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Auto merge of rust-lang#79523 - Nadrieril:fix-usize-ranges, r=varkor
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Fix overlap detection of `usize`/`isize` range patterns

`usize` and `isize` are a bit of a special case in the match usefulness algorithm, because the range of values they contain depends on the platform. Specifically, we don't want `0..usize::MAX` to count as an exhaustive match (see also [`precise_pointer_size_matching`](rust-lang#56354)). The way this was initially implemented is by treating those ranges like float ranges, i.e. with limited cleverness. This means we didn't catch the following as unreachable:
```rust
match 0usize {
    0..10 => {},
    10..20 => {},
    5..15 => {}, // oops, should be detected as unreachable
    _ => {},
}
```
This PRs fixes this oversight. Now the only difference between `usize` and `u64` range patterns is in what ranges count as exhaustive.

r? `@varkor`
`@rustbot` label +A-exhaustiveness-checking
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@bors
bors committed Nov 29, 2020
2 parents 88b8197 + bdd2bdb commit b776d1c
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Showing 4 changed files with 74 additions and 95 deletions.
147 changes: 56 additions & 91 deletions compiler/rustc_mir_build/src/thir/pattern/deconstruct_pat.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -37,14 +37,12 @@ use std::ops::RangeInclusive;
///
/// `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)]
pub(super) struct IntRange<'tcx> {
#[derive(Clone, Debug, PartialEq, Eq)]
pub(super) struct IntRange {
range: RangeInclusive<u128>,
ty: Ty<'tcx>,
span: Span,
}

impl<'tcx> IntRange<'tcx> {
impl IntRange {
#[inline]
fn is_integral(ty: Ty<'_>) -> bool {
matches!(ty.kind(), ty::Char | ty::Int(_) | ty::Uint(_) | ty::Bool)
Expand All @@ -58,14 +56,8 @@ impl<'tcx> IntRange<'tcx> {
(*self.range.start(), *self.range.end())
}

/// Don't treat `usize`/`isize` exhaustively unless the `precise_pointer_size_matching` feature
/// is enabled.
fn treat_exhaustively(&self, tcx: TyCtxt<'tcx>) -> bool {
!self.ty.is_ptr_sized_integral() || tcx.features().precise_pointer_size_matching
}

#[inline]
fn integral_size_and_signed_bias(tcx: TyCtxt<'tcx>, ty: Ty<'_>) -> Option<(Size, u128)> {
fn integral_size_and_signed_bias(tcx: TyCtxt<'_>, ty: Ty<'_>) -> Option<(Size, u128)> {
match *ty.kind() {
ty::Bool => Some((Size::from_bytes(1), 0)),
ty::Char => Some((Size::from_bytes(4), 0)),
Expand All @@ -79,12 +71,11 @@ impl<'tcx> IntRange<'tcx> {
}

#[inline]
fn from_const(
fn from_const<'tcx>(
tcx: TyCtxt<'tcx>,
param_env: ty::ParamEnv<'tcx>,
value: &Const<'tcx>,
span: Span,
) -> Option<IntRange<'tcx>> {
) -> Option<IntRange> {
if let Some((target_size, bias)) = Self::integral_size_and_signed_bias(tcx, value.ty) {
let ty = value.ty;
let val = (|| {
Expand All @@ -101,21 +92,20 @@ impl<'tcx> IntRange<'tcx> {
value.try_eval_bits(tcx, param_env, ty)
})()?;
let val = val ^ bias;
Some(IntRange { range: val..=val, ty, span })
Some(IntRange { range: val..=val })
} else {
None
}
}

#[inline]
fn from_range(
fn from_range<'tcx>(
tcx: TyCtxt<'tcx>,
lo: u128,
hi: u128,
ty: Ty<'tcx>,
end: &RangeEnd,
span: Span,
) -> Option<IntRange<'tcx>> {
) -> Option<IntRange> {
if Self::is_integral(ty) {
// Perform a shift if the underlying types are signed,
// which makes the interval arithmetic simpler.
Expand All @@ -126,14 +116,14 @@ impl<'tcx> IntRange<'tcx> {
// This should have been caught earlier by E0030.
bug!("malformed range pattern: {}..={}", lo, (hi - offset));
}
Some(IntRange { range: lo..=(hi - offset), ty, span })
Some(IntRange { range: lo..=(hi - offset) })
} else {
None
}
}

