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Update match checking.

Browse source 
fn is_useful , more skeletons

Specify a lifetime on pattern references

impl PatStack

fill impl Matrix

PatStack::pop_head_constructor

Index-based approach

struct PatCtxt

fields construction fn Fields::wildcards

split wildcard

fn Constructor::is_covered_by_any(..)

fn Matrix::specialize_constructor(..)

impl Usefulness

Initial work on witness construction

Reorganize files

Replace match checking diagnostic

Handle types of expanded patterns

unit match checking go brrr
This commit is contained in:
Dawer 2021-04-22 20:17:27 +05:00
parent 7c1d8ca635
commit c3c2893f30
6 changed files with 1471 additions and 1 deletions
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1
crates/hir_ty/Cargo.toml
View file

@ -22,6 +22,7 @@ chalk-solve = { version = "0.68", default-features = false }
chalk-ir = "0.68"
chalk-recursive = "0.68"
la-arena = { version = "0.2.0", path = "../../lib/arena" }
once_cell = { version = "1.5.0" }
stdx = { path = "../stdx", version = "0.0.0" }
hir_def = { path = "../hir_def", version = "0.0.0" }

2
crates/hir_ty/src/diagnostics.rs
View file

@ -1,6 +1,8 @@
//! Type inference-based diagnostics.
mod expr;
#[allow(unused)] //todo
mod match_check;
mod pattern;
mod unsafe_check;
mod decl_check;

70
crates/hir_ty/src/diagnostics/expr.rs
View file

@ -62,7 +62,7 @@ impl<'a, 'b> ExprValidator<'a, 'b> {
match expr {
Expr::Match { expr, arms } => {
self.validate_match(id, *expr, arms, db, self.infer.clone());
self.validate_match2(id, *expr, arms, db, self.infer.clone());
}
Expr::Call { .. } | Expr::MethodCall { .. } => {
self.validate_call(db, id, expr);
@ -277,6 +277,7 @@ impl<'a, 'b> ExprValidator<'a, 'b> {
}
}
#[allow(dead_code)]
fn validate_match(
&mut self,
id: ExprId,
@ -358,6 +359,73 @@ impl<'a, 'b> ExprValidator<'a, 'b> {
}
}
fn validate_match2(
&mut self,
id: ExprId,
match_expr: ExprId,
arms: &[MatchArm],
db: &dyn HirDatabase,
infer: Arc<InferenceResult>,
) {
use crate::diagnostics::pattern::usefulness;
use hir_def::HasModule;
let (body, source_map): (Arc<Body>, Arc<BodySourceMap>) =
db.body_with_source_map(self.owner);
let match_expr_ty = if infer.type_of_expr[match_expr].is_unknown() {
return;
} else {
&infer.type_of_expr[match_expr]
};
eprintln!("ExprValidator::validate_match2({:?})", match_expr_ty.kind(&Interner));
let pattern_arena = usefulness::PatternArena::clone_from(&body.pats);
let cx = usefulness::MatchCheckCtx {
krate: self.owner.module(db.upcast()).krate(),
match_expr,
body,
infer: &infer,
db,
pattern_arena: &pattern_arena,
};
let m_arms: Vec<_> = arms
.iter()
.map(|arm| usefulness::MatchArm { pat: arm.pat, has_guard: arm.guard.is_some() })
.collect();
let report = usefulness::compute_match_usefulness(&cx, &m_arms);
// TODO Report unreacheble arms
// let mut catchall = None;
// for (arm_index, (arm, is_useful)) in report.arm_usefulness.iter().enumerate() {
// match is_useful{
// Unreachable => {
// }
// Reachable(_) => {}
// }
// }
let witnesses = report.non_exhaustiveness_witnesses;
if !witnesses.is_empty() {
if let Ok(source_ptr) = source_map.expr_syntax(id) {
let root = source_ptr.file_syntax(db.upcast());
if let ast::Expr::MatchExpr(match_expr) = &source_ptr.value.to_node(&root) {
if let (Some(match_expr), Some(arms)) =
(match_expr.expr(), match_expr.match_arm_list())
{
self.sink.push(MissingMatchArms {
file: source_ptr.file_id,
match_expr: AstPtr::new(&match_expr),
arms: AstPtr::new(&arms),
})
}
}
}
}
}
fn validate_results_in_tail_expr(&mut self, body_id: ExprId, id: ExprId, db: &dyn HirDatabase) {
// the mismatch will be on the whole block currently
let mismatch = match self.infer.type_mismatch_for_expr(body_id) {

36
crates/hir_ty/src/diagnostics/pattern.rs Normal file
View file

@ -0,0 +1,36 @@
#![deny(elided_lifetimes_in_paths)]
#![allow(unused)] // todo remove
mod deconstruct_pat;
pub mod usefulness;
#[cfg(test)]
mod tests {
use crate::diagnostics::tests::check_diagnostics;
use super::*;
#[test]
fn unit_exhaustive() {
check_diagnostics(
r#"
fn main() {
match () { () => {} }
match () { _ => {} }
}
"#,
);
}
#[test]
fn unit_non_exhaustive() {
check_diagnostics(
r#"
fn main() {
match () { }
//^^ Missing match arm
}
"#,
);
}
}

627
crates/hir_ty/src/diagnostics/pattern/deconstruct_pat.rs Normal file
View file

