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Replace local copy of exhaustiveness checking with upstream librarified version

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This commit is contained in:
Nadrieril 2024-01-17 00:28:05 +01:00
parent d410d4a2ba
commit 2370b70f25
11 changed files with 603 additions and 1952 deletions
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100
Cargo.lock generated
View file

@ -166,7 +166,7 @@ checksum = "5676cea088c32290fe65c82895be9d06dd21e0fa49bb97ca840529e9417ab71a"
dependencies = [
"proc-macro2",
"quote",
"syn",
"syn 2.0.39",
"synstructure",
]
@ -312,6 +312,17 @@ dependencies = [
"parking_lot_core",
]
[[package]]
name = "derivative"
version = "2.2.0"
source = "registry+https://github.com/rust-lang/crates.io-index"
checksum = "fcc3dd5e9e9c0b295d6e1e4d811fb6f157d5ffd784b8d202fc62eac8035a770b"
dependencies = [
"proc-macro2",
"quote",
"syn 1.0.109",
]
[[package]]
name = "derive_arbitrary"
version = "1.3.2"
@ -320,7 +331,7 @@ checksum = "67e77553c4162a157adbf834ebae5b415acbecbeafc7a74b0e886657506a7611"
dependencies = [
"proc-macro2",
"quote",
"syn",
"syn 2.0.39",
]
[[package]]
@ -581,7 +592,8 @@ dependencies = [
"profile",
"project-model",
"ra-ap-rustc_abi",
"ra-ap-rustc_index",
"ra-ap-rustc_index 0.21.0",
"ra-ap-rustc_pattern_analysis",
"rustc-hash",
"scoped-tls",
"smallvec",
@ -1412,7 +1424,7 @@ source = "registry+https://github.com/rust-lang/crates.io-index"
checksum = "7816f980fab89e878ff2e916e2077d484e3aa1c619a3cc982c8a417c3dfe45fa"
dependencies = [
"bitflags 1.3.2",
"ra-ap-rustc_index",
"ra-ap-rustc_index 0.21.0",
"tracing",
]
@ -1423,7 +1435,18 @@ source = "registry+https://github.com/rust-lang/crates.io-index"
checksum = "8352918d61aa4afab9f2ed7314cf638976b20949b3d61d2f468c975b0d251f24"
dependencies = [
"arrayvec",
"ra-ap-rustc_index_macros",
"ra-ap-rustc_index_macros 0.21.0",
"smallvec",
]
[[package]]
name = "ra-ap-rustc_index"
version = "0.33.0"
source = "registry+https://github.com/rust-lang/crates.io-index"
checksum = "5e5313d7f243b63ef9e58d94355b11aa8499f1328055f1f58adf0a5ea7d2faca"
dependencies = [
"arrayvec",
"ra-ap-rustc_index_macros 0.33.0",
"smallvec",
]
@ -1435,7 +1458,19 @@ checksum = "66a9424018828155a3e3596515598f90e68427d8f35eff6df7f0856c73fc58a8"
dependencies = [
"proc-macro2",
"quote",
"syn",
"syn 2.0.39",
"synstructure",
]
[[package]]
name = "ra-ap-rustc_index_macros"
version = "0.33.0"
source = "registry+https://github.com/rust-lang/crates.io-index"
checksum = "a83108ebf3e73dde205b9c25706209bcd7736480820f90ded28eabaf8b469f25"
dependencies = [
"proc-macro2",
"quote",
"syn 2.0.39",
"synstructure",
]
@ -1455,10 +1490,24 @@ version = "0.21.0"
source = "registry+https://github.com/rust-lang/crates.io-index"
checksum = "d557201d71792487bd2bab637ab5be9aa6fff59b88e25e12de180b0f9d2df60f"
dependencies = [
"ra-ap-rustc_index",
"ra-ap-rustc_index 0.21.0",
"ra-ap-rustc_lexer",
]
[[package]]
name = "ra-ap-rustc_pattern_analysis"
version = "0.33.0"
source = "registry+https://github.com/rust-lang/crates.io-index"
checksum = "6c4085e0c771fd4b883930b599ef42966b855762bbe4052c17673b3253421a6d"
dependencies = [
"derivative",
"ra-ap-rustc_index 0.33.0",
"rustc-hash",
"rustc_apfloat",
"smallvec",
"tracing",
]
[[package]]
name = "rayon"
version = "1.8.0"
@ -1593,7 +1642,7 @@ dependencies = [
"heck",
"proc-macro2",
"quote",
"syn",
"syn 2.0.39",
]
[[package]]
@ -1608,6 +1657,16 @@ version = "1.1.0"
source = "registry+https://github.com/rust-lang/crates.io-index"
checksum = "08d43f7aa6b08d49f382cde6a7982047c3426db949b1424bc4b7ec9ae12c6ce2"
[[package]]
name = "rustc_apfloat"
version = "0.2.0+llvm-462a31f5a5ab"
source = "registry+https://github.com/rust-lang/crates.io-index"
checksum = "465187772033a5ee566f69fe008df03628fce549a0899aae76f0a0c2e34696be"
dependencies = [
"bitflags 1.3.2",
"smallvec",
]
[[package]]
name = "ryu"
version = "1.0.13"
@ -1670,7 +1729,7 @@ checksum = "43576ca501357b9b071ac53cdc7da8ef0cbd9493d8df094cd821777ea6e894d3"
dependencies = [
"proc-macro2",
"quote",
"syn",
"syn 2.0.39",
]
[[package]]
@ -1693,7 +1752,7 @@ checksum = "bcec881020c684085e55a25f7fd888954d56609ef363479dc5a1305eb0d40cab"
dependencies = [
"proc-macro2",
"quote",
"syn",
"syn 2.0.39",
]
[[package]]
@ -1707,9 +1766,9 @@ dependencies = [
[[package]]
name = "smallvec"
version = "1.10.0"
version = "1.12.0"
source = "registry+https://github.com/rust-lang/crates.io-index"
checksum = "a507befe795404456341dfab10cef66ead4c041f62b8b11bbb92bffe5d0953e0"
checksum = "2593d31f82ead8df961d8bd23a64c2ccf2eb5dd34b0a34bfb4dd54011c72009e"
[[package]]
name = "smol_str"
@ -1770,6 +1829,17 @@ dependencies = [
"winapi",
]
[[package]]
name = "syn"
version = "1.0.109"
source = "registry+https://github.com/rust-lang/crates.io-index"
checksum = "72b64191b275b66ffe2469e8af2c1cfe3bafa67b529ead792a6d0160888b4237"
dependencies = [
"proc-macro2",
"quote",
"unicode-ident",
]
[[package]]
name = "syn"
version = "2.0.39"
@ -1789,7 +1859,7 @@ checksum = "285ba80e733fac80aa4270fbcdf83772a79b80aa35c97075320abfee4a915b06"
dependencies = [
"proc-macro2",
"quote",
"syn",
"syn 2.0.39",
"unicode-xid",
]
@ -1876,7 +1946,7 @@ checksum = "f9456a42c5b0d803c8cd86e73dd7cc9edd429499f37a3550d286d5e86720569f"
dependencies = [
"proc-macro2",
"quote",
"syn",
"syn 2.0.39",
]
[[package]]
@ -1977,7 +2047,7 @@ checksum = "34704c8d6ebcbc939824180af020566b01a7c01f80641264eba0999f6c2b6be7"
dependencies = [
"proc-macro2",
"quote",
"syn",
"syn 2.0.39",
]
[[package]]

