| // 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. |
| |
| /// This file includes the logic for exhaustiveness and usefulness checking for |
| /// pattern-matching. Specifically, given a list of patterns for a type, we can |
| /// tell whether: |
| /// (a) the patterns cover every possible constructor for the type [exhaustiveness] |
| /// (b) each pattern is necessary [usefulness] |
| /// |
| /// The algorithm implemented here is a modified version of the one described in: |
| /// http://moscova.inria.fr/~maranget/papers/warn/index.html |
| /// However, to save future implementors from reading the original paper, I'm going |
| /// to summarise the algorithm here to hopefully save time and be a little clearer |
| /// (without being so rigorous). |
| /// |
| /// The core of the algorithm revolves about a "usefulness" check. In particular, we |
| /// are trying to compute a predicate `U(P, p_{m + 1})` where `P` is a list of patterns |
| /// of length `m` for a compound (product) type with `n` components (we refer to this as |
| /// a matrix). `U(P, p_{m + 1})` represents whether, given an existing list of patterns |
| /// `p_1 ..= p_m`, adding a new pattern will be "useful" (that is, cover previously- |
| /// uncovered values of the type). |
| /// |
| /// If we have this predicate, then we can easily compute both exhaustiveness of an |
| /// entire set of patterns and the individual usefulness of each one. |
| /// (a) the set of patterns is exhaustive iff `U(P, _)` is false (i.e., adding a wildcard |
| /// match doesn't increase the number of values we're matching) |
| /// (b) a pattern `p_i` is not useful if `U(P[0..=(i-1), p_i)` is false (i.e., adding a |
| /// pattern to those that have come before it doesn't increase the number of values |
| /// we're matching). |
| /// |
| /// For example, say we have the following: |
| /// ``` |
| /// // x: (Option<bool>, Result<()>) |
| /// match x { |
| /// (Some(true), _) => {} |
| /// (None, Err(())) => {} |
| /// (None, Err(_)) => {} |
| /// } |
| /// ``` |
| /// Here, the matrix `P` is 3 x 2 (rows x columns). |
| /// [ |
| /// [Some(true), _], |
| /// [None, Err(())], |
| /// [None, Err(_)], |
| /// ] |
| /// We can tell it's not exhaustive, because `U(P, _)` is true (we're not covering |
| /// `[Some(false), _]`, for instance). In addition, row 3 is not useful, because |
| /// all the values it covers are already covered by row 2. |
| /// |
| /// To compute `U`, we must have two other concepts. |
| /// 1. `S(c, P)` is a "specialized matrix", where `c` is a constructor (like `Some` or |
| /// `None`). You can think of it as filtering `P` to just the rows whose *first* pattern |
| /// can cover `c` (and expanding OR-patterns into distinct patterns), and then expanding |
| /// the constructor into all of its components. |
| /// The specialization of a row vector is computed by `specialize`. |
| /// |
| /// It is computed as follows. For each row `p_i` of P, we have four cases: |
| /// 1.1. `p_(i,1) = c(r_1, .., r_a)`. Then `S(c, P)` has a corresponding row: |
| /// r_1, .., r_a, p_(i,2), .., p_(i,n) |
| /// 1.2. `p_(i,1) = c'(r_1, .., r_a')` where `c ≠ c'`. Then `S(c, P)` has no |
| /// corresponding row. |
| /// 1.3. `p_(i,1) = _`. Then `S(c, P)` has a corresponding row: |
| /// _, .., _, p_(i,2), .., p_(i,n) |
| /// 1.4. `p_(i,1) = r_1 | r_2`. Then `S(c, P)` has corresponding rows inlined from: |
| /// S(c, (r_1, p_(i,2), .., p_(i,n))) |
| /// S(c, (r_2, p_(i,2), .., p_(i,n))) |
| /// |
| /// 2. `D(P)` is a "default matrix". This is used when we know there are missing |
| /// constructor cases, but there might be existing wildcard patterns, so to check the |
| /// usefulness of the matrix, we have to check all its *other* components. |
| /// The default matrix is computed inline in `is_useful`. |
| /// |
| /// It is computed as follows. For each row `p_i` of P, we have three cases: |
| /// 1.1. `p_(i,1) = c(r_1, .., r_a)`. Then `D(P)` has no corresponding row. |
| /// 1.2. `p_(i,1) = _`. Then `D(P)` has a corresponding row: |
| /// p_(i,2), .., p_(i,n) |
| /// 1.3. `p_(i,1) = r_1 | r_2`. Then `D(P)` has corresponding rows inlined from: |
| /// D((r_1, p_(i,2), .., p_(i,n))) |
| /// D((r_2, p_(i,2), .., p_(i,n))) |
| /// |
| /// Note that the OR-patterns are not always used directly in Rust, but are used to derive |
| /// the exhaustive integer matching rules, so they're written here for posterity. |
| /// |
| /// The algorithm for computing `U` |
| /// ------------------------------- |
| /// The algorithm is inductive (on the number of columns: i.e., components of tuple patterns). |
| /// That means we're going to check the components from left-to-right, so the algorithm |
| /// operates principally on the first component of the matrix and new pattern `p_{m + 1}`. |
| /// This algorithm is realised in the `is_useful` function. |
| /// |
| /// Base case. (`n = 0`, i.e., an empty tuple pattern) |
| /// - If `P` already contains an empty pattern (i.e., if the number of patterns `m > 0`), |
| /// then `U(P, p_{m + 1})` is false. |
| /// - Otherwise, `P` must be empty, so `U(P, p_{m + 1})` is true. |
| /// |
| /// Inductive step. (`n > 0`, i.e., whether there's at least one column |
| /// [which may then be expanded into further columns later]) |
| /// We're going to match on the new pattern, `p_{m + 1}`. |
| /// - If `p_{m + 1} == c(r_1, .., r_a)`, then we have a constructor pattern. |
| /// Thus, the usefulness of `p_{m + 1}` can be reduced to whether it is useful when |
