| // Copyright 2012-2016 The Rust Project Developers. See the COPYRIGHT |
| // file at the top-level directory of this distribution and at |
| // http://rust-lang.org/COPYRIGHT. |
| // |
| // Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or |
| // http://www.apache.org/licenses/LICENSE-2.0> or the MIT license |
| // <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your |
| // option. This file may not be copied, modified, or distributed |
| // except according to those terms. |
| |
| use self::Constructor::*; |
| use self::Usefulness::*; |
| use self::WitnessPreference::*; |
| |
| use rustc::middle::const_val::ConstVal; |
| use eval::{compare_const_vals}; |
| |
| use rustc_const_math::ConstInt; |
| |
| use rustc_data_structures::fx::FxHashMap; |
| use rustc_data_structures::indexed_vec::Idx; |
| |
| use pattern::{FieldPattern, Pattern, PatternKind}; |
| use pattern::{PatternFoldable, PatternFolder}; |
| |
| use rustc::hir::def_id::DefId; |
| use rustc::hir::RangeEnd; |
| use rustc::ty::{self, Ty, TyCtxt, TypeFoldable}; |
| |
| use rustc::mir::Field; |
| use rustc::util::common::ErrorReported; |
| |
| use syntax_pos::{Span, DUMMY_SP}; |
| |
| use arena::TypedArena; |
| |
| use std::cmp::{self, Ordering}; |
| use std::fmt; |
| use std::iter::{FromIterator, IntoIterator, repeat}; |
| |
| pub fn expand_pattern<'a, 'tcx>(cx: &MatchCheckCtxt<'a, 'tcx>, pat: Pattern<'tcx>) |
| -> &'a Pattern<'tcx> |
| { |
| cx.pattern_arena.alloc(LiteralExpander.fold_pattern(&pat)) |
| } |
| |
| struct LiteralExpander; |
| impl<'tcx> PatternFolder<'tcx> for LiteralExpander { |
| fn fold_pattern(&mut self, pat: &Pattern<'tcx>) -> Pattern<'tcx> { |
| match (&pat.ty.sty, &*pat.kind) { |
| (&ty::TyRef(_, mt), &PatternKind::Constant { ref value }) => { |
| Pattern { |
| ty: pat.ty, |
| span: pat.span, |
| kind: box PatternKind::Deref { |
| subpattern: Pattern { |
| ty: mt.ty, |
| span: pat.span, |
| kind: box PatternKind::Constant { value: value.clone() }, |
| } |
| } |
| } |
| } |
| (_, &PatternKind::Binding { subpattern: Some(ref s), .. }) => { |
| s.fold_with(self) |
| } |
| _ => pat.super_fold_with(self) |
| } |
| } |
| } |
| |
| impl<'tcx> Pattern<'tcx> { |
| fn is_wildcard(&self) -> bool { |
| match *self.kind { |
| PatternKind::Binding { subpattern: None, .. } | PatternKind::Wild => |
| true, |
| _ => false |
| } |
| } |
| } |
| |
| pub struct Matrix<'a, 'tcx: 'a>(Vec<Vec<&'a Pattern<'tcx>>>); |
| |
| impl<'a, 'tcx> Matrix<'a, 'tcx> { |
| pub fn empty() -> Self { |
| Matrix(vec![]) |
| } |
| |
| pub fn push(&mut self, row: Vec<&'a Pattern<'tcx>>) { |
| self.0.push(row) |
| } |
| } |
| |
| /// Pretty-printer for matrices of patterns, example: |
| /// ++++++++++++++++++++++++++ |
| /// + _ + [] + |
| /// ++++++++++++++++++++++++++ |
| /// + true + [First] + |
| /// ++++++++++++++++++++++++++ |
| /// + true + [Second(true)] + |
| /// ++++++++++++++++++++++++++ |
| /// + false + [_] + |
| /// ++++++++++++++++++++++++++ |
| /// + _ + [_, _, ..tail] + |
| /// ++++++++++++++++++++++++++ |
| impl<'a, 'tcx> fmt::Debug for Matrix<'a, 'tcx> { |
| fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result { |
| write!(f, "\n")?; |
| |
| let &Matrix(ref m) = self; |
| let pretty_printed_matrix: Vec<Vec<String>> = m.iter().map(|row| { |
| row.iter().map(|pat| format!("{:?}", pat)).collect() |
| }).collect(); |
| |
| let column_count = m.iter().map(|row| row.len()).max().unwrap_or(0); |
| assert!(m.iter().all(|row| row.len() == column_count)); |
| let column_widths: Vec<usize> = (0..column_count).map(|col| { |
| pretty_printed_matrix.iter().map(|row| row[col].len()).max().unwrap_or(0) |
| }).collect(); |
| |
| let total_width = column_widths.iter().cloned().sum::<usize>() + column_count * 3 + 1; |
| let br = repeat('+').take(total_width).collect::<String>(); |
| write!(f, "{}\n", br)?; |
| for row in pretty_printed_matrix { |
| write!(f, "+")?; |
| for (column, pat_str) in row.into_iter().enumerate() { |
| write!(f, " ")?; |
| write!(f, "{:1$}", pat_str, column_widths[column])?; |
| write!(f, " +")?; |
| } |
| write!(f, "\n")?; |
| write!(f, "{}\n", br)?; |
| } |
| Ok(()) |
| } |
| } |
| |
| impl<'a, 'tcx> FromIterator<Vec<&'a Pattern<'tcx>>> for Matrix<'a, 'tcx> { |
| fn from_iter<T: IntoIterator<Item=Vec<&'a Pattern<'tcx>>>>(iter: T) -> Self |
| { |
| Matrix(iter.into_iter().collect()) |
| } |
| } |
| |
| //NOTE: appears to be the only place other then InferCtxt to contain a ParamEnv |
| pub struct MatchCheckCtxt<'a, 'tcx: 'a> { |
| pub tcx: TyCtxt<'a, 'tcx, 'tcx>, |
| /// The module in which the match occurs. This is necessary for |
