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Merge #8717

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8717: Update match checking algorithm r=iDawer a=iDawer

I've recently got interest in the match checking to extend the current algo to support reporting witnesses of non-exhaustiveness.
It appears the algo is outdated from rustc's implementation. I decided to rewrite it based on the latest rustc's version. It is a diff-based port to ra codebase. That means you can diff-compare these files to rustc.
I'm striving to keep minimal ra-related changes in the algo to make it easier to backport future changes from the upstream.

Based on upstream algorithm of version 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

The goal of this PR is to cover the current `missing-match-arm` diagnostic.

What is remaining to do:
- [x] Error handling. The errors that are unrelated to match checking will be handled before the check. Just like how it made in rustc.
  - [x] Lowering `hir_def::expr::Pat` to `hir_ty::diagnostics::match_check::Pat`. rustc's match checking works on top of `rustc_mir_build::thir::Pat`, which is lowered from `hir::Pat` and carries some extra semantics used by the check. All unrelated checks are done there. RA could use this to rule out running the check on unimplemented cases (`Pat::ConstBlock`, etc).
  - [x] ~~Proper~~Loose typecheck of match arm patterns (https://github.com/rust-analyzer/rust-analyzer/pull/8840, https://github.com/rust-analyzer/rust-analyzer/pull/8875).
- [x] Tests from `hir_ty::diagnostics::match_check::tests`.
- [x] Clean up `todo`s
- [x] Test run on real repos https://github.com/rust-analyzer/rust-analyzer/pull/8717#issuecomment-847120265.

Co-authored-by: Dawer <7803845+iDawer@users.noreply.github.com>
This commit is contained in:
bors[bot] 2021-05-31 21:01:52 +00:00 committed by GitHub
commit 71117e6812
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7 changed files with 2823 additions and 860 deletions
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2
crates/hir_def/src/path.rs
View File

@ -166,7 +166,7 @@ impl Path {
}
/// Converts a known mod path to `Path`.
pub(crate) fn from_known_path(
pub fn from_known_path(
path: ModPath,
generic_args: Vec<Option<Interned<GenericArgs>>>,
) -> Path {

