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Co-authored-by: varkor <github@varkor.com>
This commit is contained in:
Nadrieril 2020-12-22 06:09:54 +00:00 committed by Nadrieril
parent 1c176d1150
commit 85fdb34d3a
2 changed files with 15 additions and 14 deletions

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@ -451,7 +451,7 @@ fn is_covered_by(self, other: Self) -> bool {
///
/// A slice pattern `[x, .., y]` behaves like the infinite or-pattern `[x, y] | [x, _, y] | [x, _,
/// _, y] | ...`. The corresponding value constructors are fixed-length array constructors above a
/// given minimum length. We obviously can't list all of this infinity of constructors. Thankfully,
/// given minimum length. We obviously can't list this infinitude of constructors. Thankfully,
/// it turns out that for each finite set of slice patterns, all sufficiently large array lengths
/// are equivalent.
///
@ -491,7 +491,7 @@ fn is_covered_by(self, other: Self) -> bool {
/// middle. This means that the set of witnesses for length `l >= 5` if equivalent to the set for
/// any other `l' >= 5`: simply add or remove wildcards in the middle to convert between them.
///
/// This applies to any set of slice patterns: there will be a length `L` above which all length
/// This applies to any set of slice patterns: there will be a length `L` above which all lengths
/// behave the same. This is exactly what we need for constructor splitting. Therefore a
/// variable-length slice can be split into a variable-length slice of minimal length `L`, and many
/// fixed-length slices of lengths `< L`.
@ -736,8 +736,8 @@ pub(super) fn split<'a>(
// ranges check.
IntRange(ctor_range) if !ctor_range.is_singleton() => {
let mut split_range = SplitIntRange::new(ctor_range.clone());
let intranges = ctors.filter_map(|ctor| ctor.as_int_range());
split_range.split(intranges.cloned());
let int_ranges = ctors.filter_map(|ctor| ctor.as_int_range());
split_range.split(int_ranges.cloned());
split_range.iter().map(IntRange).collect()
}
&Slice(Slice { kind: VarLen(self_prefix, self_suffix), array_len }) => {
@ -1080,7 +1080,7 @@ fn kept(self) -> Option<&'p Pat<'tcx>> {
///
/// If a private or `non_exhaustive` field is uninhabited, the code mustn't observe that it is
/// uninhabited. For that, we filter these fields out of the matrix. This is handled automatically
/// in `Fields`. This filtering is uncommon in practice, because uninhabited fields are rare used,
/// in `Fields`. This filtering is uncommon in practice, because uninhabited fields are rarely used,
/// so we avoid it when possible to preserve performance.
#[derive(Debug, Clone)]
pub(super) enum Fields<'p, 'tcx> {

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@ -19,7 +19,7 @@
//!
//! The algorithm implemented here is a modified version of the one described in [this
//! paper](http://moscova.inria.fr/~maranget/papers/warn/index.html). We have however generalized
//! it to accomodate the variety of patterns that rust supports. We thus explain our version here,
//! it to accommodate the variety of patterns that Rust supports. We thus explain our version here,
//! without being as rigorous.
//!
//!
@ -27,13 +27,13 @@
//!
//! The core of the algorithm is the notion of "usefulness". A pattern `q` is said to be *useful*
//! relative to another pattern `p` of the same type if there is a value that is matched by `q` and
//! not matched by `p`. This generalizes to many `p`s: `q` is useful wrt a list of patterns `p_1 ..
//! p_n` if there is a value that is matched by `q` and by none of the `p_i`. We write
//! not matched by `p`. This generalizes to many `p`s: `q` is useful w.r.t. a list of patterns
//! `p_1 .. p_n` if there is a value that is matched by `q` and by none of the `p_i`. We write
//! `usefulness(p_1 .. p_n, q)` for a function that returns a list of such values. The aim of this
//! file is to compute it efficiently.
//!
//! This is enough to compute reachability: a pattern in a `match` expression is reachable iff it
//! is useful wrt the patterns above it:
//! is useful w.r.t. the patterns above it:
//! ```rust
//! match x {
//! Some(_) => ...,
@ -44,8 +44,8 @@
//! ```
//!
//! This is also enough to compute exhaustiveness: a match is exhaustive iff the wildcard `_`
//! pattern is _not_ useful wrt the patterns in the match. The values returned by `usefulness` are
//! used to tell the user which values are missing.
//! pattern is _not_ useful w.r.t. the patterns in the match. The values returned by `usefulness`
//! are used to tell the user which values are missing.
//! ```rust
//! match x {
//! Some(0) => ...,
@ -102,7 +102,7 @@
//!
//! Note: this constructors/fields distinction may not straightforwardly apply to every Rust type.
//! For example a value of type `Rc<u64>` can't be deconstructed that way, and `&str` has an
//! infinity of constructors. There are also subtleties with visibility of fields and
//! infinitude of constructors. There are also subtleties with visibility of fields and
//! uninhabitedness and various other things. The constructors idea can be extended to handle most
//! of these subtleties though; caveats are documented where relevant throughout the code.
//!
@ -184,7 +184,8 @@
//!
//! `specialize(c, p0 | p1) := specialize(c, p0) ++ specialize(c, p1)`
//!
//! - We treat the other pattern constructors lik big or-patterns of all the possibilities:
//! - We treat the other pattern constructors as if they were a large or-pattern of all the
//! possibilities:
//!
//! `specialize(c, _) := specialize(c, Variant1(_) | Variant2(_, _) | ...)`
//!
@ -193,7 +194,7 @@
//! `specialize(c, [p0, .., p1]) := specialize(c, [p0, p1] | [p0, _, p1] | [p0, _, _, p1] | ...)`
//!
//! - If `c` is a pattern-only constructor, `specialize` is defined on a case-by-case basis. See
//! the discussion abount constructor splitting in [`super::deconstruct_pat`].
//! the discussion about constructor splitting in [`super::deconstruct_pat`].
//!
//!
//! We then extend this function to work with pattern-stacks as input, by acting on the first