| /// we ignore all the patterns in `P` that involve other constructors. This is where |
| /// `S(c, P)` comes in: |
| /// `U(P, p_{m + 1}) := U(S(c, P), S(c, p_{m + 1}))` |
| /// This special case is handled in `is_useful_specialized`. |
| /// - If `p_{m + 1} == _`, then we have two more cases: |
| /// + All the constructors of the first component of the type exist within |
| /// all the rows (after having expanded OR-patterns). In this case: |
| /// `U(P, p_{m + 1}) := ∨(k ϵ constructors) U(S(k, P), S(k, p_{m + 1}))` |
| /// I.e., the pattern `p_{m + 1}` is only useful when all the constructors are |
| /// present *if* its later components are useful for the respective constructors |
| /// covered by `p_{m + 1}` (usually a single constructor, but all in the case of `_`). |
| /// + Some constructors are not present in the existing rows (after having expanded |
| /// OR-patterns). However, there might be wildcard patterns (`_`) present. Thus, we |
| /// are only really concerned with the other patterns leading with wildcards. This is |
| /// where `D` comes in: |
| /// `U(P, p_{m + 1}) := U(D(P), p_({m + 1},2), .., p_({m + 1},n))` |
| /// - If `p_{m + 1} == r_1 | r_2`, then the usefulness depends on each separately: |
| /// `U(P, p_{m + 1}) := U(P, (r_1, p_({m + 1},2), .., p_({m + 1},n))) |
| /// || U(P, (r_2, p_({m + 1},2), .., p_({m + 1},n)))` |
| /// |
| /// Modifications to the algorithm |
| /// ------------------------------ |
| /// The algorithm in the paper doesn't cover some of the special cases that arise in Rust, for |
| /// example uninhabited types and variable-length slice patterns. These are drawn attention to |
| /// throughout the code below. I'll make a quick note here about how exhaustive integer matching |
| /// is accounted for, though. |
| /// |
| /// Exhaustive integer matching |
| /// --------------------------- |
| /// An integer type can be thought of as a (huge) sum type: 1 | 2 | 3 | ... |
| /// So to support exhaustive integer matching, we can make use of the logic in the paper for |
| /// OR-patterns. However, we obviously can't just treat ranges x..=y as individual sums, because |
| /// they are likely gigantic. So we instead treat ranges as constructors of the integers. This means |
| /// that we have a constructor *of* constructors (the integers themselves). We then need to work |
| /// through all the inductive step rules above, deriving how the ranges would be treated as |
| /// OR-patterns, and making sure that they're treated in the same way even when they're ranges. |
| /// There are really only four special cases here: |
| /// - When we match on a constructor that's actually a range, we have to treat it as if we would |
| /// an OR-pattern. |
| /// + It turns out that we can simply extend the case for single-value patterns in |
| /// `specialize` to either be *equal* to a value constructor, or *contained within* a range |
| /// constructor. |
| /// + When the pattern itself is a range, you just want to tell whether any of the values in |
| /// the pattern range coincide with values in the constructor range, which is precisely |
| /// intersection. |
| /// Since when encountering a range pattern for a value constructor, we also use inclusion, it |
| /// means that whenever the constructor is a value/range and the pattern is also a value/range, |
| /// we can simply use intersection to test usefulness. |
| /// - When we're testing for usefulness of a pattern and the pattern's first component is a |
| /// wildcard. |
| /// + If all the constructors appear in the matrix, we have a slight complication. By default, |
| /// the behaviour (i.e., a disjunction over specialised matrices for each constructor) is |
| /// invalid, because we want a disjunction over every *integer* in each range, not just a |
| /// disjunction over every range. This is a bit more tricky to deal with: essentially we need |
| /// to form equivalence classes of subranges of the constructor range for which the behaviour |
| /// of the matrix `P` and new pattern `p_{m + 1}` are the same. This is described in more |
| /// detail in `split_grouped_constructors`. |
| /// + If some constructors are missing from the matrix, it turns out we don't need to do |
| /// anything special (because we know none of the integers are actually wildcards: i.e., we |
| /// can't span wildcards using ranges). |
| |
| use self::Constructor::*; |
| use self::Usefulness::*; |
| use self::WitnessPreference::*; |
| |
| use rustc_data_structures::fx::FxHashMap; |
| use rustc_data_structures::indexed_vec::Idx; |
| |
| use super::{FieldPattern, Pattern, PatternKind}; |
| use super::{PatternFoldable, PatternFolder, compare_const_vals}; |
| |
| use rustc::hir::def_id::DefId; |
| use rustc::hir::RangeEnd; |
| use rustc::ty::{self, Ty, TyCtxt, TypeFoldable}; |
| use rustc::ty::layout::{Integer, IntegerExt, VariantIdx}; |
| |
| use rustc::mir::Field; |
| use rustc::mir::interpret::ConstValue; |
| use rustc::util::common::ErrorReported; |
| |
| use syntax::attr::{SignedInt, UnsignedInt}; |
| use syntax_pos::{Span, DUMMY_SP}; |
| |
| use arena::TypedArena; |
| |
| use smallvec::{SmallVec, smallvec}; |
| use std::cmp::{self, Ordering, min, max}; |
| use std::fmt; |
| use std::iter::{FromIterator, IntoIterator}; |
| use std::ops::RangeInclusive; |
| use std::u128; |
| |
| 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::Ref(_, rty, _), &PatternKind::Constant { ref value }) => { |
| Pattern { |
| ty: pat.ty, |
| span: pat.span, |