1
Cargo.toml
View file

@ -83,6 +83,7 @@ ra-ap-rustc_lexer = { version = "0.21.0", default-features = false }
ra-ap-rustc_parse_format = { version = "0.21.0", default-features = false }
ra-ap-rustc_index = { version = "0.21.0", default-features = false }
ra-ap-rustc_abi = { version = "0.21.0", default-features = false }
ra-ap-rustc_pattern_analysis = { version = "0.33.0", default-features = false }
# local crates that aren't published to crates.io. These should not have versions.
sourcegen = { path = "./crates/sourcegen" }

9
crates/hir-def/src/lib.rs
View file

@ -939,6 +939,15 @@ impl From<AssocItemId> for AttrDefId {
}
}
}
impl From<VariantId> for AttrDefId {
fn from(vid: VariantId) -> Self {
match vid {
VariantId::EnumVariantId(id) => id.into(),
VariantId::StructId(id) => id.into(),
VariantId::UnionId(id) => id.into(),
}
}
}
#[derive(Debug, Clone, Copy, PartialEq, Eq, Hash)]
pub enum VariantId {

1
crates/hir-ty/Cargo.toml
View file

@ -36,6 +36,7 @@ indexmap.workspace = true
ra-ap-rustc_abi.workspace = true
ra-ap-rustc_index.workspace = true
ra-ap-rustc_pattern_analysis.workspace = true
# local deps

38
crates/hir-ty/src/diagnostics/expr.rs
View file

@ -11,6 +11,7 @@ use hir_def::{ItemContainerId, Lookup};
use hir_expand::name;
use itertools::Itertools;
use rustc_hash::FxHashSet;
use rustc_pattern_analysis::usefulness::{compute_match_usefulness, ValidityConstraint};
use triomphe::Arc;
use typed_arena::Arena;
@ -18,8 +19,7 @@ use crate::{
db::HirDatabase,
diagnostics::match_check::{
self,
deconstruct_pat::DeconstructedPat,
usefulness::{compute_match_usefulness, MatchCheckCtx},
pat_analysis::{self, DeconstructedPat, MatchCheckCtx, WitnessPat},
},
display::HirDisplay,
InferenceResult, Ty, TyExt,
@ -152,7 +152,14 @@ impl ExprValidator {
}
let pattern_arena = Arena::new();
let cx = MatchCheckCtx::new(self.owner.module(db.upcast()), self.owner, db, &pattern_arena);
let ty_arena = Arena::new();
let cx = MatchCheckCtx::new(
self.owner.module(db.upcast()),
self.owner,
db,
&pattern_arena,
&ty_arena,
);
let mut m_arms = Vec::with_capacity(arms.len());
let mut has_lowering_errors = false;
@ -178,9 +185,10 @@ impl ExprValidator {
// If we had a NotUsefulMatchArm diagnostic, we could
// check the usefulness of each pattern as we added it
// to the matrix here.
let m_arm = match_check::MatchArm {
let m_arm = pat_analysis::MatchArm {
pat: self.lower_pattern(&cx, arm.pat, db, &body, &mut has_lowering_errors),
has_guard: arm.guard.is_some(),
arm_data: (),
};
m_arms.push(m_arm);
if !has_lowering_errors {
@ -197,7 +205,15 @@ impl ExprValidator {
return;
}
let report = compute_match_usefulness(&cx, &m_arms, scrut_ty);
let report = match compute_match_usefulness(
rustc_pattern_analysis::MatchCtxt { tycx: &cx },
m_arms.as_slice(),
scrut_ty.clone(),
ValidityConstraint::ValidOnly,
) {
Ok(report) => report,
Err(void) => match void {},
};
// FIXME Report unreachable arms
// https://github.com/rust-lang/rust/blob/f31622a50/compiler/rustc_mir_build/src/thir/pattern/check_match.rs#L200
@ -213,7 +229,7 @@ impl ExprValidator {
fn lower_pattern<'p>(
&self,
cx: &MatchCheckCtx<'_, 'p>,
cx: &MatchCheckCtx<'p>,
pat: PatId,
db: &dyn HirDatabase,
body: &Body,
@ -221,7 +237,7 @@ impl ExprValidator {
) -> &'p DeconstructedPat<'p> {
let mut patcx = match_check::PatCtxt::new(db, &self.infer, body);
let pattern = patcx.lower_pattern(pat);
let pattern = cx.pattern_arena.alloc(DeconstructedPat::from_pat(cx, &pattern));
let pattern = cx.pattern_arena.alloc(cx.lower_pat(&pattern));
if !patcx.errors.is_empty() {
*have_errors = true;
}
@ -364,16 +380,16 @@ fn types_of_subpatterns_do_match(pat: PatId, body: &Body, infer: &InferenceResul
}
fn missing_match_arms<'p>(
cx: &MatchCheckCtx<'_, 'p>,
cx: &MatchCheckCtx<'p>,
scrut_ty: &Ty,
witnesses: Vec<DeconstructedPat<'p>>,
witnesses: Vec<WitnessPat<'p>>,
arms: &[MatchArm],
) -> String {
struct DisplayWitness<'a, 'p>(&'a DeconstructedPat<'p>, &'a MatchCheckCtx<'a, 'p>);
struct DisplayWitness<'a, 'p>(&'a WitnessPat<'p>, &'a MatchCheckCtx<'p>);
impl fmt::Display for DisplayWitness<'_, '_> {
fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
let DisplayWitness(witness, cx) = *self;
let pat = witness.to_pat(cx);
let pat = cx.hoist_witness_pat(witness);
write!(f, "{}", pat.display(cx.db))
}
}