@ -0,0 +1,627 @@
use hir_def::{
expr::{Pat, PatId},
AttrDefId, EnumVariantId, HasModule, VariantId,
};
use smallvec::{smallvec, SmallVec};
use crate::{AdtId, Interner, Scalar, Ty, TyExt, TyKind};
use super::usefulness::{MatchCheckCtx, PatCtxt};
use self::Constructor::*;
#[derive(Copy, Clone, Debug, PartialEq, Eq)]
pub(super) enum ToDo {}
#[derive(Clone, Debug, PartialEq, Eq)]
pub(super) struct IntRange {
range: ToDo,
}
impl IntRange {
#[inline]
fn is_integral(ty: &Ty) -> bool {
match ty.kind(&Interner) {
TyKind::Scalar(Scalar::Char)
| TyKind::Scalar(Scalar::Int(_))
| TyKind::Scalar(Scalar::Uint(_))
| TyKind::Scalar(Scalar::Bool) => true,
_ => false,
}
}
/// See `Constructor::is_covered_by`
fn is_covered_by(&self, other: &Self) -> bool {
todo!()
}
}
/// A constructor for array and slice patterns.
#[derive(Copy, Clone, Debug, PartialEq, Eq)]
pub(super) struct Slice {
todo: ToDo,
}
impl Slice {
/// See `Constructor::is_covered_by`
fn is_covered_by(self, other: Self) -> bool {
todo!()
}
}
/// A value can be decomposed into a constructor applied to some fields. This struct represents
/// the constructor. See also `Fields`.
///
/// `pat_constructor` retrieves the constructor corresponding to a pattern.
/// `specialize_constructor` returns the list of fields corresponding to a pattern, given a
/// constructor. `Constructor::apply` reconstructs the pattern from a pair of `Constructor` and
/// `Fields`.
#[derive(Clone, Debug, PartialEq)]
pub(super) enum Constructor {
/// The constructor for patterns that have a single constructor, like tuples, struct patterns
/// and fixed-length arrays.
Single,
/// Enum variants.
Variant(EnumVariantId),
/// Ranges of integer literal values (`2`, `2..=5` or `2..5`).
IntRange(IntRange),
/// Array and slice patterns.
Slice(Slice),
/// Stands for constructors that are not seen in the matrix, as explained in the documentation
/// for [`SplitWildcard`].
Missing,
/// Wildcard pattern.
Wildcard,
}
impl Constructor {
pub(super) fn is_wildcard(&self) -> bool {
matches!(self, Wildcard)
}
fn as_int_range(&self) -> Option<&IntRange> {
match self {
IntRange(range) => Some(range),
_ => None,
}
}
fn as_slice(&self) -> Option<Slice> {
match self {
Slice(slice) => Some(*slice),
_ => None,
}
}
fn variant_id_for_adt(&self, adt: hir_def::AdtId, cx: &MatchCheckCtx<'_>) -> VariantId {
match *self {
Variant(id) => id.into(),
Single => {
assert!(!matches!(adt, hir_def::AdtId::EnumId(_)));
match adt {
hir_def::AdtId::EnumId(_) => unreachable!(),
hir_def::AdtId::StructId(id) => id.into(),
hir_def::AdtId::UnionId(id) => id.into(),
}
}
_ => panic!("bad constructor {:?} for adt {:?}", self, adt),
}
}
pub(super) fn from_pat(cx: &MatchCheckCtx<'_>, pat: PatId) -> Self {
match &cx.pattern_arena.borrow()[pat] {
Pat::Bind { .. } | Pat::Wild => Wildcard,
Pat::Tuple { .. } | Pat::Ref { .. } | Pat::Box { .. } => Single,
pat => todo!("Constructor::from_pat {:?}", pat),
// Pat::Missing => {}
// Pat::Or(_) => {}
// Pat::Record { path, args, ellipsis } => {}
// Pat::Range { start, end } => {}
// Pat::Slice { prefix, slice, suffix } => {}
// Pat::Path(_) => {}
// Pat::Lit(_) => {}
// Pat::TupleStruct { path, args, ellipsis } => {}
// Pat::ConstBlock(_) => {}
}
}
/// Some constructors (namely `Wildcard`, `IntRange` and `Slice`) actually stand for a set of actual
/// constructors (like variants, integers or fixed-sized slices). When specializing for these
/// constructors, we want to be specialising for the actual underlying constructors.
/// Naively, we would simply return the list of constructors they correspond to. We instead are
/// more clever: if there are constructors that we know will behave the same wrt the current
/// matrix, we keep them grouped. For example, all slices of a sufficiently large length
/// will either be all useful or all non-useful with a given matrix.
///
/// See the branches for details on how the splitting is done.
///
/// This function may discard some irrelevant constructors if this preserves behavior and
/// diagnostics. Eg. for the `_` case, we ignore the constructors already present in the
/// matrix, unless all of them are.
pub(super) fn split<'a>(
&self,
pcx: &PatCtxt<'_>,
ctors: impl Iterator<Item = &'a Constructor> + Clone,
) -> SmallVec<[Self; 1]> {
match self {
Wildcard => {
let mut split_wildcard = SplitWildcard::new(pcx);
split_wildcard.split(pcx, ctors);
split_wildcard.into_ctors(pcx)
}
// Fast-track if the range is trivial. In particular, we don't do the overlapping
// ranges check.
IntRange(_) => todo!("Constructor::split IntRange"),
Slice(_) => todo!("Constructor::split Slice"),
// Any other constructor can be used unchanged.
_ => smallvec![self.clone()],
}
}
/// Returns whether `self` is covered by `other`, i.e. whether `self` is a subset of `other`.
/// For the simple cases, this is simply checking for equality. For the "grouped" constructors,
/// this checks for inclusion.
// We inline because this has a single call site in `Matrix::specialize_constructor`.
#[inline]
pub(super) fn is_covered_by(&self, pcx: &PatCtxt<'_>, other: &Self) -> bool {
// This must be kept in sync with `is_covered_by_any`.
match (self, other) {
// Wildcards cover anything
(_, Wildcard) => true,
// The missing ctors are not covered by anything in the matrix except wildcards.
(Missing, _) | (Wildcard, _) => false,
(Single, Single) => true,
(Variant(self_id), Variant(other_id)) => self_id == other_id,
(Constructor::IntRange(_), Constructor::IntRange(_)) => todo!(),
(Constructor::Slice(_), Constructor::Slice(_)) => todo!(),
_ => panic!("bug"),
}
}
/// Faster version of `is_covered_by` when applied to many constructors. `used_ctors` is
/// assumed to be built from `matrix.head_ctors()` with wildcards filtered out, and `self` is
/// assumed to have been split from a wildcard.
fn is_covered_by_any(&self, pcx: &PatCtxt<'_>, used_ctors: &[Constructor]) -> bool {
if used_ctors.is_empty() {
return false;
}
// This must be kept in sync with `is_covered_by`.
match self {
// If `self` is `Single`, `used_ctors` cannot contain anything else than `Single`s.
Single => !used_ctors.is_empty(),
Variant(_) => used_ctors.iter().any(|c| c == self),
IntRange(range) => used_ctors
.iter()
.filter_map(|c| c.as_int_range())
.any(|other| range.is_covered_by(other)),
Slice(slice) => used_ctors
.iter()
.filter_map(|c| c.as_slice())
.any(|other| slice.is_covered_by(other)),
_ => todo!(),
}
}
}
/// A wildcard constructor that we split relative to the constructors in the matrix, as explained
/// at the top of the file.
///
/// A constructor that is not present in the matrix rows will only be covered by the rows that have
/// wildcards. Thus we can group all of those constructors together; we call them "missing
/// constructors". Splitting a wildcard would therefore list all present constructors individually