1
crates/hir_ty/Cargo.toml
View File

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

117
crates/hir_ty/src/diagnostics/expr.rs
View File

@ -2,9 +2,11 @@
//! through the body using inference results: mismatched arg counts, missing
//! fields, etc.
use std::sync::Arc;
use std::{cell::RefCell, sync::Arc};
use hir_def::{expr::Statement, path::path, resolver::HasResolver, AssocItemId, DefWithBodyId};
use hir_def::{
expr::Statement, path::path, resolver::HasResolver, AssocItemId, DefWithBodyId, HasModule,
};
use hir_expand::name;
use rustc_hash::FxHashSet;
use syntax::{ast, AstPtr};
@ -12,7 +14,10 @@ use syntax::{ast, AstPtr};
use crate::{
db::HirDatabase,
diagnostics::{
match_check::{is_useful, MatchCheckCtx, Matrix, PatStack, Usefulness},
match_check::{
self,
usefulness::{compute_match_usefulness, expand_pattern, MatchCheckCtx, PatternArena},
},
MismatchedArgCount, MissingFields, MissingMatchArms, MissingOkOrSomeInTailExpr,
MissingPatFields, RemoveThisSemicolon,
},
@ -294,12 +299,12 @@ impl<'a, 'b> ExprValidator<'a, 'b> {
&infer.type_of_expr[match_expr]
};
let cx = MatchCheckCtx { match_expr, body, infer: infer.clone(), db };
let pats = arms.iter().map(|arm| arm.pat);
let pattern_arena = RefCell::new(PatternArena::new());
let mut seen = Matrix::empty();
for pat in pats {
if let Some(pat_ty) = infer.type_of_pat.get(pat) {
let mut m_arms = Vec::new();
let mut has_lowering_errors = false;
for arm in arms {
if let Some(pat_ty) = infer.type_of_pat.get(arm.pat) {
// We only include patterns whose type matches the type
// of the match expression. If we had a InvalidMatchArmPattern
// diagnostic or similar we could raise that in an else
@ -315,14 +320,25 @@ impl<'a, 'b> ExprValidator<'a, 'b> {
.as_reference()
.map(|(match_expr_ty, ..)| match_expr_ty == pat_ty)
.unwrap_or(false))
&& types_of_subpatterns_do_match(pat, &cx.body, &infer)
&& types_of_subpatterns_do_match(arm.pat, &body, &infer)
{
// If we had a NotUsefulMatchArm diagnostic, we could
// check the usefulness of each pattern as we added it
// to the matrix here.
let v = PatStack::from_pattern(pat);
seen.push(&cx, v);
continue;
let m_arm = match_check::MatchArm {
pat: self.lower_pattern(
arm.pat,
&mut pattern_arena.borrow_mut(),
db,
&body,
&mut has_lowering_errors,
),
has_guard: arm.guard.is_some(),
};
m_arms.push(m_arm);
if !has_lowering_errors {
continue;
}
}
}
@ -330,34 +346,73 @@ impl<'a, 'b> ExprValidator<'a, 'b> {
// fit the match expression, we skip this diagnostic. Skipping the entire
// diagnostic rather than just not including this match arm is preferred
// to avoid the chance of false positives.
#[cfg(test)]
match_check::tests::report_bail_out(db, self.owner, arm.pat, self.sink);
return;
}
match is_useful(&cx, &seen, &PatStack::from_wild()) {
Ok(Usefulness::Useful) => (),
// if a wildcard pattern is not useful, then all patterns are covered
Ok(Usefulness::NotUseful) => return,
// this path is for unimplemented checks, so we err on the side of not
// reporting any errors
_ => return,
}
let cx = MatchCheckCtx {
module: self.owner.module(db.upcast()),
match_expr,
infer: &infer,
db,
pattern_arena: &pattern_arena,
eprint_panic_context: &|| {
use syntax::AstNode;
if let Ok(scrutinee_sptr) = source_map.expr_syntax(match_expr) {
let root = scrutinee_sptr.file_syntax(db.upcast());
if let Some(match_ast) = scrutinee_sptr.value.to_node(&root).syntax().parent() {
eprintln!(
"Match checking is about to panic on this expression:\n{}",
match_ast.to_string(),
);
}
}
},
};
let report = compute_match_usefulness(&cx, &m_arms);
if let Ok(source_ptr) = source_map.expr_syntax(id) {
let root = source_ptr.file_syntax(db.upcast());
if let ast::Expr::MatchExpr(match_expr) = &source_ptr.value.to_node(&root) {
if let (Some(match_expr), Some(arms)) =
(match_expr.expr(), match_expr.match_arm_list())
{
self.sink.push(MissingMatchArms {
file: source_ptr.file_id,
match_expr: AstPtr::new(&match_expr),
arms: AstPtr::new(&arms),
})
// FIXME Report unreacheble arms
// https://github.com/rust-lang/rust/blob/25c15cdbe/compiler/rustc_mir_build/src/thir/pattern/check_match.rs#L200-L201
let witnesses = report.non_exhaustiveness_witnesses;
// FIXME Report witnesses
// eprintln!("compute_match_usefulness(..) -> {:?}", &witnesses);
if !witnesses.is_empty() {
if let Ok(source_ptr) = source_map.expr_syntax(id) {
let root = source_ptr.file_syntax(db.upcast());
if let ast::Expr::MatchExpr(match_expr) = &source_ptr.value.to_node(&root) {
if let (Some(match_expr), Some(arms)) =
(match_expr.expr(), match_expr.match_arm_list())
{
self.sink.push(MissingMatchArms {
file: source_ptr.file_id,
match_expr: AstPtr::new(&match_expr),
arms: AstPtr::new(&arms),
})
}
}
}
}
}
fn lower_pattern(
&self,
pat: PatId,
pattern_arena: &mut PatternArena,
db: &dyn HirDatabase,
body: &Body,
have_errors: &mut bool,
) -> match_check::PatId {
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));
if !patcx.errors.is_empty() {
*have_errors = true;
}
pattern
}
fn validate_results_in_tail_expr(&mut self, body_id: ExprId, id: ExprId, db: &dyn HirDatabase) {
// the mismatch will be on the whole block currently
let mismatch = match self.infer.type_mismatch_for_expr(body_id) {

1412
crates/hir_ty/src/diagnostics/match_check.rs
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File diff suppressed because it is too large Load Diff

