'tcx, 'container> {
643 &Variant(vid) => adt.variant_with_id(vid),
644 _ => adt.struct_variant()
649 fn missing_constructors(cx: &MatchCheckCtxt, &Matrix(ref rows): &Matrix,
650 left_ty: Ty, max_slice_length: usize) -> Vec<Constructor> {
651 let used_constructors: Vec<Constructor> = rows.iter()
652 .flat_map(|row| pat_constructors(cx, row[0].0, left_ty, max_slice_length))
654 all_constructors(cx, left_ty, max_slice_length)
656 .filter(|c| !used_constructors.contains(c))
660 /// This determines the set of all possible constructors of a pattern matching
661 /// values of type `left_ty`. For vectors, this would normally be an infinite set
662 /// but is instead bounded by the maximum fixed length of slice patterns in
663 /// the column of patterns being analyzed.
664 fn all_constructors(_cx: &MatchCheckCtxt, left_ty: Ty,
665 max_slice_length: usize) -> Vec<Constructor> {
668 [true, false].iter().map(|b| ConstantValue(ConstVal::Bool(*b))).collect(),
670 (0..max_slice_length+1).map(|length| Slice(length)).collect(),
671 ty::TyAdt(def, _) if def.is_enum() =>
672 def.variants.iter().map(|v| Variant(v.did)).collect(),
677 // Algorithm from http://moscova.inria.fr/~maranget/papers/warn/index.html
679 // Whether a vector `v` of patterns is 'useful' in relation to a set of such
680 // vectors `m` is defined as there being a set of inputs that will match `v`
681 // but not any of the sets in `m`.
683 // This is used both for reachability checking (if a pattern isn't useful in
684 // relation to preceding patterns, it is not reachable) and exhaustiveness
685 // checking (if a wildcard pattern is useful in relation to a matrix, the
686 // matrix isn't exhaustive).
688 // Note: is_useful doesn't work on empty types, as the paper notes.
689 // So it assumes that v is non-empty.
690 fn is_useful<'a, 'tcx>(cx: &MatchCheckCtxt<'a, 'tcx>,
691 matrix: &Matrix<'a, 'tcx>,
692 v: &[(&Pat, Option<Ty<'tcx>>)],
693 witness: WitnessPreference)
695 let &Matrix(ref rows) = matrix;
696 debug!("is_useful({:?}, {:?})", matrix, v);
698 return match witness {
699 ConstructWitness => UsefulWithWitness(vec!()),
700 LeaveOutWitness => Useful
703 if rows[0].is_empty() {
706 assert!(rows.iter().all(|r| r.len() == v.len()));
707 let left_ty = match rows.iter().filter_map(|r| r[0].1).next().or_else(|| v[0].1) {
710 // all patterns are wildcards - we can pick any type we want
715 let max_slice_length = rows.iter().filter_map(|row| match row[0].0.node {
716 PatKind::Slice(ref before, _, ref after) => Some(before.len() + after.len()),
718 }).max().map_or(0, |v| v + 1);
720 let constructors = pat_constructors(cx, v[0].0, left_ty, max_slice_length);
721 debug!("is_useful - pat_constructors = {:?} left_ty = {:?}", constructors,
723 if constructors.is_empty() {
724 let constructors = missing_constructors(cx, matrix, left_ty, max_slice_length);
725 debug!("is_useful - missing_constructors = {:?}", constructors);
726 if constructors.is_empty() {
727 all_constructors(cx, left_ty, max_slice_length).into_iter().map(|c| {
728 match is_useful_specialized(cx, matrix, v, c.clone(), left_ty, witness) {
729 UsefulWithWitness(pats) => UsefulWithWitness({
730 let arity = constructor_arity(cx, &c, left_ty);
732 let pat_slice = &pats[..];
733 let subpats: Vec<_> = (0..arity).map(|i| {
734 pat_slice.get(i).map_or(DUMMY_WILD_PAT, |p| &**p)
736 vec![construct_witness(cx, &c, subpats, left_ty)]
738 result.extend(pats.into_iter().skip(arity));
743 }).find(|result| result != &NotUseful).unwrap_or(NotUseful)
745 let matrix = rows.iter().filter_map(|r| {
746 match raw_pat(r[0].0).node {
747 PatKind::Binding(..) | PatKind::Wild => Some(r[1..].to_vec()),
751 match is_useful(cx, &matrix, &v[1..], witness) {
752 UsefulWithWitness(pats) => {
753 let mut new_pats: Vec<_> = constructors.into_iter().map(|constructor| {
754 let arity = constructor_arity(cx, &constructor, left_ty);
755 let wild_pats = vec![DUMMY_WILD_PAT; arity];
756 construct_witness(cx, &constructor, wild_pats, left_ty)
758 new_pats.extend(pats);
759 UsefulWithWitness(new_pats)
765 constructors.into_iter().map(|c|
766 is_useful_specialized(cx, matrix, v, c.clone(), left_ty, witness)
767 ).find(|result| result != &NotUseful).unwrap_or(NotUseful)
771 fn is_useful_specialized<'a, 'tcx>(
772 cx: &MatchCheckCtxt<'a, 'tcx>,
773 &Matrix(ref m): &Matrix<'a, 'tcx>,
774 v: &[(&Pat, Option<Ty<'tcx>>)],
777 witness: WitnessPreference) -> Usefulness
779 let arity = constructor_arity(cx, &ctor, lty);
780 let matrix = Matrix(m.iter().filter_map(|r| {
781 specialize(cx, &r[..], &ctor, 0, arity)
783 match specialize(cx, v, &ctor, 0, arity) {
784 Some(v) => is_useful(cx, &matrix, &v[..], witness),
789 /// Determines the constructors that the given pattern can be specialized to.
