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internal: Sync match checking algorithm with rustc

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Original version: rust-lang/rust  68b76a483 2021-10-01
This commit is contained in:
Dawer 2021-10-07 23:33:41 +05:00 committed by iDawer
parent 0add6e95e5
commit deb05930ef
7 changed files with 605 additions and 888 deletions
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7
Cargo.lock generated
View file

@ -559,6 +559,7 @@ dependencies = [
"tracing",
"tracing-subscriber",
"tracing-tree",
"typed-arena",
]
[[package]]
@ -1775,6 +1776,12 @@ dependencies = [
"stdx",
]
[[package]]
name = "typed-arena"
version = "2.0.1"
source = "registry+https://github.com/rust-lang/crates.io-index"
checksum = "0685c84d5d54d1c26f7d3eb96cd41550adb97baed141a761cf335d3d33bcd0ae"
[[package]]
name = "ungrammar"
version = "1.14.9"

1
crates/hir_ty/Cargo.toml
View file

@ -23,6 +23,7 @@ chalk-ir = "0.75"
chalk-recursive = { version = "0.75", default-features = false }
la-arena = { version = "0.3.0", path = "../../lib/arena" }
once_cell = { version = "1.5.0" }
typed-arena = "2.0.1"
stdx = { path = "../stdx", version = "0.0.0" }
hir_def = { path = "../hir_def", version = "0.0.0" }

47
crates/hir_ty/src/diagnostics/expr.rs
View file

@ -2,7 +2,7 @@
//! through the body using inference results: mismatched arg counts, missing
//! fields, etc.
use std::{cell::RefCell, sync::Arc};
use std::sync::Arc;
use hir_def::{
expr::Statement, path::path, resolver::HasResolver, type_ref::Mutability, AssocItemId,
@ -11,12 +11,14 @@ use hir_def::{
use hir_expand::name;
use itertools::Either;
use rustc_hash::FxHashSet;
use typed_arena::Arena;
use crate::{
db::HirDatabase,
diagnostics::match_check::{
self,
usefulness::{compute_match_usefulness, expand_pattern, MatchCheckCtx, PatternArena},
deconstruct_pat::DeconstructedPat,
usefulness::{compute_match_usefulness, MatchCheckCtx},
},
AdtId, InferenceResult, Interner, Ty, TyExt, TyKind,
};
@ -275,15 +277,19 @@ impl ExprValidator {
) {
let body = db.body(self.owner);
let match_expr_ty = if infer.type_of_expr[match_expr].is_unknown() {
let match_expr_ty = &infer[match_expr];
if match_expr_ty.is_unknown() {
return;
} else {
&infer.type_of_expr[match_expr]
}
let pattern_arena = Arena::new();
let cx = MatchCheckCtx {
module: self.owner.module(db.upcast()),
db,
pattern_arena: &pattern_arena,
};
let pattern_arena = RefCell::new(PatternArena::new());
let mut m_arms = Vec::new();
let mut m_arms = Vec::with_capacity(arms.len());
let mut has_lowering_errors = false;
for arm in arms {
if let Some(pat_ty) = infer.type_of_pat.get(arm.pat) {
@ -308,13 +314,7 @@ impl ExprValidator {
// check the usefulness of each pattern as we added it
// to the matrix here.
let m_arm = match_check::MatchArm {
pat: self.lower_pattern(
arm.pat,
&mut pattern_arena.borrow_mut(),
db,
&body,
&mut has_lowering_errors,
),
pat: self.lower_pattern(&cx, arm.pat, db, &body, &mut has_lowering_errors),
has_guard: arm.guard.is_some(),
};
m_arms.push(m_arm);
@ -332,14 +332,7 @@ impl ExprValidator {
return;
}
let cx = MatchCheckCtx {
module: self.owner.module(db.upcast()),
match_expr,
infer: &infer,
db,
pattern_arena: &pattern_arena,
};
let report = compute_match_usefulness(&cx, &m_arms);
let report = compute_match_usefulness(&cx, &m_arms, match_expr_ty);
// FIXME Report unreacheble arms
// https://github.com/rust-lang/rust/blob/25c15cdbe/compiler/rustc_mir_build/src/thir/pattern/check_match.rs#L200-L201
@ -352,17 +345,17 @@ impl ExprValidator {
}
}
fn lower_pattern(
fn lower_pattern<'p>(
&self,
cx: &MatchCheckCtx<'_, 'p>,
pat: PatId,
pattern_arena: &mut PatternArena,
db: &dyn HirDatabase,
body: &Body,
have_errors: &mut bool,
) -> match_check::PatId {
) -> &'p DeconstructedPat<'p> {
let mut patcx = match_check::PatCtxt::new(db, &self.infer, body);
let pattern = patcx.lower_pattern(pat);
let pattern = pattern_arena.alloc(expand_pattern(pattern));
let pattern = cx.pattern_arena.alloc(DeconstructedPat::from_pat(cx, &pattern));
if !patcx.errors.is_empty() {
*have_errors = true;
}

27
crates/hir_ty/src/diagnostics/match_check.rs
View file

@ -5,13 +5,12 @@
//!
//! It is modeled on the rustc module `rustc_mir_build::thir::pattern`.
mod deconstruct_pat;
mod pat_util;
pub(crate) mod deconstruct_pat;
pub(crate) mod usefulness;
use hir_def::{body::Body, EnumVariantId, LocalFieldId, VariantId};
use la_arena::Idx;
use hir_def::{body::Body, expr::PatId, EnumVariantId, LocalFieldId, VariantId};
use crate::{db::HirDatabase, InferenceResult, Interner, Substitution, Ty, TyKind};
@ -19,8 +18,6 @@ use self::pat_util::EnumerateAndAdjustIterator;
pub(crate) use self::usefulness::MatchArm;
pub(crate) type PatId = Idx<Pat>;
#[derive(Clone, Debug)]
pub(crate) enum PatternError {
Unimplemented,
@ -41,12 +38,6 @@ pub(crate) struct Pat {
pub(crate) kind: Box<PatKind>,
}
impl Pat {
pub(crate) fn wildcard_from_ty(ty: Ty) -> Self {
Pat { ty, kind: Box::new(PatKind::Wild) }
}
}
/// Close relative to `rustc_mir_build::thir::pattern::PatKind`
#[derive(Clone, Debug, PartialEq)]
pub(crate) enum PatKind {
@ -100,7 +91,7 @@ impl<'a> PatCtxt<'a> {
Self { db, infer, body, errors: Vec::new() }
}
pub(crate) fn lower_pattern(&mut self, pat: hir_def::expr::PatId) -> Pat {
pub(crate) fn lower_pattern(&mut self, pat: PatId) -> Pat {
// XXX(iDawer): Collecting pattern adjustments feels imprecise to me.
// When lowering of & and box patterns are implemented this should be tested
// in a manner of `match_ergonomics_issue_9095` test.