907
crates/hir_ty/src/diagnostics/match_check/deconstruct_pat.rs Normal file
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@ -0,0 +1,907 @@
//! [`super::usefulness`] explains most of what is happening in this file. As explained there,
//! values and patterns are made from constructors applied to fields. This file defines a
//! `Constructor` enum, a `Fields` struct, and various operations to manipulate them and convert
//! them from/to patterns.
//!
//! There's one idea that is not detailed in [`super::usefulness`] because the details are not
//! needed there: _constructor splitting_.
//!
//! # Constructor splitting
//!
//! The idea is as follows: given a constructor `c` and a matrix, we want to specialize in turn
//! with all the value constructors that are covered by `c`, and compute usefulness for each.
//! Instead of listing all those constructors (which is intractable), we group those value
//! constructors together as much as possible. Example:
//!
//! ```
//! match (0, false) {
//! (0 ..=100, true) => {} // `p_1`
//! (50..=150, false) => {} // `p_2`
//! (0 ..=200, _) => {} // `q`
//! }
//! ```
//!
//! The naive approach would try all numbers in the range `0..=200`. But we can be a lot more
//! clever: `0` and `1` for example will match the exact same rows, and return equivalent
//! witnesses. In fact all of `0..50` would. We can thus restrict our exploration to 4
//! constructors: `0..50`, `50..=100`, `101..=150` and `151..=200`. That is enough and infinitely
//! more tractable.
//!
//! We capture this idea in a function `split(p_1 ... p_n, c)` which returns a list of constructors
//! `c'` covered by `c`. Given such a `c'`, we require that all value ctors `c''` covered by `c'`
//! return an equivalent set of witnesses after specializing and computing usefulness.
//! In the example above, witnesses for specializing by `c''` covered by `0..50` will only differ
//! in their first element.
//!
//! We usually also ask that the `c'` together cover all of the original `c`. However we allow
//! skipping some constructors as long as it doesn't change whether the resulting list of witnesses
//! is empty of not. We use this in the wildcard `_` case.
//!
//! Splitting is implemented in the [`Constructor::split`] function. We don't do splitting for
//! or-patterns; instead we just try the alternatives one-by-one. For details on splitting
//! wildcards, see [`SplitWildcard`]; for integer ranges, see [`SplitIntRange`]; for slices, see
//! [`SplitVarLenSlice`].
use std::{
cmp::{max, min},
iter::once,
ops::RangeInclusive,
};
use hir_def::{EnumVariantId, HasModule, LocalFieldId, VariantId};
use smallvec::{smallvec, SmallVec};
use crate::{AdtId, Interner, Scalar, Ty, TyExt, TyKind};
use super::{
usefulness::{MatchCheckCtx, PatCtxt},
FieldPat, Pat, PatId, PatKind,
};
use self::Constructor::*;
/// [Constructor] uses this in umimplemented variants.
/// It allows porting match expressions from upstream algorithm without losing semantics.
#[derive(Copy, Clone, Debug, PartialEq, Eq)]
pub(super) enum Void {}
/// An inclusive interval, used for precise integer exhaustiveness checking.
/// `IntRange`s always store a contiguous range. This means that values are
/// encoded such that `0` encodes the minimum value for the integer,
/// regardless of the signedness.
/// For example, the pattern `-128..=127i8` is encoded as `0..=255`.
/// This makes comparisons and arithmetic on interval endpoints much more
/// straightforward. See `signed_bias` for details.
///
/// `IntRange` is never used to encode an empty range or a "range" that wraps
/// around the (offset) space: i.e., `range.lo <= range.hi`.
#[derive(Clone, Debug, PartialEq, Eq)]
pub(super) struct IntRange {
range: RangeInclusive<u128>,
}
impl IntRange {
#[inline]
fn is_integral(ty: &Ty) -> bool {
match ty.kind(&Interner) {
TyKind::Scalar(Scalar::Char)
| TyKind::Scalar(Scalar::Int(_))
| TyKind::Scalar(Scalar::Uint(_))
| TyKind::Scalar(Scalar::Bool) => true,
_ => false,
}
}
fn is_singleton(&self) -> bool {
self.range.start() == self.range.end()
}
fn boundaries(&self) -> (u128, u128) {
(*self.range.start(), *self.range.end())
}
#[inline]
fn from_bool(value: bool) -> IntRange {
let val = value as u128;
IntRange { range: val..=val }
}
#[inline]
fn from_range(lo: u128, hi: u128, scalar_ty: Scalar) -> IntRange {
if let Scalar::Bool = scalar_ty {
IntRange { range: lo..=hi }
} else {
unimplemented!()
}
}
fn is_subrange(&self, other: &Self) -> bool {
other.range.start() <= self.range.start() && self.range.end() <= other.range.end()
}
fn intersection(&self, other: &Self) -> Option<Self> {
let (lo, hi) = self.boundaries();
let (other_lo, other_hi) = other.boundaries();
if lo <= other_hi && other_lo <= hi {
Some(IntRange { range: max(lo, other_lo)..=min(hi, other_hi) })