791 /// In most cases, there's only one constructor that a specific pattern
792 /// represents, such as a specific enum variant or a specific literal value.
793 /// Slice patterns, however, can match slices of different lengths. For instance,
794 /// `[a, b, ..tail]` can match a slice of length 2, 3, 4 and so on.
796 /// On the other hand, a wild pattern and an identifier pattern cannot be
797 /// specialized in any way.
798 fn pat_constructors(cx: &MatchCheckCtxt, p: &Pat,
799 left_ty: Ty, max_slice_length: usize) -> Vec<Constructor> {
800 let pat = raw_pat(p);
802 PatKind::Struct(..) | PatKind::TupleStruct(..) | PatKind::Path(..) =>
803 match cx.tcx.expect_def(pat.id) {
804 Def::Variant(id) => vec![Variant(id)],
805 Def::Struct(..) | Def::Union(..) |
806 Def::TyAlias(..) | Def::AssociatedTy(..) => vec![Single],
807 Def::Const(..) | Def::AssociatedConst(..) =>
808 span_bug!(pat.span, "const pattern should've been rewritten"),
809 def => span_bug!(pat.span, "pat_constructors: unexpected definition {:?}", def),
811 PatKind::Lit(ref expr) =>
812 vec![ConstantValue(eval_const_expr(cx.tcx, &expr))],
813 PatKind::Range(ref lo, ref hi) =>
814 vec![ConstantRange(eval_const_expr(cx.tcx, &lo), eval_const_expr(cx.tcx, &hi))],
815 PatKind::Slice(ref before, ref slice, ref after) =>
817 ty::TyArray(..) => vec![Single],
818 ty::TySlice(_) if slice.is_some() => {
819 (before.len() + after.len()..max_slice_length+1)
820 .map(|length| Slice(length))
823 ty::TySlice(_) => vec!(Slice(before.len() + after.len())),
824 _ => span_bug!(pat.span, "pat_constructors: unexpected \
825 slice pattern type {:?}", left_ty)
827 PatKind::Box(..) | PatKind::Tuple(..) | PatKind::Ref(..) =>
829 PatKind::Binding(..) | PatKind::Wild =>
834 /// This computes the arity of a constructor. The arity of a constructor
835 /// is how many subpattern patterns of that constructor should be expanded to.
837 /// For instance, a tuple pattern (_, 42, Some([])) has the arity of 3.
838 /// A struct pattern's arity is the number of fields it contains, etc.
839 pub fn constructor_arity(_cx: &MatchCheckCtxt, ctor: &Constructor, ty: Ty) -> usize {
840 debug!("constructor_arity({:?}, {:?})", ctor, ty);
842 ty::TyTuple(ref fs) => fs.len(),
844 ty::TySlice(_) => match *ctor {
845 Slice(length) => length,
846 ConstantValue(_) => 0,
850 ty::TyAdt(adt, _) => {
851 ctor.variant_for_adt(adt).fields.len()
853 ty::TyArray(_, n) => n,
858 fn range_covered_by_constructor(tcx: TyCtxt, span: Span,
860 from: &ConstVal, to: &ConstVal)
861 -> Result<bool, ErrorReported> {
862 let (c_from, c_to) = match *ctor {
863 ConstantValue(ref value) => (value, value),
864 ConstantRange(ref from, ref to) => (from, to),
865 Single => return Ok(true),
868 let cmp_from = compare_const_vals(tcx, span, c_from, from)?;
869 let cmp_to = compare_const_vals(tcx, span, c_to, to)?;
870 Ok(cmp_from != Ordering::Less && cmp_to != Ordering::Greater)
873 fn wrap_pat<'a, 'b, 'tcx>(cx: &MatchCheckCtxt<'b, 'tcx>,
875 -> (&'a Pat, Option<Ty<'tcx>>)
877 let pat_ty = cx.tcx.pat_ty(pat);
878 (pat, Some(match pat.node {
879 PatKind::Binding(hir::BindByRef(..), ..) => {
880 pat_ty.builtin_deref(false, ty::NoPreference).unwrap().ty
886 /// This is the main specialization step. It expands the first pattern in the given row
887 /// into `arity` patterns based on the constructor. For most patterns, the step is trivial,
888 /// for instance tuple patterns are flattened and box patterns expand into their inner pattern.
