/// (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-
+/// are trying to compute a predicate `U(P, p)` where `P` is a list of patterns (we refer to this as
+/// a matrix). `U(P, p)` represents whether, given an existing list of patterns
+/// `P_1 ..= P_m`, adding a new pattern `p` 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
+/// (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).
///
+/// During the course of the algorithm, the rows of the matrix won't just be individual patterns,
+/// but rather partially-deconstructed patterns in the form of a list of patterns. The paper
+/// calls those pattern-vectors, and we will call them pattern-stacks. The same holds for the
+/// new pattern `p`.
+///
/// For example, say we have the following:
/// ```
/// // x: (Option<bool>, Result<()>)
/// (None, Err(_)) => {}
/// }
/// ```
-/// Here, the matrix `P` is 3 x 2 (rows x columns).
+/// Here, the matrix `P` starts as:
/// [
-/// [Some(true), _],
-/// [None, Err(())],
-/// [None, Err(_)],
+/// [(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
+/// `[(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`.
+/// A list of patterns can be thought of as a stack, because we are mainly interested in the top of
+/// the stack at any given point, and we can pop or apply constructors to get new pattern-stacks.
+/// To match the paper, the top of the stack is at the beginning / on the left.
+///
+/// There are two important operations on pattern-stacks necessary to understand the algorithm:
+/// 1. We can pop a given constructor off the top of a stack. This operation is called
+/// `specialize`, and is denoted `S(c, p)` where `c` is a constructor (like `Some` or
+/// `None`) and `p` a pattern-stack.
+/// If the pattern on top of the stack can cover `c`, this removes the constructor and
+/// pushes its arguments onto the stack. It also expands OR-patterns into distinct patterns.
+/// Otherwise the pattern-stack is discarded.
+/// This essentially filters those pattern-stacks whose top covers the constructor `c` and
+/// discards the others.
+///
+/// For example, the first pattern above initially gives a stack `[(Some(true), _)]`. If we
+/// pop the tuple constructor, we are left with `[Some(true), _]`, and if we then pop the
+/// `Some` constructor we get `[true, _]`. If we had popped `None` instead, we would get
+/// nothing back.
///
-/// 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)))
+/// This returns zero or more new pattern-stacks, as follows. We look at the pattern `p_1`
+/// on top of the stack, and we have four cases:
+/// 1.1. `p_1 = c(r_1, .., r_a)`, i.e. the top of the stack has constructor `c`. We
+/// push onto the stack the arguments of this constructor, and return the result:
+/// r_1, .., r_a, p_2, .., p_n
+/// 1.2. `p_1 = c'(r_1, .., r_a')` where `c ≠ c'`. We discard the current stack and
+/// return nothing.
+/// 1.3. `p_1 = _`. We push onto the stack as many wildcards as the constructor `c` has
+/// arguments (its arity), and return the resulting stack:
+/// _, .., _, p_2, .., p_n
+/// 1.4. `p_1 = r_1 | r_2`. We expand the OR-pattern and then recurse on each resulting
+/// stack:
+/// S(c, (r_1, p_2, .., p_n))
+/// S(c, (r_2, p_2, .., p_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`.
+/// 2. We can pop a wildcard off the top of the stack. This is called `D(p)`, where `p` is
+/// a pattern-stack.
+/// 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.
///
-/// 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)))
+/// It is computed as follows. We look at the pattern `p_1` on top of the stack,
+/// and we have three cases:
+/// 1.1. `p_1 = c(r_1, .., r_a)`. We discard the current stack and return nothing.
+/// 1.2. `p_1 = _`. We return the rest of the stack:
+/// p_2, .., p_n
+/// 1.3. `p_1 = r_1 | r_2`. We expand the OR-pattern and then recurse on each resulting
+/// stack.
+/// D((r_1, p_2, .., p_n))
+/// D((r_2, p_2, .., p_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.
+///
+/// Both those operations extend straightforwardly to a list or pattern-stacks, i.e. a matrix, by
+/// working row-by-row. Popping a constructor ends up keeping only the matrix rows that start with
+/// the given constructor, and popping a wildcard keeps those rows that start with a wildcard.
///
-/// 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}`.
+/// operates principally on the first component of the matrix and new pattern-stack `p`.
/// 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.
+/// then `U(P, p)` is false.
+/// - Otherwise, `P` must be empty, so `U(P, p)` 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}))`
+/// We're going to match on the top of the new pattern-stack, `p_1`.
+/// - If `p_1 == c(r_1, .., r_a)`, i.e. we have a constructor pattern.
+/// Then, the usefulness of `p_1` can be reduced to whether it is useful when
+/// we ignore all the patterns in the first column of `P` that involve other constructors.
+/// This is where `S(c, P)` comes in:
+/// `U(P, p) := U(S(c, P), S(c, p))`
/// 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)))`
+///
+/// For example, if `P` is:
+/// [
+/// [Some(true), _],
+/// [None, 0],
+/// ]
+/// and `p` is [Some(false), 0], then we don't care about row 2 since we know `p` only
+/// matches values that row 2 doesn't. For row 1 however, we need to dig into the
+/// arguments of `Some` to know whether some new value is covered. So we compute
+/// `U([[true, _]], [false, 0])`.
+///
+/// - If `p_1 == _`, then we look at the list of constructors that appear in the first
+/// component of the rows of `P`:
+/// + If there are some constructors that aren't present, then we might think that the
+/// wildcard `_` is useful, since it covers those constructors that weren't covered
+/// before.
+/// That's almost correct, but only works if there were no wildcards in those first
+/// components. So we need to check that `p` is useful with respect to the rows that
+/// start with a wildcard, if there are any. This is where `D` comes in:
+/// `U(P, p) := U(D(P), D(p))`
+///
+/// For example, if `P` is:
+/// [
+/// [_, true, _],
+/// [None, false, 1],
+/// ]
+/// and `p` is [_, false, _], the `Some` constructor doesn't appear in `P`. So if we
+/// only had row 2, we'd know that `p` is useful. However row 1 starts with a
+/// wildcard, so we need to check whether `U([[true, _]], [false, 1])`.
+///
+/// + Otherwise, all possible constructors (for the relevant type) are present. In this
+/// case we must check whether the wildcard pattern covers any unmatched value. For
+/// that, we can think of the `_` pattern as a big OR-pattern that covers all
+/// possible constructors. For `Option`, that would mean `_ = None | Some(_)` for
+/// example. The wildcard pattern is useful in this case if it is useful when
+/// specialized to one of the possible constructors. So we compute:
+/// `U(P, p) := ∃(k ϵ constructors) U(S(k, P), S(k, p))`
+///
+/// For example, if `P` is:
+/// [
+/// [Some(true), _],
+/// [None, false],
+/// ]
+/// and `p` is [_, false], both `None` and `Some` constructors appear in the first
+/// components of `P`. We will therefore try popping both constructors in turn: we
+/// compute U([[true, _]], [_, false]) for the `Some` constructor, and U([[false]],
+/// [false]) for the `None` constructor. The first case returns true, so we know that
+/// `p` is useful for `P`. Indeed, it matches `[Some(false), _]` that wasn't matched
+/// before.
+///
+/// - If `p_1 == r_1 | r_2`, then the usefulness depends on each `r_i` separately:
+/// `U(P, p) := U(P, (r_1, p_2, .., p_n))
+/// || U(P, (r_2, p_2, .., p_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.
+/// throughout the code below. I'll make a quick note here about how exhaustive integer matching is
+/// accounted for, though.