@ -116,7 +107,7 @@ impl<'a> PatCtxt<'a> {
)
}
fn lower_pattern_unadjusted(&mut self, pat: hir_def::expr::PatId) -> Pat {
fn lower_pattern_unadjusted(&mut self, pat: PatId) -> Pat {
let mut ty = &self.infer[pat];
let variant = self.infer.variant_resolution_for_pat(pat);
@ -189,7 +180,7 @@ impl<'a> PatCtxt<'a> {
fn lower_tuple_subpats(
&mut self,
pats: &[hir_def::expr::PatId],
pats: &[PatId],
expected_len: usize,
ellipsis: Option<usize>,
) -> Vec<FieldPat> {
@ -207,17 +198,17 @@ impl<'a> PatCtxt<'a> {
.collect()
}
fn lower_patterns(&mut self, pats: &[hir_def::expr::PatId]) -> Vec<Pat> {
fn lower_patterns(&mut self, pats: &[PatId]) -> Vec<Pat> {
pats.iter().map(|&p| self.lower_pattern(p)).collect()
}
fn lower_opt_pattern(&mut self, pat: Option<hir_def::expr::PatId>) -> Option<Pat> {
fn lower_opt_pattern(&mut self, pat: Option<PatId>) -> Option<Pat> {
pat.map(|p| self.lower_pattern(p))
}
fn lower_variant_or_leaf(
&mut self,
pat: hir_def::expr::PatId,
pat: PatId,
ty: &Ty,
subpatterns: Vec<FieldPat>,
) -> PatKind {
@ -244,7 +235,7 @@ impl<'a> PatCtxt<'a> {
kind
}
fn lower_path(&mut self, pat: hir_def::expr::PatId, _path: &hir_def::path::Path) -> Pat {
fn lower_path(&mut self, pat: PatId, _path: &hir_def::path::Path) -> Pat {
let ty = &self.infer[pat];
let pat_from_kind = |kind| Pat { ty: ty.clone(), kind: Box::new(kind) };

679
crates/hir_ty/src/diagnostics/match_check/deconstruct_pat.rs
View file

@ -42,6 +42,7 @@
//! wildcards, see [`SplitWildcard`]; for integer ranges, see [`SplitIntRange`].
use std::{
cell::Cell,
cmp::{max, min},
iter::once,
ops::RangeInclusive,
@ -55,12 +56,29 @@ use syntax::SmolStr;
use crate::{AdtId, Interner, Scalar, Ty, TyExt, TyKind};
use super::{
usefulness::{MatchCheckCtx, PatCtxt},
FieldPat, Pat, PatId, PatKind,
usefulness::{helper::Captures, MatchCheckCtx, PatCtxt},
Pat, PatKind,
};
use self::Constructor::*;
/// Recursively expand this pattern into its subpatterns. Only useful for or-patterns.
fn expand_or_pat(pat: &Pat) -> Vec<&Pat> {
fn expand<'p>(pat: &'p Pat, vec: &mut Vec<&'p Pat>) {
if let PatKind::Or { pats } = pat.kind.as_ref() {
for pat in pats {
expand(pat, vec);
}
} else {
vec.push(pat)
}
}
let mut pats = Vec::new();
expand(pat, &mut pats);
pats
}
/// [Constructor] uses this in umimplemented variants.
/// It allows porting match expressions from upstream algorithm without losing semantics.
#[derive(Copy, Clone, Debug, PartialEq, Eq)]
@ -241,6 +259,10 @@ pub(super) struct Slice {
}
impl Slice {
fn arity(self) -> usize {
unimplemented!()
}
/// See `Constructor::is_covered_by`
fn is_covered_by(self, _other: Self) -> bool {
unimplemented!() // never called as Slice contains Void
@ -278,10 +300,13 @@ pub(super) enum Constructor {
/// for those types for which we cannot list constructors explicitly, like `f64` and `str`.
NonExhaustive,
/// Stands for constructors that are not seen in the matrix, as explained in the documentation
/// for [`SplitWildcard`].
Missing,
/// for [`SplitWildcard`]. The carried `bool` is used for the `non_exhaustive_omitted_patterns`
/// lint.
Missing { nonexhaustive_enum_missing_real_variants: bool },
/// Wildcard pattern.
Wildcard,
/// Or-pattern.
Or,
}
impl Constructor {
@ -289,6 +314,10 @@ impl Constructor {
matches!(self, Wildcard)
}
pub(super) fn is_non_exhaustive(&self) -> bool {
matches!(self, NonExhaustive)
}
fn as_int_range(&self) -> Option<&IntRange> {
match self {
IntRange(range) => Some(range),
@ -318,16 +347,39 @@ impl Constructor {
}
}
/// Determines the constructor that the given pattern can be specialized to.
pub(super) fn from_pat(cx: &MatchCheckCtx<'_>, pat: PatId) -> Self {
match cx.pattern_arena.borrow()[pat].kind.as_ref() {
PatKind::Binding { .. } | PatKind::Wild => Wildcard,
PatKind::Leaf { .. } | PatKind::Deref { .. } => Single,
&PatKind::Variant { enum_variant, .. } => Variant(enum_variant),
&PatKind::LiteralBool { value } => IntRange(IntRange::from_bool(value)),
PatKind::Or { .. } => {
never!("Or-pattern should have been expanded earlier on.");
Wildcard
/// The number of fields for this constructor. This must be kept in sync with
/// `Fields::wildcards`.
pub(super) fn arity(&self, pcx: PatCtxt<'_, '_>) -> usize {
match self {
Single | Variant(_) => match *pcx.ty.kind(Interner) {
TyKind::Tuple(arity, ..) => arity,
TyKind::Ref(..) => 1,
TyKind::Adt(adt, ..) => {
if adt_is_box(adt.0, pcx.cx) {
// The only legal patterns of type `Box` (outside `std`) are `_` and box
// patterns. If we're here we can assume this is a box pattern.
1
} else {
let variant = self.variant_id_for_adt(adt.0);
Fields::list_variant_nonhidden_fields(pcx.cx, pcx.ty, variant).count()
}
}
_ => {
never!("Unexpected type for `Single` constructor: {:?}", pcx.ty);
0
}
},
Slice(slice) => slice.arity(),
Str(..)
| FloatRange(..)
| IntRange(..)
| NonExhaustive
| Opaque
| Missing { .. }
| Wildcard => 0,
Or => {
never!("The `Or` constructor doesn't have a fixed arity");
0
}
}
}
@ -347,7 +399,7 @@ impl Constructor {
/// matrix, unless all of them are.
pub(super) fn split<'a>(
&self,
pcx: PatCtxt<'_>,
pcx: PatCtxt<'_, '_>,
ctors: impl Iterator<Item = &'a Constructor> + Clone,
) -> SmallVec<[Self; 1]> {
match self {
@ -375,13 +427,13 @@ impl Constructor {
/// 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 {
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,
(Missing { .. } | Wildcard, _) => false,
(Single, Single) => true,
(Variant(self_id), Variant(other_id)) => self_id == other_id,
@ -411,7 +463,7 @@ impl Constructor {
/// 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 {
fn is_covered_by_any(&self, _pcx: PatCtxt<'_, '_>, used_ctors: &[Constructor]) -> bool {
if used_ctors.is_empty() {
return false;
}
@ -431,7 +483,7 @@ impl Constructor {
.any(|other| slice.is_covered_by(other)),
// This constructor is never covered by anything else
NonExhaustive => false,
Str(..) | FloatRange(..) | Opaque | Missing | Wildcard => {
Str(..) | FloatRange(..) | Opaque | Missing { .. } | Wildcard | Or => {
never!("found unexpected ctor in all_ctors: {:?}", self);
true
}
@ -463,7 +515,7 @@ pub(super) struct SplitWildcard {
}
impl SplitWildcard {
pub(super) fn new(pcx: PatCtxt<'_>) -> Self {
pub(super) fn new(pcx: PatCtxt<'_, '_>) -> Self {
let cx = pcx.cx;
let make_range = |start, end, scalar| IntRange(IntRange::from_range(start, end, scalar));
@ -483,7 +535,7 @@ impl SplitWildcard {
TyKind::Scalar(Scalar::Bool) => smallvec![make_range(0, 1, Scalar::Bool)],
// TyKind::Array(..) if ... => unhandled(),
TyKind::Array(..) | TyKind::Slice(..) => unhandled(),
&TyKind::Adt(AdtId(hir_def::AdtId::EnumId(enum_id)), ref _substs) => {
&TyKind::Adt(AdtId(hir_def::AdtId::EnumId(enum_id)), ..) => {
let enum_data = cx.db.enum_data(enum_id);
// If the enum is declared as `#[non_exhaustive]`, we treat it as if it had an
@ -502,7 +554,7 @@ impl SplitWildcard {
//
// we don't want to show every possible IO error, but instead have only `_` as the
// witness.
let is_declared_nonexhaustive = cx.is_foreign_non_exhaustive_enum(enum_id);
let is_declared_nonexhaustive = cx.is_foreign_non_exhaustive_enum(pcx.ty);
// If `exhaustive_patterns` is disabled and our scrutinee is an empty enum, we treat it
// as though it had an "unknown" constructor to avoid exposing its emptiness. The
@ -512,8 +564,15 @@ impl SplitWildcard {
&& !cx.feature_exhaustive_patterns()
&& !pcx.is_top_level;
if is_secretly_empty || is_declared_nonexhaustive {
if is_secretly_empty {
smallvec![NonExhaustive]
} else if is_declared_nonexhaustive {
enum_data
.variants
.iter()
.map(|(local_id, ..)| Variant(EnumVariantId { parent: enum_id, local_id }))
.chain(Some(NonExhaustive))
.collect()
} else if cx.feature_exhaustive_patterns() {
unimplemented!() // see MatchCheckCtx.feature_exhaustive_patterns()
} else {
@ -535,6 +594,7 @@ impl SplitWildcard {
// This type is one for which we cannot list constructors, like `str` or `f64`.