} else {
None
}
}
/// See `Constructor::is_covered_by`
fn is_covered_by(&self, other: &Self) -> bool {
if self.intersection(other).is_some() {
// Constructor splitting should ensure that all intersections we encounter are actually
// inclusions.
assert!(self.is_subrange(other));
true
} else {
false
}
}
}
/// Represents a border between 2 integers. Because the intervals spanning borders must be able to
/// cover every integer, we need to be able to represent 2^128 + 1 such borders.
#[derive(Debug, Clone, Copy, PartialEq, Eq, PartialOrd, Ord)]
enum IntBorder {
JustBefore(u128),
AfterMax,
}
/// A range of integers that is partitioned into disjoint subranges. This does constructor
/// splitting for integer ranges as explained at the top of the file.
///
/// This is fed multiple ranges, and returns an output that covers the input, but is split so that
/// the only intersections between an output range and a seen range are inclusions. No output range
/// straddles the boundary of one of the inputs.
///
/// The following input:
/// ```
/// |-------------------------| // `self`
/// |------| |----------| |----|
/// |-------| |-------|
/// ```
/// would be iterated over as follows:
/// ```
/// ||---|--||-|---|---|---|--|
/// ```
#[derive(Debug, Clone)]
struct SplitIntRange {
/// The range we are splitting
range: IntRange,
/// The borders of ranges we have seen. They are all contained within `range`. This is kept
/// sorted.
borders: Vec<IntBorder>,
}
impl SplitIntRange {
fn new(range: IntRange) -> Self {
SplitIntRange { range, borders: Vec::new() }
}
/// Internal use
fn to_borders(r: IntRange) -> [IntBorder; 2] {
use IntBorder::*;
let (lo, hi) = r.boundaries();
let lo = JustBefore(lo);
let hi = match hi.checked_add(1) {
Some(m) => JustBefore(m),
None => AfterMax,
};
[lo, hi]
}
/// Add ranges relative to which we split.
fn split(&mut self, ranges: impl Iterator<Item = IntRange>) {
let this_range = &self.range;
let included_ranges = ranges.filter_map(|r| this_range.intersection(&r));
let included_borders = included_ranges.flat_map(|r| {
let borders = Self::to_borders(r);
once(borders[0]).chain(once(borders[1]))
});
self.borders.extend(included_borders);
self.borders.sort_unstable();
}
/// Iterate over the contained ranges.
fn iter(&self) -> impl Iterator<Item = IntRange> + '_ {
use IntBorder::*;
let self_range = Self::to_borders(self.range.clone());
// Start with the start of the range.
let mut prev_border = self_range[0];
self.borders
.iter()
.copied()
// End with the end of the range.
.chain(once(self_range[1]))
// List pairs of adjacent borders.
.map(move |border| {
let ret = (prev_border, border);
prev_border = border;
ret
})
// Skip duplicates.
.filter(|(prev_border, border)| prev_border != border)
// Finally, convert to ranges.
.map(|(prev_border, border)| {
let range = match (prev_border, border) {
(JustBefore(n), JustBefore(m)) if n < m => n..=(m - 1),
(JustBefore(n), AfterMax) => n..=u128::MAX,
_ => unreachable!(), // Ruled out by the sorting and filtering we did
};
IntRange { range }
})
}
}
/// A constructor for array and slice patterns.
#[derive(Copy, Clone, Debug, PartialEq, Eq)]
pub(super) struct Slice {
_unimplemented: Void,
}
impl Slice {
/// See `Constructor::is_covered_by`
fn is_covered_by(self, _other: Self) -> bool {
unimplemented!() // never called as Slice contains Void
}
}
/// A value can be decomposed into a constructor applied to some fields. This struct represents
/// the constructor. See also `Fields`.
///
/// `pat_constructor` retrieves the constructor corresponding to a pattern.
/// `specialize_constructor` returns the list of fields corresponding to a pattern, given a
/// constructor. `Constructor::apply` reconstructs the pattern from a pair of `Constructor` and
/// `Fields`.
#[allow(dead_code)]
#[derive(Clone, Debug, PartialEq)]
pub(super) enum Constructor {
/// The constructor for patterns that have a single constructor, like tuples, struct patterns
/// and fixed-length arrays.
Single,
/// Enum variants.
Variant(EnumVariantId),
/// Ranges of integer literal values (`2`, `2..=5` or `2..5`).
IntRange(IntRange),
/// Ranges of floating-point literal values (`2.0..=5.2`).
FloatRange(Void),
/// String literals. Strings are not quite the same as `&[u8]` so we treat them separately.
Str(Void),
/// Array and slice patterns.
Slice(Slice),
/// Constants that must not be matched structurally. They are treated as black
/// boxes for the purposes of exhaustiveness: we must not inspect them, and they
/// don't count towards making a match exhaustive.
Opaque,
/// Fake extra constructor for enums that aren't allowed to be matched exhaustively. Also used
/// 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,
/// Wildcard pattern.
Wildcard,
}
impl Constructor {
pub(super) fn is_wildcard(&self) -> bool {