| /// checking inhabited-ness of types because whether a type is (visibly) |
| /// inhabited can depend on whether it was defined in the current module or |
| /// not. eg. `struct Foo { _private: ! }` cannot be seen to be empty |
| /// outside it's module and should not be matchable with an empty match |
| /// statement. |
| pub module: DefId, |
| pub pattern_arena: &'a TypedArena<Pattern<'tcx>>, |
| pub byte_array_map: FxHashMap<*const Pattern<'tcx>, Vec<&'a Pattern<'tcx>>>, |
| } |
| |
| impl<'a, 'tcx> MatchCheckCtxt<'a, 'tcx> { |
| pub fn create_and_enter<F, R>( |
| tcx: TyCtxt<'a, 'tcx, 'tcx>, |
| module: DefId, |
| f: F) -> R |
| where F: for<'b> FnOnce(MatchCheckCtxt<'b, 'tcx>) -> R |
| { |
| let pattern_arena = TypedArena::new(); |
| |
| f(MatchCheckCtxt { |
| tcx, |
| module, |
| pattern_arena: &pattern_arena, |
| byte_array_map: FxHashMap(), |
| }) |
| } |
| |
| // convert a byte-string pattern to a list of u8 patterns. |
| fn lower_byte_str_pattern<'p>(&mut self, pat: &'p Pattern<'tcx>) -> Vec<&'p Pattern<'tcx>> |
| where 'a: 'p |
| { |
| let pattern_arena = &*self.pattern_arena; |
| let tcx = self.tcx; |
| self.byte_array_map.entry(pat).or_insert_with(|| { |
| match pat.kind { |
| box PatternKind::Constant { |
| value: &ty::Const { val: ConstVal::ByteStr(b), .. } |
| } => { |
| b.data.iter().map(|&b| &*pattern_arena.alloc(Pattern { |
| ty: tcx.types.u8, |
| span: pat.span, |
| kind: box PatternKind::Constant { |
| value: tcx.mk_const(ty::Const { |
| val: ConstVal::Integral(ConstInt::U8(b)), |
| ty: tcx.types.u8 |
| }) |
| } |
| })).collect() |
| } |
| _ => span_bug!(pat.span, "unexpected byte array pattern {:?}", pat) |
| } |
| }).clone() |
| } |
| |
| fn is_uninhabited(&self, ty: Ty<'tcx>) -> bool { |
| if self.tcx.sess.features.borrow().never_type { |
| self.tcx.is_ty_uninhabited_from(self.module, ty) |
| } else { |
| false |
| } |
| } |
| |
| fn is_non_exhaustive_enum(&self, ty: Ty<'tcx>) -> bool { |
| match ty.sty { |
| ty::TyAdt(adt_def, ..) => adt_def.is_enum() && adt_def.is_non_exhaustive(), |
| _ => false, |
| } |
| } |
| |
| fn is_local(&self, ty: Ty<'tcx>) -> bool { |
| match ty.sty { |
| ty::TyAdt(adt_def, ..) => adt_def.did.is_local(), |
| _ => false, |
| } |
| } |
| |
| fn is_variant_uninhabited(&self, |
| variant: &'tcx ty::VariantDef, |
| substs: &'tcx ty::subst::Substs<'tcx>) |
| -> bool |
| { |
| if self.tcx.sess.features.borrow().never_type { |
| self.tcx.is_enum_variant_uninhabited_from(self.module, variant, substs) |
| } else { |
| false |
| } |
| } |
| } |
| |
| #[derive(Clone, Debug, PartialEq)] |
| pub enum Constructor<'tcx> { |
| /// The constructor of all patterns that don't vary by constructor, |
| /// e.g. struct patterns and fixed-length arrays. |
| Single, |
| /// Enum variants. |
| Variant(DefId), |
| /// Literal values. |
| ConstantValue(&'tcx ty::Const<'tcx>), |
| /// Ranges of literal values (`2...5` and `2..5`). |
| ConstantRange(&'tcx ty::Const<'tcx>, &'tcx ty::Const<'tcx>, RangeEnd), |
| /// Array patterns of length n. |
| Slice(u64), |
| } |
| |
| impl<'tcx> Constructor<'tcx> { |
| fn variant_index_for_adt(&self, adt: &'tcx ty::AdtDef) -> usize { |
| match self { |
| &Variant(vid) => adt.variant_index_with_id(vid), |
| &Single => { |
| assert!(!adt.is_enum()); |
| 0 |
| } |
| _ => bug!("bad constructor {:?} for adt {:?}", self, adt) |
| } |
| } |
| } |
| |
| #[derive(Clone)] |
| pub enum Usefulness<'tcx> { |
| Useful, |
| UsefulWithWitness(Vec<Witness<'tcx>>), |
| NotUseful |
| } |
| |
| impl<'tcx> Usefulness<'tcx> { |
| fn is_useful(&self) -> bool { |
| match *self { |
| NotUseful => false, |
| _ => true |
| } |
| } |
| } |
| |
| #[derive(Copy, Clone)] |
| pub enum WitnessPreference { |
| ConstructWitness, |
| LeaveOutWitness |
| } |
| |
| #[derive(Copy, Clone, Debug)] |
| struct PatternContext<'tcx> { |
| ty: Ty<'tcx>, |
| max_slice_length: u64, |
| } |
| |
| /// A stack of patterns in reverse order of construction |
| #[derive(Clone)] |
| pub struct Witness<'tcx>(Vec<Pattern<'tcx>>); |
| |
| impl<'tcx> Witness<'tcx> { |
| pub fn single_pattern(&self) -> &Pattern<'tcx> { |
| assert_eq!(self.0.len(), 1); |
| &self.0[0] |
| } |
| |
| fn push_wild_constructor<'a>( |
| mut self, |
| cx: &MatchCheckCtxt<'a, 'tcx>, |
| ctor: &Constructor<'tcx>, |
| ty: Ty<'tcx>) |
| -> Self |
| { |
| let sub_pattern_tys = constructor_sub_pattern_tys(cx, ctor, ty); |
| self.0.extend(sub_pattern_tys.into_iter().map(|ty| { |
| Pattern { |
| ty, |
| span: DUMMY_SP, |
| kind: box PatternKind::Wild, |
| } |
| })); |
| self.apply_constructor(cx, ctor, ty) |
| } |
| |
| |