_ => smallvec![NonExhaustive],
};
SplitWildcard { matrix_ctors: Vec::new(), all_ctors }
}
@ -542,7 +602,7 @@ impl SplitWildcard {
/// do what you want.
pub(super) fn split<'a>(
&mut self,
pcx: PatCtxt<'_>,
pcx: PatCtxt<'_, '_>,
ctors: impl Iterator<Item = &'a Constructor> + Clone,
) {
// Since `all_ctors` never contains wildcards, this won't recurse further.
@ -552,21 +612,21 @@ impl SplitWildcard {
}
/// Whether there are any value constructors for this type that are not present in the matrix.
fn any_missing(&self, pcx: PatCtxt<'_>) -> bool {
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>(
pub(super) fn iter_missing<'a, 'p>(
&'a self,
pcx: PatCtxt<'a>,
) -> impl Iterator<Item = &'a Constructor> {
pcx: PatCtxt<'a, 'p>,
) -> impl Iterator<Item = &'a Constructor> + Captures<'p> {
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]> {
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,
@ -597,7 +657,17 @@ impl SplitWildcard {
// 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
if pcx.is_non_exhaustive {
Missing {
nonexhaustive_enum_missing_real_variants: self
.iter_missing(pcx)
.filter(|c| !c.is_non_exhaustive())
.next()
.is_some(),
}
} else {
Missing { nonexhaustive_enum_missing_real_variants: false }
}
} else {
Wildcard
};
@ -611,291 +681,334 @@ impl SplitWildcard {
/// 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]>),
/// This is constructed for a constructor using [`Fields::wildcards()`]. The idea is that
/// [`Fields::wildcards()`] constructs a list of fields where all entries are wildcards, and then
/// given a pattern we fill some of the fields with its subpatterns.
/// In the following example `Fields::wildcards` returns `[_, _, _, _]`. Then in
/// `extract_pattern_arguments` we fill some of the entries, and the result is
/// `[Some(0), _, _, _]`.
/// ```rust
/// let x: [Option<u8>; 4] = foo();
/// match x {
/// [Some(0), ..] => {}
/// }
/// ```
///
/// Note that the number of fields of a constructor may not match the fields declared in the
/// original struct/variant. This happens if a private or `non_exhaustive` field is uninhabited,
/// because the code mustn't observe that it is uninhabited. In that case that field is not
/// included in `fields`. For that reason, when you have a `mir::Field` you must use
/// `index_with_declared_idx`.
#[derive(Clone, Copy)]
pub(super) struct Fields<'p> {
fields: &'p [DeconstructedPat<'p>],
}
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])
impl<'p> Fields<'p> {
fn empty() -> Self {
Fields { fields: &[] }
}
/// Convenience; internal use.
fn wildcards_from_tys(cx: &MatchCheckCtx<'_>, tys: impl IntoIterator<Item = Ty>) -> Self {
let wilds = tys.into_iter().map(Pat::wildcard_from_ty);
let pats = wilds.map(|pat| cx.alloc_pat(pat)).collect();
Fields::Vec(pats)
fn singleton(cx: &MatchCheckCtx<'_, 'p>, field: DeconstructedPat<'p>) -> Self {
let field = cx.pattern_arena.alloc(field);
Fields { fields: std::slice::from_ref(field) }
}
/// Creates a new list of wildcard fields for a given constructor.
pub(crate) fn wildcards(pcx: PatCtxt<'_>, constructor: &Constructor) -> Self {
let ty = pcx.ty;
let cx = pcx.cx;
let wildcard_from_ty = |ty: &Ty| cx.alloc_pat(Pat::wildcard_from_ty(ty.clone()));
pub(super) fn from_iter(
cx: &MatchCheckCtx<'_, 'p>,
fields: impl IntoIterator<Item = DeconstructedPat<'p>>,
) -> Self {
let fields: &[_] = cx.pattern_arena.alloc_extend(fields);
Fields { fields }
}
fn wildcards_from_tys(cx: &MatchCheckCtx<'_, 'p>, tys: impl IntoIterator<Item = Ty>) -> Self {
Fields::from_iter(cx, tys.into_iter().map(DeconstructedPat::wildcard))
}
// In the cases of either a `#[non_exhaustive]` field list or a non-public field, we hide
// uninhabited fields in order not to reveal the uninhabitedness of the whole variant.
// This lists the fields we keep along with their types.
fn list_variant_nonhidden_fields<'a>(
cx: &'a MatchCheckCtx<'a, 'p>,
ty: &'a Ty,
variant: VariantId,
) -> impl Iterator<Item = (LocalFieldId, Ty)> + Captures<'a> + Captures<'p> {
let (adt, substs) = ty.as_adt().unwrap();
let adt_is_local = variant.module(cx.db.upcast()).krate() == cx.module.krate();
// Whether we must not match the fields of this variant exhaustively.
let is_non_exhaustive = is_field_list_non_exhaustive(variant, cx) && !adt_is_local;
let visibility = cx.db.field_visibilities(variant);
let field_ty = cx.db.field_types(variant);
let fields_len = variant.variant_data(cx.db.upcast()).fields().len() as u32;
(0..fields_len).map(|idx| LocalFieldId::from_raw(idx.into())).filter_map(move |fid| {
// TODO check ty has been normalized
let ty = field_ty[fid].clone().substitute(Interner, substs);
let is_visible = matches!(adt, hir_def::AdtId::EnumId(..))
|| visibility[fid].is_visible_from(cx.db.upcast(), cx.module);
let is_uninhabited = cx.is_uninhabited(&ty);
if is_uninhabited && (!is_visible || is_non_exhaustive) {
None
} else {
Some((fid, ty))
}
})
}
/// Creates a new list of wildcard fields for a given constructor. The result must have a
/// length of `constructor.arity()`.
pub(crate) fn wildcards(
cx: &MatchCheckCtx<'_, 'p>,
ty: &Ty,
constructor: &Constructor,
) -> Self {
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.cloned())
}
TyKind::Ref(.., rty) => Fields::from_single_pattern(wildcard_from_ty(rty)),
TyKind::Ref(.., rty) => Fields::wildcards_from_tys(cx, once(rty.clone())),
&TyKind::Adt(AdtId(adt), ref substs) => {
if adt_is_box(adt, cx) {
// Use T as the sub pattern type of Box<T>.
let subst_ty = substs.at(Interner, 0).assert_ty_ref(Interner);
Fields::from_single_pattern(wildcard_from_ty(subst_ty))
// The only legal patterns of type `Box` (outside `std`) are `_` and box
// patterns. If we're here we can assume this is a box pattern.