matches!(self, Wildcard)
}
fn as_int_range(&self) -> Option<&IntRange> {
match self {
IntRange(range) => Some(range),
_ => None,
}
}
fn as_slice(&self) -> Option<Slice> {
match self {
Slice(slice) => Some(*slice),
_ => None,
}
}
fn variant_id_for_adt(&self, adt: hir_def::AdtId) -> VariantId {
match *self {
Variant(id) => id.into(),
Single => {
assert!(!matches!(adt, hir_def::AdtId::EnumId(_)));
match adt {
hir_def::AdtId::EnumId(_) => unreachable!(),
hir_def::AdtId::StructId(id) => id.into(),
hir_def::AdtId::UnionId(id) => id.into(),
}
}
_ => panic!("bad constructor {:?} for adt {:?}", self, adt),
}
}
/// 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 { .. } => cx.bug("Or-pattern should have been expanded earlier on."),
}
}
/// Some constructors (namely `Wildcard`, `IntRange` and `Slice`) actually stand for a set of actual
/// constructors (like variants, integers or fixed-sized slices). When specializing for these
/// constructors, we want to be specialising for the actual underlying constructors.
/// Naively, we would simply return the list of constructors they correspond to. We instead are
/// more clever: if there are constructors that we know will behave the same wrt the current
/// matrix, we keep them grouped. For example, all slices of a sufficiently large length
/// will either be all useful or all non-useful with a given matrix.
///
/// See the branches for details on how the splitting is done.
///
/// This function may discard some irrelevant constructors if this preserves behavior and
/// diagnostics. Eg. for the `_` case, we ignore the constructors already present in the
/// matrix, unless all of them are.
pub(super) fn split<'a>(
&self,
pcx: PatCtxt<'_>,
ctors: impl Iterator<Item = &'a Constructor> + Clone,
) -> SmallVec<[Self; 1]> {
match self {
Wildcard => {
let mut split_wildcard = SplitWildcard::new(pcx);
split_wildcard.split(pcx, ctors);
split_wildcard.into_ctors(pcx)
}
// Fast-track if the range is trivial. In particular, we don't do the overlapping
// ranges check.
IntRange(ctor_range) if !ctor_range.is_singleton() => {
let mut split_range = SplitIntRange::new(ctor_range.clone());
let int_ranges = ctors.filter_map(|ctor| ctor.as_int_range());
split_range.split(int_ranges.cloned());
split_range.iter().map(IntRange).collect()
}
Slice(_) => unimplemented!(),
// Any other constructor can be used unchanged.
_ => smallvec![self.clone()],
}
}
/// Returns whether `self` is covered by `other`, i.e. whether `self` is a subset of `other`.
/// For the simple cases, this is simply checking for equality. For the "grouped" constructors,
/// this checks for inclusion.
// We inline because this has a single call site in `Matrix::specialize_constructor`.
#[inline]
pub(super) fn is_covered_by(&self, pcx: PatCtxt<'_>, other: &Self) -> bool {
// This must be kept in sync with `is_covered_by_any`.
match (self, other) {
// Wildcards cover anything
(_, Wildcard) => true,
// The missing ctors are not covered by anything in the matrix except wildcards.
(Missing, _) | (Wildcard, _) => false,
(Single, Single) => true,
(Variant(self_id), Variant(other_id)) => self_id == other_id,
(IntRange(self_range), IntRange(other_range)) => self_range.is_covered_by(other_range),
(FloatRange(..), FloatRange(..)) => {
unimplemented!()
}
(Str(..), Str(..)) => {
unimplemented!()
}
(Slice(self_slice), Slice(other_slice)) => self_slice.is_covered_by(*other_slice),
// We are trying to inspect an opaque constant. Thus we skip the row.
(Opaque, _) | (_, Opaque) => false,
// Only a wildcard pattern can match the special extra constructor.
(NonExhaustive, _) => false,
_ => pcx.cx.bug(&format!(
"trying to compare incompatible constructors {:?} and {:?}",
self, other
)),
}
}
/// Faster version of `is_covered_by` when applied to many constructors. `used_ctors` is
/// assumed to be built from `matrix.head_ctors()` with wildcards filtered out, and `self` is
/// assumed to have been split from a wildcard.
fn is_covered_by_any(&self, pcx: PatCtxt<'_>, used_ctors: &[Constructor]) -> bool {
if used_ctors.is_empty() {
return false;
}
// This must be kept in sync with `is_covered_by`.
match self {
// If `self` is `Single`, `used_ctors` cannot contain anything else than `Single`s.
Single => !used_ctors.is_empty(),
Variant(_) => used_ctors.iter().any(|c| c == self),
IntRange(range) => used_ctors
.iter()
.filter_map(|c| c.as_int_range())
.any(|other| range.is_covered_by(other)),
Slice(slice) => used_ctors
.iter()
.filter_map(|c| c.as_slice())
.any(|other| slice.is_covered_by(other)),
// This constructor is never covered by anything else
NonExhaustive => false,
Str(..) | FloatRange(..) | Opaque | Missing | Wildcard => {
pcx.cx.bug(&format!("found unexpected ctor in all_ctors: {:?}", self))
}
}
}
}