///
/// Exhaustive integer matching
/// ---------------------------
/// 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
+/// of the matrix `P` and new pattern `p` 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_index::vec::Idx;
+use super::{compare_const_vals, PatternFoldable, PatternFolder};
use super::{FieldPat, Pat, PatKind, PatRange};
-use super::{PatternFoldable, PatternFolder, compare_const_vals};
use rustc::hir::def_id::DefId;
-use rustc::hir::{RangeEnd, HirId};
-use rustc::ty::{self, Ty, TyCtxt, TypeFoldable, Const};
-use rustc::ty::layout::{Integer, IntegerExt, VariantIdx, Size};
+use rustc::hir::{HirId, RangeEnd};
+use rustc::ty::layout::{Integer, IntegerExt, Size, VariantIdx};
+use rustc::ty::{self, Const, Ty, TyCtxt, TypeFoldable};
+use rustc::lint;
+use rustc::mir::interpret::{truncate, AllocId, ConstValue, Pointer, Scalar};
use rustc::mir::Field;
-use rustc::mir::interpret::{ConstValue, Scalar, truncate, AllocId, Pointer};
+use rustc::util::captures::Captures;
use rustc::util::common::ErrorReported;
-use rustc::lint;
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 smallvec::{smallvec, SmallVec};
+use std::cmp::{self, max, min, Ordering};
+use std::convert::TryInto;
use std::fmt;
use std::iter::{FromIterator, IntoIterator};
use std::ops::RangeInclusive;
use std::u128;
-use std::convert::TryInto;
pub fn expand_pattern<'a, 'tcx>(cx: &MatchCheckCtxt<'a, 'tcx>, pat: Pat<'tcx>) -> Pat<'tcx> {
LiteralExpander { tcx: cx.tcx }.fold_pattern(&pat)
// the easy case, deref a reference
(ConstValue::Scalar(Scalar::Ptr(p)), x, y) if x == y => {
let alloc = self.tcx.alloc_map.lock().unwrap_memory(p.alloc_id);
- ConstValue::ByRef {
- alloc,
- offset: p.offset,
- }
- },
+ ConstValue::ByRef { alloc, offset: p.offset }
+ }
// unsize array to slice if pattern is array but match value or other patterns are slice
(ConstValue::Scalar(Scalar::Ptr(p)), ty::Array(t, n), ty::Slice(u)) => {
assert_eq!(t, u);
start: p.offset.bytes().try_into().unwrap(),
end: n.eval_usize(self.tcx, ty::ParamEnv::empty()).try_into().unwrap(),
}
- },
+ }
// fat pointers stay the same
- | (ConstValue::Slice { .. }, _, _)
+ (ConstValue::Slice { .. }, _, _)
| (_, ty::Slice(_), ty::Slice(_))
- | (_, ty::Str, ty::Str)
- => val,
+ | (_, ty::Str, ty::Str) => val,
// FIXME(oli-obk): this is reachable for `const FOO: &&&u32 = &&&42;` being used
_ => bug!("cannot deref {:#?}, {} -> {}", val, crty, rty),
}
match (&pat.ty.kind, &*pat.kind) {
(
&ty::Ref(_, rty, _),
- &PatKind::Constant { value: Const {
- val,
- ty: ty::TyS { kind: ty::Ref(_, crty, _), .. },
- } },
- ) => {
- Pat {
- ty: pat.ty,
- span: pat.span,
- kind: box PatKind::Deref {
- subpattern: Pat {
- ty: rty,
- span: pat.span,
- kind: box PatKind::Constant { value: self.tcx.mk_const(Const {
+ &PatKind::Constant {
+ value: Const { val, ty: ty::TyS { kind: ty::Ref(_, crty, _), .. } },
+ },
+ ) => Pat {
+ ty: pat.ty,
+ span: pat.span,
+ kind: box PatKind::Deref {
+ subpattern: Pat {
+ ty: rty,
+ span: pat.span,
+ kind: box PatKind::Constant {
+ value: self.tcx.mk_const(Const {
val: self.fold_const_value_deref(*val, rty, crty),
ty: rty,
- }) },
- }
- }
- }
- }
- (_, &PatKind::Binding { subpattern: Some(ref s), .. }) => {
- s.fold_with(self)
- }
- _ => pat.super_fold_with(self)
+ }),
+ },
+ },
+ },
+ },
+ (_, &PatKind::Binding { subpattern: Some(ref s), .. }) => s.fold_with(self),
+ _ => pat.super_fold_with(self),
}
}
}
impl<'tcx> Pat<'tcx> {
fn is_wildcard(&self) -> bool {
match *self.kind {
- PatKind::Binding { subpattern: None, .. } | PatKind::Wild =>
- true,
- _ => false
+ PatKind::Binding { subpattern: None, .. } | PatKind::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>(Vec<SmallVec<[&'p Pat<'tcx>; 2]>>);
+/// A row of a matrix. Rows of len 1 are very common, which is why `SmallVec[_; 2]`
+/// works well.
+#[derive(Debug, Clone)]
+pub struct PatStack<'p, 'tcx>(SmallVec<[&'p Pat<'tcx>; 2]>);
+
+impl<'p, 'tcx> PatStack<'p, 'tcx> {
+ pub fn from_pattern(pat: &'p Pat<'tcx>) -> Self {
+ PatStack(smallvec![pat])
+ }
+
+ fn from_vec(vec: SmallVec<[&'p Pat<'tcx>; 2]>) -> Self {
+ PatStack(vec)
+ }
+
+ fn from_slice(s: &[&'p Pat<'tcx>]) -> Self {
+ PatStack(SmallVec::from_slice(s))
+ }
+
+ fn is_empty(&self) -> bool {
+ self.0.is_empty()
+ }
+
+ fn len(&self) -> usize {
+ self.0.len()
+ }
+
+ fn head(&self) -> &'p Pat<'tcx> {
+ self.0[0]
+ }
+
+ fn to_tail(&self) -> Self {
+ PatStack::from_slice(&self.0[1..])
+ }
+
+ fn iter(&self) -> impl Iterator<Item = &Pat<'tcx>> {
+ self.0.iter().map(|p| *p)
+ }
+
+ /// This computes `D(self)`. See top of the file for explanations.
+ fn specialize_wildcard(&self) -> Option<Self> {
+ if self.head().is_wildcard() { Some(self.to_tail()) } else { None }
+ }
+
+ /// This computes `S(constructor, self)`. See top of the file for explanations.
+ fn specialize_constructor<'a, 'q>(
+ &self,
+ cx: &mut MatchCheckCtxt<'a, 'tcx>,
+ constructor: &Constructor<'tcx>,
+ ctor_wild_subpatterns: &[&'q Pat<'tcx>],
+ ) -> Option<PatStack<'q, 'tcx>>
+ where
+ 'a: 'q,
+ 'p: 'q,
+ {
+ let new_heads = specialize_one_pattern(cx, self.head(), constructor, ctor_wild_subpatterns);
+ new_heads.map(|mut new_head| {
+ new_head.0.extend_from_slice(&self.0[1..]);
+ new_head
+ })
+ }
+}
+
+impl<'p, 'tcx> Default for PatStack<'p, 'tcx> {
+ fn default() -> Self {
+ PatStack(smallvec![])
+ }
+}
+
+impl<'p, 'tcx> FromIterator<&'p Pat<'tcx>> for PatStack<'p, 'tcx> {
+ fn from_iter<T>(iter: T) -> Self
+ where
+ T: IntoIterator<Item = &'p Pat<'tcx>>,
+ {
+ PatStack(iter.into_iter().collect())
+ }
+}
+
+/// A 2D matrix.
+pub struct Matrix<'p, 'tcx>(Vec<PatStack<'p, 'tcx>>);
impl<'p, 'tcx> Matrix<'p, 'tcx> {
pub fn empty() -> Self {
Matrix(vec![])
}
- pub fn push(&mut self, row: SmallVec<[&'p Pat<'tcx>; 2]>) {
+ pub fn push(&mut self, row: PatStack<'p, 'tcx>) {
self.0.push(row)
}
+
+ /// Iterate over the first component of each row
+ fn heads<'a>(&'a self) -> impl Iterator<Item = &'a Pat<'tcx>> + Captures<'p> {
+ self.0.iter().map(|r| r.head())
+ }
+
+ /// This computes `D(self)`. See top of the file for explanations.
+ fn specialize_wildcard(&self) -> Self {
+ self.0.iter().filter_map(|r| r.specialize_wildcard()).collect()
+ }
+
+ /// This computes `S(constructor, self)`. See top of the file for explanations.
+ fn specialize_constructor<'a, 'q>(
+ &self,
+ cx: &mut MatchCheckCtxt<'a, 'tcx>,
+ constructor: &Constructor<'tcx>,
+ ctor_wild_subpatterns: &[&'q Pat<'tcx>],
+ ) -> Matrix<'q, 'tcx>
+ where
+ 'a: 'q,
+ 'p: 'q,
+ {
+ Matrix(
+ self.0
+ .iter()
+ .filter_map(|r| r.specialize_constructor(cx, constructor, ctor_wild_subpatterns))
+ .collect(),
+ )
+ }
}
/// Pretty-printer for matrices of patterns, example:
-/// ++++++++++++++++++++++++++
-/// + _ + [] +
-/// ++++++++++++++++++++++++++
-/// + true + [First] +
-/// ++++++++++++++++++++++++++
-/// + true + [Second(true)] +
-/// ++++++++++++++++++++++++++
-/// + false + [_] +
-/// ++++++++++++++++++++++++++
-/// + _ + [_, _, ..tail] +
-/// ++++++++++++++++++++++++++
+/// +++++++++++++++++++++++++++++
+/// + _ + [] +
+/// +++++++++++++++++++++++++++++
+/// + 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 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 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);
}
}
-impl<'p, 'tcx> FromIterator<SmallVec<[&'p Pat<'tcx>; 2]>> for Matrix<'p, 'tcx> {
+impl<'p, 'tcx> FromIterator<PatStack<'p, 'tcx>> for Matrix<'p, 'tcx> {
fn from_iter<T>(iter: T) -> Self
- where T: IntoIterator<Item=SmallVec<[&'p Pat<'tcx>; 2]>>
+ where
+ T: IntoIterator<Item = PatStack<'p, 'tcx>>,
{
Matrix(iter.into_iter().collect())
}
ConstantValue(&'tcx ty::Const<'tcx>, Span),
/// Ranges of literal values (`2..=5` and `2..5`).
ConstantRange(u128, u128, Ty<'tcx>, RangeEnd, Span),
- /// Array patterns of length n.
- Slice(u64),
+ /// Array patterns of length `n`.