let subst_ty = substs.at(Interner, 0).assert_ty_ref(Interner).clone();
Fields::wildcards_from_tys(cx, once(subst_ty))
} else {
let variant_id = constructor.variant_id_for_adt(adt);
let adt_is_local =
variant_id.module(cx.db.upcast()).krate() == cx.module.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;
cov_mark::hit!(match_check_wildcard_expanded_to_substitutions);
let field_ty_data = cx.db.field_types(variant_id);
let field_tys = || {
field_ty_data
.iter()
.map(|(_, binders)| binders.clone().substitute(Interner, substs))
};
// 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, has_no_hidden_fields is always true
unimplemented!("exhaustive_patterns feature")
}
let variant = constructor.variant_id_for_adt(adt);
let tys = Fields::list_variant_nonhidden_fields(cx, ty, variant)
.map(|(_, ty)| ty);
Fields::wildcards_from_tys(cx, tys)
}
}
ty_kind => {
never!("Unexpected type for `Single` constructor: {:?}", ty_kind);
Fields::from_single_pattern(wildcard_from_ty(ty))
Fields::wildcards_from_tys(cx, once(ty.clone()))
}
},
Slice(..) => {
unimplemented!()
}
Str(..) | FloatRange(..) | IntRange(..) | NonExhaustive | Opaque | Missing
| Wildcard => Fields::Vec(Default::default()),
Str(..)
| FloatRange(..)
| IntRange(..)
| NonExhaustive
| Opaque
| Missing { .. }
| Wildcard => Fields::empty(),
Or => {
never!("called `Fields::wildcards` on an `Or` ctor");
Fields::empty()
}
};
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)| pcx.cx.pattern_arena.borrow()[p].clone());
// FIXME(iDawer) witnesses are not yet used
const UNHANDLED: PatKind = PatKind::Wild;
let pat = match ctor {
Single | Variant(_) => match pcx.ty.kind(Interner) {
TyKind::Adt(..) | TyKind::Tuple(..) => {
// We want the real indices here.
let subpatterns = subpatterns_and_indices
.iter()
.map(|&(field, pat)| FieldPat {
field,
pattern: pcx.cx.pattern_arena.borrow()[pat].clone(),
})
.collect();
if let Some((hir_def::AdtId::EnumId(_), substs)) = pcx.ty.as_adt() {
let enum_variant = match ctor {
&Variant(id) => id,
_ => unreachable!(),
};
PatKind::Variant { substs: substs.clone(), enum_variant, subpatterns }
} else {
PatKind::Leaf { subpatterns }
}
}
// Note: given the expansion of `&str` patterns done in `expand_pattern`, we should
// be careful to reconstruct the correct constant pattern here. However a string
// literal pattern will never be reported as a non-exhaustiveness witness, so we
// can ignore this issue.
TyKind::Ref(..) => PatKind::Deref { subpattern: subpatterns.next().unwrap() },
TyKind::Slice(..) | TyKind::Array(..) => {
never!("bad slice pattern {:?} {:?}", ctor, pcx.ty);
PatKind::Wild
}
_ => PatKind::Wild,
},
Constructor::Slice(_) => UNHANDLED,
Str(_) => UNHANDLED,
FloatRange(..) => UNHANDLED,
Constructor::IntRange(_) => UNHANDLED,
NonExhaustive => PatKind::Wild,
Wildcard => return Pat::wildcard_from_ty(pcx.ty.clone()),
Opaque => {
never!("we should not try to apply an opaque constructor");
PatKind::Wild
}
Missing => {
never!(
"trying to apply the `Missing` constructor; \
this should have been done in `apply_constructors`",
);
PatKind::Wild
}
};
Pat { ty: pcx.ty.clone(), kind: Box::new(pat) }
}
/// 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<[(LocalFieldId, PatId); 2]> {
match self {
Fields::Vec(pats) => pats
.iter()
.copied()
.enumerate()
.map(|(i, p)| (LocalFieldId::from_raw((i as u32).into()), p))
.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 = (LocalFieldId, PatId)>,
) -> Self {
self.replace_fields_indexed(
new_pats.into_iter().map(|(field, pat)| (u32::from(field.into_raw()) as usize, pat)),
)
}
/// 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 = pats.into_iter().map(|pat| cx.alloc_pat(pat)).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 {
// FIXME(iDawer): Factor out pattern deep cloning. See discussion:
// https://github.com/rust-analyzer/rust-analyzer/pull/8717#discussion_r633086640
let mut arena = cx.pattern_arena.borrow_mut();
match arena[pat].kind.as_ref() {
PatKind::Deref { subpattern } => {
assert_eq!(self.len(), 1);
let subpattern = subpattern.clone();
Fields::from_single_pattern(arena.alloc(subpattern))
}
PatKind::Leaf { subpatterns } | PatKind::Variant { subpatterns, .. } => {
let subpatterns = subpatterns.clone();
let subpatterns = subpatterns
.iter()
.map(|field_pat| (field_pat.field, arena.alloc(field_pat.pattern.clone())));
self.replace_with_fieldpats(subpatterns)
}
PatKind::Wild
| PatKind::Binding { .. }
| PatKind::LiteralBool { .. }
| PatKind::Or { .. } => self.clone(),
}
/// Returns the list of patterns.
pub(super) fn iter_patterns<'a>(
&'a self,
) -> impl Iterator<Item = &'p DeconstructedPat<'p>> + Captures<'a> {
self.fields.iter()
}
}
fn is_field_list_non_exhaustive(variant_id: VariantId, cx: &MatchCheckCtx<'_>) -> bool {
/// Values and patterns can be represented as a constructor applied to some fields. This represents
/// a pattern in this form.
/// This also keeps track of whether the pattern has been foundreachable during analysis. For this
/// reason we should be careful not to clone patterns for which we care about that. Use
/// `clone_and_forget_reachability` is you're sure.
pub(crate) struct DeconstructedPat<'p> {
ctor: Constructor,
fields: Fields<'p>,
ty: Ty,
reachable: Cell<bool>,
}
impl<'p> DeconstructedPat<'p> {
pub(super) fn wildcard(ty: Ty) -> Self {
Self::new(Wildcard, Fields::empty(), ty)
}
pub(super) fn new(ctor: Constructor, fields: Fields<'p>, ty: Ty) -> Self {
DeconstructedPat { ctor, fields, ty, reachable: Cell::new(false) }
}
/// Construct a pattern that matches everything that starts with this constructor.
/// For example, if `ctor` is a `Constructor::Variant` for `Option::Some`, we get the pattern
/// `Some(_)`.
pub(super) fn wild_from_ctor(pcx: PatCtxt<'_, 'p>, ctor: Constructor) -> Self {
let fields = Fields::wildcards(pcx.cx, pcx.ty, &ctor);
DeconstructedPat::new(ctor, fields, pcx.ty.clone())
}
/// Clone this value. This method emphasizes that cloning loses reachability information and
/// should be done carefully.
pub(super) fn clone_and_forget_reachability(&self) -> Self {
DeconstructedPat::new(self.ctor.clone(), self.fields, self.ty.clone())
}
pub(crate) fn from_pat(cx: &MatchCheckCtx<'_, 'p>, pat: &Pat) -> Self {
let mkpat = |pat| DeconstructedPat::from_pat(cx, pat);
let ctor;
let fields;
match pat.kind.as_ref() {
PatKind::Binding { subpattern: Some(subpat) } => return mkpat(subpat),
PatKind::Binding { subpattern: None } | PatKind::Wild => {
ctor = Wildcard;
fields = Fields::empty();
}
PatKind::Deref { subpattern } => {
ctor = Single;
fields = Fields::singleton(cx, mkpat(subpattern));
}
PatKind::Leaf { subpatterns } | PatKind::Variant { subpatterns, .. } => {
match pat.ty.kind(Interner) {
TyKind::Tuple(_, substs) => {
ctor = Single;
let mut wilds: SmallVec<[_; 2]> = substs
.iter(Interner)
.map(|arg| arg.assert_ty_ref(Interner).clone())
.map(DeconstructedPat::wildcard)
.collect();
for pat in subpatterns {
let idx: u32 = pat.field.into_raw().into();
wilds[idx as usize] = mkpat(&pat.pattern);
}
fields = Fields::from_iter(cx, wilds)
}
TyKind::Adt(adt, substs) if adt_is_box(adt.0, cx) => {
// The only legal patterns of type `Box` (outside `std`) are `_` and box
// patterns. If we're here we can assume this is a box pattern.