| /// Constructs a partial witness for a pattern given a list of |
| /// patterns expanded by the specialization step. |
| /// |
| /// When a pattern P is discovered to be useful, this function is used bottom-up |
| /// to reconstruct a complete witness, e.g. a pattern P' that covers a subset |
| /// of values, V, where each value in that set is not covered by any previously |
| /// used patterns and is covered by the pattern P'. Examples: |
| /// |
| /// left_ty: tuple of 3 elements |
| /// pats: [10, 20, _] => (10, 20, _) |
| /// |
| /// left_ty: struct X { a: (bool, &'static str), b: usize} |
| /// pats: [(false, "foo"), 42] => X { a: (false, "foo"), b: 42 } |
| fn apply_constructor<'a>( |
| mut self, |
| cx: &MatchCheckCtxt<'a,'tcx>, |
| ctor: &Constructor<'tcx>, |
| ty: Ty<'tcx>) |
| -> Self |
| { |
| let arity = constructor_arity(cx, ctor, ty); |
| let pat = { |
| let len = self.0.len() as u64; |
| let mut pats = self.0.drain((len-arity) as usize..).rev(); |
| |
| match ty.sty { |
| ty::TyAdt(..) | |
| ty::TyTuple(..) => { |
| let pats = pats.enumerate().map(|(i, p)| { |
| FieldPattern { |
| field: Field::new(i), |
| pattern: p |
| } |
| }).collect(); |
| |
| if let ty::TyAdt(adt, substs) = ty.sty { |
| if adt.is_enum() { |
| PatternKind::Variant { |
| adt_def: adt, |
| substs, |
| variant_index: ctor.variant_index_for_adt(adt), |
| subpatterns: pats |
| } |
| } else { |
| PatternKind::Leaf { subpatterns: pats } |
| } |
| } else { |
| PatternKind::Leaf { subpatterns: pats } |
| } |
| } |
| |
| ty::TyRef(..) => { |
| PatternKind::Deref { subpattern: pats.nth(0).unwrap() } |
| } |
| |
| ty::TySlice(_) | ty::TyArray(..) => { |
| PatternKind::Slice { |
| prefix: pats.collect(), |
| slice: None, |
| suffix: vec![] |
| } |
| } |
| |
| _ => { |
| match *ctor { |
| ConstantValue(value) => PatternKind::Constant { value }, |
| _ => PatternKind::Wild, |
| } |
| } |
| } |
| }; |
| |
| self.0.push(Pattern { |
| ty, |
| span: DUMMY_SP, |
| kind: Box::new(pat), |
| }); |
| |
| self |
| } |
| } |
| |
| /// This determines the set of all possible constructors of a pattern matching |
| /// values of type `left_ty`. For vectors, this would normally be an infinite set |
| /// but is instead bounded by the maximum fixed length of slice patterns in |
| /// the column of patterns being analyzed. |
| /// |
| /// This intentionally does not list ConstantValue specializations for |
| /// non-booleans, because we currently assume that there is always a |
| /// "non-standard constant" that matches. See issue #12483. |
| /// |
| /// We make sure to omit constructors that are statically impossible. eg for |
| /// Option<!> we do not include Some(_) in the returned list of constructors. |
| fn all_constructors<'a, 'tcx: 'a>(cx: &mut MatchCheckCtxt<'a, 'tcx>, |
| pcx: PatternContext<'tcx>) |
| -> Vec<Constructor<'tcx>> |
| { |
| debug!("all_constructors({:?})", pcx.ty); |
| match pcx.ty.sty { |
| ty::TyBool => { |
| [true, false].iter().map(|&b| { |
| ConstantValue(cx.tcx.mk_const(ty::Const { |
| val: ConstVal::Bool(b), |
| ty: cx.tcx.types.bool |
| })) |
| }).collect() |
| } |
| ty::TyArray(ref sub_ty, len) if len.val.to_const_int().is_some() => { |
| let len = len.val.to_const_int().unwrap().to_u64().unwrap(); |
| if len != 0 && cx.is_uninhabited(sub_ty) { |
| vec![] |
| } else { |
| vec![Slice(len)] |
| } |
| } |
| // Treat arrays of a constant but unknown length like slices. |
| ty::TyArray(ref sub_ty, _) | |
| ty::TySlice(ref sub_ty) => { |
| if cx.is_uninhabited(sub_ty) { |
| vec![Slice(0)] |
| } else { |
| (0..pcx.max_slice_length+1).map(|length| Slice(length)).collect() |
| } |
| } |
| ty::TyAdt(def, substs) if def.is_enum() => { |
| def.variants.iter() |
| .filter(|v| !cx.is_variant_uninhabited(v, substs)) |
| .map(|v| Variant(v.did)) |
| .collect() |
| } |
| _ => { |
| if cx.is_uninhabited(pcx.ty) { |
| vec![] |
| } else { |
| vec![Single] |
| } |
| } |
| } |
| } |
| |
| fn max_slice_length<'p, 'a: 'p, 'tcx: 'a, I>( |
| _cx: &mut MatchCheckCtxt<'a, 'tcx>, |
| patterns: I) -> u64 |
| where I: Iterator<Item=&'p Pattern<'tcx>> |
| { |
| // The exhaustiveness-checking paper does not include any details on |
| // checking variable-length slice patterns. However, they are matched |
| // by an infinite collection of fixed-length array patterns. |
| // |
| // Checking the infinite set directly would take an infinite amount |
| // of time. However, it turns out that for each finite set of |
| // patterns `P`, all sufficiently large array lengths are equivalent: |
| // |
| // Each slice `s` with a "sufficiently-large" length `l ≥ L` that applies |