| kind: box PatternKind::Deref { |
| subpattern: Pattern { |
| ty: rty, |
| 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 |
| } |
| } |
| } |
| |
| /// A 2D matrix. Nx1 matrices are very common, which is why `SmallVec[_; 2]` |
| /// works well for each row. |
| pub struct Matrix<'p, 'tcx: 'p>(Vec<SmallVec<[&'p Pattern<'tcx>; 2]>>); |
| |
| impl<'p, 'tcx> Matrix<'p, 'tcx> { |
| pub fn empty() -> Self { |
| Matrix(vec![]) |
| } |
| |
| pub fn push(&mut self, row: SmallVec<[&'p Pattern<'tcx>; 2]>) { |
| self.0.push(row) |
| } |
| } |
| |
| /// Pretty-printer for matrices of patterns, example: |
| /// ++++++++++++++++++++++++++ |
| /// + _ + [] + |
| /// ++++++++++++++++++++++++++ |
| /// + true + [First] + |
| /// ++++++++++++++++++++++++++ |
| /// + true + [Second(true)] + |
| /// ++++++++++++++++++++++++++ |
| /// + false + [_] + |
| /// ++++++++++++++++++++++++++ |
| /// + _ + [_, _, ..tail] + |
| /// ++++++++++++++++++++++++++ |
| impl<'p, 'tcx> fmt::Debug for Matrix<'p, '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(total_width); |
| 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<'p, 'tcx> FromIterator<SmallVec<[&'p Pattern<'tcx>; 2]>> for Matrix<'p, 'tcx> { |
| fn from_iter<T>(iter: T) -> Self |
| where T: IntoIterator<Item=SmallVec<[&'p Pattern<'tcx>; 2]>> |
| { |
| Matrix(iter.into_iter().collect()) |
| } |
| } |
| |
| 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, |
| param_env: ty::ParamEnv<'tcx>, |
| 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>, |
| param_env: ty::ParamEnv<'tcx>, |
| module: DefId, |
| f: F) -> R |
| where F: for<'b> FnOnce(MatchCheckCtxt<'b, 'tcx>) -> R |
| { |
| let pattern_arena = TypedArena::default(); |
| |
| f(MatchCheckCtxt { |
| tcx, |
| param_env, |
| module, |
| pattern_arena: &pattern_arena, |
| byte_array_map: FxHashMap::default(), |
| }) |
| } |
| |
| fn is_uninhabited(&self, ty: Ty<'tcx>) -> bool { |
| if self.tcx.features().exhaustive_patterns { |
| 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::Adt(adt_def, ..) => adt_def.is_variant_list_non_exhaustive(), |
| _ => false, |
| } |
| } |
| |
| fn is_local(&self, ty: Ty<'tcx>) -> bool { |
| match ty.sty { |
| ty::Adt(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.features().exhaustive_patterns { |
| 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(u128, u128, Ty<'tcx>, RangeEnd), |
| /// Array patterns of length n. |
| Slice(u64), |
| } |
| |
| impl<'tcx> Constructor<'tcx> { |
| fn variant_index_for_adt(&self, adt: &'tcx ty::AdtDef) -> VariantIdx { |
| match self { |
| &Variant(vid) => adt.variant_index_with_id(vid), |
| &Single => { |
| assert!(!adt.is_enum()); |
| VariantIdx::new(0) |
| } |
| _ => bug!("bad constructor {:?} for adt {:?}", self, adt) |
| } |
| } |
| } |
| |
| #[derive(Clone, Debug)] |
| 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, Debug)] |
| pub enum WitnessPreference { |
| ConstructWitness, |
| LeaveOutWitness |
| } |
| |
| #[derive(Copy, Clone, Debug)] |
| struct PatternContext<'tcx> { |
| ty: Ty<'tcx>, |
| max_slice_length: u64, |
| } |
| |
| /// A witness of non-exhaustiveness for error reporting, represented |
| /// as a list of patterns (in reverse order of construction) with |
| /// wildcards inside to represent elements that can take any inhabitant |
| /// of the type as a value. |
| /// |
| /// A witness against a list of patterns should have the same types |
| /// and length as the pattern matched against. Because Rust `match` |
| /// is always against a single pattern, at the end the witness will |
| /// have length 1, but in the middle of the algorithm, it can contain |
| /// multiple patterns. |
| /// |
| /// For example, if we are constructing a witness for the match against |
| /// ``` |
| /// struct Pair(Option<(u32, u32)>, bool); |
| /// |
| /// match (p: Pair) { |
| /// Pair(None, _) => {} |
| /// Pair(_, false) => {} |
| /// } |
| /// ``` |
| /// |
| /// We'll perform the following steps: |
| /// 1. Start with an empty witness |
| /// `Witness(vec![])` |
| /// 2. Push a witness `Some(_)` against the `None` |
| /// `Witness(vec![Some(_)])` |
| /// 3. Push a witness `true` against the `false` |
| /// `Witness(vec![Some(_), true])` |
| /// 4. Apply the `Pair` constructor to the witnesses |
| /// `Witness(vec![Pair(Some(_), true)])` |
| /// |
| /// The final `Pair(Some(_), true)` is then the resulting witness. |
| #[derive(Clone, Debug)] |
| 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::Adt(..) | |
| ty::Tuple(..) => { |
| let pats = pats.enumerate().map(|(i, p)| { |
| FieldPattern { |
| field: Field::new(i), |
| pattern: p |
| } |
| }).collect(); |
| |
| if let ty::Adt(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::Ref(..) => { |
| PatternKind::Deref { subpattern: pats.nth(0).unwrap() } |
| } |
| |
| ty::Slice(_) | ty::Array(..) => { |
| PatternKind::Slice { |
| prefix: pats.collect(), |
| slice: None, |
| suffix: vec![] |
| } |
| } |
| |
| _ => { |
| match *ctor { |
| ConstantValue(value) => PatternKind::Constant { value }, |
| ConstantRange(lo, hi, ty, end) => PatternKind::Range { |
| lo: ty::Const::from_bits(cx.tcx, lo, ty::ParamEnv::empty().and(ty)), |
| hi: ty::Const::from_bits(cx.tcx, hi, ty::ParamEnv::empty().and(ty)), |
| ty, |
| end, |
| }, |
| _ => 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. |
| /// |
| /// 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); |
| let ctors = match pcx.ty.sty { |
| ty::Bool => { |
| [true, false].iter().map(|&b| { |
| ConstantValue(ty::Const::from_bool(cx.tcx, b)) |