// FIXME(Nadrieril): A `Box` can in theory be matched either with `Box(_,
// _)` or a box pattern. As a hack to avoid an ICE with the former, we
// ignore other fields than the first one. This will trigger an error later
// anyway.
// See https://github.com/rust-lang/rust/issues/82772 ,
// explanation: https://github.com/rust-lang/rust/pull/82789#issuecomment-796921977
// The problem is that we can't know from the type whether we'll match
// normally or through box-patterns. We'll have to figure out a proper
// solution when we introduce generalized deref patterns. Also need to
// prevent mixing of those two options.
let pat =
subpatterns.iter().find(|pat| pat.field.into_raw() == 0u32.into());
let field = if let Some(pat) = pat {
mkpat(&pat.pattern)
} else {
let ty = substs.at(Interner, 0).assert_ty_ref(Interner).clone();
DeconstructedPat::wildcard(ty)
};
ctor = Single;
fields = Fields::singleton(cx, field)
}
&TyKind::Adt(adt, _) => {
ctor = match pat.kind.as_ref() {
PatKind::Leaf { .. } => Single,
PatKind::Variant { enum_variant, .. } => Variant(*enum_variant),
_ => {
never!();
Wildcard
}
};
let variant = ctor.variant_id_for_adt(adt.0);
let fields_len = variant.variant_data(cx.db.upcast()).fields().len();
// For each field in the variant, we store the relevant index into `self.fields` if any.
let mut field_id_to_id: Vec<Option<usize>> = vec![None; fields_len];
let tys = Fields::list_variant_nonhidden_fields(cx, &pat.ty, variant)
.enumerate()
.map(|(i, (fid, ty))| {
let field_idx: u32 = fid.into_raw().into();
field_id_to_id[field_idx as usize] = Some(i);
ty
});
let mut wilds: SmallVec<[_; 2]> =
tys.map(DeconstructedPat::wildcard).collect();
for pat in subpatterns {
let field_idx: u32 = pat.field.into_raw().into();
if let Some(i) = field_id_to_id[field_idx as usize] {
wilds[i] = mkpat(&pat.pattern);
}
}
fields = Fields::from_iter(cx, wilds);
}
_ => {
never!("pattern has unexpected type: pat: {:?}, ty: {:?}", pat, &pat.ty);
ctor = Wildcard;
fields = Fields::empty();
}
}
}
&PatKind::LiteralBool { value } => {
ctor = IntRange(IntRange::from_bool(value));
fields = Fields::empty();
}
PatKind::Or { .. } => {
ctor = Or;
let pats: SmallVec<[_; 2]> = expand_or_pat(pat).into_iter().map(mkpat).collect();
fields = Fields::from_iter(cx, pats)
}
}
DeconstructedPat::new(ctor, fields, pat.ty.clone())
}
// // FIXME(iDawer): implement reporting of noncovered patterns
// pub(crate) fn to_pat(&self, _cx: &MatchCheckCtx<'_, 'p>) -> Pat {
// Pat { ty: self.ty.clone(), kind: PatKind::Wild.into() }
// }
pub(super) fn is_or_pat(&self) -> bool {
matches!(self.ctor, Or)
}
pub(super) fn ctor(&self) -> &Constructor {
&self.ctor
}
pub(super) fn ty(&self) -> &Ty {
&self.ty
}
pub(super) fn iter_fields<'a>(&'a self) -> impl Iterator<Item = &'a DeconstructedPat<'a>> + 'a {
self.fields.iter_patterns()
}
/// Specialize this pattern with a constructor.
/// `other_ctor` can be different from `self.ctor`, but must be covered by it.
pub(super) fn specialize<'a>(
&'a self,
cx: &MatchCheckCtx<'_, 'p>,
other_ctor: &Constructor,
) -> SmallVec<[&'p DeconstructedPat<'p>; 2]> {
match (&self.ctor, other_ctor) {
(Wildcard, _) => {
// We return a wildcard for each field of `other_ctor`.
Fields::wildcards(cx, &self.ty, other_ctor).iter_patterns().collect()
}
(Slice(self_slice), Slice(other_slice))
if self_slice.arity() != other_slice.arity() =>
{
unimplemented!()
}
_ => self.fields.iter_patterns().collect(),
}
}
/// We keep track for each pattern if it was ever reachable during the analysis. This is used
/// with `unreachable_spans` to report unreachable subpatterns arising from or patterns.
pub(super) fn set_reachable(&self) {
self.reachable.set(true)
}
pub(super) fn is_reachable(&self) -> bool {
self.reachable.get()
}
}
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(),
@ -904,7 +1017,7 @@ fn is_field_list_non_exhaustive(variant_id: VariantId, cx: &MatchCheckCtx<'_>) -
cx.db.attrs(attr_def_id).by_key("non_exhaustive").exists()
}
fn adt_is_box(adt: hir_def::AdtId, cx: &MatchCheckCtx<'_>) -> bool {
fn adt_is_box(adt: hir_def::AdtId, cx: &MatchCheckCtx<'_, '_>) -> bool {
use hir_def::lang_item::LangItemTarget;
match cx.db.lang_item(cx.module.krate(), SmolStr::new_inline("owned_box")) {
Some(LangItemTarget::StructId(box_id)) => adt == box_id.into(),

713
crates/hir_ty/src/diagnostics/match_check/usefulness.rs
View file

@ -1,5 +1,5 @@
//! Based on rust-lang/rust 1.52.0-nightly (25c15cdbe 2021-04-22)
//! <https://github.com/rust-lang/rust/blob/25c15cdbe/compiler/rustc_mir_build/src/thir/pattern/usefulness.rs>
//! Based on rust-lang/rust (last sync 68b76a483 2021-10-01)
//! <https://github.com/rust-lang/rust/blob/68b76a483/compiler/rustc_mir_build/src/thir/pattern/usefulness.rs>
//!
//! -----
//!
@ -271,33 +271,26 @@
//! The details are not necessary to understand this file, so we explain them in
//! [`super::deconstruct_pat`]. Splitting is done by the [`Constructor::split`] function.
use std::{cell::RefCell, iter::FromIterator};
use std::iter::once;
use hir_def::{expr::ExprId, HasModule, ModuleId};
use la_arena::Arena;
use once_cell::unsync::OnceCell;
use rustc_hash::FxHashMap;
use hir_def::{AdtId, HasModule, ModuleId};
use smallvec::{smallvec, SmallVec};
use typed_arena::Arena;
use crate::{db::HirDatabase, InferenceResult, Interner, Ty};
use crate::{db::HirDatabase, Ty, TyExt};
use super::{
deconstruct_pat::{Constructor, Fields, SplitWildcard},
Pat, PatId, PatKind, PatternFoldable, PatternFolder,
};
use super::deconstruct_pat::{Constructor, DeconstructedPat, Fields, SplitWildcard};
use self::{helper::PatIdExt, Usefulness::*, WitnessPreference::*};
use self::{helper::Captures, ArmType::*, Usefulness::*};
pub(crate) struct MatchCheckCtx<'a> {
pub(crate) struct MatchCheckCtx<'a, 'p> {
pub(crate) module: ModuleId,
pub(crate) match_expr: ExprId,
pub(crate) infer: &'a InferenceResult,
pub(crate) db: &'a dyn HirDatabase,
/// Lowered patterns from arms plus generated by the check.
pub(crate) pattern_arena: &'a RefCell<PatternArena>,
pub(crate) pattern_arena: &'p Arena<DeconstructedPat<'p>>,
}
impl<'a> MatchCheckCtx<'a> {
impl<'a, 'p> MatchCheckCtx<'a, 'p> {
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
@ -305,105 +298,51 @@ impl<'a> MatchCheckCtx<'a> {
}
/// Returns whether the given type is an enum from another crate declared `#[non_exhaustive]`.