| // to exactly the subset `Pₜ` of `P` can be transformed to a slice |
| // `sₘ` for each sufficiently-large length `m` that applies to exactly |
| // the same subset of `P`. |
| // |
| // Because of that, each witness for reachability-checking from one |
| // of the sufficiently-large lengths can be transformed to an |
| // equally-valid witness from any other length, so we only have |
| // to check slice lengths from the "minimal sufficiently-large length" |
| // and below. |
| // |
| // Note that the fact that there is a *single* `sₘ` for each `m` |
| // not depending on the specific pattern in `P` is important: if |
| // you look at the pair of patterns |
| // `[true, ..]` |
| // `[.., false]` |
| // Then any slice of length ≥1 that matches one of these two |
| // patterns can be be trivially turned to a slice of any |
| // other length ≥1 that matches them and vice-versa - for |
| // but the slice from length 2 `[false, true]` that matches neither |
| // of these patterns can't be turned to a slice from length 1 that |
| // matches neither of these patterns, so we have to consider |
| // slices from length 2 there. |
| // |
| // Now, to see that that length exists and find it, observe that slice |
| // patterns are either "fixed-length" patterns (`[_, _, _]`) or |
| // "variable-length" patterns (`[_, .., _]`). |
| // |
| // For fixed-length patterns, all slices with lengths *longer* than |
| // the pattern's length have the same outcome (of not matching), so |
| // as long as `L` is greater than the pattern's length we can pick |
| // any `sₘ` from that length and get the same result. |
| // |
| // For variable-length patterns, the situation is more complicated, |
| // because as seen above the precise value of `sₘ` matters. |
| // |
| // However, for each variable-length pattern `p` with a prefix of length |
| // `plâ‚š` and suffix of length `slâ‚š`, only the first `plâ‚š` and the last |
| // `slâ‚š` elements are examined. |
| // |
| // Therefore, as long as `L` is positive (to avoid concerns about empty |
| // types), all elements after the maximum prefix length and before |
| // the maximum suffix length are not examined by any variable-length |
| // pattern, and therefore can be added/removed without affecting |
| // them - creating equivalent patterns from any sufficiently-large |
| // length. |
| // |
| // Of course, if fixed-length patterns exist, we must be sure |
| // that our length is large enough to miss them all, so |
| // we can pick `L = max(FIXED_LEN+1 ∪ {max(PREFIX_LEN) + max(SUFFIX_LEN)})` |
| // |
| // for example, with the above pair of patterns, all elements |
| // but the first and last can be added/removed, so any |
| // witness of length ≥2 (say, `[false, false, true]`) can be |
| // turned to a witness from any other length ≥2. |
| |
| let mut max_prefix_len = 0; |
| let mut max_suffix_len = 0; |
| let mut max_fixed_len = 0; |
| |
| for row in patterns { |
| match *row.kind { |
| PatternKind::Constant { value: &ty::Const { val: ConstVal::ByteStr(b), .. } } => { |
| max_fixed_len = cmp::max(max_fixed_len, b.data.len() as u64); |
| } |
| PatternKind::Slice { ref prefix, slice: None, ref suffix } => { |
| let fixed_len = prefix.len() as u64 + suffix.len() as u64; |
| max_fixed_len = cmp::max(max_fixed_len, fixed_len); |
| } |
| PatternKind::Slice { ref prefix, slice: Some(_), ref suffix } => { |
| max_prefix_len = cmp::max(max_prefix_len, prefix.len() as u64); |
| max_suffix_len = cmp::max(max_suffix_len, suffix.len() as u64); |
| } |
| _ => {} |
| } |
| } |
| |
| cmp::max(max_fixed_len + 1, max_prefix_len + max_suffix_len) |
| } |
| |
| /// Algorithm from http://moscova.inria.fr/~maranget/papers/warn/index.html |
| /// The algorithm from the paper has been modified to correctly handle empty |
| /// types. The changes are: |
| /// (0) We don't exit early if the pattern matrix has zero rows. We just |
| /// continue to recurse over columns. |
| /// (1) all_constructors will only return constructors that are statically |
| /// possible. eg. it will only return Ok for Result<T, !> |
| /// |
| /// This finds whether a (row) vector `v` of patterns is 'useful' in relation |
| /// to a set of such vectors `m` - this is defined as there being a set of |
| /// inputs that will match `v` but not any of the sets in `m`. |
| /// |
| /// All the patterns at each column of the `matrix ++ v` matrix must |
| /// have the same type, except that wildcard (PatternKind::Wild) patterns |
| /// with type TyErr are also allowed, even if the "type of the column" |
