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use either::Either;
use rustc_apfloat::Float;
use rustc_hir as hir;
use rustc_index::Idx;
use rustc_infer::infer::{InferCtxt, TyCtxtInferExt};
use rustc_infer::traits::Obligation;
use rustc_middle::mir;
use rustc_middle::mir::interpret::ErrorHandled;
use rustc_middle::thir::{FieldPat, Pat, PatKind};
use rustc_middle::ty::{self, Ty, TyCtxt, TypeVisitableExt, ValTree};
use rustc_span::Span;
use rustc_target::abi::{FieldIdx, VariantIdx};
use rustc_trait_selection::traits::query::evaluate_obligation::InferCtxtExt;
use rustc_trait_selection::traits::ObligationCause;
use tracing::{debug, instrument, trace};
use super::PatCtxt;
use crate::errors::{
ConstPatternDependsOnGenericParameter, CouldNotEvalConstPattern, InvalidPattern, NaNPattern,
PointerPattern, TypeNotPartialEq, TypeNotStructural, UnionPattern, UnsizedPattern,
};
impl<'a, 'tcx> PatCtxt<'a, 'tcx> {
/// Converts a constant to a pattern (if possible).
/// This means aggregate values (like structs and enums) are converted
/// to a pattern that matches the value (as if you'd compared via structural equality).
///
/// Only type system constants are supported, as we are using valtrees
/// as an intermediate step. Unfortunately those don't carry a type
/// so we have to carry one ourselves.
#[instrument(level = "debug", skip(self), ret)]
pub(super) fn const_to_pat(
&self,
c: ty::Const<'tcx>,
ty: Ty<'tcx>,
id: hir::HirId,
span: Span,
) -> Box<Pat<'tcx>> {
let infcx = self.tcx.infer_ctxt().build();
let mut convert = ConstToPat::new(self, id, span, infcx);
convert.to_pat(c, ty)
}
}
struct ConstToPat<'tcx> {
id: hir::HirId,
span: Span,
param_env: ty::ParamEnv<'tcx>,
// inference context used for checking `T: Structural` bounds.
infcx: InferCtxt<'tcx>,
treat_byte_string_as_slice: bool,
}
impl<'tcx> ConstToPat<'tcx> {
fn new(
pat_ctxt: &PatCtxt<'_, 'tcx>,
id: hir::HirId,
span: Span,
infcx: InferCtxt<'tcx>,
) -> Self {
trace!(?pat_ctxt.typeck_results.hir_owner);
ConstToPat {
id,
span,
infcx,
param_env: pat_ctxt.param_env,
treat_byte_string_as_slice: pat_ctxt
.typeck_results
.treat_byte_string_as_slice
.contains(&id.local_id),
}
}
fn tcx(&self) -> TyCtxt<'tcx> {
self.infcx.tcx
}
fn type_marked_structural(&self, ty: Ty<'tcx>) -> bool {
ty.is_structural_eq_shallow(self.infcx.tcx)
}
fn to_pat(&mut self, c: ty::Const<'tcx>, ty: Ty<'tcx>) -> Box<Pat<'tcx>> {
trace!(self.treat_byte_string_as_slice);
let pat_from_kind = |kind| Box::new(Pat { span: self.span, ty, kind });
// Get a valtree. If that fails, this const is definitely not valid for use as a pattern.
let valtree = match c.eval_valtree(self.tcx(), self.param_env, self.span) {
Ok((_, valtree)) => valtree,
Err(Either::Right(e)) => {
let err = match e {
ErrorHandled::Reported(..) => {
// Let's tell the use where this failing const occurs.
self.tcx().dcx().emit_err(CouldNotEvalConstPattern { span: self.span })
}
ErrorHandled::TooGeneric(_) => self
.tcx()
.dcx()
.emit_err(ConstPatternDependsOnGenericParameter { span: self.span }),
};
return pat_from_kind(PatKind::Error(err));
}
Err(Either::Left(bad_ty)) => {
// The pattern cannot be turned into a valtree.
