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Gather rustc-specific functions around MatchCheckCtxt

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Nadrieril 2023-12-10 22:14:00 +01:00
parent 281002d42c
commit 3691a0aee5
8 changed files with 903 additions and 900 deletions
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581
compiler/rustc_pattern_analysis/src/pat.rs
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@ -2,175 +2,19 @@
//! fields. This file defines types that represent patterns in this way.
use std::cell::Cell;
use std::fmt;
use std::iter::once;
use smallvec::{smallvec, SmallVec};
use rustc_data_structures::captures::Captures;
use rustc_hir::RangeEnd;
use rustc_index::Idx;
use rustc_middle::mir;
use rustc_middle::thir::{FieldPat, Pat, PatKind, PatRange};
use rustc_middle::ty::{self, Ty, VariantDef};
use rustc_middle::ty::{self, Ty};
use rustc_span::{Span, DUMMY_SP};
use rustc_target::abi::FieldIdx;
use self::Constructor::*;
use self::SliceKind::*;
use crate::constructor::{Constructor, IntRange, MaybeInfiniteInt, OpaqueId, Slice, SliceKind};
use crate::usefulness::{MatchCheckCtxt, PatCtxt};
/// 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 for a constructor using [`Fields::wildcards()`]. The idea is that
/// [`Fields::wildcards()`] constructs a list of fields where all entries are wildcards, and then
/// given a pattern we fill some of the fields with its subpatterns.
/// In the following example `Fields::wildcards` returns `[_, _, _, _]`. Then in
/// `extract_pattern_arguments` we fill some of the entries, and the result is
/// `[Some(0), _, _, _]`.
/// ```compile_fail,E0004
/// # fn foo() -> [Option<u8>; 4] { [None; 4] }
/// let x: [Option<u8>; 4] = foo();
/// match x {
/// [Some(0), ..] => {}
/// }
/// ```
///
/// Note that the number of fields of a constructor may not match the fields declared in the
/// original struct/variant. This happens if a private or `non_exhaustive` field is uninhabited,
/// because the code mustn't observe that it is uninhabited. In that case that field is not
/// included in `fields`. For that reason, when you have a `FieldIdx` you must use
/// `index_with_declared_idx`.
#[derive(Debug, Clone, Copy)]
pub struct Fields<'p, 'tcx> {
fields: &'p [DeconstructedPat<'p, 'tcx>],
}
impl<'p, 'tcx> Fields<'p, 'tcx> {
fn empty() -> Self {
Fields { fields: &[] }
}
fn singleton(cx: &MatchCheckCtxt<'p, 'tcx>, field: DeconstructedPat<'p, 'tcx>) -> Self {
let field: &_ = cx.pattern_arena.alloc(field);
Fields { fields: std::slice::from_ref(field) }
}
pub fn from_iter(
cx: &MatchCheckCtxt<'p, 'tcx>,
fields: impl IntoIterator<Item = DeconstructedPat<'p, 'tcx>>,
) -> Self {
let fields: &[_] = cx.pattern_arena.alloc_from_iter(fields);
Fields { fields }
}
fn wildcards_from_tys(
cx: &MatchCheckCtxt<'p, 'tcx>,
tys: impl IntoIterator<Item = Ty<'tcx>>,
) -> Self {
Fields::from_iter(cx, tys.into_iter().map(|ty| DeconstructedPat::wildcard(ty, DUMMY_SP)))
}
// 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.
pub(crate) fn list_variant_nonhidden_fields<'a>(
cx: &'a MatchCheckCtxt<'p, 'tcx>,
ty: Ty<'tcx>,
variant: &'a VariantDef,
) -> impl Iterator<Item = (FieldIdx, Ty<'tcx>)> + Captures<'a> + Captures<'p> {
let ty::Adt(adt, args) = ty.kind() else { bug!() };
// Whether we must not match the fields of this variant exhaustively.
let is_non_exhaustive = variant.is_field_list_non_exhaustive() && !adt.did().is_local();
variant.fields.iter().enumerate().filter_map(move |(i, field)| {
let ty = field.ty(cx.tcx, args);
// `field.ty()` doesn't normalize after substituting.
let ty = cx.tcx.normalize_erasing_regions(cx.param_env, ty);
let is_visible = adt.is_enum() || field.vis.is_accessible_from(cx.module, cx.tcx);
let is_uninhabited = cx.tcx.features().exhaustive_patterns && cx.is_uninhabited(ty);
if is_uninhabited && (!is_visible || is_non_exhaustive) {
None
} else {
Some((FieldIdx::new(i), ty))
}
})
}
/// Creates a new list of wildcard fields for a given constructor. The result must have a
/// length of `constructor.arity()`.