| /// is not TyErr. That is used to represent private fields, as using their |
| /// real type would assert that they are inhabited. |
| /// |
| /// This is used both for reachability checking (if a pattern isn't useful in |
| /// relation to preceding patterns, it is not reachable) and exhaustiveness |
| /// checking (if a wildcard pattern is useful in relation to a matrix, the |
| /// matrix isn't exhaustive). |
| pub fn is_useful<'p, 'a: 'p, 'tcx: 'a>(cx: &mut MatchCheckCtxt<'a, 'tcx>, |
| matrix: &Matrix<'p, 'tcx>, |
| v: &[&'p Pattern<'tcx>], |
| witness: WitnessPreference) |
| -> Usefulness<'tcx> { |
| let &Matrix(ref rows) = matrix; |
| debug!("is_useful({:?}, {:?})", matrix, v); |
| |
| // The base case. We are pattern-matching on () and the return value is |
| // based on whether our matrix has a row or not. |
| // NOTE: This could potentially be optimized by checking rows.is_empty() |
| // first and then, if v is non-empty, the return value is based on whether |
| // the type of the tuple we're checking is inhabited or not. |
| if v.is_empty() { |
| return if rows.is_empty() { |
| match witness { |
| ConstructWitness => UsefulWithWitness(vec![Witness(vec![])]), |
| LeaveOutWitness => Useful, |
| } |
| } else { |
| NotUseful |
| } |
| }; |
| |
| assert!(rows.iter().all(|r| r.len() == v.len())); |
| |
| let pcx = PatternContext { |
| // TyErr is used to represent the type of wildcard patterns matching |
| // against inaccessible (private) fields of structs, so that we won't |
| // be able to observe whether the types of the struct's fields are |
| // inhabited. |
| // |
| // If the field is truely inaccessible, then all the patterns |
| // matching against it must be wildcard patterns, so its type |
| // does not matter. |
| // |
| // However, if we are matching against non-wildcard patterns, we |
| // need to know the real type of the field so we can specialize |
| // against it. This primarily occurs through constants - they |
| // can include contents for fields that are inaccessible at the |
| // location of the match. In that case, the field's type is |
| // inhabited - by the constant - so we can just use it. |
| // |
| // FIXME: this might lead to "unstable" behavior with macro hygiene |
| // introducing uninhabited patterns for inaccessible fields. We |
| // need to figure out how to model that. |
| ty: rows.iter().map(|r| r[0].ty).find(|ty| !ty.references_error()) |
| .unwrap_or(v[0].ty), |
| max_slice_length: max_slice_length(cx, rows.iter().map(|r| r[0]).chain(Some(v[0]))) |
| }; |
| |
| debug!("is_useful_expand_first_col: pcx={:?}, expanding {:?}", pcx, v[0]); |
| |
| if let Some(constructors) = pat_constructors(cx, v[0], pcx) { |
| debug!("is_useful - expanding constructors: {:?}", constructors); |
| constructors.into_iter().map(|c| |
| is_useful_specialized(cx, matrix, v, c.clone(), pcx.ty, witness) |
| ).find(|result| result.is_useful()).unwrap_or(NotUseful) |
| } else { |
| debug!("is_useful - expanding wildcard"); |
| |
| let used_ctors: Vec<Constructor> = rows.iter().flat_map(|row| { |
| pat_constructors(cx, row[0], pcx).unwrap_or(vec![]) |
| }).collect(); |
| debug!("used_ctors = {:?}", used_ctors); |
| let all_ctors = all_constructors(cx, pcx); |
| debug!("all_ctors = {:?}", all_ctors); |
| let missing_ctors: Vec<Constructor> = all_ctors.iter().filter(|c| { |
| !used_ctors.contains(*c) |
| }).cloned().collect(); |
| |
| // `missing_ctors` is the set of constructors from the same type as the |
| // first column of `matrix` that are matched only by wildcard patterns |
| // from the first column. |
| // |
| // Therefore, if there is some pattern that is unmatched by `matrix`, |
| // it will still be unmatched if the first constructor is replaced by |
| // any of the constructors in `missing_ctors` |
| // |
| // However, if our scrutinee is *privately* an empty enum, we |
| // must treat it as though it had an "unknown" constructor (in |
| // that case, all other patterns obviously can't be variants) |
| // to avoid exposing its emptyness. See the `match_privately_empty` |
| // test for details. |
| // |
| // FIXME: currently the only way I know of something can |
| // be a privately-empty enum is when the never_type |
| // feature flag is not present, so this is only |
| // needed for that case. |
| |
| let is_privately_empty = |
| all_ctors.is_empty() && !cx.is_uninhabited(pcx.ty); |
| let is_declared_nonexhaustive = |
| cx.is_non_exhaustive_enum(pcx.ty) && !cx.is_local(pcx.ty); |
| debug!("missing_ctors={:?} is_privately_empty={:?} is_declared_nonexhaustive={:?}", |
| missing_ctors, is_privately_empty, is_declared_nonexhaustive); |