/// (or grouped if they are integers or slices), and then all missing constructors together as a
/// group.
///
/// However we can go further: since any constructor will match the wildcard rows, and having more
/// rows can only reduce the amount of usefulness witnesses, we can skip the present constructors
/// and only try the missing ones.
/// This will not preserve the whole list of witnesses, but will preserve whether the list is empty
/// or not. In fact this is quite natural from the point of view of diagnostics too. This is done
/// in `to_ctors`: in some cases we only return `Missing`.
#[derive(Debug)]
pub(super) struct SplitWildcard {
/// Constructors seen in the matrix.
matrix_ctors: Vec<Constructor>,
/// All the constructors for this type
all_ctors: SmallVec<[Constructor; 1]>,
}
impl SplitWildcard {
pub(super) fn new(pcx: &PatCtxt<'_>) -> Self {
// let cx = pcx.cx;
// let make_range = |start, end| IntRange(todo!());
// This determines the set of all possible constructors for the type `pcx.ty`. For numbers,
// arrays and slices we use ranges and variable-length slices when appropriate.
//
// If the `exhaustive_patterns` feature is enabled, we make sure to omit constructors that
// are statically impossible. E.g., for `Option<!>`, we do not include `Some(_)` in the
// returned list of constructors.
// Invariant: this is empty if and only if the type is uninhabited (as determined by
// `cx.is_uninhabited()`).
let all_ctors = match pcx.ty.kind(&Interner) {
TyKind::Adt(AdtId(hir_def::AdtId::EnumId(_)), _) => todo!(),
TyKind::Adt(..) | TyKind::Tuple(..) | TyKind::Ref(..) => smallvec![Single],
_ => todo!(),
};
SplitWildcard { matrix_ctors: Vec::new(), all_ctors }
}
/// Pass a set of constructors relative to which to split this one. Don't call twice, it won't
/// do what you want.
pub(super) fn split<'a>(
&mut self,
pcx: &PatCtxt<'_>,
ctors: impl Iterator<Item = &'a Constructor> + Clone,
) {
// Since `all_ctors` never contains wildcards, this won't recurse further.
self.all_ctors =
self.all_ctors.iter().flat_map(|ctor| ctor.split(pcx, ctors.clone())).collect();
self.matrix_ctors = ctors.filter(|c| !c.is_wildcard()).cloned().collect();
}
/// Whether there are any value constructors for this type that are not present in the matrix.
fn any_missing(&self, pcx: &PatCtxt<'_>) -> bool {
self.iter_missing(pcx).next().is_some()
}
/// Iterate over the constructors for this type that are not present in the matrix.
pub(super) fn iter_missing<'a>(
&'a self,
pcx: &'a PatCtxt<'_>,
) -> impl Iterator<Item = &'a Constructor> {
self.all_ctors.iter().filter(move |ctor| !ctor.is_covered_by_any(pcx, &self.matrix_ctors))
}
/// Return the set of constructors resulting from splitting the wildcard. As explained at the
/// top of the file, if any constructors are missing we can ignore the present ones.
fn into_ctors(self, pcx: &PatCtxt<'_>) -> SmallVec<[Constructor; 1]> {
if self.any_missing(pcx) {
// Some constructors are missing, thus we can specialize with the special `Missing`
// constructor, which stands for those constructors that are not seen in the matrix,
// and matches the same rows as any of them (namely the wildcard rows). See the top of
// the file for details.
// However, when all constructors are missing we can also specialize with the full
// `Wildcard` constructor. The difference will depend on what we want in diagnostics.
// If some constructors are missing, we typically want to report those constructors,
// e.g.:
// ```
// enum Direction { N, S, E, W }
// let Direction::N = ...;
// ```
// we can report 3 witnesses: `S`, `E`, and `W`.
//
// However, 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)`. So if all constructors are missing we
// prefer to report just a wildcard `_`.
//
// The exception is: if we are at the top-level, for example in an empty match, we
// sometimes prefer reporting the list of constructors instead of just `_`.
let report_when_all_missing = pcx.is_top_level && !IntRange::is_integral(&pcx.ty);
let ctor = if !self.matrix_ctors.is_empty() || report_when_all_missing {
Missing
} else {
Wildcard
};
return smallvec![ctor];
}
// All the constructors are present in the matrix, so we just go through them all.
self.all_ctors
}
}
#[test]
fn it_works2() {}
/// Some fields need to be explicitly hidden away in certain cases; see the comment above the
/// `Fields` struct. This struct represents such a potentially-hidden field.
#[derive(Debug, Copy, Clone)]
pub(super) enum FilteredField {
Kept(PatId),
Hidden,
}
impl FilteredField {
fn kept(self) -> Option<PatId> {
match self {
FilteredField::Kept(p) => Some(p),
FilteredField::Hidden => None,
}
}
}
/// A value can be decomposed into a constructor applied to some fields. This struct represents
/// those fields, generalized to allow patterns in each field. See also `Constructor`.
/// This is constructed from a constructor using [`Fields::wildcards()`].
///
/// 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 rarely used,
/// so we avoid it when possible to preserve performance.
#[derive(Debug, Clone)]
pub(super) enum Fields {
/// Lists of patterns that don't contain any filtered fields.
/// `Slice` and `Vec` behave the same; the difference is only to avoid allocating and
/// triple-dereferences when possible. Frankly this is premature optimization, I (Nadrieril)
/// have not measured if it really made a difference.
Vec(SmallVec<[PatId; 2]>),
}
impl Fields {
/// Internal use. Use `Fields::wildcards()` instead.
/// Must not be used if the pattern is a field of a struct/tuple/variant.
fn from_single_pattern(pat: PatId) -> Self {
Fields::Vec(smallvec![pat])
}
/// Convenience; internal use.
fn wildcards_from_tys<'a>(
cx: &MatchCheckCtx<'_>,
tys: impl IntoIterator<Item = &'a Ty>,
) -> Self {
let wilds = tys.into_iter().map(|ty| (Pat::Wild, ty));
let pats = wilds.map(|(pat, ty)| cx.alloc_pat(pat, ty)).collect();
Fields::Vec(pats)
}
pub(crate) fn wildcards(pcx: &PatCtxt<'_>, constructor: &Constructor) -> Self {
let ty = &pcx.ty;
let cx = pcx.cx;
let wildcard_from_ty = |ty| cx.alloc_pat(Pat::Wild, ty);
let ret = match constructor {
Single | Variant(_) => match ty.kind(&Interner) {
TyKind::Tuple(_, substs) => {
let tys = substs.iter(&Interner).map(|ty| ty.assert_ty_ref(&Interner));
Fields::wildcards_from_tys(cx, tys)
}
TyKind::Ref(.., rty) => Fields::from_single_pattern(wildcard_from_ty(rty)),
TyKind::Adt(AdtId(adt), substs) => {
let adt_is_box = false; // TODO(iDawer): handle box patterns
if adt_is_box {
// Use T as the sub pattern type of Box<T>.
let ty = substs.at(&Interner, 0).assert_ty_ref(&Interner);
Fields::from_single_pattern(wildcard_from_ty(ty))
} else {
let variant_id = constructor.variant_id_for_adt(*adt, cx);
let variant = variant_id.variant_data(cx.db.upcast());
let adt_is_local = variant_id.module(cx.db.upcast()).krate() == cx.krate;