| }).collect() |
| } |
| ty::Array(ref sub_ty, len) if len.assert_usize(cx.tcx).is_some() => { |
| let len = len.unwrap_usize(cx.tcx); |
| if len != 0 && cx.is_uninhabited(sub_ty) { |
| vec![] |
| } else { |
| vec![Slice(len)] |
| } |
| } |
| // Treat arrays of a constant but unknown length like slices. |
| ty::Array(ref sub_ty, _) | |
| ty::Slice(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::Adt(def, substs) if def.is_enum() => { |
| def.variants.iter() |
| .filter(|v| !cx.is_variant_uninhabited(v, substs)) |
| .map(|v| Variant(v.did)) |
| .collect() |
| } |
| ty::Char => { |
| vec![ |
| // The valid Unicode Scalar Value ranges. |
| ConstantRange('\u{0000}' as u128, |
| '\u{D7FF}' as u128, |
| cx.tcx.types.char, |
| RangeEnd::Included |
| ), |
| ConstantRange('\u{E000}' as u128, |
| '\u{10FFFF}' as u128, |
| cx.tcx.types.char, |
| RangeEnd::Included |
| ), |
| ] |
| } |
| ty::Int(ity) => { |
| // FIXME(49937): refactor these bit manipulations into interpret. |
| let bits = Integer::from_attr(&cx.tcx, SignedInt(ity)).size().bits() as u128; |
| let min = 1u128 << (bits - 1); |
| let max = (1u128 << (bits - 1)) - 1; |
| vec![ConstantRange(min, max, pcx.ty, RangeEnd::Included)] |
| } |
| ty::Uint(uty) => { |
| // FIXME(49937): refactor these bit manipulations into interpret. |
| let bits = Integer::from_attr(&cx.tcx, UnsignedInt(uty)).size().bits() as u128; |
| let max = !0u128 >> (128 - bits); |
| vec![ConstantRange(0, max, pcx.ty, RangeEnd::Included)] |
| } |
| _ => { |
| if cx.is_uninhabited(pcx.ty) { |
| vec![] |
| } else { |
| vec![Single] |
| } |
| } |
| }; |
| ctors |
| } |
| |
| 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 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 |
| // `plₚ` and suffix of length `slₚ`, only the first `plₚ` and the last |
| // `slₚ` 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 } => { |
| if let Some(ptr) = value.to_ptr() { |
| let is_array_ptr = value.ty |
| .builtin_deref(true) |
| .and_then(|t| t.ty.builtin_index()) |
| .map_or(false, |t| t == cx.tcx.types.u8); |
| if is_array_ptr { |
| let alloc = cx.tcx.alloc_map.lock().unwrap_memory(ptr.alloc_id); |
| max_fixed_len = cmp::max(max_fixed_len, alloc.bytes.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) |
| } |
| |
| /// An inclusive interval, used for precise integer exhaustiveness checking. |
| /// `IntRange`s always store a contiguous range. This means that values are |
| /// encoded such that `0` encodes the minimum value for the integer, |
| /// regardless of the signedness. |
| /// For example, the pattern `-128...127i8` is encoded as `0..=255`. |
| /// This makes comparisons and arithmetic on interval endpoints much more |
| /// straightforward. See `signed_bias` for details. |
| /// |
| /// `IntRange` is never used to encode an empty range or a "range" that wraps |
| /// around the (offset) space: i.e., `range.lo <= range.hi`. |
| #[derive(Clone)] |
| struct IntRange<'tcx> { |
| pub range: RangeInclusive<u128>, |
| pub ty: Ty<'tcx>, |
| } |
| |
| impl<'tcx> IntRange<'tcx> { |
| fn from_ctor(tcx: TyCtxt<'_, 'tcx, 'tcx>, |
| ctor: &Constructor<'tcx>) |
| -> Option<IntRange<'tcx>> { |
| // Floating-point ranges are permitted and we don't want |
| // to consider them when constructing integer ranges. |
| fn is_integral<'tcx>(ty: Ty<'tcx>) -> bool { |
| match ty.sty { |
| ty::Char | ty::Int(_) | ty::Uint(_) => true, |
| _ => false, |
| } |
| } |
| |
| match ctor { |
| ConstantRange(lo, hi, ty, end) if is_integral(ty) => { |
| // Perform a shift if the underlying types are signed, |
| // which makes the interval arithmetic simpler. |
| let bias = IntRange::signed_bias(tcx, ty); |
| let (lo, hi) = (lo ^ bias, hi ^ bias); |
| // Make sure the interval is well-formed. |
| if lo > hi || lo == hi && *end == RangeEnd::Excluded { |
| None |
| } else { |
| let offset = (*end == RangeEnd::Excluded) as u128; |
| Some(IntRange { range: lo..=(hi - offset), ty }) |
| } |
| } |
| ConstantValue(val) if is_integral(val.ty) => { |
| let ty = val.ty; |
| if let Some(val) = val.assert_bits(tcx, ty::ParamEnv::empty().and(ty)) { |
| let bias = IntRange::signed_bias(tcx, ty); |
| let val = val ^ bias; |
| Some(IntRange { range: val..=val, ty }) |
| } else { |
| None |
| } |
| } |
| _ => None, |
| } |
| } |
| |
| fn from_pat(tcx: TyCtxt<'_, 'tcx, 'tcx>, |
| pat: &Pattern<'tcx>) |
| -> Option<IntRange<'tcx>> { |
| Self::from_ctor(tcx, &match pat.kind { |
| box PatternKind::Constant { value } => ConstantValue(value), |
| box PatternKind::Range { lo, hi, ty, end } => ConstantRange( |
| lo.to_bits(tcx, ty::ParamEnv::empty().and(ty)).unwrap(), |
| hi.to_bits(tcx, ty::ParamEnv::empty().and(ty)).unwrap(), |
| ty, |
| end, |
| ), |
| _ => return None, |
| }) |
| } |
| |
| // The return value of `signed_bias` should be XORed with an endpoint to encode/decode it. |
| fn signed_bias(tcx: TyCtxt<'_, 'tcx, 'tcx>, ty: Ty<'tcx>) -> u128 { |
| match ty.sty { |
| ty::Int(ity) => { |
| let bits = Integer::from_attr(&tcx, SignedInt(ity)).size().bits() as u128; |
| 1u128 << (bits - 1) |
| } |
| _ => 0 |
| } |
| } |
| |
| /// Convert a `RangeInclusive` to a `ConstantValue` or inclusive `ConstantRange`. |
| fn range_to_ctor( |
| tcx: TyCtxt<'_, 'tcx, 'tcx>, |
| ty: Ty<'tcx>, |
| r: RangeInclusive<u128>, |
| ) -> Constructor<'tcx> { |
| let bias = IntRange::signed_bias(tcx, ty); |
| let (lo, hi) = r.into_inner(); |
| if lo == hi { |
| let ty = ty::ParamEnv::empty().and(ty); |
| ConstantValue(ty::Const::from_bits(tcx, lo ^ bias, ty)) |