5
crates/hir-ty/src/diagnostics/match_check.rs
View file

@ -7,8 +7,7 @@
mod pat_util;
pub(crate) mod deconstruct_pat;
pub(crate) mod usefulness;
pub(crate) mod pat_analysis;
use chalk_ir::Mutability;
use hir_def::{
@ -27,8 +26,6 @@ use crate::{
use self::pat_util::EnumerateAndAdjustIterator;
pub(crate) use self::usefulness::MatchArm;
#[derive(Clone, Debug)]
pub(crate) enum PatternError {
Unimplemented,

1098
crates/hir-ty/src/diagnostics/match_check/deconstruct_pat.rs
View file

File diff suppressed because it is too large Load diff

475
crates/hir-ty/src/diagnostics/match_check/pat_analysis.rs Normal file
View file

@ -0,0 +1,475 @@
//! Interface with `rustc_pattern_analysis`.
use std::fmt;
use hir_def::{DefWithBodyId, EnumVariantId, HasModule, LocalFieldId, ModuleId, VariantId};
use rustc_hash::FxHashMap;
use rustc_pattern_analysis::{
constructor::{Constructor, ConstructorSet, VariantVisibility},
index::IdxContainer,
Captures, TypeCx,
};
use smallvec::SmallVec;
use stdx::never;
use typed_arena::Arena;
use crate::{
db::HirDatabase,
infer::normalize,
inhabitedness::{is_enum_variant_uninhabited_from, is_ty_uninhabited_from},
AdtId, Interner, Scalar, Ty, TyExt, TyKind,
};
use super::{is_box, FieldPat, Pat, PatKind};
use Constructor::*;
// Re-export r-a-specific versions of all these types.
pub(crate) type DeconstructedPat<'p> =
rustc_pattern_analysis::pat::DeconstructedPat<'p, MatchCheckCtx<'p>>;
pub(crate) type MatchArm<'p> = rustc_pattern_analysis::MatchArm<'p, MatchCheckCtx<'p>>;
pub(crate) type WitnessPat<'p> = rustc_pattern_analysis::pat::WitnessPat<MatchCheckCtx<'p>>;
/// [Constructor] uses this in unimplemented variants.
/// It allows porting match expressions from upstream algorithm without losing semantics.
#[derive(Copy, Clone, Debug, PartialEq, Eq)]
pub(crate) enum Void {}
#[derive(Clone)]
pub(crate) struct MatchCheckCtx<'p> {
module: ModuleId,
body: DefWithBodyId,
pub(crate) db: &'p dyn HirDatabase,
pub(crate) pattern_arena: &'p Arena<DeconstructedPat<'p>>,
ty_arena: &'p Arena<Ty>,
exhaustive_patterns: bool,
}
impl<'p> MatchCheckCtx<'p> {
pub(crate) fn new(
module: ModuleId,
body: DefWithBodyId,
db: &'p dyn HirDatabase,
pattern_arena: &'p Arena<DeconstructedPat<'p>>,
ty_arena: &'p Arena<Ty>,
) -> Self {
let def_map = db.crate_def_map(module.krate());
let exhaustive_patterns = def_map.is_unstable_feature_enabled("exhaustive_patterns");
Self { module, body, db, pattern_arena, exhaustive_patterns, ty_arena }
}
fn is_uninhabited(&self, ty: &Ty) -> bool {
is_ty_uninhabited_from(ty, self.module, self.db)
}
/// Returns whether the given type is an enum from another crate declared `#[non_exhaustive]`.
fn is_foreign_non_exhaustive_enum(&self, ty: &Ty) -> bool {
match ty.as_adt() {
Some((adt @ hir_def::AdtId::EnumId(_), _)) => {
let has_non_exhaustive_attr =
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,
}
}
fn variant_id_for_adt(&self, ctor: &Constructor<Self>, adt: hir_def::AdtId) -> VariantId {
match ctor {
&Variant(id) => id.into(),
Struct | UnionField => {
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 {self:?} for adt {adt:?}"),
}
}
// 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>(
&'a self,
ty: &'a Ty,
variant: VariantId,
) -> impl Iterator<Item = (LocalFieldId, Ty)> + Captures<'a> + Captures<'p> {
let cx = self;
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 =
cx.db.attrs(variant.into()).by_key("non_exhaustive").exists() && !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| {
let ty = field_ty[fid].clone().substitute(Interner, substs);
let ty = normalize(cx.db, cx.db.trait_environment_for_body(cx.body), ty);
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))
}
})
}
pub(crate) fn lower_pat(&self, pat: &Pat) -> DeconstructedPat<'p> {
let singleton = |pat| std::slice::from_ref(self.pattern_arena.alloc(pat));
let ctor;
let fields: &[_];
match pat.kind.as_ref() {
PatKind::Binding { subpattern: Some(subpat), .. } => return self.lower_pat(subpat),
PatKind::Binding { subpattern: None, .. } | PatKind::Wild => {
ctor = Wildcard;
fields = &[];
}
PatKind::Deref { subpattern } => {
ctor = match pat.ty.kind(Interner) {
// This is a box pattern.
TyKind::Adt(adt, _) if is_box(self.db, adt.0) => Struct,
TyKind::Ref(..) => Ref,
_ => {
never!("pattern has unexpected type: pat: {:?}, ty: {:?}", pat, &pat.ty);
Wildcard
}
};
fields = singleton(self.lower_pat(subpattern));
}
PatKind::Leaf { subpatterns } | PatKind::Variant { subpatterns, .. } => {
match pat.ty.kind(Interner) {
TyKind::Tuple(_, substs) => {
ctor = Struct;
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] = self.lower_pat(&pat.pattern);
}
fields = self.pattern_arena.alloc_extend(wilds)
}
TyKind::Adt(adt, substs) if is_box(self.db, adt.0) => {
// 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 {
self.lower_pat(&pat.pattern)
} else {
let ty = substs.at(Interner, 0).assert_ty_ref(Interner).clone();
DeconstructedPat::wildcard(ty)
};
ctor = Struct;
fields = singleton(field);
}
&TyKind::Adt(adt, _) => {
ctor = match pat.kind.as_ref() {
PatKind::Leaf { .. } if matches!(adt.0, hir_def::AdtId::UnionId(_)) => {
UnionField
}
PatKind::Leaf { .. } => Struct,
PatKind::Variant { enum_variant, .. } => Variant(*enum_variant),
_ => {
never!();
Wildcard
}
};
let variant = self.variant_id_for_adt(&ctor, adt.0);
let fields_len = variant.variant_data(self.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 = self
.list_variant_nonhidden_fields(&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] = self.lower_pat(&pat.pattern);
}
}
fields = self.pattern_arena.alloc_extend(wilds);
}
_ => {
never!("pattern has unexpected type: pat: {:?}, ty: {:?}", pat, &pat.ty);
ctor = Wildcard;
fields = &[];
}
}
}
&PatKind::LiteralBool { value } => {
ctor = Bool(value);
fields = &[];
}
PatKind::Or { pats } => {
ctor = Or;
// Collect here because `Arena::alloc_extend` panics on reentrancy.
let subpats: SmallVec<[_; 2]> =
pats.into_iter().map(|pat| self.lower_pat(pat)).collect();
fields = self.pattern_arena.alloc_extend(subpats);
}
}
DeconstructedPat::new(ctor, fields, pat.ty.clone(), ())
}
pub(crate) fn hoist_witness_pat(&self, pat: &WitnessPat<'p>) -> Pat {
let mut subpatterns = pat.iter_fields().map(|p| self.hoist_witness_pat(p));