+ FixedLenSlice(u64),
+ /// Slice patterns. Captures any array constructor of `length >= i + j`.
+ VarLenSlice(u64, u64),
+ /// Fake extra constructor for enums that aren't allowed to be matched exhaustively.
+ NonExhaustive,
}
// Ignore spans when comparing, they don't carry semantic information as they are only for lints.
fn eq(&self, other: &Self) -> bool {
match (self, other) {
(Constructor::Single, Constructor::Single) => true,
+ (Constructor::NonExhaustive, Constructor::NonExhaustive) => true,
(Constructor::Variant(a), Constructor::Variant(b)) => a == b,
(Constructor::ConstantValue(a, _), Constructor::ConstantValue(b, _)) => a == b,
(
Constructor::ConstantRange(a_start, a_end, a_ty, a_range_end, _),
Constructor::ConstantRange(b_start, b_end, b_ty, b_range_end, _),
) => a_start == b_start && a_end == b_end && a_ty == b_ty && a_range_end == b_range_end,
- (Constructor::Slice(a), Constructor::Slice(b)) => a == b,
+ (Constructor::FixedLenSlice(a), Constructor::FixedLenSlice(b)) => a == b,
+ (
+ Constructor::VarLenSlice(a_prefix, a_suffix),
+ Constructor::VarLenSlice(b_prefix, b_suffix),
+ ) => a_prefix == b_prefix && a_suffix == b_suffix,
_ => false,
}
}
impl<'tcx> Constructor<'tcx> {
fn is_slice(&self) -> bool {
match self {
- Slice { .. } => true,
+ FixedLenSlice { .. } | VarLenSlice { .. } => true,
_ => false,
}
}
VariantIdx::new(0)
}
ConstantValue(c, _) => crate::const_eval::const_variant_index(cx.tcx, cx.param_env, c),
- _ => bug!("bad constructor {:?} for adt {:?}", self, adt)
+ _ => bug!("bad constructor {:?} for adt {:?}", self, adt),
}
}
ty::Const::from_bits(tcx, *hi, ty),
)
}
- Constructor::Slice(val) => format!("[{}]", val),
+ Constructor::FixedLenSlice(val) => format!("[{}]", val),
+ Constructor::VarLenSlice(prefix, suffix) => format!("[{}, .., {}]", prefix, suffix),
_ => bug!("bad constructor being displayed: `{:?}", self),
}
}
+
+ // Returns the set of constructors covered by `self` but not by
+ // anything in `other_ctors`.
+ fn subtract_ctors(
+ &self,
+ tcx: TyCtxt<'tcx>,
+ param_env: ty::ParamEnv<'tcx>,
+ other_ctors: &Vec<Constructor<'tcx>>,
+ ) -> Vec<Constructor<'tcx>> {
+ match *self {
+ // Those constructors can only match themselves.
+ Single | Variant(_) => {
+ if other_ctors.iter().any(|c| c == self) {
+ vec![]
+ } else {
+ vec![self.clone()]
+ }
+ }
+ FixedLenSlice(self_len) => {
+ let overlaps = |c: &Constructor<'_>| match *c {
+ FixedLenSlice(other_len) => other_len == self_len,
+ VarLenSlice(prefix, suffix) => prefix + suffix <= self_len,
+ _ => false,
+ };
+ if other_ctors.iter().any(overlaps) { vec![] } else { vec![self.clone()] }
+ }
+ VarLenSlice(..) => {
+ let mut remaining_ctors = vec![self.clone()];
+
+ // For each used ctor, subtract from the current set of constructors.
+ // Naming: we remove the "neg" constructors from the "pos" ones.
+ // Remember, `VarLenSlice(i, j)` covers the union of `FixedLenSlice` from
+ // `i + j` to infinity.
+ for neg_ctor in other_ctors {
+ remaining_ctors = remaining_ctors
+ .into_iter()
+ .flat_map(|pos_ctor| -> SmallVec<[Constructor<'tcx>; 1]> {
+ // Compute `pos_ctor \ neg_ctor`.
+ match (&pos_ctor, neg_ctor) {
+ (&FixedLenSlice(pos_len), &VarLenSlice(neg_prefix, neg_suffix)) => {
+ let neg_len = neg_prefix + neg_suffix;
+ if neg_len <= pos_len {
+ smallvec![]
+ } else {
+ smallvec![pos_ctor]
+ }
+ }
+ (
+ &VarLenSlice(pos_prefix, pos_suffix),
+ &VarLenSlice(neg_prefix, neg_suffix),
+ ) => {
+ let neg_len = neg_prefix + neg_suffix;
+ let pos_len = pos_prefix + pos_suffix;
+ if neg_len <= pos_len {
+ smallvec![]
+ } else {
+ (pos_len..neg_len).map(FixedLenSlice).collect()
+ }
+ }
+ (&VarLenSlice(pos_prefix, pos_suffix), &FixedLenSlice(neg_len)) => {
+ let pos_len = pos_prefix + pos_suffix;
+ if neg_len < pos_len {
+ smallvec![pos_ctor]
+ } else {
+ (pos_len..neg_len)
+ .map(FixedLenSlice)
+ // We know that `neg_len + 1 >= pos_len >= pos_suffix`.
+ .chain(Some(VarLenSlice(
+ neg_len + 1 - pos_suffix,
+ pos_suffix,
+ )))
+ .collect()
+ }
+ }
+ _ if pos_ctor == *neg_ctor => smallvec![],
+ _ => smallvec![pos_ctor],
+ }
+ })
+ .collect();
+
+ // If the constructors that have been considered so far already cover
+ // the entire range of `self`, no need to look at more constructors.
+ if remaining_ctors.is_empty() {
+ break;
+ }
+ }
+
+ remaining_ctors
+ }
+ ConstantRange(..) | ConstantValue(..) => {
+ let mut remaining_ctors = vec![self.clone()];
+ for other_ctor in other_ctors {
+ if other_ctor == self {
+ // If a constructor appears in a `match` arm, we can
+ // eliminate it straight away.
+ remaining_ctors = vec![]
+ } else if let Some(interval) = IntRange::from_ctor(tcx, param_env, other_ctor) {
+ // Refine the required constructors for the type by subtracting
+ // the range defined by the current constructor pattern.
+ remaining_ctors = interval.subtract_from(tcx, param_env, remaining_ctors);
+ }
+
+ // If the constructor patterns that have been considered so far
+ // already cover the entire range of values, then we know the
+ // constructor is not missing, and we can move on to the next one.
+ if remaining_ctors.is_empty() {
+ break;
+ }
+ }
+
+ // If a constructor has not been matched, then it is missing.
+ // We add `remaining_ctors` instead of `self`, because then we can
+ // provide more detailed error information about precisely which
+ // ranges have been omitted.
+ remaining_ctors
+ }
+ // This constructor is never covered by anything else
+ NonExhaustive => vec![NonExhaustive],
+ }
+ }
+
+ /// This returns one wildcard pattern for each argument to this constructor.
+ fn wildcard_subpatterns<'a>(
+ &self,
+ cx: &MatchCheckCtxt<'a, 'tcx>,
+ ty: Ty<'tcx>,
+ ) -> Vec<Pat<'tcx>> {
+ debug!("wildcard_subpatterns({:#?}, {:?})", self, ty);
+
+ match self {
+ Single | Variant(_) => match ty.kind {
+ ty::Tuple(ref fs) => {
+ fs.into_iter().map(|t| t.expect_ty()).map(Pat::wildcard_from_ty).collect()
+ }
+ ty::Ref(_, rty, _) => vec![Pat::wildcard_from_ty(rty)],
+ ty::Adt(adt, substs) => {
+ if adt.is_box() {
+ // Use T as the sub pattern type of Box<T>.
+ vec![Pat::wildcard_from_ty(substs.type_at(0))]
+ } else {
+ let variant = &adt.variants[self.variant_index_for_adt(cx, adt)];
+ let is_non_exhaustive =
+ variant.is_field_list_non_exhaustive() && !cx.is_local(ty);
+ variant
+ .fields
+ .iter()
+ .map(|field| {
+ let is_visible = adt.is_enum()
+ || field.vis.is_accessible_from(cx.module, cx.tcx);
+ let is_uninhabited = cx.is_uninhabited(field.ty(cx.tcx, substs));
+ match (is_visible, is_non_exhaustive, is_uninhabited) {
+ // Treat all uninhabited types in non-exhaustive variants as
+ // `TyErr`.
+ (_, true, true) => cx.tcx.types.err,
+ // 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.
+ (false, ..) => cx.tcx.types.err,
+ (true, ..) => {
+ let ty = field.ty(cx.tcx, substs);
+ match ty.kind {
+ // If the field type returned is an array of an unknown
+ // size return an TyErr.