| } else { |
| ConstantRange(lo ^ bias, hi ^ bias, ty, RangeEnd::Included) |
| } |
| } |
| |
| /// Return a collection of ranges that spans the values covered by `ranges`, subtracted |
| /// by the values covered by `self`: i.e., `ranges \ self` (in set notation). |
| fn subtract_from(self, |
| tcx: TyCtxt<'_, 'tcx, 'tcx>, |
| ranges: Vec<Constructor<'tcx>>) |
| -> Vec<Constructor<'tcx>> { |
| let ranges = ranges.into_iter().filter_map(|r| { |
| IntRange::from_ctor(tcx, &r).map(|i| i.range) |
| }); |
| let mut remaining_ranges = vec![]; |
| let ty = self.ty; |
| let (lo, hi) = self.range.into_inner(); |
| for subrange in ranges { |
| let (subrange_lo, subrange_hi) = subrange.into_inner(); |
| if lo > subrange_hi || subrange_lo > hi { |
| // The pattern doesn't intersect with the subrange at all, |
| // so the subrange remains untouched. |
| remaining_ranges.push(Self::range_to_ctor(tcx, ty, subrange_lo..=subrange_hi)); |
| } else { |
| if lo > subrange_lo { |
| // The pattern intersects an upper section of the |
| // subrange, so a lower section will remain. |
| remaining_ranges.push(Self::range_to_ctor(tcx, ty, subrange_lo..=(lo - 1))); |
| } |
| if hi < subrange_hi { |
| // The pattern intersects a lower section of the |
| // subrange, so an upper section will remain. |
| remaining_ranges.push(Self::range_to_ctor(tcx, ty, (hi + 1)..=subrange_hi)); |
| } |
| } |
| } |
| remaining_ranges |
| } |
| |
| fn intersection(&self, other: &Self) -> Option<Self> { |
| let ty = self.ty; |
| let (lo, hi) = (*self.range.start(), *self.range.end()); |
| let (other_lo, other_hi) = (*other.range.start(), *other.range.end()); |
| if lo <= other_hi && other_lo <= hi { |
| Some(IntRange { range: max(lo, other_lo)..=min(hi, other_hi), ty }) |
| } else { |
| None |
| } |
| } |
| } |
| |
| // A request for missing constructor data in terms of either: |
| // - whether or not there any missing constructors; or |
| // - the actual set of missing constructors. |
| #[derive(PartialEq)] |
| enum MissingCtorsInfo { |
| Emptiness, |
| Ctors, |
| } |
| |
| // Used by `compute_missing_ctors`. |
| #[derive(Debug, PartialEq)] |
| enum MissingCtors<'tcx> { |
| Empty, |
| NonEmpty, |
| |
| // Note that the Vec can be empty. |
| Ctors(Vec<Constructor<'tcx>>), |
| } |
| |
| // When `info` is `MissingCtorsInfo::Ctors`, compute a set of constructors |
| // equivalent to `all_ctors \ used_ctors`. When `info` is |
| // `MissingCtorsInfo::Emptiness`, just determines if that set is empty or not. |
| // (The split logic gives a performance win, because we always need to know if |
| // the set is empty, but we rarely need the full set, and it can be expensive |
| // to compute the full set.) |
| fn compute_missing_ctors<'a, 'tcx: 'a>( |
| info: MissingCtorsInfo, |
| tcx: TyCtxt<'a, 'tcx, 'tcx>, |
| all_ctors: &Vec<Constructor<'tcx>>, |
| used_ctors: &Vec<Constructor<'tcx>>, |
| ) -> MissingCtors<'tcx> { |
| let mut missing_ctors = vec![]; |
| |
| for req_ctor in all_ctors { |
| let mut refined_ctors = vec![req_ctor.clone()]; |
| for used_ctor in used_ctors { |
| if used_ctor == req_ctor { |
| // If a constructor appears in a `match` arm, we can |
| // eliminate it straight away. |
| refined_ctors = vec![] |
| } else if let Some(interval) = IntRange::from_ctor(tcx, used_ctor) { |
| // Refine the required constructors for the type by subtracting |
| // the range defined by the current constructor pattern. |
| refined_ctors = interval.subtract_from(tcx, refined_ctors); |
| } |
| |
| // If the constructor patterns that have been considered so far |
| // already cover the entire range of values, then we the |
| // constructor is not missing, and we can move on to the next one. |
| if refined_ctors.is_empty() { |
| break; |
| } |
| } |
| // If a constructor has not been matched, then it is missing. |
| // We add `refined_ctors` instead of `req_ctor`, because then we can |
| // provide more detailed error information about precisely which |
| // ranges have been omitted. |
| if info == MissingCtorsInfo::Emptiness { |
| if !refined_ctors.is_empty() { |
| // The set is non-empty; return early. |
| return MissingCtors::NonEmpty; |
| } |
| } else { |
| missing_ctors.extend(refined_ctors); |
| } |
| } |
| |
| if info == MissingCtorsInfo::Emptiness { |
| // If we reached here, the set is empty. |
| MissingCtors::Empty |
| } else { |
| MissingCtors::Ctors(missing_ctors) |
| } |
| } |
| |
| /// 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: &[&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 truly 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); |
| split_grouped_constructors(cx.tcx, constructors, matrix, pcx.ty).into_iter().map(|c| |
| is_useful_specialized(cx, matrix, v, c, 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); |
| // `all_ctors` are all the constructors for the given type, which |
| // should all be represented (or caught with the wild pattern `_`). |
| let all_ctors = all_constructors(cx, pcx); |
| debug!("all_ctors = {:#?}", all_ctors); |
| |
| // `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 exhaustive_patterns |
| // feature flag is not present, so this is only |
| // needed for that case. |
| |
| // Missing constructors are those that are not matched by any |
| // non-wildcard patterns in the current column. We always determine if |
| // the set is empty, but we only fully construct them on-demand, |
| // because they're rarely used and can be big. |
| let cheap_missing_ctors = |