// Whether we must not match the fields of this variant exhaustively.
let is_non_exhaustive =
is_field_list_non_exhaustive(variant_id, cx) && !adt_is_local;
let field_ty_arena = cx.db.field_types(variant_id);
let field_tys =
|| field_ty_arena.iter().map(|(_, binders)| binders.skip_binders());
// In the following cases, we don't need to filter out any fields. This is
// the vast majority of real cases, since uninhabited fields are uncommon.
let has_no_hidden_fields = (matches!(adt, hir_def::AdtId::EnumId(_))
&& !is_non_exhaustive)
|| !field_tys().any(|ty| cx.is_uninhabited(ty));
if has_no_hidden_fields {
Fields::wildcards_from_tys(cx, field_tys())
} else {
//FIXME(iDawer): see MatchCheckCtx::is_uninhabited
unimplemented!("exhaustive_patterns feature")
}
}
}
_ => panic!("Unexpected type for `Single` constructor: {:?}", ty),
},
Missing | Wildcard => Fields::Vec(Default::default()),
_ => todo!(),
};
ret
}
/// Apply a constructor to a list of patterns, yielding a new pattern. `self`
/// must have as many elements as this constructor's arity.
///
/// This is roughly the inverse of `specialize_constructor`.
///
/// Examples:
/// `ctor`: `Constructor::Single`
/// `ty`: `Foo(u32, u32, u32)`
/// `self`: `[10, 20, _]`
/// returns `Foo(10, 20, _)`
///
/// `ctor`: `Constructor::Variant(Option::Some)`
/// `ty`: `Option<bool>`
/// `self`: `[false]`
/// returns `Some(false)`
pub(super) fn apply(self, pcx: &PatCtxt<'_>, ctor: &Constructor) -> Pat {
let subpatterns_and_indices = self.patterns_and_indices();
let mut subpatterns = subpatterns_and_indices.iter().map(|&(_, p)| p);
match ctor {
Single | Variant(_) => match pcx.ty.kind(&Interner) {
TyKind::Adt(..) | TyKind::Tuple(..) => {
// We want the real indices here.
// TODO indices
let subpatterns = subpatterns_and_indices.iter().map(|&(_, pat)| pat).collect();
if let Some((adt, substs)) = pcx.ty.as_adt() {
if let hir_def::AdtId::EnumId(_) = adt {
todo!()
} else {
todo!()
}
} else {
// TODO ellipsis
Pat::Tuple { args: subpatterns, ellipsis: None }
}
}
_ => todo!(),
// TyKind::AssociatedType(_, _) => {}
// TyKind::Scalar(_) => {}
// TyKind::Array(_, _) => {}
// TyKind::Slice(_) => {}
// TyKind::Raw(_, _) => {}
// TyKind::Ref(_, _, _) => {}
// TyKind::OpaqueType(_, _) => {}
// TyKind::FnDef(_, _) => {}
// TyKind::Str => {}
// TyKind::Never => {}
// TyKind::Closure(_, _) => {}
// TyKind::Generator(_, _) => {}
// TyKind::GeneratorWitness(_, _) => {}
// TyKind::Foreign(_) => {}
// TyKind::Error => {}
// TyKind::Placeholder(_) => {}
// TyKind::Dyn(_) => {}
// TyKind::Alias(_) => {}
// TyKind::Function(_) => {}
// TyKind::BoundVar(_) => {}
// TyKind::InferenceVar(_, _) => {}
},
_ => todo!(),
// Constructor::IntRange(_) => {}
// Constructor::Slice(_) => {}
// Missing => {}
// Wildcard => {}
}
}
/// Returns the number of patterns. This is the same as the arity of the constructor used to
/// construct `self`.
pub(super) fn len(&self) -> usize {
match self {
Fields::Vec(pats) => pats.len(),
}
}
/// Returns the list of patterns along with the corresponding field indices.
fn patterns_and_indices(&self) -> SmallVec<[(usize, PatId); 2]> {
match self {
Fields::Vec(pats) => pats.iter().copied().enumerate().collect(),
}
}
pub(super) fn into_patterns(self) -> SmallVec<[PatId; 2]> {
match self {
Fields::Vec(pats) => pats,
}
}
/// Overrides some of the fields with the provided patterns. Exactly like
/// `replace_fields_indexed`, except that it takes `FieldPat`s as input.
fn replace_with_fieldpats(&self, new_pats: impl IntoIterator<Item = PatId>) -> Self {
self.replace_fields_indexed(new_pats.into_iter().enumerate())
}
/// Overrides some of the fields with the provided patterns. This is used when a pattern
/// defines some fields but not all, for example `Foo { field1: Some(_), .. }`: here we start
/// with a `Fields` that is just one wildcard per field of the `Foo` struct, and override the
/// entry corresponding to `field1` with the pattern `Some(_)`. This is also used for slice
/// patterns for the same reason.
fn replace_fields_indexed(&self, new_pats: impl IntoIterator<Item = (usize, PatId)>) -> Self {
let mut fields = self.clone();
match &mut fields {
Fields::Vec(pats) => {
for (i, pat) in new_pats {
if let Some(p) = pats.get_mut(i) {
*p = pat;
}
}
}
}
fields
}
/// Replaces contained fields with the given list of patterns. There must be `len()` patterns
/// in `pats`.
pub(super) fn replace_fields(
&self,
cx: &MatchCheckCtx<'_>,
pats: impl IntoIterator<Item = Pat>,
) -> Self {
let pats = {
let mut arena = cx.pattern_arena.borrow_mut();
pats.into_iter().map(move |pat| /* arena.alloc(pat) */ todo!()).collect()
};
match self {
Fields::Vec(_) => Fields::Vec(pats),
}
}
/// Replaces contained fields with the arguments of the given pattern. Only use on a pattern
/// that is compatible with the constructor used to build `self`.
/// This is meant to be used on the result of `Fields::wildcards()`. The idea is that
/// `wildcards` constructs a list of fields where all entries are wildcards, and the pattern
/// provided to this function fills some of the fields with non-wildcards.
/// In the following example `Fields::wildcards` would return `[_, _, _, _]`. If we call
/// `replace_with_pattern_arguments` on it with the pattern, the result will be `[Some(0), _,
/// _, _]`.
/// ```rust
/// let x: [Option<u8>; 4] = foo();
/// match x {
/// [Some(0), ..] => {}
/// }
/// ```
/// This is guaranteed to preserve the number of patterns in `self`.
pub(super) fn replace_with_pattern_arguments(
&self,
pat: PatId,
cx: &MatchCheckCtx<'_>,
) -> Self {
match &cx.pattern_arena.borrow()[pat] {
Pat::Ref { pat: subpattern, .. } => {
assert_eq!(self.len(), 1);
Fields::from_single_pattern(*subpattern)
}
Pat::Tuple { args: subpatterns, ellipsis } => {
// FIXME(iDawer) handle ellipsis.
// XXX(iDawer): in rustc, this is handled by HIR->TypedHIR lowering
// rustc_mir_build::thir::pattern::PatCtxt::lower_tuple_subpats(..)
self.replace_with_fieldpats(subpatterns.iter().copied())
}
Pat::Wild => self.clone(),
pat => todo!("Fields::replace_with_pattern_arguments({:?})", pat),
// Pat::Missing => {}
// Pat::Or(_) => {}
// Pat::Record { path, args, ellipsis } => {}
// Pat::Range { start, end } => {}
// Pat::Slice { prefix, slice, suffix } => {}
// Pat::Path(_) => {}
// Pat::Lit(_) => {}
// Pat::Bind { mode, name, subpat } => {}
// Pat::TupleStruct { path, args, ellipsis } => {}
// Pat::Box { inner } => {}
// Pat::ConstBlock(_) => {}
}
}
}
fn is_field_list_non_exhaustive(variant_id: VariantId, cx: &MatchCheckCtx<'_>) -> bool {
let attr_def_id = match variant_id {
VariantId::EnumVariantId(id) => id.into(),
VariantId::StructId(id) => id.into(),
VariantId::UnionId(id) => id.into(),
};
cx.db.attrs(attr_def_id).by_key("non_exhaustive").exists()
}
#[test]
fn it_works() {}