| |
| // For privately empty and non-exhaustive enums, we work as if there were an "extra" |
| // `_` constructor for the type, so we can never match over all constructors. |
| let is_non_exhaustive = is_privately_empty || is_declared_nonexhaustive; |
| |
| if missing_ctors.is_empty() && !is_non_exhaustive { |
| all_ctors.into_iter().map(|c| { |
| is_useful_specialized(cx, matrix, v, c.clone(), pcx.ty, witness) |
| }).find(|result| result.is_useful()).unwrap_or(NotUseful) |
| } else { |
| let matrix = rows.iter().filter_map(|r| { |
| if r[0].is_wildcard() { |
| Some(r[1..].to_vec()) |
| } else { |
| None |
| } |
| }).collect(); |
| match is_useful(cx, &matrix, &v[1..], witness) { |
| UsefulWithWitness(pats) => { |
| let cx = &*cx; |
| // In this case, there's at least one "free" |
| // constructor that is only matched against by |
| // wildcard patterns. |
| // |
| // There are 2 ways we can report a witness here. |
| // Commonly, we can report all the "free" |
| // constructors as witnesses, e.g. if we have: |
| // |
| // ``` |
| // enum Direction { N, S, E, W } |
| // let Direction::N = ...; |
| // ``` |
| // |
| // we can report 3 witnesses: `S`, `E`, and `W`. |
| // |
| // However, there are 2 cases where we don't want |
| // to do this and instead report a single `_` witness: |
| // |
| // 1) If the user is matching against a non-exhaustive |
| // enum, there is no point in enumerating all possible |
| // variants, because the user can't actually match |
| // against them himself, e.g. in an example like: |
| // ``` |
| // let err: io::ErrorKind = ...; |
| // match err { |
| // io::ErrorKind::NotFound => {}, |
| // } |
| // ``` |
| // we don't want to show every possible IO error, |
| // but instead have `_` as the witness (this is |
| // actually *required* if the user specified *all* |
| // IO errors, but is probably what we want in every |
| // case). |
| // |
| // 2) If the user didn't actually specify a constructor |
| // in this arm, e.g. in |
| // ``` |
| // let x: (Direction, Direction, bool) = ...; |
| // let (_, _, false) = x; |
| // ``` |
| // we don't want to show all 16 possible witnesses |
| // `(<direction-1>, <direction-2>, true)` - we are |
| // satisfied with `(_, _, true)`. In this case, |
| // `used_ctors` is empty. |
| let new_witnesses = if is_non_exhaustive || used_ctors.is_empty() { |
| // All constructors are unused. Add wild patterns |
| // rather than each individual constructor |
| pats.into_iter().map(|mut witness| { |
| witness.0.push(Pattern { |
| ty: pcx.ty, |
| span: DUMMY_SP, |
| kind: box PatternKind::Wild, |
| }); |
| witness |
| }).collect() |
| } else { |
| pats.into_iter().flat_map(|witness| { |
| missing_ctors.iter().map(move |ctor| { |
| witness.clone().push_wild_constructor(cx, ctor, pcx.ty) |
| }) |
| }).collect() |
| }; |
| UsefulWithWitness(new_witnesses) |
| } |
| result => result |
| } |
| } |
| } |
| } |
| |
| fn is_useful_specialized<'p, 'a:'p, 'tcx: 'a>( |
| cx: &mut MatchCheckCtxt<'a, 'tcx>, |
| &Matrix(ref m): &Matrix<'p, 'tcx>, |
| v: &[&'p Pattern<'tcx>], |
| ctor: Constructor<'tcx>, |
| lty: Ty<'tcx>, |
| witness: WitnessPreference) -> Usefulness<'tcx> |
| { |
| debug!("is_useful_specialized({:?}, {:?}, {:?})", v, ctor, lty); |
| let sub_pat_tys = constructor_sub_pattern_tys(cx, &ctor, lty); |
| let wild_patterns_owned: Vec<_> = sub_pat_tys.iter().map(|ty| { |
| Pattern { |
| ty, |
| span: DUMMY_SP, |
| kind: box PatternKind::Wild, |
| } |
| }).collect(); |
| let wild_patterns: Vec<_> = wild_patterns_owned.iter().collect(); |
| let matrix = Matrix(m.iter().flat_map(|r| { |
| specialize(cx, &r, &ctor, &wild_patterns) |
| }).collect()); |
| match specialize(cx, v, &ctor, &wild_patterns) { |
| Some(v) => match is_useful(cx, &matrix, &v, witness) { |
| UsefulWithWitness(witnesses) => UsefulWithWitness( |
| witnesses.into_iter() |
| .map(|witness| witness.apply_constructor(cx, &ctor, lty)) |
| .collect() |
| ), |
| result => result |
| }, |
| None => NotUseful |
| } |
| } |
| |
| /// Determines the constructors that the given pattern can be specialized to. |
| /// |
| /// In most cases, there's only one constructor that a specific pattern |
| /// represents, such as a specific enum variant or a specific literal value. |
| /// Slice patterns, however, can match slices of different lengths. For instance, |
| /// `[a, b, ..tail]` can match a slice of length 2, 3, 4 and so on. |
| /// |
| /// Returns None in case of a catch-all, which can't be specialized. |
| fn pat_constructors<'tcx>(_cx: &mut MatchCheckCtxt, |