| compute_missing_ctors(MissingCtorsInfo::Emptiness, cx.tcx, &all_ctors, &used_ctors); |
| |
| 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!("cheap_missing_ctors={:#?} is_privately_empty={:#?} is_declared_nonexhaustive={:#?}", |
| cheap_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 || |
| (pcx.ty.is_pointer_sized() && !cx.tcx.features().precise_pointer_size_matching); |
| |
| if cheap_missing_ctors == MissingCtors::Empty && !is_non_exhaustive { |
| split_grouped_constructors(cx.tcx, all_ctors, matrix, pcx.ty).into_iter().map(|c| { |
| is_useful_specialized(cx, matrix, v, c, 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(SmallVec::from_slice(&r[1..])) |
| } 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 { |
| let expensive_missing_ctors = |
| compute_missing_ctors(MissingCtorsInfo::Ctors, cx.tcx, &all_ctors, |
| &used_ctors); |
| if let MissingCtors::Ctors(missing_ctors) = expensive_missing_ctors { |
| pats.into_iter().flat_map(|witness| { |
| missing_ctors.iter().map(move |ctor| { |
| // Extends the witness with a "wild" version of this |
| // constructor, that matches everything that can be built with |
| // it. For example, if `ctor` is a `Constructor::Variant` for |
| // `Option::Some`, this pushes the witness for `Some(_)`. |
| witness.clone().push_wild_constructor(cx, ctor, pcx.ty) |
| }) |
| }).collect() |
| } else { |
| bug!("cheap missing ctors") |
| } |
| }; |
| UsefulWithWitness(new_witnesses) |
| } |
| result => result |
| } |
| } |
| } |
| } |
| |
| /// A shorthand for the `U(S(c, P), S(c, q))` operation from the paper. I.e., `is_useful` applied |
| /// to the specialised version of both the pattern matrix `P` and the new pattern `q`. |
| fn is_useful_specialized<'p, 'a: 'p, 'tcx: 'a>( |
| cx: &mut MatchCheckCtxt<'a, 'tcx>, |
| &Matrix(ref m): &Matrix<'p, 'tcx>, |
| v: &[&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<'_, 'tcx>, |
| pat: &Pattern<'tcx>, |
| pcx: PatternContext) |
| -> Option<Vec<Constructor<'tcx>>> |
| { |
| match *pat.kind { |
| PatternKind::AscribeUserType { ref subpattern, .. } => |
| pat_constructors(cx, subpattern, pcx), |
| 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, ty, end } => |
| Some(vec![ConstantRange( |
| lo.to_bits(cx.tcx, ty::ParamEnv::empty().and(ty)).unwrap(), |
| hi.to_bits(cx.tcx, ty::ParamEnv::empty().and(ty)).unwrap(), |
| ty, |
| end, |
| )]), |
| PatternKind::Array { .. } => match pcx.ty.sty { |
| ty::Array(_, length) => Some(vec![ |
| Slice(length.unwrap_usize(cx.tcx)) |
| ]), |
| _ => 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::Tuple(ref fs) => fs.len() as u64, |
| ty::Slice(..) | ty::Array(..) => match *ctor { |
| Slice(length) => length, |
| ConstantValue(_) => 0, |
| _ => bug!("bad slice pattern {:?} {:?}", ctor, ty) |
| }, |
| ty::Ref(..) => 1, |
| ty::Adt(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::Tuple(ref fs) => fs.into_iter().map(|t| *t).collect(), |
| ty::Slice(ty) | ty::Array(ty, _) => match *ctor { |
| Slice(length) => (0..length).map(|_| ty).collect(), |
| ConstantValue(_) => vec![], |
| _ => bug!("bad slice pattern {:?} {:?}", ctor, ty) |
| }, |
| ty::Ref(_, rty, _) => vec![rty], |
| ty::Adt(adt, substs) => { |
| if adt.is_box() { |
| // Use T as the sub pattern type of Box<T>. |
| vec![substs.type_at(0)] |
| } 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>( |
| tcx: TyCtxt<'_, 'tcx, '_>, |
| _span: Span, |
| ctor: &Constructor, |
| prefix: &[Pattern<'tcx>], |
| slice: &Option<Pattern<'tcx>>, |
| suffix: &[Pattern<'tcx>] |
| ) -> Result<bool, ErrorReported> { |
| let data: &[u8] = match *ctor { |
| ConstantValue(const_val) => { |
| let val = match const_val.val { |
| ConstValue::Unevaluated(..) | |
| ConstValue::ByRef(..) => bug!("unexpected ConstValue: {:?}", const_val), |
| ConstValue::Scalar(val) | ConstValue::ScalarPair(val, _) => val, |
| }; |
| if let Ok(ptr) = val.to_ptr() { |
| tcx.alloc_map.lock().unwrap_memory(ptr.alloc_id).bytes.as_ref() |
| } else { |
| bug!("unexpected non-ptr ConstantValue") |
| } |
| } |
| _ => 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 } => { |
| let b = value.unwrap_bits(tcx, ty::ParamEnv::empty().and(pat.ty)); |
| assert_eq!(b as u8 as u128, b); |
| if b as u8 != *ch { |
| return Ok(false); |
| } |
| } |
| _ => {} |
| } |
| } |
| |
| Ok(true) |
| } |
| |
| // Whether to evaluate a constructor using exhaustive integer matching. This is true if the |
| // constructor is a range or constant with an integer type. |
| fn should_treat_range_exhaustively(tcx: TyCtxt<'_, 'tcx, 'tcx>, ctor: &Constructor<'tcx>) -> bool { |
| let ty = match ctor { |
| ConstantValue(value) => value.ty, |
| ConstantRange(_, _, ty, _) => ty, |
| _ => return false, |
| }; |
| if let ty::Char | ty::Int(_) | ty::Uint(_) = ty.sty { |
| !ty.is_pointer_sized() || tcx.features().precise_pointer_size_matching |
| } else { |
| false |
| } |
| } |
| |
| /// For exhaustive integer matching, some constructors are grouped within other constructors |
| /// (namely integer typed values are grouped within ranges). However, when specialising these |
| /// constructors, we want to be specialising for the underlying constructors (the integers), not |
| /// the groups (the ranges). Thus we need to split the groups up. Splitting them up naïvely would |
| /// mean creating a separate constructor for every single value in the range, which is clearly |
| /// impractical. However, observe that for some ranges of integers, the specialisation will be |