let kind = match pat.ctor() {
&Bool(value) => PatKind::LiteralBool { value },
IntRange(_) => unimplemented!(),
Struct | Variant(_) | UnionField => match pat.ty().kind(Interner) {
TyKind::Tuple(..) => PatKind::Leaf {
subpatterns: subpatterns
.zip(0u32..)
.map(|(p, i)| FieldPat {
field: LocalFieldId::from_raw(i.into()),
pattern: p,
})
.collect(),
},
TyKind::Adt(adt, _) if is_box(self.db, adt.0) => {
// Without `box_patterns`, the only legal pattern of type `Box` is `_` (outside
// of `std`). So this branch is only reachable when the feature is enabled and
// the pattern is a box pattern.
PatKind::Deref { subpattern: subpatterns.next().unwrap() }
}
TyKind::Adt(adt, substs) => {
let variant = self.variant_id_for_adt(pat.ctor(), adt.0);
let subpatterns = self
.list_variant_nonhidden_fields(pat.ty(), variant)
.zip(subpatterns)
.map(|((field, _ty), pattern)| FieldPat { field, pattern })
.collect();
if let VariantId::EnumVariantId(enum_variant) = variant {
PatKind::Variant { substs: substs.clone(), enum_variant, subpatterns }
} else {
PatKind::Leaf { subpatterns }
}
}
_ => {
never!("unexpected ctor for type {:?} {:?}", pat.ctor(), pat.ty());
PatKind::Wild
}
},
// 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
// ignore this issue.
Ref => PatKind::Deref { subpattern: subpatterns.next().unwrap() },
Slice(_) => unimplemented!(),
&Str(void) => match void {},
Wildcard | NonExhaustive | Hidden => PatKind::Wild,
Missing | F32Range(..) | F64Range(..) | Opaque(..) | Or => {
never!("can't convert to pattern: {:?}", pat.ctor());
PatKind::Wild
}
};
Pat { ty: pat.ty().clone(), kind: Box::new(kind) }
}
}
impl<'p> TypeCx for MatchCheckCtx<'p> {
type Error = Void;
type Ty = Ty;
type VariantIdx = EnumVariantId;
type StrLit = Void;
type ArmData = ();
type PatData = ();
fn is_exhaustive_patterns_feature_on(&self) -> bool {
self.exhaustive_patterns
}
fn ctor_arity(
&self,
ctor: &rustc_pattern_analysis::constructor::Constructor<Self>,
ty: &Self::Ty,
) -> usize {
match ctor {
Struct | Variant(_) | UnionField => match *ty.kind(Interner) {
TyKind::Tuple(arity, ..) => arity,
TyKind::Adt(AdtId(adt), ..) => {
if is_box(self.db, adt) {
// 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(ctor, adt);
self.list_variant_nonhidden_fields(ty, variant).count()
}
}
_ => {
never!("Unexpected type for `Single` constructor: {:?}", ty);
0
}
},
Ref => 1,
Slice(..) => unimplemented!(),
Bool(..) | IntRange(..) | F32Range(..) | F64Range(..) | Str(..) | Opaque(..)
| NonExhaustive | Hidden | Missing | Wildcard => 0,
Or => {
never!("The `Or` constructor doesn't have a fixed arity");
0
}
}
}
fn ctor_sub_tys(
&self,
ctor: &rustc_pattern_analysis::constructor::Constructor<Self>,
ty: &Self::Ty,
) -> &[Self::Ty] {
use std::iter::once;
fn alloc<'a>(cx: &'a MatchCheckCtx<'_>, iter: impl Iterator<Item = Ty>) -> &'a [Ty] {
cx.ty_arena.alloc_extend(iter)
}
match ctor {
Struct | Variant(_) | UnionField => match ty.kind(Interner) {
TyKind::Tuple(_, substs) => {
let tys = substs.iter(Interner).map(|ty| ty.assert_ty_ref(Interner));
alloc(self, tys.cloned())
}
TyKind::Ref(.., rty) => alloc(self, once(rty.clone())),
&TyKind::Adt(AdtId(adt), ref substs) => {
if is_box(self.db, adt) {
// 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();
alloc(self, once(subst_ty))
} else {
let variant = self.variant_id_for_adt(ctor, adt);
let tys = self.list_variant_nonhidden_fields(ty, variant).map(|(_, ty)| ty);
alloc(self, tys)
}
}
ty_kind => {
never!("Unexpected type for `{:?}` constructor: {:?}", ctor, ty_kind);
alloc(self, once(ty.clone()))
}
},
Ref => match ty.kind(Interner) {
TyKind::Ref(.., rty) => alloc(self, once(rty.clone())),
ty_kind => {
never!("Unexpected type for `{:?}` constructor: {:?}", ctor, ty_kind);
alloc(self, once(ty.clone()))
}
},
Slice(_) => unreachable!("Found a `Slice` constructor in match checking"),
Bool(..) | IntRange(..) | F32Range(..) | F64Range(..) | Str(..) | Opaque(..)
| NonExhaustive | Hidden | Missing | Wildcard => &[],
Or => {
never!("called `Fields::wildcards` on an `Or` ctor");
&[]
}
}
}
fn ctors_for_ty(
&self,
ty: &Self::Ty,
) -> Result<rustc_pattern_analysis::constructor::ConstructorSet<Self>, Self::Error> {
let cx = self;
// Unhandled types are treated as non-exhaustive. Being explicit here instead of falling
// to catchall arm to ease further implementation.
let unhandled = || ConstructorSet::Unlistable;
// This determines the set of all possible constructors for the type `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()`).
Ok(match ty.kind(Interner) {
TyKind::Scalar(Scalar::Bool) => ConstructorSet::Bool,
TyKind::Scalar(Scalar::Char) => unhandled(),
TyKind::Scalar(Scalar::Int(..) | Scalar::Uint(..)) => unhandled(),
TyKind::Array(..) | TyKind::Slice(..) => unhandled(),
TyKind::Adt(AdtId(hir_def::AdtId::EnumId(enum_id)), subst) => {
let enum_data = cx.db.enum_data(*enum_id);
let is_declared_nonexhaustive = cx.is_foreign_non_exhaustive_enum(ty);
if enum_data.variants.is_empty() && !is_declared_nonexhaustive {
ConstructorSet::NoConstructors
} else {
let mut variants = FxHashMap::default();
for &(variant, _) in enum_data.variants.iter() {
let is_uninhabited =
is_enum_variant_uninhabited_from(variant, subst, cx.module, cx.db);
let visibility = if is_uninhabited {
VariantVisibility::Empty
} else {
VariantVisibility::Visible
};
variants.insert(variant, visibility);
}
ConstructorSet::Variants {
variants: IdxContainer(variants),
non_exhaustive: is_declared_nonexhaustive,
}
}
}
TyKind::Adt(AdtId(hir_def::AdtId::UnionId(_)), _) => ConstructorSet::Union,
TyKind::Adt(..) | TyKind::Tuple(..) => {
ConstructorSet::Struct { empty: cx.is_uninhabited(ty) }
}
TyKind::Ref(..) => ConstructorSet::Ref,
TyKind::Never => ConstructorSet::NoConstructors,
// This type is one for which we cannot list constructors, like `str` or `f64`.
_ => ConstructorSet::Unlistable,
})
}
fn debug_pat(
_f: &mut fmt::Formatter<'_>,
_pat: &rustc_pattern_analysis::pat::DeconstructedPat<'_, Self>,
) -> fmt::Result {
unimplemented!()
}
fn bug(&self, fmt: fmt::Arguments<'_>) -> ! {
panic!("{}", fmt)
}
}
impl<'p> fmt::Debug for MatchCheckCtx<'p> {
fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
f.debug_struct("MatchCheckCtx").finish()
}
}