#[instrument(level = "trace")]
pub(super) fn wildcards(pcx: &PatCtxt<'_, 'p, 'tcx>, constructor: &Constructor<'tcx>) -> Self {
let ret = match constructor {
Single | Variant(_) => match pcx.ty.kind() {
ty::Tuple(fs) => Fields::wildcards_from_tys(pcx.cx, fs.iter()),
ty::Ref(_, rty, _) => Fields::wildcards_from_tys(pcx.cx, once(*rty)),
ty::Adt(adt, args) => {
if adt.is_box() {
// 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.
Fields::wildcards_from_tys(pcx.cx, once(args.type_at(0)))
} else {
let variant = &adt.variant(constructor.variant_index_for_adt(*adt));
let tys = Fields::list_variant_nonhidden_fields(pcx.cx, pcx.ty, variant)
.map(|(_, ty)| ty);
Fields::wildcards_from_tys(pcx.cx, tys)
}
}
_ => bug!("Unexpected type for `Single` constructor: {:?}", pcx),
},
Slice(slice) => match *pcx.ty.kind() {
ty::Slice(ty) | ty::Array(ty, _) => {
let arity = slice.arity();
Fields::wildcards_from_tys(pcx.cx, (0..arity).map(|_| ty))
}
_ => bug!("bad slice pattern {:?} {:?}", constructor, pcx),
},
Bool(..)
| IntRange(..)
| F32Range(..)
| F64Range(..)
| Str(..)
| Opaque(..)
| NonExhaustive
| Hidden
| Missing { .. }
| Wildcard => Fields::empty(),
Or => {
bug!("called `Fields::wildcards` on an `Or` ctor")
}
};
debug!(?ret);
ret
}
/// Returns the list of patterns.
pub(super) fn iter_patterns<'a>(
&'a self,
) -> impl Iterator<Item = &'p DeconstructedPat<'p, 'tcx>> + Captures<'a> {
self.fields.iter()
}
}
/// Recursively expand this pattern into its subpatterns. Only useful for or-patterns.
fn expand_or_pat<'p, 'tcx>(pat: &'p Pat<'tcx>) -> Vec<&'p Pat<'tcx>> {
fn expand<'p, 'tcx>(pat: &'p Pat<'tcx>, vec: &mut Vec<&'p Pat<'tcx>>) {
if let PatKind::Or { pats } = &pat.kind {
for pat in pats.iter() {
expand(pat, vec);
}
} else {
vec.push(pat)
}
}
let mut pats = Vec::new();
expand(pat, &mut pats);
pats
}
use crate::constructor::{Constructor, SliceKind};
use crate::cx::MatchCheckCtxt;
use crate::usefulness::PatCtxt;
/// Values and patterns can be represented as a constructor applied to some fields. This represents
/// a pattern in this form.
@ -178,9 +22,14 @@ fn expand_or_pat<'p, 'tcx>(pat: &'p Pat<'tcx>) -> Vec<&'p Pat<'tcx>> {
/// during analysis. For this reason they cannot be cloned.
/// A `DeconstructedPat` will almost always come from user input; the only exception are some
/// `Wildcard`s introduced during specialization.
///
/// Note that the number of fields may not match the fields declared in the original struct/variant.
/// This happens if a private or `non_exhaustive` field is uninhabited, because the code mustn't
/// observe that it is uninhabited. In that case that field is not included in `fields`. Care must
/// be taken when converting to/from `thir::Pat`.
pub struct DeconstructedPat<'p, 'tcx> {
ctor: Constructor<'tcx>,
fields: Fields<'p, 'tcx>,
fields: &'p [DeconstructedPat<'p, 'tcx>],
ty: Ty<'tcx>,
span: Span,
/// Whether removing this arm would change the behavior of the match expression.