| /// identical across all values in that range (i.e., there are equivalence classes of ranges of |
| /// constructors based on their `is_useful_specialized` outcome). These classes are grouped by |
| /// the patterns that apply to them (in the matrix `P`). We can split the range whenever the |
| /// patterns that apply to that range (specifically: the patterns that *intersect* with that range) |
| /// change. |
| /// Our solution, therefore, is to split the range constructor into subranges at every single point |
| /// the group of intersecting patterns changes (using the method described below). |
| /// And voilà! We're testing precisely those ranges that we need to, without any exhaustive matching |
| /// on actual integers. The nice thing about this is that the number of subranges is linear in the |
| /// number of rows in the matrix (i.e., the number of cases in the `match` statement), so we don't |
| /// need to be worried about matching over gargantuan ranges. |
| /// |
| /// Essentially, given the first column of a matrix representing ranges, looking like the following: |
| /// |
| /// |------| |----------| |-------| || |
| /// |-------| |-------| |----| || |
| /// |---------| |
| /// |
| /// We split the ranges up into equivalence classes so the ranges are no longer overlapping: |
| /// |
| /// |--|--|||-||||--||---|||-------| |-|||| || |
| /// |
| /// The logic for determining how to split the ranges is fairly straightforward: we calculate |
| /// boundaries for each interval range, sort them, then create constructors for each new interval |
| /// between every pair of boundary points. (This essentially sums up to performing the intuitive |
| /// merging operation depicted above.) |
| fn split_grouped_constructors<'p, 'a: 'p, 'tcx: 'a>( |
| tcx: TyCtxt<'a, 'tcx, 'tcx>, |
| ctors: Vec<Constructor<'tcx>>, |
| &Matrix(ref m): &Matrix<'p, 'tcx>, |
| ty: Ty<'tcx>, |
| ) -> Vec<Constructor<'tcx>> { |
| let mut split_ctors = Vec::with_capacity(ctors.len()); |
| |
| for ctor in ctors.into_iter() { |
| match ctor { |
| // For now, only ranges may denote groups of "subconstructors", so we only need to |
| // special-case constant ranges. |
| ConstantRange(..) if should_treat_range_exhaustively(tcx, &ctor) => { |
| // We only care about finding all the subranges within the range of the constructor |
| // range. Anything else is irrelevant, because it is guaranteed to result in |
| // `NotUseful`, which is the default case anyway, and can be ignored. |
| let ctor_range = IntRange::from_ctor(tcx, &ctor).unwrap(); |
| |
| /// Represents a border between 2 integers. Because the intervals spanning borders |
| /// must be able to cover every integer, we need to be able to represent |
| /// 2^128 + 1 such borders. |
| #[derive(Clone, Copy, PartialEq, Eq, PartialOrd, Ord)] |
| enum Border { |
| JustBefore(u128), |
| AfterMax, |
| } |
| |
| // A function for extracting the borders of an integer interval. |
| fn range_borders(r: IntRange<'_>) -> impl Iterator<Item = Border> { |
| let (lo, hi) = r.range.into_inner(); |
| let from = Border::JustBefore(lo); |
| let to = match hi.checked_add(1) { |
| Some(m) => Border::JustBefore(m), |
| None => Border::AfterMax, |
| }; |
| vec![from, to].into_iter() |
| } |
| |
| // `borders` is the set of borders between equivalence classes: each equivalence |
| // class lies between 2 borders. |
| let row_borders = m.iter() |
| .flat_map(|row| IntRange::from_pat(tcx, row[0])) |
| .flat_map(|range| ctor_range.intersection(&range)) |
| .flat_map(|range| range_borders(range)); |
| let ctor_borders = range_borders(ctor_range.clone()); |
| let mut borders: Vec<_> = row_borders.chain(ctor_borders).collect(); |
| borders.sort_unstable(); |
| |
| // We're going to iterate through every pair of borders, making sure that each |
| // represents an interval of nonnegative length, and convert each such interval |
| // into a constructor. |
| for IntRange { range, .. } in borders.windows(2).filter_map(|window| { |
| match (window[0], window[1]) { |
| (Border::JustBefore(n), Border::JustBefore(m)) => { |
| if n < m { |
| Some(IntRange { range: n..=(m - 1), ty }) |
| } else { |
| None |
| } |
| } |
| (Border::JustBefore(n), Border::AfterMax) => { |
| Some(IntRange { range: n..=u128::MAX, ty }) |
| } |
| (Border::AfterMax, _) => None, |
| } |
| }) { |
| split_ctors.push(IntRange::range_to_ctor(tcx, ty, range)); |
| } |
| } |
| // Any other constructor can be used unchanged. |
| _ => split_ctors.push(ctor), |
| } |
| } |
| |
| split_ctors |
| } |
| |
| /// Check whether there exists any shared value in either `ctor` or `pat` by intersecting them. |
| fn constructor_intersects_pattern<'p, 'a: 'p, 'tcx: 'a>( |
| tcx: TyCtxt<'a, 'tcx, 'tcx>, |
| ctor: &Constructor<'tcx>, |
| pat: &'p Pattern<'tcx>, |
| ) -> Option<SmallVec<[&'p Pattern<'tcx>; 2]>> { |
| if should_treat_range_exhaustively(tcx, ctor) { |
| match (IntRange::from_ctor(tcx, ctor), IntRange::from_pat(tcx, pat)) { |
| (Some(ctor), Some(pat)) => { |
| ctor.intersection(&pat).map(|_| { |
| let (pat_lo, pat_hi) = pat.range.into_inner(); |
| let (ctor_lo, ctor_hi) = ctor.range.into_inner(); |
| assert!(pat_lo <= ctor_lo && ctor_hi <= pat_hi); |
| smallvec![] |
| }) |
| } |
| _ => None, |
| } |
| } else { |
| // Fallback for non-ranges and ranges that involve floating-point numbers, which are not |
| // conveniently handled by `IntRange`. For these cases, the constructor may not be a range |
| // so intersection actually devolves into being covered by the pattern. |