736
crates/hir_ty/src/diagnostics/pattern/usefulness.rs Normal file
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@ -0,0 +1,736 @@
// Based on rust-lang/rust 1.52.0-nightly (25c15cdbe 2021-04-22)
// rust/compiler/rustc_mir_build/src/thir/pattern/usefulness.rs
use std::{cell::RefCell, iter::FromIterator, ops::Index, sync::Arc};
use base_db::CrateId;
use hir_def::{
body::Body,
expr::{ExprId, Pat, PatId},
};
use la_arena::Arena;
use once_cell::unsync::OnceCell;
use rustc_hash::FxHashMap;
use smallvec::{smallvec, SmallVec};
use crate::{db::HirDatabase, InferenceResult, Ty};
use super::deconstruct_pat::{Constructor, Fields, SplitWildcard};
use self::{
helper::{Captures, PatIdExt},
Usefulness::*,
WitnessPreference::*,
};
pub(crate) struct MatchCheckCtx<'a> {
pub(crate) krate: CrateId,
pub(crate) match_expr: ExprId,
pub(crate) body: Arc<Body>,
pub(crate) infer: &'a InferenceResult,
pub(crate) db: &'a dyn HirDatabase,
/// Patterns from self.body.pats plus generated by the check.
pub(crate) pattern_arena: &'a RefCell<PatternArena>,
}
impl<'a> MatchCheckCtx<'a> {
pub(super) fn is_uninhabited(&self, ty: &Ty) -> bool {
// FIXME(iDawer) implement exhaustive_patterns feature. More info in:
// Tracking issue for RFC 1872: exhaustive_patterns feature https://github.com/rust-lang/rust/issues/51085
false
}
pub(super) fn alloc_pat(&self, pat: Pat, ty: &Ty) -> PatId {
self.pattern_arena.borrow_mut().alloc(pat, ty)
}
/// Get type of a pattern. Handles expanded patterns.
pub(super) fn type_of(&self, pat: PatId) -> Ty {
let type_of_expanded_pat = self.pattern_arena.borrow().type_of_epat.get(&pat).cloned();
type_of_expanded_pat.unwrap_or_else(|| self.infer[pat].clone())
}
}
#[derive(Clone)]
pub(super) struct PatCtxt<'a> {
pub(super) cx: &'a MatchCheckCtx<'a>,
/// Type of the current column under investigation.
pub(super) ty: Ty,
/// Whether the current pattern is the whole pattern as found in a match arm, or if it's a
/// subpattern.
pub(super) is_top_level: bool,
}
impl PatIdExt for PatId {
fn is_wildcard(self, cx: &MatchCheckCtx<'_>) -> bool {
matches!(cx.pattern_arena.borrow()[self], Pat::Bind { subpat: None, .. } | Pat::Wild)
}
fn is_or_pat(self, cx: &MatchCheckCtx<'_>) -> bool {
matches!(cx.pattern_arena.borrow()[self], Pat::Or(..))
}
/// Recursively expand this pattern into its subpatterns. Only useful for or-patterns.
fn expand_or_pat(self, cx: &MatchCheckCtx<'_>) -> Vec<Self> {
fn expand(pat: PatId, vec: &mut Vec<PatId>, pat_arena: &PatternArena) {
if let Pat::Or(pats) = &pat_arena[pat] {
for &pat in pats {
expand(pat, vec, pat_arena);
}
} else {
vec.push(pat)
}
}
let pat_arena = cx.pattern_arena.borrow();
let mut pats = Vec::new();
expand(self, &mut pats, &pat_arena);
pats
}
}
/// A row of a matrix. Rows of len 1 are very common, which is why `SmallVec[_; 2]`
/// works well.
#[derive(Clone)]
pub(super) struct PatStack {
pats: SmallVec<[PatId; 2]>,
/// Cache for the constructor of the head
head_ctor: OnceCell<Constructor>,
}
impl PatStack {
fn from_pattern(pat: PatId) -> Self {
Self::from_vec(smallvec![pat])
}
fn from_vec(vec: SmallVec<[PatId; 2]>) -> Self {
PatStack { pats: vec, head_ctor: OnceCell::new() }
}
fn is_empty(&self) -> bool {
self.pats.is_empty()
}
fn len(&self) -> usize {
self.pats.len()
}
fn head(&self) -> PatId {
self.pats[0]
}
#[inline]
fn head_ctor(&self, cx: &MatchCheckCtx<'_>) -> &Constructor {
self.head_ctor.get_or_init(|| Constructor::from_pat(cx, self.head()))
}
fn iter(&self) -> impl Iterator<Item = PatId> + '_ {
self.pats.iter().copied()
}
// Recursively expand the first pattern into its subpatterns. Only useful if the pattern is an
// or-pattern. Panics if `self` is empty.
fn expand_or_pat(&self, cx: &MatchCheckCtx<'_>) -> impl Iterator<Item = PatStack> + '_ {
self.head().expand_or_pat(cx).into_iter().map(move |pat| {
let mut new_patstack = PatStack::from_pattern(pat);
new_patstack.pats.extend_from_slice(&self.pats[1..]);
new_patstack
})
}
/// This computes `S(self.head_ctor(), self)`. See top of the file for explanations.
///
/// Structure patterns with a partial wild pattern (Foo { a: 42, .. }) have their missing
/// fields filled with wild patterns.
///
/// This is roughly the inverse of `Constructor::apply`.
fn pop_head_constructor(
&self,
ctor_wild_subpatterns: &Fields,
cx: &MatchCheckCtx<'_>,
) -> PatStack {
// We pop the head pattern and push the new fields extracted from the arguments of
// `self.head()`.
let mut new_fields =
ctor_wild_subpatterns.replace_with_pattern_arguments(self.head(), cx).into_patterns();
new_fields.extend_from_slice(&self.pats[1..]);
PatStack::from_vec(new_fields)
}
}
impl Default for PatStack {
fn default() -> Self {
Self::from_vec(smallvec![])
}
}
impl PartialEq for PatStack {
fn eq(&self, other: &Self) -> bool {
self.pats == other.pats
}
}
impl FromIterator<PatId> for PatStack {
fn from_iter<T>(iter: T) -> Self
where
T: IntoIterator<Item = PatId>,
{
Self::from_vec(iter.into_iter().collect())
}
}
#[derive(Clone)]
pub(super) struct Matrix {
patterns: Vec<PatStack>,
}
impl Matrix {
fn empty() -> Self {
Matrix { patterns: vec![] }
}
/// Number of columns of this matrix. `None` is the matrix is empty.
pub(super) fn column_count(&self) -> Option<usize> {
self.patterns.get(0).map(|r| r.len())
}
/// Pushes a new row to the matrix. If the row starts with an or-pattern, this recursively
/// expands it.
fn push(&mut self, row: PatStack, cx: &MatchCheckCtx<'_>) {
if !row.is_empty() && row.head().is_or_pat(cx) {
for row in row.expand_or_pat(cx) {
self.patterns.push(row);
}
} else {
self.patterns.push(row);
}
}
/// Iterate over the first component of each row
fn heads(&self) -> impl Iterator<Item = PatId> + '_ {