// The return value of `signed_bias` should be XORed with an endpoint to encode/decode it.
fn signed_bias(tcx: TyCtxt<'tcx>, ty: Ty<'tcx>) -> u128 {
fn signed_bias(tcx: TyCtxt<'_>, ty: Ty<'_>) -> u128 {
match *ty.kind() {
ty::Int(ity) => {
let bits = Integer::from_attr(&tcx, SignedInt(ity)).size().bits() as u128;
Expand All @@ -147,20 +137,13 @@ impl<'tcx> IntRange<'tcx> {
other.range.start() <= self.range.start() && self.range.end() <= other.range.end()
}

fn intersection(&self, tcx: TyCtxt<'tcx>, other: &Self) -> Option<Self> {
let ty = self.ty;
fn intersection(&self, other: &Self) -> Option<Self> {
let (lo, hi) = self.boundaries();
let (other_lo, other_hi) = other.boundaries();
if self.treat_exhaustively(tcx) {
if lo <= other_hi && other_lo <= hi {
let span = other.span;
Some(IntRange { range: max(lo, other_lo)..=min(hi, other_hi), ty, span })
} else {
None
}
if lo <= other_hi && other_lo <= hi {
Some(IntRange { range: max(lo, other_lo)..=min(hi, other_hi) })
} else {
// If the range should not be treated exhaustively, fallback to checking for inclusion.
if self.is_subrange(other) { Some(self.clone()) } else { None }
None
}
}

Expand All @@ -181,24 +164,23 @@ impl<'tcx> IntRange<'tcx> {
lo == other_hi || hi == other_lo
}

fn to_pat(&self, tcx: TyCtxt<'tcx>) -> Pat<'tcx> {
fn to_pat<'tcx>(&self, tcx: TyCtxt<'tcx>, ty: Ty<'tcx>) -> Pat<'tcx> {
let (lo, hi) = self.boundaries();

let bias = IntRange::signed_bias(tcx, self.ty);
let bias = IntRange::signed_bias(tcx, ty);
let (lo, hi) = (lo ^ bias, hi ^ bias);

let ty = ty::ParamEnv::empty().and(self.ty);
let lo_const = ty::Const::from_bits(tcx, lo, ty);
let hi_const = ty::Const::from_bits(tcx, hi, ty);
let env = ty::ParamEnv::empty().and(ty);
let lo_const = ty::Const::from_bits(tcx, lo, env);
let hi_const = ty::Const::from_bits(tcx, hi, env);

let kind = if lo == hi {
PatKind::Constant { value: lo_const }
} else {
PatKind::Range(PatRange { lo: lo_const, hi: hi_const, end: RangeEnd::Included })
};

// This is a brand new pattern, so we don't reuse `self.span`.
Pat { ty: self.ty, span: DUMMY_SP, kind: Box::new(kind) }
Pat { ty, span: DUMMY_SP, kind: Box::new(kind) }
}

/// For exhaustive integer matching, some constructors are grouped within other constructors
Expand Down Expand Up @@ -233,13 +215,11 @@ impl<'tcx> IntRange<'tcx> {
/// boundaries for each interval range, sort them, then create constructors for each new interval
/// between every pair of boundary points. (This essentially sums up to performing the intuitive
/// merging operation depicted above.)
fn split<'p>(
fn split<'p, 'tcx>(
&self,
pcx: PatCtxt<'_, 'p, 'tcx>,
hir_id: Option<HirId>,
) -> SmallVec<[Constructor<'tcx>; 1]> {
let ty = pcx.ty;

/// 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.
Expand All @@ -250,7 +230,7 @@ impl<'tcx> IntRange<'tcx> {
}