+ ty::Array(_, len)
+ if len
+ .try_eval_usize(cx.tcx, cx.param_env)
+ .is_none() =>
+ {
+ cx.tcx.types.err
+ }
+ _ => ty,
+ }
+ }
+ }
+ })
+ .map(Pat::wildcard_from_ty)
+ .collect()
+ }
+ }
+ _ => vec![],
+ },
+ FixedLenSlice(_) | VarLenSlice(..) => match ty.kind {
+ ty::Slice(ty) | ty::Array(ty, _) => {
+ let arity = self.arity(cx, ty);
+ (0..arity).map(|_| Pat::wildcard_from_ty(ty)).collect()
+ }
+ _ => bug!("bad slice pattern {:?} {:?}", self, ty),
+ },
+ ConstantValue(..) | ConstantRange(..) | NonExhaustive => vec![],
+ }
+ }
+
+ /// 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 arity<'a>(&self, cx: &MatchCheckCtxt<'a, 'tcx>, ty: Ty<'tcx>) -> u64 {
+ debug!("Constructor::arity({:#?}, {:?})", self, ty);
+ match self {
+ Single | Variant(_) => match ty.kind {
+ ty::Tuple(ref fs) => fs.len() as u64,
+ ty::Slice(..) | ty::Array(..) => bug!("bad slice pattern {:?} {:?}", self, ty),
+ ty::Ref(..) => 1,
+ ty::Adt(adt, _) => {
+ adt.variants[self.variant_index_for_adt(cx, adt)].fields.len() as u64
+ }
+ _ => 0,
+ },
+ FixedLenSlice(length) => *length,
+ VarLenSlice(prefix, suffix) => prefix + suffix,
+ ConstantValue(..) | ConstantRange(..) | NonExhaustive => 0,
+ }
+ }
+
+ /// Apply a constructor to a list of patterns, yielding a new pattern. `pats`
+ /// must have as many elements as this constructor's arity.
+ ///
+ /// Examples:
+ /// `self`: `Constructor::Single`
+ /// `ty`: `(u32, u32, u32)`
+ /// `pats`: `[10, 20, _]`
+ /// returns `(10, 20, _)`
+ ///
+ /// `self`: `Constructor::Variant(Option::Some)`
+ /// `ty`: `Option<bool>`
+ /// `pats`: `[false]`
+ /// returns `Some(false)`
+ fn apply<'a>(
+ &self,
+ cx: &MatchCheckCtxt<'a, 'tcx>,
+ ty: Ty<'tcx>,
+ pats: impl IntoIterator<Item = Pat<'tcx>>,
+ ) -> Pat<'tcx> {
+ let mut subpatterns = pats.into_iter();
+
+ let pat = match self {
+ Single | Variant(_) => match ty.kind {
+ ty::Adt(..) | ty::Tuple(..) => {
+ let subpatterns = subpatterns
+ .enumerate()
+ .map(|(i, p)| FieldPat { field: Field::new(i), pattern: p })
+ .collect();
+
+ if let ty::Adt(adt, substs) = ty.kind {
+ if adt.is_enum() {
+ PatKind::Variant {
+ adt_def: adt,
+ substs,
+ variant_index: self.variant_index_for_adt(cx, adt),
+ subpatterns,
+ }
+ } else {
+ PatKind::Leaf { subpatterns }
+ }
+ } else {
+ PatKind::Leaf { subpatterns }
+ }
+ }
+ ty::Ref(..) => PatKind::Deref { subpattern: subpatterns.nth(0).unwrap() },
+ ty::Slice(_) | ty::Array(..) => bug!("bad slice pattern {:?} {:?}", self, ty),
+ _ => PatKind::Wild,
+ },
+ FixedLenSlice(_) => {
+ PatKind::Slice { prefix: subpatterns.collect(), slice: None, suffix: vec![] }
+ }
+ &VarLenSlice(prefix_len, _) => {
+ let prefix = subpatterns.by_ref().take(prefix_len as usize).collect();
+ let suffix = subpatterns.collect();
+ let wild = Pat::wildcard_from_ty(ty);
+ PatKind::Slice { prefix, slice: Some(wild), suffix }
+ }
+ &ConstantValue(value, _) => PatKind::Constant { value },
+ &ConstantRange(lo, hi, ty, end, _) => PatKind::Range(PatRange {
+ 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)),
+ end,
+ }),
+ NonExhaustive => PatKind::Wild,
+ };
+
+ Pat { ty, span: DUMMY_SP, kind: Box::new(pat) }
+ }
+
+ /// Like `apply`, but where all the subpatterns are wildcards `_`.
+ fn apply_wildcards<'a>(&self, cx: &MatchCheckCtxt<'a, 'tcx>, ty: Ty<'tcx>) -> Pat<'tcx> {
+ let subpatterns = self.wildcard_subpatterns(cx, ty).into_iter().rev();
+ self.apply(cx, ty, subpatterns)
+ }
}
#[derive(Clone, Debug)]
pub enum Usefulness<'tcx> {
Useful,
UsefulWithWitness(Vec<Witness<'tcx>>),
- NotUseful
+ NotUseful,
}
impl<'tcx> Usefulness<'tcx> {
+ fn new_useful(preference: WitnessPreference) -> Self {
+ match preference {
+ ConstructWitness => UsefulWithWitness(vec![Witness(vec![])]),
+ LeaveOutWitness => Useful,
+ }
+ }
+
fn is_useful(&self) -> bool {
match *self {
NotUseful => false,
- _ => true
+ _ => true,
+ }
+ }
+
+ fn apply_constructor(
+ self,
+ cx: &MatchCheckCtxt<'_, 'tcx>,
+ ctor: &Constructor<'tcx>,
+ ty: Ty<'tcx>,
+ ) -> Self {
+ match self {
+ UsefulWithWitness(witnesses) => UsefulWithWitness(
+ witnesses
+ .into_iter()
+ .map(|witness| witness.apply_constructor(cx, &ctor, ty))
+ .collect(),
+ ),
+ x => x,
+ }
+ }
+
+ fn apply_wildcard(self, ty: Ty<'tcx>) -> Self {
+ match self {
+ UsefulWithWitness(witnesses) => {
+ let wild = Pat::wildcard_from_ty(ty);
+ UsefulWithWitness(
+ witnesses
+ .into_iter()
+ .map(|mut witness| {
+ witness.0.push(wild.clone());
+ witness
+ })
+ .collect(),
+ )
+ }
+ x => x,
+ }
+ }
+
+ fn apply_missing_ctors(
+ self,
+ cx: &MatchCheckCtxt<'_, 'tcx>,
+ ty: Ty<'tcx>,
+ missing_ctors: &MissingConstructors<'tcx>,
+ ) -> Self {
+ match self {
+ UsefulWithWitness(witnesses) => {
+ let new_patterns: Vec<_> =
+ missing_ctors.iter().map(|ctor| ctor.apply_wildcards(cx, ty)).collect();
+ // Add the new patterns to each witness
+ UsefulWithWitness(
+ witnesses
+ .into_iter()
+ .flat_map(|witness| {
+ new_patterns.iter().map(move |pat| {
+ let mut witness = witness.clone();
+ witness.0.push(pat.clone());
+ witness
+ })
+ })
+ .collect(),
+ )
+ }
+ x => x,
}
}
}
#[derive(Copy, Clone, Debug)]
pub enum WitnessPreference {
ConstructWitness,
- LeaveOutWitness
+ LeaveOutWitness,
}
#[derive(Copy, Clone, Debug)]
struct PatCtxt<'tcx> {
ty: Ty<'tcx>,
- max_slice_length: u64,
span: Span,
}
self.0.into_iter().next().unwrap()
}
- 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| {
- Pat {
- ty,
- span: DUMMY_SP,
- kind: box PatKind::Wild,
- }
- }));
- self.apply_constructor(cx, ctor, ty)
- }
-
/// Constructs a partial witness for a pattern given a list of
/// patterns expanded by the specialization step.