self.patterns.iter().map(|r| r.head())
}
/// Iterate over the first constructor of each row.
fn head_ctors<'a>(
&'a self,
cx: &'a MatchCheckCtx<'_>,
) -> impl Iterator<Item = &'a Constructor> + Clone {
self.patterns.iter().map(move |r| r.head_ctor(cx))
}
/// This computes `S(constructor, self)`. See top of the file for explanations.
fn specialize_constructor(
&self,
pcx: &PatCtxt<'_>,
ctor: &Constructor,
ctor_wild_subpatterns: &Fields,
) -> Matrix {
let rows = self
.patterns
.iter()
.filter(|r| ctor.is_covered_by(pcx, r.head_ctor(pcx.cx)))
.map(|r| r.pop_head_constructor(ctor_wild_subpatterns, pcx.cx));
Matrix::from_iter(rows, pcx.cx)
}
fn from_iter(rows: impl IntoIterator<Item = PatStack>, cx: &MatchCheckCtx<'_>) -> Matrix {
let mut matrix = Matrix::empty();
for x in rows {
// Using `push` ensures we correctly expand or-patterns.
matrix.push(x, cx);
}
matrix
}
}
#[derive(Debug, Clone)]
enum SubPatSet {
/// The empty set. This means the pattern is unreachable.
Empty,
/// The set containing the full pattern.
Full,
/// If the pattern is a pattern with a constructor or a pattern-stack, we store a set for each
/// of its subpatterns. Missing entries in the map are implicitly full, because that's the
/// common case.
Seq { subpats: FxHashMap<usize, SubPatSet> },
/// If the pattern is an or-pattern, we store a set for each of its alternatives. Missing
/// entries in the map are implicitly empty. Note: we always flatten nested or-patterns.
Alt {
subpats: FxHashMap<usize, SubPatSet>,
/// Counts the total number of alternatives in the pattern
alt_count: usize,
/// We keep the pattern around to retrieve spans.
pat: PatId,
},
}
impl SubPatSet {
fn full() -> Self {
SubPatSet::Full
}
fn empty() -> Self {
SubPatSet::Empty
}
fn is_empty(&self) -> bool {
match self {
SubPatSet::Empty => true,
SubPatSet::Full => false,
// If any subpattern in a sequence is unreachable, the whole pattern is unreachable.
SubPatSet::Seq { subpats } => subpats.values().any(|set| set.is_empty()),
// An or-pattern is reachable if any of its alternatives is.
SubPatSet::Alt { subpats, .. } => subpats.values().all(|set| set.is_empty()),
}
}
fn is_full(&self) -> bool {
match self {
SubPatSet::Empty => false,
SubPatSet::Full => true,
// The whole pattern is reachable only when all its alternatives are.
SubPatSet::Seq { subpats } => subpats.values().all(|sub_set| sub_set.is_full()),
// The whole or-pattern is reachable only when all its alternatives are.
SubPatSet::Alt { subpats, alt_count, .. } => {
subpats.len() == *alt_count && subpats.values().all(|set| set.is_full())
}
}
}
/// Union `self` with `other`, mutating `self`.
fn union(&mut self, other: Self) {
use SubPatSet::*;
// Union with full stays full; union with empty changes nothing.
if self.is_full() || other.is_empty() {
return;
} else if self.is_empty() {
*self = other;
return;
} else if other.is_full() {
*self = Full;
return;
}
match (&mut *self, other) {
(Seq { .. }, Seq { .. }) => {
todo!()
}
(Alt { .. }, Alt { .. }) => {
todo!()
}
_ => panic!("bug"),
}
}
/// Returns a list of the spans of the unreachable subpatterns. If `self` is empty (i.e. the
/// whole pattern is unreachable) we return `None`.
fn list_unreachable_spans(&self) -> Option<Vec<()>> {
if self.is_empty() {
return None;
}
if self.is_full() {
// No subpatterns are unreachable.
return Some(Vec::new());
}
todo!()
}
/// When `self` refers to a patstack that was obtained from specialization, after running
/// `unspecialize` it will refer to the original patstack before specialization.
fn unspecialize(self, arity: usize) -> Self {
use SubPatSet::*;
match self {
Full => Full,
Empty => Empty,
Seq { subpats } => {
todo!()
}
Alt { .. } => panic!("bug"),
}
}
/// When `self` refers to a patstack that was obtained from splitting an or-pattern, after
/// running `unspecialize` it will refer to the original patstack before splitting.
///
/// For example:
/// ```
/// match Some(true) {
/// Some(true) => {}
/// None | Some(true | false) => {}
/// }
/// ```
/// Here `None` would return the full set and `Some(true | false)` would return the set
/// containing `false`. After `unsplit_or_pat`, we want the set to contain `None` and `false`.
/// This is what this function does.
fn unsplit_or_pat(mut self, alt_id: usize, alt_count: usize, pat: PatId) -> Self {
todo!()
}
}
/// This carries the results of computing usefulness, as described at the top of the file. When
/// checking usefulness of a match branch, we use the `NoWitnesses` variant, which also keeps track
/// of potential unreachable sub-patterns (in the presence of or-patterns). When checking
/// exhaustiveness of a whole match, we use the `WithWitnesses` variant, which carries a list of
/// witnesses of non-exhaustiveness when there are any.
/// Which variant to use is dictated by `WitnessPreference`.
#[derive(Clone, Debug)]
enum Usefulness {
/// Carries a set of subpatterns that have been found to be reachable. If empty, this indicates
/// the whole pattern is unreachable. If not, this indicates that the pattern is reachable but
/// that some sub-patterns may be unreachable (due to or-patterns). In the absence of
/// or-patterns this will always be either `Empty` (the whole pattern is unreachable) or `Full`
/// (the whole pattern is reachable).
NoWitnesses(SubPatSet),
/// Carries a list of witnesses of non-exhaustiveness. If empty, indicates that the whole
/// pattern is unreachable.
WithWitnesses(Vec<Witness>),
}
impl Usefulness {
fn new_useful(preference: WitnessPreference) -> Self {
match preference {
ConstructWitness => WithWitnesses(vec![Witness(vec![])]),
LeaveOutWitness => NoWitnesses(SubPatSet::full()),