/// A wildcard constructor that we split relative to the constructors in the matrix, as explained
/// at the top of the file.
///
/// A constructor that is not present in the matrix rows will only be covered by the rows that have
/// wildcards. Thus we can group all of those constructors together; we call them "missing
/// constructors". Splitting a wildcard would therefore list all present constructors individually
/// (or grouped if they are integers or slices), and then all missing constructors together as a
/// group.
///
/// However we can go further: since any constructor will match the wildcard rows, and having more
/// rows can only reduce the amount of usefulness witnesses, we can skip the present constructors
/// and only try the missing ones.
/// This will not preserve the whole list of witnesses, but will preserve whether the list is empty
/// or not. In fact this is quite natural from the point of view of diagnostics too. This is done
/// in `to_ctors`: in some cases we only return `Missing`.
#[derive(Debug)]
pub(super) struct SplitWildcard {
/// Constructors seen in the matrix.
matrix_ctors: Vec<Constructor>,
/// All the constructors for this type
all_ctors: SmallVec<[Constructor; 1]>,
}
impl SplitWildcard {
pub(super) fn new(pcx: PatCtxt<'_>) -> Self {
let cx = pcx.cx;
let make_range = |start, end, scalar| IntRange(IntRange::from_range(start, end, scalar));
// Unhandled types are treated as non-exhaustive. Being explicit here instead of falling
// to catchall arm to ease further implementation.
let unhandled = || smallvec![NonExhaustive];
// This determines the set of all possible constructors for the type `pcx.ty`. For numbers,
// arrays and slices we use ranges and variable-length slices when appropriate.
//
// If the `exhaustive_patterns` feature is enabled, we make sure to omit constructors that
// are statically impossible. E.g., for `Option<!>`, we do not include `Some(_)` in the
// returned list of constructors.
// Invariant: this is empty if and only if the type is uninhabited (as determined by
// `cx.is_uninhabited()`).
let all_ctors = match pcx.ty.kind(&Interner) {
TyKind::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) => {
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
// additional "unknown" constructor.
// There is no point in enumerating all possible variants, because the user can't
// actually match against them all themselves. So we always return only the fictitious
// constructor.
// E.g., in an example like:
//
// ```
// let err: io::ErrorKind = ...;
// match err {
// io::ErrorKind::NotFound => {},
// }
// ```
//
// 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);
// 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
// exception is if the pattern is at the top level, because we want empty matches to be
// considered exhaustive.
let is_secretly_empty = enum_data.variants.is_empty()
&& !cx.feature_exhaustive_patterns()
&& !pcx.is_top_level;
if is_secretly_empty || is_declared_nonexhaustive {
smallvec![NonExhaustive]
} else if cx.feature_exhaustive_patterns() {
unimplemented!() // see MatchCheckCtx.feature_exhaustive_patterns()
} else {
enum_data
.variants
.iter()
.map(|(local_id, ..)| Variant(EnumVariantId { parent: enum_id, local_id }))
.collect()
}
}
TyKind::Scalar(Scalar::Char) => unhandled(),
TyKind::Scalar(Scalar::Int(..)) | TyKind::Scalar(Scalar::Uint(..)) => unhandled(),
TyKind::Never if !cx.feature_exhaustive_patterns() && !pcx.is_top_level => {
smallvec![NonExhaustive]
}
TyKind::Never => SmallVec::new(),
_ if cx.is_uninhabited(&pcx.ty) => SmallVec::new(),
TyKind::Adt(..) | TyKind::Tuple(..) | TyKind::Ref(..) => smallvec![Single],
// This type is one for which we cannot list constructors, like `str` or `f64`.
_ => smallvec![NonExhaustive],
};
SplitWildcard { matrix_ctors: Vec::new(), all_ctors }
}
/// Pass a set of constructors relative to which to split this one. Don't call twice, it won't
/// do what you want.
pub(super) fn split<'a>(
&mut self,
pcx: PatCtxt<'_>,
ctors: impl Iterator<Item = &'a Constructor> + Clone,
) {
// Since `all_ctors` never contains wildcards, this won't recurse further.
self.all_ctors =
self.all_ctors.iter().flat_map(|ctor| ctor.split(pcx, ctors.clone())).collect();
self.matrix_ctors = ctors.filter(|c| !c.is_wildcard()).cloned().collect();
}
/// Whether there are any value constructors for this type that are not present in the matrix.
fn any_missing(&self, pcx: PatCtxt<'_>) -> bool {
self.iter_missing(pcx).next().is_some()
}
/// Iterate over the constructors for this type that are not present in the matrix.
pub(super) fn iter_missing<'a>(
&'a self,
pcx: PatCtxt<'a>,
) -> impl Iterator<Item = &'a Constructor> {
self.all_ctors.iter().filter(move |ctor| !ctor.is_covered_by_any(pcx, &self.matrix_ctors))
}