// A function for extracting the borders of an integer interval.
fn range_borders(r: IntRange<'_>) -> impl Iterator<Item = Border> {
fn range_borders(r: IntRange) -> impl Iterator<Item = Border> {
let (lo, hi) = r.range.into_inner();
let from = Border::JustBefore(lo);
let to = match hi.checked_add(1) {
Expand All @@ -268,21 +248,23 @@ impl<'tcx> IntRange<'tcx> {
// class lies between 2 borders.
let row_borders = pcx
.matrix
.head_ctors(pcx.cx)
.filter_map(|ctor| ctor.as_int_range())
.filter_map(|range| {
let intersection = self.intersection(pcx.cx.tcx, &range);
.head_ctors_and_spans(pcx.cx)
.filter_map(|(ctor, span)| Some((ctor.as_int_range()?, span)))
.filter_map(|(range, span)| {
let intersection = self.intersection(&range);
let should_lint = self.suspicious_intersection(&range);
if let (Some(range), 1, true) = (&intersection, row_len, should_lint) {
// FIXME: for now, only check for overlapping ranges on simple range
// patterns. Otherwise with the current logic the following is detected
// as overlapping:
// match (10u8, true) {
// (0 ..= 125, false) => {}
// (126 ..= 255, false) => {}
// (0 ..= 255, true) => {}
// }
overlaps.push(range.clone());
// ```
// match (0u8, true) {
// (0 ..= 125, false) => {}
// (125 ..= 255, true) => {}
// _ => {}
// }
// ```
overlaps.push((range.clone(), span));
}
intersection
})
Expand All @@ -291,7 +273,7 @@ impl<'tcx> IntRange<'tcx> {
let mut borders: Vec<_> = row_borders.chain(self_borders).collect();
borders.sort_unstable();

self.lint_overlapping_patterns(pcx.cx.tcx, hir_id, ty, overlaps);
self.lint_overlapping_patterns(pcx, hir_id, overlaps);

// We're going to iterate through every adjacent pair of borders, making sure that
// each represents an interval of nonnegative length, and convert each such
Expand All @@ -309,33 +291,32 @@ impl<'tcx> IntRange<'tcx> {
[Border::JustBefore(n), Border::AfterMax] => Some(n..=u128::MAX),
[Border::AfterMax, _] => None,
})
.map(|range| IntRange { range, ty, span: pcx.span })
.map(|range| IntRange { range })
.map(IntRange)
.collect()
}

fn lint_overlapping_patterns(
&self,
tcx: TyCtxt<'tcx>,
pcx: PatCtxt<'_, '_, '_>,
hir_id: Option<HirId>,
ty: Ty<'tcx>,
overlaps: Vec<IntRange<'tcx>>,
overlaps: Vec<(IntRange, Span)>,
) {
if let (true, Some(hir_id)) = (!overlaps.is_empty(), hir_id) {
tcx.struct_span_lint_hir(
pcx.cx.tcx.struct_span_lint_hir(
lint::builtin::OVERLAPPING_PATTERNS,
hir_id,
self.span,
pcx.span,
|lint| {
let mut err = lint.build("multiple patterns covering the same range");
err.span_label(self.span, "overlapping patterns");
for int_range in overlaps {
err.span_label(pcx.span, "overlapping patterns");
for (int_range, span) in overlaps {
// Use the real type for user display of the ranges:
err.span_label(
int_range.span,
span,
&format!(
"this range overlaps on `{}`",
IntRange { range: int_range.range, ty, span: DUMMY_SP }.to_pat(tcx),
int_range.to_pat(pcx.cx.tcx, pcx.ty),
),
);
}
Expand All @@ -346,8 +327,8 @@ impl<'tcx> IntRange<'tcx> {
}

/// See `Constructor::is_covered_by`
fn is_covered_by<'p>(&self, pcx: PatCtxt<'_, 'p, 'tcx>, other: &Self) -> bool {
if self.intersection(pcx.cx.tcx, other).is_some() {
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));
Expand All @@ -358,13 +339,6 @@ impl<'tcx> IntRange<'tcx> {
}
}

/// Ignore spans when comparing, they don't carry semantic information as they are only for lints.
impl<'tcx> std::cmp::PartialEq for IntRange<'tcx> {
fn eq(&self, other: &Self) -> bool {
self.range == other.range && self.ty == other.ty
}
}