///
/// pats: [(false, "foo"), 42] => X { a: (false, "foo"), b: 42 }
fn apply_constructor<'a>(
mut self,
- cx: &MatchCheckCtxt<'a,'tcx>,
+ cx: &MatchCheckCtxt<'a, 'tcx>,
ctor: &Constructor<'tcx>,
- ty: Ty<'tcx>)
- -> Self
- {
- let arity = constructor_arity(cx, ctor, ty);
+ ty: Ty<'tcx>,
+ ) -> Self {
+ let arity = ctor.arity(cx, ty);
let pat = {
let len = self.0.len() as u64;
- let mut pats = self.0.drain((len - arity) as usize..).rev();
-
- match ty.kind {
- ty::Adt(..) |
- ty::Tuple(..) => {
- let pats = pats.enumerate().map(|(i, p)| {
- FieldPat {
- field: Field::new(i),
- pattern: p
- }
- }).collect();
-
- if let ty::Adt(adt, substs) = ty.kind {
- if adt.is_enum() {
- PatKind::Variant {
- adt_def: adt,
- substs,
- variant_index: ctor.variant_index_for_adt(cx, adt),
- subpatterns: pats
- }
- } else {
- PatKind::Leaf { subpatterns: pats }
- }
- } else {
- PatKind::Leaf { subpatterns: pats }
- }
- }
-
- ty::Ref(..) => {
- PatKind::Deref { subpattern: pats.nth(0).unwrap() }
- }
-
- ty::Slice(_) | ty::Array(..) => {
- PatKind::Slice {
- prefix: pats.collect(),
- slice: None,
- suffix: vec![]
- }
- }
-
- _ => {
- match *ctor {
- ConstantValue(value, _) => PatKind::Constant { value },
- ConstantRange(lo, hi, ty, end, _) => PatKind::Range(PatRange {
- 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)),
- end,
- }),
- _ => PatKind::Wild,
- }
- }
- }
+ let pats = self.0.drain((len - arity) as usize..).rev();
+ ctor.apply(cx, ty, pats)
};
- self.0.push(Pat {
- ty,
- span: DUMMY_SP,
- kind: Box::new(pat),
- });
+ self.0.push(pat);
self
}
) -> Vec<Constructor<'tcx>> {
debug!("all_constructors({:?})", pcx.ty);
let ctors = match pcx.ty.kind {
- ty::Bool => {
- [true, false].iter().map(|&b| {
- ConstantValue(ty::Const::from_bool(cx.tcx, b), pcx.span)
- }).collect()
- }
+ ty::Bool => [true, false]
+ .iter()
+ .map(|&b| ConstantValue(ty::Const::from_bool(cx.tcx, b), pcx.span))
+ .collect(),
ty::Array(ref sub_ty, len) if len.try_eval_usize(cx.tcx, cx.param_env).is_some() => {
let len = len.eval_usize(cx.tcx, cx.param_env);
- if len != 0 && cx.is_uninhabited(sub_ty) {
- vec![]
- } else {
- vec![Slice(len)]
- }
+ if len != 0 && cx.is_uninhabited(sub_ty) { vec![] } else { vec![FixedLenSlice(len)] }
}
// Treat arrays of a constant but unknown length like slices.
- ty::Array(ref sub_ty, _) |
- ty::Slice(ref sub_ty) => {
+ ty::Array(ref sub_ty, _) | ty::Slice(ref sub_ty) => {
if cx.is_uninhabited(sub_ty) {
- vec![Slice(0)]
+ vec![FixedLenSlice(0)]
} else {
- (0..pcx.max_slice_length+1).map(|length| Slice(length)).collect()
+ vec![VarLenSlice(0, 0)]
}
}
- ty::Adt(def, substs) if def.is_enum() => {
- def.variants.iter()
- .filter(|v| {
- !cx.tcx.features().exhaustive_patterns ||
- !v.uninhabited_from(cx.tcx, substs, def.adt_kind()).contains(cx.tcx, cx.module)
- })
- .map(|v| Variant(v.def_id))
- .collect()
- }
+ ty::Adt(def, substs) if def.is_enum() => def
+ .variants
+ .iter()
+ .filter(|v| {
+ !cx.tcx.features().exhaustive_patterns
+ || !v
+ .uninhabited_from(cx.tcx, substs, def.adt_kind())
+ .contains(cx.tcx, cx.module)
+ })
+ .map(|v| Variant(v.def_id))
+ .collect(),
ty::Char => {
vec![
// The valid Unicode Scalar Value ranges.
}
}
};
- ctors
-}
-fn max_slice_length<'p, 'a, 'tcx, I>(cx: &mut MatchCheckCtxt<'a, 'tcx>, patterns: I) -> u64
-where
- I: Iterator<Item = &'p Pat<'tcx>>,
- 'tcx: 'p,
-{
- // 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 {
- PatKind::Constant { value } => {
- // extract the length of an array/slice from a constant
- match (value.val, &value.ty.kind) {
- (_, ty::Array(_, n)) => max_fixed_len = cmp::max(
- max_fixed_len,
- n.eval_usize(cx.tcx, cx.param_env),
- ),
- (ConstValue::Slice{ start, end, .. }, ty::Slice(_)) => max_fixed_len = cmp::max(
- max_fixed_len,
- (end - start) as u64,
- ),
- _ => {},
- }
- }
- PatKind::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);
- }
- PatKind::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);
- }
- _ => {}
- }
+ // 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.
+ let is_privately_empty = ctors.is_empty() && !cx.is_uninhabited(pcx.ty);
+ let is_declared_nonexhaustive = cx.is_non_exhaustive_enum(pcx.ty) && !cx.is_local(pcx.ty);
+ let is_non_exhaustive = is_privately_empty
+ || is_declared_nonexhaustive
+ || (pcx.ty.is_ptr_sized_integral() && !cx.tcx.features().precise_pointer_size_matching);
+ if is_non_exhaustive {
+ // 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.
+ //
+ // If the enum is declared as `#[non_exhaustive]`, we treat it as if it had an additionnal
+ // "unknown" constructor. However there is no point in enumerating all possible variants,
+ // because the user can't actually match against them themselves. So we return only the
+ // fictitious constructor.
+ // 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 only `_` as the witness.
+ return vec![NonExhaustive];
}
- cmp::max(max_fixed_len + 1, max_prefix_len + max_suffix_len)
+ ctors
}
/// An inclusive interval, used for precise integer exhaustiveness checking.
// This is a more general form of the previous branch.
val
} else {
- return None
+ return None;
};
let val = val ^ bias;
Some(IntRange { range: val..=val, ty, span })
}
box PatKind::AscribeUserType { ref subpattern, .. } => {
pat = subpattern;
- },
+ }
_ => return None,
}
}
let bits = Integer::from_attr(&tcx, SignedInt(ity)).size().bits() as u128;
1u128 << (bits - 1)
}
- _ => 0
+ _ => 0,
}
}
param_env: ty::ParamEnv<'tcx>,
ranges: Vec<Constructor<'tcx>>,
) -> Vec<Constructor<'tcx>> {
- let ranges = ranges.into_iter().filter_map(|r| {
- IntRange::from_ctor(tcx, param_env, &r).map(|i| i.range)
- });
+ let ranges = ranges
+ .into_iter()
+ .filter_map(|r| IntRange::from_ctor(tcx, param_env, &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 {
+ 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, self.span),
- );
+ remaining_ranges.push(Self::range_to_ctor(
+ tcx,
+ ty,
+ subrange_lo..=subrange_hi,
+ self.span,
+ ));
} 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), self.span),
- );
+ remaining_ranges.push(Self::range_to_ctor(
+ tcx,
+ ty,
+ subrange_lo..=(lo - 1),
+ self.span,
+ ));
}
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, self.span),
- );
+ remaining_ranges.push(Self::range_to_ctor(
+ tcx,
+ ty,
+ (hi + 1)..=subrange_hi,
+ self.span,
+ ));
}
}
}
}
}
-// 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,
+// A struct to compute a set of constructors equivalent to `all_ctors \ used_ctors`.
+struct MissingConstructors<'tcx> {
+ tcx: TyCtxt<'tcx>,
+ param_env: ty::ParamEnv<'tcx>,
+ all_ctors: Vec<Constructor<'tcx>>,
+ used_ctors: Vec<Constructor<'tcx>>,
}
-// Used by `compute_missing_ctors`.
-#[derive(Debug, PartialEq)]
-enum MissingCtors<'tcx> {
- Empty,
- NonEmpty,
+impl<'tcx> MissingConstructors<'tcx> {
+ fn new(
+ tcx: TyCtxt<'tcx>,
+ param_env: ty::ParamEnv<'tcx>,
+ all_ctors: Vec<Constructor<'tcx>>,
+ used_ctors: Vec<Constructor<'tcx>>,
+ ) -> Self {
+ MissingConstructors { tcx, param_env, all_ctors, used_ctors }
+ }
- // Note that the Vec can be empty.
- Ctors(Vec<Constructor<'tcx>>),
-}
+ fn into_inner(self) -> (Vec<Constructor<'tcx>>, Vec<Constructor<'tcx>>) {
+ (self.all_ctors, self.used_ctors)
+ }
-// 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<'tcx>(
- info: MissingCtorsInfo,
- tcx: TyCtxt<'tcx>,
- param_env: ty::ParamEnv<'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, param_env, 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, param_env, refined_ctors);
- }
+ fn is_empty(&self) -> bool {
+ self.iter().next().is_none()
+ }
+ /// Whether this contains all the constructors for the given type or only a
+ /// subset.
+ fn all_ctors_are_missing(&self) -> bool {
+ self.used_ctors.is_empty()
+ }
- // 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);
- }
+ /// Iterate over all_ctors \ used_ctors
+ fn iter<'a>(&'a self) -> impl Iterator<Item = Constructor<'tcx>> + Captures<'a> {
+ self.all_ctors.iter().flat_map(move |req_ctor| {
+ req_ctor.subtract_ctors(self.tcx, self.param_env, &self.used_ctors)
+ })
}
+}
- if info == MissingCtorsInfo::Emptiness {
- // If we reached here, the set is empty.