890 /// OTOH, slice patterns with a subslice pattern (..tail) can be expanded into multiple
891 /// different patterns.
892 /// Structure patterns with a partial wild pattern (Foo { a: 42, .. }) have their missing
893 /// fields filled with wild patterns.
894 pub fn specialize<'a, 'b, 'tcx>(
895 cx: &MatchCheckCtxt<'b, 'tcx>,
896 r: &[(&'a Pat, Option<Ty<'tcx>>)],
897 constructor: &Constructor, col: usize, arity: usize)
898 -> Option<Vec<(&'a Pat, Option<Ty<'tcx>>)>>
900 let pat = raw_pat(r[col].0);
902 id: pat_id, ref node, span: pat_span
904 let wpat = |pat: &'a Pat| wrap_pat(cx, pat);
905 let dummy_pat = (DUMMY_WILD_PAT, None);
907 let head: Option<Vec<(&Pat, Option<Ty>)>> = match *node {
908 PatKind::Binding(..) | PatKind::Wild =>
909 Some(vec![dummy_pat; arity]),
911 PatKind::Path(..) => {
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(..) => Some(Vec::new()),
918 def => span_bug!(pat_span, "specialize: unexpected \
919 definition {:?}", def),
923 PatKind::TupleStruct(_, ref args, ddpos) => {
924 match cx.tcx.expect_def(pat_id) {
925 Def::Const(..) | Def::AssociatedConst(..) =>
926 span_bug!(pat_span, "const pattern should've \
928 Def::Variant(id) if *constructor != Variant(id) => None,
929 Def::Variant(..) | Def::Struct(..) => {
932 let mut pats: Vec<_> = args[..ddpos].iter().map(|p| {
935 pats.extend(repeat((DUMMY_WILD_PAT, None)).take(arity - args.len()));
936 pats.extend(args[ddpos..].iter().map(|p| wpat(p)));
939 None => Some(args.iter().map(|p| wpat(p)).collect())
946 PatKind::Struct(_, ref pattern_fields, _) => {
947 let adt = cx.tcx.node_id_to_type(pat_id).ty_adt_def().unwrap();
948 let variant = constructor.variant_for_adt(adt);
949 let def_variant = adt.variant_of_def(cx.tcx.expect_def(pat_id));
950 if variant.did == def_variant.did {
951 Some(variant.fields.iter().map(|sf| {
952 match pattern_fields.iter().find(|f| f.node.name == sf.name) {
953 Some(ref f) => wpat(&f.node.pat),
962 PatKind::Tuple(ref args, Some(ddpos)) => {
963 let mut pats: Vec<_> = args[..ddpos].iter().map(|p| wpat(p)).collect();
964 pats.extend(repeat(dummy_pat).take(arity - args.len()));
965 pats.extend(args[ddpos..].iter().map(|p| wpat(p)));
968 PatKind::Tuple(ref args, None) =>
969 Some(args.iter().map(|p| wpat(&**p)).collect()),
971 PatKind::Box(ref inner) | PatKind::Ref(ref inner, _) =>
972 Some(vec![wpat(&**inner)]),
974 PatKind::Lit(ref expr) => {
975 if let Some(&ty::TyS { sty: ty::TyRef(_, mt), .. }) = r[col].1 {
976 // HACK: handle string literals. A string literal pattern
977 // serves both as an unary reference pattern and as a
978 // nullary value pattern, depending on the type.