let e = match bad_ty.kind() {
ty::Adt(def, ..) => {
assert!(def.is_union());
self.tcx().dcx().emit_err(UnionPattern { span: self.span })
}
ty::FnPtr(..) | ty::RawPtr(..) => {
self.tcx().dcx().emit_err(PointerPattern { span: self.span })
}
_ => self
.tcx()
.dcx()
.emit_err(InvalidPattern { span: self.span, non_sm_ty: bad_ty }),
};
return pat_from_kind(PatKind::Error(e));
}
};
// Convert the valtree to a const.
let inlined_const_as_pat = self.valtree_to_pat(valtree, ty);
if !inlined_const_as_pat.references_error() {
// Always check for `PartialEq` if we had no other errors yet.
if !self.type_has_partial_eq_impl(ty) {
let err = TypeNotPartialEq { span: self.span, non_peq_ty: ty };
let e = self.tcx().dcx().emit_err(err);
let kind = PatKind::Error(e);
return Box::new(Pat { span: self.span, ty, kind });
}
}
inlined_const_as_pat
}
#[instrument(level = "trace", skip(self), ret)]
fn type_has_partial_eq_impl(&self, ty: Ty<'tcx>) -> bool {
let tcx = self.tcx();
// double-check there even *is* a semantic `PartialEq` to dispatch to.
//
// (If there isn't, then we can safely issue a hard
// error, because that's never worked, due to compiler
// using `PartialEq::eq` in this scenario in the past.)
let partial_eq_trait_id = tcx.require_lang_item(hir::LangItem::PartialEq, Some(self.span));
let partial_eq_obligation = Obligation::new(
tcx,
ObligationCause::dummy(),
self.param_env,
ty::TraitRef::new_from_args(
tcx,
partial_eq_trait_id,
tcx.with_opt_host_effect_param(
tcx.hir().enclosing_body_owner(self.id),
partial_eq_trait_id,
[ty, ty],
),
),
);
// This *could* accept a type that isn't actually `PartialEq`, because region bounds get
// ignored. However that should be pretty much impossible since consts that do not depend on
// generics can only mention the `'static` lifetime, and how would one have a type that's
// `PartialEq` for some lifetime but *not* for `'static`? If this ever becomes a problem
// we'll need to leave some sort of trace of this requirement in the MIR so that borrowck
// can ensure that the type really implements `PartialEq`.
self.infcx.predicate_must_hold_modulo_regions(&partial_eq_obligation)
}
fn field_pats(
&self,
vals: impl Iterator<Item = (ValTree<'tcx>, Ty<'tcx>)>,
) -> Vec<FieldPat<'tcx>> {
vals.enumerate()
.map(|(idx, (val, ty))| {
let field = FieldIdx::new(idx);
// Patterns can only use monomorphic types.
let ty = self.tcx().normalize_erasing_regions(self.param_env, ty);
FieldPat { field, pattern: self.valtree_to_pat(val, ty) }
})
.collect()
}
// Recursive helper for `to_pat`; invoke that (instead of calling this directly).
#[instrument(skip(self), level = "debug")]
fn valtree_to_pat(&self, cv: ValTree<'tcx>, ty: Ty<'tcx>) -> Box<Pat<'tcx>> {
let span = self.span;
let tcx = self.tcx();
let param_env = self.param_env;
let kind = match ty.kind() {
ty::Adt(adt_def, _) if !self.type_marked_structural(ty) => {
// Extremely important check for all ADTs! Make sure they opted-in to be used in
// patterns.
debug!("adt_def {:?} has !type_marked_structural for cv.ty: {:?}", adt_def, ty,);
let err = TypeNotStructural { span, non_sm_ty: ty };
let e = tcx.dcx().emit_err(err);
// We errored. Signal that in the pattern, so that follow up errors can be silenced.
PatKind::Error(e)
}
ty::Adt(adt_def, args) if adt_def.is_enum() => {
let (&variant_index, fields) = cv.unwrap_branch().split_first().unwrap();
let variant_index = VariantIdx::from_u32(variant_index.unwrap_leaf().to_u32());
PatKind::Variant {
adt_def: *adt_def,
args,
variant_index,
subpatterns: self.field_pats(
fields.iter().copied().zip(
adt_def.variants()[variant_index]
.fields
.iter()
.map(|field| field.ty(self.tcx(), args)),
),
),
}
}
ty::Adt(def, args) => {
assert!(!def.is_union()); // Valtree construction would never succeed for unions.