824
crates/hir-ty/src/diagnostics/match_check/usefulness.rs
View file

@ -1,824 +0,0 @@
//! Based on rust-lang/rust (last sync f31622a50 2021-11-12)
//! <https://github.com/rust-lang/rust/blob/f31622a50/compiler/rustc_mir_build/src/thir/pattern/usefulness.rs>
//!
//! -----
//!
//! This file includes the logic for exhaustiveness and reachability checking for pattern-matching.
//! Specifically, given a list of patterns for a type, we can tell whether:
//! (a) each pattern is reachable (reachability)
//! (b) the patterns cover every possible value for the type (exhaustiveness)
//!
//! The algorithm implemented here is a modified version of the one described in [this
//! paper](http://moscova.inria.fr/~maranget/papers/warn/index.html). We have however generalized
//! it to accommodate the variety of patterns that Rust supports. We thus explain our version here,
//! without being as rigorous.
//!
//!
//! # Summary
//!
//! The core of the algorithm is the notion of "usefulness". A pattern `q` is said to be *useful*
//! relative to another pattern `p` of the same type if there is a value that is matched by `q` and
//! not matched by `p`. This generalizes to many `p`s: `q` is useful w.r.t. a list of patterns
//! `p_1 .. p_n` if there is a value that is matched by `q` and by none of the `p_i`. We write
//! `usefulness(p_1 .. p_n, q)` for a function that returns a list of such values. The aim of this
//! file is to compute it efficiently.
//!
//! This is enough to compute reachability: a pattern in a `match` expression is reachable iff it
//! is useful w.r.t. the patterns above it:
//! ```rust
//! match x {
//! Some(_) => ...,
//! None => ..., // reachable: `None` is matched by this but not the branch above
//! Some(0) => ..., // unreachable: all the values this matches are already matched by
//! // `Some(_)` above
//! }
//! ```
//!
//! This is also enough to compute exhaustiveness: a match is exhaustive iff the wildcard `_`
//! pattern is _not_ useful w.r.t. the patterns in the match. The values returned by `usefulness`
//! are used to tell the user which values are missing.
//! ```rust
//! match x {
//! Some(0) => ...,
//! None => ...,
//! // not exhaustive: `_` is useful because it matches `Some(1)`
//! }
//! ```
//!
//! The entrypoint of this file is the [`compute_match_usefulness`] function, which computes
//! reachability for each match branch and exhaustiveness for the whole match.
//!
//!
//! # Constructors and fields
//!
//! Note: we will often abbreviate "constructor" as "ctor".
//!
//! The idea that powers everything that is done in this file is the following: a (matcheable)
//! value is made from a constructor applied to a number of subvalues. Examples of constructors are
//! `Some`, `None`, `(,)` (the 2-tuple constructor), `Foo {..}` (the constructor for a struct
//! `Foo`), and `2` (the constructor for the number `2`). This is natural when we think of
//! pattern-matching, and this is the basis for what follows.
//!
//! Some of the ctors listed above might feel weird: `None` and `2` don't take any arguments.
//! That's ok: those are ctors that take a list of 0 arguments; they are the simplest case of
//! ctors. We treat `2` as a ctor because `u64` and other number types behave exactly like a huge
//! `enum`, with one variant for each number. This allows us to see any matcheable value as made up
//! from a tree of ctors, each having a set number of children. For example: `Foo { bar: None,
//! baz: Ok(0) }` is made from 4 different ctors, namely `Foo{..}`, `None`, `Ok` and `0`.
//!
//! This idea can be extended to patterns: they are also made from constructors applied to fields.
//! A pattern for a given type is allowed to use all the ctors for values of that type (which we
//! call "value constructors"), but there are also pattern-only ctors. The most important one is
//! the wildcard (`_`), and the others are integer ranges (`0..=10`), variable-length slices (`[x,
//! ..]`), and or-patterns (`Ok(0) | Err(_)`). Examples of valid patterns are `42`, `Some(_)`, `Foo
//! { bar: Some(0) | None, baz: _ }`. Note that a binder in a pattern (e.g. `Some(x)`) matches the
//! same values as a wildcard (e.g. `Some(_)`), so we treat both as wildcards.
//!
//! From this deconstruction we can compute whether a given value matches a given pattern; we
//! simply look at ctors one at a time. Given a pattern `p` and a value `v`, we want to compute
//! `matches!(v, p)`. It's mostly straightforward: we compare the head ctors and when they match
//! we compare their fields recursively. A few representative examples:
//!
//! - `matches!(v, _) := true`
//! - `matches!((v0, v1), (p0, p1)) := matches!(v0, p0) && matches!(v1, p1)`
//! - `matches!(Foo { bar: v0, baz: v1 }, Foo { bar: p0, baz: p1 }) := matches!(v0, p0) && matches!(v1, p1)`
//! - `matches!(Ok(v0), Ok(p0)) := matches!(v0, p0)`
//! - `matches!(Ok(v0), Err(p0)) := false` (incompatible variants)
//! - `matches!(v, 1..=100) := matches!(v, 1) || ... || matches!(v, 100)`
//! - `matches!([v0], [p0, .., p1]) := false` (incompatible lengths)
//! - `matches!([v0, v1, v2], [p0, .., p1]) := matches!(v0, p0) && matches!(v2, p1)`
//! - `matches!(v, p0 | p1) := matches!(v, p0) || matches!(v, p1)`
//!
//! Constructors, fields and relevant operations are defined in the [`super::deconstruct_pat`] module.
//!
//! Note: this constructors/fields distinction may not straightforwardly apply to every Rust type.
//! For example a value of type `Rc<u64>` can't be deconstructed that way, and `&str` has an
//! infinitude of constructors. There are also subtleties with visibility of fields and
//! uninhabitedness and various other things. The constructors idea can be extended to handle most
//! of these subtleties though; caveats are documented where relevant throughout the code.
//!
//! Whether constructors cover each other is computed by [`Constructor::is_covered_by`].