| pat: &Pattern<'tcx>, |
| pcx: PatternContext) |
| -> Option<Vec<Constructor<'tcx>>> |
| { |
| match *pat.kind { |
| PatternKind::Binding { .. } | PatternKind::Wild => |
| None, |
| PatternKind::Leaf { .. } | PatternKind::Deref { .. } => |
| Some(vec![Single]), |
| PatternKind::Variant { adt_def, variant_index, .. } => |
| Some(vec![Variant(adt_def.variants[variant_index].did)]), |
| PatternKind::Constant { value } => |
| Some(vec![ConstantValue(value)]), |
| PatternKind::Range { lo, hi, end } => |
| Some(vec![ConstantRange(lo, hi, end)]), |
| PatternKind::Array { .. } => match pcx.ty.sty { |
| ty::TyArray(_, length) => Some(vec![ |
| Slice(length.val.to_const_int().unwrap().to_u64().unwrap()) |
| ]), |
| _ => span_bug!(pat.span, "bad ty {:?} for array pattern", pcx.ty) |
| }, |
| PatternKind::Slice { ref prefix, ref slice, ref suffix } => { |
| let pat_len = prefix.len() as u64 + suffix.len() as u64; |
| if slice.is_some() { |
| Some((pat_len..pcx.max_slice_length+1).map(Slice).collect()) |
| } else { |
| Some(vec![Slice(pat_len)]) |
| } |
| } |
| } |
| } |
| |
| /// This computes the arity of a constructor. The arity of a constructor |
| /// is how many subpattern patterns of that constructor should be expanded to. |
| /// |
| /// For instance, a tuple pattern (_, 42, Some([])) has the arity of 3. |
| /// A struct pattern's arity is the number of fields it contains, etc. |
| fn constructor_arity(_cx: &MatchCheckCtxt, ctor: &Constructor, ty: Ty) -> u64 { |
| debug!("constructor_arity({:?}, {:?})", ctor, ty); |
| match ty.sty { |
| ty::TyTuple(ref fs, _) => fs.len() as u64, |
| ty::TySlice(..) | ty::TyArray(..) => match *ctor { |
| Slice(length) => length, |
| ConstantValue(_) => 0, |
| _ => bug!("bad slice pattern {:?} {:?}", ctor, ty) |
| }, |
| ty::TyRef(..) => 1, |
| ty::TyAdt(adt, _) => { |
| adt.variants[ctor.variant_index_for_adt(adt)].fields.len() as u64 |
| } |
| _ => 0 |
| } |
| } |
| |
| /// This computes the types of the sub patterns that a constructor should be |
| /// expanded to. |
| /// |
| /// For instance, a tuple pattern (43u32, 'a') has sub pattern types [u32, char]. |
| fn constructor_sub_pattern_tys<'a, 'tcx: 'a>(cx: &MatchCheckCtxt<'a, 'tcx>, |
| ctor: &Constructor, |
| ty: Ty<'tcx>) -> Vec<Ty<'tcx>> |
| { |
| debug!("constructor_sub_pattern_tys({:?}, {:?})", ctor, ty); |
| match ty.sty { |
| ty::TyTuple(ref fs, _) => fs.into_iter().map(|t| *t).collect(), |
| ty::TySlice(ty) | ty::TyArray(ty, _) => match *ctor { |
| Slice(length) => (0..length).map(|_| ty).collect(), |
| ConstantValue(_) => vec![], |
| _ => bug!("bad slice pattern {:?} {:?}", ctor, ty) |
| }, |
| ty::TyRef(_, ref ty_and_mut) => vec![ty_and_mut.ty], |
| ty::TyAdt(adt, substs) => { |
| if adt.is_box() { |
| // Use T as the sub pattern type of Box<T>. |
| vec![substs[0].as_type().unwrap()] |
| } else { |
| adt.variants[ctor.variant_index_for_adt(adt)].fields.iter().map(|field| { |
| let is_visible = adt.is_enum() |
| || field.vis.is_accessible_from(cx.module, cx.tcx); |
| if is_visible { |
| field.ty(cx.tcx, substs) |
| } else { |
| // Treat all non-visible fields as TyErr. They |
| // can't appear in any other pattern from |
| // this match (because they are private), |
| // so their type does not matter - but |
| // we don't want to know they are |
| // uninhabited. |
| cx.tcx.types.err |
| } |
| }).collect() |
| } |
| } |
| _ => vec![], |
| } |
| } |
| |
| fn slice_pat_covered_by_constructor(_tcx: TyCtxt, _span: Span, |
| ctor: &Constructor, |
| prefix: &[Pattern], |
| slice: &Option<Pattern>, |
| suffix: &[Pattern]) |
| -> Result<bool, ErrorReported> { |
| let data = match *ctor { |
| ConstantValue(&ty::Const { val: ConstVal::ByteStr(b), .. }) => b.data, |
| _ => bug!() |
| }; |
| |
| let pat_len = prefix.len() + suffix.len(); |
| if data.len() < pat_len || (slice.is_none() && data.len() > pat_len) { |
| return Ok(false); |
| } |
| |
| for (ch, pat) in |
| data[..prefix.len()].iter().zip(prefix).chain( |
| data[data.len()-suffix.len()..].iter().zip(suffix)) |
| { |
| match pat.kind { |
| box PatternKind::Constant { value } => match value.val { |
| ConstVal::Integral(ConstInt::U8(u)) => { |
| if u != *ch { |
| return Ok(false); |
| } |
| }, |
| _ => span_bug!(pat.span, "bad const u8 {:?}", value) |
| }, |
| _ => {} |
| } |
| } |
| |
| Ok(true) |
| } |
| |
| fn constructor_covered_by_range(tcx: TyCtxt, span: Span, |
| ctor: &Constructor, |
| from: &ConstVal, to: &ConstVal, |
| end: RangeEnd) |
| -> Result<bool, ErrorReported> { |
| let cmp_from = |c_from| Ok(compare_const_vals(tcx, span, c_from, from)? != Ordering::Less); |