#[derive(Copy, Clone, Debug, PartialEq, Eq)]
enum SliceKind {
/// Patterns of length `n` (`[x, y]`).
Expand Down Expand Up @@ -558,7 +532,7 @@ pub(super) enum Constructor<'tcx> {
/// Enum variants.
Variant(DefId),
/// Ranges of integer literal values (`2`, `2..=5` or `2..5`).
IntRange(IntRange<'tcx>),
IntRange(IntRange),
/// Ranges of floating-point literal values (`2.0..=5.2`).
FloatRange(&'tcx ty::Const<'tcx>, &'tcx ty::Const<'tcx>, RangeEnd),
/// String literals. Strings are not quite the same as `&[u8]` so we treat them separately.
Expand All @@ -581,7 +555,7 @@ impl<'tcx> Constructor<'tcx> {
matches!(self, Wildcard)
}

fn as_int_range(&self) -> Option<&IntRange<'tcx>> {
fn as_int_range(&self) -> Option<&IntRange> {
match self {
IntRange(range) => Some(range),
_ => None,
Expand Down Expand Up @@ -616,8 +590,7 @@ impl<'tcx> Constructor<'tcx> {
Variant(adt_def.variants[variant_index].def_id)
}
PatKind::Constant { value } => {
if let Some(int_range) = IntRange::from_const(cx.tcx, cx.param_env, value, pat.span)
{
if let Some(int_range) = IntRange::from_const(cx.tcx, cx.param_env, value) {
IntRange(int_range)
} else {
match pat.ty.kind() {
Expand All @@ -641,7 +614,6 @@ impl<'tcx> Constructor<'tcx> {
hi.eval_bits(cx.tcx, cx.param_env, hi.ty),
ty,
&end,
pat.span,
) {
IntRange(int_range)
} else {
Expand Down Expand Up @@ -694,11 +666,7 @@ impl<'tcx> Constructor<'tcx> {
Wildcard => Constructor::split_wildcard(pcx),
// Fast-track if the range is trivial. In particular, we don't do the overlapping
// ranges check.
IntRange(ctor_range)
if ctor_range.treat_exhaustively(pcx.cx.tcx) && !ctor_range.is_singleton() =>
{
ctor_range.split(pcx, hir_id)
}
IntRange(ctor_range) if !ctor_range.is_singleton() => ctor_range.split(pcx, hir_id),
Slice(slice @ Slice { kind: VarLen(..), .. }) => slice.split(pcx),
// Any other constructor can be used unchanged.
_ => smallvec![self.clone()],
Expand Down Expand Up @@ -740,9 +708,7 @@ impl<'tcx> Constructor<'tcx> {
(Single, Single) => true,
(Variant(self_id), Variant(other_id)) => self_id == other_id,

(IntRange(self_range), IntRange(other_range)) => {
self_range.is_covered_by(pcx, other_range)
}
(IntRange(self_range), IntRange(other_range)) => self_range.is_covered_by(other_range),
(
FloatRange(self_from, self_to, self_end),
FloatRange(other_from, other_to, other_end),
Expand Down Expand Up @@ -803,15 +769,15 @@ impl<'tcx> Constructor<'tcx> {
IntRange(range) => used_ctors
.iter()
.filter_map(|c| c.as_int_range())
.any(|other| range.is_covered_by(pcx, other)),
.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 | Wildcard => {
bug!("found unexpected ctor in all_ctors: {:?}", self)
span_bug!(pcx.span, "found unexpected ctor in all_ctors: {:?}", self)
}
}
}
Expand All @@ -832,8 +798,7 @@ fn all_constructors<'p, 'tcx>(pcx: PatCtxt<'_, 'p, 'tcx>) -> Vec<Constructor<'tc
let make_range = |start, end| {
IntRange(
// `unwrap()` is ok because we know the type is an integer.
IntRange::from_range(cx.tcx, start, end, pcx.ty, &RangeEnd::Included, pcx.span)
.unwrap(),
IntRange::from_range(cx.tcx, start, end, pcx.ty, &RangeEnd::Included).unwrap(),
)
};
match pcx.ty.kind() {
Expand Down Expand Up @@ -1238,7 +1203,7 @@ impl<'p, 'tcx> Fields<'p, 'tcx> {
},
&Str(value) => PatKind::Constant { value },
&FloatRange(lo, hi, end) => PatKind::Range(PatRange { lo, hi, end }),
IntRange(range) => return range.to_pat(pcx.cx.tcx),
IntRange(range) => return range.to_pat(pcx.cx.tcx, pcx.ty),
NonExhaustive => PatKind::Wild,
Opaque => bug!("we should not try to apply an opaque constructor"),
Wildcard => bug!(
Expand Down
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