//!
//!
//! # Specialization
//!
//! Recall that we wish to compute `usefulness(p_1 .. p_n, q)`: given a list of patterns `p_1 ..
//! p_n` and a pattern `q`, all of the same type, we want to find a list of values (called
//! "witnesses") that are matched by `q` and by none of the `p_i`. We obviously don't just
//! enumerate all possible values. From the discussion above we see that we can proceed
//! ctor-by-ctor: for each value ctor of the given type, we ask "is there a value that starts with
//! this constructor and matches `q` and none of the `p_i`?". As we saw above, there's a lot we can
//! say from knowing only the first constructor of our candidate value.
//!
//! Let's take the following example:
//! ```
//! match x {
//! Enum::Variant1(_) => {} // `p1`
//! Enum::Variant2(None, 0) => {} // `p2`
//! Enum::Variant2(Some(_), 0) => {} // `q`
//! }
//! ```
//!
//! We can easily see that if our candidate value `v` starts with `Variant1` it will not match `q`.
//! If `v = Variant2(v0, v1)` however, whether or not it matches `p2` and `q` will depend on `v0`
//! and `v1`. In fact, such a `v` will be a witness of usefulness of `q` exactly when the tuple
//! `(v0, v1)` is a witness of usefulness of `q'` in the following reduced match:
//!
//! ```
//! match x {
//! (None, 0) => {} // `p2'`
//! (Some(_), 0) => {} // `q'`
//! }
//! ```
//!
//! This motivates a new step in computing usefulness, that we call _specialization_.
//! Specialization consist of filtering a list of patterns for those that match a constructor, and
//! then looking into the constructor's fields. This enables usefulness to be computed recursively.
//!
//! Instead of acting on a single pattern in each row, we will consider a list of patterns for each
//! row, and we call such a list a _pattern-stack_. The idea is that we will specialize the
//! leftmost pattern, which amounts to popping the constructor and pushing its fields, which feels
//! like a stack. We note a pattern-stack simply with `[p_1 ... p_n]`.
//! Here's a sequence of specializations of a list of pattern-stacks, to illustrate what's
//! happening:
//! ```
//! [Enum::Variant1(_)]
//! [Enum::Variant2(None, 0)]
//! [Enum::Variant2(Some(_), 0)]
//! //==>> specialize with `Variant2`
//! [None, 0]
//! [Some(_), 0]
//! //==>> specialize with `Some`
//! [_, 0]
//! //==>> specialize with `true` (say the type was `bool`)
//! [0]
//! //==>> specialize with `0`
//! []
//! ```
//!
//! The function `specialize(c, p)` takes a value constructor `c` and a pattern `p`, and returns 0
//! or more pattern-stacks. If `c` does not match the head constructor of `p`, it returns nothing;
//! otherwise if returns the fields of the constructor. This only returns more than one
//! pattern-stack if `p` has a pattern-only constructor.
//!
//! - Specializing for the wrong constructor returns nothing
//!
//! `specialize(None, Some(p0)) := []`
//!
//! - Specializing for the correct constructor returns a single row with the fields
//!
//! `specialize(Variant1, Variant1(p0, p1, p2)) := [[p0, p1, p2]]`
//!
//! `specialize(Foo{..}, Foo { bar: p0, baz: p1 }) := [[p0, p1]]`
//!
//! - For or-patterns, we specialize each branch and concatenate the results
//!
//! `specialize(c, p0 | p1) := specialize(c, p0) ++ specialize(c, p1)`
//!
//! - We treat the other pattern constructors as if they were a large or-pattern of all the
//! possibilities:
//!
//! `specialize(c, _) := specialize(c, Variant1(_) | Variant2(_, _) | ...)`
//!
//! `specialize(c, 1..=100) := specialize(c, 1 | ... | 100)`
//!
//! `specialize(c, [p0, .., p1]) := specialize(c, [p0, p1] | [p0, _, p1] | [p0, _, _, p1] | ...)`
//!
//! - If `c` is a pattern-only constructor, `specialize` is defined on a case-by-case basis. See
//! the discussion about constructor splitting in [`super::deconstruct_pat`].
//!
//!
//! We then extend this function to work with pattern-stacks as input, by acting on the first
//! column and keeping the other columns untouched.
//!
//! Specialization for the whole matrix is done in [`Matrix::specialize_constructor`]. Note that
//! or-patterns in the first column are expanded before being stored in the matrix. Specialization
//! for a single patstack is done from a combination of [`Constructor::is_covered_by`] and
//! [`PatStack::pop_head_constructor`]. The internals of how it's done mostly live in the
//! [`Fields`] struct.
//!
//!
//! # Computing usefulness
//!
//! We now have all we need to compute usefulness. The inputs to usefulness are a list of
//! pattern-stacks `p_1 ... p_n` (one per row), and a new pattern_stack `q`. The paper and this
//! file calls the list of patstacks a _matrix_. They must all have the same number of columns and
//! the patterns in a given column must all have the same type. `usefulness` returns a (possibly
//! empty) list of witnesses of usefulness. These witnesses will also be pattern-stacks.
//!
//! - base case: `n_columns == 0`.
//! Since a pattern-stack functions like a tuple of patterns, an empty one functions like the
//! unit type. Thus `q` is useful iff there are no rows above it, i.e. if `n == 0`.
//!
//! - inductive case: `n_columns > 0`.
//! We need a way to list the constructors we want to try. We will be more clever in the next
//! section but for now assume we list all value constructors for the type of the first column.
//!
//! - for each such ctor `c`:
//!
//! - for each `q'` returned by `specialize(c, q)`:
//!
//! - we compute `usefulness(specialize(c, p_1) ... specialize(c, p_n), q')`
//!
//! - for each witness found, we revert specialization by pushing the constructor `c` on top.
//!
//! - We return the concatenation of all the witnesses found, if any.
//!
//! Example:
//! ```
//! [Some(true)] // p_1
//! [None] // p_2
//! [Some(_)] // q
//! //==>> try `None`: `specialize(None, q)` returns nothing
