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Make
PatternColumn part of the public API
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,90 @@ | ||
| use crate::constructor::{Constructor, SplitConstructorSet}; | ||
| use crate::pat::{DeconstructedPat, PatOrWild}; | ||
| use crate::{Captures, MatchArm, TypeCx}; | ||
|
|
||
| /// A column of patterns in a match, where a column is the intuitive notion of "subpatterns that | ||
| /// inspect the same subvalue/place". | ||
| /// This is used to traverse patterns column-by-column for lints. Despite similarities with the | ||
| /// algorithm in [`crate::usefulness`], this does a different traversal. Notably this is linear in | ||
| /// the depth of patterns, whereas `compute_exhaustiveness_and_usefulness` is worst-case exponential | ||
| /// (exhaustiveness is NP-complete). The core difference is that we treat sub-columns separately. | ||
| /// | ||
| /// This is not used in the usefulness algorithm; only in lints. | ||
| #[derive(Debug)] | ||
| pub struct PatternColumn<'p, Cx: TypeCx> { | ||
| /// This must not contain an or-pattern. `expand_and_push` takes care to expand them. | ||
| patterns: Vec<&'p DeconstructedPat<'p, Cx>>, | ||
| } | ||
|
|
||
| impl<'p, Cx: TypeCx> PatternColumn<'p, Cx> { | ||
| pub fn new(arms: &[MatchArm<'p, Cx>]) -> Self { | ||
| let patterns = Vec::with_capacity(arms.len()); | ||
| let mut column = PatternColumn { patterns }; | ||
| for arm in arms { | ||
| column.expand_and_push(PatOrWild::Pat(arm.pat)); | ||
| } | ||
| column | ||
| } | ||
| /// Pushes a pattern onto the column, expanding any or-patterns into its subpatterns. | ||
| /// Internal method, prefer [`PatternColumn::new`]. | ||
| fn expand_and_push(&mut self, pat: PatOrWild<'p, Cx>) { | ||
| // We flatten or-patterns and skip algorithm-generated wildcards. | ||
| if pat.is_or_pat() { | ||
| self.patterns.extend( | ||
| pat.flatten_or_pat().into_iter().filter_map(|pat_or_wild| pat_or_wild.as_pat()), | ||
| ) | ||
| } else if let Some(pat) = pat.as_pat() { | ||
| self.patterns.push(pat) | ||
| } | ||
| } | ||
|
|
||
| pub fn head_ty(&self) -> Option<&Cx::Ty> { | ||
| self.patterns.first().map(|pat| pat.ty()) | ||
| } | ||
| pub fn iter<'a>(&'a self) -> impl Iterator<Item = &'p DeconstructedPat<'p, Cx>> + Captures<'a> { | ||
| self.patterns.iter().copied() | ||
| } | ||
|
|
||
| /// Do constructor splitting on the constructors of the column. | ||
| pub fn analyze_ctors( | ||
| &self, | ||
| cx: &Cx, | ||
| ty: &Cx::Ty, | ||
| ) -> Result<SplitConstructorSet<Cx>, Cx::Error> { | ||
| let column_ctors = self.patterns.iter().map(|p| p.ctor()); | ||
| let ctors_for_ty = cx.ctors_for_ty(ty)?; | ||
| Ok(ctors_for_ty.split(column_ctors)) | ||
| } | ||
|
|
||
| /// Does specialization: given a constructor, this takes the patterns from the column that match | ||
| /// the constructor, and outputs their fields. | ||
| /// This returns one column per field of the constructor. They usually all have the same length | ||
| /// (the number of patterns in `self` that matched `ctor`), except that we expand or-patterns | ||
| /// which may change the lengths. | ||
| pub fn specialize( | ||
| &self, | ||
| cx: &Cx, | ||
| ty: &Cx::Ty, | ||
| ctor: &Constructor<Cx>, | ||
| ) -> Vec<PatternColumn<'p, Cx>> { | ||
| let arity = ctor.arity(cx, ty); | ||
| if arity == 0 { | ||
| return Vec::new(); | ||
| } | ||
|
|
||
| // We specialize the column by `ctor`. This gives us `arity`-many columns of patterns. These | ||
| // columns may have different lengths in the presence of or-patterns (this is why we can't | ||
| // reuse `Matrix`). | ||
| let mut specialized_columns: Vec<_> = | ||
| (0..arity).map(|_| Self { patterns: Vec::new() }).collect(); | ||
| let relevant_patterns = | ||
| self.patterns.iter().filter(|pat| ctor.is_covered_by(cx, pat.ctor())); | ||
| for pat in relevant_patterns { | ||
| let specialized = pat.specialize(ctor, arity); | ||
| for (subpat, column) in specialized.into_iter().zip(&mut specialized_columns) { | ||
| column.expand_and_push(subpat); | ||
| } | ||
| } | ||
| specialized_columns | ||
| } | ||
| } |