- MissingCtors::Empty
- } else {
- MissingCtors::Ctors(missing_ctors)
+impl<'tcx> fmt::Debug for MissingConstructors<'tcx> {
+ fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+ let ctors: Vec<_> = self.iter().collect();
+ write!(f, "{:?}", ctors)
}
}
pub fn is_useful<'p, 'a, 'tcx>(
cx: &mut MatchCheckCtxt<'a, 'tcx>,
matrix: &Matrix<'p, 'tcx>,
- v: &[&Pat<'tcx>],
- witness: WitnessPreference,
+ v: &PatStack<'_, 'tcx>,
+ witness_preference: WitnessPreference,
hir_id: HirId,
) -> Usefulness<'tcx> {
let &Matrix(ref rows) = matrix;
// 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,
- }
+ Usefulness::new_useful(witness_preference)
} else {
NotUseful
- }
+ };
};
assert!(rows.iter().all(|r| r.len() == v.len()));
- let (ty, span) = rows.iter()
- .map(|r| (r[0].ty, r[0].span))
+ let (ty, span) = matrix
+ .heads()
+ .map(|r| (r.ty, r.span))
.find(|(ty, _)| !ty.references_error())
- .unwrap_or((v[0].ty, v[0].span));
+ .unwrap_or((v.head().ty, v.head().span));
let pcx = PatCtxt {
// TyErr is used to represent the type of wildcard patterns matching
// against inaccessible (private) fields of structs, so that we won't
// introducing uninhabited patterns for inaccessible fields. We
// need to figure out how to model that.
ty,
- max_slice_length: max_slice_length(cx, rows.iter().map(|r| r[0]).chain(Some(v[0]))),
span,
};
- debug!("is_useful_expand_first_col: pcx={:#?}, expanding {:#?}", pcx, v[0]);
+ debug!("is_useful_expand_first_col: pcx={:#?}, expanding {:#?}", pcx, v.head());
- if let Some(constructors) = pat_constructors(cx, v[0], pcx) {
- debug!("is_useful - expanding constructors: {:#?}", constructors);
+ if let Some(constructor) = pat_constructor(cx, v.head(), pcx) {
+ debug!("is_useful - expanding constructor: {:#?}", constructor);
split_grouped_constructors(
- cx.tcx, cx.param_env, constructors, matrix, pcx.ty, pcx.span, Some(hir_id),
- ).into_iter().map(|c|
- is_useful_specialized(cx, matrix, v, c, pcx.ty, witness, hir_id)
- ).find(|result| result.is_useful()).unwrap_or(NotUseful)
+ cx.tcx,
+ cx.param_env,
+ pcx,
+ vec![constructor],
+ matrix,
+ pcx.span,
+ Some(hir_id),
+ )
+ .into_iter()
+ .map(|c| is_useful_specialized(cx, matrix, v, c, pcx.ty, witness_preference, hir_id))
+ .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();
+ let used_ctors: Vec<Constructor<'_>> =
+ matrix.heads().filter_map(|p| pat_constructor(cx, p, pcx)).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 `_`).
// 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, cx.param_env, &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);
+ // Missing constructors are those that are not matched by any non-wildcard patterns in the
+ // current column. We only fully construct them on-demand, because they're rarely used and
+ // can be big.
+ let missing_ctors = MissingConstructors::new(cx.tcx, cx.param_env, all_ctors, used_ctors);
- // 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_ptr_sized_integral() && !cx.tcx.features().precise_pointer_size_matching);
+ debug!("missing_ctors.empty()={:#?}", missing_ctors.is_empty(),);
- if cheap_missing_ctors == MissingCtors::Empty && !is_non_exhaustive {
- split_grouped_constructors(
- cx.tcx, cx.param_env, all_ctors, matrix, pcx.ty, DUMMY_SP, None,
- )
+ if missing_ctors.is_empty() {
+ let (all_ctors, _) = missing_ctors.into_inner();
+ split_grouped_constructors(cx.tcx, cx.param_env, pcx, all_ctors, matrix, DUMMY_SP, None)
.into_iter()
- .map(|c| is_useful_specialized(cx, matrix, v, c, pcx.ty, witness, hir_id))
+ .map(|c| {
+ is_useful_specialized(cx, matrix, v, c, pcx.ty, witness_preference, hir_id)
+ })
.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, hir_id) {
- 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(Pat {
- ty: pcx.ty,
- span: DUMMY_SP,
- kind: box PatKind::Wild,
- });
- witness
- }).collect()
- } else {
- let expensive_missing_ctors = compute_missing_ctors(
- MissingCtorsInfo::Ctors, cx.tcx, cx.param_env, &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
+ let matrix = matrix.specialize_wildcard();
+ let v = v.to_tail();
+ let usefulness = is_useful(cx, &matrix, &v, witness_preference, hir_id);
+
+ // 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 is a case where we don't want
+ // to do this and instead report a single `_` witness:
+ // 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.
+ if missing_ctors.all_ctors_are_missing() {
+ // All constructors are unused. Add a wild pattern
+ // rather than each individual constructor.
+ usefulness.apply_wildcard(pcx.ty)
+ } else {
+ // Construct for each missing constructor 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`, we get the pattern `Some(_)`.
+ usefulness.apply_missing_ctors(cx, pcx.ty, &missing_ctors)
}
}
}
/// to the specialised version of both the pattern matrix `P` and the new pattern `q`.
fn is_useful_specialized<'p, 'a, 'tcx>(
cx: &mut MatchCheckCtxt<'a, 'tcx>,
- &Matrix(ref m): &Matrix<'p, 'tcx>,
- v: &[&Pat<'tcx>],
+ matrix: &Matrix<'p, 'tcx>,
+ v: &PatStack<'_, 'tcx>,
ctor: Constructor<'tcx>,
lty: Ty<'tcx>,
- witness: WitnessPreference,
+ witness_preference: WitnessPreference,
hir_id: HirId,
) -> 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| {
- Pat {
- ty,
- span: DUMMY_SP,
- kind: box PatKind::Wild,
- }
- }).collect();
- let wild_patterns: Vec<_> = wild_patterns_owned.iter().collect();
- let matrix = Matrix(
- m.iter()
- .filter_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, hir_id) {
- UsefulWithWitness(witnesses) => UsefulWithWitness(
- witnesses.into_iter()
- .map(|witness| witness.apply_constructor(cx, &ctor, lty))
- .collect()
- ),
- result => result
- }
- None => NotUseful
- }
+
+ let ctor_wild_subpatterns_owned: Vec<_> = ctor.wildcard_subpatterns(cx, lty);
+ let ctor_wild_subpatterns: Vec<_> = ctor_wild_subpatterns_owned.iter().collect();
+ let matrix = matrix.specialize_constructor(cx, &ctor, &ctor_wild_subpatterns);
+ v.specialize_constructor(cx, &ctor, &ctor_wild_subpatterns)
+ .map(|v| is_useful(cx, &matrix, &v, witness_preference, hir_id))
+ .map(|u| u.apply_constructor(cx, &ctor, lty))
+ .unwrap_or(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.
-///
+/// Determines the constructor that the given pattern can be specialized to.
/// Returns `None` in case of a catch-all, which can't be specialized.
-fn pat_constructors<'tcx>(
+fn pat_constructor<'tcx>(
cx: &mut MatchCheckCtxt<'_, 'tcx>,
pat: &Pat<'tcx>,
pcx: PatCtxt<'tcx>,
-) -> Option<Vec<Constructor<'tcx>>> {
+) -> Option<Constructor<'tcx>> {
match *pat.kind {
- PatKind::AscribeUserType { ref subpattern, .. } =>
- pat_constructors(cx, subpattern, pcx),
+ PatKind::AscribeUserType { ref subpattern, .. } => pat_constructor(cx, subpattern, pcx),
PatKind::Binding { .. } | PatKind::Wild => None,
- PatKind::Leaf { .. } | PatKind::Deref { .. } => Some(vec![Single]),
+ PatKind::Leaf { .. } | PatKind::Deref { .. } => Some(Single),
PatKind::Variant { adt_def, variant_index, .. } => {
- Some(vec![Variant(adt_def.variants[variant_index].def_id)])
+ Some(Variant(adt_def.variants[variant_index].def_id))
}
- PatKind::Constant { value } => Some(vec![ConstantValue(value, pat.span)]),
- PatKind::Range(PatRange { lo, hi, end }) =>
- Some(vec![ConstantRange(
- lo.eval_bits(cx.tcx, cx.param_env, lo.ty),
- hi.eval_bits(cx.tcx, cx.param_env, hi.ty),
- lo.ty,
- end,
- pat.span,
- )]),
+ PatKind::Constant { value } => Some(ConstantValue(value, pat.span)),
+ PatKind::Range(PatRange { lo, hi, end }) => Some(ConstantRange(
+ lo.eval_bits(cx.tcx, cx.param_env, lo.ty),
+ hi.eval_bits(cx.tcx, cx.param_env, hi.ty),
+ lo.ty,
+ end,
+ pat.span,
+ )),
PatKind::Array { .. } => match pcx.ty.kind {
- ty::Array(_, length) => Some(vec![
- Slice(length.eval_usize(cx.tcx, cx.param_env))
- ]),
- _ => span_bug!(pat.span, "bad ty {:?} for array pattern", pcx.ty)
+ ty::Array(_, length) => Some(FixedLenSlice(length.eval_usize(cx.tcx, cx.param_env))),
+ _ => span_bug!(pat.span, "bad ty {:?} for array pattern", pcx.ty),
},
PatKind::Slice { ref prefix, ref slice, ref suffix } => {
- let pat_len = prefix.len() as u64 + suffix.len() as u64;
+ let prefix = prefix.len() as u64;
+ let suffix = suffix.len() as u64;
if slice.is_some() {
- Some((pat_len..pcx.max_slice_length+1).map(Slice).collect())
+ Some(VarLenSlice(prefix, suffix))
} else {
- Some(vec![Slice(pat_len)])
+ Some(FixedLenSlice(prefix + suffix))
}
}
PatKind::Or { .. } => {
}
}
-/// 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<'a, 'tcx>, ctor: &Constructor<'tcx>, ty: Ty<'tcx>) -> u64 {
- debug!("constructor_arity({:#?}, {:?})", ctor, ty);
- match ty.kind {
- 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(cx, 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>(
- cx: &MatchCheckCtxt<'a, 'tcx>,
- ctor: &Constructor<'tcx>,
- ty: Ty<'tcx>,
-) -> Vec<Ty<'tcx>> {
- debug!("constructor_sub_pattern_tys({:#?}, {:?})", ctor, ty);
- match ty.kind {
- ty::Tuple(ref fs) => fs.into_iter().map(|t| t.expect_ty()).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 {
- let variant = &adt.variants[ctor.variant_index_for_adt(cx, adt)];
- let is_non_exhaustive = variant.is_field_list_non_exhaustive() && !cx.is_local(ty);
- variant.fields.iter().map(|field| {
- let is_visible = adt.is_enum()
- || field.vis.is_accessible_from(cx.module, cx.tcx);
- let is_uninhabited = cx.is_uninhabited(field.ty(cx.tcx, substs));
- match (is_visible, is_non_exhaustive, is_uninhabited) {
- // Treat all uninhabited types in non-exhaustive variants as `TyErr`.