//! //==>> try `Some`: `specialize(Some, q)` returns a single row
//! [true] // p_1'
//! [_] // q'
//! //==>> try `true`: `specialize(true, q')` returns a single row
//! [] // p_1''
//! [] // q''
//! //==>> base case; `n != 0` so `q''` is not useful.
//! //==>> go back up a step
//! [true] // p_1'
//! [_] // q'
//! //==>> try `false`: `specialize(false, q')` returns a single row
//! [] // q''
//! //==>> base case; `n == 0` so `q''` is useful. We return the single witness `[]`
//! witnesses:
//! []
//! //==>> undo the specialization with `false`
//! witnesses:
//! [false]
//! //==>> undo the specialization with `Some`
//! witnesses:
//! [Some(false)]
//! //==>> we have tried all the constructors. The output is the single witness `[Some(false)]`.
//! ```
//!
//! This computation is done in [`is_useful`]. In practice we don't care about the list of
//! witnesses when computing reachability; we only need to know whether any exist. We do keep the
//! witnesses when computing exhaustiveness to report them to the user.
//!
//!
//! # Making usefulness tractable: constructor splitting
//!
//! We're missing one last detail: which constructors do we list? Naively listing all value
//! constructors cannot work for types like `u64` or `&str`, so we need to be more clever. The
//! first obvious insight is that we only want to list constructors that are covered by the head
//! constructor of `q`. If it's a value constructor, we only try that one. If it's a pattern-only
//! constructor, we use the final clever idea for this algorithm: _constructor splitting_, where we
//! group together constructors that behave the same.
//!
//! 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::iter::once;
use hir_def::{AdtId, DefWithBodyId, HasModule, ModuleId};
use smallvec::{smallvec, SmallVec};
use typed_arena::Arena;
use crate::{db::HirDatabase, inhabitedness::is_ty_uninhabited_from, Ty, TyExt};
use super::deconstruct_pat::{Constructor, DeconstructedPat, Fields, SplitWildcard};
use self::{helper::Captures, ArmType::*, Usefulness::*};
pub(crate) struct MatchCheckCtx<'a, 'p> {
pub(crate) module: ModuleId,
pub(crate) body: DefWithBodyId,
pub(crate) db: &'a dyn HirDatabase,
/// Lowered patterns from arms plus generated by the check.
pub(crate) pattern_arena: &'p Arena<DeconstructedPat<'p>>,
exhaustive_patterns: bool,
}
impl<'a, 'p> MatchCheckCtx<'a, 'p> {
pub(crate) fn new(
module: ModuleId,
body: DefWithBodyId,
db: &'a dyn HirDatabase,
pattern_arena: &'p Arena<DeconstructedPat<'p>>,
) -> Self {
let def_map = db.crate_def_map(module.krate());
let exhaustive_patterns = def_map.is_unstable_feature_enabled("exhaustive_patterns");
Self { module, body, db, pattern_arena, exhaustive_patterns }
}
pub(super) fn is_uninhabited(&self, ty: &Ty) -> bool {
if self.feature_exhaustive_patterns() {
is_ty_uninhabited_from(ty, self.module, self.db)
} else {
false
}
}
/// Returns whether the given type is an enum from another crate declared `#[non_exhaustive]`.
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(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's unstable feature described as "Allows exhaustive pattern matching on types that contain uninhabited types."
pub(super) fn feature_exhaustive_patterns(&self) -> bool {
self.exhaustive_patterns
}
}
#[derive(Copy, Clone)]
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,
/// Whether 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<'p> {
pats: SmallVec<[&'p DeconstructedPat<'p>; 2]>,
}
impl<'p> PatStack<'p> {
fn from_pattern(pat: &'p DeconstructedPat<'p>) -> Self {
Self::from_vec(smallvec![pat])
}
fn from_vec(vec: SmallVec<[&'p DeconstructedPat<'p>; 2]>) -> Self {
PatStack { pats: vec }
}
fn is_empty(&self) -> bool {
self.pats.is_empty()
}
fn len(&self) -> usize {
self.pats.len()
}
fn head(&self) -> &'p DeconstructedPat<'p> {
self.pats[0]
}
// 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) -> 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.
///
/// 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, 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: SmallVec<[_; 2]> = self.head().specialize(cx, ctor);
new_fields.extend_from_slice(&self.pats[1..]);
PatStack::from_vec(new_fields)
}
}
/// A 2D matrix.
#[derive(Clone)]
pub(super) struct Matrix<'p> {
patterns: Vec<PatStack<'p>>,
}
impl<'p> Matrix<'p> {
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.first().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<'p>) {
if !row.is_empty() && row.head().is_or_pat() {
self.patterns.extend(row.expand_or_pat());
} else {
self.patterns.push(row);
}
}
/// Iterate over the first component of each row
fn heads(&self) -> impl Iterator<Item = &'p DeconstructedPat<'p>> + Clone + Captures<'_> {
self.patterns.iter().map(|r| r.head())
}
/// This computes `S(constructor, self)`. See top of the file for explanations.
fn specialize_constructor(&self, pcx: PatCtxt<'_, 'p>, ctor: &Constructor) -> Matrix<'p> {
let mut matrix = Matrix::empty();
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
}
}
/// 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 `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<'p>>),
}
impl<'p> Usefulness<'p> {
fn new_useful(preference: ArmType) -> Self {
match preference {
// A single (empty) witness of reachability.
FakeExtraWildcard => WithWitnesses(vec![Witness(vec![])]),
RealArm => NoWitnesses { useful: true },
}
}
fn new_not_useful(preference: ArmType) -> Self {
match preference {
FakeExtraWildcard => WithWitnesses(vec![]),
RealArm => NoWitnesses { useful: false },
}
}
fn is_useful(&self) -> bool {
match self {
Usefulness::NoWitnesses { useful } => *useful,
Usefulness::WithWitnesses(witnesses) => !witnesses.is_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 { useful: s_useful }, NoWitnesses { useful: o_useful }) => {
*s_useful = *s_useful || o_useful
}
_ => unreachable!(),
}
}