pub(super) fn is_foreign_non_exhaustive_enum(&self, enum_id: hir_def::EnumId) -> bool {
pub(super) fn is_foreign_non_exhaustive_enum(&self, ty: &Ty) -> bool {
match ty.as_adt() {
Some((adt @ AdtId::EnumId(_), _)) => {
let has_non_exhaustive_attr =
self.db.attrs(enum_id.into()).by_key("non_exhaustive").exists();
let is_local =
hir_def::AdtId::from(enum_id).module(self.db.upcast()).krate() == self.module.krate();
self.db.attrs(adt.into()).by_key("non_exhaustive").exists();
let is_local = adt.module(self.db.upcast()).krate() == self.module.krate();
has_non_exhaustive_attr && !is_local
}
_ => false,
}
}
// Rust feature described as "Allows exhaustive pattern matching on types that contain uninhabited types."
pub(super) fn feature_exhaustive_patterns(&self) -> bool {
// FIXME see MatchCheckCtx::is_uninhabited
false
}
pub(super) fn alloc_pat(&self, pat: Pat) -> PatId {
self.pattern_arena.borrow_mut().alloc(pat)
}
/// Get type of a pattern. Handles expanded patterns.
pub(super) fn type_of(&self, pat: PatId) -> Ty {
self.pattern_arena.borrow()[pat].ty.clone()
}
}
#[derive(Copy, Clone)]
pub(super) struct PatCtxt<'a> {
pub(super) cx: &'a MatchCheckCtx<'a>,
pub(super) struct PatCtxt<'a, 'p> {
pub(super) cx: &'a MatchCheckCtx<'a, 'p>,
/// Type of the current column under investigation.
pub(super) ty: &'a 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,
}
pub(crate) fn expand_pattern(pat: Pat) -> Pat {
LiteralExpander.fold_pattern(&pat)
}
struct LiteralExpander;
impl PatternFolder for LiteralExpander {
fn fold_pattern(&mut self, pat: &Pat) -> Pat {
match (pat.ty.kind(Interner), pat.kind.as_ref()) {
(_, PatKind::Binding { subpattern: Some(s), .. }) => s.fold_with(self),
_ => pat.super_fold_with(self),
}
}
}
impl Pat {
fn _is_wildcard(&self) -> bool {
matches!(*self.kind, PatKind::Binding { subpattern: None, .. } | PatKind::Wild)
}
}
impl PatIdExt for PatId {
fn is_or_pat(self, cx: &MatchCheckCtx<'_>) -> bool {
matches!(*cx.pattern_arena.borrow()[self].kind, PatKind::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: &mut PatternArena) {
if let PatKind::Or { pats } = pat_arena[pat].kind.as_ref() {
// FIXME(iDawer): Factor out pattern deep cloning. See discussion:
// https://github.com/rust-analyzer/rust-analyzer/pull/8717#discussion_r633086640
let pats = pats.clone();
for pat in pats {
let pat = pat_arena.alloc(pat.clone());
expand(pat, vec, pat_arena);
}
} else {
vec.push(pat)
}
}
let mut pat_arena = cx.pattern_arena.borrow_mut();
let mut pats = Vec::new();
expand(self, &mut pats, &mut pat_arena);
pats
}
/// Wether the current pattern is from a `non_exhaustive` enum.
pub(super) is_non_exhaustive: bool,
}
/// 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>,
pub(super) struct PatStack<'p> {
pats: SmallVec<[&'p DeconstructedPat<'p>; 2]>,
}
impl PatStack {
fn from_pattern(pat: PatId) -> Self {
impl<'p> PatStack<'p> {
fn from_pattern(pat: &'p DeconstructedPat<'p>) -> Self {
Self::from_vec(smallvec![pat])
}
fn from_vec(vec: SmallVec<[PatId; 2]>) -> Self {
PatStack { pats: vec, head_ctor: OnceCell::new() }
fn from_vec(vec: SmallVec<[&'p DeconstructedPat<'p>; 2]>) -> Self {
PatStack { pats: vec }
}
fn is_empty(&self) -> bool {
@ -414,73 +353,42 @@ impl PatStack {
self.pats.len()
}
fn head(&self) -> PatId {
fn head(&self) -> &'p DeconstructedPat<'p> {
self.pats[0]
}
#[inline]
fn head_ctor(&self, cx: &MatchCheckCtx<'_>) -> &Constructor {
self.head_ctor.get_or_init(|| Constructor::from_pat(cx, self.head()))
}
// 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| {
fn expand_or_pat(&self) -> impl Iterator<Item = PatStack<'p>> + Captures<'_> {
self.head().iter_fields().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.
/// 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 {
fn pop_head_constructor(&self, cx: &MatchCheckCtx<'_, 'p>, ctor: &Constructor) -> PatStack<'p> {
// 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();
let mut new_fields: SmallVec<[_; 2]> = self.head().specialize(cx, ctor);
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())
}
}
/// A 2D matrix.
#[derive(Clone)]
pub(super) struct Matrix {
patterns: Vec<PatStack>,
pub(super) struct Matrix<'p> {
patterns: Vec<PatStack<'p>>,
}
impl Matrix {
impl<'p> Matrix<'p> {
fn empty() -> Self {
Matrix { patterns: vec![] }
}
@ -492,9 +400,9 @@ impl Matrix {
/// 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) {
fn push(&mut self, row: PatStack<'p>) {
if !row.is_empty() && row.head().is_or_pat() {
for row in row.expand_or_pat() {
self.patterns.push(row);
}
} else {
@ -503,317 +411,56 @@ impl Matrix {
}
/// Iterate over the first component of each row
fn heads(&self) -> impl Iterator<Item = PatId> + '_ {
fn heads(&self) -> impl Iterator<Item = &'p DeconstructedPat<'p>> + Clone + Captures<'_> {
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 {
fn specialize_constructor(&self, pcx: PatCtxt<'_, 'p>, ctor: &Constructor) -> Matrix<'p> {
let mut matrix = Matrix::empty();
for x in rows {
// Using `push` ensures we correctly expand or-patterns.
matrix.push(x, cx);
for row in &self.patterns {
if ctor.is_covered_by(pcx, row.head().ctor()) {
let new_row = row.pop_head_constructor(pcx.cx, ctor);
matrix.push(new_row);
}
}
matrix
}
}
/// Given a pattern or a pattern-stack, this struct captures a set of its subpatterns. We use that
/// to track reachable sub-patterns arising from 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). When there are or-patterns, some subpatterns may be reachable while others
/// aren't. In this case the whole pattern still counts as reachable, but we will lint the
/// unreachable subpatterns.
///
/// This supports a limited set of operations, so not all possible sets of subpatterns can be
/// represented. That's ok, we only want the ones that make sense for our usage.
///
/// What we're doing is illustrated by this:
/// ```
/// match (true, 0) {
/// (true, 0) => {}
/// (_, 1) => {}
/// (true | false, 0 | 1) => {}
/// }
/// ```
/// When we try the alternatives of the `true | false` or-pattern, the last `0` is reachable in the
/// `false` alternative but not the `true`. So overall it is reachable. By contrast, the last `1`
/// is not reachable in either alternative, so we want to signal this to the user.
/// Therefore we take the union of sets of reachable patterns coming from different alternatives in
/// order to figure out which subpatterns are overall reachable.
///
/// Invariant: we try to construct the smallest representation we can. In particular if
/// `self.is_empty()` we ensure that `self` is `Empty`, and same with `Full`. This is not important
/// for correctness currently.
#[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 { subpats: s_set }, Seq { subpats: mut o_set }) => {
s_set.retain(|i, s_sub_set| {
// Missing entries count as full.
let o_sub_set = o_set.remove(i).unwrap_or(Full);
s_sub_set.union(o_sub_set);
// We drop full entries.