@ -189,227 +38,18 @@ pub struct DeconstructedPat<'p, 'tcx> {
impl<'p, 'tcx> DeconstructedPat<'p, 'tcx> {
pub(super) fn wildcard(ty: Ty<'tcx>, span: Span) -> Self {
Self::new(Wildcard, Fields::empty(), ty, span)
Self::new(Wildcard, &[], ty, span)
}
pub(super) fn new(
ctor: Constructor<'tcx>,
fields: Fields<'p, 'tcx>,
fields: &'p [DeconstructedPat<'p, 'tcx>],
ty: Ty<'tcx>,
span: Span,
) -> Self {
DeconstructedPat { ctor, fields, ty, span, useful: Cell::new(false) }
}
/// Note: the input patterns must have been lowered through
/// `rustc_mir_build::thir::pattern::check_match::MatchVisitor::lower_pattern`.
pub fn from_pat(cx: &MatchCheckCtxt<'p, 'tcx>, pat: &Pat<'tcx>) -> Self {
let mkpat = |pat| DeconstructedPat::from_pat(cx, pat);
let ctor;
let fields;
match &pat.kind {
PatKind::AscribeUserType { subpattern, .. }
| PatKind::InlineConstant { subpattern, .. } => return mkpat(subpattern),
PatKind::Binding { subpattern: Some(subpat), .. } => return mkpat(subpat),
PatKind::Binding { subpattern: None, .. } | PatKind::Wild => {
ctor = Wildcard;
fields = Fields::empty();
}
PatKind::Deref { subpattern } => {
ctor = Single;
fields = Fields::singleton(cx, mkpat(subpattern));
}
PatKind::Leaf { subpatterns } | PatKind::Variant { subpatterns, .. } => {
match pat.ty.kind() {
ty::Tuple(fs) => {
ctor = Single;
let mut wilds: SmallVec<[_; 2]> =
fs.iter().map(|ty| DeconstructedPat::wildcard(ty, pat.span)).collect();
for pat in subpatterns {
wilds[pat.field.index()] = mkpat(&pat.pattern);
}
fields = Fields::from_iter(cx, wilds);
}
ty::Adt(adt, args) if adt.is_box() => {
// 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 pattern = subpatterns.into_iter().find(|pat| pat.field.index() == 0);
let pat = if let Some(pat) = pattern {
mkpat(&pat.pattern)
} else {
DeconstructedPat::wildcard(args.type_at(0), pat.span)
};
ctor = Single;
fields = Fields::singleton(cx, pat);
}
ty::Adt(adt, _) => {
ctor = match pat.kind {
PatKind::Leaf { .. } => Single,
PatKind::Variant { variant_index, .. } => Variant(variant_index),
_ => bug!(),
};
let variant = &adt.variant(ctor.variant_index_for_adt(*adt));
// 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>> =
(0..variant.fields.len()).map(|_| None).collect();
let tys = Fields::list_variant_nonhidden_fields(cx, pat.ty, variant)
.enumerate()
.map(|(i, (field, ty))| {
field_id_to_id[field.index()] = Some(i);
ty
});
let mut wilds: SmallVec<[_; 2]> =
tys.map(|ty| DeconstructedPat::wildcard(ty, pat.span)).collect();
for pat in subpatterns {
if let Some(i) = field_id_to_id[pat.field.index()] {
wilds[i] = mkpat(&pat.pattern);
}
}
fields = Fields::from_iter(cx, wilds);
}
_ => bug!("pattern has unexpected type: pat: {:?}, ty: {:?}", pat, pat.ty),
}
}
PatKind::Constant { value } => {
match pat.ty.kind() {
ty::Bool => {
ctor = match value.try_eval_bool(cx.tcx, cx.param_env) {
Some(b) => Bool(b),
None => Opaque(OpaqueId::new()),
};
fields = Fields::empty();
}
ty::Char | ty::Int(_) | ty::Uint(_) => {
ctor = match value.try_eval_bits(cx.tcx, cx.param_env) {
Some(bits) => IntRange(IntRange::from_bits(cx.tcx, pat.ty, bits)),
None => Opaque(OpaqueId::new()),
};
fields = Fields::empty();
}
ty::Float(ty::FloatTy::F32) => {
ctor = match value.try_eval_bits(cx.tcx, cx.param_env) {
Some(bits) => {
use rustc_apfloat::Float;
let value = rustc_apfloat::ieee::Single::from_bits(bits);
F32Range(value, value, RangeEnd::Included)
}
None => Opaque(OpaqueId::new()),
};
fields = Fields::empty();
}
ty::Float(ty::FloatTy::F64) => {
ctor = match value.try_eval_bits(cx.tcx, cx.param_env) {
Some(bits) => {
use rustc_apfloat::Float;
let value = rustc_apfloat::ieee::Double::from_bits(bits);
F64Range(value, value, RangeEnd::Included)
}
None => Opaque(OpaqueId::new()),
};
fields = Fields::empty();
}
ty::Ref(_, t, _) if t.is_str() => {
// We want a `&str` constant to behave like a `Deref` pattern, to be compatible
// with other `Deref` patterns. This could have been done in `const_to_pat`,
// but that causes issues with the rest of the matching code.