| let cmp_to = |c_to| compare_const_vals(tcx, span, c_to, to); |
| match *ctor { |
| ConstantValue(value) => { |
| let to = cmp_to(&value.val)?; |
| let end = (to == Ordering::Less) || |
| (end == RangeEnd::Included && to == Ordering::Equal); |
| Ok(cmp_from(&value.val)? && end) |
| }, |
| ConstantRange(from, to, RangeEnd::Included) => { |
| let to = cmp_to(&to.val)?; |
| let end = (to == Ordering::Less) || |
| (end == RangeEnd::Included && to == Ordering::Equal); |
| Ok(cmp_from(&from.val)? && end) |
| }, |
| ConstantRange(from, to, RangeEnd::Excluded) => { |
| let to = cmp_to(&to.val)?; |
| let end = (to == Ordering::Less) || |
| (end == RangeEnd::Excluded && to == Ordering::Equal); |
| Ok(cmp_from(&from.val)? && end) |
| } |
| Single => Ok(true), |
| _ => bug!(), |
| } |
| } |
| |
| fn patterns_for_variant<'p, 'a: 'p, 'tcx: 'a>( |
| subpatterns: &'p [FieldPattern<'tcx>], |
| wild_patterns: &[&'p Pattern<'tcx>]) |
| -> Vec<&'p Pattern<'tcx>> |
| { |
| let mut result = wild_patterns.to_owned(); |
| |
| for subpat in subpatterns { |
| result[subpat.field.index()] = &subpat.pattern; |
| } |
| |
| debug!("patterns_for_variant({:?}, {:?}) = {:?}", subpatterns, wild_patterns, result); |
| result |
| } |
| |
| /// This is the main specialization step. It expands the first pattern in the given row |
| /// into `arity` patterns based on the constructor. For most patterns, the step is trivial, |
| /// for instance tuple patterns are flattened and box patterns expand into their inner pattern. |
| /// |
| /// OTOH, slice patterns with a subslice pattern (..tail) can be expanded into multiple |
| /// different patterns. |
| /// Structure patterns with a partial wild pattern (Foo { a: 42, .. }) have their missing |
| /// fields filled with wild patterns. |
| fn specialize<'p, 'a: 'p, 'tcx: 'a>( |
| cx: &mut MatchCheckCtxt<'a, 'tcx>, |
| r: &[&'p Pattern<'tcx>], |
| constructor: &Constructor, |
| wild_patterns: &[&'p Pattern<'tcx>]) |
| -> Option<Vec<&'p Pattern<'tcx>>> |
| { |
| let pat = &r[0]; |
| |
| let head: Option<Vec<&Pattern>> = match *pat.kind { |
| PatternKind::Binding { .. } | PatternKind::Wild => { |
| Some(wild_patterns.to_owned()) |
| }, |
| |
| PatternKind::Variant { adt_def, variant_index, ref subpatterns, .. } => { |
| let ref variant = adt_def.variants[variant_index]; |
| if *constructor == Variant(variant.did) { |
| Some(patterns_for_variant(subpatterns, wild_patterns)) |
| } else { |
| None |
| } |
| } |
| |
| PatternKind::Leaf { ref subpatterns } => { |
| Some(patterns_for_variant(subpatterns, wild_patterns)) |
| } |
| PatternKind::Deref { ref subpattern } => { |
| Some(vec![subpattern]) |
| } |
| |
| PatternKind::Constant { value } => { |
| match *constructor { |
| Slice(..) => match value.val { |
| ConstVal::ByteStr(b) => { |
| if wild_patterns.len() == b.data.len() { |
| Some(cx.lower_byte_str_pattern(pat)) |
| } else { |
| None |
| } |
| } |
| _ => span_bug!(pat.span, |
| "unexpected const-val {:?} with ctor {:?}", value, constructor) |
| }, |
| _ => { |
| match constructor_covered_by_range( |
| cx.tcx, pat.span, constructor, &value.val, &value.val, RangeEnd::Included |
| ) { |
| Ok(true) => Some(vec![]), |
| Ok(false) => None, |
| Err(ErrorReported) => None, |
| } |
| } |
| } |
| } |
| |
| PatternKind::Range { lo, hi, ref end } => { |
| match constructor_covered_by_range( |
| cx.tcx, pat.span, constructor, &lo.val, &hi.val, end.clone() |
| ) { |
| Ok(true) => Some(vec![]), |
| Ok(false) => None, |
| Err(ErrorReported) => None, |
| } |
| } |
| |
| PatternKind::Array { ref prefix, ref slice, ref suffix } | |
| PatternKind::Slice { ref prefix, ref slice, ref suffix } => { |
| match *constructor { |
| Slice(..) => { |
| let pat_len = prefix.len() + suffix.len(); |
| if let Some(slice_count) = wild_patterns.len().checked_sub(pat_len) { |
| if slice_count == 0 || slice.is_some() { |
| Some( |
| prefix.iter().chain( |
| wild_patterns.iter().map(|p| *p) |
| .skip(prefix.len()) |
| .take(slice_count) |
| .chain( |
| suffix.iter() |
| )).collect()) |
| } else { |
| None |
| } |
| } else { |
| None |
| } |
| } |
| ConstantValue(..) => { |
| match slice_pat_covered_by_constructor( |
| cx.tcx, pat.span, constructor, prefix, slice, suffix |
| ) { |
| Ok(true) => Some(vec![]), |
| Ok(false) => None, |
| Err(ErrorReported) => None |
| } |
| } |
| _ => span_bug!(pat.span, |
| "unexpected ctor {:?} for slice pat", constructor) |
| } |
| } |
| }; |
| debug!("specialize({:?}, {:?}) = {:?}", r[0], wild_patterns, head); |
| |
| head.map(|mut head| { |
| head.extend_from_slice(&r[1 ..]); |
| head |
| }) |
| } |