| match constructor_covered_by_range(tcx, ctor, pat) { |
| Ok(true) => Some(smallvec![]), |
| Ok(false) | Err(ErrorReported) => None, |
| } |
| } |
| } |
| |
| fn constructor_covered_by_range<'a, 'tcx>( |
| tcx: TyCtxt<'a, 'tcx, 'tcx>, |
| ctor: &Constructor<'tcx>, |
| pat: &Pattern<'tcx>, |
| ) -> Result<bool, ErrorReported> { |
| let (from, to, end, ty) = match pat.kind { |
| box PatternKind::Constant { value } => (value, value, RangeEnd::Included, value.ty), |
| box PatternKind::Range { lo, hi, ty, end } => (lo, hi, end, ty), |
| _ => bug!("`constructor_covered_by_range` called with {:?}", pat), |
| }; |
| trace!("constructor_covered_by_range {:#?}, {:#?}, {:#?}, {}", ctor, from, to, ty); |
| let cmp_from = |c_from| compare_const_vals(tcx, c_from, from, ty::ParamEnv::empty().and(ty)) |
| .map(|res| res != Ordering::Less); |
| let cmp_to = |c_to| compare_const_vals(tcx, c_to, to, ty::ParamEnv::empty().and(ty)); |
| macro_rules! some_or_ok { |
| ($e:expr) => { |
| match $e { |
| Some(to) => to, |
| None => return Ok(false), // not char or int |
| } |
| }; |
| } |
| match *ctor { |
| ConstantValue(value) => { |
| let to = some_or_ok!(cmp_to(value)); |
| let end = (to == Ordering::Less) || |
| (end == RangeEnd::Included && to == Ordering::Equal); |
| Ok(some_or_ok!(cmp_from(value)) && end) |
| }, |
| ConstantRange(from, to, ty, RangeEnd::Included) => { |
| let to = some_or_ok!(cmp_to(ty::Const::from_bits( |
| tcx, |
| to, |
| ty::ParamEnv::empty().and(ty), |
| ))); |
| let end = (to == Ordering::Less) || |
| (end == RangeEnd::Included && to == Ordering::Equal); |
| Ok(some_or_ok!(cmp_from(ty::Const::from_bits( |
| tcx, |
| from, |
| ty::ParamEnv::empty().and(ty), |
| ))) && end) |
| }, |
| ConstantRange(from, to, ty, RangeEnd::Excluded) => { |
| let to = some_or_ok!(cmp_to(ty::Const::from_bits( |
| tcx, |
| to, |
| ty::ParamEnv::empty().and(ty) |
| ))); |
| let end = (to == Ordering::Less) || |
| (end == RangeEnd::Excluded && to == Ordering::Equal); |
| Ok(some_or_ok!(cmp_from(ty::Const::from_bits( |
| tcx, |
| from, |
| ty::ParamEnv::empty().and(ty))) |
| ) && end) |
| } |
| Single => Ok(true), |
| _ => bug!(), |
| } |
| } |
| |
| fn patterns_for_variant<'p, 'a: 'p, 'tcx: 'a>( |
| subpatterns: &'p [FieldPattern<'tcx>], |
| wild_patterns: &[&'p Pattern<'tcx>]) |
| -> SmallVec<[&'p Pattern<'tcx>; 2]> |
| { |
| let mut result = SmallVec::from_slice(wild_patterns); |
| |
| 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<'tcx>, |
| wild_patterns: &[&'p Pattern<'tcx>], |
| ) -> Option<SmallVec<[&'p Pattern<'tcx>; 2]>> { |
| let pat = &r[0]; |
| |
| let head = match *pat.kind { |
| PatternKind::AscribeUserType { ref subpattern, .. } => { |
| specialize(cx, ::std::slice::from_ref(&subpattern), constructor, wild_patterns) |
| } |
| |
| PatternKind::Binding { .. } | PatternKind::Wild => { |
| Some(SmallVec::from_slice(wild_patterns)) |
| } |
| |
| 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(smallvec![subpattern]) |
| } |
| |
| PatternKind::Constant { value } => { |
| match *constructor { |
| Slice(..) => { |
| // we extract an `Option` for the pointer because slices of zero elements don't |
| // necessarily point to memory, they are usually just integers. The only time |
| // they should be pointing to memory is when they are subslices of nonzero |
| // slices |
| let (opt_ptr, n, ty) = match value.ty.builtin_deref(false).unwrap().ty.sty { |
| ty::TyKind::Array(t, n) => (value.to_ptr(), n.unwrap_usize(cx.tcx), t), |
| ty::TyKind::Slice(t) => { |
| match value.val { |
| ConstValue::ScalarPair(ptr, n) => ( |
| ptr.to_ptr().ok(), |
| n.to_bits(cx.tcx.data_layout.pointer_size).unwrap() as u64, |
| t, |
| ), |
| _ => span_bug!( |
| pat.span, |
| "slice pattern constant must be scalar pair but is {:?}", |
| value, |
| ), |
| } |
| }, |
| _ => span_bug!( |
| pat.span, |
| "unexpected const-val {:?} with ctor {:?}", |
| value, |
| constructor, |
| ), |
| }; |
| if wild_patterns.len() as u64 == n { |
| // convert a constant slice/array pattern to a list of patterns. |
| match (n, opt_ptr) { |
| (0, _) => Some(SmallVec::new()), |
| (_, Some(ptr)) => { |
| let alloc = cx.tcx.alloc_map.lock().unwrap_memory(ptr.alloc_id); |
| let layout = cx.tcx.layout_of(cx.param_env.and(ty)).ok()?; |
| (0..n).map(|i| { |
| let ptr = ptr.offset(layout.size * i, &cx.tcx).ok()?; |
| let scalar = alloc.read_scalar( |
| &cx.tcx, ptr, layout.size, |
| ).ok()?; |
| let scalar = scalar.not_undef().ok()?; |
| let value = ty::Const::from_scalar(cx.tcx, scalar, ty); |
| let pattern = Pattern { |
| ty, |
| span: pat.span, |
| kind: box PatternKind::Constant { value }, |
| }; |
| Some(&*cx.pattern_arena.alloc(pattern)) |
| }).collect() |
| }, |
| (_, None) => span_bug!( |
| pat.span, |
| "non zero length slice with const-val {:?}", |
| value, |
| ), |
| } |
| } else { |
| None |
| } |
| } |
| _ => { |
| // If the constructor is a: |
| // Single value: add a row if the constructor equals the pattern. |
| // Range: add a row if the constructor contains the pattern. |
| constructor_intersects_pattern(cx.tcx, constructor, pat) |
| } |
| } |
| } |
| |
| PatternKind::Range { .. } => { |
| // If the constructor is a: |
| // Single value: add a row if the pattern contains the constructor. |
| // Range: add a row if the constructor intersects the pattern. |
| constructor_intersects_pattern(cx.tcx, constructor, pat) |
| } |
| |
| 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(smallvec![]), |
| 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 |
| }) |
| } |