PatKind::Leaf {
subpatterns: self.field_pats(
cv.unwrap_branch().iter().copied().zip(
def.non_enum_variant()
.fields
.iter()
.map(|field| field.ty(self.tcx(), args)),
),
),
}
}
ty::Tuple(fields) => PatKind::Leaf {
subpatterns: self.field_pats(cv.unwrap_branch().iter().copied().zip(fields.iter())),
},
ty::Slice(elem_ty) => PatKind::Slice {
prefix: cv
.unwrap_branch()
.iter()
.map(|val| self.valtree_to_pat(*val, *elem_ty))
.collect(),
slice: None,
suffix: Box::new([]),
},
ty::Array(elem_ty, _) => PatKind::Array {
prefix: cv
.unwrap_branch()
.iter()
.map(|val| self.valtree_to_pat(*val, *elem_ty))
.collect(),
slice: None,
suffix: Box::new([]),
},
ty::Ref(_, pointee_ty, ..) => match *pointee_ty.kind() {
// `&str` is represented as a valtree, let's keep using this
// optimization for now.
ty::Str => PatKind::Constant {
value: mir::Const::Ty(ty, ty::Const::new_value(tcx, cv, ty)),
},
// All other references are converted into deref patterns and then recursively
// convert the dereferenced constant to a pattern that is the sub-pattern of the
// deref pattern.
_ => {
if !pointee_ty.is_sized(tcx, param_env) && !pointee_ty.is_slice() {
let err = UnsizedPattern { span, non_sm_ty: *pointee_ty };
let e = tcx.dcx().emit_err(err);
// We errored. Signal that in the pattern, so that follow up errors can be silenced.
PatKind::Error(e)
} else {
// `b"foo"` produces a `&[u8; 3]`, but you can't use constants of array type when
// matching against references, you can only use byte string literals.
// The typechecker has a special case for byte string literals, by treating them
// as slices. This means we turn `&[T; N]` constants into slice patterns, which
// has no negative effects on pattern matching, even if we're actually matching on
// arrays.
let pointee_ty = match *pointee_ty.kind() {
ty::Array(elem_ty, _) if self.treat_byte_string_as_slice => {
Ty::new_slice(tcx, elem_ty)
}
_ => *pointee_ty,
};
// References have the same valtree representation as their pointee.
let subpattern = self.valtree_to_pat(cv, pointee_ty);
PatKind::Deref { subpattern }
}
}
},
ty::Float(flt) => {
let v = cv.unwrap_leaf();
let is_nan = match flt {
ty::FloatTy::F16 => v.to_f16().is_nan(),
ty::FloatTy::F32 => v.to_f32().is_nan(),
ty::FloatTy::F64 => v.to_f64().is_nan(),
ty::FloatTy::F128 => v.to_f128().is_nan(),
};
if is_nan {
// NaNs are not ever equal to anything so they make no sense as patterns.
// Also see <https://github.com/rust-lang/rfcs/pull/3535>.
let e = tcx.dcx().emit_err(NaNPattern { span });
PatKind::Error(e)
} else {
PatKind::Constant {
value: mir::Const::Ty(ty, ty::Const::new_value(tcx, cv, ty)),
}
}
}
ty::Pat(..) | ty::Bool | ty::Char | ty::Int(_) | ty::Uint(_) | ty::RawPtr(..) => {
// The raw pointers we see here have been "vetted" by valtree construction to be
// just integers, so we simply allow them.
PatKind::Constant { value: mir::Const::Ty(ty, ty::Const::new_value(tcx, cv, ty)) }
}
ty::FnPtr(..) => {
unreachable!(
"Valtree construction would never succeed for FnPtr, so this is unreachable."
)
}
_ => {
let err = InvalidPattern { span, non_sm_ty: ty };
let e = tcx.dcx().emit_err(err);
// We errored. Signal that in the pattern, so that follow up errors can be silenced.
PatKind::Error(e)
}
};
Box::new(Pat { span, ty, kind })
}
}