- (_, true, true) => cx.tcx.types.err,
- // 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.
- (false, ..) => cx.tcx.types.err,
- (true, ..) => {
- let ty = field.ty(cx.tcx, substs);
- match ty.kind {
- // If the field type returned is an array of an unknown
- // size return an TyErr.
- ty::Array(_, len)
- if len.try_eval_usize(cx.tcx, cx.param_env).is_none() =>
- cx.tcx.types.err,
- _ => ty,
- }
- },
- }
- }).collect()
- }
- }
- _ => vec![],
- }
-}
-
// checks whether a constant is equal to a user-written slice pattern. Only supports byte slices,
// meaning all other types will compare unequal and thus equal patterns often do not cause the
// second pattern to lint about unreachable match arms.
let n = n.eval_usize(tcx, param_env);
let ptr = Pointer::new(AllocId(0), offset);
alloc.get_bytes(&tcx, ptr, Size::from_bytes(n)).unwrap()
- },
+ }
(ConstValue::Slice { data, start, end }, ty::Slice(t)) => {
assert_eq!(*t, tcx.types.u8);
let ptr = Pointer::new(AllocId(0), Size::from_bytes(start as u64));
data.get_bytes(&tcx, ptr, Size::from_bytes((end - start) as u64)).unwrap()
- },
+ }
// FIXME(oli-obk): create a way to extract fat pointers from ByRef
(_, ty::Slice(_)) => return Ok(false),
_ => bug!(
"slice_pat_covered_by_const: {:#?}, {:#?}, {:#?}, {:#?}",
- const_val, prefix, slice, suffix,
+ const_val,
+ prefix,
+ slice,
+ suffix,
),
};
return Ok(false);
}
- for (ch, pat) in
- data[..prefix.len()].iter().zip(prefix).chain(
- data[data.len()-suffix.len()..].iter().zip(suffix))
+ for (ch, pat) in data[..prefix.len()]
+ .iter()
+ .zip(prefix)
+ .chain(data[data.len() - suffix.len()..].iter().zip(suffix))
{
match pat.kind {
box PatKind::Constant { value } => {
///
/// `hir_id` is `None` when we're evaluating the wildcard pattern, do not lint for overlapping in
/// ranges that case.
+///
+/// This also splits variable-length slices into fixed-length slices.
fn split_grouped_constructors<'p, 'tcx>(
tcx: TyCtxt<'tcx>,
param_env: ty::ParamEnv<'tcx>,
+ pcx: PatCtxt<'tcx>,
ctors: Vec<Constructor<'tcx>>,
- &Matrix(ref m): &Matrix<'p, 'tcx>,
- ty: Ty<'tcx>,
+ matrix: &Matrix<'p, 'tcx>,
span: Span,
hir_id: Option<HirId>,
) -> Vec<Constructor<'tcx>> {
+ let ty = pcx.ty;
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
let mut overlaps = vec![];
// `borders` is the set of borders between equivalence classes: each equivalence
// class lies between 2 borders.
- let row_borders = m.iter()
+ let row_borders = matrix
+ .0
+ .iter()
.flat_map(|row| {
- IntRange::from_pat(tcx, param_env, row[0]).map(|r| (r, row.len()))
+ IntRange::from_pat(tcx, param_env, row.head()).map(|r| (r, row.len()))
})
.flat_map(|(range, row_len)| {
let intersection = ctor_range.intersection(&range);
lint_overlapping_patterns(tcx, hir_id, ctor_range, ty, overlaps);
- // 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]) {
+ // We're going to iterate through every adjacent 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, span })
Some(IntRange { range: n..=u128::MAX, ty, span })
}
(Border::AfterMax, _) => None,
- }
- }) {
+ })
+ {
split_ctors.push(IntRange::range_to_ctor(tcx, ty, range, span));
}
}
+ VarLenSlice(self_prefix, self_suffix) => {
+ // 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(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 = self_prefix;
+ let mut max_suffix_len = self_suffix;
+ let mut max_fixed_len = 0;
+
+ for row in matrix.heads() {
+ match *row.kind {
+ PatKind::Constant { value } => {
+ // extract the length of an array/slice from a constant
+ match (value.val, &value.ty.kind) {
+ (_, ty::Array(_, n)) => {
+ max_fixed_len =
+ cmp::max(max_fixed_len, n.eval_usize(tcx, param_env))
+ }
+ (ConstValue::Slice { start, end, .. }, ty::Slice(_)) => {
+ max_fixed_len = cmp::max(max_fixed_len, (end - start) as u64)
+ }
+ _ => {}
+ }
+ }
+ PatKind::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);
+ }
+ PatKind::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);
+ }
+ _ => {}
+ }
+ }
+
+ // For diagnostics, we keep the prefix and suffix lengths separate, so in the case
+ // where `max_fixed_len + 1` is the largest, we adapt `max_prefix_len` accordingly,
+ // so that `L = max_prefix_len + max_suffix_len`.
+ if max_fixed_len + 1 >= max_prefix_len + max_suffix_len {
+ // The subtraction can't overflow thanks to the above check.
+ // The new `max_prefix_len` is also guaranteed to be larger than its previous
+ // value.
+ max_prefix_len = max_fixed_len + 1 - max_suffix_len;
+ }
+
+ // `ctor` originally covered the range `(self_prefix + self_suffix..infinity)`. We
+ // now split it into two: lengths smaller than `max_prefix_len + max_suffix_len`
+ // are treated independently as fixed-lengths slices, and lengths above are
+ // captured by a final VarLenSlice constructor.
+ split_ctors.extend(
+ (self_prefix + self_suffix..max_prefix_len + max_suffix_len).map(FixedLenSlice),
+ );
+ split_ctors.push(VarLenSlice(max_prefix_len, max_suffix_len));
+ }
// Any other constructor can be used unchanged.
_ => split_ctors.push(ctor),
}
err.span_label(ctor_range.span, "overlapping patterns");
for int_range in overlaps {
// Use the real type for user display of the ranges:
- err.span_label(int_range.span, &format!(
- "this range overlaps on `{}`",
- IntRange::range_to_ctor(tcx, ty, int_range.range, DUMMY_SP).display(tcx),
- ));
+ err.span_label(
+ int_range.span,
+ &format!(
+ "this range overlaps on `{}`",
+ IntRange::range_to_ctor(tcx, ty, int_range.range, DUMMY_SP).display(tcx),
+ ),
+ );
}
err.emit();
}
_ => 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, param_env, ty)
- .map(|res| res != Ordering::Less);
+ let cmp_from = |c_from| {
+ compare_const_vals(tcx, c_from, from, param_env, ty).map(|res| res != Ordering::Less)
+ };
let cmp_to = |c_to| compare_const_vals(tcx, c_to, to, param_env, ty);
macro_rules! some_or_ok {
($e:expr) => {
match *ctor {
ConstantValue(value, _) => {
let to = some_or_ok!(cmp_to(value));
- let end = (to == Ordering::Less) ||
- (end == RangeEnd::Included && to == Ordering::Equal);
+ 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);
+ 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);
+ 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)
+ ty::ParamEnv::empty().and(ty)
+ ))) && end)
}
Single => Ok(true),
_ => bug!(),
fn patterns_for_variant<'p, 'a: 'p, 'tcx>(
cx: &mut MatchCheckCtxt<'a, 'tcx>,
subpatterns: &'p [FieldPat<'tcx>],
- wild_patterns: &[&'p Pat<'tcx>],
+ ctor_wild_subpatterns: &[&'p Pat<'tcx>],
is_non_exhaustive: bool,
-) -> SmallVec<[&'p Pat<'tcx>; 2]> {
- let mut result = SmallVec::from_slice(wild_patterns);
+) -> PatStack<'p, 'tcx> {
+ let mut result = SmallVec::from_slice(ctor_wild_subpatterns);
for subpat in subpatterns {
if !is_non_exhaustive || !cx.is_uninhabited(subpat.pattern.ty) {
}
}
- debug!("patterns_for_variant({:#?}, {:#?}) = {:#?}", subpatterns, wild_patterns, result);
- result
+ debug!(
+ "patterns_for_variant({:#?}, {:#?}) = {:#?}",
+ subpatterns, ctor_wild_subpatterns, result
+ );
+ PatStack::from_vec(result)
}
-/// This is the main specialization step. It expands the first pattern in the given row
+/// This is the main specialization step. It expands the pattern
/// 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.