// So here, the constructor for a `"foo"` pattern is `&` (represented by
// `Single`), and has one field. That field has constructor `Str(value)` and no
// fields.
// Note: `t` is `str`, not `&str`.
let subpattern =
DeconstructedPat::new(Str(*value), Fields::empty(), *t, pat.span);
ctor = Single;
fields = Fields::singleton(cx, subpattern)
}
// All constants that can be structurally matched have already been expanded
// into the corresponding `Pat`s by `const_to_pat`. Constants that remain are
// opaque.
_ => {
ctor = Opaque(OpaqueId::new());
fields = Fields::empty();
}
}
}
PatKind::Range(patrange) => {
let PatRange { lo, hi, end, .. } = patrange.as_ref();
let ty = pat.ty;
ctor = match ty.kind() {
ty::Char | ty::Int(_) | ty::Uint(_) => {
let lo =
MaybeInfiniteInt::from_pat_range_bdy(*lo, ty, cx.tcx, cx.param_env);
let hi =
MaybeInfiniteInt::from_pat_range_bdy(*hi, ty, cx.tcx, cx.param_env);
IntRange(IntRange::from_range(lo, hi, *end))
}
ty::Float(fty) => {
use rustc_apfloat::Float;
let lo = lo.as_finite().map(|c| c.eval_bits(cx.tcx, cx.param_env));
let hi = hi.as_finite().map(|c| c.eval_bits(cx.tcx, cx.param_env));
match fty {
ty::FloatTy::F32 => {
use rustc_apfloat::ieee::Single;
let lo = lo.map(Single::from_bits).unwrap_or(-Single::INFINITY);
let hi = hi.map(Single::from_bits).unwrap_or(Single::INFINITY);
F32Range(lo, hi, *end)
}
ty::FloatTy::F64 => {
use rustc_apfloat::ieee::Double;
let lo = lo.map(Double::from_bits).unwrap_or(-Double::INFINITY);
let hi = hi.map(Double::from_bits).unwrap_or(Double::INFINITY);
F64Range(lo, hi, *end)
}
}
}
_ => bug!("invalid type for range pattern: {}", ty),
};
fields = Fields::empty();
}
PatKind::Array { prefix, slice, suffix } | PatKind::Slice { prefix, slice, suffix } => {
let array_len = match pat.ty.kind() {
ty::Array(_, length) => {
Some(length.eval_target_usize(cx.tcx, cx.param_env) as usize)
}
ty::Slice(_) => None,
_ => span_bug!(pat.span, "bad ty {:?} for slice pattern", pat.ty),
};
let kind = if slice.is_some() {
VarLen(prefix.len(), suffix.len())
} else {
FixedLen(prefix.len() + suffix.len())
};
ctor = Slice(Slice::new(array_len, kind));
fields =
Fields::from_iter(cx, prefix.iter().chain(suffix.iter()).map(|p| mkpat(&*p)));
}
PatKind::Or { .. } => {
ctor = Or;
let pats = expand_or_pat(pat);
fields = Fields::from_iter(cx, pats.into_iter().map(mkpat));
}
PatKind::Never => {
// FIXME(never_patterns): handle `!` in exhaustiveness. This is a sane default
// in the meantime.
ctor = Wildcard;
fields = Fields::empty();
}
PatKind::Error(_) => {
ctor = Opaque(OpaqueId::new());
fields = Fields::empty();
}
}
DeconstructedPat::new(ctor, fields, pat.ty, pat.span)
}
pub(super) fn is_or_pat(&self) -> bool {
matches!(self.ctor, Or)
}
@ -435,7 +75,7 @@ impl<'p, 'tcx> DeconstructedPat<'p, 'tcx> {
pub fn iter_fields<'a>(
&'a self,
) -> impl Iterator<Item = &'p DeconstructedPat<'p, 'tcx>> + Captures<'a> {
self.fields.iter_patterns()
self.fields.iter()
}
/// Specialize this pattern with a constructor.
@ -448,7 +88,7 @@ impl<'p, 'tcx> DeconstructedPat<'p, 'tcx> {
match (&self.ctor, other_ctor) {
(Wildcard, _) => {
// We return a wildcard for each field of `other_ctor`.