!s_sub_set.is_full()
});
// Everything left in `o_set` is missing from `s_set`, i.e. counts as full. Since
// unioning with full returns full, we can drop those entries.
}
(Alt { subpats: s_set, .. }, Alt { subpats: mut o_set, .. }) => {
s_set.retain(|i, s_sub_set| {
// Missing entries count as empty.
let o_sub_set = o_set.remove(i).unwrap_or(Empty);
s_sub_set.union(o_sub_set);
// We drop empty entries.
!s_sub_set.is_empty()
});
// Everything left in `o_set` is missing from `s_set`, i.e. counts as empty. Since
// unioning with empty changes nothing, we can take those entries as is.
s_set.extend(o_set);
}
_ => panic!("bug"),
}
if self.is_full() {
*self = Full;
}
}
/// Returns a list of the unreachable subpatterns. If `self` is empty (i.e. the
/// whole pattern is unreachable) we return `None`.
fn list_unreachable_subpatterns(&self, cx: &MatchCheckCtx<'_>) -> Option<Vec<PatId>> {
/// Panics if `set.is_empty()`.
fn fill_subpats(
set: &SubPatSet,
unreachable_pats: &mut Vec<PatId>,
cx: &MatchCheckCtx<'_>,
) {
match set {
SubPatSet::Empty => panic!("bug"),
SubPatSet::Full => {}
SubPatSet::Seq { subpats } => {
for sub_set in subpats.values() {
fill_subpats(sub_set, unreachable_pats, cx);
}
}
SubPatSet::Alt { subpats, pat, alt_count, .. } => {
let expanded = pat.expand_or_pat(cx);
for (i, &expanded) in expanded.iter().enumerate().take(*alt_count) {
let sub_set = subpats.get(&i).unwrap_or(&SubPatSet::Empty);
if sub_set.is_empty() {
// Found an unreachable subpattern.
unreachable_pats.push(expanded);
} else {
fill_subpats(sub_set, unreachable_pats, cx);
}
}
}
}
}
if self.is_empty() {
return None;
}
if self.is_full() {
// No subpatterns are unreachable.
return Some(Vec::new());
}
let mut unreachable_pats = Vec::new();
fill_subpats(self, &mut unreachable_pats, cx);
Some(unreachable_pats)
}
/// 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 } => {
// We gather the first `arity` subpatterns together and shift the remaining ones.
let mut new_subpats = FxHashMap::default();
let mut new_subpats_first_col = FxHashMap::default();
for (i, sub_set) in subpats {
if i < arity {
// The first `arity` indices are now part of the pattern in the first
// column.
new_subpats_first_col.insert(i, sub_set);
} else {
// Indices after `arity` are simply shifted
new_subpats.insert(i - arity + 1, sub_set);
}
}
// If `new_subpats_first_col` has no entries it counts as full, so we can omit it.
if !new_subpats_first_col.is_empty() {
new_subpats.insert(0, Seq { subpats: new_subpats_first_col });
}
Seq { subpats: new_subpats }
}
Alt { .. } => panic!("bug"), // `self` is a patstack
}
}
/// 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 {
use SubPatSet::*;
if self.is_empty() {
return Empty;
}
// Subpatterns coming from inside the or-pattern alternative itself, e.g. in `None | Some(0
// | 1)`.
let set_first_col = match &mut self {
Full => Full,
Seq { subpats } => subpats.remove(&0).unwrap_or(Full),
Empty => unreachable!(),
Alt { .. } => panic!("bug"), // `self` is a patstack
};
let mut subpats_first_col = FxHashMap::default();
subpats_first_col.insert(alt_id, set_first_col);
let set_first_col = Alt { subpats: subpats_first_col, pat, alt_count };
let mut subpats = match self {
Full => FxHashMap::default(),
Seq { subpats } => subpats,
Empty => unreachable!(),
Alt { .. } => panic!("bug"), // `self` is a patstack
};
subpats.insert(0, set_first_col);
Seq { subpats }
}
}
/// 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),
/// Which variant to use is dictated by `ArmType`.
enum Usefulness<'p> {
/// If we don't care about witnesses, simply remember if the pattern was useful.
NoWitnesses { useful: bool },
/// Carries a list of witnesses of non-exhaustiveness. If empty, indicates that the whole
/// pattern is unreachable.
WithWitnesses(Vec<Witness>),
WithWitnesses(Vec<Witness<'p>>),
}
impl Usefulness {
fn new_useful(preference: WitnessPreference) -> Self {
impl<'p> Usefulness<'p> {
fn new_useful(preference: ArmType) -> Self {
match preference {
ConstructWitness => WithWitnesses(vec![Witness(vec![])]),
LeaveOutWitness => NoWitnesses(SubPatSet::full()),
// A single (empty) witness of reachability.
FakeExtraWildcard => WithWitnesses(vec![Witness(vec![])]),
RealArm => NoWitnesses { useful: true },
}
}
fn new_not_useful(preference: WitnessPreference) -> Self {
fn new_not_useful(preference: ArmType) -> Self {
match preference {
ConstructWitness => WithWitnesses(vec![]),
LeaveOutWitness => NoWitnesses(SubPatSet::empty()),
FakeExtraWildcard => WithWitnesses(vec![]),
RealArm => NoWitnesses { useful: false },
}
}
fn is_useful(&self) -> bool {
match self {
Usefulness::NoWitnesses { useful } => *useful,
Usefulness::WithWitnesses(witnesses) => !witnesses.is_empty(),
}
}
@ -823,89 +470,78 @@ impl Usefulness {
(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),
(NoWitnesses { useful: s_useful }, NoWitnesses { useful: o_useful }) => {
*s_useful = *s_useful || o_useful
}
_ => 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
/// After calculating usefulness after a specialization, call this to reconstruct 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,
pcx: PatCtxt<'_, 'p>,
matrix: &Matrix<'p>,
ctor: &Constructor,
ctor_wild_subpatterns: &Fields,
) -> Self {
match self {
WithWitnesses(witnesses) if witnesses.is_empty() => WithWitnesses(witnesses),
NoWitnesses { .. } => self,
WithWitnesses(ref witnesses) if witnesses.is_empty() => self,
WithWitnesses(witnesses) => {
let new_witnesses = if matches!(ctor, Constructor::Missing) {
let new_witnesses = if let Constructor::Missing { .. } = ctor {
// We got the special `Missing` constructor, so each of the missing constructors
// gives a new pattern that is not caught by the match. We list those patterns.
let new_patterns = if pcx.is_non_exhaustive {
// Here we don't want the user to try to list all variants, we want them to add
// a wildcard, so we only suggest that.
vec![DeconstructedPat::wildcard(pcx.ty.clone())]
} else {
let mut split_wildcard = SplitWildcard::new(pcx);
split_wildcard.split(pcx, matrix.head_ctors(pcx.cx));
split_wildcard.split(pcx, matrix.heads().map(DeconstructedPat::ctor));
// 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(_)`.
let new_patterns: Vec<_> = split_wildcard
split_wildcard
.iter_missing(pcx)
.map(|missing_ctor| {
Fields::wildcards(pcx, missing_ctor).apply(pcx, missing_ctor)
})
.collect();
.cloned()
.map(|missing_ctor| DeconstructedPat::wild_from_ctor(pcx, missing_ctor))
.collect()
};
witnesses
.into_iter()
.flat_map(|witness| {
new_patterns.iter().map(move |pat| {
let mut witness = witness.clone();
witness.0.push(pat.clone());
Witness(
witness
.0
.iter()
.chain(once(pat))
.map(DeconstructedPat::clone_and_forget_reachability)
.collect(),
)
})
})
.collect()
} else {
witnesses
.into_iter()
.map(|witness| witness.apply_constructor(pcx, ctor, ctor_wild_subpatterns))
.map(|witness| witness.apply_constructor(pcx, ctor))
.collect()
};
WithWitnesses(new_witnesses)
}
NoWitnesses(subpats) => NoWitnesses(subpats.unspecialize(ctor_wild_subpatterns.len())),
}
}
}
#[derive(Copy, Clone, Debug)]
enum WitnessPreference {
ConstructWitness,
LeaveOutWitness,
enum ArmType {
FakeExtraWildcard,
RealArm,
}
/// A witness of non-exhaustiveness for error reporting, represented
@ -941,12 +577,11 @@ enum WitnessPreference {
/// `Witness(vec![Pair(Some(_), true)])`
///
/// The final `Pair(Some(_), true)` is then the resulting witness.