/// Return the set of constructors resulting from splitting the wildcard. As explained at the
/// top of the file, if any constructors are missing we can ignore the present ones.
fn into_ctors(self, pcx: PatCtxt<'_>) -> SmallVec<[Constructor; 1]> {
if self.any_missing(pcx) {
// Some constructors are missing, thus we can specialize with the special `Missing`
// constructor, which stands for those constructors that are not seen in the matrix,
// and matches the same rows as any of them (namely the wildcard rows). See the top of
// the file for details.
// However, when all constructors are missing we can also specialize with the full
// `Wildcard` constructor. The difference will depend on what we want in diagnostics.
// If some constructors are missing, we typically want to report those constructors,
// e.g.:
// ```
// enum Direction { N, S, E, W }
// let Direction::N = ...;
// ```
// we can report 3 witnesses: `S`, `E`, and `W`.
//
// However, if the user didn't actually specify a constructor
// in this arm, e.g., in
// ```
// let x: (Direction, Direction, bool) = ...;
// let (_, _, false) = x;
// ```
// we don't want to show all 16 possible witnesses `(<direction-1>, <direction-2>,
// true)` - we are satisfied with `(_, _, true)`. So if all constructors are missing we
// prefer to report just a wildcard `_`.
//
// The exception is: if we are at the top-level, for example in an empty match, we
// sometimes prefer reporting the list of constructors instead of just `_`.
let report_when_all_missing = pcx.is_top_level && !IntRange::is_integral(pcx.ty);
let ctor = if !self.matrix_ctors.is_empty() || report_when_all_missing {
Missing
} else {
Wildcard
};
return smallvec![ctor];
}
// All the constructors are present in the matrix, so we just go through them all.
self.all_ctors
}
}
/// A value can be decomposed into a constructor applied to some fields. This struct represents
/// those fields, generalized to allow patterns in each field. See also `Constructor`.
/// This is constructed from a constructor using [`Fields::wildcards()`].
///
/// If a private or `non_exhaustive` field is uninhabited, the code mustn't observe that it is
/// uninhabited. For that, we filter these fields out of the matrix. This is handled automatically
/// in `Fields`. This filtering is uncommon in practice, because uninhabited fields are rarely used,
/// so we avoid it when possible to preserve performance.
#[derive(Debug, Clone)]
pub(super) enum Fields {
/// Lists of patterns that don't contain any filtered fields.
/// `Slice` and `Vec` behave the same; the difference is only to avoid allocating and
/// triple-dereferences when possible. Frankly this is premature optimization, I (Nadrieril)
/// have not measured if it really made a difference.
Vec(SmallVec<[PatId; 2]>),
}
impl Fields {
/// Internal use. Use `Fields::wildcards()` instead.
/// Must not be used if the pattern is a field of a struct/tuple/variant.
fn from_single_pattern(pat: PatId) -> Self {
Fields::Vec(smallvec![pat])
}
/// Convenience; internal use.
fn wildcards_from_tys(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)
}
/// 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()));
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::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))
} 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")
}
}
}
ty_kind => {
cx.bug(&format!("Unexpected type for `Single` constructor: {:?}", ty_kind))
}
},
Slice(..) => {
unimplemented!()
}
Str(..) | FloatRange(..) | IntRange(..) | NonExhaustive | Opaque | Missing
| Wildcard => Fields::Vec(Default::default()),
};
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((adt, substs)) = pcx.ty.as_adt() {
if let hir_def::AdtId::EnumId(_) = adt {
let enum_variant = match ctor {
&Variant(id) => id,
_ => unreachable!(),
};
PatKind::Variant { substs: substs.clone(), enum_variant, subpatterns }
} else {
PatKind::Leaf { 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(..) => {
pcx.cx.bug(&format!("bad slice pattern {:?} {:?}", ctor, pcx.ty))
}
_ => 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 => pcx.cx.bug("we should not try to apply an opaque constructor"),
Missing => pcx.cx.bug(
"trying to apply the `Missing` constructor;\
this should have been done in `apply_constructors`",
),
};
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(),
}
}
}
fn is_field_list_non_exhaustive(variant_id: VariantId, cx: &MatchCheckCtx<'_>) -> bool {
let attr_def_id = match variant_id {
VariantId::EnumVariantId(id) => id.into(),
VariantId::StructId(id) => id.into(),
VariantId::UnionId(id) => id.into(),
};
cx.db.attrs(attr_def_id).by_key("non_exhaustive").exists()
}
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(), "owned_box".into()) {
Some(LangItemTarget::StructId(box_id)) => adt == box_id.into(),
_ => false,
}
}