}
}
fn new_not_useful(preference: WitnessPreference) -> Self {
match preference {
ConstructWitness => WithWitnesses(vec![]),
LeaveOutWitness => NoWitnesses(SubPatSet::empty()),
}
}
/// Combine usefulnesses from two branches. This is an associative operation.
fn extend(&mut self, other: Self) {
match (&mut *self, other) {
(WithWitnesses(_), WithWitnesses(o)) if o.is_empty() => {}
(WithWitnesses(s), WithWitnesses(o)) if s.is_empty() => *self = WithWitnesses(o),
(WithWitnesses(s), WithWitnesses(o)) => s.extend(o),
(NoWitnesses(s), NoWitnesses(o)) => s.union(o),
_ => unreachable!(),
}
}
/// When trying several branches and each returns a `Usefulness`, we need to combine the
/// results together.
fn merge(pref: WitnessPreference, usefulnesses: impl Iterator<Item = Self>) -> Self {
let mut ret = Self::new_not_useful(pref);
for u in usefulnesses {
ret.extend(u);
if let NoWitnesses(subpats) = &ret {
if subpats.is_full() {
// Once we reach the full set, more unions won't change the result.
return ret;
}
}
}
ret
}
/// After calculating the usefulness for a branch of an or-pattern, call this to make this
/// usefulness mergeable with those from the other branches.
fn unsplit_or_pat(self, alt_id: usize, alt_count: usize, pat: PatId) -> Self {
match self {
NoWitnesses(subpats) => NoWitnesses(subpats.unsplit_or_pat(alt_id, alt_count, pat)),
WithWitnesses(_) => panic!("bug"),
}
}
/// After calculating usefulness after a specialization, call this to recontruct a usefulness
/// that makes sense for the matrix pre-specialization. This new usefulness can then be merged
/// with the results of specializing with the other constructors.
fn apply_constructor(
self,
pcx: &PatCtxt<'_>,
matrix: &Matrix,
ctor: &Constructor,
ctor_wild_subpatterns: &Fields,
) -> Self {
match self {
WithWitnesses(witnesses) if witnesses.is_empty() => WithWitnesses(witnesses),
WithWitnesses(w) => {
let new_witnesses = if matches!(ctor, Constructor::Missing) {
let mut split_wildcard = SplitWildcard::new(pcx);
split_wildcard.split(pcx, matrix.head_ctors(pcx.cx));
} else {
todo!("Usefulness::apply_constructor({:?})", ctor)
};
todo!("Usefulness::apply_constructor({:?})", ctor)
}
NoWitnesses(subpats) => NoWitnesses(subpats.unspecialize(ctor_wild_subpatterns.len())),
}
}
}
#[derive(Copy, Clone, Debug)]
enum WitnessPreference {
ConstructWitness,
LeaveOutWitness,
}
#[derive(Clone, Debug)]
pub(crate) struct Witness(Vec<Pat>);
impl Witness {
/// Asserts that the witness contains a single pattern, and returns it.
fn single_pattern(self) -> Pat {
assert_eq!(self.0.len(), 1);
self.0.into_iter().next().unwrap()
}
/// Constructs a partial witness for a pattern given a list of
/// patterns expanded by the specialization step.
///
/// When a pattern P is discovered to be useful, this function is used bottom-up
/// to reconstruct a complete witness, e.g., a pattern P' that covers a subset
/// of values, V, where each value in that set is not covered by any previously
/// used patterns and is covered by the pattern P'. Examples:
///
/// left_ty: tuple of 3 elements
/// pats: [10, 20, _] => (10, 20, _)
///
/// left_ty: struct X { a: (bool, &'static str), b: usize}
/// pats: [(false, "foo"), 42] => X { a: (false, "foo"), b: 42 }
fn apply_constructor(
mut self,
pcx: &PatCtxt<'_>,
ctor: &Constructor,
ctor_wild_subpatterns: &Fields,
) -> Self {
let pat = {
let len = self.0.len();
let arity = ctor_wild_subpatterns.len();
let pats = self.0.drain((len - arity)..).rev();
ctor_wild_subpatterns.replace_fields(pcx.cx, pats).apply(pcx, ctor)
};
self.0.push(pat);
self
}
}
/// Algorithm from <http://moscova.inria.fr/~maranget/papers/warn/index.html>.
/// The algorithm from the paper has been modified to correctly handle empty
/// types. The changes are:
/// (0) We don't exit early if the pattern matrix has zero rows. We just
/// continue to recurse over columns.
/// (1) all_constructors will only return constructors that are statically
/// possible. E.g., it will only return `Ok` for `Result<T, !>`.
///
/// This finds whether a (row) vector `v` of patterns is 'useful' in relation
/// to a set of such vectors `m` - this is defined as there being a set of
/// inputs that will match `v` but not any of the sets in `m`.
///
/// All the patterns at each column of the `matrix ++ v` matrix must have the same type.
///
/// This is used both for reachability checking (if a pattern isn't useful in
/// relation to preceding patterns, it is not reachable) and exhaustiveness
/// checking (if a wildcard pattern is useful in relation to a matrix, the
/// matrix isn't exhaustive).
///
/// `is_under_guard` is used to inform if the pattern has a guard. If it
/// has one it must not be inserted into the matrix. This shouldn't be
/// relied on for soundness.
fn is_useful(
cx: &MatchCheckCtx<'_>,
matrix: &Matrix,
v: &PatStack,
witness_preference: WitnessPreference,
is_under_guard: bool,
is_top_level: bool,
) -> Usefulness {
let Matrix { patterns: rows, .. } = matrix;
// The base case. We are pattern-matching on () and the return value is
// based on whether our matrix has a row or not.
// NOTE: This could potentially be optimized by checking rows.is_empty()
// first and then, if v is non-empty, the return value is based on whether
// the type of the tuple we're checking is inhabited or not.
if v.is_empty() {
let ret = if rows.is_empty() {
Usefulness::new_useful(witness_preference)
} else {
Usefulness::new_not_useful(witness_preference)
};
return ret;
}
assert!(rows.iter().all(|r| r.len() == v.len()));
// FIXME(Nadrieril): Hack to work around type normalization issues (see rust-lang/rust#72476).
// TODO(iDawer): ty.as_reference()