979 Some(vec![(pat, Some(mt.ty))])
981 let expr_value = eval_const_expr(cx.tcx, &expr);
982 match range_covered_by_constructor(
983 cx.tcx, expr.span, constructor, &expr_value, &expr_value
985 Ok(true) => Some(vec![]),
987 Err(ErrorReported) => None,
992 PatKind::Range(ref from, ref to) => {
993 let from_value = eval_const_expr(cx.tcx, &from);
994 let to_value = eval_const_expr(cx.tcx, &to);
995 match range_covered_by_constructor(
996 cx.tcx, pat_span, constructor, &from_value, &to_value
998 Ok(true) => Some(vec![]),
1000 Err(ErrorReported) => None,
1004 PatKind::Slice(ref before, ref slice, ref after) => {
1005 let pat_len = before.len() + after.len();
1006 match *constructor {
1008 // Fixed-length vectors.
1010 before.iter().map(|p| wpat(p)).chain(
1011 repeat(dummy_pat).take(arity - pat_len).chain(
1012 after.iter().map(|p| wpat(p))
1015 Slice(length) if pat_len <= length && slice.is_some() => {
1017 before.iter().map(|p| wpat(p)).chain(
1018 repeat(dummy_pat).take(arity - pat_len).chain(
1019 after.iter().map(|p| wpat(p))
1022 Slice(length) if pat_len == length => {
1024 before.iter().map(|p| wpat(p)).chain(
1025 after.iter().map(|p| wpat(p))
1028 SliceWithSubslice(prefix, suffix)
1029 if before.len() == prefix
1030 && after.len() == suffix
1031 && slice.is_some() => {
1032 // this is used by trans::_match only
1033 let mut pats: Vec<_> = before.iter()
1034 .map(|p| (&**p, None)).collect();
1035 pats.extend(after.iter().map(|p| (&**p, None)));
1042 debug!("specialize({:?}, {:?}) = {:?}", r[col], arity, head);
1044 head.map(|mut head| {
1045 head.extend_from_slice(&r[..col]);
1046 head.extend_from_slice(&r[col + 1..]);
1051 fn check_local(cx: &mut MatchCheckCtxt, loc: &hir::Local) {
1052 intravisit::walk_local(cx, loc);
1054 let pat = StaticInliner::new(cx.tcx).fold_pat(loc.pat.clone());
1055 check_irrefutable(cx, &pat, false);
1057 // Check legality of move bindings and `@` patterns.
1058 check_legality_of_move_bindings(cx, false, slice::ref_slice(&loc.pat));
1059 check_legality_of_bindings_in_at_patterns(cx, &loc.pat);
1062 fn check_fn(cx: &mut MatchCheckCtxt,
1069 FnKind::Closure(_) => {}
1070 _ => cx.param_env = ty::ParameterEnvironment::for_item(cx.tcx, fn_id),
1073 intravisit::walk_fn(cx, kind, decl, body, sp, fn_id);
1075 for input in &decl.inputs {
1076 check_irrefutable(cx, &input.pat, true);
1077 check_legality_of_move_bindings(cx, false, slice::ref_slice(&input.pat));
1078 check_legality_of_bindings_in_at_patterns(cx, &input.pat);
1082 fn check_irrefutable(cx: &MatchCheckCtxt, pat: &Pat, is_fn_arg: bool) {
1083 let origin = if is_fn_arg {
1089 is_refutable(cx, pat, |uncovered_pat| {
1090 let pattern_string = pat_to_string(uncovered_pat);
1091 struct_span_err!(cx.tcx.sess, pat.span, E0005,
1092 "refutable pattern in {}: `{}` not covered",
1095 ).span_label(pat.span, &format!("pattern `{}` not covered", pattern_string)).emit();
1099 fn is_refutable<A, F>(cx: &MatchCheckCtxt, pat: &Pat, refutable: F) -> Option<A> where
1100 F: FnOnce(&Pat) -> A,
1102 let pats = Matrix(vec!(vec!(wrap_pat(cx, pat))));
1103 match is_useful(cx, &pats, &[(DUMMY_WILD_PAT, None)], ConstructWitness) {
1104 UsefulWithWitness(pats) => Some(refutable(&pats[0])),
1110 // Legality of move bindings checking
1111 fn check_legality_of_move_bindings(cx: &MatchCheckCtxt,
1114 let mut by_ref_span = None;
1116 pat_bindings(&pat, |bm, _, span, _path| {
1117 if let hir::BindByRef(..) = bm {
1118 by_ref_span = Some(span);
1123 let check_move = |p: &Pat, sub: Option<&Pat>| {
1124 // check legality of moving out of the enum
1126 // x @ Foo(..) is legal, but x @ Foo(y) isn't.