+/// Returns `None` if the pattern does not have the given constructor.
///
-/// OTOH, slice patterns with a subslice pattern (..tail) can be expanded into multiple
+/// 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>(
+fn specialize_one_pattern<'p, 'a: 'p, 'q: 'p, 'tcx>(
cx: &mut MatchCheckCtxt<'a, 'tcx>,
- r: &[&'p Pat<'tcx>],
+ mut pat: &'q Pat<'tcx>,
constructor: &Constructor<'tcx>,
- wild_patterns: &[&'p Pat<'tcx>],
-) -> Option<SmallVec<[&'p Pat<'tcx>; 2]>> {
- let pat = &r[0];
+ ctor_wild_subpatterns: &[&'p Pat<'tcx>],
+) -> Option<PatStack<'p, 'tcx>> {
+ while let PatKind::AscribeUserType { ref subpattern, .. } = *pat.kind {
+ pat = subpattern;
+ }
- let head = match *pat.kind {
- PatKind::AscribeUserType { ref subpattern, .. } => {
- specialize(cx, ::std::slice::from_ref(&subpattern), constructor, wild_patterns)
- }
+ if let NonExhaustive = constructor {
+ // Only a wildcard pattern can match the special extra constructor
+ return if pat.is_wildcard() { Some(PatStack::default()) } else { None };
+ }
+
+ let result = match *pat.kind {
+ PatKind::AscribeUserType { .. } => bug!(), // Handled above
PatKind::Binding { .. } | PatKind::Wild => {
- Some(SmallVec::from_slice(wild_patterns))
+ Some(PatStack::from_slice(ctor_wild_subpatterns))
}
PatKind::Variant { adt_def, variant_index, ref subpatterns, .. } => {
let is_non_exhaustive = variant.is_field_list_non_exhaustive() && !cx.is_local(pat.ty);
Some(Variant(variant.def_id))
.filter(|variant_constructor| variant_constructor == constructor)
- .map(|_| patterns_for_variant(cx, subpatterns, wild_patterns, is_non_exhaustive))
+ .map(|_| {
+ patterns_for_variant(cx, subpatterns, ctor_wild_subpatterns, is_non_exhaustive)
+ })
}
PatKind::Leaf { ref subpatterns } => {
- Some(patterns_for_variant(cx, subpatterns, wild_patterns, false))
+ Some(patterns_for_variant(cx, subpatterns, ctor_wild_subpatterns, false))
}
- PatKind::Deref { ref subpattern } => {
- Some(smallvec![subpattern])
- }
+ PatKind::Deref { ref subpattern } => Some(PatStack::from_pattern(subpattern)),
PatKind::Constant { value } if constructor.is_slice() => {
// We extract an `Option` for the pointer because slices of zero
// just integers. The only time they should be pointing to memory
// is when they are subslices of nonzero slices.
let (alloc, offset, n, ty) = match value.ty.kind {
- ty::Array(t, n) => {
- match value.val {
- ConstValue::ByRef { offset, alloc, .. } => (
- alloc,
- offset,
- n.eval_usize(cx.tcx, cx.param_env),
- t,
- ),
- _ => span_bug!(
- pat.span,
- "array pattern is {:?}", value,
- ),
+ ty::Array(t, n) => match value.val {
+ ConstValue::ByRef { offset, alloc, .. } => {
+ (alloc, offset, n.eval_usize(cx.tcx, cx.param_env), t)
}
+ _ => span_bug!(pat.span, "array pattern is {:?}", value,),
},
ty::Slice(t) => {
match value.val {
- ConstValue::Slice { data, start, end } => (
- data,
- Size::from_bytes(start as u64),
- (end - start) as u64,
- t,
- ),
+ ConstValue::Slice { data, start, end } => {
+ (data, Size::from_bytes(start as u64), (end - start) as u64, t)
+ }
ConstValue::ByRef { .. } => {
// FIXME(oli-obk): implement `deref` for `ConstValue`
return None;
- },
+ }
_ => span_bug!(
pat.span,
"slice pattern constant must be scalar pair but is {:?}",
value,
),
}
- },
+ }
_ => span_bug!(
pat.span,
"unexpected const-val {:?} with ctor {:?}",
constructor,
),
};
- if wild_patterns.len() as u64 == n {
+ if ctor_wild_subpatterns.len() as u64 == n {
// convert a constant slice/array pattern to a list of patterns.
let layout = cx.tcx.layout_of(cx.param_env.and(ty)).ok()?;
let ptr = Pointer::new(AllocId(0), offset);
- (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 = Pat {
- ty,
- span: pat.span,
- kind: box PatKind::Constant { value },
- };
- Some(&*cx.pattern_arena.alloc(pattern))
- }).collect()
+ (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 =
+ Pat { ty, span: pat.span, kind: box PatKind::Constant { value } };
+ Some(&*cx.pattern_arena.alloc(pattern))
+ })
+ .collect()
} else {
None
}
}
- PatKind::Constant { .. } |
- PatKind::Range { .. } => {
+ PatKind::Constant { .. } | PatKind::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.
if should_treat_range_exhaustively(cx.tcx, constructor) {
- match (IntRange::from_ctor(cx.tcx, cx.param_env, constructor),
- IntRange::from_pat(cx.tcx, cx.param_env, 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![]
- })
- }
+ match (
+ IntRange::from_ctor(cx.tcx, cx.param_env, constructor),
+ IntRange::from_pat(cx.tcx, cx.param_env, 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);
+ PatStack::default()
+ }),
_ => None,
}
} else {
// range so intersection actually devolves into being covered
// by the pattern.
match constructor_covered_by_range(cx.tcx, cx.param_env, constructor, pat) {
- Ok(true) => Some(smallvec![]),
+ Ok(true) => Some(PatStack::default()),
Ok(false) | Err(ErrorReported) => None,
}
}
}
- PatKind::Array { ref prefix, ref slice, ref suffix } |
- PatKind::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
- }
+ PatKind::Array { ref prefix, ref slice, ref suffix }
+ | PatKind::Slice { ref prefix, ref slice, ref suffix } => match *constructor {
+ FixedLenSlice(..) | VarLenSlice(..) => {
+ let pat_len = prefix.len() + suffix.len();
+ if let Some(slice_count) = ctor_wild_subpatterns.len().checked_sub(pat_len) {
+ if slice_count == 0 || slice.is_some() {
+ Some(
+ prefix
+ .iter()
+ .chain(
+ ctor_wild_subpatterns
+ .iter()
+ .map(|p| *p)
+ .skip(prefix.len())
+ .take(slice_count)
+ .chain(suffix.iter()),
+ )
+ .collect(),
+ )
} else {
None
}
+ } else {
+ None
}
- ConstantValue(cv, _) => {
- match slice_pat_covered_by_const(
- cx.tcx, pat.span, cv, prefix, slice, suffix, cx.param_env,
- ) {
- Ok(true) => Some(smallvec![]),
- Ok(false) => None,
- Err(ErrorReported) => None
- }
+ }
+ ConstantValue(cv, _) => {
+ match slice_pat_covered_by_const(
+ cx.tcx,
+ pat.span,
+ cv,
+ prefix,
+ slice,
+ suffix,
+ cx.param_env,
+ ) {
+ Ok(true) => Some(PatStack::default()),
+ Ok(false) => None,
+ Err(ErrorReported) => None,
}
- _ => span_bug!(pat.span,
- "unexpected ctor {:?} for slice pat", constructor)
}
- }
+ _ => span_bug!(pat.span, "unexpected ctor {:?} for slice pat", constructor),
+ },
PatKind::Or { .. } => {
bug!("support for or-patterns has not been fully implemented yet.");
}
};
- debug!("specialize({:#?}, {:#?}) = {:#?}", r[0], wild_patterns, head);
+ debug!("specialize({:#?}, {:#?}) = {:#?}", pat, ctor_wild_subpatterns, result);
- head.map(|mut head| {
- head.extend_from_slice(&r[1 ..]);
- head
- })
+ result
}
projects / rust.git / blobdiff