let ty = matrix.heads().next().map_or(cx.type_of(v.head()), |r| cx.type_of(r));
let pcx = PatCtxt { cx, ty, is_top_level };
// If the first pattern is an or-pattern, expand it.
let ret = if v.head().is_or_pat(cx) {
//expanding or-pattern
let v_head = v.head();
let vs: Vec<_> = v.expand_or_pat(cx).collect();
let alt_count = vs.len();
// We try each or-pattern branch in turn.
let mut matrix = matrix.clone();
let usefulnesses = vs.into_iter().enumerate().map(|(i, v)| {
let usefulness = is_useful(cx, &matrix, &v, witness_preference, is_under_guard, false);
// If pattern has a guard don't add it to the matrix.
if !is_under_guard {
// We push the already-seen patterns into the matrix in order to detect redundant
// branches like `Some(_) | Some(0)`.
matrix.push(v, cx);
}
usefulness.unsplit_or_pat(i, alt_count, v_head)
});
Usefulness::merge(witness_preference, usefulnesses)
} else {
let v_ctor = v.head_ctor(cx);
// if let Constructor::IntRange(ctor_range) = v_ctor {
// // Lint on likely incorrect range patterns (#63987)
// ctor_range.lint_overlapping_range_endpoints(
// pcx,
// matrix.head_ctors_and_spans(cx),
// matrix.column_count().unwrap_or(0),
// hir_id,
// )
// }
// We split the head constructor of `v`.
let split_ctors = v_ctor.split(&pcx, matrix.head_ctors(cx));
// For each constructor, we compute whether there's a value that starts with it that would
// witness the usefulness of `v`.
let start_matrix = matrix;
let usefulnesses = split_ctors.into_iter().map(|ctor| {
// debug!("specialize({:?})", ctor);
// We cache the result of `Fields::wildcards` because it is used a lot.
let ctor_wild_subpatterns = Fields::wildcards(&pcx, &ctor);
let spec_matrix =
start_matrix.specialize_constructor(&pcx, &ctor, &ctor_wild_subpatterns);
let v = v.pop_head_constructor(&ctor_wild_subpatterns, cx);
let usefulness =
is_useful(cx, &spec_matrix, &v, witness_preference, is_under_guard, false);
usefulness.apply_constructor(&pcx, start_matrix, &ctor, &ctor_wild_subpatterns)
});
Usefulness::merge(witness_preference, usefulnesses)
};
ret
}
/// The arm of a match expression.
#[derive(Clone, Copy)]
pub(crate) struct MatchArm {
pub(crate) pat: PatId,
pub(crate) has_guard: bool,
}
/// Indicates whether or not a given arm is reachable.
#[derive(Clone, Debug)]
pub(crate) enum Reachability {
/// The arm is reachable. This additionally carries a set of or-pattern branches that have been
/// found to be unreachable despite the overall arm being reachable. Used only in the presence
/// of or-patterns, otherwise it stays empty.
Reachable(Vec<()>),
/// The arm is unreachable.
Unreachable,
}
/// The output of checking a match for exhaustiveness and arm reachability.
pub(crate) struct UsefulnessReport {
/// For each arm of the input, whether that arm is reachable after the arms above it.
pub(crate) arm_usefulness: Vec<(MatchArm, Reachability)>,
/// If the match is exhaustive, this is empty. If not, this contains witnesses for the lack of
/// exhaustiveness.
pub(crate) non_exhaustiveness_witnesses: Vec<Pat>,
}
pub(crate) fn compute_match_usefulness(
cx: &MatchCheckCtx<'_>,
arms: &[MatchArm],
) -> UsefulnessReport {
let mut matrix = Matrix::empty();
let arm_usefulness: Vec<_> = arms
.iter()
.copied()
.map(|arm| {
let v = PatStack::from_pattern(arm.pat);
let usefulness = is_useful(cx, &matrix, &v, LeaveOutWitness, arm.has_guard, true);
if !arm.has_guard {
matrix.push(v, cx);
}
let reachability = match usefulness {
NoWitnesses(subpats) if subpats.is_empty() => Reachability::Unreachable,
NoWitnesses(subpats) => {
Reachability::Reachable(subpats.list_unreachable_spans().unwrap())
}
WithWitnesses(..) => panic!("bug"),
};
(arm, reachability)
})
.collect();
let wild_pattern = cx.pattern_arena.borrow_mut().alloc(Pat::Wild, &cx.infer[cx.match_expr]);
let v = PatStack::from_pattern(wild_pattern);
let usefulness = is_useful(cx, &matrix, &v, LeaveOutWitness, false, true);
let non_exhaustiveness_witnesses = match usefulness {
// TODO: ConstructWitness
// WithWitnesses(pats) => pats.into_iter().map(Witness::single_pattern).collect(),
// NoWitnesses(_) => panic!("bug"),
NoWitnesses(subpats) if subpats.is_empty() => Vec::new(),
NoWitnesses(subpats) => vec![Pat::Wild],
WithWitnesses(..) => panic!("bug"),
};
UsefulnessReport { arm_usefulness, non_exhaustiveness_witnesses }
}
pub(crate) struct PatternArena {
arena: Arena<Pat>,
/// Types of expanded patterns.
type_of_epat: FxHashMap<PatId, Ty>,
}
impl PatternArena {
pub(crate) fn clone_from(pats: &Arena<Pat>) -> RefCell<Self> {
PatternArena { arena: pats.clone(), type_of_epat: Default::default() }.into()
}
fn alloc(&mut self, pat: Pat, ty: &Ty) -> PatId {
let id = self.arena.alloc(pat);
self.type_of_epat.insert(id, ty.clone());
id
}
}
impl Index<PatId> for PatternArena {
type Output = Pat;
fn index(&self, pat: PatId) -> &Pat {
&self.arena[pat]
}
}
mod helper {
use hir_def::expr::{Pat, PatId};
use super::MatchCheckCtx;
pub(super) trait PatIdExt: Sized {
fn is_wildcard(self, cx: &MatchCheckCtx<'_>) -> bool;
fn is_or_pat(self, cx: &MatchCheckCtx<'_>) -> bool;
fn expand_or_pat(self, cx: &MatchCheckCtx<'_>) -> Vec<Self>;
}
// Copy-pasted from rust/compiler/rustc_data_structures/src/captures.rs
/// "Signaling" trait used in impl trait to tag lifetimes that you may
/// need to capture but don't really need for other reasons.
/// Basically a workaround; see [this comment] for details.
///
/// [this comment]: https://github.com/rust-lang/rust/issues/34511#issuecomment-373423999
// FIXME(eddyb) false positive, the lifetime parameter is "phantom" but needed.
#[allow(unused_lifetimes)]
pub trait Captures<'a> {}
impl<'a, T: ?Sized> Captures<'a> for T {}
}
#[test]
fn it_works() {}