56
crates/hir_ty/src/diagnostics/match_check/pat_util.rs Normal file
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@ -0,0 +1,56 @@
//! Pattern untilities.
//!
//! Originates from `rustc_hir::pat_util`
use std::iter::{Enumerate, ExactSizeIterator};
pub(crate) struct EnumerateAndAdjust<I> {
enumerate: Enumerate<I>,
gap_pos: usize,
gap_len: usize,
}
impl<I> Iterator for EnumerateAndAdjust<I>
where
I: Iterator,
{
type Item = (usize, <I as Iterator>::Item);
fn next(&mut self) -> Option<(usize, <I as Iterator>::Item)> {
self.enumerate
.next()
.map(|(i, elem)| (if i < self.gap_pos { i } else { i + self.gap_len }, elem))
}
fn size_hint(&self) -> (usize, Option<usize>) {
self.enumerate.size_hint()
}
}
pub(crate) trait EnumerateAndAdjustIterator {
fn enumerate_and_adjust(
self,
expected_len: usize,
gap_pos: Option<usize>,
) -> EnumerateAndAdjust<Self>
where
Self: Sized;
}
impl<T: ExactSizeIterator> EnumerateAndAdjustIterator for T {
fn enumerate_and_adjust(
self,
expected_len: usize,
gap_pos: Option<usize>,
) -> EnumerateAndAdjust<Self>
where
Self: Sized,
{
let actual_len = self.len();
EnumerateAndAdjust {
enumerate: self.enumerate(),
gap_pos: gap_pos.unwrap_or(expected_len),
gap_len: expected_len - actual_len,
}
}
}

1188
crates/hir_ty/src/diagnostics/match_check/usefulness.rs Normal file
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