1127 if sub.map_or(false, |p| pat_contains_bindings(&p)) {
1128 struct_span_err!(cx.tcx.sess, p.span, E0007,
1129 "cannot bind by-move with sub-bindings")
1130 .span_label(p.span, &format!("binds an already bound by-move value by moving it"))
1132 } else if has_guard {
1133 struct_span_err!(cx.tcx.sess, p.span, E0008,
1134 "cannot bind by-move into a pattern guard")
1135 .span_label(p.span, &format!("moves value into pattern guard"))
1137 } else if by_ref_span.is_some() {
1138 struct_span_err!(cx.tcx.sess, p.span, E0009,
1139 "cannot bind by-move and by-ref in the same pattern")
1140 .span_label(p.span, &format!("by-move pattern here"))
1141 .span_label(by_ref_span.unwrap(), &format!("both by-ref and by-move used"))
1148 if let PatKind::Binding(hir::BindByValue(..), _, ref sub) = p.node {
1149 let pat_ty = cx.tcx.node_id_to_type(p.id);
1150 //FIXME: (@jroesch) this code should be floated up as well
1151 cx.tcx.infer_ctxt(None, Some(cx.param_env.clone()),
1152 Reveal::NotSpecializable).enter(|infcx| {
1153 if infcx.type_moves_by_default(pat_ty, pat.span) {
1154 check_move(p, sub.as_ref().map(|p| &**p));
1163 /// Ensures that a pattern guard doesn't borrow by mutable reference or
1165 fn check_for_mutation_in_guard<'a, 'tcx>(cx: &'a MatchCheckCtxt<'a, 'tcx>,
1166 guard: &hir::Expr) {
1167 cx.tcx.infer_ctxt(None, Some(cx.param_env.clone()),
1168 Reveal::NotSpecializable).enter(|infcx| {
1169 let mut checker = MutationChecker {
1172 let mut visitor = ExprUseVisitor::new(&mut checker, &infcx);
1173 visitor.walk_expr(guard);
1177 struct MutationChecker<'a, 'gcx: 'a> {
1178 cx: &'a MatchCheckCtxt<'a, 'gcx>,
1181 impl<'a, 'gcx, 'tcx> Delegate<'tcx> for MutationChecker<'a, 'gcx> {
1182 fn matched_pat(&mut self, _: &Pat, _: cmt, _: euv::MatchMode) {}
1183 fn consume(&mut self, _: NodeId, _: Span, _: cmt, _: ConsumeMode) {}
1184 fn consume_pat(&mut self, _: &Pat, _: cmt, _: ConsumeMode) {}
1185 fn borrow(&mut self,
1189 _: &'tcx ty::Region,
1190 kind:ty:: BorrowKind,
1194 struct_span_err!(self.cx.tcx.sess, span, E0301,
1195 "cannot mutably borrow in a pattern guard")
1196 .span_label(span, &format!("borrowed mutably in pattern guard"))
1199 ty::ImmBorrow | ty::UniqueImmBorrow => {}
1202 fn decl_without_init(&mut self, _: NodeId, _: Span) {}
1203 fn mutate(&mut self, _: NodeId, span: Span, _: cmt, mode: MutateMode) {
1205 MutateMode::JustWrite | MutateMode::WriteAndRead => {
1206 struct_span_err!(self.cx.tcx.sess, span, E0302, "cannot assign in a pattern guard")
1207 .span_label(span, &format!("assignment in pattern guard"))
1210 MutateMode::Init => {}
1215 /// Forbids bindings in `@` patterns. This is necessary for memory safety,
1216 /// because of the way rvalues are handled in the borrow check. (See issue
1218 fn check_legality_of_bindings_in_at_patterns(cx: &MatchCheckCtxt, pat: &Pat) {
1219 AtBindingPatternVisitor { cx: cx, bindings_allowed: true }.visit_pat(pat);
1222 struct AtBindingPatternVisitor<'a, 'b:'a, 'tcx:'b> {
1223 cx: &'a MatchCheckCtxt<'b, 'tcx>,
1224 bindings_allowed: bool
1227 impl<'a, 'b, 'tcx, 'v> Visitor<'v> for AtBindingPatternVisitor<'a, 'b, 'tcx> {
1228 fn visit_pat(&mut self, pat: &Pat) {
1230 PatKind::Binding(.., ref subpat) => {
1231 if !self.bindings_allowed {
1232 span_err!(self.cx.tcx.sess, pat.span, E0303,
1233 "pattern bindings are not allowed after an `@`");
1236 if subpat.is_some() {
1237 let bindings_were_allowed = self.bindings_allowed;
1238 self.bindings_allowed = false;
1239 intravisit::walk_pat(self, pat);
1240 self.bindings_allowed = bindings_were_allowed;
1243 _ => intravisit::walk_pat(self, pat),