/// 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<'_, 'p>,
matrix: &Matrix<'p>,
ctor: &Constructor,
) -> Self {
match self {
NoWitnesses { .. } => self,
WithWitnesses(ref witnesses) if witnesses.is_empty() => self,
WithWitnesses(witnesses) => {
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.heads().map(DeconstructedPat::ctor));
// This lets us know if we skipped any variants because they are marked
// `doc(hidden)` or they are unstable feature gate (only stdlib types).
let mut hide_variant_show_wild = false;
// 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 mut new: Vec<DeconstructedPat<'_>> = split_wildcard
.iter_missing(pcx)
.filter_map(|missing_ctor| {
// Check if this variant is marked `doc(hidden)`
if missing_ctor.is_doc_hidden_variant(pcx)
|| missing_ctor.is_unstable_variant(pcx)
{
hide_variant_show_wild = true;
return None;
}
Some(DeconstructedPat::wild_from_ctor(pcx, missing_ctor.clone()))
})
.collect();
if hide_variant_show_wild {
new.push(DeconstructedPat::wildcard(pcx.ty.clone()))
}
new
};
witnesses
.into_iter()
.flat_map(|witness| {
new_patterns.iter().map(move |pat| {
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))
.collect()
};
WithWitnesses(new_witnesses)
}
}
}
}
#[derive(Copy, Clone, Debug)]
enum ArmType {
FakeExtraWildcard,
RealArm,
}
/// A witness of non-exhaustiveness for error reporting, represented
/// as a list of patterns (in reverse order of construction) with
/// wildcards inside to represent elements that can take any inhabitant
/// of the type as a value.
///
/// A witness against a list of patterns should have the same types
/// and length as the pattern matched against. Because Rust `match`
/// is always against a single pattern, at the end the witness will
/// have length 1, but in the middle of the algorithm, it can contain
/// multiple patterns.
///
/// For example, if we are constructing a witness for the match against
///
/// ```
/// struct Pair(Option<(u32, u32)>, bool);
///
/// match (p: Pair) {
/// Pair(None, _) => {}
/// Pair(_, false) => {}
/// }
/// ```
///
/// We'll perform the following steps:
/// 1. Start with an empty witness
/// `Witness(vec![])`
/// 2. Push a witness `true` against the `false`
/// `Witness(vec![true])`
/// 3. Push a witness `Some(_)` against the `None`
/// `Witness(vec![true, Some(_)])`
/// 4. Apply the `Pair` constructor to the witnesses
/// `Witness(vec![Pair(Some(_), true)])`
///
/// The final `Pair(Some(_), true)` is then the resulting witness.
pub(crate) struct Witness<'p>(Vec<DeconstructedPat<'p>>);
impl<'p> Witness<'p> {
/// Asserts that the witness contains a single pattern, and returns it.
fn single_pattern(self) -> DeconstructedPat<'p> {
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<'_, 'p>, ctor: &Constructor) -> Self {
let pat = {
let len = self.0.len();
let arity = ctor.arity(pcx);
let pats = self.0.drain((len - arity)..).rev();
let fields = Fields::from_iter(pcx.cx, pats);
DeconstructedPat::new(ctor.clone(), fields, pcx.ty.clone())
};
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<'p>(
cx: &MatchCheckCtx<'_, 'p>,
matrix: &Matrix<'p>,
v: &PatStack<'p>,
witness_preference: ArmType,
is_under_guard: bool,
is_top_level: bool,
) -> Usefulness<'p> {
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;
}
debug_assert!(rows.iter().all(|r| r.len() == v.len()));
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 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();
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);
}
}
} else {
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.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;
for ctor in split_ctors {
// We cache the result of `Fields::wildcards` because it is used a lot.
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);
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<'p> {
pub(crate) pat: &'p DeconstructedPat<'p>,
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.
// FIXME: store unreachable subpattern IDs
Reachable,
/// The arm is unreachable.
Unreachable,
}
/// The output of checking a match for exhaustiveness and arm reachability.
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<'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<DeconstructedPat<'p>>,
}
/// The entrypoint for the usefulness algorithm. Computes whether a match is exhaustive and which
/// of its arms are reachable.
///
/// Note: the input patterns must have been lowered through
/// `check_match::MatchVisitor::lower_pattern`.
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);
is_useful(cx, &matrix, &v, RealArm, arm.has_guard, true);
if !arm.has_guard {
matrix.push(v);
}
let reachability = if arm.pat.is_reachable() {
Reachability::Reachable
} else {
Reachability::Unreachable
};
(arm, reachability)
})
.collect();
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, FakeExtraWildcard, false, true);
let non_exhaustiveness_witnesses = match usefulness {
WithWitnesses(pats) => pats.into_iter().map(Witness::single_pattern).collect(),
NoWitnesses { .. } => panic!("bug"),
};
UsefulnessReport { _arm_usefulness: arm_usefulness, non_exhaustiveness_witnesses }
}
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.
/// 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(crate) trait Captures<'a> {}
impl<'a, T: ?Sized> Captures<'a> for T {}
}

3
crates/hir-ty/src/lib.rs
View file

@ -15,6 +15,9 @@ extern crate rustc_abi;
#[cfg(not(feature = "in-rust-tree"))]
extern crate ra_ap_rustc_abi as rustc_abi;
// No need to use the in-tree one.
extern crate ra_ap_rustc_pattern_analysis as rustc_pattern_analysis;
mod builder;
mod chalk_db;
mod chalk_ext;

1
crates/rust-analyzer/tests/slow-tests/tidy.rs
View file

@ -154,6 +154,7 @@ fn check_licenses() {
Apache-2.0
Apache-2.0 OR BSL-1.0
Apache-2.0 OR MIT
Apache-2.0 WITH LLVM-exception
Apache-2.0 WITH LLVM-exception OR Apache-2.0 OR MIT
Apache-2.0/MIT
BSD-3-Clause