Fields::wildcards(pcx, other_ctor).iter_patterns().collect()
pcx.cx.ctor_wildcard_fields(other_ctor, pcx.ty).iter().collect()
}
(Slice(self_slice), Slice(other_slice))
if self_slice.arity() != other_slice.arity() =>
@ -464,8 +104,8 @@ impl<'p, 'tcx> DeconstructedPat<'p, 'tcx> {
let (ty::Slice(inner_ty) | ty::Array(inner_ty, _)) = *self.ty.kind() else {
bug!("bad slice pattern {:?} {:?}", self.ctor, self.ty);
};
let prefix = &self.fields.fields[..prefix];
let suffix = &self.fields.fields[self_slice.arity() - suffix..];
let prefix = &self.fields[..prefix];
let suffix = &self.fields[self_slice.arity() - suffix..];
let wildcard: &_ = pcx
.cx
.pattern_arena
@ -476,7 +116,7 @@ impl<'p, 'tcx> DeconstructedPat<'p, 'tcx> {
}
}
}
_ => self.fields.iter_patterns().collect(),
_ => self.fields.iter().collect(),
}
}
@ -521,94 +161,7 @@ impl<'p, 'tcx> DeconstructedPat<'p, 'tcx> {
/// `Display` impl.
impl<'p, 'tcx> fmt::Debug for DeconstructedPat<'p, 'tcx> {
fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
// Printing lists is a chore.
let mut first = true;
let mut start_or_continue = |s| {
if first {
first = false;
""
} else {
s
}
};
let mut start_or_comma = || start_or_continue(", ");
match &self.ctor {
Single | Variant(_) => match self.ty.kind() {
ty::Adt(def, _) if def.is_box() => {
// 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.
let subpattern = self.iter_fields().next().unwrap();
write!(f, "box {subpattern:?}")
}
ty::Adt(..) | ty::Tuple(..) => {
let variant = match self.ty.kind() {
ty::Adt(adt, _) => Some(adt.variant(self.ctor.variant_index_for_adt(*adt))),
ty::Tuple(_) => None,
_ => unreachable!(),
};
if let Some(variant) = variant {
write!(f, "{}", variant.name)?;
}
// Without `cx`, we can't know which field corresponds to which, so we can't
// get the names of the fields. Instead we just display everything as a tuple
// struct, which should be good enough.
write!(f, "(")?;
for p in self.iter_fields() {
write!(f, "{}", start_or_comma())?;
write!(f, "{p:?}")?;
}
write!(f, ")")
}
// Note: given the expansion of `&str` patterns done in `expand_pattern`, we should
// be careful to detect strings here. However a string literal pattern will never
// be reported as a non-exhaustiveness witness, so we can ignore this issue.
ty::Ref(_, _, mutbl) => {
let subpattern = self.iter_fields().next().unwrap();
write!(f, "&{}{:?}", mutbl.prefix_str(), subpattern)
}
_ => write!(f, "_"),
},
Slice(slice) => {
let mut subpatterns = self.fields.iter_patterns();
write!(f, "[")?;
match slice.kind {
FixedLen(_) => {
for p in subpatterns {
write!(f, "{}{:?}", start_or_comma(), p)?;
}
}
VarLen(prefix_len, _) => {
for p in subpatterns.by_ref().take(prefix_len) {
write!(f, "{}{:?}", start_or_comma(), p)?;
}
write!(f, "{}", start_or_comma())?;
write!(f, "..")?;
for p in subpatterns {
write!(f, "{}{:?}", start_or_comma(), p)?;
}
}
}
write!(f, "]")
}
Bool(b) => write!(f, "{b}"),
// Best-effort, will render signed ranges incorrectly
IntRange(range) => write!(f, "{range:?}"),
F32Range(lo, hi, end) => write!(f, "{lo}{end}{hi}"),
F64Range(lo, hi, end) => write!(f, "{lo}{end}{hi}"),
Str(value) => write!(f, "{value}"),
Opaque(..) => write!(f, "<constant pattern>"),
Or => {
for pat in self.iter_fields() {
write!(f, "{}{:?}", start_or_continue(" | "), pat)?;
}
Ok(())
}
Wildcard | Missing { .. } | NonExhaustive | Hidden => write!(f, "_ : {:?}", self.ty),
}
MatchCheckCtxt::debug_pat(f, self)
}
}
@ -633,11 +186,9 @@ impl<'tcx> WitnessPat<'tcx> {
/// For example, if `ctor` is a `Constructor::Variant` for `Option::Some`, we get the pattern
/// `Some(_)`.