#[derive(Clone, Debug)]
pub(crate) struct Witness(Vec<Pat>);
pub(crate) struct Witness<'p>(Vec<DeconstructedPat<'p>>);
impl Witness {
impl<'p> Witness<'p> {
/// Asserts that the witness contains a single pattern, and returns it.
fn single_pattern(self) -> Pat {
fn single_pattern(self) -> DeconstructedPat<'p> {
assert_eq!(self.0.len(), 1);
self.0.into_iter().next().unwrap()
}
@ -964,17 +599,13 @@ impl Witness {
///
/// 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 {
fn apply_constructor(mut self, pcx: PatCtxt<'_, 'p>, ctor: &Constructor) -> Self {
let pat = {
let len = self.0.len();
let arity = ctor_wild_subpatterns.len();
let arity = ctor.arity(pcx);
let pats = self.0.drain((len - arity)..).rev();
ctor_wild_subpatterns.replace_fields(pcx.cx, pats).apply(pcx, ctor)
let fields = Fields::from_iter(pcx.cx, pats);
DeconstructedPat::new(ctor.clone(), fields, pcx.ty.clone())
};
self.0.push(pat);
@ -1005,14 +636,14 @@ impl Witness {
/// `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,
fn is_useful<'p>(
cx: &MatchCheckCtx<'_, 'p>,
matrix: &Matrix<'p>,
v: &PatStack<'p>,
witness_preference: ArmType,
is_under_guard: bool,
is_top_level: bool,
) -> Usefulness {
) -> Usefulness<'p> {
let Matrix { patterns: rows, .. } = matrix;
// The base case. We are pattern-matching on () and the return value is
@ -1031,67 +662,60 @@ fn is_useful(
assert!(rows.iter().all(|r| r.len() == v.len()));
// FIXME(Nadrieril): Hack to work around type normalization issues (see rust-lang/rust#72476).
let ty = matrix.heads().next().map_or(cx.type_of(v.head()), |r| cx.type_of(r));
let pcx = PatCtxt { cx, ty: &ty, is_top_level };
let ty = v.head().ty();
let is_non_exhaustive = cx.is_foreign_non_exhaustive_enum(ty);
let pcx = PatCtxt { cx, ty, is_top_level, is_non_exhaustive };
// 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();
let mut ret = Usefulness::new_not_useful(witness_preference);
if v.head().is_or_pat() {
// We try each or-pattern branch in turn.
let mut matrix = matrix.clone();
let usefulnesses = vs.into_iter().enumerate().map(|(i, v)| {
for v in v.expand_or_pat() {
let usefulness = is_useful(cx, &matrix, &v, witness_preference, is_under_guard, false);
ret.extend(usefulness);
// 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);
matrix.push(v);
}
}
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,
// )
// }
let v_ctor = v.head().ctor();
// FIXME: implement `overlapping_range_endpoints` lint
// We split the head constructor of `v`.
let split_ctors = v_ctor.split(pcx, matrix.head_ctors(cx));
let split_ctors = v_ctor.split(pcx, matrix.heads().map(DeconstructedPat::ctor));
// 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);
for ctor in split_ctors {
// 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 spec_matrix = start_matrix.specialize_constructor(pcx, &ctor);
let v = v.pop_head_constructor(cx, &ctor);
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)
let usefulness = usefulness.apply_constructor(pcx, start_matrix, &ctor);
// FIXME: implement `non_exhaustive_omitted_patterns` lint
ret.extend(usefulness);
}
};
if ret.is_useful() {
v.head().set_reachable();
}
ret
}
/// The arm of a match expression.
#[derive(Clone, Copy)]
pub(crate) struct MatchArm {
pub(crate) pat: PatId,
pub(crate) struct MatchArm<'p> {
pub(crate) pat: &'p DeconstructedPat<'p>,
pub(crate) has_guard: bool,
}
@ -1101,18 +725,19 @@ 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<PatId>),
// FIXME: store ureachable subpattern IDs
Reachable,
/// The arm is unreachable.
Unreachable,
}
/// The output of checking a match for exhaustiveness and arm reachability.
pub(crate) struct UsefulnessReport {
pub(crate) struct UsefulnessReport<'p> {
/// For each arm of the input, whether that arm is reachable after the arms above it.
pub(crate) _arm_usefulness: Vec<(MatchArm, Reachability)>,
pub(crate) _arm_usefulness: Vec<(MatchArm<'p>, 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) non_exhaustiveness_witnesses: Vec<DeconstructedPat<'p>>,
}
/// The entrypoint for the usefulness algorithm. Computes whether a match is exhaustive and which
@ -1120,53 +745,41 @@ pub(crate) struct UsefulnessReport {
///
/// Note: the input patterns must have been lowered through
/// `check_match::MatchVisitor::lower_pattern`.
pub(crate) fn compute_match_usefulness(
cx: &MatchCheckCtx<'_>,
arms: &[MatchArm],
) -> UsefulnessReport {
pub(crate) fn compute_match_usefulness<'p>(
cx: &MatchCheckCtx<'_, 'p>,
arms: &[MatchArm<'p>],
scrut_ty: &Ty,
) -> UsefulnessReport<'p> {
let mut matrix = Matrix::empty();
let arm_usefulness = arms
.iter()
.copied()
.map(|arm| {
let v = PatStack::from_pattern(arm.pat);
let usefulness = is_useful(cx, &matrix, &v, LeaveOutWitness, arm.has_guard, true);
is_useful(cx, &matrix, &v, RealArm, arm.has_guard, true);
if !arm.has_guard {
matrix.push(v, cx);
matrix.push(v);
}
let reachability = match usefulness {
NoWitnesses(subpats) if subpats.is_empty() => Reachability::Unreachable,
NoWitnesses(subpats) => {
Reachability::Reachable(subpats.list_unreachable_subpatterns(cx).unwrap())
}
WithWitnesses(..) => panic!("bug"),
let reachability = if arm.pat.is_reachable() {
Reachability::Reachable
} else {
Reachability::Unreachable
};
(arm, reachability)
})
.collect();
let wild_pattern =
cx.pattern_arena.borrow_mut().alloc(Pat::wildcard_from_ty(cx.infer[cx.match_expr].clone()));
let wild_pattern = cx.pattern_arena.alloc(DeconstructedPat::wildcard(scrut_ty.clone()));
let v = PatStack::from_pattern(wild_pattern);
let usefulness = is_useful(cx, &matrix, &v, ConstructWitness, false, true);
let usefulness = is_useful(cx, &matrix, &v, FakeExtraWildcard, false, true);
let non_exhaustiveness_witnesses = match usefulness {
WithWitnesses(pats) => pats.into_iter().map(Witness::single_pattern).collect(),
NoWitnesses(_) => panic!("bug"),
NoWitnesses { .. } => panic!("bug"),
};
UsefulnessReport { _arm_usefulness: arm_usefulness, non_exhaustiveness_witnesses }
}
pub(crate) type PatternArena = Arena<Pat>;
mod helper {
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>;
}
pub(crate) mod helper {
// 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.

1
crates/ide_diagnostics/src/handlers/missing_match_arms.rs
View file

@ -821,7 +821,6 @@ fn main() {
#[test]
fn pattern_type_is_of_substitution() {
cov_mark::check!(match_check_wildcard_expanded_to_substitutions);
check_diagnostics_no_bails(
r#"
struct Foo<T>(T);