pub(super) fn wild_from_ctor(pcx: &PatCtxt<'_, '_, 'tcx>, ctor: Constructor<'tcx>) -> Self {
// Reuse `Fields::wildcards` to get the types.
let fields = Fields::wildcards(pcx, &ctor)
.iter_patterns()
.map(|deco_pat| Self::wildcard(deco_pat.ty()))
.collect();
let field_tys =
pcx.cx.ctor_wildcard_fields(&ctor, pcx.ty).iter().map(|deco_pat| deco_pat.ty());
let fields = field_tys.map(|ty| Self::wildcard(ty)).collect();
Self::new(ctor, fields, pcx.ty)
}
@ -648,96 +199,6 @@ impl<'tcx> WitnessPat<'tcx> {
self.ty
}
/// Convert back to a `thir::Pat` for diagnostic purposes. This panics for patterns that don't
/// appear in diagnostics, like float ranges.
pub fn to_diagnostic_pat(&self, cx: &MatchCheckCtxt<'_, 'tcx>) -> Pat<'tcx> {
let is_wildcard = |pat: &Pat<'_>| matches!(pat.kind, PatKind::Wild);
let mut subpatterns = self.iter_fields().map(|p| Box::new(p.to_diagnostic_pat(cx)));
let kind = match &self.ctor {
Bool(b) => PatKind::Constant { value: mir::Const::from_bool(cx.tcx, *b) },
IntRange(range) => return range.to_diagnostic_pat(self.ty, cx.tcx),
Single | Variant(_) => match self.ty.kind() {
ty::Tuple(..) => PatKind::Leaf {
subpatterns: subpatterns
.enumerate()
.map(|(i, pattern)| FieldPat { field: FieldIdx::new(i), pattern })
.collect(),
},
ty::Adt(adt_def, _) if adt_def.is_box() => {
// 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() }
}
ty::Adt(adt_def, args) => {
let variant_index = self.ctor.variant_index_for_adt(*adt_def);
let variant = &adt_def.variant(variant_index);
let subpatterns = Fields::list_variant_nonhidden_fields(cx, self.ty, variant)
.zip(subpatterns)
.map(|((field, _ty), pattern)| FieldPat { field, pattern })
.collect();
if adt_def.is_enum() {
PatKind::Variant { adt_def: *adt_def, args, variant_index, 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
// ignore this issue.
ty::Ref(..) => PatKind::Deref { subpattern: subpatterns.next().unwrap() },
_ => bug!("unexpected ctor for type {:?} {:?}", self.ctor, self.ty),
},
Slice(slice) => {
match slice.kind {
FixedLen(_) => PatKind::Slice {
prefix: subpatterns.collect(),
slice: None,
suffix: Box::new([]),
},
VarLen(prefix, _) => {
let mut subpatterns = subpatterns.peekable();
let mut prefix: Vec<_> = subpatterns.by_ref().take(prefix).collect();
if slice.array_len.is_some() {
// Improves diagnostics a bit: if the type is a known-size array, instead
// of reporting `[x, _, .., _, y]`, we prefer to report `[x, .., y]`.
// This is incorrect if the size is not known, since `[_, ..]` captures
// arrays of lengths `>= 1` whereas `[..]` captures any length.
while !prefix.is_empty() && is_wildcard(prefix.last().unwrap()) {
prefix.pop();
}
while subpatterns.peek().is_some()
&& is_wildcard(subpatterns.peek().unwrap())
{
subpatterns.next();
}
}
let suffix: Box<[_]> = subpatterns.collect();
let wild = Pat::wildcard_from_ty(self.ty);
PatKind::Slice {
prefix: prefix.into_boxed_slice(),
slice: Some(Box::new(wild)),
suffix,
}
}
}
}
&Str(value) => PatKind::Constant { value },
Wildcard | NonExhaustive | Hidden => PatKind::Wild,
Missing { .. } => bug!(
"trying to convert a `Missing` constructor into a `Pat`; this is probably a bug,
`Missing` should have been processed in `apply_constructors`"
),
F32Range(..) | F64Range(..) | Opaque(..) | Or => {
bug!("can't convert to pattern: {:?}", self)
}
};
Pat { ty: self.ty, span: DUMMY_SP, kind }
}
pub fn iter_fields<'a>(&'a self) -> impl Iterator<Item = &'a WitnessPat<'tcx>> {
self.fields.iter()
}